Temporal range: Middle Jurassic
|An artist's interpretation of Poekilopleuron bucklandii|
| †Poekilopleuron bucklandii|
Poekilopleuron (meaning "various ribs") is an extinct genus of large basal tetanuran theropod dinosaur, perhaps belonging to the clade Allosauroidea. It grew 30 feet in length and weighed 1 ton in mass. The genus comes from the Middle Jurassic (Bathonian stage) of France, about 168 to 165 million years ago.
Poekilopleuron is known from a partial skeleton discovered by Jacques Amand Eudes-Deslongchamps in July 1835 near La Maladrerie in Normandy, France, in a layer of the Calcaire de Caen Formation. This skeleton, part of the collection Musee de la Falcutee des Sciences de Caen, was in 1944 destroyed during the Battle of Caen in World War 2, and the taxon has since had to be studied on the basis of cast replicas. One set is present in the Museum National d'Histoire Naturelle in Paris with inventory number MNHN 1897-2, a second in the Yale Peabody Museum, YPM 4938. The remains consisted of caudal vertebrae, cervical ribs, ribs, belly ribs (gastralia), a forelimb and a hindlimb.
Eudes-Deslongchamps named the type species Poekilopleuron bucklandii in 1837 or 1838. The generic name comes from the Greek poikilos, "varied" or "various", and pleuron, "side" or "rib". The name describes the three types of rib present. The only known species, P.bucklandii, honoring William Buckland, is very identical to that of Megalosaurus bucklandii. Eudes-Deslongchamps thought the specimen might well be proven to belong to this earlier named species; if so, merely the generic name would have to be changed. Indeed, following 1879, Poekilopleuron was often subsumed under Megalosaurus bucklandii. Eudes-Deslongchamps' choice caused problems however, when Friedrich von Huene in 1923 concluded it was part of Megalosaurus but as a seperate species within that genus. As both species carried the same epithet bucklandii, they could no longer be distinguished. Von Huene therefore renamed the species into Megalosaurus poekilopleuron. Most later authors continued using the generic name Poekilopleuron.
Another problem was caused by the fact that the name was only partially latinised. In correct Greek it would have been "poikilopleuron", in Latin "poecilopleurum". This induced later writers to improve the spelling, leading to such variants such as Poecilopleuron and Poikilopleuron (still used as late as 2006). However, the original name has priority and is valid.
Five other species would be named in the genus. In 1869 Edward Drinker Cope renamed Laelaps gallicus into Poekilopleuron gallicum. In 1870 Joseph Leidy created a Poicilopleuron valens based on a fossil probably belonging to an Allosaurus. In 1876 Richard Owen named a Poikilopleuron pusillus, in 1879 renamed by Cope to Poekilopleuron minor, in 1887 Harry Govier Seeley made it a seperate genus: Aristosuchus. In 1883 W.A. Kiprijanow created a Poekilopleuron schmidti, of which the specific name honors Friedrich Schmidt, based on some indeterminate ribs and a sauropod metatarsal. This chimera is a nomen dubium. A much later named species is Poekilopleuron valesdunensis created by Ronan Allain in 2002. In 2005 it was renamed Dubreuillosaurus valesdunensis.
The most distinctive feature of Poekilopleuron were its forelimbs. Their length, about 2 feet long, was a sign of this theropod's more original build. Unlike later Theropoda, whose forelimbs tened toward reduction in length in proportion to the animal's body size, Poekilopleuron's arms were long and, by implication, potent. The length mostly resided in the elongated but powerfully muscled humerus. The antebrachia (forearms) were markedly short and robust, a characteristic shared with Poekilopleuron's slightly larger and considerably American cousin Torvosaurus. A unique feature is the lack of the olecranon process on the ulna.
Because the original fossil was destroyed and no other remains of Poekilopleuron have since been found, and also because of its name change, there is much controversy surrounding its classification that cannot be resolved.