Unquillosaurus (/"oon-kee-loh-SORE-us"/; "Unquillo river lizard") is a genus of possible maniraptoran theropod dinosaur from the Late Cretaceous (Campanian age), approximately 75 million years ago. Its remains were discovered in the Bajo de la Carpa Formation of Patagonia, Argentina. Paleontologist Jorge Powell initially described it in 1979.

Description and Classification

The classification of Unquillosaurus is uncertain, with ongoing debate among paleontologists about its placement within the theropod group. Here's what we can say about it so far:

  • Theropod Characteristics: It was a bipedal carnivore within the wider Theropoda group.
  • Possible Maniraptoran: Some analyses suggest it may belong to the Maniraptora clade, a group of theropods including birds and their close relatives like dromaeosaurids (raptors) and oviraptorosaurs.

Distinguishing Features

Unfortunately, Unquillosaurus is known only from fragmentary remains, including:

  • Pubis: A partial left pubis bone (part of the pelvis).
  • Other Bones: Fragments of vertebrae and limb bones.

These limited remains make it difficult to determine its overall size, appearance, and its exact relationship to other theropods.

Paleoenvironment and Diet

The Bajo de la Carpa Formation represents a semi-arid environment with river systems and floodplains. As a carnivorous theropod, Unquillosaurus likely preyed upon smaller dinosaurs, lizards, and mammals. Potential neighbors could have included other theropods, titanosaurian sauropods, and possibly early hadrosaurs.

Significance and Ongoing Research

While currently enigmatic due to incomplete fossils, Unquillosaurus still offers some valuable insights:

  • Theropod Diversity: It adds to our understanding of theropod diversity in South America during the Late Cretaceous.
  • Maniraptoran Possibilities: Even with its uncertain classification, it hints at the potential presence of maniraptorans in this region during the Late Cretaceous.

Future discoveries in the Bajo de la Carpa Formation could unearth more complete remains of Unquillosaurus, finally clarifying its appearance and position within the theropod family tree.

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