MEMOIRS OF THE CAKNEGIE MUSEUM. VOL. II. NO. 9. NOTES ON OSTEOLOGY OF BAPTANODON. With a Description of a New Species. By Charles W. Gilmore. During the season of 1903, while in the service of the Carnegie Museum, the writer collected from the marine beds of the Jurassic in the Freeze Out Mountains in Carbon County, Wyoming, quite a complete Baptanodon skull (No. 1441 1 ) and lower jaws associated with other parts of the skeleton. Through the courtesy of the Director, Dr. W. J. Holland, 2 the writer was accorded the privilege of studying this specimen, thinking perhaps it would give some infor- mation regarding the obscure points in our knowledge of the anatomy of this interesting reptile. The skeleton like nearly all of the American Jurassic Ichthyosaurians was enclosed in a very hard limestone concretion 3 much seamed and cracked by expo- sure to the elements. Since publishing a paper on the Osteology of Baptanodon 4 additional discoveries have thrown new light on the structure of this animal. It thus becomes necessary 1 Card catalogue number, Department of Vertebrate Fossils of the Carnegie Museum. 2 My acknowledgmentsare especially due Dr. W. J. Holland, and I take this opportunity to express my appreciation of the many courtesies extended during the preparation of these notes. The text-figures were drawn by Mr. H. W. Hendley, of the U. S. National Museum, Washington, D. C. 3 A recent letter from W. H. Reed, of the Museum of the University of Wyoming, informs me that during the past .summer he collected a very complete Ichthyosaurian skeleton, which was quite free from the refractory matrix men- tioned above. He regards this specimen as coming from a lower horizon than those found in the concretionary layer. 326 MEMOIRS OF THE CARNEGIE MUSEUM to make certain alterations and additions to the description and drawings then given, especially those relating to the elements of the skull and lower jaws. The parts of specimen No. 1441 recovered consist of a skull and lower jaws lacking a median section of the rostrum, the coossified atlas and axis, third and fourth cervicals, besides vertebrae in various stages of preservation from other parts of the vertebral column. With the exception of the proximal end of one humerus, the ulna, and a few paddle bones, all other elements are missing. The Skull. The cranium, although subjected to severe pressure, which has somewhat dis- torted the outlines of the skull, appears very similar to those previously described in the paper above mentioned, with the exception that it pertains to a somewhat smaller individual. The superior view shows the transverse displacement between the anterior end of the postfrontal and the posterior end of the nasal, and, as breaks occur in identi- cally the same place, and take the same transverse direction in two other crania (Nos. 603 and 878) in the collections of the Carnegie Museum, the writer now as- sumes this displacement as following the line of suture, and in the corrected draw- ing (See Plate XXXVII., Fig. 1), they are indicated as absolutely determined. The suture separating the premaxillse at the anterior third of the rostrum is plainly shown in this specimen. Another point of interest is the wide prefrontal developed in this individual. Viewed laterally this skull sheds new light on the posterior termination of the premaxillary. In Baptanodon the posterior end of the premaxillary is somewhat forked as in many forms of the Ichthyosauria. The lower posterior branch extends back under the nares, laps over and hides from a lateral view most of the anterior prolongation of the maxillary. (See Plate XXXVI.) The longitudinal channel along the side of both the premaxillaries and dentaries, just above and below the dental grooves (See Fig. 3), has many more nerve pits for the entrance of nerves to the teeth than was indicated in the first restoration of the skull of Baptanodon. A pineal foramen appears to be present and occupying essentially the same position as in the other skulls in this museum. The posterior part of the skull is so badly dis- arranged that nothing of importance is shown. The other views of the skull show nothing new, and, as the other elements have been fully described in a previous paper, it is unnecessary to repeat the description here. GILMORE : NOTES OX