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A new species of the theropod dinosaur Syntarsus from the Early Jurassic Kayenta Formation of Arizona

Taylor & Francis
Journal of Verterbrate Paleontology
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Abstract

Until now, Syntarsus was based on a single species, S. rhodesiensis, known only from southern Africa. The discovery of Syntarsus in North America adds significantly to the increasingly detailed resemblance of African and North American Early Jurassic terrestrial vertebrate faunas. The new species, Syntarsus kayentakatae, is based on a complete skull and partial skeleton, and more fragmentary remains of at least 16 additional individuals, all from a narrow stratigraphie interval in the Kayenta Formation. Syntarsus kayentakatae is diagnosed by parasagittal cranial crests and fusion of the fibula to the calcaneum in adults. Syntarsus is the most derived member of the newly diagnosed theropod taxon Ceratosauria, possessing 22 apomorphies that arose subsequent to the divergence of ceratosaurs from other theropods. Syntarsus shares 20 of these with Coelophysis bauri, one of the earliest well-known theropods. By their first appearance, probably late Carnian, ceratosaurs already possessed a history involving considerable morphological transformation. A number of these characters arose convergently much later in time in ornithurine birds.
A New Species of the Theropod Dinosaur Syntarsus from the Early Jurassic Kayenta
Formation of Arizona
Author(s): Timothy Rowe
Source:
Journal of Vertebrate Paleontology,
Vol. 9, No. 2 (Jun. 30, 1989), pp. 125-136
Published by: The Society of Vertebrate Paleontology
Stable URL: http://www.jstor.org/stable/4523249
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... Though theropod hyoids have been known for well over a century (Marsh 1884) and have been reported in several well-preserved specimens (e.g., Marsh 1884;Gilmore 1946;Rowe 1989;Russell and Dong 1993;Hu et al. 2018), they remain poorly described. They are universally described as thin and rod-like, and have little morphological diversity among non-paravian theropods, which largely retain plesiomorphic archosaurian hyoid morphology . ...
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... The co-ossification between these two bones occurs in specimens of Coelophysoidea (e.g. Camposaurus arizonensis, Coelophysis bauri, Megapnosaurus rhodesiensis, 'Syntarsus' kayentakatae : Raath 1977;Rowe 1989;Ezcurra and Brusatte 2011;Griffin 2018) and Ceratosauria (e.g. Ceratosaurus nasicornis: USNM 4735; Eoabelisaurus mefi: MPEF-PV 3990; Masiakasaurus knopfleri: Carrano et al. 2002) with a considerable degree of skeletal maturity. ...
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... The known dentitions of coelophysoid theropods are characterized by blade-like serrated maxillary and non-mesial dentary teeth, indicating a mostly macrophagous carnivorous diet for these taxa [60,68,76]. It is therefore highly likely that P. milnerae had a similar dentition and diet even though no craniodental remains from Pant-y-ffynnon can unequivocally be attributed to this species. ...
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