AMERICAN MUSEUM NovJitates PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY CENTRAL PARK WEST AT 79TH STREET, NEW YORK, N.Y. 10024 Number 2815, pp. 1-10, figs. 1-7, table 1 April 11, 1985

Preserved Ammonitellas of Scaphites (Ammonoidea, Ancyloceratina)

NEIL H. LANDMAN'

ABSTRACT Ammonitellas, embryonic shells ofammonites, and body chamber angles less than 600. However, occur in the Upper Cretaceous (Turonian) ofCol- the lack of a body chamber during life is an im- orado associated with adults of Scaphites ferro- possibility and suggests that the primary varix must nensis Cobban. They average 650 ,um in diameter be a point of weakness for postmortem breakage. and are similar to the embryonic whorls of the This, plus the presence of young postembryonic associated scaphite species to which they probably shells that extend beyond the primary constriction belong. They terminate at the primary constriction and reveal two to six septa, implies that variation and accompanying varix but display variation in in number of embryonic septa above the prosep- number of embryonic septa from shells with only tum may be false. Based on functional morphol- a single prismatic proseptum and body chamber ogy, the newly hatched ammonite may have led a angles of2900 to shells completely filled with septa planktic existence for some time after hatching. INTRODUCTION Embryonic shells of ammonites (called other shelled cephalopods. I report here the ammonitellas by Drushits and Khiami, 1970) results ofa study on minute ammonite shells have been discovered in Mesozoic deposits identified as ammonitellas of Scaphites from throughout the world (Dreyfuss, 1933; True- the Upper Cretaceous (Turonian) of Colo- man, 1940; Wetzel, 1959; Drushits and rado. Khiami, 1970; Birkelund, 1979; Blind, 1979; Kulicki, 1979; Bandel, 1982; Dietl in letter AND cited in Bandel, 1982; Landman, 1982a). In- MATERIAL METHODS spection of intact, well-preserved shells per- Several thousand minute ammonite shells mits the determination ofthe number ofem- were discovered in the body chambers and bryonic septa and the patterns of embryonic adhering matrix of 15 mature specimens of development. The mode oflife ofthese newly Scaphitesferronensis Cobban, an Upper Cre- hatched ammonites is based on their func- taceous (Turonian) heteromorph. These 15 tional morphology, faunal association, and specimens were collected by W. A. Cobban mode of occurrence. These observations on in 1967 from the top of the Juana Lopez morphology and mode of life form the basis Member of the Mancos Shale 1.7 miles for comparison with the early ontogenies of northeast of Austin in Delta Co., Colorado

I Assistant Curator, Department of Invertebrates, American Museum of Natural History.

Copyright © American Museum of Natural History 1985 ISSN 0003-0082 / Price $1.50 2 AMERICAN MUSEUM NOVITATES NO. 2815

The original shell microstructure is generally preserved and the chambers are filled with shale and orange-colored calcite. Associated with these ammonites are thousands of tiny clams, fish scales, and vertebrae. The clams range from 300 to 550 ,um in length and ap- pear to have already undergone metamor- phosis from a planktic larval state (Lutz, per- sonal commun., 1984). Several minute ammonite specimens were worked out ofthe matrix but tended to break or emerge as internal molds without shell. A more reliable method to view the entire spec- imen and avoid breakage was to embed shells still retaining matrix in epoxy. Prior to embedding, these specimens were mounted onto an epoxy base and oriented. They were subsequently ground and polished to the me- FIG. 1. Diagram of median section of am- dian plane of symmetry through the siphun- monitella illustrating protoconch diameter (PD), cle. All size measurements and counting of ammonitella diameter (AD), and ammonitella an- gle (<). The ammonitella angle is equivalent to septa were made on the median plane. Spec- the body chamber angle of an ammonitella with imens were also uncovered by grinding down only a proseptum. chunks of ammonitiferous material. This method sometimes revealed the most com- plete specimens but because orientation was (USGS Locality no. D6022). No other am- not preset, measurements of diameter and monite species were present at this locality other dimensions were subject to error. Al- (Cobban, personal commun., 1984). The body though preservation was generally very good, chambers of these 15 specimens are largely the presence of calcite fracture surfaces and internal molds and are composed of calcar- obscuring sedimentary matrix in some shells eous shale and coarsely crystalline calcite in made counting of septa problematic, so such addition to the accumulations of small am- shells were omitted from study. Therefore, of monites. These ammonites, less than 1 mm 85 polished sections prepared, 65 were used in diameter, co-occur with numerous slightly in this study. larger specimens up to 2 mm in diameter. Five standard measurements were made

