SMILODONICHTHYS RAST1?0SUS A NEW PLIOCENE SALMONID FISH FROM WESTERN UNITED STATES SMILODONICHTHYS RASTROSUS A NEW PLIOCENE SALMONID FISH FROM WESTERN UNITED STATES

by

TED M. CAVENDER and ROBERT RUSH MILLER

Bulletin No. 18 Museum of Natural History University of Oregon Eugene, Oregon March 1972 1 SMILODONICHTHYS RASTROSUS, A NEW PLIOCENE SALMONID FISH FROM WESTERN UNITED STATES

by

TED M. CAVENDER ROBERT RUSH MILLER

Museum of Zoology AND Museum of Zoology

Ohio State University The University of Michigan

INTRODUCTION

In western North America, the family Sal- main context of the present paper and which monidae is comprised of a diverse number of has allowed fruitful comparison to be made species (upwards of 30) belonging to seven with living salmonids. genera assigned to three subfamilies ( Norden, The name Smilodonichthys rastrosus is pro- 1961) . Though more than half of these species posed for this previously undescribed species. are endemic to the area, an astonishingly few Because of its high degree of morphological fossil specimens have been discovered which distinction from other members of the Salmon- can help document the evolution that has taken idae, this species is made the type of a new place in this group. An exception is the one genus. A number of its osteological features in- described in this paper which adds importantly dicate a phyletic relationship closest to Oncor- to our understanding of the past life of these hynchus, yet none of the extant species of that fishes. genus approaches the fossil in the specializa- Materials of this fossil salmonid were col- tion of its feeding mechanism. lected over a period of fifty years from Plio- cene, Pacific-slope localities in California and ACKNOWLEDGMENTS Oregon. As early as 1917, vertebrae, teeth and Cooperation from many sources has enabled skull fragments of an extremely large but un- the completion of this study. We are particu- familiar type of fish were unearthed, along with larly indebted to J. Arnold Shotwell of the Uni- mammalian remains, at Pinole, Contra Costa versity of Oregon Museum of Natural History, County, California. Only within recent years, who loaned the material that has provided the however, has it been possible to identify these basis for distinguishing the new genus. For the with certainty as being the remains of an extinct loan and gift of other specimens we thank Don- form of salmonid that once was distributed in ald E. Savage of the University of California the coastal regions of the Pacific Northwest, Museum of Paleontology, C. A. Repenning of probably much the way that Pacific salmon the U.S. Geological Survey, and Norman V. (Oncorhynchus) are today. In 1950 and again Peterson of the Oregon State Department of in 1964, more complete specimens were dis- Geology and Mineral Industries. W. I. Follett covered of this unusual species from a Pliocene provided information leading to study of the gravel pit in northcentral Oregon. The last find Turlock material and Dennis Garber made consisted of a large skull which is outstanding available the specimens from Turlock Lake. for its completeness and detail of preservation. James 0. Berkland collected material and pro- It is a description of this skull that forms the vided information on the Worden fossils. H. A. 2 BULLETIN, MUSEUM OF NATURAL HISTORY, UNIVERSITY OF OREGON No. 18

Vibbert donated material from Gateway, as did tions of three branchiostegal rays; part of the Phil F. Brogan. C. H. Ellis and H. A. Demorest right preopercle; posterior part of the right of the Washington State Department of Fisher- cleithrum; complete right posttemporal and in- ies generously donated a large breeding male complete left posttemporal; miscellaneous Chinook salmon for skeletal preparation. Eliz- fragments including parts of opercle, pectoral abeth S. Wing loaned a large tarpon skeleton. fin, basihyal plate, neural and hemal spines, Richard L. Wilson provided technical help. branchial arches; approximately 40 vertebrae, The carefully executed drawings of the type both from the caudal and precaudal series; left specimen are the work of Martha B. Lackey, epihyal; left interopercle; left lacrimal; right staff artist of The University of Michigan Mu- supraorbital. seum of Zoology, and Louis P. Martonyi took UMMP V58061, about 20 vertebrae prob- the photograph of the large vertebra. Financial ably belonging to the paratype, Gateway Local- support from the National Science Foundation, ity, R. R. Miller and field party, 1961. GB-4854X and GB-14871 (to R. R. Miller), UMMP V58062, five vertebrae probably including publication subsidy, is gratefully belonging to the paratype, Gateway Locality, acknowledged. P. F. Brogan, Bend, Oregon, about 1950. UMMP V58063, left hyomandibular pos- MATERIAL sibly from the paratype, Gateway Locality, H. Institutional abbreviations are: University A. Vibbert, Madras, Oregon. of Oregon Museum of Natural History (UO), UMMP V58064, anterior portion of right University of California Museum of Paleontol- dentary (Fig. 13) from a juvenile, Worden ogy (UCMP), University of Michigan Museum Locality, Norman V. Peterson, 1968. of Paleontology (UMMP), and University of Listed below is the material from California. Michigan Museum of Zoology (UMMZ) . UCMP 65630, broken premaxillary tooth, The following material is all from Oregon. Pinole Locality, C. Stock, 1917. Holotype, UO 26799, Gateway Locality, col- UCMP 22560, water-worn precaudal cen- lected by Mrs. George Iiames and Scott Mc- trum, Pinole Locality, C. Stock, 1917. Kain, summer 1964: skull with jaws and an- UCMP 34566, central part of left preopercle terior gill arches in articulated condition; op- and seven vertebral centra (some broken or ercles and subopercles missing (see Figs. 3-6, crushed), Pinole Locality, WPA field party, 10). 1938. Paratype, UO F3335, Gateway Locality, col- UCMP 37584, left premaxilla and tooth, lected by J. A. Shotwell and first discovered Pinole Locality, WPA field party, 1940. by Miss Ann Brownhill about 1950; associated UCMP 65629, fragments of one vertebral parts from a single individual of very large centrum, Pinole Locality, C. Hotton, 1960. size (somewhat larger than holotype) are listed UCMP 58570, incomplete, precaudal verte- as follows: badly crushed neurocranium show- bral centrum, Pinole Locality, D. Savage and ing posterior portion of parasphenoid, basioc- field party, 1961. cipital, both exoccipitals and prootics ; flattened UCMP 61554, water-worn premaxillary on top of these bones are portions of the frontal, tooth, Pinole Locality, Preston Ritter, 1962. parietal, epiotic and pterotic ( all of the left UCMP 61039, broken premaxillary tooth, side), plus part of the supraoccipital ; complete Pinole Locality, Jean Firby, 1962. right and left mandibles and premaxillae, to UCMP 64100, parts of three vertebral cen- each of which is firmly attached an extremely tra, Pinole Locality. large breeding tooth (Fig. 9) with ossified UCMP 61550, right premaxillary tooth with base; left maxilla; right and left quadrate; tip missing, Pinole Locality, Melvin Washing- right hyomandibular ; right ceratohyal; por- ton. 1972 CA VENDER AND MILLER: SMILODONICHTHYS, A NEW SALMONID FISH 3

