Master's Theses

Date of Award

Fall 1999

Degree Name

Master of Science (MS)

Department

Geosciences

Advisor

Richard Zawerksi

Abstract

The remains of Spinosuchus caseanus Huene, 1932 were collected in Crosby County, Texas from Late Triassic Dockum Group rocks. These rocks cropped out along the breaks of the White River that are just north of an old postal road in Crosby County, Texas. With the exception of these remains, the immediate type locality was otherwise barren of fossils. The 22 postaxial presacral vertebrae that comprise the type specimen of Spinosuchus caseanus correspond to the kind and number observed in basal dinosauromorphs and basal archosauromorphs, especially Trilophosaurus buetineri. The enigmatic neodiapsid S. caseanus was initially considered to be a basal saurischian dinosaur (Coelophysis aff longicollis Case). This idea was based largely on Case's referrals of questionable cranial, caudal, and pelvic material from Crosby and nearby counties which did not duplicate any elements of the type specimen. These referrals are not accepted in the present study and no new ones are proposed. The diagnostic characters of Spinosuchus Caseanus relate to the extreme elongation of the dorsal neural spines. The shafts of the neural spines are elongate rods with a squarish cross section whose comers are blended into the zygapophyses by well developed and fragile webs of bone reminiscent of the vertebral lamellae of diplodocoid sauropods. The distal tips of the neural spines are anteriorly expanded into an elongate asymmetrical "hatchet blade" in lateral view. Spinosuchus Caseanus lacks the incorporation of posterior dorsal vertebrae into the sacrum. S caseanus retains synacephalous ribs and synapophyses on more than just the last dorsal vertebra. In S. Caseanus, the parapophyses and diapophyses on the first few cervical vertebrae are flush with the anterior edges of their respective centra whereby the diapophyses overhang the parapophyses. S caseanus lacks hyposphenes and hypantra on the neural arches. None of the preserved vertebrae of S. caseanus are sacrals. [More in manuscript]

Rights

Copyright 1999 H. Robbins Richards

Comments

Notice: This material may be protected by copyright law (Title 17 U.S. Code).

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