AMERICAN MUSEUM NOVITATES Published by Number 1301 THm AMERICAN MUSEUM OF NATURAL HIsTORY November 6, 1945 New York City THE HYOID BONES IN PROTOCERA TOPS AND IN. PSITTACOSA URUS1 By EDWIN H. COLBERT INTRODUCTION During the preparation of a skeleton of in order that the published knowledge con- Protoceratops, Mr. Otto Falkenbach of the cerning Protoceratops, contained in several American Museum Paleontological Labora- papers but especially in the study by tory discovered two small bones which Brown and Schlaikjer (1940), may be as when first seen appeared to be quite unlike complete as possible. At the same time, it any elements hitherto known in this dino- was felt that certain comparisons with other saur. At first it was thought that these dinosaurs of varying relationships to bones might be portions of the sternum, Protoceratops should be included in this but comparisons soon showed that such study. Such is the subject matter that will could not be the case. Indeed, various be treated in the following pages. comparisons with the known osteological The author wishes to express his appre- elements of Protoceratops confirmed the ciation to Mr. Falkenbach, who in the first impression, namely, that these were course of his skillful preparation of the bones hitherto undescribed, so the question specimen of Protoceratops made the discov- arose as to what these bones might be. ery of these new bones. To Dr. Gregory Several possibilities were considered and must go the credit of making the suggestion several opinions were sought, with the re- as to their being hyoids, and to him my full- sult that Dr. William King Gregory of the est acknowledgments are hereby expressed. American Museum suggested that these Subsequently a portion of another bone was might be hyoid elements. The more this found, and this may represent an addi- possibility was investigated, the more tional element in the hyoid apparatus of likely it seemed to be. All subsequent in- Protoceratops. The translation from FiXr- vestigations have tended to confirm this bringer was made by Dr. Otto Haas. view. Finally credit should go to Mr. John C. It has been felt desirable to bring out a Germann, Staff Artist, for the excellent il- description of these supposed hyoid bones, lustrations that appear in this paper. DESCRIPTION AND DISCUSSION Before making a formal description of the hyoids in modern reptiles was set forth these supposed hyoids of Protoceratops, it by Fuirbringer in his monograph on the min,y be well to consider briefly the homolo- hyoids of the vertebrates (1922). A trans- gies of the hyoid bones in the tetrapods, lation of this statement follows: and their development particularly in mod- "As has been known in the main for a ern reptiles. long time, the hyoid of living reptiles con- A very illuminating statement describ- sists, at its highest stage of development, ing the development and the homologies of of an unpaired body, the corpus (Copula; 1 Publications of the Asiatic Expeditions of the basihyal and basibranchial) [basibranchial American Museum of Natural History, Contribution No. 148. and hypobranchial according to Goodrich] 2 AMERICAN MUSEUM NOVITA TES [No. 1301 tapering in a forward direction into a nar- mellar apparatus of the middle ear, also, rower process, the processus lingualis (proc- an element in the hyoid arch, but this con- essus entoglossus), which varies in length nection has been lost in most of the reptiles and is bound into the posterior part of the and has undergone considerable redqction tongue, and of three pairs of horns con- in many of them. This horn is very sig- nected laterally in various ways with the nificant morphologically and therefore has corpus, an anterior pair, the cornu hyale, been named the cornu principale by Gaupp, a middle pair, the cornu branchiale I, and a but it is inferior in size and strength to the C B Ch1 Ch CbI Cb2 C Cb2 Cblt A E D )CJkCh Cb2, Fig. 1. A comparison of the hyoids in the living reptiles. A, Crocodilia: Crocodilus, original. B, Rhynchocephalia: Sphenodon, after Furbringer. C, Squamata: Lacerta, after Goodrich. D, Squamata, Vipera, after Ftrbringer. E, Chelonia: Clemmys, after Forbringer. Not to scale. Key to abbreviations: C-corpus, including the hypohyal or entoglossal. Ch-ceratohyal and epi- hyal; cornu hyale. Cbl-ceratobranchial I; cornu branchiale I. Cb2-ceratobranchial II; cornu branchiale II. posterior pair, the cornu branchiale II, following horn. This horn, the cornu and these are derived from the ordinary branchiale I, which is derived from the first hyoid arch and the first two gill arches. branchial or third visceral arch, is dorsally In the more primitive forms the cornu hy- free and it proves by its permanence and ale is found to be connected with the colu- by the fact that it is ossified when all other 1945] HYOID BONES IN PROTOCERATOPS AND PSITTACOSAURUS 3 portions of the hyoid