UCMP 48657, part of vertical limb of left A. Gateway Locality—U0 loc 2250. Collected preopercle and part of sensory canal bone, Tur- from a coarse boulder and gravel facies in lock Locality. the "Torrential Beds" ( Shotwell's informal UCMP 44668, right frontal and 2 vertebral name) of the Madras Formation, near the town centra, Turlock Locality, 1954. of Gateway, Jefferson County, Oregon; elev. The following California material was col- ca. 2,250 ft. (Figs. 1-2 ) . This unit consists of a lected at the Turlock Locality by Dennis Garber mass of boulders, tree fragments, chunks of of Modesto, California, from 1957 to about sediment from the underlying formation of 1964. Barstovian (Late Miocene) age, and numerous UCMP 93170, anterior end of right dentary. small sand lenses. Large salmonid vertebrae UCMP 93171, articular fossa of right oper- and, less frequently, teeth have been found de. along the bottom of these lenses. UCMP 93172, portion of left frontal. The age of the "Torrential" unit is not definite- three large fragments in- UCMP 93173-75, ly established. It contains reworked Barstovian terpreted as parts of the vertical limbs of vertebrates. According to Shotwell ( pers. preopercles. comm.) , the age can be no older than Barsto- UCMP 93176, fragmentary right premax- vian nor younger than Hemphillian (Middle illa with osseous base of large tooth, in 2 pieces. Pliocene) . There is a strong possibility that the UCMP 93177, water-worn left premaxilla Torrential Unit is of Hemphillian age. Smilo- with tooth base. donichthy s vertebrae have been recovered from UCMP 93178, right premaxilla with tooth Early Pliocene to Late Middle Pliocene depos- base. its along the Columbia River in the vicinity of UCMP 93179, complete right premaxilla Arlington, Oregon, and twenty miles to the east. and tooth. UCMP 93180, left premaxilla with complete B. Worden Locality—Abandoned railroad cut tooth, most of enamel present, anterior portion near Worden, Klamath County, Oregon, lo- of premaxilla broken off. cated in the Klamath Falls Quadrangle, col- UCMP 93181-83, three left premaxillae lected by Norman Peterson, Oregon State De- with teeth, enamel portions mostly broken off, partment of Geology and Mineral Industries, osseous bases complete. April 15, 1968. This locality consists of a 20- UCMP 93184, complete right premaxilla foot deep exposure of tuffaceous sandstone dip- and tooth, enamel portion worn. ping 10 degrees to the northeast which is trun- UCMP 93185, eight vertebral centra ( 4 cated at the east and west edges of the railroad complete) , largest 40 mm diameter, smallest cut by basaltic intrusions. The sandstone in 30 mm. places is cross-bedded and moderately well ce- UCMP 93186, four bone fragments. mented. It may belong to the Yonna Formation UCMP 93187, one tooth fragment. which is Pliocene (Newcomb, 1958 ) . Bones, in- cluding those of land mammals, found at the LOCATION AND AGE site were disarticulated and haphazardly as- Fossils referable to Smilodonichthys have sembled during deposition of the sand. Other been found at four main localities, two in Cali- fish remains that are associated with the sal- fornia and two in Oregon, plus additional monids belong to the families Cyprinidae and minor sites along the Columbia River of Ore- Catostomidae. gon. In two of the four localities, mammalian C. Pinole Locality—Pinole Tuff at Pinole, fossils have been recovered along with the fish Contra Costa County, California, about 17 remains and have supplied the valuable mam- miles north of Oakland; UC loc V2572, V3425 malian-age determinations. and V3837. The locality has yielded a frag- 4 BULLETIN, MUSEUM OF NATURAL HISTORY, UNIVERSITY OF OREGON No. 18

Figure 1. Gateway Locality, showing exposure of the "Torrential beds" of the Madras Formation, at gravel pit near Gateway, Oregon, 1961. mentary mammalian fauna (Stirton, 1939). SYSTEMATICS There is a potassium argon date of 5.2 million ORDER SALMONIFORMES years (Evernden et al., 1964) for the Pinole FAMILY SALMONIDAE Tuff. SMILODONICHTHYS, new genus D. Turlock Locality—This locality consists of TYPE SPECIES: Smilodonichthys rastrosus, new exposures of the Mehrten Formation which out- species crop at the edge of Turlock Lake, Stanislaus (Figs. 3-13) County, California, 22 miles east of Modesto. UCMP loc V5405 lies in the NW of SE 1/4 DIAGNOSIS: Distinguished from all known sal- of Sec. 8, T4S, R13E, Turlock Lake Quad- monid species by its numerous gill rakers, over rangle (USGS 1953) . This site has also yielded 100 on the first branchial arch in the adult. a fragmentary land mammalian fauna. Jaws and palate without feeding teeth; lower The Turlock Lake and Pinole Localities are jaw very deep at coronoid process (greatest chronologically very closely related in terms depth 3 times in length), without tooth-bearing of the land-mammal fossils which, according to region except an abbreviated shelf adjacent to D. E. Savage (pers. comm.), are judged to be the symphysis ; maxilla toothless, apparently a Late Hemphillian (Late Middle Pliocene) no teeth on palate and tongue; gill rakers and river-border fauna. basibranchials toothless. Teeth of breeding in- 1972 CA VENDER AND MILLER: SMILODONICHTHYS, A NEW SALMONID FISH 5