OSTEOLOGY OF BAPTANODON 327 Lower Jaws. A study of the well preserved jaws of No. 1441, not only shows the exact number of elements composing the mandible as six pairs of bones ; but it also indicates clearly the extent and relative positions of these elements, particularly those bones sag. s.ag. A Fig. 1. Internal view of the right mandibular ramus of Baptanodon nctlans (No. 1441). One fourth natural size. art, articular ; ag., angular ; cor., coronoid ; for., foramen ; s.ag., surangular ; apt, splenial ; sym., beginning of the symphysis. composing the posterior portion of the rami, which previous to the discovery of this specimen had not been well understood. This specimen (No. 1441) gives the first positive knowledge of the shape and extent of the coronoid in Baptanodon. Figs. 1 and 2 show it to be a thin plate of bone extending along the inner side of the posterior end of the ramus. Its lower border laps along the upper internal border of the angu- lar except anteriorly where it overlaps the posterior pro- longation of the splenial. The anterior termination is somewhat in advance of the node-like protuberance developed upon the upper border of the surangular, where it is overlapped by the posterior end of the splenial. Posteriorly the coronoid is narrow, and laps along the articular, thus assisting the surangular in holding that element in position. More anteriorly the coronoid widens rapidly, the upper margin being elevated in a dorsal process which is nearly the height of the protuber- ance on the surangular. Anterior to this process it grad- ually narrows to the point where it meets the overlap- ping splenial. The posterior end of the splenial is wholly confined to the internal side of the ramus. The exact extent of the lower posterior prolongation could not be determined from this specimen. The splenials enter the symphysis and entirely separate the dentaries posteriorly. art. £or. Fig. 2. Cross-section of posterior end of left mandibular ramus of Bap- tanodon nalans (No. 1441). Natural size, art., articular ; ag. , angular ; cor., coronoid ; s.ag., surangular. 328 MEMOIRS OF THE CARNEGIE MUSEUM The anterior part of the splenial has been fully described in a previous paper. The oval foramen present in the jaws of No. 603 (loc. cit, p. 96) is also present near the symphysis in this individual. (See for., Fig. 1.) The suture between the surangular and angular on the external posterior end of the ramus now appears to be accurately determined, as following nearly the course provisionally indicated in the first restoration of the skull and jaws. (See Plate XXXVI.) Fig. 2 shows how the angular laps over and along the surangular, although the two elements were probably more closely applied than is shown by the cross-section. The articular appears very similar to those described previously, though perhaps more robust and occupying a more nearly horizontal position in the ramus. The rami are very slender for their length and height. Measurements. No. 1441. Greatest length of coronoid, about 220 mm. " 1441. " width " " " 45 " " 1441. " " " posterior end of ramus 70 " " 1441. " " " anterior " " " 18 " Thyrohyal. This specimen, as in No. 878 in the collections of the museum, has the right th} T rohyal preserved quite intact. It was retained in the matrix parallel to the inner posterior part of the ramus of that side. The anterior extremity while some- what expanded is more circular in cross-section than was indicated by the element mentioned above. There is evidence of the opposite element in a fragmentary posterior end found in the matrix along the other ramus. Otherwise the shape and proportions are very similar to the thyrohyal of No. 878 described and figured previously. Sclerotic Plates. Although crushing has badly distorted the sclerotic rings of both orbits there appears to be essentially the same number of plates (14) as observed in other mem- bers of this genus. The distortion mentioned above has so displaced the plates that the manner in which they overlap one another is clearly shown. (See Fig. 3.) The plates lap over one another from left to right, the bev- scierotic plates of Baptanodon elled edge of one over-lapping the reverse bevel of the other. «atan 8 (No.i44i). onehaif xhis long free union of the plates would allow the sclerotic natural