Abstract
The cranial and postcranial anatomy of the basal hadrosaurid dinosaur Eotrachodon orientalis, from the uppermost Santonian of southern Appalachia (southeastern U.S.A.), is described in detail. This animal is the only known pre-Campanian non-lambeosaurine hadrosaurid, and the most complete hadrosauroid known from Appalachia. E. orientalis possesses a mosaic of plesiomorphic and derived characters in the context of Hadrosauroidea. Characters shared with basal hadrosauroids include a short and sloping maxillary ectopterygoid shelf, caudally prominent maxillary jugal process, one functional tooth per alveolus on the maxillary occlusal plane, a jugal rostral process with a shallow caudodorsal margin and medioventrally facing articular facet, a vertical dentary coronoid process with a poorly expanded apex, and tooth crowns with accessory ridges. Derived characters shared with other hadrosaurids include a circumnarial depression compartmented into three fossae (as in brachylophosaurins and Edmontosaurus), a thin everted premaxillary oral margin (as in Gryposaurus, Prosaurolophus, and Saurolophus), and a maxilla with a deep and rostrocaudally extensive rostrodorsal region with a steeply sloping premaxillary margin (as in Gryposaurus). Eotrachodon orientalis differs primarily from the other hadrosauroid from the Mooreville Chalk of Alabama, Lophorhothon atopus, in having a slender and crestless nasal whose caudodorsal margin is not invaded by the circumnarial depression. Hadrosaurus foulkii, the only other known hadrosaurid from Appalachia, is distinct from E. orientalis in having dentary teeth lacking accessory ridges and a dorsally curved shaft of the ischium. A histological section of the tibia of the E. orientalis holotype (MSC 7949) suggests that this individual was actively growing at the time of death and, thus, had the potential to become a larger animal later in development.
Highlights
Hadrosaurids are facultatively bipedal ornithopod dinosaurs characterized by densely packed dental batteries (Erickson et al, 2012), mediolaterally expanded rostra (Morris, 1970), and hypertrophied nasal passages that are often associated to elaboratedHow to cite this article Prieto-Marquez et al (2016), Anatomy and Osteohistology of the basal hadrosaurid dinosaur Eotrachodon from the uppermost Santonian (Cretaceous) of southern appalachia
During the Late Cretaceous, this region was located in Appalachia, a continent that was separated from the western Laramidia by the Western Interior Seaway (Gates, Prieto-Marquez & Zanno, 2012)
The basal hadrosaurid Eotrachodon orientalis, from the uppermost Santonian section of the Mooreville Chalk of Alabama, is the most complete and best-preserved member of this dinosaurian clade yet known from the eastern half of North America
Summary
Hadrosaurids are facultatively bipedal ornithopod dinosaurs characterized by densely packed dental batteries (Erickson et al, 2012), mediolaterally expanded rostra (Morris, 1970), and hypertrophied nasal passages that are often associated to elaboratedHow to cite this article Prieto-Marquez et al (2016), Anatomy and Osteohistology of the basal hadrosaurid dinosaur Eotrachodon from the uppermost Santonian (Cretaceous) of southern appalachia. This bone is slightly curved caudally; the rostral margin of the dorsal segment of the quadrate forms an angle of 167 with the long axis of the quadratojugal notch (Fig. 10E). The ventral ramus projects and wedges rostroventrally, forming about half of the caudal and rostral margins of the orbit and the infratemporal fenestra, respectively
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