Figure 2. Detail of the horizon (sand lens being worked) which yielded the paratype of Smilodonichthys rastrosus at Gateway, 1961. dividuals consist of one massive tooth on each to the posterior end of the supraoccipital meas- premaxilla and much smaller teeth on the den- ures 307 mm. Ventrally the length measured taries, usually one at each side of the mandib- from the anterior tip of the vomer to the poste- ular symphysis. Supramaxilla exceptionally rior end of the basioccipital is 316 mm. Inter- large, attaining 80% of length of oral border orbital width about 157 mm; width at the at- of maxilla. Posterior (basicranial) part of tachment of the nasals 103 mm, and width at parasphenoid strongly compressed in the form the frontal-supraethmoid junction 77 mm. of a keel. Posttemporal fossa very shallow and Width between the sphenotic processes is 170 of small area; dermal part of pterotic lateral mm, between the pterotics 166 mm. Greatest to posttemporal fossa, relatively wide. Inter- posterior width of parasphenoid ( at the ascend- opercle with pronounced dorsal extension. ing wings) 89 mm, greatest anterior width 67 Vomer diamond-shaped, with no tooth-bearing mm. Depth of the neurocranium is markedly 4 distorted due to the dorsoventral compression platform on shaft. Urohyal /5 as long as lower jaw. Ornamentation of vertebral centra con- and loss of cartilage during fossilization. sisting of many fine, elevated ridges running In the branchiocranium, the distance on the longitudinally. right side between the anterior end of the man- dible and the posterior border of the preopercle MEASUREMENTS: The length of the neurocran- is 385 mm. The vertical distance on the right ium from the anterior tip of the supraethmoid side from the horizontal line formed by the 6 BULLETIN, MUSEUM OF NATURAL HISTORY, UNIVERSITY OF OREGON No. 18 ventral border of the interopercle to the dorsal part housed in the meckelian fossa of the lower border of the hyomandibular is 240 mm. jaw and a posterior part covering a large area The right mandible measures 264 mm in of the cheek between the preopercle and eye length and 87 mm in depth at the coronoid (Greene and Greene, 1914) . In addition, the process. The maxilla, with supramaxilla in posterior part is split into three poorly defined place, measures 150 mm in length and 47 mm divisions (Ai, A2, and A3 of Allis, 1897) which in greatest depth. The supramaxilla is 104 mm are best delineated where the muscle takes its in length and 32 mm in greatest depth. origin. The longest division, Ai, has its origin The right preopercle, with ventral border dorsally on the well developed adductor ridge broken, measures about 200 mm in height. of the hyomandibular. It runs downward be- The right premaxilla is 76 mm long; the os- hind the eye to the aponeurosis situated at the seous base of the single large tooth on the right coronoid margin of the articular. The second premaxilla is 35 mm in greatest width and and largest division, A2, originates principally about 50 mm in greatest length. on the anterior edge of the preopercle and ad- The basioccipital condyle is about 45 mm ductor ridge but fibers are also attached to the wide (somewhat distorted due to dorsoventral quadrate and symplectic. The A3 division runs compression). A precaudal centrum, taken underneath and obliquely to the first two. It originates on the lateral face of the ascending from the paratype, is 35 mm in greatest diam- wing of the metapterygoid. The mandibular eter and 25.5 mm in anterior-posterior length portion of the adductor muscle inserts on the (the largest vertebra of Smilodonichthys exam- ined, UCMP 44668, from Turlock Lake, meas- strong ledge that runs along the ventromesial ures 48 mm greatest diameter and 28.5 mm part of the dentary. This ledge is a prominent feature on the dentary of Smilodonichthys. The long). extent of the meckelian fossa which provides In order to obtain some idea of overall size room for the expansion of the adductor muscle of the holotype, we have made corresponding during contraction is greater in Smilodonich- measurements on skulls of two Oncorhynchus thys than in Oncorhynchus. Also, in the former, tshawytscha: UMMZ 178987-S, 985 mm S.L., the adductor ridge presumably serving as the 391/2 lbs., male, and UMMZ 186299-S, 845 area of origin for the Ai and A2 divisions is mm S.L., 281/2 lbs., female. In that species the more pronounced and may exclude part of the length of the opercle averages about 20 per- upper limb of the preopercle as a place of cent of head length. Using this proportion, the muscle attachment. head length of the fossil (opercle missing) is estimated to be 462 mm. Through a linear pro- Two muscles that operate the suspensorium gression taken from the proportion of head are the adductor and levator arcus palatini. The length to standard length, the fossil is calculat- former originates on the lateral face of the ed to have had a standard length of 1900 mm. ascending process of the parasphenoid and on the anterior rim of the prootic. It inserts on the CRANIAL MUSCULATURE: A number of the indi- posteromesial extension of the endopterygoid. vidual characteristics of the skull bones in Both of these areas are developed to a greater Smilodonichthys are associated with places of degree in Smilodonichthys than in Oncorhyn- muscle and ligamentous attachment. In order chus. A ridge transversely crosses the endop- to interpret more accurately some of these terygoid beneath the orbit of Smilodonichthys, structures, comparisons are made between the possibly marking the anterior limit of insertion fossil and a living salmonid, Oncorhynchus of the adductor arcus palatini. The levator has kisutch, in the areas of the lower jaw and two major divisions. The anterior ( outer) divi- suspensorium. sion inserts on the mesial side of the ascending The adductor mandibulae is divided by an wing of the metapterygoid. The innermost pos- aponeurosis into an anterior (mandibular) terior division inserts on the lateral surface of 1972 CA VENDER AND MILLER: SMILODONICHTHYS, A NEW SALMONID FISH 7 the hyomandibular head. The levator origin is sphenoid-pterosphenoid region) occurred in on the sphenotic process and the pterotic. The fossilization. opposite (mesial) side of the hyomandibular Cranial Roof .—The most striking character- head forms a large area for insertion of the istics of the cranial roof (Fig. 3) are: (1) the hyomandibulae muscle that takes its origin overall size and elongate shape; (2) the heav- principally from the prootic. In Oncorhynchus ily ossified construction of the component kisutch, this muscle is subdivided into an ante- bones, especially the frontals; (3) the com- rior and posterior part at its insertion. In both pleteness of the bone-roofing posteriorly and Smilodonichthys and Oncorhynchus, the head the shallow posttemporal fossae; (4) the supra- of the hyomandiublar is exceptionally broad. occipital separating the parietals; (5) the fron- On the back of the braincase at each side of tals not entirely meeting over part of their mid- the foramen magnum are shallow fossae for line; and (6) the triangular-shaped supra- insertion of anterior trunk musculature. These ethmoid. muscles pass forward between the vertebral In area covered, the frontals are the major column and pectoral girdle to their place of at- bones of the cranial roof. An incomplete right tachment (Gosline, 1969) . The posterior proc- frontal, UCMP 44668, showing the central and esses of the pterotics lie lateral to them and ap- lateral portions of the bone where it articulates parently form a support for the pectoral girdle with the sphenotic, is thick and massive in ap- at the point where the posttemporal is expanded pearance. It indicates that the frontals were ventrally. They also serve as a place of origin very strong where they form a low arch between for part of the levator operculi. The fossae at the sphenotics. The oblique ridge on the lower each side of the foramen magnum appear to frontal surface that unites with the sphenotic be in line with the row of anterior epineural is exceptionally well developed. It lies under ribs. Even when taking into consideration sig- the heaviest part of the frontal. As in Recent nificant depression of the braincase during Oncorhynchus, the fit between the frontal and preservation, the depth of the rear wall of the sphenotic is so close that the line of junction is braincase is greater in Oncorhynchus than it is barely perceptible. Mesially, the frontals are in Smilodonichthys. The former also has much very thin. They meet in the rnidline where they larger posttemporal fossae for insertion of the overlap the supraoccipital, near the middle of more dorsal portions of the anterior trunk mus- the cranium between the sphenotics, and prob- cles. The difference pointed out in rear skull ably also at their anterior ends where they con- proportions and body muscle attachment may tact the supraethmoid. Two large spaces in the indicate that Oncorhynchus has a greater body midline, one ahead and one behind the zone of depth than was present in Smilodonichthys. frontal contact in the area between the spheno- ETYMOLOGY: Named Smilodonichthys, from tics, indicate regions occupied by cartilage. A the fossil genus of sabre-toothed cat, in refer- similar separation of the frontals by cartilage ence to the pair of large teeth at the anterior occurs in Recent Oncorhynchus. The frontals end of the upper jaw, and rastrosus, from the are very long bones with most of the trabeculae Latin word for raker, in reference to the numer- running longitudinally. The trabeculae can be ous gill rakers. traced by ridges on the surface of the bone. Structurally, the frontals form strong bracing DESCRIPTION beams between the pterotics at the rear of the cranial roof and the supraethmoid in front. NEuRocRANIum: The neurocranium was dis- The pattern of the surface ridges in the cen- articulated from the rest of the skull to enable tral portion of the frontals, where they bridge careful study and illustration. Preservation between the sphenotics, indicates that they meet was virtually complete, but some lateral distor- compressional stresses from the sides probably tion and depression (especially in the orbito- set up by the suspensorium. 8 BULLETIN, MUSEUM OF NATURAL HISTORY, UNIVERSITY OF OREGON No. 18

