Photograph bJ, fames Wagoner.

LIFE RESTORATION OF CHAMPSOSAURUS HUNTING. Painting by J erome Connolly in The Science Museum of Minnesota. THE LEPIDOSAURIAN REPTILE CHAMPSOSAURUS IN NORTH AMERICA

BRUCE R. ERICKSON CURATOR OF PALEONTOLOGY

MONOGRAPH VOLUME 1: PALEONTOLOGY Published by THE SCIENCE MUSEUM OF MINNESOTA ST. PAUL: March 31, 1972 MONOGRAPH OF THE SCIENCE MUSEUM OF MINNESOTA VOLUME 1

Library of Congress Catalog Card Number 77-186470 Standard Boole Number 911338-78-0 CONTENTS

Page Illustrations ...... 2

Introduction ...... 5

Species of Champsosaurus ...... 7 Skull of Cha;rnpsosauru.s gigas, New Species...... 12 Postcranial Skeleton of Champsosaurus gigas, New Species ... 26

General Morphology ...... 52 Skull ...... 52 Postcranial Skeleton ...... 53

Some Aspects of Functional Morphology ...... 72 Responsive Functions ...... 75

Correlations and Distribution...... 82

Phylogeny ...... 86

Summary ...... 89

Bibliography ...... 90 ILLUSTRATIONS

FIGURES Page 1. Correlation Chart of Champsosaurs...... 9 2. Skull of Champsosaurus gigas, dorsal view, PU 16239...... 13 3. Skull of Champsosaurus gigas, ventral view, PU 16239...... 14 4. Skull of Champsosaurus gigas, dorsal view, PU 16240...... 15 5. Skull of Champsosaurus gigas, ventral view, PU 16240...... 16 6. Restoration of skull, C hampsosaurus gig as, dorsal view...... 19 7. Restoration of skull, Champsosaurus gigas, ventral view...... 22 8. Occipital region of skull, Cha.mpsosaurus gigas...... 23 9. Lateral view of mandible, Champsosaurus gigas...... 25 10. Cervical vertebrae, Champsosa.urus gigas...... 27 11. Pleurocentrum of atlas, Champsosaurus gigas...... 28 12. Hypocentrum of atlas, Champsosaurus gigas...... 28 13. Posterior cervical centrum, Champsosaurus gigas...... 29 14. Intercentrum of cervical vertebra, Chmnpsosaurus gigas...... 29 15. Dorsal vertebra, Champsosaurus gigas...... 30 16. Sacrum, lateral view, Champsosaurus gigas...... 32 17. Sacrum, dorsal view, Champsosaurus gigas...... 33 18. Large sacral vertebra, Champsosaurus gigas...... 33 19. Representative caudal vertebrae, Champsosaut·us gigas...... 34 20. Second caudal vertebra, Champsosaurus gigas...... 34 21. Typical chevrons, Champsosaurus gigas...... 35 22. Cervical rib of Champsosaurus lara.miensis...... 36 23. Dorsal rib with uncinate process, Champsosaurus gigas...... 36 24. Posterior dorsal rib, Champsosaurus gigas...... 37 25. First sacral rib and vertebra, Champsosa.urus gi_qas...... 38 26. Second sacral rib, Champsosaurus gigas...... 38 27. First caudals, Charnpsosaurus gigas...... 38 28. First caudal, Charnpsosaurus gigas...... 39 29. Scapula, Charnpsosaurus gigas...... 39 30. Coracoid, Champsosaurus gigas...... 40 31. Shoulder girdle, anterior view, Champsosaurus gigas...... 42 32. Clavicle, dorsal view1 Champsosaurus gigas ...... 43 33. Interclavicle, dorsal view, Champsosaurus gigas ...... 44

2 ILLUSTRATIONS

Page

34. Humerus, Champsosaurus gigas ...... 45 35. Radius, Champsosauna; gigas ...... 46 36. Foreleg, Champsosaurus gigas ...... , , ...... , .. 46 37. Ilium, Champsosaurus gigas ...... , ...... , ...... , . , 47 38. Ventral plates of pelvis, Champsosaurus gigas . . , ...... , . , . , . 47 39. Femur, Chanipsosaurus gigas ...... 48 40. Tibia-fibula, Champsosaurus gigas . .. , ... , ..... , ... , ...... 49 41. Astragalus, Champsosaurus ,(Jigas ...... , ...... 49 42. Metatarsal V, Champsosa·urus gigas ...... , ...... , .. 49 43. Gastralia, Champsosaurus gigas ...... , 49 44. Age variation in axis pleurocentra ...... 56 45. Juvenile cervical vertebrae...... , ...... , ...... , ...... 56 46. Cervical vertebra, Chanipsosaurus lara1niensis ...... 57 47. Mounted skeleton of Champsosaurus laramieusis. , ... , , ... , ...... , 59 48. Juvenile sacrum, Chanipsosaurus laraniiensis ...... 61 49. Coracoid, Champsosaurus natator ...... 63 50. Humeri of different species, Champsosaurus . .. , . , ...... , , , ...... 64 51. Ontogenetic development of humerus, Chamvsosaurus ...... 65 52. Forefoot of Cha1npsosau-rus larwmiensis ...... 66 53. Forefoot of Champsosaurus laramiensis (in situ) ...... 66 54, Ontogenetic development of ilium, Charnpsosaurus . . , , . , ...... , . 67 55. Pubis of Champsosaurus gigas . . , .... , ...... 68 56. Hind foot of Champsosaw·us laramiensis ...... 70 57, Diagrammatic posture of head ...... , ...... , , ...... , ...... , 74 58. Transverse section of rib cage, C ham,psosaurus gigas ...... 76 59, Restoration of lungs in Champsosaurus ...... , .... . 77 60. Cross section of rib shaft, Champsosaurus gigas ...... , , .... . 78 61. Juvenile cross section of rib shaft, Chamvsosaurus laramiensis, .... . 79 62. Adult cross section of rib shaft, Chamvsosaurus laramiensis . .. , .... . 79 63. Map, Cretaceous distribution of Champsosaurus ...... 84 64. Map, Tertiary distribution of Charnpsosaurus ...... , . 85 65. Phylogenetic Chart ...... , .. 87

TABLES 1. Measurements of Chanipsosanrus gigas ...... 50 2. Comparison of adult and juvenile proportions in Champsosaurus . ... . 54

3 INTRODUCTION

Remains of the moderate-s,ized eosuchian features. Age and individual variations reptile, Champsosaurus, are common in have definite trends as well that have been many late Cretaceous and early Tertiary helpful in the present overall study. Age deposits of western North America and in variations, however, are much easier to the Tertiary of Europe; yet, they are poor­ determine than the latter, which must be ly represented in major museum collections regarded as only suggestive. and, by and large, not identified to specific Most informative of this group is a very level. The prime limiting factor responsi­ large form from the late Paleocene that is ble for the latter situation is the incom­ herein referred to as the new species, pleteness of materials and the extreme mor­ Champsosaurus gigas. In being very abun­ phological uniformity that runs through­ dant and fairly complete, it presents much out the group. interesting morphological evidence-some new and some in a better light; hence, the During the course of several seasons, discussions of general morphology and the writer made extensive collections of functional morphology draw heavily from fossil vertebrates in western North Amer­ it. ica. A sizable quantity of champsosaurian The present study treats Champsosau­ material was included in these collections. rus, the long-snouted North American Confusion in trying to work out the tax­ form. Only brief reference is made to onomy of this material provided the in­ other champsosaurids. In addition to the centive for the initiation of the present rather large sample of Champsosaurus now study, in The Science Museum of Minnesota, ma­ terials from seven other institutions were Handicaps encountered by most workers examined. Certain other materials, namely, have been due chiefly to inadequate sam­ those in the Royal Ontario Museum, were ples resulting in much synonymy. It was not examined but are referred to in the felt, however, that if enough material was present work. analyzed, specific taxonomy could be im­ proved upon. As comparisons were made, In the present work, the term "Clark­ characters that are considered significant forkian" is used rather than Tiffanian in delineating species were found. Many (Wood, 1967) to designate the late Paleo­ are subtle in expression, yet are consistent cene span from Olive to the Eocene boun­ in their occurrence. Due to the lack of dary. Figure 1 is a correlation chart for skulls, most distinctions rest on postcranial North American champsosaurs.

5 INTRODUCTION ACKNOWLEDGMENTS

The writer is indebted to numerous per­ staff artists of The Science Museum of sons who have assisted with the present Minnesota, with all of whom I have en­ work. Sincere thanks are extended to joyed working. I am indebted, first of all, Drs. Donald Baird of Princeton University to the late Alexander Oja who was respon­ and Rainer Zangerl of the Field Museum sible for figures 11, 13, 18, 26, 41, and 55; of Natural History for their encourage­ second to Chief Artist, Paul Snyder, who ment and suggestions, as well as providing contributed figures 25, 30, 58, and sug­ the loan of specimens critical to this study. gestions on others; and especially to James Without the loan of other materials as Wagoner who contributed the bulk of the well, this project would have suffered. For illustrations: 6-9, 12, 14, 16, 17, 20, 21, the loan of additional specimens from the 23, 28, 29, 32, 33, 35, 38, 42, 44-46, 48-53, following respective institutions, I wish to 56, and all photographs except figure 47. thank Drs. David Dunkle, formerly of the The frontispiece was painted by Jerome United States National Museum; Robert Connolly. Maps and figures 54, 57, 59, 60, W. Wilson of the South Dakota School of and 65 are the work of the writer who also Mines and Technology; Robert E. Sloan accepts the responsibility for all omissions of the University of Minnesota; and Mr. and inaccuracies in this publication. Fred G. Bard, director of the Saskatche­ Messrs. Ray and Eugene Lingk are to wan Museum of Natural History, Regina. be commended for their diligent and care­ Further thanks are in order to Dr. Dale A. ful recovery of the type specimen of Russell for supplying information on the Champsosaur gigas from the field. champsosaur materials housed in the Na­ Special thanks are due also to Mrs. Mary tional Museum of Canada, Ottawa. I would DesLauriers for her typing efforts and to also like to express my appreciation to Mrs. Inez Roach for layout and editing of Dr. Donald E. Russell for providing the this work. facilities to examine Simoedosaurus ma­ Finally, I would like to express my most terials in the Museum National d'Histoire sincere thanks to Mrs. Geneste M. Ander­ Naturelle, Paris. son for her sustaining interest in this proj­ The excellent illustrations in this work ect and for making the publication of this were accomplished by the efforts of three work possible. ABBREVIATIONS

The following list refers to the abbrevia­ PU Museum of Princeton tions for the institutions cited in the pres­ University ent work: ROM Royal Ontario Museum, AMNH American Museum of Natural History Toronto FMNH Field Museum of Natural SDSM South Dakota School of Mines History and Technology USNM United States National SMM Science Museum of Minnesota Museum NMNS National Museum of Natural SMNH Saskatchewan Museum of Sciences, Ottawa Natural History, Regina

6 SPECIES OF CHAMPSOSAURS

In 1876, E. D. Cope erected the suborder and readily identified as belonging to Choristodera referring to the "noncoossi­ champsosaur, have often been regarded as fications" of certain reptiles as distinctive. diagnostic on the specific taxonomic level N oncoossifications of the sacral vertebrae and are the basis for new names. This has with one another and the neural arches been found not to be the case by Brown with the centra, and the absence of the (1905), Russell (1956), and the present chordal perforation of the centra were study. Consequently, a number of species his major diagnostic criteria. To this taxon he assigned his newly founded "rhyncho­ have been placed in synonymy. cephalian" Champsosaurus. Allocation of Cope's original description (1876) of this genus to the rhynchocephalia was later Charnpsosaurus included four species based amended by Romer ( 1945) on grounds that on vertebrae largely from the Judith River the typical rhynchocephalian beak is want­ beds (late Cretaceous) of Montana. In ing. The subordinal status of Champso­ later publications (1881 and 1882), he de­ saur11s remains. scribed three additional species, again on In recent communication to the writer, vertebrae, bringing the total number to Dr. Donald Baird has pointed out an inter­ seven. These latter three are from the esting first account of charnpsosaur re­ Puerco (lower Paleocene) of New Mexico. mains. In 1873, 3 years prior to Cope's In reviewing the osteology of the genus, description, Joseph Leidy described and Brown (1905) considered only four of figured a single sacral vertebra for which Cope's types acceptable because of insuffi­ he proposed the name N othosaurus oc­ cient and eroded remains. Those accepted ciduus. This specimen is that of a champso­ by Brown (ibid.) are : the type species, saurid, but further determination is doubt­ C. annectens, C. profnndus, C. anstralis, ful. and C. saponensis. Three are considered invalid: C. brevicollis, C. vaccinsulensis, It is debatable whether to use Notho­ and C. puercensis. In his account, Brown saurus as a senior synonym or not. How­ (ibid.) describes two additional new ever, it is my contention that Nothosaurus species. These are C. laramiensis and C. is no longer a valid term and is, therefore, ambulator from the Hell Creek beds of declared a nomen vanum (ref. p. 11) . Montana. Both of these descriptions are based on nearly complete skeletons. Aside from a few exceptionally fine skeletons that are descriptive of the "valid" In his description of C. albertensis, species, collections mostly comprise assort­ Parks (1927) states that C. albertensis is ments of vertebrae, heavy limb extremities, very close to and may be identical with and rib fragments. The characteristic C. annectens. In a subsequent report, Parks spool-shaped vertebral centra, which are (1933) states concerning the occurrence of the most abundant remnants of skeletons this genus in the Belly River sediments of

7 8 MONOGRAPH OF THE SCIENCE MUSEUM OF MINNESOTA VOL. 1

Alberta, Canada: "On the basis of scat­ ? Champsow.urus profundus Cope, 1876. tered vertebrae alone, eight to ten species ? Champ.1osaurus brevicollis Cope, 1876. might be differentiated with reasonable Champsosaurus natator Parks, 1933, p. 122. assurance." He recognized C. natator, C. Champso.wurus infiatus Parks, 1933, p. 131. infiatus, C. cf. profundus, C. cf. australis, and C. inelegans from the Belly River beds. Champsosaurus inelegans Parks, 1933, p. 135. In addition, he acknowledges C. saponensis TYPE. ROM 5737 ct. of Cope and C. laramiensis and C. ambula­ HORIZON AND LOCALITY. Belly tor of Brown as valid. Russell (1956) be­ River formation, Upper Cretaceous, Red lieves that not only are those species re­ Deer River, Alberta, Canada. jected by Brown invalid but C. annectens, REFERRED SPECIMENS. ROM 5738 C. australis, C. infiatus, and C. inelegans ct., 5739; SMM P68.55.1. as well. The uncertainty of identifications DISCUSSION. The type from the Old­ relying on vertebrae of the various por­ man formation of Alberta, Canada is well tions of the column are grounds for the documented by essentially complete skele­ exceptions taken. tal materials including the skull (Parks, In attempting to evaluate the present 1933; Russell, 1956; Fox, 1968). Other large number of vertebrae available both described species from the Oldman and as complete columns and as individual equivalent Judith River beds are based on bones, it was extremely difficult and most very incomplete materials. often impossible to delineate species. Many Cope described four species in 1876 from juvenile bones and a few nearly complete the Judith River beds of Montana. Three skeletons are included in the sample as of these seem best included under C. natator well, but specific morphological distinctions as senior synonyms because no differences based on vertebrae are not made easier that are considered significant can be because of it. Differences between young found. However, this allocation is made and old specimens are a matter of degree provisionally as their inclusion here is and proportion. It is for this reason that mostly because of stratigraphic agreement. the juvenile specimens are considered such The species are C. annectens, the type rather than merely as smaller species. species of Champsoswurus, which was All species considered valid in the pres­ founded on a single centrum of indetermin­ ent work show other morphological differ­ able specific affinities; and C. profundus, ences and are stratigraphically separated defined on vertebral measurements that from one another except for C. laramiensis differ slightly from C. natator (Parks and C. ambulator, (Fig. 1). These, how­ 1933). The unreliability of this argument ever, are readily separated morphologically for distinction has been substantiated; and when sufficient materials are available. C. brevicollis, which is indeterminable be­ Russell's conclusions of validity of species cause of weathering effects, is probably are concurred with generally. The follow­ part of the same population as well. ing species are recognized in the present In 1933, Parks described C. 'inflatus from work: the Belly River formation distinguishing it Order CHORISTODERA from C. natator by its ilium, which has a Family CHAMPSOSAURIDAE forward extension of the blade, and a Genus CHAMPSOSAURUS Champsosaurus natator Parks, 1933 partial sacrum in which the neural spines ? Cha111psosaurus anneclens Cope, 1876. are unusually short. ALBE'RTA SASKATcUEWAN MONTANA DAKOTAS WYOMII-IG- C0WRADO NEW MEXICO

·, '.' : ' ··•··· ,J ' u GoU,,, Valley 0 w .. ''\ -· ·.·..· az C>.. Ar.apa hoe.. V) ::, L~'rCHnle.. Kiv-+land Fox H,11s Fox Hills 0 Fruif Ia t1d w ":_.\·. -·C ,·, c·,"'•:·:,·._,c'• Eastehd Lewis u Bearpdw Bearpaw Lewis <( Piene- Pierre, I- ' w J.,)UJiW:4'- ~1!9~•v•r Gia e--tt •··. f:apJe, °'u

:::)

Fig. 1. Correlation chart of champsosaur-bearing strata in North America. Occurrence indicated by stip­ pling. The names "Circle" and "Olive" refer to local faunas containing champsosaurs.

