70-5 A reevaluation of Late Jurassic megalosaur material from the Nail Quarry, Morrison Formation.

Session: Paleontology, Biogeography/Biostratigraphy & Phylogenetic/Morphological Patterns (Posters)

Presenting Author:

Authors:

Abstract:

Since its initial description, the validity of the Late Jurassic North American megalosaur, Edmarka rex has been brought into question. The uncertain validity of E. rex comes from the fragmentary nature of the original material (CPS coll.), and the subsequent material in the same quarry. We offer a reevaluation of the type and two associated large megalosaur specimens: GPM/TATE 0012 and GPM/TATE 0050. Siegwarth et. al (unpublished) informally referred to TATE/GPM 0012 as “Brontoraptor”. GPM/TATE 0012 is represented by a nearly complete right pelvis and left hindlimb, with a sacrum and several caudal vertebrae. The ilium of GPM/TATE 0012 possesses a straight dorsal margin (opposed to the convex dorsal margin in T. tanneri), a brevis fossa with an expanded medial shelf (not present in T. tanneri), and a pubic peduncle that is proportionately wider than in T. tanneri. The pubis of GPM/TATE 0012 has a marginal synthesis, as opposed to the broad synthesis of T. tanneri. The femur of GPM/TATE 0012 is remarkably robust, with a circumference/length ratio of 0.4. GPM/TATE 0050 represents a pubis and partial ischium. The pubis has the same marginal synthesis as in GPM/TATE 0012. The ischium of GPM/TATE 0050 possesses a foramen ventral to the obturator plate, which may be present but is not preserved in either GPM/TATE 0012 or any T. tanneri material. We unite GPM/TATE 0012 and GPM/TATE 0050 based on the shared presence of two pubic foramen. We find no traits sufficient to distinguish GPM/TATE 0012 and GPM/TATE 0050 from the type of Edmarka rex and unite all three based on the similar robustness of the scapula of GPM/TATE 0012 and CPS 1002. Together, the three referred specimens provide an extensive suite of characters that differ from Torvosaurus tanneri. On this basis, we propose the retention of Edmarka rex. Overall, E. rex was a more robust animal than T. tanneri, with a stouter shoulder girdle, an expanded brevis fossa that presumably supported an enlarged M. caudofemoralis brevis, and a proportionately thick femoral shaft.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9126

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