asteroideans

Asterodeans are a group of extinct marine reptiles that belonged to the order Thalattosauria, which thrived during the Late Triassic period, approximately 228 to 201 million years ago. These reptiles were semi-aquatic predators, adapted to life in both water and on land, though they were primarily marine. The name "Asterodeans" is derived from the genus *Asterodeus*, one of the earliest known thalattosaurs, though the term is sometimes used more broadly to refer to all members of the Thalattosauria.

Asterodeans were characterized by their elongated, streamlined bodies, which resembled those of modern-day dolphins or crocodiles. They typically measured between 1.5 to 3 meters (5 to 10 feet) in length, though some species may have grown larger. Their skulls were elongated with sharp teeth, indicating a diet primarily consisting of fish and possibly other marine reptiles. Their limbs were modified into flippers, suggesting they were strong swimmers capable of navigating open ocean environments.

Fossil evidence of asterodeans has been found primarily in marine sedimentary deposits across Europe, Asia, and North America. The most well-known fossils come from sites in Germany, China, and the southwestern United States. These reptiles likely played a significant ecological role in their ecosystems, occupying a niche similar to that of modern marine predators like seals or sharks.

The extinction of asterodeans coincided with the end-Triassic mass extinction event, which wiped out many species across multiple groups. Their disappearance may have been linked to environmental changes, including volcanic activity, climate shifts, and oceanic anoxia, which altered marine habitats and food availability. Despite their extinction, asterodeans remain an important subject of study in paleontology, offering insights into the evolution of marine reptile adaptations and the ecological dynamics of the Late Triassic seas.