Mexidracon

MEANING: Mexican dragon

PERIOD: Late Cretaceous

CONTINENT: North America

Mexidracon is a relatively small ornithomimid theropod dinosaur at approximately 2.5 m in length. Typical of ornithomimids, it was likely covered in feathers, and had a long neck and legs. Mexidracon is notable for its extremely lengthened metacarpals, or hand bones, not seen in other ornithomimids.

Abstract from paper: New ornithomimosaur material discovered from the Upper Cretaceous Cerro del Pueblo Formation (CdP) of Coahuila, Mexico represents a new genus and species of Ornithomimidae. The new taxon, Mexidracon longimanus sp. nov., is represented by an individual preserving axial and appendicular elements. M. longimanus is characterised by the following combination of characters: extreme lengthening of the metacarpals that are longer than the metatarsals, proximal end of metacarpal II with a narrow subtriangular outline, a pubic peduncle of the ilium with a flared, zig-zag articular margin that is wider anteriorly than posteriorly and an ischiadic peduncle that is similar in size to the pubic peduncle, a pubic boot where the distal margin of the anterior expansion is separated from the shaft by a deep notch, a femur that is slightly longer than the tibia, an arctometatarsalian pes, a metatarsal II that has a D-shaped cross-section, and a metatarsal IV longer than metatarsal II, among other features. A phylogenetic analysis places M. longimanus within Ornithomimidae forming a polytomic relationship with other members of this clade. The finding of M. longimanus adds to the increasing diversity and paleobiogeographic distribution of the group during the Campanian of southern Laramidia. The ornithomimosaur record of the CdP represents yet another instance of the coexistence of ornithomimids and deinocheirids spanning a wide range of body sizes within this clade of ‘ostrich’ dinosaurs.

Mexidracon is from the Late Cretaceous. The Cretaceous is the third and final geological period of the Mesozoic Era, with the Late Cretaceous making up roughly the second half of it, lasting from about 100 to 66 million years ago. It was a time of significant evolutionary change, with dinosaurs reaching their greatest diversity before the mass extinction at the end of the Cretaceous.

The Cretaceous was a period with a relatively warm climate, though the Late Cretaceous experienced a global cooling trend, caused by falling levels of carbon dioxide in the atmosphere. The continents were nearing their present positions, but high sea levels flooded low-lying regions, turning Europe into an archipelago, and forming the Western Interior Seaway in North America. These seas were home to a variety of marine reptiles, including mosasaurs and plesiosaurs, while pterosaurs and birds shared the skies.

On land, dinosaurs continued to thrive and diversify during the Late Cretaceous, producing many of the most well-known goups, including tyrannosaurs, hadrosaurs, and pachycephalosaurs. Established Cretaceous dinosaur clades like the ceratopsians, ankylosaurs, and dromaeosaurs continued to flourish. Sauropod species consisted almost exclusively of titanosaurs, which seemed to be confined to the Southern Hemisphere for much of the Late Cretaceous. Flowering plants and grasses diversified and spread, becoming the dominant flora similar to what we see today.

The Cretaceous (along with the Mesozoic) ended with the Cretaceous–Paleogene (K–Pg) extinction event, a large mass extinction in which many groups, including non-avian dinosaurs, pterosaurs, and large marine reptiles, died out. This event, likely triggered by an asteroid impact, is marked by the abrupt K–Pg boundary, a distinct geologic layer separating the Mesozoic and Cenozoic Eras. In its aftermath, mammals and avian dinosaurs rapidly diversified, becoming the dominant land animals of the Cenozoic Era.

Mexidracon is an ornithomimosaur. Ornithomimosauria was a unique group of theropod dinosaurs whose name means "bird mimics," as their general body plan resembles modern ostriches. Part of the larger group Coelurosauria, they were characterized by their small heads, long necks, lightly built bodies, and long, powerful legs built for fast running. Most ornithomimosaurs had toothless beaks, and some evidence suggests they may have been omnivorous or herbivorous rather than strict predators like many other theropods. As they evolved, the derived ornithomimids became some of the most specialized runners of the Mesozoic Era.

Ornithomimosaur fossils have been discovered in North America, Asia, and possibly other regions, showing that they had a wide distribution by the Late Cretaceous. Their success in multiple environments suggests they were highly adaptable, capable of thriving in a variety of ecosystems ranging from floodplains to deserts. Though ornithomimosaurs were not top predators, their speed and agility likely helped them evade the larger carnivores of their time.