The anterior part of the cranial roof tapers to At the anterior end of the ossified braincase, a point through the triangular shape of the me- the ascending wings of the parasphenoid extend dian supraethmoid. The posterior extensions of high up on the anterior margins of the prootics this bone overlap the frontals on each side. The and may have reached as far as the sphenotics. posterior limits of the supraethmoid are not Each ascending wing has a long free anterior clear. However, there may be a notch in the edge that curves to a junction with the main posterior border. In outline, the supraethmoid longitudinal part of the parasphenoid. At this is similar to that of Oncorhynchus kisutch and point of junction, the parasphenoid is quite nar- 0. masou (Vladykov, 1962: Figs. 28-29) . It row but very thick. The thickened area and the differs in its sturdier construction. Norden ascending wings present an exceptionally long (1961) found that within the salmonines, the and sturdy place of origin for the adductor supraethmoid has the greatest taxonomic signfi- arcus palatini muscles already mentioned in cance of all the dorsal roofing bones. Nasals Oncorhynchus. Just posterior and mesial to the are present, fastened to the lateral edges of the ascending wings, a pair of foramina are visible frontals just behind the supraethmoid. that penetrate the parasphenoid directly below One of the obvious differences in the cranial the anteroventral corner of the prootic. They roof between the fossil and Oncorhynchus is the are the openings for the internal carotid arter- very limited development of the posttemporal ies that are positioned as in Recent Oncorhyn- fossae. There may be some distortion, due to chus. Unlike the latter, however, there appear partial flattening of the neurocranium, but even to be no openings for passage of the efferent accounting for this, the fossae are shallow and pseudobranchial arteries within the parasphen- short. The floor of the fossa, formed by the oid itself. frontal, epiotic and pterotic, is apparently a Anterior to the ascending wings, the thicken- continuous covering of bone. There is no carti- ing of the parasphenoid extends forward along laginous interspace as in Recent salmonines. its lateral edges as the bone gradually widens. Ventral Bones of the Neurocranium.—When The parasphenoid reaches its greatest width viewed from below, the general appearance of just ahead of the lateral ethmoids. The broad the neurocranium ( Fig. 4) again is that of an anterior portion of the parasphenoid is matched Oncorhynchus. The parasphenoid is very broad by a broad posterior half of the vomer which anteriorly. With the vomer attached, it domi- overlaps it. The latter possesses a distinctive nates the whole lower surface. In addition to its shape when compared with other salmonines. anterior breadth and total length, this bone is It looks like an elongated diamond. At the ta- distinctive in the form of its posterior extension pered anterior end, the lateral edges parallel and in the length of its ascending wings. The those of the supraethmoid above. Also, at the posterior extension forms the bottom of the eye. anterior end, the vomer is thickened, but there muscle canal or posterior myodome and meets is no evidence of a pronounced constriction that the basioccipital and prootics. Instead of being sets it off from the posterior part. It is possible broadly rounded, allowing the myodome to that the edges may have extended farther later- have a substantial opening to the posterior as in ally forming a "head," since there is some evi- Oncorhynchus, it is laterally compressed to a dence of breakage. One striking feature of the point where the myodome is a narrow channel. vomer is the absence of teeth or of any kind of Thus the parasphenoid is markedly keel- tooth-bearing platform. shaped. The closest comparison among the Sal- There are no other ossifications visible in the monidae can be found in Coregonus, in which ethmoid region than those described. It is con- the posterior part of the parasphenoid is some- cluded that the area between the supraethmoid what keel-shaped, with large lateral surfaces. and vomer must have been occupied by a large However, this part is not much compressed and ethmoid cartilage, as in Oncorhynchus and the myodome has a wide posterior opening. other salmonines.

1972 CA VENDER AND MILLER: SMILODONICHTHYS, A NEW SALMONID FISH 9

The bones of the otic region are similar to ABBREVIATIONS USED ON THE ILLUSTRATIONS those of Oncorhynchus in their shape and rela- Ao = antorbital L lop = left inter- tionships to each other. One apparent difference A R = adductor ridge opercle concerns the lateral process of the sphenotic of hyomandibular R lop = right inter- which projects directly outward instead of curv- Art = articular opercle Bh = basihyal La = lacrimal ing backward to form a well defined fossa. Boc = basioccipital L E = lateral ethmoid Also, the anterior border of the prootic is in Br = branchiostegals M Ca = mandibular contact for most of its length with the ascending L Br = left branchios- canal wing of the parasphenoid. tegals Met = metapterygoid Both posterior processes of the pterotics are R Br = right branchi- Mx = maxilla broken off in the holotype. These are well de- ostegals L Mx = left maxilla C I = cartilage inter- R Mx = right maxilla veloped in Oncorhynchus and other salmonines space Na = nasal but less pronounced in coregonines. There is a L DA 1, 2, 3 = left OBT =. osseous base long, well-defined groove on the ventral surface dorsal limb of gill of tooth of each pterotic which extends obliquely for- arch Op = opercle ward along the zone of contact between the R DA 1, 2, 3 = right Pa = parietal prootic and sphenotic. This groove seats the dorsal limb of gill Pal = palatine Pmx =. premaxilla head of the hyomandibular. The intercalars are arch De = dentary Pmx T = premaxil- present at the posterior corners of the brain- L De =_ left dentary lary tooth case. They possess long projections that extend R De = right dentary Pop = preopercle anteriorly to unite with, and partly extend onto, De T = dentary teeth Pra = proatlas (fused the prootics. At the posterior end of the basi- Dsph = dermos- first centrum) cranium the basioccipital condyle is formed by phenotic Pro = prootic the fusion of the first vertebral centrum ( pro- Ect = ectopterygoid Ps = parasphenoid End = endopterygoid Pt f = posttemporal atlas ) with the basioccipital in both the hobo- Eoc = exoccipital fossa type and paratype. This structure forms the Epo =. epiotic Pto = pterotic entire circular facet for articulation with the Fr = frontal Pts pterosphenoid vertebral column, excluding the exoccipitals. f ic = foramen for in- Qu -=. quadrate The lines of contact between the exoccipitals ternal carotid artery Se = supraethmoid and the proatlas are visible in these two f j = jugular foramen Smx supramaxilla f VII = foramen for So = supraorbital specimens. 7th cranial nerve Soc = supraoccipital At the anterior end of the braincase a pair f X = foramen for So Ca = supraorbital of badly crushed, highly cavernous ossifica- 10th cranial nerve canal tions are present that represent the pterosphen- D Hh =_ dorsal Sph sphenotic oids. Neither the orbitosphenoid nor basisphen- hypohyal Sop = subopercle oid was preserved. V Hh = ventral Spop = suprapre- hypohyal opercle BRANCHIOCRANIUM: Except for the absence of Hm = hyomandibular Sy = symplectic the gill covers, the external bones of the branch- L Hm = left Uh = urohyal iocranium (Figs. 5-6) are nicely displayed on hyomandibular L VA 1, 2, 3 = left R Hm = right ventral limb of gill the holotype and needed very little preparation. hyomandibular arch Internally, however, the orobranchial cavity Int =. intercalar R VA 1, 2, 3 = right was completely filled with coarse sand and lo 2-6 = infraorbitals ventral limb of gill gravel which had to be removed to expose the 2-6 arch gill arches and associated elements. Vo = vomer The branchiocranium possesses a complex of distinctive, yet interrelated, characters that nearly all appear to be associated with the un- 10 BULLETIN, MUSEUM OF NATURAL HISTORY, UNIVERSITY OF OREGON No. 18

5 cm

Figure 3. Cranial roof of holotype of Smilodonichthys rastrosus. Abbreviations are given on the preced- ing page. 1972 CA VENDER AND MILLER: SMILODONICHTHYS, A NEW SALMON1D FISH 11

