mesosuchians

Mesosuchians are an extinct informal group of mesosuchian crocodylomorphs. This group lived from the Early Jurassic to the Late Cretaceous periods. They are characterized by a transitional form between primitive crocodylomorphs and the more advanced eusuchians. Mesosuchians were a diverse group, inhabiting freshwater and possibly some brackish environments. Their anatomy often displayed a mosaic of primitive and derived features.

Notable mesosuchian families include the Goniopholididae, known for their robust build and osteoderms, and the Pholidosauridae, which were generally more slender and had a more advanced skull morphology. Another significant family was the Dyrosauridae, which survived the Cretaceous-Paleogene extinction event and persisted into the Eocene, showcasing a remarkable adaptation to marine or estuarine environments.

The evolutionary position of mesosuchians is crucial for understanding the development of modern crocodilians. They represent a significant branch on the crocodylomorph family tree, bridging the gap between earlier forms and the direct ancestors of extant crocodiles. Their fossil record provides valuable insights into the paleobiogeography and evolutionary trends within the group during the Mesozoic Era. The group's eventual decline and replacement by eusuchians in many ecological niches is a testament to the dynamic nature of vertebrate evolution.