theropod from the Late CretaceousCerro del Pueblo Formation of Coahuila in Mexico. The genus contains a single species, P. normalensis, which is known from a few bones of tail, hips, hands, and feet. The specific epithet was given in honor of the Benemérita Normal School of Coahuila, a teacher training institution, where the fossils were reposited. It is a member of the family Deinocheiridae and is the only member of that clade known from Laramidia.[2]
Discovery
An outcrop of the Cerro del Pueblo Formation, where Paraxenisaurus was found
During the 1990s,
paleontologists Claudia Inés Serrano-Brañas, Belinda Espinosa-Chávez, Sarah Augusta Maccracken, Cirene Gutiérrez-Blando, Claudio de León-Dávila and José Flores Ventura.[2]
The
caudal vertebrae. Each named specimen consists of several bones that were disarticulated when they were found. However, the authors of the description stated that all the bones of each specimen were found in association with one another and were almost certainly from the same animal.[2]
Description
Hypothetical life reconstruction of Paraxenisaurus based on Deinocheirus and Beishanlong
The known remains of Paraxenisaurus are highly incomplete, and it is not known how
fossilized, so making an accurate estimate of their full size in life is very difficult. The authors who described the fossils estimated that Paraxenisaurus was about 5.7 metres (19 ft) long and weighed about 600 kilograms (1,300 lb). They suggested this based on the size estimates for the similarly-sized and more completely known genus Beishanlong, which is believed to be a close relative.[2]
The holotype specimen, BENC 2/2-001, is relatively fragmentary, but it preserves enough detail to identify Paraxenisaurus as a genus of
ginglymoid distal articular surface of the third metatarsal, and broad, strongly curved toe claws with enlarged and vertical proximodorsal processes.[2]
One of the manual claws of Paraxenisaurus with a ruler for scale
Several other specimens were found at nearby localities. These include BENC 1/2-0054 (a few metacarpal and phalanx elements), BENC 1/2-0091 (part of a femur, several toe fragments, and vertebrae), BENC 1/2-0092 (caudal vertebrae), BENC 30/2-001 (two pedal unguals). The quality of their preservation varies considerably between the specimens. While these elements were described in detail by Serrano-Brañas and colleagues, they were not used to diagnose the genus.[2]
Paraxenisaurus had distinct morphology from many other ornithomimosaurs in several regards. Their caudal vertebrae were highly elongated in comparison with most other ornithomimosaurs, with only
In their 2020 description of Paraxenisaurus, Serrano-Brañas and colleagues conducted a
ornithomimosaurs[2] using the data set developed by Jonah Choiniere and colleagues in 2012[3] combined with character information compiled by Hans Dieter-Sues and Alexander Averianov in 2016.[4] Their analysis included 103 taxa coded for 568 characters, including most named ornithomimosaur taxa.[2]
In their analysis, they were able to assign Paraxenisaurus to ornithomimosauria based on the following
phalanges between Paraxenisaurus, Deinocheirus, and Garudimimus. Their analysis differed from previous analyses such as that from Yuong-Nam Lee and colleagues in 2014 in that they recovered Beishanlong as a basal ornithomimosaur outside Deinocheiridae in a polytomy with Pelecanimimus and Shenzhousaurus.[2][5] They also recovered Harpymimus as a deinocheirid, in a more basal position than Deinocheirus, Paraxenisaurus, and Garudimimus.[2] This was consistent with the results of Dieter-Sues and Averianov (2016).[4] An abbreviated version of the consensus tree they provide can be seen below.[2]
The most recent phylogenetic analysis to be conducted which included Paraxenisaurus was the one published by Soki Hattori and colleagues in 2023 in their description of the new genus Tyrannomimus. Their analysis was compiled from most of the same data, and they obtained the same results with respect to Deinocheiridae. They found Harpymimus as being basal to a polytomy which included Deinocheirus, Garudimimus, and Paraxenisaurus, but not Beishanlong, which has been previously recovered as a member of Deinocheiridae.[6]
Paleoecology
Coexistence with other ornithomimosaurs
Paraxenisaurus is the first
caudal vertebrae. A large portion of this material is more slender or lightweight than the holotype or referred specimens of Paraxenisaurus. It is difficult to determine if these elements are from unique taxa or juvenile Paraxenisaurus individuals, so the precise ecological diversity of the ornithomimosaur fauna of the Cerro del Pueblo Formation remains uncertain pending further study. However, several of the morphological differences between the unnamed specimens and referred specimens of Paraxenisaurus are believed to relate to characteristics which are not a result of ontogeny, such as the proximal processes on the unguals.[2]
Paleoenvironment
A reconstruction of North America during the Campanian
The
bivalves suggests a heavily vegetated riverine ecosystem. The abundance of dinosaur teeth and bone fragments also suggests that the region was replete with vegetation and supported a diverse assemblage of megafauna.[7]
lived in this environment in addition to the above mentioned ornithomimosaurs.
A reconstruction of Velafrons in the environment of the Cerro del Pueblo Formation
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