Sph

Eoc 12 BULLETIN, MUSEUM OF NATURAL HISTORY, UNIVERSITY OF OREGON No. 18

5 cm

Figure 4. Ventral view of neurocranium of holotype. Abbreviations are given on the page preceding Figure 3. 1972 CA VENDER AND MILLER: SMILODONICHTHYS, A NEW SALMONID FISH 13 18 BULLETIN, MUSEUM OF NATURAL HISTORY, UNIVERSITY OF OREGON No. 18 usual feeding mechanism. The most important the largest component. Dorsally, it has a single of these are the very high gill-raker number on broad head for articulation with the neurocran- the branchial arches, the enlarged endoptery- ium. The bone tapers ventrally into a strong goid, the shape of the quadrate, the massive vertical limb that meets the symplectic. Poste- interopercle with its elevated posterior end, the riorly, the opercular condyle is barely repre- shape and relationships of the upper and lower sented by a rounded protuberance and must jaw bones, and the absence of teeth on any of have consisted almost entirely of cartilage. the bones except a pair of breeding teeth on the One of the important characters of the hyo- lower and upper jaws, the upper premaxillary mandibular is the adductor ridge protruding pair being enormous in size. from its lateral surface. This ridge meets the Hyoid Region.—Almost nothing is known upper arm of the preopercle to form the place of the opercle and subopercle of Smilodonich- of origin of the major portion (A2) of the ad- thys. A small portion of the right opercle show- ductor mandibulae muscle. It also forms a ing the opercular fossa is present on the para- notch posteriorly for passage of the hyoman- type. It is similar to that part of the opercle in dibular trunk of the facial nerve. Oncorhynchus. Both the vertical and horizontal The remaining bones in the hyoid arch are limbs of the preopercle are well developed. The too obscured by the branchial arches or other anterior margin of the vertical limb is particu- bones to allow satisfactory study. A portion of larly thick and heavy. It fits firmly together the symplectic is visible below the hyomandib- with the hyomanidbular where it contacts the ular and the epihyal can barely be seen pressed adductor ridge to form a large, strong area of against the mesial surface of each interopercle. attachment for the adductor mandibulae mus- Anteriorly, the hypohyals are situated in their cles. The proportions of the preopercle are un- normal position but are in a poor state of pres- usual for salmonines. The ventral and horizon- ervation. The basihyal plate (sometimes tal limbs have very broad laminate expansions termed supralingual or glossohyal) is missing that coalesce into a curved sheet of bone cover- from the holotype. This bone may be present in ing much of the cheek region. the paratype as a disarticulated element; how- A small tube-shaped bone, the suprapreop- ever, its identification is too uncertain to war- ercle, is present on the left side of the holotype rant description as such. Belonging to the par- just above the preopercle. It transfers the pre- atype are several bones of the hyoid arch, operculo-mandibular canal from the pterotic among them a left epihyal and a right cerato- to the preopercle. hyal. These elements are large and strong. A The interopercle is developed to a similar distinct groove for the hyoidean artery crosses degree as the preopercle. It is a large bone, the entire length of the ceratohyal and part way quite thick through its central and posterior across the epihyal to a large foramen, as in regions. An important feature of this bone in- Oncorhynchus keta ( Hikita, 1962: Fig. 48). volves the posterior portion which is projected The urohyal is one of the longest bones in dorsally, much as the upper limb of the pre- the branchiocranium. The holotype possesses a opercle, and occupies a position taken by the complete urohyal measuring 215 mm from the anterior end of the subopercle in Oncorhynchus anterior end at the hypohyals to the posterior (Fig. 7). border situated almost beyond the termination The branchiostegal series appears to be com- of the epihyals. In the same individual, the plete in the holotype. There are 14 branchios- complete right mandible measures 265 mm tegal rays on the left side and 15 on the right. long. The shape of the urohyal resembles that The individual rays are long, wide, and broad- in Oncorhynchus where it is proportionately ly overlapping. longer than in other salmonines. Nevertheless, In the suspensorium, the hyo mandibular is the urohyal in Oncorhynchus barely reaches 1972 CA VENDER AND MILLER: SMILODONICHTHYS, A NEW SALMONID FISH 19

A

Anterodorsal process of Sop Op Pop

Dorsal process of lop Sop

Figure 7. Comparison of right interopercles in Oncorhynchus tshawytscha (A), UMMZ 178987-S, and the holotype (B). Position of the anterodorsal process of the subopercle in relation to the interopercle (with dashed margin) shown at (C), drawn from same specimen as (A) but mesial view of left side. Note the similarities between the dorsal process of the interopercle in the holotype and that of the subopercle in Oncorhynchus. Scale bars, 1 cm. 20 BULLETIN, MUSEUM OF NATURAL HISTORY, UNIVERSITY OF OREGON No. 18

75% of the proportionate length of the fossil both the ectopterygoid and endopterygoid pos- urohyal. The increased size of this element can teriorly. Anteriorly, it combines with the max- be correlated with similar development of jaw illa to form a large fossa for articulation with bones, branchial apparatus, and opercular se- the ethmoid cartilage. Such a large fossa re- ries. It probably reflects the size of the sterno- flects the importance of a strong hinge between hyoideus muscle and the important role this the palatoquadrate and ethmoid region facili- muscle plays in opening the mouth and bran- tating the swinging out of the upper jaw on the chial apparatus. rostrum. There appears to be no anterior pala- tine extension beyond this point of junction Palatoquadrate.—The bones of the palato- with the maxilla, as sometimes occurs in salmo- quadrate, although similar to those in other nines that have a continuous row of vomerine salmonines, show some pronounced modifica- and palatine teeth. No teeth are present on the tions associated with the feeding mechanism. palatines of the holotype. However, there is a The endopterygoid and quadrate are the most shelf on each bone that could have supported altered from their typical condition in preda- several strong teeth. A peculiarity of the pala- tory salmonines. tine exists at its junction with the endoptery- Posteriorly, the endopterygoid is extended goid. In Oncorhynchus, the endopterygoid ex- mesial to the metapterygoid and across the top tends forward along the mesial side of the pala- of the quadrate (possibly reaching to the hyo- tine for a considerable distance and is usually mandibular ) . It is in direct contact with the only joined to it by cartilage and soft tissue. quadrate over this entire extension. In most There is no interdigitation of the two bones. As other salmonines, the endopterygoid joins only observed in the holotype of Smilodonichthys, the anterior dorsal corner of the quadrate while the posterior end of the palatine overlaps, and the metapterygoid is fastened by cartilage fits tightly with, the anterior lateral face of the along most of the quadrate's dorsal border. The endopterygoid in the same area where it joins endopterygoid of Salvelinus namaycush par- the ectopterygoid. The overlap involves only allels that of the fossil in its contact with the the posterior 1/3 of the palatine. It should be quadrate. The metapterygoid in the fossil has noted that the palatine is immovably joined to been displaced somewhat by the endopterygoid both pterygoids in coregonines. but it still may have had a cartilaginous con- Besides the broad junction with the endop- nection with part of the dorsal edge of the terygoid, the quadrate differs from that of other quadrate. A pronounced ridge transversely salmonines in its posterior proportions. Behind crosses the dorsolateral surface of the endop- the deep notch ( on the mesial side) for the terygoid at a point just in front of the junction symplectic, the quadrate is extended downward with the metapterygoid and can be seen through and backward, forming a broad lateral surface the orbital opening. The metapterygoid is to seat the anterior end of the preopercle. firmly seated on the curved posterodorsal por- tion of the endopterygoid and also is securely Circumorbital Series.—In a number of its fastened to the hyomandibular. The construc- characteristics, including the proportions of the tion and arrangement of these two pterygoid posterior infraorbitals, the circumorbital series bones provide an extensive but strong area of is similar to that of Oncorhynchus. Except for insertion for divisions of the levator and adduc- a small missing piece below the eye at the lower tor arcus palatini muscles which function in orbital margin, the circumorbitals are intact on lifting the palatoquadrate arches and pulling the left side of the holotype. There are a total of them toward the midline, thus assisting in the nine, one more than is usually found in Salmo closure of the mouth. and Oncorhynchus. Five infraorbital bones are The ectopterygoid is present as in other sal- situated behind the eye, the uppermost one, in monines. The palatine is rigidly united with this case infraorbital 7 ( dermosphenotic, Nel- 1972 CA VENDER AND MILLER: SMILODONICHTHYS, A NEW SALMONID FISH 21 son, 1969), receives the infraorbital canal brief shelf at the anterior end of each lower jaw from the pterotic. The next two posterior infra- near the symphysis. One tooth is present on orbitals situated below the dermosphenotic UCMP 93170; a main cusp and an accessory have broken posterior ends; the fourth ( infra- cusp are present on each side in the holotype. orbital 4) extends at least 2/3 of the distance A single-cusped tooth is present on the dentar- from the orbital rim to the anterior edge of the ies of the paratype; in addition, on the right preopercle. side, there is a smaller replacement tooth The slender bone carrying the infraorbital seated in a reclined position behind the first. canal under the eye (infraorbital 2) is not com- These teeth have large osseous bases fused to plete as stated above. It joins the lacrimal, a the dentary and resemble in certain aspects the heavy, elongate bone shaped something like a breeding teeth in male Pacific salmon such as common milkweed pod. It has a blunt anterior Oncorhynchus keta. Excepting the short tooth- projection and tapered posterior end. The lacri- bearing shelf, the oral border of the dentary is mal articulates directly, over an extended area, a sharp ridge which shows no evidence of bear- with another large element, the antorbital. Dor- ing teeth. In contrast, the tooth-bearing shelf on sal and posterior to the antorbital is a tear- the dentary in Oncorhynchus extends nearly shaped supraorbital. The form and relation- the entire length of the oral border. The thick ships of the individual elements in the circum- anterior portions of the fossil dentaries indi- orbital series indicate that the eye and nares of cate that this area was subject to considerable the fossil were similar to those of other salmo- stress. The anterior ends of the dentaries curve nines. The major difference noted is the en- toward the symphysis. When the two bones are largement of the three bones (lacrimal, antor- united at their symphysial joint, a wide inter- bital, supraorbital) associated with the pump- space results. The lower jaw is quite straight, ing mechanism of the olfactory organ (see Gos- without an upturned anterior end (Fig. 8) . line, 1961) and the extended contact between Another easily identifiable character of the the lacrimal and antorbital. lower jaw is the dorsal process of the articular which projects from behind the articular fossa Mandibular Region.—The upper and lower and carries the mandibular canal. This process jaw bones of the fossil are so distinctive that forms an angle of 30 degrees with a line drawn the species can be identified from their isolated through the symphysis to the floor of the fossa occurrence such as at the Oregon Worden Lo- (Fig. 8) . In other salmonines, this angle is cality (Fig. 13) . In lateral view, the lower jaw close to 90 degrees. The angle reflects the width has a massive appearance, being long, very of the articular fossa. deep, especially at the coronoid process, and heavy through the anterior part of the dentary. Upper Jaw.—When viewed from their me- The shape is much different from the long slim sial side (Fig. 9 A), the premaxillae show, an- jaw of Oncorhynchus (Fig. 8) which has a teriorly, flat triangular surfaces that were depth at the coronoid process of 20-25% of its seated against a bluntly shaped azygous ros- length. Reconstructed, the depth of the fossil trum. In lateral and dorsal views (Fig. 9 B, C), lower jaw is about 34% of its length. Other the premaxilla has the appearance of a curved, proportional differences are apparent in the wing-like bone, proportioned longer than wide shorter oral border of the dentary and in the and tapered anteriorly. The lateral surface is longer elevated border of the articular. A lin- convex and faces slightly upwards. The curve ear analysis of the lower jaw is given in of the dorsal border in the holotype inscribes Figure 8. a 65 degree arc of a circle 140 mm in diameter. The short oral border of the dentary can Since the lateral surfaces of the premaxillae be correlated with the reduction of its denti- help mold the contour of the snout in salmo- tion. One or two small teeth are seated on a nines, it is possible to obtain some idea of the 22 BULLETIN, MUSEUM OF NATURAL HISTORY, UNIVERSITY OF OREGON No. 18

