Description and Classification

Angulomastacator was a plant-eating dinosaur. Like other hadrosaurs, it likely walked on all four legs most of the time but could also stand and move on its two hind legs when needed, perhaps to reach higher vegetation or to run. It would have had a broad, duck-like beak at the front of its mouth, which was toothless and used for cropping leaves and twigs. Further back in its jaws, it possessed complex stacks of teeth called dental batteries, perfect for grinding tough plant material.

Based on the partial remains found, which consist mainly of a left upper jaw bone (maxilla), Angulomastacator is estimated to have been a medium-sized hadrosaur, possibly reaching lengths of around 7 to 9 meters (23 to 30 feet). It belongs to the family Hadrosauridae, and more specifically to the subfamily Lambeosaurinae. Lambeosaurines are known for often having elaborate, hollow crests on their heads, although a complete skull of Angulomastacator has not yet been found to confirm the shape of its crest. The discovery of a lambeosaurine like Angulomastacator in Texas from this time period is significant, as these types of hadrosaurs were thought to be less common in the southern parts of North America compared to the north during the Late Campanian age.

Distinguishing Features

Angulomastacator had unique characteristics that help paleontologists identify it:

• The most distinctive feature is a sharp, downward bend of about 45 degrees in the front part of its upper jaw bone (maxilla). This “bent chewer” feature is unlike that of other known hadrosaurs.
• It is classified as a lambeosaurine hadrosaur, a group known for their hollow head crests. Its presence in Texas during the Late Cretaceous is noteworthy for understanding dinosaur distribution.
• Like other hadrosaurs, it possessed sophisticated dental batteries, which are many small teeth packed together to form a large grinding surface, ideal for its herbivorous diet.

Paleoenvironment and Diet

Angulomastacator lived in what is now Texas during the Late Cretaceous period. The Aguja Formation, where its fossils were found, represents a coastal plain environment. This area included rivers, deltas, and was close to the ancient Western Interior Seaway. The climate was likely warm and humid, supporting a rich ecosystem with diverse plant life.

As an herbivore, Angulomastacator would have fed on the available plants, such as conifers, ferns, and early flowering plants. Its strong jaws and specialized teeth were well-suited for breaking down tough vegetation. The unique bend in its upper jaw might suggest a particular way of feeding or a preference for certain types of plants, but more fossils are needed to understand this fully. It shared its world with other dinosaurs, including horned dinosaurs like Agujaceratops, other types of hadrosaurs, armored ankylosaurs, and predatory tyrannosaurs. The waters were home to crocodilians, turtles, and fish.

Significance and Ongoing Research

The discovery of Angulomastacator is important because it provides new information about the diversity of hadrosaurs and where they lived. Its presence in Texas offers evidence that lambeosaurine hadrosaurs were more widespread in southern North America during the Campanian stage of the Late Cretaceous than previously believed. This challenges earlier ideas about distinct northern and southern dinosaur communities on the continent and suggests there might have been more mixing or movement of these animals.

Ongoing research focuses on finding more complete fossil remains of Angulomastacator. More bones would help paleontologists understand its full anatomy, including the true nature of its crest (if present) and how its unusual jaw functioned. Scientists are also interested in studying its evolutionary relationships with other lambeosaurine hadrosaurs from North America and Asia. Future discoveries in the Aguja Formation and other areas in the southern United States and Mexico could reveal more about this interesting dinosaur and the ecosystem it inhabited.