Description and Classification

Pycnonemosaurus was a sizable carnivorous dinosaur, estimated to have reached lengths of around 8.9 meters (29 feet). This makes it one of the largest known members of the Abelisauridae family. Like other abelisaurids, such as its distant relatives Carnotaurus and Majungasaurus, Pycnonemosaurus would have had a short, deep skull (though skull material for Pycnonemosaurus itself is scarce), extremely small and stubby forelimbs, and powerful hind legs built for walking and running.

It belongs to the group Theropoda, which includes most meat-eating dinosaurs. Within Theropoda, it is classified under Ceratosauria and more specifically, the family Abelisauridae. Abelisaurids were the dominant predators in the southern supercontinent Gondwana (which included South America, Africa, India, Antarctica, and Australia) during the Late Cretaceous. Pycnonemosaurus is considered part of a subgroup of abelisaurids called Brachyrostra, known for their particularly short snouts.

Distinguishing Features

While the fossils of Pycnonemosaurus are incomplete, scientists have identified some features that help distinguish it from other abelisaurid dinosaurs:

• It was one of the largest abelisaurids, potentially exceeding the size of many of its relatives.
• The tibia (shinbone) possessed a distinctively hatchet-shaped cnemial crest, which is a bony projection at the upper front part of the bone where leg muscles attached.
• Features of its tail vertebrae, including the shape of certain projections, are also considered characteristic.
• Its teeth were relatively small for its size and not strongly curved, though some details about serrations are uncertain due to preservation.

Paleoenvironment and Diet

Pycnonemosaurus lived in what is now central Brazil during the Maastrichtian age, the very end of the Cretaceous Period. The environment at that time, represented by the Bauru Group rock formations, was likely a semi-arid landscape with seasonal rivers and floodplains. This ecosystem supported a variety of life, including long-necked herbivorous dinosaurs like titanosaurs (such as Aeolosaurus and Baurutitan), which could have been prey for Pycnonemosaurus. Other animals in this environment included different types of crocodiles (like Baurusuchus), turtles, and fish.

As a large abelisaurid, Pycnonemosaurus was an apex predator. Its strong jaws and robust build, typical of abelisaurids, suggest it hunted large animals. Young or smaller titanosaurs would have been primary targets, but it might have also preyed on other herbivores or scavenged carcasses.

Significance and Ongoing Research

The discovery of Pycnonemosaurus is significant because it highlights the diversity of large predatory dinosaurs in South America just before the mass extinction event that wiped out the non-avian dinosaurs. It confirms Brazil as an important location for finding unique abelisaurid fossils and helps paleontologists understand the distribution and evolution of this group across Gondwana. Its large size also provides insights into the ecological structure of Late Cretaceous ecosystems, showing that very large abelisaurids were present.

Ongoing research focuses on finding more complete fossil material of Pycnonemosaurus, which would provide a clearer picture of its anatomy, especially its skull. Scientists continue to study its relationships with other abelisaurids like Abelisaurus and Skorpiovenator through phylogenetic analyses. Further investigation of the Bauru Group’s geology and fossil record will also help to better understand the world in which Pycnonemosaurus lived and hunted.