A 111■111

Figure 8. Linear analysis of left mandibles in Oneorhynchus keta (A), UMMZ 175915-S male, and the paratype (B). a, length of mandible; b, length of oral margin of dentary; c, length of ascending margin of articular; d, height of coronoid process (determined from complete mandible of holotype); anterior angle measuring slope of ascending margin of articular; posterior angle measuring orientation of dorsal process. Scale bar, 1 cm. 1972 CA VENDER AND MILLER: SMILODONICHTHYS, A NEW SALMONID FISH 23

Premaxilla

Osseous base of tooth

A Enameled portion Pigmented portion of tooth

OBT Pmx

1 cm

Figure 9. Right prernaxilla of paratype with breeding tooth attached. A, mesial view; B, lateral view; C, dorsal view.

ITS POSITION ON INE GILL ILL ELL, GIL U11 UIV 24 BULLETIN, MUSEUM OF NATURAL HISTORY, UNIVERSITY OF OREGON No. 18

- tim afl 0v1 1l nfl t.a.111 vvrartrA rl

32 BULLETIN, MUSEUM OF NATURAL HISTORY, UNIVERSITY OF OREGON No. 18

TABLE 3 COMPARISON OF OSTEOLOGICAL CHARACTERS BETWEEN Smilodonichthys AND SOME OTHER SALMONID GENERA

Smilodon- Onco- Salve- Core- Character ichthys rhyttchus Salmo linus gonines Rostral cartilage azygous (not forked) Supramaxilla greatly enlarged Premaxillary breeding teeth much enlarged (0. keta) Mandible with high coronoid process X Dorsal process of articular (except obliquely oriented Stenodus) Cephalic sensory canal with many small pores Preopercle with well developed horizontal limb Anterior process of intercalar (except (except reaching pterotic X X S. gairdneri) S. alpinus) Anterior part of parasphenoid exceptionally broad (spatulate) X Posterior myodome strongly compressed Supraethmoid triangular, usually (subgenus notched posteriorly X Parasalmo Posttemporal fossa small Interopercle with strong dorsal process Branchiostegal rays over 15 X Gill rakers over 100 Gill rakers long and compressed (subgenus Leucichthys)