9 10 MONOGRAPH OF THE SCIENCE MUSEUM OF MINNESOTA VOL. 1

The ilium is smaller, lighter, and very DISCUSSION. This species is known likely of a younger specimen than that to only from the Edmonton. Its lower limbs which it is compared by Parks (ibid., Plate are significantly shorter than those of C. IV, Figs. 2 and 3). In figure 54 of the pres­ natator, which has elongated epipodials. ent work, a series of ilia are compared to It is also substantially shorter in lower illustrate age variations. Note the shape limbs than other species. Neither cervical of the blade in younger forms. nor anterior dorsal ribs are noted as hav­ From Parks' description and figures of ing uncinate processes as is the case of the sacral vertebrae of C. injiatus, it would C. ncitator and C. lrumniensis also from appear that they differ from C. natator the Cretaceous. only in the neural spines. These, however, Champsosaurus laramiensis Brown, 1905 look to be abnormal in his figures (ibid., ? Champsosrwrn:- austrcli.1 Cope, 1881, p. 670. Plate II, Figs. 10, 11, and Plate III, Fig. ? Champsosrwru.r pueru:nsisCope, 1882, p. 195. 10), lacking definite dorsal terminations ? Champsosauru.s 1aponl'nsis Cope, 1882, p. 196. and the height that would make them con­ ChampsosauruJ lammien,is Brown, H)05, p. 8. sistent with those of the dorsal series. For TYPE. AMNH 982. example, the vertebra in figure 3 (Parks HORIZON AND LOCALITY. Hell Creek ibid., Plate II) is one of the last few dor­ beds, Tullock formation, Garfield County, sals. The height of the neural spine is much Montana. greater than that of the first sacral of C. injiatus, which has probably been re­ REFERRED SPECIMENS. AMNH duced by weathering or disease. 981; SMM P62.10.l, P63.13.1, P63.14.l, P64.10.1, P65.3.1, P65.9.l, P68.55.1, In further description, Parks (ibid.) P68.68.l, P69.10.l, P69.13.1, P69.14.1. misinterpreted the third cervical vertebra, which he designated as the type of C. DISCUSSION. The type specimen is ineler1ans, as a more posterior element. As a nearly complete skeleton. As far as can a consequence, in his comparison with his be determined, it is the sole representative type of C. natator in which the third cervi­ of the genus in the Hell Creek formation. cal vertebra is missing, he found dissimi­ Its range includes the Frenchman forma­ larity. Russell (1956, part VII, Figs. 6, 7, tion of Saskatchewan and is perhaps wider. and 8) shows the tbird cervical of C. It extends into the Tullock (Paleocene) natato!'. It does not differ significantly formation in northeastern Montana and from that of C. inelegans; therefore, this evidently to the Puerco of New Mexico. species and that discussed above are both It is clearly distinct from C. ambulator, herein regarded as junior synonyms of also of the Tullock; viz., having a less C. natator. spatula-shaped termination of the snout Champsosaurus albertensis Parks, 1H27 and fewer palatal teeth. In the postcranial Chumprnwurus alberlensis Parks, 1B27, p. 10. skeleton, the girdles are of lighter con­ struction and the limbs somewhat longer. TYPE. ROM. The humerus of C. laramiensis shows Jess HORIZON AND LOCALITY. Edmon­ twisting of the shaft ; the ento- and ecto­ ton formation, Red Deer River, Alberta, tuberosities are higher and more confluent Canada. with the proximal head. The delta-pectoral DIAGNOSIS. Relatively large species ridge is only moderately developed, and the with shortened epipodials. distal end is Jess massive with an ectepi- ERICKSON: CHAMPSOSAURUS IN NORTH AMERICA 11 condylar groove like all other species ex­ this arrangement, the geographic range cept C. arnbulator. The femur has the of C. laramiensis is extended even further. trochanter located higher on the shaft than C. ambulator, as far as the record indicates, in C. arnbulator. comprised a more limited population with None of Brown's specimens of C. lara­ a much smaller geographic and geologic miensfa show the incising of certain dorsal range. ribs that are present in larger specimens Champsosaurus ambulator Brown, 1905 of this species; nor is development of Champsosaurus ambulalor Brown, 1905, p. 22. uncina te processes on the cervical and TYPE. AMNH 983. dorsal ribs indicated-features that it has REFERRED SPECIMEN. SMM P63. in common with C. natator and C. gigas. 14.1. Cope described C. austra/:is upon eleven vertebral centra, four of which he figured HORIZON AND LOCALITY. Hell Creek (1884, Plate XXIIIb, Figs. 1-4). These are beds, Tullock formation, Garfield County, juvenile elements and may represent more Montana. than a single individual. Their charac­ DIAGNOSIS. A relatively short-limbed teristically greater width as compared to species with heavy girdles. length and height that Cope used as dis­ DISCUSSION. This species occurs only tinguishing features is attributed to im­ in the Tullock formation where it is asso­ maturity and is typical of all extremely ciated with C. laramiensis. Differences be­ young forms. tween it and the latter are noted in the C. saponensi.s is also included here be­ preceding discussion. Following are a num­ cause its size and form of the six cervicals ber of salient morphological features that and dorsals that are preserved agree close­ distinguish this species : prominent in­ ly with those of C. laramiensis, especially fraglenoid process on the coracoid, strong the pronounced ventral carina more typi­ deltoid ridge and radial condyle on the cally C. lararniensis than C. ambulcdor. humerus, ectepicondylar groove closed Cope's figures of his type of C. puercen­ distally on the humerus, low position of sis (1884, part XXIII, Figs. 5, 6, and 10) trochanter on the femur, and very elongate are probably of posterior dorsal vertebrae inner border on the pubis. of an adult animal. Narrowing of the base Champsosaurus vaccinsulensis Cope, 1876 of the anterior face is a striking feature nomen vanum that occurs to various degrees in C. lara­ Champwsaurus r'accinsulensis Cope, 1876. rniensis. It seems to be more of an individ­ ual variation than one of age. Size and TYPE. In AMNH. form, such as, development of the facets HORIZON AND LOCALITY. Judith on both atlas and axis, also indicate adult River beds, Montana. development like that seen in C. lara1nien­ DISCUSSION. The type specimen is a sis as well as other species (Figs. 7, 8, and weathered vertebral centrum and belongs 9, ibid.). to a different order, as Brown (1905) has Because of stratigraphic occurrence of indicated. the above and general agreement with C. N othosaurus occiduus Leidy, 1873 larconicnsis, these forms seem most appro­ nomen vanum priately inserted here as senior synonyms; Nothosaurw occiduus Leidy, 1873, p. 287, figures however, this is done provisionally. Under 11-13, pl. xv 12 MONOGRAPH OF THE SCIENCE MUSEUM OF MINNESOTA VOL. 1

Nothosaurops occiduus Leidy, 1873, figures 11- DIAGNOSIS. A very large species hav­ 13, pl. xv ing unusually long hind limbs and a pro­ TYPE. Not located. nounced development of rib incising. The HORIZON AND LOCALITY. Moreau geographic range of this form is quite River, upper Missouri River. large. DISCUSSION. This species is based on DISCUSSION. The occurrence of a large a single sacral vertebral centrum of some champsosaur in the late Paleocene of west­ champsosaurid of uncertain stratigraphic tern North America has been of interest and geographic position. It was collected for some time (Langston 1958). Its size by Professor Hayden on the Moreau River, identifies it in the latest Paleocene ("Clark­ a tributary of the upper Missouri. Unfor­ forkian") Tiffanian deposits where it is tunately, no reliable stratigraphic level can found in prodigious numbers. A possible be stated for this specimen as the Moreau ancestor, C. lara1niensis, is abundant in flows through a variety of sedimentary Puercan strata; but neither it nor any of deposits of different ages. Nothosaurus is the other abundantly represented early herein considered a nomen vanit1n because Paleocene champsosaurs shows a tendency of the above and lack of general use. toward gigantism. Because of the extreme In the description of plate XV (Leidy, conservativeness exhibited throughout this 1873), the name Nothosaurops occiduus group, particular attention has been given appears. This is interpreted as a typo­ to subtlety of morphological detail. During graphical error and is included as a junior the course of many comparisons upon an synonym being that NothosauruB occiduus, admixture of juvenile and adult specimens, as it appears in the title, is the correct some relationships were brought out that spelling. are considered significant. This, in addi­ tion to its stratigraphic position and its Champsosaurus gigas, new species size, has resulted in recognition of a new TYPE. SMM P71.2.1. A nearly complete species herein described as Champsosaurus skeleton with a partial skull and lower gigClS, jaw of young adult animal. HORIZON AND LOCALITY. Sentinel SKULL Butte formation, Ft. Union Gp., late Paleo­ Of the eight specimens used in the pres­ cene, NE¼SW¼ sec. 28, T. 141 N., R. ent study, two have complete skulls (Figs. 104 W., Golden Valley County, North 2, 3, 4, and 5) . Both are of similar size, and Dakota. judged to be adults. They are generally REFERRED SPECIMENS. SMM P60. well preserved but crushed as well as other­ 2004, postcranial skeleton lacking portions wise distorted. There is displacement of of limbs and girdles and the feet; PU elements especially in the posterior regions. 16239, complete skull, somewhat distorted PU 16239 has essentially one half of the with partial lower jaw; PU 16240, com­ lower jaw associated with it. Teeth are plete skull, somewhat distorted; SDSM present in both specimens. The skull and 53508, postcranial skeleton lacking most jaws of the type SMM P71.2.l are pre­ of the anterior half; USNM 20521, partial served in part but badly fragmented and postcranial skeleton ; FMNH PR93 and of use mainly in a determination of sutural P26132, partial skulls and .skeletons. paths. 0

() 3

Fig. 2. Skull of Champsosaurus gigas, PU 16239. Dorsal view.

13 0 n 3

Fig. 3. Skull of Champsosaurus gzgas, PU 16239. Ventral view.

14 Fig. 4. Skull of Champsosaurus gigas, PU 16240. Dorsal view.

15 Fig. 5. Skull of Champsosaurus g1gas, PU 16240. Ventral View.

16 ERICKSON: CHAMPSOSAURUS IN NORTH AMERICA 17

PREMAXILLAE snout. They contact the premaxillae at a The premaxillae are short and form the slight posterior constriction of the latter bluntly rounded, somewhat bulbous tip of and extend rearward until they unite with the snout. The sutures defining these ele­ the prefrontals and lachrymals medially ments are not entirely clear in either and the jugals intertonguing laterally. PU 16239 or PU 16240, probably due to They are separated for their length medi­ age; and they are not preserved in the ally by the nasals and the tapering pre­ ;;: frontals. Above the oral margin, a series •I type. Laterally, the maxillo-premaxillary suture begins at about the level of the of pits that are in line with that noted in seventh tooth and meanders dorsally to­ the premaxillae characterize this bone. I ward midline. In dorsal aspect, the pre­ Ventrally, the maxillae continue below I maxillae narrow slightly as they approach the orbits, being separated from them by i the maxillae. Just anterior to the maxillo­ the overlying jugals. Posteriorly, on their premaxillary junction, there is a deep inner surfaces they border the palatine lateral groove, probably vascular, that opening and adjoin the palatines, vomers, emerges from a small lateral foramen near and finally the thin, neomorphic ossifica­ Ii tion called internarial by Russell (1956) the suture and arches forward toward the oral margin. It is a marked feature on both and ethmoid by Brown (1905). Teeth are PU 16239 and PU 16240. present along the oral borders of these ele­ ments. In PU 16240, there are from 25-27 Anteriorly, these elements nearly enclose teeth present in each element. The teeth in I the fused external nares. The anteriormost l the hinder one third are appreciably projection of the nasals interrupts them smaller-a condition consistent with other dorsally on midline. This area is somewhat species. crushed in the present skulls, and separa­ tion has taken place along the sutures. NASALS Medially, they are separated for their As in other forms, the nasals are coossi­ I..i entire length by the narrow nasals. The t fied medially. Their length is about two external nares open forward with the floor thirds that of the snout, extending from of the narial chamber extending a bit the narial rim rearward along midline and further forward than the upper rim of forming a wedge as they do in C. lara­ the opening. miensfa between the anterior points of the Ventrally, the maxillo-premaxillary su­ paired prefrontals. The nasals are not as tures apparently follow much the same noticeably tapered for most of their length course as they do dorsally. Centrally, these as in this form, however. The extreme bones have a direct connection. There is a anterior end probably extended beyond the small shallow pit present on the midline adjacent portions of the premaxillae, con­ near the anterior end. This does not pene­ tributing to the dorsal part of the narial trate to the interior surface as it does in opening. In both PU 16239 and PU 16240, some forms. There are provisions for seven crushing has opened the lateral nasal su­ teeth in each premaxilla-the third and tures (Figs. 2 and 4) on one side or the fourth being the largest in the entire skull. other.

MAXILLAE INTERNARIAL The maxillae of C. gigas are long ele­ This bone is well defined in C. gigas I ments comprising the greater part of the (Fig. 6). It is shorter than the overlying I 'I I I 18 MONOGRAPH OF THE SCIENCE MUSEUM OF MINNESOTA VOL. 1 nasals, beginning somewhat ahead of them Beyond the orbit, the jugal swings out­ and continuing forward to about the level ward and joins the quadratojugal in an of the maxillo-premaxillary suture. The oblique posterior suture-the jugal being narial passages were divided, at least along internal to the quadratojugal at the ends. this portion of the skull. An anterior carti­ The angle of this suture apparently has laginous extension may have also existed been reversed in ventral aspect for C. and functioned in separating the chambers ncltor (Russell, 1956; Fig. 2, p. 7). completely. A small tuber at the extreme tip of the floor of the opening that may FRONTALS have served as an anchor for this extension These bones meet along the median and suggests this. form a dorsal continuation of the orbits. The frontal joins the prefrontal in an PREFRONTALS interlocking step-like suture dorsal to the These are centrally located bones sutur­ orbit, and the parietal in similar fashion ally united along the median and form the posteriorly. Laterally and behind the orbit, upper anterior border of the orbits and a it lies next to what has been called the post­ very thick portion of the face. Suturally orbital (Brown, 1905 and Russell, 1956) attached at the side is the lachrymal, which but is herein interpreted as the postfrontal. forms a continuation of the anterior orbital This will be discussed below. The surface rim. The prefrontals expand gradually in of the frontal is deeply sculptured with width along the lachrymal edge, then nar­ the most characteristic feature of orna­ row along the maxillary edge. At the an­ mentation on the head. About two thirds terior extremity, they are divided by the of the way back from the front of this intertongning nasals. element is a lateral projection or tubercle that is more or less opposite its mate on LACHRYMALS the other frontal (Fig. 6). The bone is The lachrymal is a small triangular ele­ sharply depressed between the ridge bear­ ment. Its posterior side is part of the for­ ing this feature and its lateral border. The ward orbital rim, as noted above. The rim bone is thickened to form the internal is nodular in texture in this area. Above, orbital wall. Along all suture contacts, the this bone meets the prefrontal. Along its bone thins to more normal thickness. lateral margin, it embraces the maxilla in front and the jugal behind. POSTFRONTALS The postfrontals (Fig. 6) in C. gigas JUGALS resemble those (postorbitals) of C. natator In dorsal aspect, the jugals match C. (Russell, 1956) in that they run from the laramiensis more nearly than C. natator in posterior edge of the orbit to the supra­ that the extent of their forward projections temporal opening contacting both the are about the same. The anterior wedge of frontals and parietals along their superior this bone penetrates the maxilla. Its dorsal margins. As compared with bones more edge joins the lachrymal and continues median to them, the surfaces are relatively posteriorly to complete the lower margin smooth except for some heavy striations of the orbit and eventually meets the post­ just behind the orbits. Laterally, a strong frontal behind the orbit. Laterally, it lies union with the jugal is achieved by omitting above the posterior extension of the maxilla most of the postorbital contact with this whereby the suborbital arch is constituted. bone. Posteriorly, the postfrontals and the I I

Fig. 6. Restoration of the skull of Champsosauru1· gigrz.r in dorsal view. Bo, basioccipital; F, frontal; J, jugal; L. lachrymal; Mx, maxilla; Na, nasal; P. parietal; Pf, postfrontal; Pm, prcmaxilla; Po, postorbital; Prf, prcfrontal: Q, quadratc; Qj, quadratojugal. Based on PU 16239 and PU 16240. 19 20 MONOGRAPH OF THE SCIENCE MUSEUM OF MINNESOTA VOL. 1 postorbitals meet obliquely. is sharply defined in PU 16240. Ventral relationships between the various bones POSTORBITALS are obscured in the present skulls, but it The bones posterior to the postfrontals would seem that they were not too unlike and making up the anterior portion of the those of their dorsal patterns. supratemporal bar are considered to be The inner wall is exposed in PU 16239 the postorbitals (Fig. 6 and p. 52). They (Fig. 2), although the sutural contacts are are flat and smooth. The postorbitals are indistinct. separated from the postfrontals by a Z­ At its base, the parietal appears to be shaped suture in both external and internal bound to at least two elements: the squa­ views. At their anterolateral extremity, mosal (prootic of Rus,sell, 1956) posterior­ they retain connection with the jugals ly, and a second bone forward, which has ventrally. As seen in figure 4, they taper been referred to as the prootic ( Fox, 1968) rearward and form a long, oblique junction and epipterygoid (Russell, 1956). Demar­ with the squamosals. cation of this forward bone in C. gigas is vague, and neither is there good evidence PARIETALS of a neomorphic segment like that reported In C. gigas, PU 16240, the skull is open­ for C. natator (Fox, 1968). The presence ed along the heavy interparietal suture. of the columellar-shaped "epipterygoid" as Here the exposed contact area, which can described by Fox (ibid.) is uncertain also. be observed in sagital section (Fig. 4), is The anterior edge is a smooth arch to very thick; and a minor crest is developed. which the supposed anterior cartilaginous The posterior end of the midline, where portion of the braincase adhered. On the the crest projects upward and is the high­ posterior ends, they overlie a small supra­ est, is not well preserved in PU 16239. occipital of uncertain configuration. However, a slight medial depression, as has been described in other forms (Brown, SQUAMOSALS 1905; Russell, 1956), is indicated forward. As indicated above, the posterior con­ In PU 16240, no such depression is appar­ tact of the lateral wall of the parietal is ent. Instead, between midline and the outer either with the squamosal or prootic, de­ edges, the bones are concave. Sutures be­ pending on interpretation. Based on the tween these elements and the postfrontals evidence offered by C. gigas, however, the and frontals are very sinuous in nature. sutures are not well enough preserved to The parietals do share a short suture also argue the point. The bone areas in ques­ with the postorbitals at the hindermost tion are badly distorted in both skulls. A point of the postfrontals. Behind the level small foramen (pterygoquadrate foramen) of the postfrontal, the inner side of the is present in both skulls along the pre­ superior temporal opening is formed; and served suture. a posterior projection, although not well The squamosa1s occupy the posterior­ preserved in either specimen, was present most part of the skull and contribute the for contact with the most posterior portion rear support of the bars defining both of the squamosal. temporal openings. They present three long The oblique ridge on the inner wall of diagonal sutural unions with the, quadra­ the superior temporal opening, presumably tojugal, postorbitals, and the parietals re­ for demarcation of different temporal spectively. Below the level of the temporal muscle areas as noted by Russell (1956), fossae, they are continuous with the ERICKSON: CHAMPSOSAURUS IN NORTH AMERICA 21

quadratojugals, quadrates, and the pa­ tionships. Each is constricted above its rietals/prootics that form a broad, flat base. Presumably, the upper, inner ends ventral plate giving the head its charac­ of these bones met the supraoccipital and teristic shape. The opisthotics (exoccipitals carried posterior projections for contact of Brown, 1905) lie in close contact also. with the atlas. Lateral to the foramen Posteriorly, the outer rims of the squa­ magnum are deeply incised areas along the mosals are smoothly rounded. exoccipital-opisthotic fusion. Deep within these areas are a pair of foramina for QUADRATOJUGALS posterior cranial nerves, X and XII, ac­ cording to Fox (1968). In C. gigas, PU 16240, this bone is pre­ sented as a thin, flat bar between the jugal OPISTHOTICS and the squamosal that forms the outer side Orientation of these elements is clearly of the infratemporal opening. Ventrally, shown in the type also (Fig. 8) . They it also merges with the quadrate in a well originate at the level of the exoccipital defined suture immediately behind the ar­ contact, which is much higher up on the ticular facet for the lower jaw. occipital region than in other forms. They QUADRATES angle downward and rearward to lie in close opposition to the squamosals (prootics The quadrate is completely immobile, of Russell, 1956) and the quadrates. The forming as it does an integral part of the dorsal squamosal sutural surface on this ventral plate of the temporal region. It is bone is very broad and partially extended interior to the quadratojugal and anterior over the outer, upper end of the exoccipital. to most of the squamosal. Its anteromedian Its outer end is broadly squared. end blends into the posterior pterygoid ramus. Ventrally, it is overlapped by the BASIOCCIPITAL distal end of the opisthotic. Sutures in the This element consists of a massive, I vicinity of its inner border are not clear rounded occipital condyle that is set out in either skull, as noted. The broad sur­ by transverse depressions above and below. faces of this bone are thin and smooth. There is a central groove that runs for Along its anterior edge arises a stout, most of its vertical length. Dorsally, the articular condyle for the lower jaw. This basioccipital affords a foundation for the feature is elongated transversely and de­ lateral occipitals between which it con­ pressed obliquely through its center. tributes the floor of the foramen magnum. SUPRAOCCIPITALS The somewhat deformed element is seen in PU 16239 and PU 16240, and a relatively As indicated above, this small solitary undisturbed condition is seen in SMM bone cannot be described accurately in any P71.2.1 (Fig. 8). Its basal posterior pro­ of the present skulls because of distortion jections are steeply inclined and deflected and fragmentation of the skulls. caudad. The amount of rearward projec­ tion probably reflects age as development EXOCCIPITALS of these projections is greater in larger The exoccipitals surmount the basioccipi­ specimens. The hinder margins have promi­ tal to form the sides of the foramen mag­ nent, striated areas that distinguish them num. They are largely preserved in the from the tightly fused overlying parasphe­ type (Fig. 8) and show most of the rela- noid sheath. I j Fig. 7. Resloration of the skull of Champsosauru, gigas in ventral view. Bo, basioccipital; Ee, ectopterygoid; In, internarial; J, jugal; Mx, maxilla; Op, opislhotic; P, parietal; Pl, palatine; Pm, premaxilla; Po, postorbital; Ps, parasphenoid; Pt, pterygoid Q, quadrate; Qj, quadratojugal; Sq, squamosal; V, vomer. Note the conical shape of the maxillary and premaxillary teeth and the shallow pits for their reception. Based on PU 16239 and PU 16240.

