illisilla

Illisilla is a genus of extinct marine reptiles belonging to the order Plesiosauria, specifically within the family Polycotylidae. The genus was first described in 2021 based on fossil remains discovered in the Late Cretaceous deposits of the Western Interior Seaway in North America. The type species, Illisilla ad Parnassum, is known from a remarkably complete fossil skeleton.

Key characteristics of Illisilla include its relatively small size compared to other polycotylids, with an estimated body length of around 3 meters. It possessed a short neck and a long, narrow skull, features common to polycotylids, which are thought to have allowed for rapid prey capture. The limbs were paddle-shaped, adapted for efficient swimming.

The discovery of Illisilla provides further insight into the diversity and evolution of plesiosaurs during the final stages of the Cretaceous period. Its phylogenetic placement within Polycotylidae highlights the adaptive radiation of this group in shallow marine environments. The specific anatomical details of Illisilla help paleontologists refine our understanding of the relationships between different plesiosaur families and the ecological roles they occupied. Further research on its skeletal structure and potential diet continues to illuminate the life of this ancient marine predator.