Gill rakers without teeth X (teeth reduced (teeth reduced in some species) in some species) Adductor ridge of hyomandibular well developed X (some species) Most cranial bones highly cavernous X X Laminar parts of dermal skull bones expanded and with fimbriate margins X X Lower jaw hooked in spawing male X X (some species) stands apart among the Salmoninae by posses- bound to the cartilaginous rostrum, a conclu- sion of the toothless maxilla and enormous pre- sion that can be reached after comparing the maxillary breeding teeth. fossil premaxilla with that of other salmonines. The premaxilla is an elongate, wing-shaped Only Oncorhynchus among Recent salmonids bone that is slightly curved ( convex side faces possesses a premaxilla similar to the above dorsally) , most likely to conform to the shape type. Its characteristics, along with those of the of the snout. There is no anterior ascending snout, clearly separate Oncorhynchus from process. The mesial side of the bone is flat, with- other salmonines. The latter all possess a pre- out any articular fossa. This side was intimately maxilla with an anterior articular fossa on its 1972 CA VENDER AND MILLER: SMILODONICHTHYS, A NEW SALMONID FISH 33 mesial side which receives a cartilaginous knob members of the genus Oncorhynchus, is a high- protruding from each side of the rostrum (la- ly specialized feature for teleostean fishes. bial cartilage of Tchernavin, 1938, 1943 ) . The These breeding teeth are a secondary sex char- rostrum in Oncorhynchus is azygous, without acter best developed in the largest mature protruding cartilages. In addition this genus spawning males of those forms that migrate has an extended area of attachment for the pos- upstream to spawning areas. Their function ap- terior wing of the premaxilla. pears to be in display and fighting behavior A toothless condition of the maxilla has oc- between male individuals for possession of fe- curred a number of times in the evolution of males and territory as well as display in mating the Salmoniformes, both in conjunction with with the female. Among living Salmoninae, the microphagous and piscivorous adaptations of breeding teeth reach their largest size in mem- the jaws and teeth. When piscivorous, the max- bers of the genus Oncorhynchus. In Smilodon- illa tends to be excluded from the gape by an ichthys the premaxillary breeding teeth have enlarged premaxilla and the palatines tend to reached an extreme size, so large that there is form a powerful dentition that becomes a room for only one tooth on each side of the major part of the bite. Examples can be found snout. in the esocids, galaxioids, and the extinct Apa- The black pigmentation of the tips of these teodus, Cimolichthys, Enchodus and Eurypho- breeding teeth appears to be a further speciali- lis pulchellus ( Goody, 1969). Among the Sal- zation, perhaps accentuating the display behav- monidae, the predaceous types possess strong ior of the breeding male. Large black teeth are maxillary teeth but these teeth have been lost in found in Smilodonichthys ( both those of the the microphagous feeders, such as the Corego- premaxilla and dentary) and in certain species ninae. Smilodonichthys has no trace of the max- of Salmo ( Tchernavin, 1943 ) . illary teeth, although the bone itself enters a A stout mandible with a high coronoid region large part of the gape. The oral border is slight- is found in Smilodonichthys and the Corego- ly convex (suggestive of the condition in the ninae among the Salmonidae. This type of man- coregonines) which appears to be a primitive dible is characteristic of umbrids, clupeoids, teleostean feature. some elopoids, ichthyodectids and leptolepids. Besides the toothless oral border of the max- It may be primitive for at least some of the illa, a further distinctive feature of the upper lower teleosts. A similar lower jaw also occurs jaw of Smilodonichthys is the exceptionally in the pholidophorids. Dimensions of the Smi- large supramaxilla. This bone is usually an lodonichthys lower jaw are indicated in Figure elongate structure positioned along the dorso- 8. There is a large area on its mesial side for lateral part of the maxilla in salmonines. In insertion of the adductor mandibulae muscle. Salvelinus it is very slender but in Salmo and There was little encapsulation of the muscle Oncorhynchus a deep laminal portion extends anteriorly by the dentary. An unusual feature down over the outer side of the maxilla. The of the lower jaw is its open articular fossa. supramaxilla is deepest in Oncorhynchus, Typically in salmonines a dorsal process of the where it is similar in form to that of Smilodo- articular forms the posterior enclosure of the nichthys. None of the living salmonines possess articular fossa. This process is bound to a ridge a supramaxilla of the size found in this extinct on the posteroventral margin of the quadrate genus. Nor do we know of any teleost possess- by a strong ligament. The articular fossa is ing a supramaxilla of comparable size. deep and narrow and closely bound to the artic- The possession of modified anterior jaw ulating condyle on the quadrate. teeth in anadromous breeding male individuals In Smilodonichthys the dorsal process of the of some salmonine species, such as Salmo salar, articular is well developed but unlike the con- Salmo trutta, Salvelinus fontinalis and all dition in other salmonines it is directed ob- 36 BULLETIN, MUSEUM OF NATURAL HISTORY, UNIVERSITY OF OREGON No. 18 fossa is formed by the parietal, a part of which operation of the lower jaw and the expansion of still covers a small anterior area of the fossa. the branchial cavity. The epaxial body muscles that insert in the There is a total of 29 branchiostegal rays in posttemp oral fossa bury most of the dorsal por- the holotype of Smilodonichthys (14 on the left tion of the pterotic in salmonines, including and 15 on the right side) . Salmonid species Oncorhynchus. Only a narrow ridge of the with this many branchiostegals are found only pterotic bone forming the lateral wall of the in the Salmoninae. Coregoninae have up to 12 fossa and carrying the supratemporal sensory on one side (Stenodus). Sal velinus usually has canal extends above the muscle mass. In Smi- 10 to 12 on each side but may have an extreme lodonichthys the fossa is a very shallow cavity of 31 rays (15 right, 16 left) in the interior of limited extent but entirely open above. The western North American form of S. "malma." floor appears to be formed completely of bone Norden (1961 ) , Rounsefell (1962), and Mc- without intervening cartilage. The small size Allister (1968) have summarized branchioste- of this fossa is explained by the fact that it has gal ray counts in salmonids. Of all the salmonid not extended as far forward as in other salmo- genera, Oncorhynchus possesses the highest nines nor has it eroded into most of the dorsal counts, up to 19 or 20 on one side. Hucho has part of the pterotic. A considerable area of this up to 14 and Salmo 13. Smilodonichthys ap- bone was exposed to the surface and not cov- pears to be closest to Oncorhynchus and Salve- ered by the inserting muscle mass. The small linus in this character. McAllister (1968) con- and shallow depth of the posttemporal fossa in cluded that the higher branchiostegal-ray Smilodonichthys appears to be a primitive fea- counts were most likely primitive for the Sal- ture, since an evolutionary trend in the sub- monoidei. A similar conclusion was reached by family often has been toward an enlargement Nelson (1970) for clupeoids. In Smilodonich- of the fossa in forms with large jaws and teeth. thys the branchiostegal formula is 9-1-5, with 5 The small size of the fossa may also be corre- supported by the epihyal, 9 by the ceratohyal, lated with the simple type of basicranial-verte- and 1 articulating with the cartilage between bral joint. these two bones. A bone associated with the articular of the Smilodonichthys has upwards of 110 gill lower jaw is the interopercle. A strong ligament rakers on the first arch. The number is probably joins the posterior margin of the articular with not complete for there are more than this on the anterior end of the interopercle. All salmo- the second arch, which is better exposed than nids possess an interopercle—in which the the first and easier to count. This is an excep- height is typically less than its length ( except tionally high number for a salmonid as it ex- possibly in some Oncorhynchus)—as appears ceeds the highest known number by more than to be true of most lower teleosts. A deep inter- 30. Coregonus muksun, a species of the sub- opercle is found in the myctophoid Aulopus genus Coregonus living in northern and western filamentosus ( Goody, 1969 ) . Among the ex- Siberia, has been reported by Himberg ( 1970) tinct suborders Cimolichthyoidei and Encho- to range as high as 78 gill rakers. Prosopium dontoidei, discussed by Goody (1969 ) , the in- may have up to 45 in P. gemmiferum (Norden, teropercle is absent. These are large-jawed 1970 ) , Stenodus has a maximum of about 30, predators with strong teeth. In Smilodonichthys 32 in Salmo (S. obtusirostris, Behnke, 1968 ) , the shape of the interopercle with its strong Brachymystax 31 (Shaposhnikova, 1968) , Hu- dorsal process is unique among salmonids and cho 19 (Shaposhnikova, 1968), Salvelinus 33 apparently exceptional among most other lower ( Berg, 1948) and a maximum of 42 in Oncor- teleosts. We suggest that the peculiar interop- hynchus ( Hikita, 1962) . The upper limit for ercle of Smilodonichthys is associated with the the number of gill rakers on the first arch in the 1972 CA VENDER AND MILLER: SMILODONICHTHYS, A NEW SALMONID FISH 37