22 ERICKSON: CHAMPSOSAURUS IN NORTH AMERICA 23 aspect in figure 7. They differ some from those of other described species in the path Ex of the sutures. Their midline opposition is incomplete at the distal end where they N split from one another and branch lat­ Op eralJy to make a long overlapping contact with the quadrates, and at about the level of the ectopterygoids where an elongate interpterygoid vacuity is present. In speci­ men PU 16240, the anterior suture with the palatine is just visible (Fig. 5). It enters from the palatine vacuity and arches anteromedialJy. Its relationship to the vomer is simple and direct to midline. The interpterygoid vacuity is bordered on either side by two tooth-bearing ridges 3 cm that diverge forward. One is at the edge of the opening, the other at the lateral border of the bone. A restored view is Fig. 8. Champ.wsaurus gigas, type specimen SMM available in figure 7. P71.2.1. Occipital region of the skull. Bo, basioccipital; Ex, exoccipital; Fm, foramcn magnum; N, openings EJCTOPTERYGOIDS for cranial nerves; Op. opisthotic. This structure in the form of a bar separates the palatine vacuity from the BASJSPHENOID temporal opening. Its proximal sutural The basisphenoid is completely concealed definition is indistinct in both specimens ventralJy or is lacking in the present mate­ and appears to be completely ankylosed rial. The lateral gaps between it and the with the pterygoid. Attachments to the pterygoids are present but have been closed j ugal and maxilla, on the other hand, are by lateral compression; hence, any view of very bold and in the form of a lateral the internal structures, as seen in C. buttress. As in other species, a keen ridge natator (Fox 1968) for example, is un­ on the ventral surface of the pterygoid is available. In PU 16239 and PU 16240 continuous onto this surface and changes ( Figs. 3 and 5) , the parasphenoid narrows in that teeth are borne here on the ridge. rapidly toward the front and makes an This ridge begins far back on the pterygoid acute insertion between the pterygoid ends. and follows the expansion of the element DorsalJy, portions of the above skulls, to remain lateral to the two anterior seemingly contiguous with the basisphe­ tooth-bearing ridges mentioned earlier. noid (basisphenoid of Fox, 1968 and post­ optics of Russell, 1956), are preserved in a PALATINES crushed condition. It is best shown in The palatine fills the space between the PU 16239 (Fig. 2) as an anterior extended posterior maxillary projection and the trough on the floor of the braincase. vomer. It narrows forward to about the level of the last occurrence of palatal teeth PTERYGOIDS and ends in a point. Laterally, it forms The pterygoids are outlined in ventral about half of the wall and roof of the in- 24 MONOGRAPH OF THE SCIENCE MUSEUM OF MINNESOTA VOL. 1 ternal narial opening. Its suture with the DENTARIES vomer passes approximately through the The dentary comprises most of the length center of this opening and the posterior and lateral area of the mandible. It unites trough into which it opens. A tooth with the opposing half of the lower jaw shagreen continues atop a narrow lateral along a symphysis that covers close to the elevation on the outside of this bone from anterior half of the length of the jaw. A a similar elevation on the pterygoid be­ deep Meckelian groove runs the length of hind. Teeth are numerous and more nearly the symphysis a bit below longitudinal cen­ dispersed like C. laramiensis than other ter. Anteriorly, the groove becomes shallow species. and fades into the distal alveolus. The dentary bows ventrad to the region of the VOMERS posterior point of the symphysis and rises The vomers lie in juxtaposition from posteriorly to join the surangular. The about half way along the medial length of union with this bone is obscured but was the maxillae tu the level of the forward probably in the striated area. The very edge of the palatine vacuity. At their ex­ smooth surface beyond this is believed to treme tips, their lateral edges converge be mostly surangular. Medially, it is over­ to touch the internarial bone. At about lain by the splenial, and aside from the midlength, they are constricted and con­ symphysis is exposed only along the dorsal tinue rearward as a narrow elevation rim of the jaw. A single row of teeth is dividing the internal openings of the nos­ present on the rim and decreases in size trils. The elevation descends gradually to from front to rear. The last few remain the level of the posterior palate or the just beyond the level of the coronoid. floor of the narial openings. In forming the medial half or so of the narial trough SPLENIALS mentioned above, they join the palatines The splenial is about half the length of laterally in the bottom of the trough and the dentary and lies, for the most part, extend posteriorly together until inter­ internal to it. It contributes to the sym­ cepted by the pterygoids. Just above the physis that posterior portion beyond the narial openings, the vomers briefly em­ deep Meckelian groove and runs caudad brace the palatines. Vomerine teeth are to meet the dentary along its lateral sur­ present along a central row throughout face and above until it is separated from most of the length of the bones except for this element by the anterior prong of the the most anterior tips. coronoid internally and by a wedge-shaped projection of the angular, laterally. The MANDIBLE splenial terminates ventrally in a short A single, lower jaw-half of C. gigas is diagonal suture with the angular just be­ represented in PU 16239 (Fig. 9). It lacks yond the level of the Meckelian notch. It only the end of the angular and the articu­ is quite smooth on its exposed surface. lar. This portion is, however, conveniently preserved in the type SMM P71.2.l. The CORONOIDS jaw is long and slender and looks much The coronoid is an exaggerated diamond­ like that of the rest of the group, although shaped piece interposed between the pos­ the symphysis is somewhat longer. The terior reaches of the dentary and the single jaw preserved is flattened so that in splenial on the inside of the mandible. dorsal view it is straight. Medially, it covers a dorsal portion of the Ir I I

•

Fig. 9. A. Lateral view of left mandible, Champsosaurus gigas, PU 16239. B. Internal view of same. An, angular; Ar, articular; C, coronoid; D, dentary; Sa, surangular; Sp, splcnial; T, tooth, note recurving, crenu~ lated base and marginal notching of jaw for skull teeth.

25 I I 26 MONOGRAPH OF THE SCIENCE MUSEUM OF MINNESOTA VOL. 1

surangular, and its lower posterior side surangular and angular. A large articular forms the upper rim of the Meckelian facet is provided on a posterodorsal en­ notch, which enters at an acute angle largement to match a corresponding facet rather than as the rounded notch seen in as described for the quadrate. some forms.

SURANGULARS POSTCRANIAL SKELETON This element is located dorsally at the ATLAS-AXIS COMPLEX rear end of the jaw. The surangular bears characteristic striations for muscle attach­ Except for portions of the neurocentra, ments upon its dorsal edge including the this complex is complete in the type (Fig. front end where it enters between the 10). As indicated, the type is regarded as coronoid and dentary. The bone is thin and a small adult and shows essentially adult smooth elsewhere. Its union with the den­ development of features. tary is not clear but is suspected to re­ The atlas had four parts. The two major semble that of other species wherein the portions, the pleurocentrum and the hypo­ suture between these elements angles centrum, are preserved. The pleurocen­ ventrad from tbe striated area across the trum, as seen in its fullest development in outer surface. This bone encloses the dor­ SMM P60.2004 (Fig. 11), is a key piece sal half of the articular on its lateral sur­ in this complex. It is longer and heavier face. Medially, it has the internal flange than that of other forms. It furnishes mentioned by Russell (1956) that extends major support with a wide, flat posterior in front of the articular and nearly meets articular face for the axis. Its narrow base the angular coming around from below. also has a flat face that is angled slightly caudad and expanded laterally to meet a ANGULARS similar expansion on the axis hypocentrum. This element also resembles its homo­ Just ahead of this and below its main an­ logues closely, making up the lo,wer pos­ terior face is a transverse notch that is terior border of the jaw from the rear faceted along its lower border for reception surface of the spleniaI to the articular. A of the crescent-shaped hypocentrum of the well preserved extremity of the jaw in the atlas. The main anterior face spreads lat­ type, SMM P71.2.l, shows that the ex­ erally to furnish support and space for the treme posterior extension of this bone bases of the neurocentra. It also develops overlay the internal suture between the a central process that enlarges with age surangular and articular but failed to and engages the occipital condyle above. reach the extreme angle of the jaw, which The hypocentrum is made up of articular was formed above by the surangular and facets behind, above, and forward. The below by the articular. Dorsally, the angu­ anteroventral surface of this piece is lar extended forward along the base of the curved rearward and forms an irregular surangular and dentary until it merged contact surface that abuts, the combined with the splenial-dentary suture. forward edges of the axis hypocentrum and the above noted surface of the pleuro­ ARTICULAR centrum. The ventral projection mentioned This element as preserved in the type for an immature specimen of C. lara1nien­ contributes the posteriormost edge of the sis (Brown, 1905) is not present; nor is the jaw. Most of it, however, is internal to the subsequently expanded modification of this ERICKSON: CHAMPSOSAURUS IN NORTH AMERICA 27 projection indicated in the adult as it is only a slight median crest but well de­ in C. laraniiensis (Brown, ibid.). There is veloped zygapophyses. only a small, irregular edge in its place. Together, the pleurocentrum and the sub­ CERVICALS ordinate piece form a loose socket affair (3-9). The cervical series of C. gigas for articulation with the occipital condyle containing nine vertebrae is shown in fig­ of the skull. The axis pleurocentrum is the ure 10. A large specimen, the eighth ver­ largest portion of the complex-about one tebra, is shown in figure 13 and illustrates third longer than the pleurocentrum of the the diagnostic form of a squared centrum atlas. The centrum is of normal form pos­ having anterior and posterior faces parallel teriorly. The anterior surface has two to one another and noticeably depressed articular facet~ wherein the main face is sides. The anterior half of the series differs divided into a large, superior portion to in presenting a profile of smaller centra join the atlas and a lower portion that is with nonparallel articulating faces. This set back but still looks forward to support is especially noticeable in the third verte­ its hypocentrum (Fig. 10). The sides of bra. Parapophyses and diapophyses are the centrum are concave and ventrally prominent on all and are deflected rear­ roughened. The diapophyses are located ward. The former migrates in position on near the center of the length of the bone the lateral side of the centrum from the and are directed straight outward. The anterior perimeter of the vertebra where neural canal is quite wide. Figure 12 shows it is inconspicuous to a more central posi­ i I the crescent-shaped hypocentrum with its tion where it is obvious, and finally merges large dorsal facet and concave rear face. with the diapophyses on the last and The partially preserved neurocentra ap­ largest cervical. The latter feature is pear the same as in other species having strongly developed throughout the series.

ant. 2cm

Fig. 10. Champsosaurus gigas, type specimen SMM P71.2.1. Lateral view of cervical vertebrae. 28 MONOGRAPH OF THE SCIENCE MUSEUM OF MINNESOTA VOL. 1 ant.--+

post.

A

A

2 cm B 3 Cm

B

Fig. It. Atlas pleuroccntrum of Champsosaurus Fig. 12. Champsosaurus gigas, type specimen gigas, SMM P60-2004. A. Lateral view. B. Posterior SMM P71.2.l. A. Ventral view of interc entrum of view. C. Anterior view. axis. B. Posterior view of same.

A ventral carina is present in C. gigas but have been associated with any adjacent less salient by comparison with some pair of anterior caudal vertebrae as their species. Maximum development of this fea­ intercentra had not been modified into ture is on the seventh and eighth vertebrae. chevrons (ref. p. 58). General description The neural arch is wide and carries well is that of a very small, wedge-shaped piece developed anterior and posterior zygapo­ tapering at both lateral extensions and physes. The neural spine is relatively nar­ having one well developed central facet for row, long, and pitched rearward. The lead­ contact with a centrum (Fig. ibid.). ing edge curves and at its highest point de­ velops a narrow facet for ligament attach­ DORSAL VERTEBRAE ment. This is expanded into a wider facet Seventeen dorsals are preserved in the at the posterodorsal aspect of the spine, type (Fig. 15). This is the normal number giving the spine a slightly smaller termi­ for the species. They are more uniform in nus. A small curious element believed to size than the cervicals but show a slight represent the intercentrum of the third or decrease in size posteriorly. The sides of fourth vertebra is shown in figure 14. By the centra are depressed as well, and stout way of further analysis, this element could paradiapophyses exist throughout. The A B C 3 cm

Fig. 13. Cervical vertebral centrum of Champso­ rnurus gtgas. A. Ventral view. B. Dorsal view. C. Lat­ r'ral view.

1 2. 5 mm

Fig. 14. Champso:,aurus gzgas, type specimen SMM P7l.2.J. A. Vt>ntral view of "intcrcentrurn." B. Latnal view of same.

29 ant. A

B 3 cm

C

Fig. 15. Champsosaurus gigas, type specimen SMM P71.2.1. A. First through sixth dorsal vertebra. B. Seventh through eleventh dorsal vertebra. C. Twelfth through seventeenth dorsal vertebra. All numbers refer from right to left. Note pathological condition in A and B near ventral intervertebral areas. 30 ERICKSON: CHAMPSOSAURUS IN NORTH AMERICA 31 first three look straight outward; the nite overlap of the last with the second remainder become increasingly angled centrum is a constant condition. It would caudad. seem otherwise in other species ( ref. The anterior two thirds of the dorsal p. 58). The diapophyses look directly out­ series in the type show marked deforma­ ward toward the iliac blades. Each neural tion of the centra, probably due to injury. arch is broad and supports a stout spine. However, the ventral carina are clearly The first is erect and siightly shorter than continued into the series from the neck that of the last dorsal ahead of it. The region, being quite distinct on the first second and third spines are expanded rear­ ward along their posterior edges. A pair of four elements. lateral processes located posterodorsally, Much of the material of the neurocentra as seen in the last dorsal, increase in promi­ is present but fragmented. In figure 15 nence to the last sacral, continue in the note the second dorsal vertebra in which first few caudals, then gradually fade. The the zygapophyses are of modest size. The zygapophyses are essentially like those of anterior ones face up and are mildly tipped the posterior dorsal vertebrae. out; whereas, the posterior zygapophyses face down and are angled inward. The neural spine is long, squared off dorsally, CAUDAL VERTEBRAE AND and directed rearward. The last dorsal CHEVRONS vertebra has broad zygapophyses that are Twenty-five caudal vertebrae are present nearly in opposition to each other anterior­ in the type and are represented by various ly and "back to back" posteriorly with a elements from the tail in figure 19. This is steep ventral pitch. The neural spine is probably about one half of the total num­ wider and shorter than the one in the ber. Caudals are also present in lesser num­ anterior bone. It is vertical and expanded bers in USNM 20521 and SDSM 53508. In appreciably at its distal extremity. Small USNM 20521, the first five elements are processes near the posterodorsal corner present in sequence. No definite chevron are also present but not to the extent facets are noted on the third vertebra. If that they are in the sacrals and anterior a chevron was present, it must have been caudals. There is a gradation of the neuro­ indeed loosely fixed and probably reduced central features between these two extreme in size. In any event, the base of the tail vertebra. The spines on the last few are may be said to consist of the first three more or less erect and swollen distally. vertebrae. Figure 20 illustrates the second caudal vertebra of the type. SACRAL VERTEBRAE Sutured ribs are in evidence in the type, The sacrum consists of three fused cen­ as well as USNM 20521, on the first ten­ tra. This portion of the column is preserved eleven vertebrae. It would seem from both in excellent condition in the type (Figs. 16 that one or two more uncoossified ribs also and 17). The centra are not as compressed exist. Lateral processes may have extend­ dorsoventrally as they are in older and ed to about the fifteenth or so vertabra. larger individuals, e.g., SMM P60.2004 The neurocentra remain stout with strong (Fig. 18). Of the present sacrals of C. zygapophyses. Coossification of neurocen­ gigas, the absence of overlap of the para­ tra with the centra in C. gigas is estab­ diapophysial surfaces of the second cen­ lished at about the level of the twelfth trum with the first centrum, and the defi- vertebra. From this region, ribs and sepa- 32 MONOGRAPH OF THE SCIENCE MUSEUM OF MINNESOTA VOL. 1

5 cm

Fig. lfi. Champsosaurus gigas, type specimen SMM P71.2.1. Right lateral view of sacral vertebrae.

rate neurocentra are not distinguishable; least one has an anterior spike positioned and the remaining caudals become simpli­ between the capitulum and the tubercu­ fied in form. The zygapophyses on these lum. In this case, the spike is double­ are much reduced and finally lost, the pos­ pronged, as it is only to a very subtle de­ terior ones disappearing first. The neural gree in the smaller species. As in other spine thins and loses its distal expansion forms, the tubercle is larger than the ca­ by the medial caudals. In the distal ele­ pitulum. The posterior cervicals are mostly ments, the neural spine is decreased fur­ lacking but an uncinate is indicated among ther; and the sides of the centra become the fragments present. laterally and ventrally ridged. Chevrons continue to the end of the series. Typical DORSAL RIBS medial and distal chevrons are illustrated Dorsal ribs are borne on seventeen verte­ in figure 21. brae. Nowhere are the peculiarities of the ribs of this genus better observed than in RIBS C. gigas. The dorsals are heavy, mildly arched, and show a fusion of tubercle and CERVICAL RIBS capitulum, the former becoming greatly Unfortunately, little is known of the expanded over the latter. Mild pachyostosis cervical ribs in C. gigas. The type presents persists throughout the series. The distal a number of fragments belonging to an­ end is swollen and abruptly terminated in terior ribs. These indicate the presence of the longest ribs. The first three ribs are at least four, short, Y-shaped ribs that thin distally and expanded into an uncinate curve posteriorly and are of the type illus­ projection (Fig. 23). From the fourth trated in figure 22 for C. laramiensis. At through the eleventh rib, there is a pro- ant

5 Cm

Fig. 17. Champsosaurus gigas, type specimen SMM P71.2.1. Dorsal view of sacrum.

C A B 3 cm

fig. 18. Sacral vertebral ccnlrum of Champsosaurus gigas. A. Ventral view. B. Dorsal Yicw. C. Lateral view.

33 A B C D E F

2 cm

Fig. 19. Champsosaurus gigas, type specimen SMM P7 l.2. l. Lateral view of caudal vertebrae from various regions. A.-D. Distal vertebrae. E. and F. median vertebrae.

w n 3

A C

Fig. 20. Champsosaurus gigas, type specimen SMM P71.2.l. A. Anterior view of second caudal vertebra. B. Lateral view of same. C. Posterior view of same.

34 ERICKSON: CHAMPSOSAURUS IN NORTH AMERICA 35 er and overlaps the posterior edge of the second centrum. The distal expansion is also different because of the thinning of the end into a posterior flange carrying only a narrow facet that is directed rear­ ward and outward but not for direct con­ l~ tact with the ilium. CAUDAL RIBS Unlike the caudal vertebrae, the ribs in C this section cannot be conveniently differ­ A B entiated by region. They are all similar in form and show a uniform gradation in size Fig, 21. Cht:vrons of Champsosaurus gigas. A. An­ from the first, which is the largest, to the terior view of proximal element. B. Lateral view of tenth. They angle ventrad and are strongly same. C. Lateral view of distal clement. curved caudad, especially the first few. nounced incising believed to be the result Their bases join the centra on broad, cen­ of pressure erosion induced by internal trally depressed surfaces. The first five are organs-the lungs. (ref. General Morphol­ shown in USNM 20521 in figure 27. Figure ogy, p. 76 and Figs. 58 and 59). Ribs 12 28 illustrates the first caudal rib of the through 17 are simple with reduced distal type in ventral aspect. Note the lateral swellings and gradual reduction in length rugosities and distal facet, which diminish toward the sacrals (Fig. 24). Unlike other rapidly. forms, all retain a strong facet at the distal PECTORAL GIRDLE extremity for cartilaginous attachment. In the type SMM P71.2.l, all elements SACRAL RIBS are represented with only portions of some Of the three sacral ribs of the type (Fig. lacking. It differs from other forms pri­ 17), the first is the longest and narrowest. marily in magnitude. H is curved rearward and expanded dis­ SCAPULAE tally (Fig. 25). It joins the first sacral The scapulae are both incomplete in the vertebra in an excavation formed at the type SMM P71.2.l, but a near complete meeting of diapophysis and parapophysis. restoration is possible because of the pres­ All ribs are compressed from above and ence of complementary portions between below along their shafts, are slightly the two. The scapula differs from most ridged in front and behind for most of their others in that its distal end is markedly lengths, and are similarly united with the expanded anteroposteriorly into a hatchet­ vertebral column. shaped blade (Fig. 29) ; whereas, in most The second or middle rib is greatly en­ other forms it is nearly uniform in width larged distally, especially in older individ­ for its length. In this respect, it is close to uals, to increase contact areas for ilium and that seen in C. la.raniiensis. However, in adjacent ribs (Figs. 17 and 26). This is both species, there are some individuals the stoutest rib of the sacral triplet. The possessing a blade that is not expanded last rib is much like its predecessor except distally. This may be an immature char­ the proximal articulation is greater in that acteristic or an expression of sexual dimor­ the anterior parapophysial portion is long- phism (ref. p. 62, General Morphology). n 3

A B

Fig. 22. Left anterior cervical rib of Champsosaurus laranziensis, juvenile. A. Internal view. B. External view.

w n 3

Fig. 23. Anterior dorsal rib of Champsosaurus gzgas, SDSM 53508, with uncinate process restored.

