Huehuecanauhtlus

The holotype and the relevant material were found in 2003 in the location of Barranca Los Bonetes in layers of a nameless formation dated to Santono , a late Cretaceous, in the state of Michoacan , Mexico . The remains were dispersed over an area of ​​1.5 m². All bones are dissected, with the exception of two dorsal vertebrae and seven spinous processes of the sacral vertebrae. Most skeletal elements found in fragmented, incomplete or deformed state. There was a slight shift. The proximity of the bones to each other indicates that they all most likely belong to the same individual. The absence of neurocentral sutures suggests that the individual at the time of death was semi-adult or adult. Among the remnants of Huehuecanauhtlus , two teeth and a Theropod chevron were found. In another part of the site, dinosaur remains were found, attributed to Huehuecanauhtlus . They are also incomplete and dissected. There was a significant transfer. In size belong smaller than the holotype, individuals.

The holotype of IGM 6253 includes a partial left jawbone, a fragment of dentary, 4 cervical vertebrae (including an epistrophy ), 9 dorsal vertebrae, 4 spinous processes of the dorsal vertebrae, one diapophysis of the spinal vertebra, 5 right and 7 left dorsal ribs, 7 spinous processes processes of the sacral vertebrae, 7 diapophysis of the sacral vertebrae and one caudal, 3 caudal vertebra, 2 spinous processes of the caudal vertebrae, 8 fragmentary petrified tendons, partial left and right iliac and pubic bones.

Paratype IGM 6254 includes a fragment of the left dentary, two teeth, and one presigapophysis of the cervical vertebra ^[1] .

Huehuecanauhtlus has a unique combination of the following features: two teeth are located on the occlusal plane of the rostral third of the dentary and the posterior third of the jawbone; seven sacral vertebrae; spinous processes of the posterior vertebrae 3.5–4 times as large as the corresponding vertebral bodies; the nadectile process has a length of 75% of the length of the central plate of the Ilium, its apex is above the posteroventral angle of the sciatic tubercle, as in Claosaurus agilis ; a short and trapezoidal (in lateral projection) rolling trail process of the Ilium, whose length is less than 80% of the length of the central plate of the Ilium. Also, Huehuecanauhtlus differs from other hadrosauroids by the presence of a strongly curved prevertal process of the ilium, the long axis of which forms an angle with the horizontal plane formed by the sciatic and pubic legs, less than 130 degrees. Huehuecanauhtlus differs from other basal hadrosauroids in the strongly concave profile of the dorsomedial edge of the iliac bone adjacent to the supracarpal process ^[1] .

Based on a study of Prieto-Marquez, 2010, phylogenetic analysis was performed using 287 characters (197 cranial and 90 postcranial) for 90 taxa. As a result of the analysis, 113 the most economical trees were obtained. A strict consensus displays the Huehuecanauhtlus part of the great politomy of the basal hadrosauroids. However, the most consistent subtree displays Huehuecanauhtlus , as the closest external taxon to the family of hadrosaurids ^[1] .

A cladogram based on a 2012 study by Ramirez-Velasco and colleagues:

Since everyone close to the clade including Huehuecanauhtlus , as well as the last common ancestor and all his descendants, hadrosauroids (for example, Gilmoreosaurus , Bactrosaurus ) were widely distributed in Asia , the existence of a new Mexican species in southern North America in Santon can be attributed to migration from Asia to North America no later alba . Another explanation is that the last common ancestor of this clade could have spread widely throughout Asia and North America; Following this scenario, the presence of Huehuecanauhtlus in North America can be the result of a vicariate ^[1] .