are cartilaginous, to are pictured. This diagram will, of course, be the most prominent part of the hyoid supplement the summary written by Fiur- complex. The cornu branchiale II, derived bringer and presented above. Homologies from the second branchial or fourth visceral are derived from a comparison with the con- arch, is considerably reduced, and fre- dition in fishes. quently in many reptiles it is split up into a Various names have been applied to the ventral and a dorsal portion, while it may hyoid elements shown in this diagram. It disappear completely in some forms. This may be well, therefore, to include at this horn, too, is as a rule dorsally free, but in place a table to show the system of nomen- some isolated cases it is connected with the clature used for the hyoid elements by dorsal end of the cornu hyale. Starting Futrbringer in 1922, as compared with the with the highest level of development, the system used by Goodrich in 1930, and that hyoid of many reptiles, most of which may followed by Camp in his classification of be considered as advanced forms, is subject the lizards, 1923, and more recent papers. FtRBRINGER GOODRICH CAMP Corpus Corpus or Copula Corpus Entoglossal Entoglossal process Hypohyal Cornu hyale Hyoid cornu Ceratohyal Epihyal Cornu branchiale I First branchial cornu Ceratobranchial I Epibranchial I Cornu branchiale II Second branchial cornu Ceratobranchial II Epibranchial II to reduction. This may start sometimes In the present work Camp's terminology with the first horn, the cornu hyale, some- is used. times with the last one, the cornu bran- In this present discussion our interest, as chiale II, or it may take place simulta- far as recent reptiles are concerned, is cen- neously at the anterior and posterior ends. tered upon the Crocodilia since these ani- "(For a more detailed survey, reference mals, most closely among the living forms, is made to Gaupp's excellent synthesis of approach the dinosaurs in their morphologi- the ontogeny and phylogeny of the sound cal development. conducting apparatus in vertebrates as The hyoids of the Crocodilia are de- well as of the evolution of the cranial and scribed at some length by Fuirbringer, who the hyobranchial skeleton.) shows that in these reptiles the hyoids con- "Simultaneously the hyoid bone consti- sist of a large corpus, ventrally convex, tutes in various ways the ventral basis from the side of which project large, well- and, when well developed, the support for ossified first ceratobranchials. The corpus the respiratory organs (larynx, i.e., cricoid, is cartilaginous and broader anteriorly with adjacent cartilages, the trachea). than posteriorly. In its dorsal concavity The connection between both is sometimes are the cricoid and arytenoid cartilages. loose, sometimes solid, and it may exist According to Fiirbringer, the existence between hyoid and cricoid or between hyoid of a ceratohyal is not certain in the Croco- and trachea, with all transitions from the dilia. It would seem probable, from the cricoid to the trachea" (Futrbringer, 1922, ontogenetic work of Parker, that it was p. 6). suppressed at an early stage of develcp- For the purpose of orienting ourselves ment. and avoiding a long, detailed discussion, The first ceratobranchial, says Fur- the manner in which the hyoid apparatus bringer, projects from the lateral border of is developed in the modern reptiles may be the corpus and is directed somewhat lat- shown by a diagram in which typical ex- erally and somewhat dorsally. This is a amples of the hyoids in turtles, rhynchoce- very strong, highly ossified element, which phalians, crocodilians, lizards, and snakes often shows, according to the age of the 4 AMERICAN MUSEUM NOVITATES [No. 1301 Fig. 2. The hyoid apparatus of Crocodilus porosus. Ventral view, natural size. Abbreviations as in figure 1. animal or the species, a longer or shorter Crocodilia, condensed and paraphrased cartilaginous epiphysis at the free end. above, with a few notes regarding the hy- In young embryos this element is cartilagi- oids of Crocodilus porosus as shown by a nous, but it begins to ossify during embry- specimen at hand. Evidently this came onic life. from a fairly large animal, so that ossifica- The second ceratobranchials are con- tion has proceeded to a considerable extent. tained in the two posterior corners of the The corpus or copula, however, is com- hyoid body or corpus. It might be helpful pletely cartilaginous. It is broad, and its at this place to supplement briefly Fur- lateral edges are extended; these may rep- bringer's remarks as to the hyoids in the resent in part at least the ceratohyals, 19451 HYOID BONES IN PROTOCERATOPS AND PSITTACOSAURUS 5 As Fulrbringer has shown, this is a debatable thickened edge of each bone is the lateral question upon the basis of such evidence as one, and the thin, sinuous curved edge the is now available to us.