36 ERICKSON: CHAMPSOSAURUS IN NORTH AMERICA 37

~1

Fig. 24. Champsosaurus gigas, type specimen SMM P71.2.l. Last six ribs (Nos. 12-17). All except the largest are from the right side of the animal. These are the only dorsal ribs other than the first three having no incising for the lungs.

The blade is thin and more or less the CORACOID same thickness, except for the anterior Like the other ventral girdle elements, edge, in the region of contact with the portions of this bone are frequently found clavicle, which is heavier. Near the base with specimens that are fragmented. The of the blade, the bone swells and two point­ blade is often shattered or otherwise warp­ ed tubercles are present on the lateral and ed because of its thinness. The coracoid of posterolateral surfaces. The base of this SMM P60.2004 is shown in figure 30. It bone turns rearward into a massive ex­ reflects this condition of being shattered pansion consisting of a posterolateral face and is actually concave below and convex that forms the anterior half of the glenoid above, which is the reverse of the normal cavity and a larger irregular surface medial condition. Its shape is like that seen in to it that matches a similar area on the C. laramiensis but is distinguished from front edge of the coracoid. Medially, the other species by its well developed in­ scapula is incomplete but is reduced to a fraglenoid process. It is a large, flat bone thin plate that follows the curve of the thickened anterolaterally to form the large, clavicle. centrally excavated surface of the posterior w

("\ 3

A B

Fig. 25. Anterior view of first sacral rib of Fig. 26. Middle right sacral rib of Champsosaurus Champsosaurus gigas, SMM P60-2004. gzgas, SMM P60-2004. A. Dorsal view. B. Ventral view.

Fig. 27. First five caudal vertebrae and ribs USNM 20521.

38 Fig. 28. Champsosaurus gigas, type specimen SMM P71.2.l. Left first caudal rib in ventral view.

w n 3

Fig. 29. Champsosaurus gzgas, type specimen SMM P71.2.1. External view of right scapula, partially restored.

39 40 MONOGRAPH OF THE SCIENCE MUSEUM OF MINNESOTA VOL. 1 half or so of the glenoid fossa and a smaller INTERCLAVICLE rugose area medial to it for union with the The most complete interclavicle is repre­ posterior flange of the scapula. The in­ sented by the type (Fig. 33). Unfortu­ ternal rim of the plate has a broadly nately, most of the central blade is want­ curved cartilaginous border. ing. The transverse portion is massive. In overlying the horizontal portion of the clavicle, it bulges upward and spreads laterally almost to the base of the upright arm of the clavicle. At the center of the transverse portion, the front edge is de­ pressed and projected forward and nearly covers the junction of the proximal tips of the clavicles. The large posterior blade is intact for only about an estimated one third of its length. However, indications in SMM P60.2004 are that the blade was gen­ erally straight-sided, somewhat serrated, and not as expanded as in some forms. E Near its distal end, it was constricted and V drawn out into a point. The normal blade is gently concave dorsally. Ventrally, su­ tural surfaces occupy the transverse area; and the central blade is smooth. An inter­ esting pair of small foramina are located one on either side of midline just behind Fig. '.10. Left coracoid of ChamP.rosaurus gigas, the clavicle contact area. SM!v[ P60-200+, in dorsal view, partially restored. FORELIMB The forelimb is preserved in the type as CLAVICLE well as partially in SDSM 53504 and Both clavicles are present in the type USNM 20521. A forelimb to hind limb ra­ (Figs. 31 and 32). They form a wide, flat­ tio may be expressed as 100/135 for this tened, U structure across the anterior part species. of the chest. Their bases lie anteroventrally to the interclavicle, being joined to it by HUMERI heavy interlocking sutures. Their front The humerus (Fig. 34) is a stout bone edges form the leading edge of the pectoral with a slender shaft and wide expansions girdle, and at midline touch one another at both extremities-the distal end always at the extreme forward tip of the inter­ somewhat greater than the proximal. The clavicle. In dorsal view (Fig. 32), the shaft is twisted about 85°. This bone is not clavicle is strongly flared rearward to ac­ as massive as that of C. ambulator. Its commodate the wide interclavicle branch. proximal end also differs from this species The upright arm of the clavicle is narrow and C. lara-miensis in lacking a prominent by comparison with the horizontal portion entotuberosity. The ectotuberosity, as well, and is coarsely striated laterally where it is less pronounced but is partially sepa­ engages the anterior border of the scapula. rated from the head. A deltopectoral crest ERICKSON: CHAMPSOSAURUS IN NORTH AMERICA 41

running down from its edge is only mildly 37. This specimen is unweathered and developed. Distally, the humerus closely gives a good detailed view of the striated resembles C. lararniensis, having a large areas both internal and external. The base radial condyle and a lesser entotuberosity is broad with anterior and posterior sur­ and entepicondyle. A deep ectepicondylar faces that angle ventrad to receive respec­ sulcus is developed adjacent to the radial tively the pubis and ischium. Laterally, condyle. there is a large, smooth concavity that con­ RADII tributes the upper part of the acetabulum. Figures 35 and 36 illustrate the radius, Above this is a roughened buttress. The which bears no important morphological posteriorly projecting iliac blade is ovoid distinction from other species. The upper in form without parallel edges. At the an­ end is greater than the lower in surface terior base of the blade, a small tubercle area. The shaft has the characteristic curve projects inward. The length of the blade of the group and shows a ridge on its closely approximates. the height of the en­ external surface. tire bone.

ULNAE PUBES The ulna is very heavy proximally and The publis (Fig. 38) is a smooth, rec­ reduced and flattened distally (Fig. 36). tangular plate that has a deep sulcus along The most outstanding aspect of this bone its anterior edge and a straight posterior is its high, acute olecranon, which is in border that is in close contact with the contrast to the lower silhouette of some ischium for its entire length. Proximally, species. The radial facet is smooth and it is angulated for union with the anterior centrally depressed. The shaft is constrict­ slope of the base of the ilium and to form ed and carries a trace of a ridge distally the anterior portion of the acetabulum. The on its ventral side. The distal articular plate projects forward from the acetabu­ surface is slightly rugose and convex in lar area and expands to form a large, shape. rugose, downturned lip presumably for at­ tachment of ambiens or pubotibialis mus­ CARPUS AND MANUS cles. Distally, the public plate thins and is The forefoot of C. gigas is represented truncated to form the interpubic symphy­ by numerous unassociated elements; un­ sis. An obturator foramen is located to­ fortunately, no carpals are included. From ward the heavy end of the plate. what can be observed, its structure adheres closely to that illustrated for C. lararnien­ ISCHIA sis in figure 52 and referred to on page 66. The ischium (Fig. 38) is a smooth, No attempt at a formula is possible with triangular plate roughly the size of the the present materials. pubis. Its anterior edge abuts the posterior edge of the pubis in a straight contact. Its PELVIC GIRDLE posterior border angles rearward toward The upright ilium as well as the ventral the median from the acetabular area and plate-like ischium and pubis are preserved is strongly tuberculate about two thirds of for the most part in most of the present the way from the acetabulum. This feature specimens including the type. is acutely developed for a large tail liga­ ment and tendon. The prmcimal apex of the ILIA bone is thickened for union with the pos­ The ilium of the type is shown in figure terior slope of the ilium base and to form 42 MONOGRAPH OF THE SCIENCE MUSEUM OF MINNESOT A VOL. 1

3 cm

Fig. 31. Chamj1sosaurus gigas, type specimen SMM P7 l .2.1. Anterior view of the dermal shoulder girdle clements. the posterior portion of the acetabulum with the exception of C. ambulator. It is below. Medially, the plate is truncated to connected with the head by a narrow neck form the interischial symphysis. The on the postaxial side of the bone. It is median margin is dorsally swollen at about coarsely striated on its sides as well as midlength to lend transverse structural in the deep intertrochanteric fossa. The support. distal articular face is somewhat greater HIND LIMB in size than the proximal face, occupying the entire broadly rounded end of the bone. The hind limb was recovered in the type and in SMM P60.2004. As already indi­ TIBIAE cated, its length appreciably exceeds that This bone is characterized by a greatly of the forelimb. This suggests a greater swollen upper end, which is ovoid and use of the hind limb for the giant species, slightly domed, and consists of articulat­ perhaps related to the hypothesized lung­ ing area entirely (Fig. 40). The shaft is ing behavior mentioned elsewhere in this slender and has minor development of a paper. longitudinal distal ridge on the fibular side, FEMORA but the marked proximal ridge of some This bone (Fig. 39) is long and expand­ species is inconspicuous. The distal end is ed at each end. The shaft is twisted some strongly reflexed toward the fibula and 80° and has an open S shape. The proximal abruptly cut by a broad, flat, astragular articular surface is broad and occupies the facet. Below this, the shaft is terminated entire oval head. The internal trochanter in an oval articular surface about one third is much like that seen in all other forms that of the upper end of the bone. ERICKSON: CHAMPSOSAURUS IN NORTH AMERICA 43

3cm

Fig. 32. Champwsaurus gigas, type specimen SMM P71.2.1. Dorsal view of right clavicle.

FIBULAE This bone is essentially the same as that The fibula is paddle-shaped. Figure 40 in C. lara1niensis, except for size. Articu­ illustrates the element of the type speci­ lating surfaces surrounding the margin, men. The upper end is simple, being slight­ except for a brief space between the tibia ly swollen and rounded off as an articular and fibula, are expanded a bit more; there­ area. The shaft is nearly straight and of fore, a concavity of the dorsal and ventral similar thickness throughout. About mid­ sides is deeper. In the type, there is no way on the tibia side, there is a longitudinal suggestion of the usual perforating ar­ groove paralleling a short, low ridge that terial foramen on the lateral dorsal edge is opposite the longer ridge on the tibia as there is in the larger specimen. Proper noted above. The shaft begins to expand orientation of the single distal tarsal is about three fifths of the way down and uncertain. Its shape is subangular; and finally quits in a wide, arcuate surface the one reduced, nonarticulating surface is having a tapering area laterally and a concave. small oval area that is mildly excavated and turned medially to embrace the as­ PES Like the tarsus, only minor portions tragalus. The anterior side is convex and remain. From both feet, parts of seven or the posterior, flat in the type, and only eight metatarsals are represented. Meta­ perceptibly concave in SMM P60.2004- tarsals II-IV match those of other species a very large animal. nicely. Number V, shown in figure 42, presents the most diagnostic shape of all. TARSUS This bone is shorter than the others in the Two of the four component elements of series as far as known. Its upper end the tarsus are preserved in the type-the spreads out laterally for a distance more astragalus (intermedium) and a smaller than half that of the total length of the distal bone. Both are somewhat eroded. bone. It has a wide obtuse crown for The astragalus is also present in SMM association with the calcaneum proximally P60.2004 in an uneroded state (Fig. 41). and a flat medial facet, which is directed to 44 MONOGRAPH OF THE SCIENCE MUSEUM OF MINNESOTA VOL. 1

Fig. 33. Champrnsaurus gigas, type specimen SMM P71.2.l. Dorsal view of interclavicle with posterior portion of blade restored. the outer distal tarsal. The dorsal side has is made up of a stout, median segment with a low, central ridge and the ventral side, a a slight bow and a lateral pair joined to shallow proximal excavation. The distal it at each end by overlapping contacts. extremity is only a bit wider than the shaft; and there is a smooth, simple ovoid, The medial segment is grooved for about articular area. There is also a small ventral one fourth of its length at each end on its expansion of this area with a small tubercle anterior side. This is to accommodate the above it. Of the dozen or so remaining corresponding feature on the posterior side phalanges, all have normal terminal flaring of the inner end of each lateral segment. and facets. A long, fluted, claw-like ungual The posterior surface of the longer akin to that of other species is also noted. composite elements is incised longitudinally probably as a means, of better alignment GASTRALIA with adjoining elements or intervening The gastralia segments, judging from cartilage. the various specimens at hand, were well distributed over most of the ventral sur­ Measurements of the postcranial skele­ face of the body from the pelvis to the ton of Champsosaurus gigas are given in anterior dorsal region. Figure 43 shows the following table. All measurements are sections of these rod-like elements from of maximum dimensions unless otherwise various parts of the body. Each element indicated. B

Fig. 34. Champsosaurus gzgas, type specimen SMM P71.2.1. A. Postaxial view of right humerus. B. Pre­ axial view of sam~.

45 w n 3

Fig. 35. Left radius of Champsosaurus gigas, USNM 20521.

N

(') 3

V \ \ \ A B

Fig. 36. Champsosaurus gigas, type specimen SMM P71.2.1. A. Dorsal view of left foreleg. B. Ventral view of same.

46 p

,,I

lj'.

E u

C'?

,1! ,I I B

Fig. 37. Champsosaurus gzgas, type specimen SMM P71.2. l. A. Internal view of left ilium. B. External view of same.

ant. 3 cm >

Fig. 38. Champsosaurus gigas, type specimen SMM P7 l.2. l. Dorsal view of left side of puboischiadic plate. 47 0,

n 3

A B

Fig. '.l9. Champsosaurus gigas, type specimen SMM P7 1.2.1. A. Postaxial view of ~ t fem ur. B. Preaxial view of same.

48 w 0 3

B

Fig. 40. Champsosaurus gigas, type specimen SMM P71.2.l. A. Ventral view of rgiht tibia and fibula. B. Dorsal view of same.

w l'I 3

A

Fig. 41. Astragalus of Champsosaurus gigas, SMM P60-2004.

B

w n 3 2 Cm

Fig. 43. Champsosaurus gigas, type specimen SMM P7 l.2. l. A. and B. Ends of lateral portions of gastralia. C. Central bar of same. A B

Fig. 42. Champsosaurus gigas, type specimen SMM P7 l.2. l. A. Dorsal view of right metatarsal V. B. Medial view of same.

49 TABLE 1.

Height of Centrum Width of Centrum Length of at anterior end at anterior end Centrum Champsosaurus gigas, type SMM P71.2.1 Cervical Vertebrae

atlas 20.2 mm. 28.8 mm. 19 mm. axis 26.9 22.2 24 third 24.8 26.1 24,l fourth 24 27.6 25 fifth 26 27.7 24.3 sixth 27.2 29 24.7 seventh 26.1 29 25.9 eighth 25.9 28 26 ninth 26.1 29 26 Dorsal Vertebrae first 26.7 30.6 26 second 28.5 31.8 27 third 29.2 31.5 25.6 fourth 28:5 31.2 27.4 fifth 30,9 30.8 (est.) 27.1 sixth 28.6 30.7 28.5 seventh 28.2 29.6 28.5 eighth 28 (est.) 31.7 28 ninth 28.7 (est.) 31.5 ( est.) 29 tenth 29 32.5 27 eleventh 28.1 29.5 28.4 twelfth 27.6 28.9 28.8 thirteenth 26 29,9 29 fourteenth 26 28.6 28.7 fifteenth 25 27.6 28 sixteenth 24.7 27.9 28.3 seventeenth 23.5 27.6 28

Sacral Vertebrae first 23 26 28 second 21.9 28,7 27.2 third 21.1 28.8 26.l Caudal Vertebrae first 20.6 23 25 Height of last cervical vertebra including neural spine .. 73.2 mm. Height of second dorsal vertebra including neural spine ... . 74.8 Height of last dorsal vertebra including neural spine...... 62 Height of middle sacral vertebra including neural spine ...... 57.2 Height of first caudal vertebra including neural spine .. . 56 Total length of cervical' series including atlas and axis ...... 227 Total length of dorsal series ... 469 Total length of sacral series .. 81 Length of first sacral rib .. 53.9 Length of second sacral rib .... . 51.6 Length of third sacral rib ...... 49.7 Length of first caudal rib (along outside curve). 55.4 Height of scapula ... 90.8 (est.)

50 TABLE 1.-Continued

·width of shoulder girdle at clavicles .. . 180 mm. Height of ilium...... 63.5 Width (at base) ...... 29 Length (blade) ...... 63.4 Width of pubis ...... 80.6 Length (along inner border) .. 59.4 Width of ischium ...... 70 Length (along inner border) ...... 68.7 ·width of pelvic girdle (at ilia) .. 180.4 Length of humerus ...... 142 Greatest dimension at proximal end ...... 48.8 Greatest dimension at distal end .. 53.4 Length of l'adius ... 72 (est.) Length of ulna . 82.1 Length of femur .. 178.3 Greatest dimension at proximal end .. 36.4 Greatest dimension at distal end. 42 Length 0f tibia ...... 123 Length of fibula. 115.7 C. gigas, SMM PG0.2004 Total length of dorsal vertebral series .. 561 Total length of sacral series...... 96.3 Length of first sacral rib...... 67 Length of second sacral rib ..... 61.2 Length of third sacral rib .. 56 (est.) C. gigas, SMM P60.2004 Length of first caudal rib ... 57.2

• Width of coracoid (blade) .1 94.9 (est.) Length (blade) .. . 87 (est.) Height of ilium ...... 78.9 Width (at base) .. . 33.2 Length (blade) .. 78.8 Width of pubis ... 105 (est.) Width of ischium. 91.2 Length ... 90.7 (est.) Width of pelvic girdle (at ilia) ..... 240 Length of femur .... 207.4 Greatest dimension at proximal end. 46.5 Greatest dimension at distal end ...... 50 Length of tibia .. 140.6 Length of fibula .. 136

r

51 GENERAL MORPHOLOGY

As well as the general review of skeletal to the lack of materials of certain sized morphology, one aim of this study has individuals and the intergradation of age been to isolate juvenile and adult charac­ and individual character variations. Cer­ ters. Further separation of age variations tain trends were found, however. These from individual variations was attempted. are discussed below. The results of the latter are limited owing

SKULL

Osteology of the skull has had adequate shape, being elongated in some forms, description by Brown (1905), Russell abbreviated in others. Proper identifica­ (1956), and Fox (1965), in addition to tion of these two elements is also a point that attempted for C. giga,B in the present of conjecture lying as they do with only paper. one contributing to formation of the pos­ Relatively few skulls of Charnpsosaurus terior orbital rim and the other to the are known, and these show a remarkable anterior part of the temporal bar (Fig. 6). consistence in form. The minor differ­ In the champsosaurs, the postorbitals ences that do exist are largely variations may have spread to the entire posterior in the shape of some bones. These are ex­ border of the orbit and excluded the pre­ pressed by sutural patterns and are pre­ frontals completely from the orbit as in­ sumed to indicate differences between vari­ terpreted by Brown (1905); or, as in the ous species. Age variations and individual case of C. natator (Russell, 1956), dis­ variations found among those of compar­ placed the postfrontal from the orbit as able age cannot be determined reliably for well as separating it from the frontal. the skull. Therefore, only brief note will On the other hand, the prefrontal may be made regarding the variations observed. have, in retaining its more normal associa­ Notable among these are the prefrontal, tion with the frontal, encroached upon the which is longest in C. natator due to the position of the postorbital to the extent manner of joining the nasals, and the ju­ of eliminating it from the orbital rim. gal, which is also extended farther forward With exaggerated expansion of the tem­ than in other species. The relative length poral region in this form, it would seem of the snout remains unaffected, however. more convenient to have stretched the Most interesting of all of the skull ele­ postorbital into the base of the temporal ments are the postfrontals and postorbitals. bar away from the orbit and pressed the These bones show the most variation in postfrontal, a more medial element, into

52 ERICKSON: CHAMPSOSAURUS IN NORTH AMERICA 53 service as the sole contributor to the pos­ extent, of variations occurring among in­ terior orbital rim and as the major dorsal dividuals of approximately the same age. support of the jugal. The postorbital, in In regard to individual variations, the any case, still retains its ventral contact picture is not easily diagnosed. Conditions with the j ugal. such as discussed under the various head­ With normal relationships of these ele­ ings in this section are encountered and ments in a less modified skull, the postor­ may be indicative of variations not solely bital is lateral to the postfrontal, and, as governed by age. Designation of certain pointed out by Romer (1956, p. 105), ontogenetic states, e.g., juvenile, young normally makes up part of the temporal adult, etc., was arrived at in part by ob­ bar. These elements have been interpreted serving the relative numbers of various­ in this light in the present paper. sized individuals present from a single horizon. The average-sized specimens com­ Details of the braincase are not clear prising the majority were probably young in any of the specimens of C. gigas; hence, breeding adults and are regarded as such no discussion beyond what has been de­ for this analysis. In all situations encoun­ scribed for this species in the previous tered where champsosaur remains occur section will be made. in large numbers, immature specimens, in­ cluding the extremely small, are repre­ MANDIBLE sented. This indicates that both young and Lengthening of the distal Jaw may be adult forms. occupied the same habitat and related to age as is probably the slight that the young were hatched or born in the dorsad flare of the extreme tip as shown immediate vicinity of the normal habitat in figure 9 and Russell (1956, p. 38, Plate of the adult. VI) for C. natator. This is not as notice­ A second criterion applied in judging able in small jaws. the relative age of a specimen employs proportional comparisons between small, average-sized, and large specimens. It was POSTCRANIAL SKELETON found that the limb length and individual The postcranial skeleton of Charnpso­ limb bone ratios within a species nearly saurus is of modest proportions ranging match regardless of age (Table 2). How­ from a few feet to upwards of eight feet ever, limb bone extremities do change in in length and presenting a somewhat croco­ proportion with age. The long bones and dilian-like appearance. In this section, an girdle elements of the young are also attempt has been made to review the gen­ straight or flat, depending on the element eral osteology and separate juvenile and considered, and are relatively featureless; adult osteological characters. Features in whereas, homologous elements of the adult one or the other groups are expressed become quite expressive of features and largely as a matter of proportion and de­ curvature. Other bones, such as vertebrae, gree but are, nonetheless, important con­ show delicate structures like the ventral siderations in understanding the group as carina that become merely heavier and less a whole. acute with increasing age. The postcranial skeleton affords ample Another difference indicative of age is points of comparison not only between the amount of layerng found in the peri­ young and adult stages, but, to a limited osteal portion of the long bones and ribs 54 MONOGRAPH OF THE SCIENCE MUSEUM OF MINNESOTA VOL. 1 TABLE 2.

