Great Basin Naturalist Volume 45 Number 4 Article 8 10-31-1985 Uncompahgre dinosaur fauna: a preliminary report James A. Jensen Brigham Young University Follow this and additional works at: https://scholarsarchive.byu.edu/gbn Recommended Citation Jensen, James A. (1985) "Uncompahgre dinosaur fauna: a preliminary report," Great Basin Naturalist: Vol. 45 : No. 4 , Article 8. Available at: https://scholarsarchive.byu.edu/gbn/vol45/iss4/8 This Article is brought to you for free and open access by the Western North American Naturalist Publications at BYU ScholarsArchive. It has been accepted for inclusion in Great Basin Naturalist by an authorized editor of BYU ScholarsArchive. For more information, please contact [email protected], [email protected]. UNCOMPAHGRE DINOSAUR FAUNA: A PRELIMINARY REPORT James A. Jensen Abstract.—A diverse late Jurassic dinosaur fauna, discovered in western Colorado in 1963, contains many unde- scribed taxa that may represent evolutionary trends at the generic level not previously reported from the Morrison Formation. A preliminary faunal hst is given. Bones of the largest known dinosaur, Ultrasaurus , are present as are a variety of small animals, including Pterosaurs, in which one sacrum displays avianlike fused sacral neural spines. A new family, the Torvosauridae , erected, based on the genus Torvosaunis that is redescribed. One of the most diverse Jurassic dinosaur their field investigations "failed to find any faunas in North America was found on the convincing evidence of evolution at the Uncompahgre Upwarp in western Colorado generic level within the Morrison Forma- in 1963. This fauna contains more unde- tion." There are familiar forms in the Uncom- scribed taxa than has been encountered in any pahgre fauna, but there is also consistent evi- other North American Jurassic assemblage in dence of change, or "evolution at the generic this century. The first vertebrate fossil collect- level" as demonstrated by: (1) giganticism in ing on the upwarp was by the author in 1964 more than one sauropod family; (2) at least a and continued for the next 20 years. More 100% increase in carnosaur genera; (3) the than 50 tons of dinosaur bone and matrix were presence of the first relatively abundant collected from an area stretching 35 miles pterosaur elements, previously known in the along the upwarp's eastern monocline. North American Jurassic from one phalangial Very little systematic work was done during fragment from Como BluflP; (4) undescribed those two decades of collecting for several variations in sauropod skeletal morphology', reasons: (1) all available funds were used for particularly the axial skeleton; and (5) the collecting; (2) the most productive quarries presence of ornithischians above the Mor- being worked contained masses of disarticu- rison average, plus various other novel differ- lated bones that could not be separated with ences. confidence into specific sets; (3) the author A problem of identification in this diverse Un- thinks that any attempt to sort and describe compahgre fauna is focused on the question extensive deposits of disarticulated material "How far must an evolving genus move from before the largest possible sample is taken will parent stock, i.e., change morphologically, be- not produce the most comprehensive results; fore it qualifies as a new genus?" Satisfactory and (4) the collecting program was so produc- criteria to deal with this question do not exist. tive that it acquired more material each sea- Other Morrison (juarries today generally pro- son than could be prepared for study in five or duce specimens that can be confidently identi- more years. However, many representative fied with described material in genera that are specimens were prepared for study, and one comfortabK' distinct from one another. The Un- unique carnosaur was described and named compahgre fauna displays so man\' variations on Torvosatirus tanneri (Galton and Jensen classical niorpholog}- that it probably represents 1979). either an ad\ anced or \ ounger fauna. It contains The author believes the fauna will demon- many specimens that look familiar, as if the>' are strate substantial evolution at the generic closely related, yet vary enough in structure to level when compared to classical Morrison qualify as new taxa. They may represent exolii- assemblages. Dodson et. al. (1980) state that tion at the generic level. 'Earth Science Mus: Briuliam Vouns University, Provo, Utali 84602 :2821 North 7(H) East. Pn 710 October 1985 JENSEN: UNCOMPAHCRE DINOSAUHS 711 Detailed studies of the Unconipahgre fauna Dia(;n()SIS. — Characterized by robust long may at least provide a new window on di- bones; skull short, massive, and moderately nosaur evolution and possibly shed some light low; forelimb very short with ratio of maxi- on the time-transgressive evolution ofJinassic mum length of humerus to radius at more than dinosaurs into Cretaceous forms. 