AMERICAN MUSEUM NOVITATES Published by Number 1316 Tim AMERICAN MUSEUM of NATURAL HISTORY April 3, 1946 New York City

AMERICAN MUSEUM NOVITATES Published by Number 1316 Tim AMERICAN MUSEUM OF NATURAL HISTORY April 3, 1946 New York City THE ANTERO-SUPRAGNATHAL OF GORGONICHTHYS BY DAVID H. DUNKLE' AND PETER A. BUNGART' INTRODUCTION Newberry proposed the generic name identification of the upper mouth parts of Titanichthys in 1885 for the remains of a Titanichthys was announced by Dr. Louis spectacularly large arthrodiran fish from Hussakof (1930) before the twenty-first the upper Devonian Ohio Shales formation. annual meeting of the Paleontological During the ensuing 60 years, bones refer- Society at Washington, D. C. Un- able to the genus have proved to be as fortunately neither figures nor formal commonly encountered in collecting description of the specimen have subse- throughout the northern Ohio field as are quently appeared. A meager abstract, as those of the various, more widely and more the only published account of this report, popularly recognized species of Dinichthys has remained a source of intriguing inter- which occur contemporaneously in the est to all students of the Arthrodira. same formation. Titanichthys, in conse- Recently, Mrs. John Bull, working quence, has become well established as a among the collections of fossil fishes in the distinctive member of the fish fauna of the American Museum of Natural History Ohio Shales, and although no thorough under the direction of Dr. Edwin H. Col- revisionary work has been attempted for bert, came upon two associated bones many years, six species are tentatively which bear the identifying labels, re- assigned to the genus at the present time. spectively, of a "left antero-supra-gnathal" Despite this, the details of titanichthyid and indeterminate "cranial bone" of structure are still very imperfectly under- Titanichthys. These were submitted to stood. Peculiarly modified in a bottom- and gratefully received by the present feeding adaptation (Dunkle and Bungart, writers. Careful comparisons with the 1942), many of their skeletal elements are, abstract indicate the bones to be those on in addition, so excessively thin that they which Hussakof based his original report. cannot be removed from the matrix. An They (A.M.N.H. No. 7908) were collected inability to observe either the presence or by Peter A. Bungart in 1910 from exposures absence of the usually characteristic sensory of the Cleveland Shale member of the canals and the number and nature of over- Ohio Shales formation on the shore of Lake lap areas by adjacent bones often makes Erie, 1/2 mile east of the Avon Plant of the impossible the determination, as to particu- Cleveland Electric Illuminating Company lar skeletal part, of isolated specimens. in Avon Township, Lorain County, Ohio. More important, these conditions of preser- The specimen is here described and figured vation and unfamiliar modification have led for the first time because the characters of to a complete failure to recognize for the supragnathal element preclude its Titanichthys any of the supragnathal ele- reference to the genus Titanichthys, as do ments and some of the dorsal and ventral also those of the "cranial plate" which is body armoring plates. revealed as a fragmentary anterolateral In connection with one of these latter un- solved structural issues, the first definitive plate. These specimens are here referred to Gorgonichthys. ' The Cleveland Museum of Natural History, Cleveland, Onio. These writers sincerely appreciate the 2!i AMERICAN MUMSEUM NOVITATES [No. 1316 pQurtesy of the officials of the American in permitting this study and for the privi- M{useum of Natural History, New York, lege of publication in this series. DESCRIPTION The present specimen consists of two section, and is also convex, although to bones: one, a left antero-supragnathal; much less degree, in any parasagittal plane. and the other, as here interpreted, a frag- Its internal surface is concave in both of mentary right anterolateral plate. The these respective sections. outlines and relationships between the The lateral lamina of the antero-supra- separate parts of these two bones are gnathal comprises the main body of the illustrated in figures 1 and 2, respectively. element. With regard to general shape, it A Fig. 1. Gorgonichthys clarki Claypole (A.M.N.H. No. 7908). Left antero-supragnathal in (A) lateral aspect, (B) mesial aspect, and (C) frontal sections. Reproduction approximately X 1/e. a-a', Plane of frontal section (C) indicated on B; al, mesially directed anterior lamina of the antero- supragnathal; avc, anteroventral cusp; b-b', plane of frontal section indicated on B; f. ig., incised area worn by the anterodorsal cusp of the inferognathal; f. sn., fossa for the articulation with the sub- nasal element; in, internal surface of the antero-supragnathal; 11, longitudinally directed lateral lamina of the antero-supragnathal; n, notch on posteroventral margin of the element worn by the oral margin of the opposing inferognathal plate; p. ev., external vertical ridge marking the thickening of the anteroventral cusp; and p. pd., backwardly directed posterodorsal