| Angulomastacator | |
|---|---|
 | |
| Reconstructed skull | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Clade: | †Ornithischia |
| Clade: | †Ornithopoda |
| Family: | †Hadrosauridae |
| Subfamily: | †Lambeosaurinae |
| Genus: | †Angulomastacator Wagner & Lehman, 2009 |
| Species: | †A. daviesi |
| Binomial name | |
| †Angulomastacator daviesi Wagner & Lehman, 2009 | |
Angulomastacator (meaning "bend chewer", in reference to both the shape of its upper jaw and to theBig Bend area of theRio Grande, where thetype specimen was found) is agenus ofduck-billeddinosaur from theCampanian-aged (Late Cretaceous)Aguja Formation ofBig Bend National Park,Texas.
It is known from a single specimen,TMM43681–1, a partial leftmaxilla (the main tooth-bearing bone of the upper jaw). This bone is curved down approximately 45° at itsanterior end, with the tooth row bent to fit, unlike any other hadrosaur. The unusual characteristics of the maxilla, which have not been reported from elsewhere, supports the hypothesis that the dinosaurs of the Aguja Formation wereendemic forms. It was discovered in the upper shale member of the Aguja Formation, among plant, bone, and clam fragments in a bed interpreted as the deposits of a small tributary channel. This bed is just below rocks of the overlyingJavelina Formation.[1]
Angulomastacator is classified as alambeosaurine, the group of hadrosaurs with hollow cranial crests. It was described in 2009 by Wagner and Lehman in 2009.[1] Thetype species isA. daviesi, named for Kyle L. Davies, who in 1983 was the first to postulate the presence of a lambeosaurine in the Aguja Formation. As a hadrosaurid,Angulomastacator would have been abipedal/quadrupedalherbivore, eating plants with sets of ever-replacing teeth stacked on each other.[2]
The first reports ofLambeosaurinae from theAguja Formation ofTexas were suggested in 1983 in the thesis of American paleontologist Kyle Davies, based upon the proportions of postcranial bones.[3] While limb proportions have since been shown to not be distinctive of lambeosaurines, a later specimen was discovered in the field by a group fromTexas Memorial Museum led by American paleontologist Thomas Lehman, at the "Dawson Creek" locality TMM 43681. J. Browning discovered a partialmaxilla and somevertebrae in the dark greymudstone, with weathering to suggest that they had been transported by water from a disarticulated skeleton during a flooding event.[4][1] This locality is from the uppershale of the Aguja Formation, just below the youngerJavelina Formation, ofBig Bend, Texas, and is comparable in age to a nearbypyroclastic flow dated to 76.9 ± 1.2million years ago, suggesting a reasonable middleCampanian age of 76.6 mya.[1]
The maxilla, TMM 43681-1, shows the first clear anatomy of a hadrosaurid from Big Bend, and displayed a diagnostic downturned snout leading Lehman and Jonathan Wagner to describe it as the new taxonAngulomastacator daviesi in2009. Thegenus name is a combination of theLatin wordangulus ("angle" or "corner"),Ancient Greek word μάσταξ (mastax, "jaw" or "mouth") and the Latin suffix-tor describingagency, with the preferred translation of "bend chewer" in reference to both the location and the shape of the jaw. Thespecific name is in honor of Davies for his work on Big Bend hadrosaurs and his predictions of a lambeosaurine. Uniqueness ofAngulomastacator lends to the idea that thefauna of the Aguja Formation wasendemic and provincialized, being different from other contemporaneous faunae of similar age inAlberta andMontana.[1]