No. 982 (adult) Juvenile, C. laramiensis from Brown (1905) SMM P65.3.1 length of humerus ...... 120 mm. 77 mm. length of ulna .. . 75 47 length of radius ...... 73 47.2 length of scapula ...... 92 67 length of coracoid ...... 68 47.5 width of coracoid ...... 65 41.2 length of femur ...... 144 93.5 length of tibia ...... 107 69.5 length of fibula .. 98 64.5 humero-femoral ratio .83 .82 ulna-humeral ratio ... .63 .61 tibia-femoral ratio ...... 75 .73 length of 1st dorsal centrum ...... 25 17 height of 1st dorsal centTum .... . 23 14.2 width of 1st dorsal centrum. 26 17.6 length of 1st sacral centrum ... 25 15.6 height of .1st sacral centrum. 19 13.1 width of 1st sacral centrum .. . 25 15 length of 1st caudal centrum .. . 24 (?) 15.5 height of lst caudal centrum .. 15 14.9 width of 1st caudal centrum. 16 15.6

(ref. p. 78). the propo1·tional disparities between small In this work, the words "young," "juve­ (young) and adults. For example, regard­ nile," and "immature-" are used inter­ ing the pleurocentrum of the atlas, the changeably to describe nonadult conditions whole forward face changes. The anterior or individuals. The term "subadult" is projecting process on the superior surface used to indicate a form that is older than is a prominent feature in the adult and al­ tbese but not possessing strictly adult most nonexistent in the juvenile. The an­ features. terior articular face widens in the adult and becomes prominent (Fig. 11). This VERTEBRAL COLUivlN unit of the atlas is described ,in further detail for C. gigas in the preceding section CERVICAL VERTEBRAE and may be applied to all species. Of the (Atlas-axis complex). As stated (Parks, three remaining units comprising the atlas, 1927), the atlas and axis are of great deter­ a pair of neurocentra (neural arch) and minative value. In the context of determin­ an intercentrum (hypocentrum) are simi­ ing species, this has not proved to be the lar in form wherever known. Their form case. However, in determining relative age is simple and considered primitive. Each of a particular specimen, it does have value. is separate from any other unit. Each half The atlas is known only in C. laramiensis, of the neural arch is formed by a unit that C. ambulator, and C. gigas. It is partially is more or less T-shaped in profile. Arching known in C. natator. The axis is represent­ across to midline, the anterior arm meets ed in the above two former species and the exoccipital forming the superior seg­ partially in the latter two. Of the various ment of the atlantal ring and provides a homologous elements making up the atlas­ protective shield for the spinal cord. The axis complex, a constancy of shape and other arm of the T is directed caudad and form is the rule. Greatest exceptions are forms good articulation with the anterior ERICKSON: CHAMPSOSAURUS IN NORTH AMERICA 55 zygapophyses of the axis. The stem of the T As preserved in C. laramiensis and C. angles downward and diminishes as it con­ natator, the neural arches differ only tacts the hypocentrum. Medially, the stem slightly from each other. The character­ of the T is expanded forming a solid articu­ istic features of this unit are a very slight lation with the laterally expanded surfaces neural crest that is directed posteriorly of the anterior side of the pleurocentrum. to form the post zygapophyses and a short The lower segment of the atlantal ring is forward projection that reduces to a nar­ formed by the wedge-shaped intercentrum. row wedge and supports the anterior This is an interlocking piece adding to the zygapophyses. The intercentrum of the support and control of the neck. Articula­ axis fills an intervertebral position ventral tion facets cover the entire posterior sur­ to the main articular facets for the atlas face of this element (for contact above pleurocentrum ( odontoid) and the axis with the pleurocentrum and below with centrum. Its expanded posterior face, which the intercentrum of the axis), superiorly is concave to a greater degree in younger at each extremity (for contact with the animals, embraces the corresponding in­ neural arches-neurocentra), and anterior­ ferior facet of the axis. Dorsally, it con­ ly in a concavity for union with the occipi­ tacts the axis pleurocentrum and its inter­ tal condyle (Fig. 12). centrum at its forward extremity.

The axis is less complicated, having only CERVICALS (three to nine) three separate units: centrum, neural arch, There are judged to be nine cervicals and intercentrum. The centrum only is in all species of the group. However, a com­ preserved in C. gigas (refer description, plete series is known for C. laramiensis, p. 27). This unit of the axis regularly has C. ambulator, and C. gigas. The cervical three articular areas in the same places centra are subcylindrical and more or less and occupying proportionally equal areas isometric, having three axes of nearly in each species. The anterior surface has equal length. If anything, they are a bit a large superior facet for union with the dorsoventrally compressed and concave on pleurocentrum of the atlas. Below this is a the sides. There is a gradual increase in size smaller facet that is set in and looks an­ posteriorly. The oblique faces of the centra, teroventrally in both young and old individ­ mentioned by most authors, account for uals. In C. gigas, it appears to have a more the modest dorsal curvature of the neck­ forward facing attitude. In figure 10, the especially noticeable near the front. In life, profile of this unit is shown. In anterior great mobility was provided by the re­ views (Fig. 44), the centra of young and flexed perimeters of the articular faces of adult specimens are shown to differ also. the centra, as noted by Brown (1905). In the juvenile, there is a more acute base There is a ventral carina that is more and a suggestion of a ventral carina. The salient in certain species. Brown's (ibid.) adult does not have this condition as the cervical carina are very pronounced in C. ventral surface is squared off. The neural laramiensis, reaching their greatest de­ arch arises from the lateral diapophysial velopment at the seventh vertebra, then sutures on the dorsal surface of the cen­ decreasing to the eleventh vertebra. Figure trum, the bases of which are much ex­ 45 illustrates the series in a subadult. This panded and indeed characteristic, and the feature is also impressive in very young most readily recognizable feature of champ­ specimens of this species ( viz., SMM sosaur vertebrae. P.65.3.1, mounted skeleton, Fig. 46). The 56 MONOGRAPH OF THE SCIENCE MUSEUM OF MINNESOTA VOL. 1

w n 3

A B C

Fig. 44. Anterior view of axis pleuroccntrum in: A. Champsosaurus laramiensiJ, juvenile. B. C. natator, subadult to young adult. C. C. gigas, mature adult. feature diminishes with increasing age. do not become well defined until the fourth In examination of numerous specimens of or fifth vertebra where there is no longer C. gigas, some very young, the ventral a contiguity with the anterior face of the carina was found to be much less pro­ centrum. They gradually increase in promi­ nounced. nence and finally merge with the diapo­ physes at about the beginning of the Diapophyses are well developed and also increase in size from the front towards dorsals. the rear of the column. Parapophyses, Occasionally, one or both parapophyses Brown (ibid.) states, begin on the fourth on the ninth vertebra may be confluent vertebra in C. laramiensis; other authors, with the diapophyses; or one or both may (Russell, 1956), note their appearance on still be separated on the tenth vertebra. the fifth vertebra of C. natator. Actually, This condition seems to be independent capitular articulation areas (parapophy­ of the relative age of the individual and ses) are found throughout the cervical within the realm of normal variability. series with the exception of the atlas, which Intercentra have been mentioned for the bears no rib, and the axis (Fig. 10). They first five cervicals (Brown, 1905). These

3cm

Fig. 4-5. Cervical centra 3-9 of Champsosaurus laramiensis, juvenile size. ERICKSON: CHAMPSOSAURUS IN NORTH AMERICA 57 were obviously very small elements and (Parks, 1927). The dorsals (Fig. 15) are perhaps to a large extent cartilaginous. usually circular in section with slight dor­ There is evidence that the intercentra, a soventral compression posteriorly. The ar­ rather primitive feature, were retained ticular faces are amphiplatyan. There is in the full cervical series. Figures- 45 and no marked change in the length of the 46 show juvenile aspects of the ventral centra from front to rear. The sides are carina wherein the anterior portion of the always slightly concave, and prominent carina is carried far forward and ventral parapophyses are situated a little ahead to the intervertebral space and spread of center on the first few centra. These presumably to accommodate the intercen­ gradually move back along the sides and trum. Subsequent development of the main are always confluent with the diapophyses, articular faces overgrew and displaced the with the possible exception already noted intercentra with the possible exception of for the first vertebra. Unlike the cervicals, the first few elements. As indicated in the the first few dorsal diapophyses look type (Fig. 14), a single "intercentrum" is straight out, not caudad. Any reference preserved and believed to represent that to the degree of concavity as being diag­ of the third or fourth vertebra. nostic of species seems hardly valid. It is more likely a condition of individual variation.

- The neurocentral suture is an outstand­ 2 cm ing part of the superior surface of the - .- 0 centrum as it fills most of the surface area 0 on either side of a centrally constructed A B neural canal floor. It is positioned more forward on the centrum. Fig, 46. Anterior view of cervical centra, Champ­ A ventral keel or carina is observed on sosaurus laram.iensis, juvenile specimen. A. Anterior the first few dorsals of all species. Ac­ cervical. B. Posterior cervical. Note modification of carina in B. cording to Brown ( 1905), only the first dorsal of the adult has it; but juveniles Neurocentra are heavy with a large carry it on the first four vertebrae. From canal that is higher than it is wide. Zyga­ the present materials of C. laramiensis, it pophyses are strong. Anteriorly, they tip was found that carina occur on the first outward; posteriorly, they tip slightly in­ few vertebrae of adults, although some ward. The neural spines are long and nar­ are very much reduced and rounded; hence, row. The extremities are rounded, and the condition appears to be a variable one. there is a distinct ligamentous facet at the As further evidence in adults of C. gigas, posterior point. The last is the heaviest the feature can be very rugose or smooth and most nearly resembles that of the and varies in extent between the first and squared first dorsals. the middle of the fourth vertebra. Brown (ibid.) indicates a shift in the DORSAL VERTEBRAE attitude of the parapophyses from an out­ The dorsal vertebral series appears to be ward facing position in the anterior region stable in a number of elements. All species to a rearward, oblique position in the pos­ have seventeen dorsals although a com­ terior vertebrae. A shift of this kind takes plete set is unknown for C. albertensis place in C. gigas at about the level of the 58 MONOGRAPH OF THE SCIENCE MUSEUM OF MINNESOTA VOL. 1 third dorsal, a point at which the ribs are adult specimens examined in this study no longer confined by the shoulder girdle show evidence of a firm joining (fusion) and the body begins to bulge outward. At of the third and second sacral centra. The this point, also, the tighter radius of the third sacral rib, as well, is changed by juvenile rib accounts for a more slender adulthood and makes substantial contact body form (Fig. 47, A). Body bulge in­ with the ilium. No distinction of a "sacro­ creases with size and perhaps varies be­ caudal" in any species seems justJified. tween sexes. Individuals of modest pro­ The areas of insertion (diapophyses) for portions (subadults), however, seem to the rib heads are large-sized on all three have acquired most of the bulge that is vertebrae and are located toward the front to be attained. In C. gigas, at the level of of each centrum. An ontogenetic trend is the third rib, it is judged that the trachea separation of the ribs from one another became bifurcated forming paired bronchi. as effected by lengthening of the sacrum. The remainder of the neural arch is a In young animals, e.g., C. lararniensis, the massive structure similar to that described last two ribs at their proximal ends over­ for the cervicals. The canal is reduced in lap upon the centrum in front of their own. size and more circular. There is no marked In other words, the middle rib is partially break in neural spine shape or pitch be­ supported by the first centrum as is the tween the neck and trunk regions. Spines third rib by the middle (second) centrum. are best developed anteriorly and decrease In larger specimens of this species, the in height and angle to a vertical blade near overlap between the first and second centra the middle of the series. In juveniles there is lost; and in the largest specimens, the is much less erectness of the blade, and overlap between the second and third is it remains constantly pitched rearward sometimes lost. In C. gigas and C. alberten­ throughout the column (Fig. 47, B). sis, the overlap condition between the sec­ "Squaring off" of the spines with age gives ond and third is retained in all specimens the blade its upright orientation. examined-a condition that would lend ad­ ditional strength to the column at this SACRAL VERTEBRAE point. The neurocentra are well formed, General form of the sacral portion of as in the dorsals, with stout spines that are the column is a flattened set of three verte­ greatly thickened at their tips-a feature brae fused together. The first is the largest. established at an early age. As best shown The last is more circular in cross section in C. gigas, the spine extremity becomes as well as being the smallest of the three. complicated with lateral processes and a The ventral surfaces are broad and flat­ posterior facet. The spines are erect in more so in adults. Brown (1905) states, adults and swept back in juveniles. "Sacrals consist of two true sacral verte­ brae and a sacrocaudal." The basis for CAUDAL VERTEBRAE AND CHEVRONS this observation is the lack of fusion of A complete caudal series is unknown. the third vertebra of the sacrum triplex to Estimates of the number of vertebrae run the second (middle) centrum, and the fact from 36 upward. It would seem that a that the distal rib end on the "sacrocaudal" dozen or so should be added to this num­ is only in partial contact with the ilium. ber to complete the series. The caudals A similar condition is also found in the have been divided into as many as four mounted skeleton of C. lararniensis, SMM types by Brown (1905), Parks (1927), P65.3.l, which is an immature animal. All and others according to the presence of ERICKSON: CHAMPSOSAURUS IN NORTH AMERICA 59 'I