*_ t46* B s * _ ;* s S o.,.' ' s |L* s .|.Mt- W; . ;

FIG. 2. (A). Ammonitella of Scaphites freed from the matrix. It is a steinkem but retains some shell near the primary constriction which displays a tuberculate micro-ornamentation{aX.-.(B). The -arrow.points. to the ventral saddle of the prosuture, the only suture present on the specimen. 1985 LANDMAN: SCAPHITES 3

TABLE 1 Ammonitella Diameter (in Microns), Angle (in Degrees), and Protoconch Diameter (in Microns) for Minute Ammonite Shells from USGS Locality No. D6022a Scaphites ferronensis and Group I Group II Group III Group IV Scaphites whitfieldi X SD n x SD n x SD n X SD n x SD n AD 645.7 77.76 18 605.8 33.05 19 617.3 39.42 10 648.0 67.1 15 619.0 42.49 199 AA 286.6 11.66 16 283.8 18.23 18 280.44 6.00 9 286.9 11.26 14 284.0 11.68 169 PD 322.3 21.30 9 327.1 10.86 9 319.1 15.79 7 331.0 19.31 3 320.1 29.09 184 a Group I refers to shells that end in the primary varix and possess only a proseptum. Group II refers to shells that end in the primary varix and are completely filled with septa. Group III refers to shells that end in the primary varix and possess 2 to 8 septa. Group IV refers to shells that extend beyond the primary varix. The last column on the right represents values for adults of S. ferronensis and S. whitfieldi from Landman, 1982b. Abbreviations: AD, ammonitella diameter; AA, ammonitella angle; PD, protoconch diameter; X, mean; SD, standard deviation; n, number of specimens measured. on all specimens wherever possible (fig. 1). and Waage, 1982). In exceptionally well-pre- (1) Protoconch diameter taken through the served specimens, the proseptum appeared center ofthe protoconch and the ventral edge prismatic; all later septa appeared nacreous. ofthe proseptum. (2) Maximum diameter of The caecum and prosiphon were not pre- the ammonitella measured through the cen- served in any specimens. ter of the protoconch and the primary varix, Based on the number ofsepta present these the conspicuous nacreous thickening near the 50 ammonitellas fell into three groups (fig. end of the first whorl (Landman and Waage, 3A-C, table 1). 1982). (3) Ammonitella angle measured from I: Twenty specimens featured only the pro- the proseptum to the end ofthe primary con- septum with body chamber angles (equiva- striction and accompanying varix. This is lent to ammonitella angles) ranging from equivalent to the body chamber angle of an about 270° to about 3100 (average approxi- ammonitella with only a proseptum. (4) Body mately 2900, fig. 4). Their average diameter chamber angle. This measurement may be was about 650 ,um. Their protoconch diam- particularly liable to underestimation be- eter averaged about 320 um. cause postmortem breakage may have short- II: A nearly equal number (19) were com- ened the body chamber. (5) Number ofsepta pletely filled with septa, with body chamber counting the proseptum as one septum. angles less than 600. In most specimens, the primary varix was perfectly intact and marked the end of the shell. In a few specimens the RESULTS varix was broken. Broken, curved fragments Fifty shells in polished section terminated of shell were sometimes observed near the at the end of the primary constriction and specimens. The ammonitella diameter and accompanying varix or at the varix trace. angle ofthese specimens averaged about 610 These features mark the end ofthe embryonic ,um and 2800, respectively. Their protoconch shell or ammonitella (Drushits and Khiami, diameter averaged about 330 ,tm. 1970; Drushits, Doguzhayeva, and Mikhay- III: Eleven specimens featured two to eight lova, 1977; Kulicki, 1979; Tanabe, Fukada, septa. Shells with two septa had body cham- and Obata, 1980; Bandel, 1982; Landman, ber angles of 2500 to 2600. Shells with four 1982a). Similar shells freed from the matrix septa had body chamber angles of 2000 to and viewed in the round displayed the tu- 2100. Those with six to eight septa had body berculate micro-ornamentation previously chamber angles less than 1500. Ammonitella observed on the embryonic whorls ofvarious diameter and angle averaged about 620 ,um species ofScaphites (fig. 2; Bandel, Landman, and 2800, respectively. Protoconch diameter 4 AMERICAN MUSEUM NOVITATES NO. 2815