size. . . ring to expand and contract considerably. One orbit shows the bony covering extending back 40 mm. from the periphery, and it appears quite probable that this covering extended to the very back of the eyeball as in some GILMORE : NOTES ON OSTEOLOGY OF BAPTANODON 329 birds. It may prove to be the case tbat these bony plates curve in on the back of the eye similar to the cartilaginous protection of the eyes in some of the whales. The surface markings of the sclerotic plates have been fully described in a pre- vious paper. Dentition. No. 1441 gives but little information regarding the teeth of this form. Only one tooth was found intact, this being in position near the anterior end of the rostrum. (See Fig. 4.) This tooth measures 13 mm. in length and is a good example of the anterior teeth as known'in two other individuals of this group. There is no swelling at the base, as may be observed in the teeth of some of the Ichthyosaurs. This tooth is circular in cross-section, ending in a sub-acute apex, the top being covered with ptox.- t __,,-pJnit p. 330 MEMOIRS OF THE CARNEGIE MUSEUM with the hasioccipital. These elements are smaller than the homologous parts of B. marshi and B. discus and are hardly more than half the size of B. robustus. They differ in several minor characteristics. The atlas resembles B. marshi and B. robustus in having a single hypapophysis on the lower anterior surface of the cen- trum. The third and fourth cervicals differ from the same elements of B. marshi in having well developed parapophyses, and very small diapophyses. There is no indication of the parapophysis on the axis as found in both B. marshi and B. discus. Just below the diapophysis and separated from it by a non- articular tract is a faint antero-posterior ridge, which anteriorly probably represents GILMORE : NOTES ON OSTEOLOGY OF BAPTANODON 331 end is somewhat weathered and worn, and does not show the very rugose nature observed in better preserved specimens. The head is very convex, the portion for cartilaginous attachment extending far around both anteriorly and posteriorly. There is a well developed trochanter on the dorsal surface. The ulna is a pentagonal block of bone, the proximal being thicker than the distal end. The proximal end is slightly convex and was opposed to the concave 4 III "" \8iyf5l. Fig. 8. View of the proximal end Fig. 9. Ulna of Baptano- Fig. 10. Radius of Bap- of the humerus of Baptanodon natans donnatans (No. 144] ). One lanodon nalans (No. 1441). (No. 1441). One half natural size, d., half natural size, d., [distal One half natural size, d., dorsal surface. end; p., proximal end. distalend;/., lateral border, restored ; p , proximal end. facet on the distal end of the humerus though probably separated by cartilage. The other sides are slightly convex and were evidently surrounded by a thick cartilage as indicated by their rugose surfaces. The upper and lower surfaces are slightly concave antero-posteriorly. The element appears to be more angular than the ulna of Baptanodon marshi. Measurements. No. 1441. Greatest length of ulna antero-posteriorly 40 mm. " 1441. " breadth of ulna 50 " " 1441. " thickness of ulna, proximal end 35 " " 1441. " " " distal " 25 " The radius is a sub-quadrate element somewhat wider than long and like the ulna thicker on the proximal than on the distal end. The external margin is miss- ing but apparently reduced to a comparatively thin edge. The radius is larger than the ulna in all of its dimensions. The proximal end is convex and was opposed to the largest of the three concave facets on the distal end of the humerus. The inner side is slightly convex, the distal flat, and all except the external side are rugose. The upper and lower surfaces are slightly concave antero-posteriorly. Measurements. No. 1441. Greatest length of ladius antero-posteriorly, estimated 51mm. " 1441. " breadth of radius 65 " "' 1441. " thickness of radius, proximal end 42 " " 1441. " " " distal " 30 " 332 MEMOIRS OF THE CARNEGIE MUSEUM Pelvic Element. With specimen 603 in the collection of the Carnegie Museum is a portion of a bone which at the time of preparing my memoir on Baptanodon I was unable to identify but since have concluded that it represents the acetabular end of the ilium. This end is expanded into a thickened head