This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
Due to the usual frustrating inability of being unable to finish any of the in-prep Tet Zoo articles (and… I’ve been away), I give you the following short article.
Coelophysoids are best known for Coelophysis from the Upper Triassic of the USA; extremely similar (perhaps congeneric) forms are known from the Lower Jurassic of Zimbabwe, South Africa, China and Europe. These are gracile theropods, approximately 3 m long and less, with shallow, slender skulls where a subnarial gap is present between the posterior-most premaxillary teeth and first maxillary tooth.
Larger coelophysoids from the Late Triassic (including Gojirasaurus and Liliensternus) are 5-6 m long. Dilophosaurus from the Lower Jurassic of the USA and China (though read on) is also large at 7 m and is famous for its paired, semicircular cranial crests. These crests are extremely fragile and presumably served an exclusive role in visual display. The Chinese Dilophosaurus – D. sinensis (named in 1993) – was recently argued to be synonymous with the previously obscure Sinosaurus triassicus (named in 1948) (Xing et al. 2013) [image below by Ghedoghedo].
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Inclusion of Dilophosaurus and related taxa – informally referred to as dilophosaurids – within Coelophysoidea has been questioned by some researchers since these animals are similar to tetanurans in a few details of cranial anatomy (Yates 2005). However, a coelophysoid clade that includes the dilophosaurids has been recovered in several studies. Coelophysoid monophyly is supported by the elongate, shallow proportions of the skull, subnarial gap, a deepened tip to the dentary, a proportionally large antorbital fenesta and other characters (Holtz 2000, Ezcurra & Novas 2006). Members of the group persisted to the end of the Early Jurassic.
Skull and jaw anatomy, as well as body size, suggests that coelophysoids were mostly predators of small vertebrates. Stomach contents known for Coelophysis [adjacent image by Smokeybjb] were long thought to demonstrate cannibalism in this taxon but the fossils concerned are actually the remains of a small crocodylomorph (Nesbitt et al. 2006).
An especially intriguing aspect of the coelophysoid fossil record concerns the enormous aggregation of Coelophysis specimens known from Ghost Ranch, New Mexico. Why so many of these dinosaurs gathered in the same place, and then died together, is unknown: perhaps they were exploiting a super-abundant resource and died due to poisoning of some sort. Specimens of the bipedal rauisuchian Effigia and early theropod Daemonosaurus was also discovered within the Coelophysis mass death assemblage.
For previous Tet Zoo articles on Dilophosaurus and various other archaic theropods, see…
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Ezcurra, M. D. & Novas, F. E. 2006. Phylogenetic relationships of the Triassic theropod Zupaysaurus rougieri from NW Argentina. Historical Biology 19, 35-72.
Holtz, T. R. 2000. A new phylogeny of the carnivorous dinosaurs. Gaia 15, 5-61.
Nesbitt, S. J., Turner, A. H., Erickson, G. M. & Norell, M. A. 2006. Prey choice and cannibalistic behaviour in the theropod Coelophysis. Biology Letters 2, 611-614.
Xing, L., Bell, P. R., Rothschild, B. M., Ran, H., Zhang, J., Dong, Z., Zhang, W. & Currie, P. J. 2013. Tooth loss and alveolar remodeling in Sinosaurus triassicus (Dinosauria: Theropoda) from the Lower Jurassic strata of the Lufeng Basin, China. Chinese Science Bulletin 58, 1931-1935.
Yates, A. M. 2005. A new theropod dinosaur from the Early Jurassic of South Africa and its implications for the early evolution of theropods. Palaeontologica Africana 41, 105-122.