FIG. 3. Median cross-sections of minute ammonite shells from the Upper Cretaceous (Turonian) of Colorado. Shells A-C terminate in the primary constriction and accompanying varix, features that mark the end of embryonic development. Shell A displays only a single proseptum, Shell B is filled with septa (the "color changes" between adjacent chambers help to emphasize the positions ofthe septa), and Shell C displays 6 septa. Shell D extends beyond the varix trace (the impression of the primary varix on the steinkem) and is clearly postembryonic. It possesses six septa.

averaged about 320 ,um. The termination in bryonic whorls also resembled the shape of the primary varix was frequently clear-cut the corresponding whorls of closely related but sometimes indefinite. species of Scaphites (fig. 5). Three of the 15 Another 15 specimens in polished section shells featured two, six, and six septa with were slightly larger, measuring up to 2 mm body chambers extending beyond the pri- in diameter. These shells extended beyond mary constriction. Their body chamber an- the primary constriction with intact or bro- gles measured 2700, 2200, and 2800, respec- ken body chambers. Their ammonitella di- tively. ameter and angle averaged about 650 ,tm and In all the specimens measured, the proto- 2900, respectively. Their protoconch diame- conch diameter was approximately half the ter averaged about 330 ,um (fig. 3D, table 1). ammonitella diameter and the two measure- Similar shells freed from the matrix and ments showed a positive correlation. The viewed in the round displayed the same tu- correlation coefficient equaled 0.707 (fig. 6). berculate micro-ornamentation on their em- bryonic whorls as previously observed on the DISCUSSION smaller shells and on the embryonic whorls ATTRIBUTION TO Scaphites: All the speci- of Scaphites. The shape of the early postem- mens studied including the postembryonic 1985 LANDMAN: SCAPHITES 5

FIG. 4. Close-up of proseptum (A) and primary varix (B) of specimen shown in figure 3A. shells show considerable overlap in proto- of Scaphites. They also display the same se- conch diameter, ammonitella diameter, and quence of septal microstructure; the prosep- ammonitella angle (fig. 7, table 1). The av- tum is prismatic and all later septa are na- erages are similar and extreme values are creous. Additionally, the shape ofthe whorls probably artifacts due to measurement of ofyoung postembryonic shells resembles the poorly oriented shells. These values are sim- shape of the corresponding whorls of S. fer- ilar to those obtained for the embryonic ronensis and S. whitfieldi (fig. 5). The body whorls of adults of co-occurring S. ferronen- chamber angles ofintact postembryonic shells sis and of the closely related species S. whit- measure 2200 to 2800 and are similar to val- fieldi Cobban. In a survey ofnearly 200 adults ues obtained for a sample of 40 juveniles of of these two species, the protoconch diame- the Coniacian and Santonian scaphite species ter, ammonitella diameter, and ammonitella S. preventricosus Cobban and Clioscaphites angle averaged 320 ,um, 620 ,um, and 2800, vermiformis (Meek & Hayden), respectively respectively (table 1; Landman, 1982b). The (Landman, 1982b). Finally, S. ferronensis is embryonic shells and the embryonic whorls the only ammonite present at this locality, of the young postembryonic shells also dis- and in view of the above similarities the mi- play the same tuberculate micro-ornamen- nute ammonite shells are referred to the ge- tation as that present on the embryonic whorls nus Scaphites.

