Velafrons

Holotype CPC-59 was found in the layer of the Cerro del Pueblo formation dating to about 73.5 Ma, Coahuila , Mexico . In 1986, the Royal Ontario Museum launched the first major paleontological expedition to the Cerro del Pueblo Formation. Their efforts were concentrated on clusters of hadrosaurids bones around the city of Presa de San Antonio and individual collections from the city of Rincon Colorado. From 1992 to 2001, a skeleton of a new lamboseosaurin without cranial material was removed from quarry 7A near this city. In 2002, a joint expedition involving the Utah Museum of Natural History , the Royal Tyrrell Paleontological Museum, and the Saltillo Desert Museum resumed excavations at 7A, mining a skull and several cervical vertebrae. The skull and the postcranial skeleton of the holotype are dissected (with the exception of the roof of the skull), but are tightly connected in a highly cemented calcareous gray mudstone.

The holotype includes the almost complete left and right premaxillary and jaw bones, the right zygomatic, nasal and square bones, mainly the full roof of the skull, the dentary bones (excluding teeth) and the partial postcranial skeleton. The latter was not described by the authors.

The velafrons holotype, apparently, is a half-adult individual. This opinion is based on the relative size and degree of development of the ridge, as well as on a comparison with the total size of the skull in other specimens of young lambaeosaurins. Nevertheless, despite the incompletely developed crest, the sample possesses a number of taxonomically important characters that can be separated from ontogenetic changes. With the exception of size, the morphology of the zygomatic and square bones does not significantly change during the growth process, in addition, these elements are morphologically practically indistinguishable from adults in the adolescent stage of growth. As a result of this, the diagnostic signs present in these elements of the Velafrons are considered valid and are not the result of ontogenetic changes. On the contrary, the postorbital bone undergoes significant changes in ontogenesis. Young individuals lack a fully developed crest and the scaly process of the orbital bone is located almost horizontally, but with growth, the scaly process turns dorsally, since the most caudal edge of this process articulates with the rising protrusion of the scaly bone. The degree of inclination depends on the height of the protrusion of one or another kind of lamboseosaurins. Velafrons, however, is outside the well-known range of variation of this feature. The scaly process then rises almost vertically and levels contact with the protrusion of the scaly bone ^[1] .

Velafrons is characterized by the following autapomorphies : a square bone with a narrow square-cheeked notch; the postorbital bone with a dorsally arching scaly process; ceratobranchial (bone; part of a hyoid) with a rounded front end; as well as a unique set of features: a flat fan-shaped comb formed by the nasal and premaxillary bones; the zygomatic bone with a poorly developed posterioventral protrusion located more posterior than in other lambaeosaurins; anteriorly bent posterior process and well-developed ascending scaly protrusion ^[1] .

According to the results of phylogenetic analysis using 94 characters for 18 taxa, the Velafrons forms a polytomy with a coritosaurus , olorotitan , a clade consisting of two types of hypacrosaurs , and a clade that includes two types of lambeosaurs . All these taxa have a fan-shaped crest, but the crest of a velafrons looks more like crests of a coritosaurus and a hypacrosaurus than it does a lambeosaur or olorotitan. The coritosaurus and the hypacrosaurus have long, branched anterior processes of the nasal bones that surround the dorsal process of the maxilla. The latter, in turn, lies on the nasal bone between these processes. The relationship between the anterior process of the nasal bone and the dorsal process of the premaxillary is unique for these two taxa. The Velafrons have a long anterior process of the nasal bone, as in the Coritosaurus and Hypacrosaurus, but in the typical specimen of the dinosaur this part of the crest has not been preserved, therefore, the exact morphology cannot be established. Interestingly, despite the fact that the velafrons and amurosaurus have many similar features, including the morphology of the zygomatic bone and the raised posterior process of the orbital bone, the amurosaurus is positioned as a taxon more primitive to velafrons ^[1] .

Cladogram based on research by Prieto-Marquez and colleagues, 2013 ^[2] :