:, 'I

B

Fig. 47. A. Dorsal view of Champsosaurus laramiensis, SMM P65.3.l. Mounted skeleton of juvenile. B. Lateral view of same. Total length of specimen along vetebral column including skull: approx. 1610 mm. chevrons, rib attachments, and type of of ribs. In some specimens of C. gigas, for neurocentral joining. Because of inconsist­ example, as many as fourteen or fifteen ence in a demarcation between types, it vertebrae may have carried ribs or lateral seems best to consider the tail by regions. processes. The last few of these, however, The first region, or the base of the tail, were not suturally joined to the centra and consists of the first two or possibly three may not constitute "ribs." Coossification of vertebrae and is the only region that bears rib and centrum occurs between the level no chevrons. A loosely attached chevron, of the ninth through fourteenth vertebrae. however, may have been present on num­ Coossification of the neurocentra and cen­ ber three in some. Neurocentra and ribs tra also occurs within this range but not here are suturally united to the centra. perforce at the same point. In C. gigas, the The second region of the tail begins with tenth neurocentrum and the ribs are still attached suturally. In some C. laramiensis the third or fourth vertebra and may ex­ they are already fused on the ninth. In tend through the fourteenth. SMM P63.13.l of the same species, they According to Brown (ibid.), ribs are are not. The neurocentrum fuses in C. carried on the first twelve vertebrae only. gigas at about the eleventh or twelfth ver­ His number thirteen has no trace of a rib tebra; and the ribs-it is estimated from or lateral process. Parks ( 1933) indicates their size in the eleventh vertebra-remain eleven on an interrupted sequence. Further uncoossified beyond this point, perhaps only evidence shows variability in the extent to the twelfth vertebra. Beyond this, sev- 60 MONOGRAPH OF THE SCIENCE MUSEUM OF MINNESOTA VOL. 1 era! smaller lateral processes persist. Fig­ bers two and three in C. gigas. The form ure 19, E and F, shows persistent lateral of the cervical rib varies. Only in C. nata­ processes on what are considered to be tor, C. laramiensis, and C. gigas is there a near the fifteenth caudal vertebra. The re­ posterior uncinate prominence. In the first, maining caudals of C. natator after eleven the uncinate is present from the sixth are alike (Parks, 1933). The arrangement through the last cervical. It is suspected in C. albertensis is uncertain, although it to be similar for the latter two also. appears that lateral processes or parapo­ physes extended to the fourteenth or so. DORSAL RIBS A third region of the tail, beginning be­ Most interesting of all the ribs are the tween the ninth and fourteenth vertebrae, dorsals. All vertebrae in this series have is noted as having the neurocentra and ribs ribs. They are rather heavy elements with coossified with the centra. Ribs are lost single heads, except occasionally the first around the twelfth through sixteenth, in immature animals. In the young of wherein begins a fourth region, including C. laramiensis, (Brown, 1905) and SMM all remaining elements. A heavy dorsal fin P65.3.1, there is a slight separation into was a feature shared by the first dozen or two articulating heads. This situation can so vertebrae in life. Beyond this, the distal be expected in the young of all species. The expansion of the neural spine is drastically tubercular facet is always confluent with reduced, but a thin fin probably remained. the capitular by the second dorsal and be­ comes very broad in older individuals as RIBS well as superior in position to the lower head. It is especially noticeable in C. gigas CERVICAL RIBS wherein its area is twice that of the capitu­ Ribs are borne by all cervical vertebrae lar area in the region of the longest (7th- except the first. The absence of parapo­ 8th) dorsal rib. physes (Parks, 1933 and Russell, 1956) The general shape is a stout shaft that on the first few vertebrae does not reflect curves gently caudad and is twisted medi­ the absence of ribs. All ribs are divided ally and somewhat swollen distally. All proximally into a small capitular head and terminate abruptly. There is a keen ridge a larger tuberculum. As the parapophyses both in front and behind. This is especially climb on the centra and progress rearward, marked on the proximal half of the shaft. the lower head moves in beneath the upper. The distal extremity is fluted usually The ribs increase in length until the eighth with numerous open canals in the peri­ (last), which is disproportionately longer osteal surface. The first few ribs are flat­ and heavier than the preceding ribs. The tened against the body rather than swollen first rib is simple, smooth, and rather. distally in C. natator, C. laramiensis, and straight. The succeeding elements are curv­ C. gigas. With this terminal modification, ed rearward and angle ventrad. Along the a posterior uncinate process develops, anterior surface of each rib is a ridge that which is simply a continuation from the ends proximally in a small spike between cervicals. With proper alignment, the unci­ the capitular and tubercular processes nate process actually projects more upward (Fig. 22). This feature exists on ribs one than posteriorly. The uncinate gradually to five in C. laramiensis, two• to eight in moves down the blade and diminishes. This C. natator. It is missing on the sixth in feature, when present, is an indication of C. albertensis and preserved only on num- maturity; in C. laramiensis, at least, it is ERICKSON: CHAMPSOSAURUS IN NORTH AMERICA 61 totally lacking in juvenile skeletons. It is mated to cover nearly the same extent in probable that the appearance of this fea­ the smaller species also. As the ribs become ture is correlated with the time at which more robust with age, incising becomes major body bulge is being attained or deeper. The last six ribs (Fig. 24) are "subadult" size. simple and without visceral ,incising. A In C. natator (Russell, 1956), the un­ ridge persists on both front and rear edges. cinate is distinct on the ninth and tenth The anterior ridge covers essentially the ribs but rudimentary on the eleventh and entire length of the shaft. Brown ( 1905) lost in the remainder. A complete set of indicates that the last three are without dorsals for an adult of C. laramiensis is cartilaginous attachments. These are dis­ not available, but a prominent uncinate tinct in all specimens as having reduced is indicated by the flared tip of what is distal ends that may have been unattached. considered to be the eleventh adult rib in However, some a:ttachment is indicated, at SMM 64.10.1, by comparison with C. nata­ least in C. gigas, by the existence of small tor. An even stronger uncinate is preserved but well marked facets (ref. p. 22). on what is taken as the tenth rib in C. gigas (SDSM 53508, Fig. 23). The eleventh rib SACRAL RIBS also of this species (USNM 20521) has an The sacrum contains three ribs. It is incipient process nearly at the base of the their nature to be consistent in the func­ shaft of the same rib. The twelfth rib tion of support as all engage the ilia at shows no sign of the feature. Correspond­ their distal ends. The overall result is a ing elements in C. albertensis and C. ambu­ strong pelvic bridge. The shape of the lator (supposedly adults) are more uni­ sacrum with ribs in place is square. A juve­ form in shape, and none show expanded nile characteristic is a tapering form (Fig. extremities or uncinates. 48) mainly because of the underdeveloped At about the level of the third or fourth last rib. The center rib is the largest of the rib, there is a general lengthening of the ribs; and they become directed more rear­ ward from their bases. The lengthening is accompanied by a lateral spreading and widening of the rib cage. As noted above, it is within this anterior region of the, body that the lungs also expand. This develop­ ment is believed to be responsible for the modification in the form of incising observ­ ed in certain forms. It is seen in large specimens of C. lararniensis (adults) and in all individual ribs of C. gigas examined (possibly all adults). The incised area oc­ Fig. 48. Dorsal view of the sacrum, Champso­ cupies up to one third the length of the saurus laramienJis, SMM P65.3-.1. Mounted skeleton visceral surface of the rib starting slightly of juvenile. above the distal end. It is best developed three and lends most support. Ontogenetic­ on the longest (7th-8th) rib. Incising is ally, the third rib becomes more involved inclusive of ribs four through at least and eventually shares about equally in sup­ number eleven-nearly one half of the port of the pelvis. This seems to be es­ total dorsal length of the series. It is esti- pecially true in C. gigas and C. albertensis, 62 MONOGRAPH OF THE SCIENCE MUSEUM OF MINNESOTA VOL. 1 the largest species in which the base of the SCAPULAE third rib retains its minor overlap condi­ The scapula consists of a short, vertical tion onto the second centrum. The base of blade that is generally uniform in thick­ the third rib actually becomes larger than ness and width but varies to an expanded that of the second rib. Its distal end en­ hatchet-shaped blade in some individuals larges as well but never quite reaches the of C. gigas and C. laramiensis. Because of size of the second rib. sampling limitations, it is difficult to judge The first rib is curved backward (Brown, if this variation is one of age or individ­ ibid.) . It is also thinned on the forward uals. In C. laramiensis, for example, the border and projected forward on its distal uniform blade is a character of the young­ end. A similar shape prevails in all species. est specimens. Large individuals have a This bone in C. gigas, however, has a more pronounced broadening of the distal end. distinct backward hook with little thinning In C. gigas, a similar condition exists. of the border and projecting of the distal However, a thin, unexpanded blade also end. The second rib, as noted, is most uni­ occurs in the adult stage. From what can form throughout the developmental growth be determined from these individuals, stages. The third rib shows changes; viz., there is an accompanying condition in in the very young, this bone is straight or which there is slighter development of the may arch weakly forward, and the proxi­ limb bone extremities and girdle elements. mal end shows most expansion. As stated This leads one to suspect that some ex­ above, it overlaps the posterior part of the pression of sexual dimorphism exists in the second (middle) centrum. The distal and skeleton. proximal ends expand appreciably in the In all specimens, the suprascapular bor­ subadult stage, and on the rear edge there der truncates the blade in a gentle arc. appears a prominence that migrates with Anteriorly, the edge of the blade provides age outwardly. As a result, larger speci­ a small, roughened surface for attachment mens show a distinctive flare at the most of the vertically inclined end of the clavi­ posterior distal corner of this bone. cle. Below this at the anteroinferior angle of the bone is developed an acromial CAUDAL RIBS process. The inferior end of the scapula Distribution and comments on the caudal consists of a short, anterior, subcircular ribs within their respective regions of the blade that curves inward (following the tail are made elsewhere. Figure 28 shows curve of the clavicle) toward the medial a typical caudal rib with its distal and interclavicle and in life probably had carti­ proximal attachment areas. laginous connections with both of these elements. The posterior portion is thick­ PECTORAL GIRDLE ened externally and thinned medially for The pectoral girdle forms a shield affair reception of a corresponding surface on the over the anteroventral portion of the body. coracoid. In one form (Russell, 1956), a It is composed of scapulae with short, out­ fusion of these bones is reported ; yet none wardly spreading, upright blades; ventral of the materials examined showed this. The disc-like coracoids; and an elongate inter­ forward portion of the glenoid cavity is clavicle that is tied firmly to the endo­ formed laterally adjacent to the coracoid chondral elements by a pair of stoutly curv­ surface. The height of the blade increases ing clavicles. Ventral interconnecting carti­ very little with age; whereas, the inferior lages evidently were present in life. portion expands noticeably. ERICKSON: CHAMPSOSAURUS IN NORTH AMERICA 63

CORACOIDS unite with the median interclavicle about A major component of the ventral pec­ at the level of the eighth rib and tie the toral shield, the coracoid, is positioned be­ girdle together. These elements are stout hind the scapula. As indicated above, its throughout, thinning at their ends. As it outer anterior portion is heavy as, it forms reaches the base of the scapula, the shaft the posterior half or better of the glenoid of the clavicle is twisted and becomes cavity and the adjacent scapular connec­ coarsely striated as it turns dorsad to lie tion. Immediately posterior to the glenoid in close contact with this element. Medially, fossa is a prominent laterally projecting the horizontal portion is striated and ex­ infraglenoid process that is the principal panded for a solid interlock with the cross structure of variation among spedes. arm of the T-shaped interclavicle. In C. natator, this process is continuous with the glenoid surface (Fig. 49) and, INTERCLAVICLE consequently, of little prominence. Neither The shape of this bone is that of a T. is it an oustanding feature in C. alberten­ When united with the clavicles, its cross sis. In C. laraniiensis, C. ambualtor, and arm extends to form a channel (Fig. 31) C. gigas, it is bold and located well apart that gives Champsosaurus its characteris­ from the glenoid surface at all ages. (Fig. tically flattened chest. The stem of the in­ 30). The remainder of the bone is a large, terclavicle projects rearward into a blunt ovoid plate that reaches nearly to the inter­ point and shows variations of length and clavicle to which it was most likely joined shape among species. The stem is thin by cartilage in life. A supracoracoid fora­ dorsoventrally, concave above, and except men is located near the scapular border for its anterior end has a cartilaginous about at the center of the element in all border surrounding it. species. FORELIMB CLAVICLES Structurally the forelimb bones, as the The shaft-like right and left clavicles hind limb bones, exhibit a condition of the compact periosteal bone that is generally nonvascular. This condition in which canals are sparse or absent is typically lepido­ saurian (Gans, et al., 1969, p. 61). A sec­ ond condition found at middiaphysis is also lepidosaurian in character in that it resembles the condition found in lizards wherein the cancellous trabeculae are greatly limited and in some specimens al­ most totally absent. Ratios between the front and rear limb lengths of both adults and subadults give an idea of the relative lengths that one might expect in various species. The number of specimens available for this analysis was small because both forelimbs and hind limbs are not often pre­ Fig. 49. Right coracoid of Champsosaurus natator served intact and together, therefore, im­ in dorsal view. posing obvious limitations. From a total of r If 64 MONOGRAPH OF THE SCIENCE MUSEUM OF MINNESOTA VOL. 1

nine suitable skeletons (7 adults and 2 ju­ arrangement is around 80°. This condition veniles), ratios of 100/125 - 100/135 were is variable. A deltopectoral crest is a salient found. Extrapolation on several less com­ feature on the shaft in C. ambiilator, mild­ plete specimens suggests similar ratios. In ly developed in C. laramiensis and C. gigas, each case, the hind limb is longer ( all meas­ but nearly lacking in C. natator and C. urements perforce exclusive of the foot). albertensis. The extremities of this bone Three specimens of C. gigas account for the are widely expanded but vary considerably greater ratio of 100/135. Both the femur among adults. The proximal end or head and epipodials become noticeably extended is always shorter in breadth (widest dimen­ in this form. C. natator is the only species sion) but thicker in width than the distal without complete enough material for a de­ end. A large, articular surface is available termination. C. ambiilator appears to have proximally. Ento- and ectotuberosities are been the shortest limbed form as judged developed to a greater or lesser degree and from a single skeleton (Brown, 1905). most often continuous with the head. Brown (1905) notes a distinct separation HUMERI of these tuberosities from the head in C. Morphologically, this bone has diagnostic ambnlato1· as well as in an immature speci­ value in specific differentiation. Humeri of men of C. laramiens·is. This is found to be four species are compared in figure 50. This variable in the young and not a unique is a stout bone with a narrow shaft that is condition. At its distal end, the humerus is ovoid in cross section. The shaft is twisted compressed dorsoventrally with the limb causing the ends to align 45° - 85° with extended in a horizontal plane. The articu­ one another. The most commonly observed lar surface covers the, entire end. In one

n 3

A B C D

Fig. 50. Humeri of four species of Champwsaurus. A. C. laramiensis, juvenile, B. C. ambulator. C. C. nalator. D. C. gigas. All in prcaxial view. ERICKSON: CHAMPSOSAURUS IN NORTH AMERICA 65

form, C. ambulator, the radial condyle is RADII robust indicating the emphasis. of support The radius (Fig. 35) is not a diagnostic on this supposedly more ambulatory form. element. It is a rather fragile bone well The feature is only moderately developed over half the length of the humerus in all in other species; and in C. natator and C. species with expansions at each end. The albertensis, there is very slight develop­ upper end is the largest-ovoid and flat, or ment. Immediately above the radial con­ slightly excavated to fit the condyle of the dyle is an ectepicondylar sulcus instead of humerus. The lower end is convex and more a foramen. This increases in depth toward circular in cross section. The shaft has a the distal end to where it nearly penetrates distinctive twist, probably related to the to the ventral side but is unknown to ac­ posture of the foot (Romer, 1956), and a tually do so. The sulcus becomes deeper ridge on its external surface. with increasing age. It is distally closed, or nearly so, in C. ambulator but remains ULNAE open in other species. Its status in C. The ulna (Fig. 36) is essentially equal albertensis is uncertain (Parks, 1927). in length to the radius, heavier, and gen­ The remainder of the articular surface erally just as undiagnostic. There is a varies somewhat in breadth. Centrally, heavy proximal end of subtriangular form there is a mild swelling-the entotuberos­ in cross section. The olecranon is large and ity. This is lacking in juveniles. Posteriorly, of modest elevation in all except C. gigas the entepicondyle extends up the side of the where it is exaggerated in height. It is shaft a bit. Ontogenetic development of least obvious in C. natator. The shaft is these aspects of the humerus is illustrated flared on its internal side at the head to for C. natator in figure 51. provide a radial facet. The shaft narrows

A B C D

3 cm

A'

Fig. 51. Ontogenetic development of the distal end of the humerus in Champsosaurus natator. A-A'. Young, has simple articular surfaces, ectepicondylar su lcus incipient. B-B'. Larger juvenile, beginning to de­ velop radial condyle. C-C'. Subadult, shows all condyles. D-D'. Adult, full development of condyles; ectepicon­ dylar sukus deep. 66 MONOGRAPH OF THE SCIENCE MUSEUM OF MINNESOTA VOL. 1

rapidly below this and becomes flat dist­ ally. It expands slightly near its extremity and supports a low ridge near the tip on the ventral surface. The articular area is simple and mildly convex.

w E "3 u M

Fig. 52. Restoration of forefoot of Champsosaurus Fig. 51. Foreleg and foot of Champsosaurus lara­ laramiensis, SMM P65.3. l. miensis, SMM P65.3.1., in situ.

CARPUS ments. Their interpretation as follows is Incompleteness of the carpus in aquatic based largely on their original disposition reptiles is not unusual (Romer, 1956, p. in situ (Fig. 53). 378) because of imperfect ossifications of Of the three proximal elements of the the elements comprising this structure. A carpus, the radial is missing. It must have fairly good idea of the carpus in Champso­ been in accord, however, with that de­ saurus has resulted, however, from the scribed for C. natator by Russell (ibid.) as present composite analysis. being a flat, triangular bone fused to the Brown (1905) described five carpals: centrale at its distal end. The ulnar is a the intermedium, an ulnar, plus three distal squared bone with both dorsal and ventral carpals. The rest he dismissed as being aspects concave. A rectangular-shaped in­ cartilaginous; therefore, not represented. termedium separates the radial and ulnar. In C. natator (Russell, 1956), seven car­ It approximates them in size but is longer pals are known: a radial, a centrale, the and is rather flat and thin. ulnar, and four distal carpals. The present Articulated in situ (Fig. 53) with the forefoot of C. laramiensis (SMM P65.3.l, distal end of the ulnar is a smaller square Fig. 52) also contains seven carpal ele- element that is considered to represent the ERICKSON: CHAMPSOSAURUS IN NORTH AMERICA 67

E

Fig. 54. Ontogcnetic development of the ilium of Champsosaurus. A. Very young, probably not over one season old. B. and C. Juveniles, note increase in height of blade. D. and E. Older juvenile and subadult, blade first lengthens then "squarcs-olI." F. Mature adult, blade becomes robust. In aged individuals the blade is heavier and rugosity increases. All figures arc based on specimens of C. laramiensis except A., which is C. natator. fourth carpal. It is slightly concave dor­ squared off as are the phalanges. These are sally. The distal end is oblique, and strong simple in form and decrease in length dist­ articular areas are present on both ends. ally. They are terminated abruptly. The A second bone about the same size and unguals are claw-like and in life probably medial to this joins the oblique distal edge supported claws resembling those of croco­ of the intermedium and appears to be a dilians. proximal centrale. A distal centrale seems also to have existed adjoining the lower PELVIC GIRDLE end of the radial (Russell, ibid.) . The three The pelvic girdle is a primitive structure remaining, small distal elements in this with small but strong parts. It has a low specimen are the first, second, and third silhouette because of a flat, ventral surface. carpals increasing in size respectively. In All three elements of the pelvis share in light of the above, the fifth carpal and a formation of the acetabulum-the ilium pisiform member are still unknown. The contributing the greatest amount, the pubis total number of carpals was probably ten. and ischium about equally. The puboischia­ The carpus, in general, is also unknown in dic plate is penetrated by only a small C. albertensis and C. gigas. obturator foramen.

MANUS ILIA The manus is composed of five elongate The ilium is in general like that described metacarpals and five digits with apparent for C. gigas (p. 41 and Fig. 37). The blade formulae of 2, 3, 4, 4, 3 and 2, 3, 4, 5, 4, as shows greatest change in shape between far as can be judged (Russell, ibid.). Fig­ species and age groups. The inner face has ure 52 shows the arrangement of the strong rugosities, the outer face much less manus in C. laramiensis. The metacarpals and often with an inversion for axial and are flat dorsoventrally, constricted medi­ limb muscle attachments. ally, and flared proximally. At their distal The ilium is a durable bone and, aside ends, they are only slightly expanded and from vertebral centra, is one most fre- 68 MONOGRAPH OF THE SCIENCE MUSEUM OF MINNESOTA VOL. 1 quently preserved. Ontogenetic stages of length of its medial border. For example, this hone are illustrated in figure 54. Com­ C. ambulator with a much extended in­ parisons of individuals of assumed similar ternal border is eas.ily distinguished from ages from different species show a growth other forms in which the border barely pattern similar to that presented; hence, stretches beyond the overall length of the the proportions ohserved may he taken as bone. There is a "pectineal tubercle" at the a rough gauge of the relative age of an forward end of this bone that is very individual. Individual variation may in­ subtly indicated in juveniles and only mild­ volve the extent of rugosity or the size of ly in the average adult. In older specimens, posterior ligament facets on the blade of however, it becomes an important feature the ilium. that characterizes the bone (Fig. 55). Its From the very smallest specimen and the best development is seen in the largest in­ young in general (A, B, and C, Fig. 54), dividuals of C. gigas. there is a uniform, overall increase in height and length of the ilium. This is ISCHIA followed by a period in which the iliac This element lends little by the way of blade elongates (D, Fig. ibid.). By the diagnostic evidence for species determina­ time the individual is subadult size, the tion, and about the only developmental blade "squares up" again (E, Fig. ibid.). change is in size and amount of tubercula­ In the largest individuals (F, Fig. ibid.), tion on the rear edge. the blade becomes very thick and rugose. There is always a strong cartilaginous HIND LIMB facet on the distal terminus of the blade A most noticeable feature about the hind and a small foramen just above the limb is that it is much longer than the acetabular buttress. forelimb. The normal ratio between fore­ limb and hind limb for Champsosaurus is PUBES about 100/125, holding regardless of age of The pubis (Fig. 38) shows little vari­ the individual. In C. gigas, a ratio of 100/ ance from one species to another, and the 135 is attained and previously noted. The description given for C. gigas is applicable humerofemoral ratio of C. gigas is about to the group. Differences are mainly in the 100/130. For its supposed closest kin, C.