FIG. 5. Comparison between a postembryonic specimen associated with the ammonitellas (A) and the early whorls of an adult S. whitfieldi (B). The primary constriction (or varix trace) is on top. 6 AMERICAN MUSEUM NOVITATES NO. 2815

770 760 0 750 740 730 AD=1.9PD +0.5 r =707 720 710 A 700 690 . I.-- 680 w 670 660 650 A w 0 640

I- 630 620 A *0 0 610 A I"

600 0 590 580 570 0 . 560 550 280 290 300 310 320 330 340 350 360 PROTOCONCH DIAMETER (,pm) FIG. 6. Graph of protoconch diameter versus ammonitella diameter for minute ammonite shells from USGS Locality no. D6022. 0 refers to shells that end in the primary varix and possess only a proseptum. 0 refers to shells that end in the primary varix and are completely filled with septa. A refers to shells which end in the primary varix and possess two to eight septa. * refers to shells that extend beyond the primary varix.

EXACT NATURE OF EMBRYONIC SHELL: The bryonic stage and this pattern of septal oc- primary constriction and accompanying va- currence has actually been documented in rix mark the end of the embryonic shell. Of preserved ammonitellas of Quenstedtoceras the 50 minute shells that end in the primary and Baculites (Blind, 1979; Landman, 1982a). varix, 20 possessed only a prismatic prosep- The 20 shells ofScaphites sp. are, however, tum (fig. 3A). Their body chamber angles av- accompanied by 11 other ammonitellas which erage 2900 and approach the body chamber possess two to eight septa, one to seven of angles of older scaphite juveniles (Landman, which are nacreous (fig. 3C). These 11 shells 1982b). The presence ofonly a prismatic pro- terminate in the primary varix although this septum within the embryonic shell agrees with feature is sometimes broken. Their body claims that the transition from prismatic to chamber angles are up to halfthat ofthe shells nacreous septa coincides with the boundary with only a proseptum. A comparison of av- from embryonic to postembryonic develop- erage ammonitella diameter and angle be- ment (Drushits, Doguzhayeva, and Mikhay- tween the two groups, however, indicates no lova, 1977; Birkelund and Hansen, 1974). significant difference that could suggest a cor- Nacreous septa only appear in the postem- relation between number of septa and di- 1985 LANDMAN: SCAPHITES 7

840 830 820 810 800 790 780 . 770 760 * 750 E 740 730 cruJ . 720 710 . 700 A 690 680 . -j -j 670 . . 660 0

0 650 A 640 630 0 620 A 0 A 610 0 A* * s 600 a 0 0 590 * *:A* A* 580 0 570 0 0@%

560 A 550

c. n D4U I _ __ 250 255 260 265 270 275 280 285 290 295 300 305 310 315 320 AMMONITELLA ANGLE (degrees) FIG. 7. Graph of ammonitella angle versus ammonitella diameter for minute ammonite shells from USGS Locality no. D6022. Symbols are the same as in figure 6.

