Tuesday, March 20, 2018

[Paleontology • 2018] Arkansaurus fridayi • A New Ornithomimosaur from the Lower Cretaceous Trinity Group of Arkansas


Arkansaurus fridayi  Hunt & Quinn, 2018


Illustration by Brian Engh   twitter.com/GreyGriffon 

ABSTRACT
Whereas ornithomimosaurs (ostrich-mimic dinosaurs) are well known from Asia during the Early Cretaceous, they are less well known from this time in North America. Represented by a single specimen consisting of pedal elements, a new North American taxonArkansaurus fridayi, gen. et sp. nov., consists of a nearly complete right foot, recovered from the Lower Cretaceous (Albian–Aptian) Trinity Group of Arkansas. Arkansaurus fridayi can be distinguished from other ornithomimosaurs based on differentiated pedal unguals, a laterally compressed third metatarsal that is ovoid in proximal view, and a distal ungual with a very weak flexor tubercle, lacking spurs. The condition of this third metatarsal suggests that Arkansaurus fridayi is more basal than Asiatic ornithomimosaurs of similar age, but consistent with older North American forms. This specimen provides knowledge of a poorly understood radiation of ornithomimosaurs in Appalachia and is the only known saurischian dinosaurian fossil from the state of Arkansas.


FIGURE 3. Arkansaurus fridayi, UAM-74–16-1 to UAM-74–16-3, holotype,
articulated right metatarsals, in A, proximal and B, anterior views. Scale bar equals 10 cm. 

FIGURE 4. Arkansaurus fridayi, holotype, digital surface scans of pedal phalanges.
 UAM-74–16-5, phalanx II-1, in A, proximal, B, distal, C, extensor, D, flexor, E, lateral, and F, medial views.
UAM-74–16-4, phalanx III-1, in G, proximal, H, distal, I, extensor, J, flexor, K, lateral, and L, medial views.
UAM74–16-6, phalanx IV-1, in M, proximal, N, distal, O, extensor, P, flexor, Q, lateral, and R, medial views.
UAM-74–16-7, phalanx III-2, in S, proximal, T, distal, U, extensor, V, flexor, W, lateral, and X, medial views.
 UAM-74–16-8, large ungual, in Y, extensor, Z, lateral, AA, flexor, BB, medial, and CC, proximal views.
UAM-74–16-8, ungual, in DD, proximal, EE, extensor, FF, lateral, GG, flexor, and HH, medial views.
UAM-74–16-8, small ungual, in II, extensor, JJ, lateral, KK, flexor, and LL, medial views.
Scale bar equals 10 cm.

SYSTEMATIC PALEONTOLOGY 
DINOSAURIA Owen, 1842 
SAURISCHIA Seeley, 1887 
THEROPODA Marsh, 1881; Gauthier, 1986 
ORNITHOMIMOSAURIA Barsbold, 1976; Lee et al., 2014 

ARKANSAURUS FRIDAYI, gen. et sp. nov.

Etymology—The genus is named for the state of Arkansas, where the specimen was discovered. The species name is in honor of Joe B. Friday, who discovered the remains in 1972.

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CONCLUSION:
Arkansaurus fridayi currently is one of the oldest basal ornithomimosaurs known from North America. Its occurrence in the southeastern portion of the North American continent is significant biogeographically, because most of the Early Cretaceous basal ornithomimosaurs were flourishing in Asia at the time, but are otherwise not well represented in North America. Further discoveries of similar ornithomimosaur taxa in North America will provide better understanding of additional, currently unknown, characters.



 ReBecca K. Hunt and James H. Quinn. 2018. A New Ornithomimosaur from the Lower Cretaceous Trinity Group of Arkansas. Journal of Vertebrate Paleontology. DOI:  10.1080/02724634.2017.1421209

   

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