Salmoninae is close to 40 and almost twice that Tarpon, and Esox. The ridge appears in the number in the Coregoninae. Thymallus has a Myctophiformes, Percopsiformes, Beryci- maximum of 33 gill rakers ( Berg, 1948). Smi- formes and widely through the Perciformes. lodonichthys has a greater resemblance to the The adductor ridge is assumed to be a primitive Coregoninae in its numerous gill rakers. character where it occurs in the Salmonidae in- Those teleosts that possess a great number of cluding Smilodonichthys. closely spaced, long and attenuated gill rakers The dermal bone structure in Smilodonich- are in most cases adapted for feeding on plank- thys combines a highly cavernous internal or- tonic organisms. Examples can be found in ganization throughout the thicker portions of the Clupeiodei, Scombroidei, Chanoidei, Cy- the bone with very thin laminate-like marginal prinoidei, Characoidei, Elopoidei, Atherino- areas. The latter are expanded in the bones of morpha, and Carangidae. the cheek region such as the posterior infraorbi- The length and spacing of individual gill tals, preopercle, and interopercle, and probably rakers may indicate as much about the diet as also in the opercle and subopercle. Due to the does the number (Kliewer, 1970) . Among the delicate nature of the peripheral parts of these species of Prosopium, P. gemmiferum, is a expanded areas, preservation was poor. What planktonic feeder with the longest and greatest sections remain, as on infraorbital 3, indicate number of gill rakers of any species in that that the margins were not entire but fimbriate genus. Unlike Smilodonichthys, however, the as in Oncorhynchus. gill rakers of P. gemmiferum are well equipped The cavernous internal structure is nicely with many small teeth ( Norden, 1970) . Those displayed in bones that have been fractured coregonines in the subgenus Leucichthys that transversely to the longitudinal course of the are characteristically planktonic feeders, such trabeculae such as the right interopercle of the as Coregonus artedii, have long, tapered gill holotype. Here the cross section of the bone has rakers equipped with many small teeth. These the apperance of a honeycomb with numerous teeth form an interlocking mesh as illustrated partitions enclosing interstices. The total effect by Vladykov (1970, Fig. 13) . The same is true is probably one of lightness plus strength. of Allothunnus fallai (Tominaga, 1966, Fig. Other salmonines exhibit this type of dermal 2 B) of the Scombroidei. bone structure but to a lesser degree. Trans- In Smilodonichthys the large number of verse sections were made through the anterior long, attenuated rakers, their toothless condi- dentaries of Smilodonichthys, Oncorhynchus, tion and closely spaced and overlapped ar- and Salmo for the purpose of comparison (Fig. rangement, plus the elongation of the rows, 12). It is readily apparent that the cavernulous suggest a feeding method adaptable to small condition of Oncorhynchus exceeds that of pelagic organisms such as are now present in Salmo and approaches the condition in Smilo- the North Pacific Ocean. The special features donichthys. Various authors have remarked of this feeding mechanism and the geographic about the fat storage ability of muscle and bone location of the fossil leave little doubt that this in anadromous Oncorhynchus. The unusual species fed in the ocean during its life history. structure of the fossil bone described here Among the Salmonidae a well developed might be correlated with anadromous behavior. (laterally projecting) adductor ridge of the The lower jaw of large male salmonines in hyomandibular is found in the Coregoninae, spawning condition is often curved upward or Thymallinae and sporadically through the Sal- hooked at the tip ( Morton, 1965 ) . This hook moninae where it occurs in Brachymystax and or kype is both the result of growth of the in some species of Oncorhynchus and Salmo. dentary bone at the symphysial region and ad- Elsewhere among lower teleosts it is variously dition of soft tissues dorsal to the symphysis. developed but particularly noticeable in Elops, Tchernavin (1943, in reference to Salmo 38 BULLETIN, MUSEUM OF NATURAL HISTORY, UNIVERSITY OF OREGON No. 18

A

Figure 12. Transverse sections of dentaries showing bone structure. A, Smilodonichthys rastrosus, UCMP 93170; B, Oncorhynchus tshawytscha, UMMZ 178987-S male; C, Salmo trutta, UMMZ 175169-S male. Scale bar, 0.2 cm. salar) stated that the extent of the kype is a fairly large-mouthed predaceous genus that mainly dependent on the size of the individual is believed to have evolved from a smaller- but it is also better developed in anadromous mouthed microphagous feeder like Coregonus than in resident populations of the same spe- (Norden, 1961 ) . The primary evidence for cies. UMMZ collections include examples of believing this is that Stenodus has lost its max- male fish with hooked lower jaws among the illary teeth and that it possesses an enlarged following species: all North American species branchial apparatus with long, finely toothed of Oncorhynchus, Salmo trutta, S. gairdneri, S. gill rakers. The toothless maxilla unites all the aguabonita, Salvelinus fontinalis, S. alp inus Coregoninae but can no longer be regarded as and S. malma. diagnostic for this subfamily if the toothless The absence of any apparent modifications character of the fossil maxilla proves to be con- in the symphysial area of the lower jaw of in- stant. In Stenodus, the oral margin of the max- dividuals believed to be males in spawning con- illa is convex, the supramaxilla is large, and the dition, indicates that no kype was developed in mouth opening is slightly superior. The ante- Smilodonichthys. rior ends of the maxillae bend sharply inward Comparison with Stenodus.—A fruitful and have rounded articular surfaces for effi- comparison can be made between the fossil and cient rotation on the palatine and rostral car- Stenodus because of certain important cranial tilages. The lower jaw is particularly interest- characters shared by both genera. Stenodus is ing because it shares with the fossil: a nearly 1972 CA VENDER AND MILLER: SMILODONICHTHYS, A NEW SALMONID FISH 39

and the parietals partly divided by the supra- occipital. Boulenger (1895) recognized some of these intermediate characters in Stenodus. The complete circumorbital ring in Stenodus appears to be a very primitive character in tele- ost fishes (Gosline, 1965), as well as its com- pletely toothed tongue and basibranchials

0.5 cm (Nelson, 1969; Vladykov, 1970) . It is sug- gested here, in light of evidence brought forth, that Stenodus possesses many primitive fea- tures shared by both the Coregoninae and Salmoninae. Comparison with Other Fossil Salmonids- There is practically no published fossil record for Oncorhynchus in North America. Jordan (1907) referred to a few toothed bones from Pleistocene Fossil Lake, Oregon, but these Figure 13. Right dentary referred to Smilodonich- specimens are very doubtfully those of an On- thys, from Warden Locality, UMMP V58064. A, corhynchus (see Uyeno and Miller, 1963) . An lateral view; B, mesial view. otolith of 0. tshawytscha was recently reported and illustrated from Pleistocene sands in northern California (Fitch, 1970: 27) . Al- straight ventral border, a high coronoid proc- though Neave (1958) expressed the view that ess, a large area for Meckel's cartilage and the Oncorhynchus arose from Salmo during Pleis- insertion of the mandibular portion of the ad- tocene time, evidence presented below shows ductor mandibulae muscle, a similarly placed that Oncorhynchus is at least as old as Middle corono-meckelian ossification, a heavy con- Pliocene. struction of the dentary, teeth present only near Fragmentary remains of what appears to be the symphysis, a pronounced inward curve of an extinct species of Oncorhynchus have been the anterior end of the dentary, and an open ar- recovered from the Glenns Ferry Formation of ticular fossa. The articular has a tube-like pos- southern Idaho. Identification is based on the terior projection that receives the preoperculo- anterior part of a dentary with three enlarged mandibular canal. Other characters of Steno- breeding teeth attached (Fig. 14 A) of the type dus of interest in reference to the fossil are its characteristic of the spawning male Oncorhyn- large preopercle with well developed horizontal chus. An incomplete left dentary and posterior arm, and the long, tapered gill rakers, mostly half of a parasphenoid closely resemble those with denticulations. of Oncorhynchus. A median ridge located at The agreement in features of the mouth and the point of flection on the fossil parasphenoid gill rakers between Stenodus and the fossil in- (Fig. 14 B) matches that of Oncorhynchus, dicates similarities in the method of feeding. particularly 0. kisutch. However, this may not be the only explanation. Abundant remains of at least one extinct Some of the osteological characters which in Oncorhynchus-like species have recently been the past have been used to divide the salmo- found at the Worden Locality near Klamath nines and coregonines break down in this com- Falls, southwestern Oregon (Fig. 14 E-I ) . They parison. This is further evident in the branchi- occur there in association with Smilodonich- ostegal count of Stenodus, highest among the thys. The Worden specimens are distinguished Coregoninae, the large, heavy orbitosphenoid, from Recent species by the high coronoid re- 44 BULLETIN, MUSEUM OF NATURAL HISTORY, UNIVERSITY OFOREGON No. 18

Uyeno, T., and R. R. Miller, 1963, Summary of late Cenozoic freshwater fish records for North America: Occ. Pap. Mus. Zool. Univ. Mich., no. 631, 34 pp. Vladykov, V. D., 1962, Osteological studies on Pa- cific salmon of the genus Oncorhynchus: Bull. no. 136, Fish. Res. Bd. Canada, 172 pp. , 1970, Pearl tubercles and certain cranial peculiarities useful in the taxonomy of coregonid genera. In: Biology of coregonid fishes, C. C. Lind- sey and C. S. Woods, eds., pp. 167-193. Univ. Man- itoba Press, Winnipeg. Weitzman, S. H., 1967, The origin of the stomiatoid fishes with comments on the classification of sal- moniform fishes: Copeia, 1967, no. 3, pp. 507-540.