ameter or number of septa and ammonitella caution in interpreting this variation in num- angle. Do these 11 shells express the range of ber of embryonic septa as natural. First, an variation in number ofembryonic septa pos- additional 19 shells end in the primary varix sible within a genus? This would also imply and are nearly or completely filled with septa that nacreous septa may be deposited em- (fig. 3B). Their termination at the end of the bryonically. Such species-specific variation primary varix is often quite precise although in the number ofembryonic septa has, in fact, sometimes this feature is broken and stray been demonstrated in modem sepioids (Ban- fragments of shell are located nearby. The del and Boletzky, 1979). lack of a body chamber during life is impos- However, two lines of evidence suggest sible and implies that additional postem- 8 AMERICAN MUSEUM NOVITATES NO. 2815 bryonic shell must have existed. The primary ta were probably nacreous. Such variation in varices of the shells with two to eight septa the number of embryonic septa in the same are similarly complete although breakage at genus over broad geographic areas cannot, of their anterior end is also sometimes indicat- course, be ruled out, but the results of the ed. As pointed out by Kulicki (1974, 1979), present study strongly suggest that such vari- the primary varix strengthens the apertural ation is the result of postmortem breakage. edge of the ammonitella and abuts against the new postembryonic outer shell. This junction provides a natural point for post- MODE OF LIFE AT HATCHING mortem breakage and separation of embry- FUNCTIONAL MORPHOLOGY: The embry- onic from postembryonic shell. onic shells average 650 ,um in diameter and Secondly, three postembryonic shells with represent the lower end of the size spectrum two to six septa have preserved body cham- of ammonite embryonic shells. The embry- bers extending beyond the primary constric- onic shells ofMesozoic ammonites range from tion and accompanying varix (fig. 3D). Their approximately 600 to 1500 ,um in diameter body chamber angles range from 2200 to 2800 (Zakharov, 1972) and are small relative to although even these values may be under- adult body size, e.g., approximately 2 percent estimates due to postmortem breakage. Two of the adult body size of S. ferronensis. All ofthe specimens, with six septa, display larg- embryonic shells consist of a body chamber, er body chamber angles than shells with the a protoconch, and one or possibly more sep- same number ofsepta that end in the primary ta. A caecum and prosiphon are also reported varix. The body chamber angles ofthese two in the preserved embryonic shells from postembryonic shells are also nearer the body Ul'Yanovsk (Drushits and Khiami, 1970) al- chamber angles of larger juveniles of Sca- though these features are not preserved in the phites (Landman, 1982b). ammonitellas studied here. The protoconch These facts plus the abundance of shells or initial chamber is relatively large and its with a single prismatic proseptum suggest that diameter is approximately one-half that of the shells with two to eight septa ending in the ammonitella. Protoconch diameter is also the primary varix do not represent natural positively correlated with ammonitella di- variation in number of embryonic septa but ameter both within and among species (fig. are postmortem artifacts. A similar interpre- 6; Tanabe, 1979; Landman, 1982b). tation may apply to data derived from finds Based on the appearance ofthe embryonic of preserved ammonitellas of Baculites. Up- ammonite shell, at least two modes of life per Cretaceous (Coniacian-Santonian) am- have been suggested. Wetzel (1959) envi- monitellas ofBaculites from Montana ending sioned that the fragile shells ofnewly hatched in the primary varix revealed only a pris- ammonites would allow them to crawl along matic proseptum with body chamber angles the bottom and only after secretion ofseveral of approximately 3300 (Landman, 1982a). more whorls would they become free swim- Young postembryonic specimens with outer ming. He argued that the caecum, at least shells extending beyond the primary constric- initially, would perform a function other than tion and forming a shaft displayed nacreous that related to buoyancy regulation. On the septa. A broken embryonic shell of B. chi- other hand, Kulicki (1974, 1979), Birkelund coensis (Trask) from the Campanian of Cal- and Hansen (1974), Drushits, Doguzhayeva, ifornia also revealed only a prismatic pro- and Mikhaylova (1977), and Landman septum (Smith, 1901). However, complete (1982a, 1982b) have proposed that the newly ammonitellas of Baculites from the Campa- hatched ammonite was planktic. A