Paraxenisaurus (/pɛərəkˌsɪniːˈsɔːrəs/, meaning "strange lizard") is an extinct genus of ornithomimosaurian theropod from the Late Cretaceous Cerro del Pueblo Formation of Coahuila in Mexico.

In 2020, they were named and described by Mexican paleontologists Claudia Inés Serrano-Brañas, Belinda Espinosa-Chávez, Sarah Augusta Maccracken, Cirene Gutiérrez-Blando, Claudio de León-Dávila and José Flores Ventura.

It consists of a manual phalanx, an astragalus, a calcaneum, and several bones of the feet including a partial metatarsal, several pedal phalanges, and unguals.

[2] The known remains of Paraxenisaurus are highly incomplete, and it is not known how ontogenetically old the known specimens were when they died and became fossilized, so making an accurate estimate of their full size in life is very difficult.

These synapomorphies include: laterally-compressed hand claws with a deep sulcus along the flexor tubercle, a proximally-expanded articular surface of the third metacarpal, the presence of a first pedal digit, a semi-ginglymoid distal articular surface of the third metatarsal, and broad, strongly curved toe claws with enlarged and vertical proximodorsal processes.

The anterior portion of the tail of Paraxenisaurus was also likely quite stiff and rod-like in comparison with related taxa and it likely had very little dorsoventral mobility based on the articulation of the zygapophyses.

Serrano-Brañas and colleagues also noted that Paraxenisaurus has numerous morphological similarities to an unnamed taxon from the Dinosaur Park Formation, known only as TMP 1967.19.14.

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.

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] Paraxenisaurus is the first ornithomimosaur to be named from the Cerro del Pueblo Formation, but several specimens from the area are known which are believed to be distinct taxa.

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.

The abundance of dinosaur teeth and bone fragments also suggests that the region was replete with vegetation and supported a diverse assemblage of megafauna.

Teeth from theropods are very common and have shown that tyrannosaurids, dromaeosaurids, troodontids,[8] and caenagnathids[9] lived in this environment in addition to the above mentioned ornithomimosaurs.

[8] Like most fluvial sediments from the Campanian of Laramidia, the Cerro del Pueblo Formation was home to a wide array of turtles including pleurodires, paracryptodires, cheloniids, kinosternids, and trionychids.