2; lachrymal with a 9()-degree angle between The Uncompahgre fauna will be discussed maxillary and jugal rami; very distinctive further and illustrated in a larger paper, "New pelvic girdle with ilium dolichoiliac; pubis and and Undescribed Dinosaurs of the Southwest- ischium brachyiliac; pubis with closed obtura- ern Colorado Plateau," now in preparation. tor foramen. Pubis with an almost continuous median symphysis; very small non-weight- bearing pubic foot. Taxonomic Revision Type genus. — Torvosaurus Galton & Jensen 1979. Romer (1956) listed four carnosaur families: Palaeosauridae, Teratosauridae, Megalosaur- Revised description of Torvosaurus: A idae, and Tyrannosauridae. A conservative large, heavily built theropod with a short skull modern interpretation of the infraorder Carn- and a total body length of at least 10 m. Three osauria, as used by Russell (1984), retains the premaxillary teeth with no rectilinear grooves Megalosauridae and Tyrannosauridae but dis- (Figs. 2D, Di); 10 maxillary teeth (Fig. 1, Bi); cards the other two families and adds Cer- open foramina along superior border of fused atosauridae, Allosauridae, Aublysodontidae, interdental plates exposing germinal teeth; and Dryptosauridae. short dentary with 10 teeth (Figs. 3A-B); un- sutured median symphysis; no meckelian Galton and Jensen (1979) placed the genus groove on medial surface (Fig. Lachry- Torvosaurus in the family Megalosauridae, SAJ. mal horn absent (Fig. lA^); lachrymal vacuity but subsequent laboratory work has doubled opening forward (Fig. lAj. Dorsoventrally the number of elements available for study, broad jugal with narrow preorbital ramus. revealing a number of diagnostic features in Forelimb with heavy himierus and short fore- Torvosaurus not seen in the Megalosauridae. arm with ratios of length of Although unique morphological characteris- maximum humerus to radius at 2.2; humerus straight tics of this genus set it apart from the families with large deltopectoral crest, broad distal listed by Russell, it shares a few common fea- and proximal ends (Fig. 4D); proximal of tures with the Megalosauridae. In contrast, end ulna massive with ratio Allosaurus and Tyrannosaurus, representing of maximum length to maximum proximal width at 2. 1; metacarpal I two different families, share common charac- with square proximolateral corner; first pha- teristics to a much greater degree than either one resembles Torvosaurus. lanx of digit I stout, short, and helically twisted along its length; metacarpal II short The genus Torvosaurus is best character- but extremely massive with ratio of maximum ized as being a theropod with both primitive length to maximum proximal width at 1.5; and advanced characteristics: the pubis and metacarpal III massive, ratio 2.2. Ilium heavy ischium are of the prosauropod, brachyiliac with low dorsal blade, broad brevis shelf and type; the ilium is of the coelurosaurian, doli- transversely wide acetabular surface. Pubis choiliac type. This combination has not been with closed obturator foramen and a nearly seen in any North American theropod (Galton continuous median symphysis on both pubis and Jensen 1979) and may be the only exam- and ischium. Pubis with no horizontal weight- ple from any age. bearing ventral plane. Astragalus massive, as- cending ramus thick and truncated toward Torvosauridae, family calcaneum. (See Galton and Jensen 1979 for previously published figures). Metatarsals The new family Torvosauridae is proposed massive with no distal lateral or medial pits. to receive the genus, species, Torvosaurus Cervical vertebrae with subcircular ball-and- tanneri. Order Saurischia, Suborder Therop- socket joints, the vertical axes being shorter oda, Infraorder Carnosauria, New Family than the horizontal axes; large pleurocoels Torvosauridae. openly communicating with internal pneu- 712 Great Basin Naturalist view. Al, lateral view. B-Bl, Torvosauru.s tmrncri. Fig. 1. A-Al, Torvosaurus tanneri , left lachrymal: A, medial left maxilla. B, lateral view. Bl, medial view. interclintal plati's; idt, niterdentai Abbreviations: a, alveoli; ar, anterior ramu.s; dr. de.seendinii nmnis; fip. iused sulnre. foramen; If, lachrvmal foramen; 1\', lachrymal vacnit\'; ps, prema.\illar\ October 1985 JENSEN; UNCOMPAIICHE DINOSAURS 713 fj 10 cm Fig. 2. A-Al, Torvosaurtis tanncri atlas intercentriiin with coossified left neuropophysis. A, anterior view. Al, posterior view. B, right lateral view. C, ventral view. D-Dl, Torvosaurtis tanneri right prema.xilla. D, medial view. Dl, right, lateral view. Abbreviations: A In, atlas intercentrum; N, neuropophysis;