planktic nian of Jordan showed five to seven septa mode of life at hatching is common among with body chamber angles of approximately many modern coleoids including planktic and 1800, almost halfthat ofthe North American nektic squids, sepioids, and benthic octopods species (Bandel, 1982). Although these Jor- with relatively small eggs (Boletzky, 1974, danian shells were silicified and septal mi- 1977). crostructure could not be verified, based on At a diameter ofapproximately 1 mm, the the North American species, some ofthe sep- newly hatched ammonite would belong to the 1985 LANDMAN: SCAPHITES 9 macroplankton and would approach the size instead a limited dispersal capability for some of the largest modem bivalve and gastropod time after hatching. Future finds of young planktic larvae (Ockelmann, 1965; Spight, postembryonic shells in environments in 1976). The potentially buoyant protoconch, which benthos are excluded, e.g., anoxic black comprising a large portion of the ammoni- shales, may provide more substantial support tella, would act as a float. The caecum and for a planktic posthatching mode of life. possibly the prosiphon would function as part of the buoyancy system. Nevertheless, some ACKNOWLEDGMENTS time would have had to elapse before or after hatching to allow the evacuation of liquid I thank Dr. W. A. Cobban for the loan of from the protoconch (Mapes, personal com- the specimens and Drs. K. M. Waage, N. mun., 1984). After hatching, the ammonite Eldredge, J. Maisey, and G. Musser for re- could have remained in the plankton for sev- viewing the manuscript. Miss S. Klofak as- eral days or weeks depending on the size of sisted in preparation, Miss J. Whelan in scan- the embryonic shell and the mode of life of ning electron microscopy, Miss B. Heimberg the adult. During this time, it may have been in statistics and drafting, and Mr. P. Harries passive (Birkelund and Hansen, 1974) or de- in photography. pendent on vertical movements (Kulicki, 1974). However, the presence of a ventral LITERATURE CITED sinus in the growth lines immediately after Bandel, K. the primary constriction may indicate the ex- 1982. Morphologie und Bildung der friuonto- istence ofa hyponome which could have per- genetischen Gehause bei conchiferen mitted more active swimming (House, 1965; Mollusken. Facies, vol. 7, pp. 1-198. Erben, Flajs, and Siehl, 1969). Bandel, K., and S. V. Boletzky FAUNAL ASSOCIATION AND OCCURRENCE: 1979. A comparative study of the structure, The embryonic shells studied occur profusely development and morphological rela- in the body chambers and adhering matrix tionships of chambered cephalopod shells. The Veliger, vol. 21, pp. 318- of 15 adult S. ferronensis and may have been 354. even more extensive on the outcrop. The Bandel, K., N. H. Landman, and K. M. Waage shells are frequently broken and are inter- 1982. Micro-ornament on early whorls ofMe- mixed with clams, fish scales, and numerous sozoic ammonites; implications for ear- juveniles less than 2 mm in diameter sug- ly ontogeny. Jour. Paleont., vol. 56, pp. gesting, therefore, that they are not undis- 386-391. turbed spawn. Their occurrence is similar to Birkelund, T. that ofother newly hatched ammonites which 1979. The last Maastrichtian ammonites. In are found in large concentrations frequently Birkelund, T., and R. G. Bromley (eds.), associated with small Cretaceous-Tertiary boundary events gastropods, bivalves, symposium 1. The Maastrichtian and foraminifers, and juvenile and adult am- Danian of Denmark. Univ. Copenha- monites (Wetzel, 1959; Kulicki, 1979; Birke- gen, pp. 51-57. lund, 1979; Landman, 1982a). These simi- Birkelund, T., and J. Hansen larities may indicate a common benthic living 1974. Shell ultrastructures ofsome Maastrich- association or, perhaps more likely, a mixed tian Ammonoidea and Coleoidea and thanatocoenosis composed oforganisms from their taxonomic implications. Kong. a variety of habitats. This latter interpreta- Danske. Videnskab. Sel. Biol. Skr., vol. tion would be consistent with the hypothesis 20, pp. 2-34. of a planktic posthatching mode of life in Blind, W. ammonites. Plankton are pre- 1979. The early ontogentic development of frequently ammonoids by investigation of shell served in otherwise benthic associations and, structures. Symp. on Ammonoidea, Syst. due to a variety of postmortem processes, Assoc. York, Abstracts, p. 32. may display a patchy distribution incon- Boletzky, S. V. gruent with that of the living population. On 1974. The "larvae" ofCephalopoda: a review. the other hand, the typical occurrence ofam- Thalassia Jugoslavica, vol. 10, pp. 45- monitellas in mass concentrations may imply 76. 10 AMERICAN MUSEUM NOVITATES NO. 2815