T T w n 3

Fig. 55. Right pubis of Champsosaurus gigas, SMM PU0-2004, showing pronounced development of an­ krior tubercle (T) in a very large individual. A. Dorsal view. B. Ventral view. C. Anterior view. ERICKSON: CHAMPSOSAURUS IN NORTH AMERICA 69 lararniensis, it runs close to 100/120. side that runs from a distal point about half way up. A second ridge occurs above FEMORA The femur is a rather long, slender bone this on the anterior face. It is best devel­ oped in C. lamrniensis and C. arnbulator, (Fig. 39). The mark of conservativeness being very keen in juvenile specimens also. is nowhere more evident than in this ele­ ment. The degree of separation of the in­ FIBULAE ternal trochanter from the head has been Unlike the tibia, the rod-like fibula shows considered important in differentiating only feeble swelling proximally. A small, species. Parks (1933) states that this oval, articular end is formed. Laterally, the separation is significantly greater in C. shaft is striated near the end presumably lararniensis and C. arnbulator than in C. for attachment of iliofibulatis muscles natator. Brown (1905) considers place­ (Romer, 1956, p. 375). This bone is a bit ment and its separation from the head shorter and straighter than the tibia. A descriptive, being lower on the shaft short, low ridge appears on the shaft oppo­ and not contiguous with the head in site the long ridge on the tibia. Distally, C. ainbulator. The trochanter is a salient there is a wide flange on the shaft. Pos­ feature in all forms including the small­ teriorly, it is either flat or only mildly ex­ est specimens. The shaft of the femur cavated. On its opposite side, it is convex. is straight and modestly expanded at its Two adjacent facets are present: one ends in small individuals. It becomes curv­ angled medially for contact with the ed and further expanded at its ends with astragalus and one laterally to receive the age. At the proximal end, an articular head calcaneum. is well developed with a broadly rounded area of travel. The intertrochanteric fossa TARSUS becomes deeper and its surface more irregu­ Mobility of the hind foot appears to have lar with age also. It is least pronounced in been good as accomplished chiefly by the C. ambulator. Distally, the articular sur­ method of articulation between the tarsus face is broad and without distinctive con­ and epipodials; viz., angle of attachment dyles for the epipodials. It is oriented some and the possible rotational capabilities be­ 70° - 80° off the long axis of the proximal tween the two. head. There were apparently only four ele­ TIBIAE ments comprising the tarsus: calcaneum, Expansions of the extremities in the astragalus, and two distal tarsals. The tar­ adult are the most remarkable changes sus is preserved in C. natator (Parks, noted in development of the tibia. The shaft 1933) and, but for one distal tarsal, in is slender and curved. Proximally, it is SMM P65.3.l, a juvenile specimen (Fig. greatly swollen into a large, flat, articular Fig. 56) . In other forms the tarsals are region with little indication of a cnemial not fully represented and exist as isolated crest in any species. The opposite end of elements of uncertain affinities. the shaft is curved toward the fibula, and The calcaneum (fibulare) is a thin, flat, the articular surface at this end is oval rectangular piece that is thickened medially in shape and half or less that of the outer for contact with the astragalus. Its proxi­ end in size. A somewhat concave, inner mal border has a narrow face to match a facet is present for union with the astraga­ corresponding face on the fibula. Its distal lus. The shaft bears a ridge on the fibular margin is rounded and lies above the fourtJ- 70 MONOGRAPH OF THE SCIENCE MUSEUM OF MINNESOTA VOL. 1 distal and fifth metatarsal. This bone in most specimens, the dorsolateral edge is C. laraniiensis is more triangular in shape, interrupted by a foramen for the perforat­ possibly due to its immature nature. ing artery. The rest of the margin remains Adjoining the calcaneum medially is the thick and becomes roughened distally. astragalus (intermedium of Brown, 1905, and Fig. 56). This is a larger bone and is PES slightly concave both dorsally and ven­ The length of the pes is about one third trally. A large, tibial angulation occupies longer than the manus. Metatarsals II - much of the proximal area. Just lateral to IV are long, slender, and moderately en­ this at a right angle is a similar although larged at both ends. Proximally, they are smaller articular surface that is slightly flattened and somewhat wider laterally excavated to fit the fibula. These two sur­ than at the opposite ends. The articular faces of the astragalus are separated by facets are more or less flat. Numbers I and a small area that is the only nonarticulat­ V are the shortest and stoutest. Each has ing surface on the margin of the bone. a wide spread to its proximal end, the fifth Adjacent and below this is another broad, being hook-shaped (Figs. 42 and 56) prob­ articular surface for the calcaneum. In ably as a means of joining the compara­ tively narrow tarsus (Romer, 1956, p. 411). The formula for the pes is probably 2, 3, 4, 4, 3, as indicated chiefly by one intact specimen figured by Parks (1933). Numerous disassociated elements are ti known and seem to be morphologically sim­ ilar throughout the group. As in the manus, the phalanges are sim­ ple and have some indications of flexibility between elements, especially distally. The unguals are also claw-like.

n GASTRALIA 3 Gastralia are well developed in this group and obviously afforded considerable protection to the underside of the body. Unlike contemporary crocodilians, how­ ever, this was evidently their only "ar­ mor." No evidence of other dermal pro­ tection is known. Increase in weight and bluntness of extremities with age are ap­ parent changes. C. laramiensis is the only species in which a fairly complete, juvenile skeleton was available for analysis. In table 2 (p. 54), note that linear limb bone propor­ tions are nearly identical, vertebral centra Fig. 56. Right hind foot of Champsosaurus lara- are quite similar, and the height of the 1menszs, SM).,f Pfi5.3.1 .. juvenile. Restoration shown in outline. scapula is little affected by age. Differences r I f

ERICKSON: CHAMPSOSAURUS IN NORTH AMERICA 71 in the lengths of the radii and ulnae are close agreement of proportions in spite of due to lagging development of the ole­ the individual age difference. In the case cranon on the latter. A comparison of an of the juvenile, proportions of an extreme­ average-sized adult and a medium-sized ly young animal would show greater dif­ juvenile of the same species shows this ferences. SOME ASPECTS OF FUNCTIONAL MORPHOLOGY

All evidence points to Champsosaurus be gained if we compare these two reptiles as being an aggressive predator endowed relating to an extent on known habits of with remarkable aquatic capabilities of living crocodilians. movement and capture of prey. Related Comparisons can also be made with responsive functions are reflected in its phytosaurs in reference to skull architee­ hydrodynamically suited body form and ture and possible related functions. As its elongate, tooth-lined snout that had a evidenced by their stratigraphic distribu­ slicing effect through water. A number of tion and occurrence in a variety of litholo­ gross structural similarities to certain of gies, the champsosaurs were quite diverse the crocodilians are noted, and it would be in habitat preference. Their distribution is expected that some behavioral parallels discussed elsewhere in this paper. From existed in life as well. On the other hand, the geologic record of the phytosaurs, we competition between the two may have surmise that some like tolerances of habitat imposed certain restrictions especially upon prevailed as well (Colbert, 1965). How­ the subordinate champsosaurs. Analysis ever, the phytosaurs lacked some of the of the present material poses what is be­ advancements, such as a secondary palate, lieved to be some legitimate speculation that the crocodilians acquired to a con­ on behavioral patterns for champsosaurs. siderable degree. Consequently, these less That extant habitats can in no positive specialized types yielded their position to way be regarded as equal to those of ex­ the better equipped crocodilians at the tinct habitats will not be argued. I shall, close of the Triassic-a time before• the nevertheless, make some comparisons here champsosaurs were part of the scene. Con­ on the premise that behavioral traits that versely, the appearance of the latter and would have been influenced by structural their subsequent development seems to attributes, regardless of environmental have wrought no critical pressures for pressures, might be determined. change upon the crocodilians. Divergent There is little evidence contrary to the behavior evidently accounts in large part idea that crocodilians today inhabit en­ for their rather lengthy coexistence. vironments similar to those that they Comparisons of phytosaur, crocodilian, and their champsosaur contemporaries oc­ and champsosaur skulls, in particular the cupied during their earlier history. They nasal and optic regions, suggest the fol­ seem also to have been as diversified in lowing kinds of related activities. By virtue their preference then, as now. These two of placement of the external narial aper­ reptiles are most often associated as fos­ ture, it appears that the phytosaurs and sils. Therefore, some insight into the mode crocodilians may have had similar means of life of the extinct champsosaurs might of obtaining food, relying on both olfactory

72 ERICKSON: CHAMPSOSAURUS IN NORTH AMERICA 73 and visual equipment. The high placement and a keen sense of smell to locate a poten­ of the external narial opening in the phyto­ tial food source ( Oliver, 1955, p. 176). The saur skull is ideally situated for resting olfactory apparatus here is remarkably nearly in total submergence in water with well developed. More piscivorous forms, little more than the nostrils and eyes pro­ such as, gavials, garfishes, and champso­ truding above the surface (Fig. 57, A), saurs, may have depended less on this sense much like the posture managed by the and perhaps in some cases to the exclusion crocodilians. The champsosaur skull, with of it completely in their quest for food. its external narial opening at the terminus However, olfaction can be· a primary means of the snout, could not lend itself to the of detection underwater (Walls, 1967). practice of lying submerged immediately Gavialis has been compared to Champso­ below and parallel to the surface of the saurus by Romer (1956), Fox (1968), and water with its nostrils exposed to the air others. The narial apparatus in the former above. In effect, its long snout would be is typically crocodilian. Fox (ibid.) and forced to break water at a considerable others suggest that the niche occupied angle to the air-water interface in order by Gavictlis was previously filied by the to expose the nostrils. This would not have champsosaurs, as the appearance of the been an advantageous pose for stalking former during the Eocene coincides with prey. Alternatives might have been a more the disappearance of the latter. Inasmuch terrestrial feeding habit or, much more as both were long-snouted and Champso­ plausibly, underwater detection and cap­ sa-urus may have had either nasal sphincter ture of prey. The marked dorsoventral valves or highly vascularized tissues for streamlining of the skulI with its dorsad prevention of water entering, it would eye location suggests a practice of "cruis­ seem reasonable that it did resemble the ing off the bottom" or lying in wait at or gavials in some of its underwater activi­ near the bottom. ties. However, a peculiar behavior for the The crocodilian skull in figure 57, B champsosaurs-one that did not totally presents the most effective arrangement come to be mimicked by the gavials-is of skull features for achieving dominance indicated by: the terminal location of the of the surface of the water with the ac­ narial opening and its questionable olfac­ companying behavior that the phytosaurs tory function, the choanae only at mid­ acquired to some degree and the champso­ length on the palate whereby inspired air saurs probably not at all. Resting thus woald not be separated entirely from the near the air-water contact, the crocodilian mouth cavity as in the gavials with their could avail itself of any opportunities that more complete secondary palate, the vision might come along. This behavioral charac­ more aquatic than aerial as in crocodilians, ter very likely had a profound effect on and other bottom type features. their success through time. The probable position that the head of Olfaction and vision are most reliable Champsosaurus assumed while at the air­ telesthetic senses, hence, important in ob­ water contact to replenish its oxygen stores taining food both in and out of the water. is suggested in figure 57, C. In this posi­ For crocodilians, especially broad-snouted tion, just the tip of the snout would be types that are generally more omnivorous, above the surface of the water while the the ability to detect and recognize objects mouth was closed tightly. In such a posi­ or events at a distance is vital to feeding. tion, the animal could remain submerged Crocodilians are known to rely on vision almost entirely and, therefore, incon- A

B

C

Fig. 57. Diagramrnalic posture for the heads of: A. a phytosaur, B. a crocodilian, and C. Champsosaurus, while at the air-water interface. Nasal passages shown in silhouette.

74 ERICKSON: CHAMPSOSAURUS IN NORTH AMERICA 75 spicuous. could also provide a defense mechanism A generalization that all species of this that, unlike that of its crocodilian con­ taxon were aggressive, underwater preda­ temporaries, is lacking in any other struc­ tors-"sight feeders," relying on visual tural form. detection of prey that would normally be restricted to relatively well-lit waters up RESPONSIVE FUNCTIONS to several meters in depth~seems sound. Of the champsosaurs, C. gigus is es­ It should also be mentioned that hunting pecially interesting in that it demonstrates in dim underwater conditions may have certain morphological peculiarities of the posed problems dependent on the acuteness group best. These are herein considered of vision. In this connection, the use of smell and even touch, as is kno\Vll in some with an eye to their possible functional importance. "hunting" turtles (Walls, 1967, p. 437), may have been required. Olfactory epi­ C. gigas is among the last of the genus thelium may have been present in ample to make its appearance. It is unusually supply along the airways of the long snout large and has somewhat longer hind limbs and could have been as vital as vision in than average. It also shows greatest locating prey. pachyostosis of the ribs and, perhaps of The eyes of Champsosaurus were stra­ most interest, is what is considered to be tegically placed for fairly good binocular a specialization of the rib cage in which vision. If vision was the main means of the visceral side of the dorsal ribs has detection of prey, an aquatic vision quite been modified in conj unction with under­ unlike the specialized aerial vision of the water behavior. It should be mentioned crocodilian was present; or some means of here that this specialization is not peculiar accommodation to aquatic vision must have to the largest species; it is only best ex­ existed. No evidence exists in the fossil emplified here. These characters favor the record. Discussion of the reliance on vis.ion largest champsosaur as well as adults of for location and capture of prey is pre­ some other species in the roll of specialized sented by Walls (1967, p. 293) in which predators that would lie in wait near the crocodilians are cited as having about 25° bottom of a stream or pool instead of cruis­ of binocular field of vision. This field is ing or giving active pursuit, giving them described as the spatial cone or zone with­ the same effectiveness of smaller prede­ in which separate monocular fields overlap. cessors and perhaps the young of its own The highly predaceous snapping turtle species. Chelydra has about 38° of binocularity, Food procurement for the champsosaurs, according to Walls (ibid.). Most of the in general, would not seem to have been food of the snapper is animal, and half of difficult; but for very large forms es­ this consists of fast-moving fishes; there­ pecially, which are necessarily slower be­ fore, the need of good distance judgment cause of their bulk, an alternative means is realized by its good binocularity. Meas­ of securing food might have proven ad­ urements of visual angles in Champsosau­ vantageous. rus are not possible, but estimates based Expenditure of oxygen is rapid and on the position of the orbits suggest a commensurable to energy output in active­ decidedly more upward direction of visual ly swimming animals. Certain reptiles are fields and a binocularity exceeding that of known to remain submerged in water for Chelydra in that direction. This position hours and even days. The advantages of 76 MONOGRAPH OF THE SCIENCE MUSEUM OF MINNESOTA VOL. 1 being able to do this and conserve energy ried on by lungs, existed and was associ­ at the same time are obvious. It is conceiv­ ated with the described modifications of able that C. gigas departed some from the certain dorsal ribs. more typical hunting pattern and stalked Regarding the plasticity and histological its prey by lying in wait at or near the nature of bone, especially during onto­ bottom not unlike Macroclemys, the alliga­ genetic development, the "fit" of ribs to tor snapping turtle. Without benefit of a lungs, as shown in the above figures where­ distensible neck, the powerful hind legs in the ribs have conformed in shape and might have aided in the seizure of prey by partially enclosed the lungs, would easily providing means of a quick lunge forward. have been accomplished.

C

5 cm ~ Left I ung A

Fig. 58. A. Partial transverse section at level of the eight dorsal rib. B. Right seventh rib. C. Attempted restoration of lung position. All figures in poslerior view. Maximum rib length and lung development is at the level of the seventh and eighth dorsal ribs.

A keynote to aquatic prowess of this Incising of the visceral side is believed kind is reflected in the configuration of the to have been caused by the existence of the anterior part of the rib cage. Figure 58 lungs in close proximity to the ribs. It does represents a transverse section through not indicate a condition of pathomorphism. the part of the skeleton showing the dorsal The feature is consistent in its occurrence ribs and their internal incising. In this in dorsal ribs four through eleven in C. and figure 59, also, are shown restorations gigas, showing most extensive develop­ of the hypothetical lungs and associated ment in the longest ribs, the least develop­ respiratory apparatus. We do not know the ment in the anterior and posterior ribs shape of the lungs very precisely nor to (Fig. 59). Cross sections were made of what extent they conformed to the ribs. numerous rib shafts of several specimens. We can only speculate about more bizarre Figure 60 illustrates diagrammatically a kinds of underwater respiration that may typical section through the incised area have existed and any possible hydrostatic of a long, dorsal, adult rib. The cortex is functions that may have been present. layered and for the most part nonvascular From the evidence, it is my impression in its outer zone but mildly vascular in its that a normal type of respiration, as car- inner zone. Thin, circumferential, cortical A --trachea

Fig. 59. Dorsal view of the rib cage of Champsosaurus with attempted :restoration of the respiratory ap­ paratus. Ribs indicate the presence of paired lungs of about equal length. Presumable the bronchi were well developed. A. First dorsal rib. B. First sacral rib.

77 78 MONOGRAPH OF THE SCIENCE MUSEUM OF MINNESOTA VOL. 1

C

B

Fig. 60. Diagrammatic cross section of dorsal rib of Champsosaurus gigas. A. Incised area of shaft. B. Compacted cancellous born~. C. Canals in endostcal region. D. Thin cortical bone layers of incised area. laminae of the most recently deposited bone ence of the lung but for growth and the surround the shaft, the only lamellar bone accompanying change in curvature of the present in the incised area (Fig. ibid. A). entire shaft. This process of bone modifica­ This very thin, cortical layer may often be tion, or remodeling, by differential deposi­ missing in places, including the incised tion and resorption of bone is the mecha­ area, due to the effects of only minor nism by which the incising of the ribs, weathering. The inner portion of the shaft such as, described for Champsosaurus, can or medulla is filled with noncompacted tis­ be explained. sue having many cancellous spaces. Those The dorsal rib of a juvenile, mounted near the endosteal margin are frequently skeleton, SMM P65.3.l, is shown in cross enlarged into resorptive spaces. In the area section through the area in which the adult of incising, the cancellous tissue is com­ rib is normally modified by incising (Fig. posed of compacted endosteal bone (Fig. 61). In the juvenile bone, fewer periosteal ibid., B) indicating "drifting" of the cortex laminae are present than in the adult. In (Gans, et al., 1969) wherein cancellous ma­ the very young of crocodilians, only a single terial has been converted to compact bone. lamina is present (Gans, et al., ibid.). This Resorption of bone in other regions, es­ layer of the present immature specimen is pecially on the opposite side of the shaft, fairly heavy, nonvascular, and in other resulted in a gradual migration of the cor­ respects Eke that of the adult except where tex to compensate, not only for the pres- incising occurs. Compare with an adult I' I

ERICKSON: CHAMPSOSAURUS IN NORTH AMERICA 79

E E u u ......

Fig. 6 I. Cross section of dorsal rib of juvenile Fig. 62. Cross section of dorsal rib of adult champsosaur through area, which is modified by in­ champsosaur through incised area of the shaft. Note cising in the adult. Note the continuous uniform thick­ interrupted cortical layer (below at incising) and the ness of the cortical layer around the perimeter and amount of compacted cancellous bone. the lack of compacted cancellous hone. specimen (Fig. 62). Note, also, the con­ dorsal rib to enter the lungs on either side. tinuous cortical layer (Fig. 61) in the The lungs of the alligator have a similar juvenile. The cancellous portion is uniform position adjacent to the ribs, which are of showing little compacted area. much lighter construction and more widely Incising of the dorsal ribs evidently took spread. Charnpsosaurus of somewhat sim­ place as maturity and expansion of the ilar build but with much heavier ribs and rib cage progressed. Materials are not a narrower chest cavity simply compro­ available in sufficient quantity, however, mised the form of the ribs for the over­ to make a definite statement about the sized lungs it possessed. amount of age variation involved. As men­ It is well to note that merely increasing tioned above, the feature is not exclusively the size of the external dimensions of the that of C. gigas. It is present in the larger lung, however, would not automatically individuals of C. larmniensis, a possible an­ bring about a proportional increase in their cestor from the late Cretaceous and early functional capabilities, as this is deter­ Paleocene. mined by the size of the alveoli as well as In C. gigas, dorsal ribs four through other factors. It does seem reasonable, eleven express the feature indicating the however, to assume a certain increase of minimum length of the lungs. The condi­ respiratory surface by enlargement of the tion was contrasted to a specimen of the total organ. American alligator, Alligator rnississippi­ If we are to consider Chanipsosaurus as ensis, SMM Z69.26.l, which upon dissec­ having behavior characters as proposed, tion was found to have lungs that span the we cannot overlook the potentials of its first through the eighth dorsal ribs. The diving capabilities. The depths reached bronchi branch, at the level of the third might not be excessive but would pre- 80 MONOGRAPH OF THE SCIENCE MUSEUM OF MINNESOTA VOL. 1 sumably exceed those frequented by croco­ accomplishing a prolonged submergence; dilians. Any modification of respiratory such as, relatively high hemoglobin content apparatus that would prove beneficial in the blood, a larger blood volume, and a should be noted. higher myog!obin concentration in the Distensibility of the lungs is a point to muscles~all of which increase oxygen I consider. Any compression of the lungs by stores. Scholander (ibid.) points out also, pressures caused by descending through however, that during a prolonged dive the t the water, which would compress the chest oxygen stores afford much less oxygen than cavity and consequently the lungs inward necessary to maintain a predive level of potentially to a state of full collapse, might oxygen consumption. However, modern be alleviated if the shape of the rib cage, animals are, and presumably extinct forms f viz., incised area, would not in effect allow were, capable of remaining submerged for complete collapse of the lungs by permit­ time periods several times longer than ting some retention of lung shape. Pro­ would be anticipated as judged from their longed diving or "bottom time" (suspen­ basal oxygen consumption and the oxygen sion of breathing) may have been the rule stores. This suspended breathing is a per­ for some species of the group. Such be­ fectly normal phenomenon of many modern I t havior is a widespread phenomenon among animals. The enlarged lung capacity in all classes of vertebrates. There are fea­ Champsosaurus may have been an early tures common in many of these diving attempt at increasing oxygen stores and I forms, as shown by Scholander ( 1964, p. complying in part with requirements for I 229). prolonged submergence. Aquatic animals of widely divergent taxa One feature applicable to the present show certain similarities of rib construc­ discussion is that of asphyxia! defense. As tion. Pachyostosis is a condition found to stated by Scholander (ibid.), "The simplest varying degrees of development in many conceivable mechanism for coping with a forms including the champsosaurs. The prolonged dive might operate through large l reasons for this condition in diving animals oxygen stores and a great capacity for is not entirely understood. The functional i buffering carbon dioxide and other metabo­ ' implications of a heavy ( cancellous) rib lic acids. The animal would then merely as related to aquatic activities may be use these resources during the dive and many. The condition in Champsosauriis recharge the stores in recovery." may bear on metabolic and circulatory reg­ The complete collapse of the lungs, which ulation, which in turn is a vital consider­ presumably takes place in certain deep ation in the responsive functions related diving mammals, offers no problem; for to underwater activity suggested here. I"' ' there is ample pressure available from the The lungs of Champsosaiwus occupied expanding air to force the lungs open upon positions lateral to the esophagus and ex­ ascent. This is possible because of the high­ tended caudad on either side of the body. ly specialized alveolar system found, for Whether or not they were posteriorly sac­ example, in cetaceans. In reptiles, such culated as in some living reptiles, e.g. total collapse would be fatal; therefore, a chameleons, is unknown--nor if respira­ simpler mechanism for prevention of total tory epithelium was present throughout. lung collapse must have been in operation With paired lungs, the trachea must have if Chcinipsosai1,1·us was indeed a "diver." bifurcated and sent one branch (bronchus) Many animals have devices that assist in to each lung as depicted in figure 59, much ERICKSON: CHAMPSOSAURUS IN NORTH AMERICA 81 as in the American alligator. Their effi­ head and body and good sensory apparatus, ciency would presumably be augmented by the underwater behavior in which a pro­ their increased size and the condition seen longed bottom time was normal would seem in the ribs. to fulfill the basic requirements. for success­ Coupled with considerable mobility of ful predation by Champsosaurus. CORRELATIONS AND DISTRIBUTION