somewhat roughened on the acetabular surface. The shaft above the head is constricted up to the fractured end, both antero-posteriorly and internally. One side of the bone is flattened and probably represents the internal surface. The frac- tured end is nearby half oval in cross-section. (See (3), Fig. 11.) If correctly determined this is the first evidence we have of the character of the pelvic region in Baptanodon and it appears to indicate a weak posterior extremity as compared with the strong anterior limb. It also furnishes additional evidence that Profes- sor Marsh was mistaken in his identification of the limb in the type of B. discus (1955) 6 as a posterior extremity, a question dis- cussed in my previous paper. This element resembles somewhat the ilium of Toretocnemus californicus, a Triassic Ichthyosaurian described by Dr. J. C. Merriam. Fig. 11. (1), ex- ternal view of the ace- tabular end of the ilium of Baptanodon discus (No- 603), one half natural size, a., articular end ; (2), view of articular end of same; (3), cross sec- tion of th e brok en end . Measurements. No. G03. Greatest width antero-posteriorly of acetabular end 45 mm. " 603. " " 'GILMORE : NOTES ON OSTEOLOGY OF BAPTANODON 333 Wyoming, and was collected by Mr. W. H. Utterback from the marine beds of the Jurassic in 1902. It is now in the collection of the Carnegie Museum. The large size of all of the vertebrae and the long straight border of the external ends of the coracoids for articulation with the humeri appear to indicate a new species for which I propose the name Baptanodon robustus, Although the material at hand is insufficient for a satisfactory diagnosis of this form, yet the dimensions of the parts preserved, particularly the vertebra? and ribs, show this to be the largest member of the Baptanodontidse. A right coracoid, No. 1953, in the Museum of Yale University shows the same long straight border on the external end and may per- tain to this species. Vertebra:,. 334 MEMOIRS OF THE CARNEGIE MUSEUM to the ninth cervicals have a vertical ridge connecting the di- and parapophyses on the anterior margin of the centra. This character may also prove to be a feature of this species. The anterior or median dorsals have two well defined apophyses (See Fig. 13) placed well down on the anterior margins of the centra. The diapophysis is the larger of the two. In these verte- brae the pedicels of the upper arches are extended antero-posteriorly, being nearly as wide as the centra upon which they rest. The spines are somewhat compressed later- ally, and very high. The arches in what is considered the anterior dorsal region are held together by single zygapophyses, which are of considerable extent obliquely. The pedicels do not project later- ally as in some of the Ichthyopter- ygians but form a smooth surface with the upper lateral surfaces of the centra. The series of posterior dorsals appear very similar, except in size, to those from this region of B. dis- cus. The single apophyses pos- teriorly recede to the lowermost border of the centra as in the other GILMORE : NOTES ON OSTEOLOGY OF BAPTANODON 335 Measurements of Vertebrae of No. 919. Atlas and Cervicals axis 3d 4th 5th 6th 7th 8th 9th 10th 11th Greatest length of centrum in mm. 57 34 34 30 35 35 35 35 b 336 MEMOIRS OF THE CARNEGIE MUSEUM The anterior border of the parts preserved is slightly rounded, but, as it approaches the articular end it widens into flattened oblique surfaces which look forward and upward and probably represent the points of attachment for the ligaments which held the clavicles in position. (See PI. XXXVIII. , Fig. 1.) The ventral surface of the scapulae antero-posteriorly at the expanded articular ends is somewhat concave. Between the point of attachment for the clavicle and the articulation with the coracoid the internal border is especially compressed and remains free. The clavicles and interclavicular bones were not found with this specimen. Measurements. No. 919. Greatest width of coraeoids, transversely 430 mm. " 919. " length of articular surface for scapula 85 " " 919. " " of straight external border 110 " " 919. " width of scapulae, antero-posteriorly 175 " " 919. " length of glenoid articular face 60 " Comments on Recent Literature. In discussing the age of the Baptanodon Beds Dr. S. W. Williston 