extremity of the antero- supragnathal. The antero-supragnathal possesses an is roughly triangular in either lateral or over-all length of 207 mm. The maximum lingual views with the slightly concave depth of the element, as preserved, is 194 posteroventral margin the longer of the nmn. Its ventral cusp, however, is incom- three sides, and the posterodorsal angle plete, and the total restored height should truncated. This plate-like expanse of approximate 230 mm. Typically arthro- bone is so situated that its broad internal diran in development, the plate may be and external surfaces are vertically in- said, for purposes of description, to be com- clined. The thin, although relatively posed of anterior and lateral laminae which deep, posterodorsal extremity shows little are united anterolaterally in an externally mesial curvature, but is extended virtually rounded angle of less than 90 degrees. straight backward. Anteroventrally, a The anterior lamina, quadrangular in stout cusp is developed whose thickening is outline from forward view, exhibits a depth marked by a vertical ridge, externally. of more than three-quarters the total re- Worn internally by the ventrally opposing stored height of the bone. The width of inferognathal, the cusp is triangular in this mesiad extension is less than one- frontal section. This cusp development, fourth the maximum depth. The external in so large a plate, is restricted to-a surface of the part is acutely convex in frontal prisingly low ventral area. Immediately ANTERO-SUPRAGNATHAL OF GORGONICHTHYS 3 above the external vertical ridge of the row, and deeply incised area forward from thickened cusp a depression is displayed the ventral cusp of the antero-supragnathal whose margins diverge dorsally across both resulting from wear by the anterodorsal the anterior and lateral laminae of the bone. cusp of the inferognathal. Finally, the Similar concavities occur on the antero- posteroventral margin of the plate is supragnathals, where known, of all the di- angularly notched just behind the antero- nichthyid arthrodires. They mark the areas ventral cusp in a manner indicative of an A C B Fig. 2. Gorgonichthys clarki Claypole (A.M.N.H. No. 7908). Fragmentary right anterolateral plate in (A) lateral aspect, (B) mesial aspect, and (C) transverse section. Reproduction approximately X 1/6. a-a', Plane of transverse section (C) indicated on A; b, restored posterodorsal ex- pansion of the anterolateral plate; ex, external face of the element; f. il., rugose surface on the external surface of the mesial arm for the articulation of the interolateral plate; pe, lateral anteroventrally projecting arm; pm, mesial anteroventrally projecting arm; and x, unexplained rugosities on the inner face of the mesial arm. for articulation with the paired sub-nasal externally overlapping opposition upon a elements which will be fully described and decidedly obtuse inferognathal oral margin. determined as anterior ossifications of the As regards the second of the two bones primary palatoquadrate complex in a forth- comprising the present specimen, the de- coming paper by the present writers. termination of fragmentary arthrodiran Lingually, the surface of the lateral lamina bones as to particular skeletal part is often is featureless except for a very high, nar- admittedly hazardous. In this case, how- 4 AMERICAN MUSEUM NOVITATES [No. 1316 ever, the recognition of definite structures this particular specimen, and support our is possible, and this redetermination of the convictions as to the identity of the frag- erstwhile "cranial plate" as an antero- ment. It may be noted that the lateral lateral element is considered of unquestion- arm vestige, depicted in figure 2, is very able validity. weakly developed and that the main body The preserved crescentic portion repre- of the element, paralleling the concave sents the anteroventrally projecting limbs anterodorsal margin, is only moderately of an anterolateral plate of the type known thickened. At present the rugosities dis- to be possessed by Gorgonichthys, Heintz- played on the inner face of the mesial arm ichthys, and Titanichthys (Dunkle and are not explained, although they are un- Bungart, 1940; Heintz, 1931). In these doubtedly concerned with the cartilaginous genera the external arm of the anterolateral primary shoulder girdle. Worthy of men- elements, well developed and bearing spinal tion, also, is the general delicate structure plates in Coccosteus and the members of the of this anterolateral plate compared with Dinichthys terrelli group, is reduced to a the truly massive and powerful dentition laterally upfolded flange, in varying de- which the associated antero-supragnathal grees of completeness, on the ventral *denotes. This apparently reflects a tend- margin of the mesial arm. In addition, ency toward the further reduction of the these genera invariably exhibit the rugose dorsal body armor following the phylo- overlap area on the lateral face of the mesial genetic loss, in turn, of the connection be- arm which marks the articulatory surface tween dorsal and ventral armor, the spinal for the interolateral plate.

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