Description and Classification

Poekilopleuron was a large carnivorous dinosaur for its time, estimated to have reached lengths of around 7 to 9 meters (23 to 30 feet) and weighed over a ton. Like other theropods, it was bipedal, meaning it walked on two powerful hind legs, and had a long tail that helped with balance. Its forelimbs, though smaller than its hindlimbs, were robust. The skull of Poekilopleuron is not well known from the original material, but it would have possessed sharp teeth suited for a predatory lifestyle.

The classification of Poekilopleuron has been a subject of debate since its discovery. It was initially compared to Megalosaurus, another large theropod from Europe. Today, most paleontologists consider Poekilopleuron to be a type of megalosauroid, a group that includes dinosaurs like Megalosaurus and Torvosaurus. It is generally placed within the family Megalosauridae. The type species is Poekilopleuron bucklandii.

Distinguishing Features

Poekilopleuron had several features that helped set it apart from other theropods:

• Its name-giving characteristic: the ribs (pleura) were “varied” (poikilos), meaning they had different forms along the rib cage. Some were slender, while others were more robust.
• The astragalus and calcaneum (ankle bones) were not fused together in the adult specimen. This was unusual for large theropods of its size and time and initially led to some confusion, as unfused ankle bones are often seen in younger animals.
• It possessed relatively long gastralia (belly ribs).
• The forearms were proportionally quite long and robust compared to many other large theropods.
• Specific features in its tail vertebrae, including chevrons (bones on the underside of tail vertebrae) that were forked.

Paleoenvironment and Diet

Poekilopleuron lived in what is now Europe during the Middle Jurassic. The environment of Normandy, France, at that time was likely a coastal or lagoonal system, with a warm climate. Fossil deposits from this area, such as the Calcaire de Caen, suggest a shallow marine-influenced environment. This ecosystem supported a variety of life, including other dinosaurs such as sauropods like Bothriospondylus, marine reptiles like plesiosaurs and ichthyosaurs, and various types of fish and invertebrates.

As a large theropod, Poekilopleuron was a carnivore and likely one of the top predators in its habitat. Its diet would have consisted of other dinosaurs, such as herbivorous ornithopods or juvenile sauropods, and it may have also scavenged carcasses.

Significance and Ongoing Research

Poekilopleuron is historically significant as one of the earliest large theropod dinosaurs to be named and described from Europe. Its discovery contributed to the early understanding of dinosaur diversity. However, the most challenging aspect of studying Poekilopleuron is that the original, nearly complete skeleton (the holotype) was housed in the Musée de la Nature de Caen and was completely destroyed during an Allied bombing raid in 1944 during World War II.

This loss means that modern research on Poekilopleuron must rely on detailed casts made before the fossils were destroyed, as well as the original 19th-century descriptions and illustrations by Eudes-Deslongchamps. Ongoing research focuses on re-evaluating these sources to better understand the anatomy of Poekilopleuron and its precise evolutionary relationships with other theropods, particularly within the Megalosauroidea. Clarifying its distinctiveness from contemporary theropods like Megalosaurus remains an important goal. The story of Poekilopleuron serves as a stark reminder of the importance of preserving fossil specimens and making detailed records and casts.