1977. Post-hatching behavior and mode of shells of Mesozoic ammonites. Jour. life in cephalopods. Zoological Society Paleont., vol. 56, pp. 1293-1295. ofLondon Symposium, no. 38, pp. 557- Ockelmann, K. W. 567. 1965. Developmental types in marine bi- Dreyfuss, M. valves and their distribution along the 1933. Decouverte de nodules phosphates a Atlantic coast of Europe. In Cox, L. R., jeunes ammonites dans le Toarcien de and J. F. Peake (eds.), Proceedings of Creveney (Haute-Saone). C.R. Somm. the First Malacological Congress, Lon- Soc. Geol. France, no. 14, pp. 224-226. don, 1962. Conchological Society of Drushits, V. V., and N. Khiami Great Britain and Ireland and the Mal- 1970. Structure ofthe septa, protoconch walls acological Society of London, London, and initial whorls in early Cretaceous pp. 25-35. ammonites. Paleont. Jour., vol. 4, pp. Smith, J. P. 26-38. 1901. The larval coil of Baculites. Am. Nat., Drushits, V. V., L. A. Doguzhayeva, and I. A. vol. 35, pp. 39-49. Mikhaylova Spight, T. M. 1977. The structure of the ammonitella and 1976. Ecology of hatching size for marine the direct development of ammonites. snails. Oecologia, vol. 24, pp. 283-294. Paleont. Jour., vol. 11, pp. 188-199. Tanabe, K., I. Obata, Y. Fukuda, and M. Futa- Erben, H. K., G. Flajs, and A. Siehl kami 1969. Die frUhontogenetische Entwicklung der 1979. Early shell growth in some Upper Cre- Schalenstruktur ectocochleater Ceph- taceous ammonites and its implications alopoden. Palaeontographica, vol. 132, to major taxonomy. Bull. Natl. Sci. pp. 1-54. Mus., Ser. C (Geol.), vol. 5, pp. 153- House, M. R. 176. 1965. A study in the Tornoceratidae: the Tanabe, K., Y. Fukuda, and I. Obata succession of Tornoceras and related 1980. Ontogenetic development and func- genera in the North American Devo- tional morphology in the early growth- man. Philos. Trans. R. Soc. London, Ser. stages of three Cretaceous ammonites. B, vol. 250, pp. 79-130. Bull. Natl. Sci. Mus., Ser. C (Geol.), vol. Kulicki, C. 6, pp. 9-26. 1974. Remarks on the embryogeny and post- Trueman, A. E. embryonal development ofammonites. 1940. The ammonite body chamber with spe- Acta. Paleontol. Pol., vol. 19, pp. 201- cial reference to the buoyancy and mode 224. of life of the living ammonite. Quart. 1979. The ammonite shell: its structure, de- Jour. Geol. Soc. London, vol. 96, pp. velopment and biological significance. 339-383. Ibid., vol. 39, pp. 97-142. Wetzel, W Landman, N. H. 1959. Uber Ammoniten-Larven. Neues Jb. 1982a. Embryonic shells ofBaculites. Jour. Pa- Geol. u. Palaont., Abh., vol. 107, pp. leont., vol. 56, pp. 1235-1241. 240-252. 1982b. Ontogeny and evolution of Late Cre- Zakharov, Y. D. taceous (Turonian-Santonian) Sca- 1972. Formation of the caecum and prosi- phites. Unpublished Ph.D. dissertation. phon in ammonoids. Paleont. Jour., vol. Yale Univ., New Haven, Connecticut, 6, pp. 201-206. 341 pp. Landman, N. H., and K. M. Waage 1982. Terminology ofstructures in embryonic