Monday, July 15, 2019

[Paleontology • 2019] Aquilarhinus palimentus • An Unusual ‘Shovel-billed’ Dinosaur with Trophic Specializations from the early Campanian of Trans-Pecos Texas, and the Ancestral Hadrosaurian Crest

Aquilarhinus palimentus 
Prieto-Márquez, Wagner & Lehman, 2019

We describe a new genus and species of hadrosaurid dinosaur, Aquilarhinus palimentus, from the lower shale member of the Aguja Formation (lower Campanian) of Big Bend National Park, south-western Texas. This species is characterized by several autapomorphies of the facial skeleton and mandible, including a crest composed of broadly arched nasals. Notably, the symphyseal processes of the dentary are elongated and reflected dorsally, causing the dentaries to meet with a ‘W’-shaped anterior profile. A hypothesized shovel-shaped ‘bill’, associated with widening of the skull, in A. palimentus might have been used in shovelling out and scooping up semiaquatic vegetation. This animal is otherwise superficially similar to kritosaurins like Gryposaurus but differs in the retention of key plesiomorphic character states in the maxilla and jugal. Phylogenetic analysis reveals Aquilarhinus to be a non-saurolophid hadrosaurid allied to Latirhinus from the late Campanian of Mexico, which bears a similar broadly arched nasal. The recognition of this lineage adds to the diversity of non-saurolophid hadrosaurids and points to the existence of a hitherto unknown diversity of ‘duck-billed’ dinosaurs outside of the saurolophine-lambeosaurine radiation. Cranial crests were ancestral for early hadrosaurids and evolved before the saurolophid radiation. Ancestrally, crests were ‘solid’, and consisted of arched nasals. These were retained among kritosaurins and subsequently modified into the diverse crest morphologies observed among derived saurolophines. Lambeosaurine ‘hollow-crested’ crest morphology departed from the ancestral, ‘solid-crested’ pre-saurolophid condition early following the origin of that clade.

Keywords: Dinosauria, Hadrosauridae, phylogeny, evolution, Cretaceous, North America

The dentary of Aquilarhinus, showing the unusual upturned end of the mandible.

Photo by Albert Prieto-Marquez;
material housed at the Texas Vertebrate Paleontology Collections at The University of Texas at Austin.

Systematic palaeontology
Dinosauria Owen, 1842 
Ornithischia Seeley, 1887 
Ornithopoda Marsh, 1881 

Iguanodontia Dollo, 1888 
Hadrosauridae Cope, 1870 (sensu Prieto-Márquez, 2010)

Aquilarhinus gen. nov.

Type species. Aquilarhinus palimentus sp. nov.

Etymology. From the Latin ‘aquila’, meaning ‘eagle’, and the Greek ‘rhinos’, meaning ‘nose’. The combination of these two words references the morphology of the rostrum.

Aquilarhinus palimentus sp. nov.

Kritosaurus sp. nov. Wagner, 2001; Wagner & Lehman, 2001  

Etymology. The specific name is a combination of the Latin words ‘pala’, shovel, and ‘mentus’, chin, in reference to the assumed resemblance of the predentary to a spade or shovel given the dorsomedial projection of the symphyseal process of the dentary.

Albert Prieto-Márquez, Jonathan R. Wagner and Thomas Lehman. 2019. An Unusual ‘Shovel-billed’ Dinosaur with Trophic Specializations from the early Campanian of Trans-Pecos Texas, and the Ancestral Hadrosaurian Crest. Journal of Systematic Palaeontology.    DOI: 10.1080/14772019.2019.1625078

Strange new species of duck-billed dinosaur identified via @physorg_com