76 BULLETIN 110, UNITED STATES NATIONAL MUSEUM. 



Family CERATOSAURIDAE 



In 1884 ' at the time of creating the genus and species, Ceratosaurus nasicornis 

 Prof. O. C. Marsh proposed the new family Ceratosauridae which was defined as 

 follows : 



Horn on skull, Cervical vertebrae plano-concave, remaining vertebrae biconcave. Pubes 

 slender. Pelvic bones coossified. Osseous dermal plates, Astragalus with ascending process. 



The standing of the family Ceratosauridae was consistently maintained by 

 Marsh in his later writings, though the distinctness of this family was not generally 

 accepted by other authorities. Lydekker, in 1888 ^ included it under the Megalo- 

 sauridae, a view adopted in succeeding years by other paleontologists. The genus 

 Ceratosaurus, however, so far as I am able to discover, has been accepted by everyone 

 except Cope,^ who in 1892 referred the species to Megdlosaurus. 



The general nonacceptance of Marsh's family I now believe was largely due 

 to the inadequateness of his definition, for, as originally stated and subsequently 

 amended on at least two occasions, there were only one or two characters enumerated 

 that would not apply to any of the large Theropod dinosaurs. The presence of a 

 horn on the skull is the one distinctive character, and that may prove to be a sexual 

 feature. 



Although in many respects Ceratosaurus approaches the megalosauroid forms, 

 several generalized features of the skeleton, as the presence of four digits in the 

 manus; a closed obturator pubic foramen; the long quadrate and the closer 

 resemblance of the presacral vertebrae to the earlier Triassic forms, in my opinion, 

 makes it the most conservative Theropod known above the Triassic. 



After a thorough study of the genotype as compared with Antrodemus, Tyran- 

 nesaurus, Gorgosaurus, and other American carnivorous dinosaurs, convinces me of 

 the family distinctness of this genus as originally classified by Marsh. 



The family I would now define as follows : 



FAMILY CHARACTERS — Horn on skull; pubes meeting on median line at proximal end. 

 Manus with four digits, lateral digits reduced. 



The genus Ceratosaurus I would define as follows: 



GENERIC CHARACTERS: Premaxillaries with three teeth; maxiUaries with 15 teeth; dentary 

 with 15 teeth; 9 cervical vertebrae plano-concave; dorsal vertebrae biconcave; 6 sacrals; distal caudals 

 without special lengthening of prezygapophyses; pelvis coossified; pubis with closed obturator 

 foramen; i digits in manus, first and fourth reduced; probably 3 digits in pes; dermal ossifications; 

 abdominal ribs present. 



Genus CERATOSAURUS Marsh, 1884. 



CERATOSAURUS NASICORNIS Marsh, 1884. 



Ceratosaurus nasicornis Marsh, Amer. Journ. Sci., ser. 3, vol. 27, 1884, pp. 300-337, pis. 8, 9, figs. 1, 10, 

 11; vol. 28, 1884, p. 161, fig. 1; Bull, du Musee Royal d'Hist. Nat. de Belgique, vol. 4, 1884, 

 pp. 136, 140, 145, 146, pi. fi, figs. 6, 16. — Menzbier, M., Bull. Soc. Im'p. Natur. Moscou (new ser.), 

 vol. 2, 1887, p. 533. — Lydekker, R., Cat. of Fossil Reptilia and Amphibia in the British Museum, 

 pt. 1, 1888, p. 157, fig. 2G.— ZiTTEL, K. A., Handbuch der Palaeontologie, vol. 3, 1890, p. 727, figs. 

 629-635.— Marsh, Amer. Journ. Sci., ser. 3, vol. 44, 1892, p. 347, pi. 7.— Cope, Trans. Amer. Philos. 



1 Amer. Journ. Sci., vol. 27, 1884, p. 330. 



2 Cat. of Fossil Eeptilia and Amphibia in the British Museum, pt. 1, 1888, p. 157. 



3 Proe. Amer. Philos. Soc, vol. 30, 1892, p. 241. 