8 speaks of the relationship of Baptanodon and Ophthalmosauras and makes the statement that the two species of Ophthalmosaurus are probably not congeneric and "it is also apparently quite true that Baptanodon seems to be as closely allied to the Cretaceous as to the Jurassic species." In a previous paper 9 I have shown that 0. icenicus (the Jurassic form) and Baptanodon are very closely allied, while 0. cantabrigiensis is not similar in any respect. The discovery the past season (1905) by Mr. W. H. Reed of an Ichthyosaurian in the Benton Cretaceous is of considerable interest as showing the occurrence in North America of this group at a much later period than hitherto supposed. Dr. J. C. Merriam, who has examined the fragmentary specimen collected by Reed, says : 10 " The centrum is very thin antero-posteriorly and in this respect some- what resembles the corresponding centra in Baptanodon discus. . . . When more material is available it will be interesting to learn whether this form really repre- sents a true Ichthyosaurus or possibly a more highly specialized form of Baptanodon than those we know from the Baptanodon beds. Should it be Baptanodon, it will 8 Williston, S. W., "Hallopus, Baptanodon and Atlantosaurus Beds of Marsh," Jour, of Geology, Vol. XIII., No. 4, May- June, 1905. 9 Gilmore, C. W., "Osteology of Baptanodon," Memoirs of the Carnegie Museum, Vol. II., No. 2, August, 1905. 10 Merriam, J. C, " The Occurrence of Ichthyosaur-like Remains in the Upper Cretaceous of Wyoming," Science, X. S., Vol. XXII., No. 568, pp. 640-641, November 17, 1905. GILMORE : NOTES ON OSTEOLOGY OF BAPTANODON 337 probably show some extreme specializations, as the time separating the Benton from the Baptanodon beds is considerable." Moreover, it would be of interest to note the presence of this group in the Cre- taceous of this country, which has already been shown to be the geological range of the closely allied European genus Ophthalmosaurus. U.S. National Museum, February 6, 1906. EXPLANATION OF PLATE XXXVI. Side view of skull of Baptanodon discus Marsh (No. 878). One fifth natural size. Restored. ag., angular ; d., dentary ; j., jugal ; la., lachrymal ; mx., maxillary ; na., nasal ; nar., narial opening ; occ.c, occipital condyle ; pa., parietal ; pm.v., premaxillary ; prf., prefrontal ; ptf., postfrontal ; pto., postorbital ; q.j., quadrato-jugal ; qu., quadrate ; s.ag., surangular ; s.t., supra- temporal ; scl., sclerotic plates ; sta., stapes ; spl., splenial ; sq., squamosal. 338 Memoirs Carnegie Museum, Vol. II. Plate XXXVI. Side View ok Skill of BAPTANODON DISCUS Marsh (No. 878). \ Natural Size. Eestored. Some sutures drawn after No. 1441. OCR text unavailable for this page.OCR text unavailable for this page.EXPLANATION OF PLATE XXXVII. 1. Top view of skull of Baptanodon discus Marsh (No. 878). One fifth natural size. Restored. . art., articular; ex.oec., exoecipital ; Jr., frontal; na., nasal ; nar., nares ; occ.c, occipital condyle; pa., parietal; pin., pineal foramen ; pmx., premaxilla ; prf., prefrontal; ptf., postfrontal ; s.ay., surangular ; s.occ, supraoccipital ; s.t., supratemporal ; s.t.f., supratemporal fossa ; sq., squamosal. 2. Inferior view of skull of Baptanodon discus (No. 603). One fifth natural size. Restored. ag., angular ; art., articular ; b. occ. , basioccipital ; b.s., basisphenoid ; cor., corouoid ; d., dentary; ipt., interpterygoid vacuity ; occ.c, occipital condyle ; pi., palatine ; prs., presphenoid ; pt, ptery- goid ; spl., splenial ; v., vomer. MO Memoirs Carnegie Museum, Vol. II. Plate xxxvii. c "r:. Skull of BAPTANODON DISCUS. 1, Superior View (No. 878); 2, Inferior View (No. 603). Both | Natural Size. Some sutures drawn after No. 1441. OCR text unavailable for this page.OCR text unavailable for this page.EXPLANATION OF PLATE XXXVIII. 1. Anterior view of pectoral girdle of Baptanodon robusius (No. 919). Type. One fifth natural size, co., coracoids ; sc, scapulae; x., surfaces for attachment of the clavicles. 2. Dorsal view of the same girdle. One fifth natural size, co., coracoids ; sc, scapulas ; x., surfaces for attachment of the clavicles. 342 Memoirs Carnegie Museum, Vol. II. Plate XXXVIII Pectoral Girdle of BAPTANODON BOBUSTUS (type specimen). 1, Anterior View ; 2, Dorsal View (No. 919). Both A Natural Size.