Compilations of data on the geographic by one or more species in the late Paleo­ distribution of North American species cene, becoming rare by early Eocene comprising the genus Champsosaurus show (Sparncian) time. This suggests prior pro­ a considerable range (see maps, Figs. 63 liferation and earlier (pre-Tertiary) radia­ and 64). The principal champsosaur-pro­ tion, which led to entering Europe by way ducing strata lie in the western plains of of a Laurasian land connection, probably North America along the eastern flanks of during the late Cretaceous. the Rocky Mountains from southern Al­ Giant forms like C. gigas and Sinwedo­ berta to New Mexico. Their remains are saurus of the late Paleocene, as well as the most conspicuous in the Cretaceous bad­ North American short-snouted form and lands of the Red Deer River of southern those of the basal Eocene in Europe, should Alberta and the transitional Cretaceous then be considered as more specialized and Paleocene beds exposed in the brakes "climax" populations. The Cretaceous­ of the Missouri River in Montana. Other Tertiary transition was perhaps unevent­ localities scattered from southern Saskat­ ful, yet was unsuccessfully executed by chewan to New Mexico produce fewer many groups. It is interesting to ponder numbers, most as unarticulated elements. what environmental conditions may have Highly productive concentrations of speci­ existed and the extent of vested influence mens have been found in late Paleocene for survival or initiation of decline upon sediments ("Clarkforkian") of eastern the champsosaurs. Colbert (1967) notes Montana and western North Dakota. that the culmination of eusuchian evolution Sirnoedosaurus of the European Tertiary may have been attained also during the is considered congeneric and implies an late Cretaceous. even more cosmopolitan status for the The crocodilians and the champsosaurs group. apparently made an easy transition from By their numbers, it would appear that Cretaceous to Tertiary time. If any diffi­ thefr peak of development was during the culties were encountered in making adjust­ span of Oldman through Hell Creek time ments to cooler or warmer Tertiary temper­ (late Cretaceous) - a time when many atures, whatever the case may have been, other groups of reptiles also flourished. they left little visible impression on either Greatest geographic range was attained form. Tertiary crocodilian populations were during this and the earliest Tertiary time progressive in morphological development, (map, Fig. 64). The Puercan (early Paleo­ and the accompanying refinements con­ cene) is the only horizon, so far, that defi­ cerned with tolerance for temperature nitely documents more than one species. changes were successful. Speculation on Sirnoedosaurus in Europe is represented the reasons for a seemingly uneventful

82 ERICKSON: CHAMPSOSAURUS IN NORTH AMERICA 83 transition for both crocodilians and champ­ tary material; hence, its correlative use­ sosaurs is not necessary. Suffice it to note fulness is small. Suffice it to note that that the environmental tolerances ,in living this species represents a sizable population reptiles as shown by Colbert, et al., (1946) that existed near center of this group's were likely similar to those of extinct geographic radiation. Populations persist forms that were making the transition. throughout the Oldman and Edmonton as As .i udged from the present materials, two recognizable species: C. natator and the greatest populations of champsosaurs C. albertensis, respectively. inhabited coastal flood plains and swampy Intensive collecting of the marine Bear­ situations, later forms becoming more re­ paw shale in southeastern Alberta and the moved from any coastal areas but still transitional sandy clays of the underlying remaining very aquatic. During their early Oldman deposits in this region turned up development (late Cretaceous), there is evi­ several specimens of Cha1npsosaurus. As dence that they may have frequented salt suggested previously, this material may marshes and estuarine waters, but perhaps have been derived from the Oldman origi­ not to the extent that certain crocodilians nally. Nearly all are vertebrae lacking did. This is indicated by the succession of neural arches; and without more complete North American champsosaur species oc­ materials, the only choice is to refer it to curring in sediments interspersed between C. natator. intervals of marine deposits belonging to Hell Creek and Tullock species from the Pakowki and Bearpaw formations. For Montana and North Dakota are more stratigraphic references, see Russell, 1967. easily separated. Brown (1905) described Possible early Eocene marine associations these, and in doing so stated that they are also indicated by the occurrence of were obtained from the lower strata of champsosaurids in the Sparnacian, near lignite above the "Ceratops Beds" in what Reims in Europe, which is deltaic in na­ is now Garfield County, Montana. Russell ture (Brinkmann, 1960, p. 120). The rather (1956) correctly observed that these spotty record of specimens from marine species should be considered as Paleocene, transitional sediments, such as, the shales coming as they do from the lignites, not of the Oldman, Bearpaw, and Hell Creek Cretaceous. Brown's types undoubtedly formations, might be mentioned. Only a originated from the Tullock (Paleocene) few bones have actually been recovered lignites that are so characteristic of the directly from marine facies, and these are exposures overlying the Hell Creek at this suspected as being materials of redeposi­ locality. While collecting these deposits tion; yet a proximity to salt water environ­ during several seasons, it became evident ments existed. The association of champ­ to the writer that C. laramiensis is found sosaurs with remains belonging to other regularly in both the Hell Creek and Tul­ possible brackish types, such as turtles that lock; at least the Hell Creek form cannot may have ventured forth to lay their eggs be distinguished from C. laramiensis of the upon land and in the process were detained Tullock. It is clearly not C. ambulator. Re­ permanently, is an interesting aspect of mains from the younger rocks are gener­ some latest Cretaceous horizons; viz, ally less disturbed, especially in or adja­ Frenchman and Hell Creek formations. cent to lignites. C. laramiensis is present Cape's type species, C. annectens, is from in the Hell Creek as far east as the Mis­ the Judith River beds of Montana. Unfor­ souri River in central North Dakota; and tunately, the record consists of fragmen- a femur, SMM P69.19.l, from the French- 84 MONOGRAPH OF THE SCIENCE MUSEUM OF MINNESOTA VOL. 1

-----,-i ..( ----.,'---/ ------\\\ !! i \ ,' 1- - ·\:;_ ,11 ------

'··---·-·,i~ .. J...r··-··

---1 -----1' -

1' ·....,_

'

Distribution of Cretaceous champsosaurs

Fig. 63. Distribution of Cretaceous champsosaurs in North America. A. C. natator. B. C. albertensis. C. C. laramiensis. Stippled areas indicate approximate range within which champsosaurs have been found. man of southern Saskatchewan extends its can be made, however, with one of the lat­ geographic range northward (Fig. 63). est species. Champsosaurus is also known from C. gigas would appear to be suited as a the Tiffanian-pre-"Clarkforkian" (circle "guide fossil," a means of identification, fauna) and the Lebo formation of Mon­ primarily because of its size and its rela­ tana. So far, all materials collected are 'tively wide geographic distribution. C. small, badly eroded, vertebral centra, not gigas occurs in the following formations sufficent for meaningful description. or as part of the following local faunas: As far as can be demonstrated, strati­ Sentinel Butte and Tongue River forma­ graphic correlations by champsosaur re­ tions, North Dakota; Ravenscrage forma­ mains are difficult for the most part. The tion, southern Saskatchewan; Bear Creek limiting factor, of course, is that specific formation, Montana; Plateau Valley for­ determinations depend on fairly complete mation, Colorado; Olive fauna, Montana materials. Some correlative application (Fig. 64), all of which are here noted as ERICKSON: CHAMPSOSAURUS IN NORTH AMERICA 85

< ' ' ' ' ' ' '

/ ''

Distribution of Tertiary champsosaurs I

~-""' "~---,,,r-.,, """ ------r- -. ------

Fig. 64. Distribution of Tertiary champsosaurs in North America. A. C. laramiensis. A'. C. laramiensis ( ?) B. C. ambulator. C. C. gigas. D. Short-snouted champsosaur. Stippled areas indicate approximate range within which charnpsosaurs have been found. comprising "Clarkforkian" horizons. By larger, in some cases surpassing associated early Eocene (Willwood), all the "large" crocodilians in size. The crocodilians, how­ champsosaurids are gone and only a short­ ever, are known from recorded materials snouted form remains. as being much more numerous. This shift An interesting generalization may be in balance through the Paleocene may have made with regard to relative abundance been governed by modification of behavior of champsosaurs and crocodilians. In al­ of the champsosaurs in order to survive most every occurrence of champsosaurs, competition or simply an indication of remains of crocodilians are also found. In losing the struggle to survive in a changing their earlier history (Cretaceous and basal environment. Paleocene), the champsosaurs were physi­ cally small but far outnumbered croco­ dilians in their occurrence together. By late Paleocene, the champsosaurs were PHYLOGENY

The isolated phylogenetic status of long-snouted, perhaps more piscivorous, Cha,mpsosaurus as a specialized late-sur­ species became well established in the viving eosuchian has remained unchanged former land area by the late Cretaceous by the present study. Recognition of ances­ as did the short-snouters in Europe by late tral stock from which it may have sprung Paleocene times. Earlier Paleocene deposits will have to await further discoveries of are absent, and as yet no Cretaceous ma­ new material. Present evidence would seem terial has been found in Europe. This is due to place it in the uncertain position of being perhaps to the lack of work on the Creta­ a derivative of some generalized primitive ceous (D. E. Russell, 1971, personal com­ diapsid, possibly even a marine type, as munication). A short-snouted branch per­ could easily be inferred from the occur­ sisted in North America and is represented rence of some of the Cretaceous members by the Polecat Bench (early Eocene) form. of the group. Both this and its European counterpart Within the champsosauridae, however, from the Sparnacian (also early Eocene), there exists some interesting possible con­ may be derived from Simoedosaurus, a nections that may, of course, be altered by relatively short-snouted champsosaur with subsequent discoveries of intermediate an abbreviated mandibular symphysis forms. It is obvious that the long-snouted from the late Paleocene of Europe, or in "typical" Chmnpsosaurus evolved in mod­ the case of the former, more likely from est fashion giving rise to few remarkably some earlier short-snouted simoedosaur­ similar species between Oldman and like form. "Clarkforkian" time. It is interesting to note the trend At some point during their development, toward gigantism in both lines. This is a short-snouted variety was produced. In best observed in C. gigas and Simoedosau­ fact, it seems most reasonable to speculate ru.s of the late Paleocene-a point in time that the long snout arose as a specializa­ that marks broad development of the tion toward a more aquatic mode of life group. The rare lingering basal Eocene out of the more generalized, short-snouted forms represent the rather abrupt culmi­ stock. At any rate, two distinct lines are native phase of champsosaurian evolution. in evidence. In attempting to relate the long-snouted A common North American origin seems species to each other on morphological most feasible, followed by separation dur­ grounds, difficulties were encountered. ing the Cretaceous with ensuing geo­ Lack of cranial materials from various graphic radiation. The result was wide horizons is a most unfortunate situation. dispersal in North America and into However, with the following limitations in Europe via a Laurasian land route. The mind, some links seemingly valid at this

86 .--- N 0. AMER.----~ ~ EUROPE-,

C.gigas I Simoedosaurs

C.ambulator

C. laramiensis

LONG• SNOUTED SHORT· SNOUTED

Fig. 65. Suggested phylogeny for the champsosaurs.

87 ------'

88 MONOGRAPH OF THE SCIENCE MUSEUM OF MINNESOTA VOL. 1 time are made: The vertebral column, other The Puercan (basal Paleocene) saw the than the cervical and sacral series, is of persistence of C. lararniensis from the Cre­ little use in segregating specific characters taceous and the appearance of C. arnbula­ ( even these are of small use) ; the hu­ tor in the Tullock formation of Montana. merus and femur are diagnostic in most This rather short-limbed contemporary of cases; the ribs that either possess or lack C. lararniensis is distinctive. Morphologi­ uncinate processes or visceral incising are cally, it shows the greatest departure of of value; some girdle elements, especially any long-snouted species. those of the pelvis, show distinctions of Present evidence indicates, however, importance, and limb length ratios as well. that it was a small population as it is The type species, C. annectens, is of little known from but a few specimens from a taxonomic use. It is here considered along restricted area (Fig. 63). Brown (1905) with C. natator and C. lararniensis as part suggests more ambulatory habits for it, of a line that developed during the latter which might explain its scarcity in deposits part of the Cretaceous. Features relating containing a relative abundance of other the latter two are found in the ribs. Both champsosaur remains. Structurally, it does have uncinate features on the last few not qualify as ancestral to later species cervicals and the first few dorsals. The and is probably best regarded as a short­ main dorsals are deeply incised (ref. p. 61) lived side branch. in the latter. It is suspected that incipient Relatively little champsosaurian mate­ incising of ribs may have existed in C. rial has been recovered between the Puer­ natator. C. albertensis is thought to be a can and "Clarkforkian." These are, for the minor offshoot because it appears to lack most part, small, isolated, vertebral centra the above features and has shortened epipodial elements. A tendency toward in­ and limb bone extremities, usually eroded, and not considered reliable enough for crease in the length of the hind limbs is taxonomic purposes. noted from C. natator to C. gigas. In the latter, the hind limbs are considerably A suggested phylogeny for the champso­ lengthened and rib incising very acute. saurs is given in figure 65. SUMMARY

In ,Cha1n1,sosrut1·us we see a rather spe­ A most interesting feature of this species cialized reptile of uncertain ancestry but is the incising found on the dorsal ribs exhibiting sufficiently adequate evidence to that leads to observations about functional retain its status in the lepidosauria. anatomy and the associated underwater The North American champsosaurs were behavior. primarily adapted to a dependence on The unreliability of categorizing mate­ underwater predation. This mode of life rial on size is debated. Generally, it was was carried out successfully in spite of the found to be unwise; yet in view of the ever present potential of competition and consistency of size difference between the perhaps predation from various croco­ late Paleocene species, C. gigas and other dilians. An attempt has been made to forms, there seems to be some validity in demonstrate how they, by remaining con­ its application. On these grounds, it is sug­ servative in their evolution and habits, gested that C. gigas is of use as a "guide might have managed to meet the chal­ fossil" for the "Clarkforkian." lenge as a subordinate and, in turn, be­ It would seem unfounded, as has been come a highly successful group. If any the practice, to regard Champsosaurus as progressive trends can be sited, increase strictly a freshwater type. Ample strati­ in overall size and in the length of the hind graphic evidence is sited to indicate at limbs might be noted, as well as a tendency least an early (Cretaceous) proximity to to modify the rib cage in certain species. transitional marine ( coastal and estuarine) Five species have been recognized in this environments. This undoubtedly had in­ work on the basis of new and reevaluated fluence on distribution. The geographic materials. This was facilitated by distin­ range of the champsosaurs, not only in guishing juvenile and adult characters. In North America but in Europe as well, was doing this, age variations became clearer; appreciable and was apparently maintain­ and to a limited degree, individual varia­ ed throughout nearly all of their history. tions were brought out. As it turns out, The middle Paleocene will, hopefully, be most significant differences between species filled in with future discoveries. The appar­ are found in the postcranial skeleton. Much ent ease of adaptability and broad habitat of the information was derived from the tolerances would then also account for the large form referred to as the new species, wide dispersal and considerable success Champsosaurus gigas. of the entire family.

89 BIBLIOGRAPHY

BRINKMANN, R. 1960. Geologic evolution of Europe, Hafner, New York. BROWN, B. 1905. The osteology of Champsosaitrus Cope. Amer. Mus. Nat. Hist. Mem., Vol. IX, part I, pp. 1-26. COLBERT, E. H., COWLES, R. and BOGERT, C. 1946. Temperature tolerances in the American alligator and their bearing on the habits, evolution, and extinction of the dinosaurs. Amer. Mus. Nat. Hist. Bull., Vol. 86, art. 7, pp. 327-374. COLBERT, E. H. 1965. A phytosaur from North Bergen, New Jersey. Amer. Mus. Nat. Hist. Nov., No. 2230, pp. 1-25. ----- 1967. The age of reptiles. COPE, E. D. 1876. On some extinct reptiles and Batrachia from the Judith River and Fox Hills beds of Montana. Proc. Acad. Nat. Sci. Phil., pp. 340-359.

---1881. A Laramie saurian in the Eocene. Amer. Naturalist, Vol. 15, pp. 669-670. _____ 1882. Contributions to the history of the vertebrata of the lower Eocene of Wyoming and New Mexico made during 1881. Proc. Amer. Philos. Soc., Vol. 20, pp. 139-197. FOX, R. C. 1968. Studies of late Cretaceous vertebrates I. The braincase of Champso­ sauri,s Cope (Reptilia: Eosuchia). Copeia. 1968, No. 1, pp. 100-109. GANS, C., Blllairs, A. d'A., Parsons, T. S. 1969. Biology of the reptiles. Academic Press, London and New York. LANGSTON, W. JR. 1958. Champsosaur giants. Nat. Hist. Papers. Nat. Mus. Can., No. 2, pp. 1-4. LEIDY, ,J. 1873. Extinct vertebrate fauna of the western territories. Rept. U.S.G.S. Vol. 1, pp. 287-288. OLIVER, J. A. 1955. North American amphibians and reptiles. New York. PARKS, W. E. 1927. Champsosaurus albertensi.s, a new species of rhynchocephalian from the Edmonton formation of Alberta. Univ. Toronto Studies. Geo!. Ser., No. 25, pp, 1-48. _____ 1933. New species of Champsosaurus from the Belly River formation of Alberta, Canada. Trans. Royal Soc. Canada. Ser. 3, Sec. IV, Vol. XXVII, pp. 121- 137.

90 ERICKSON: CHAMPSOSAURUS IN NORTH AMERICA 91

ROMER, A. S. 1945. Vertebrate paleontology. Univ. Chicago Press. _____ 1956. Osteology of the reptiles. Chicago. Univ. of Chicago Press. RUSSELL, D. A. 1967. A census of dinosaur specimens collected in western Canada. Nat. Mus. Canada. Nat. Hist. Papers, No. 36, pp. 1-13. RUSSELL, L. S. 1956. The Cretaceous reptile Chainpsosaurus natator Parks. Bull. Nat. Mus. Canada, No. 145, pp. 1-51. SCHOLANDER, P. F. 1964. Animals in aquatic environments: diving mammals and birds. Handbook of Physiology, Amer. Physiological Soc., Wash., D. C. Sec. 4, pp. 729-739. WALLS, G. L. 1967. The vertebrate eye and its adaptive radiation. Hafner, New York. WOOD, R. C. 1967. A review of the Clark Fork vertebrate fauna. Mus. Comparative Zoo!. Breviora, No. 257, pp. 1-30.