Poekilopleuron (meaning 'varied ribs') is an extinct genus of large basal megalosauroid tetanuran theropod dinosaur, perhaps belonging to the clade Allosauroidea.[1] It measured 9 metres (30 feet) long and 1 ton (1 tonne) in mass. It dates from the Bathonian (Middle Jurassic), 168 to 165 million years ago.

Discovery and namingEdit

Poekilopleuron is a genus of theropod with a long and complex history. The genus was first named and described by Jacques Amand Eudes-Deslongchamps in 1838, based on holotype material that is now destroyed. The holotype, which was housed in Musée de la Faculté des Sciences de Caen and destroyed during World War II, included gastralia, phalanges, a left forelimb, caudal vertebrae, chevrons, ribs and a hindlimb. Of all the material, few is still preserved, although the gastralia, phalanges and forelimb were casted and now represent the plastotype, with casts in the Muséum National d'Histoire Naturelle (specimen MNHN 1897-2) and Yale Peabody Museum (specimen YPM 4938). The original material was uncovered in a layer of the Calcaire de Caen in Normandy, France. Poekilopleuron can be assigned to the middle Bathonian in age,[1] about 167.7 to 164.7 million years ago.[2]

In the same 1838 publication, Eudes-Deslongchamps also named the type species of Poekilopleuron, P. bucklandii.[3] Eudes-Deslongchapms noted similarities with some material of Megalosaurus bucklandii and Poekilopleuron, and chose the species name bucklandii for Poekilopleuron, so that it the two genera were synonymized, only the genus name would be suppressed.[1] The generic name is derived from Greek ποίκιλος, poikilos, "varied", and πλευρών, pleuron, "rib", a reference to the three types of rib present. The specific name, honouring William Buckland, was deliberately identical to that of Megalosaurus bucklandii.


Poekilopleuron is a hard taxon to classify, as its original material is lost, and few casts are known. Poekilopleuron has a history of being renamed under different species and genera, most of which are now its junior synonyms.

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.[4] Eudes-Deslongchamps' choice caused problems however, when Friedrich von Huene in 1923 concluded it was part of Megalosaurus but as a separate 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.[citation needed]

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 as Poecilopleuron and Poikilopleuron (still used as late as 2006). However, the original name has priority and is valid.[citation needed]

Five other species would be named in the genus. In 1869 Edward Drinker Cope renamed Laelaps gallicus into Poekilopleuron gallicum.[citation needed] In 1870 Joseph Leidy created a Poicilopleuron valens based on a fossil probably belonging to Allosaurus.[5] In 1876 Richard Owen named a Poikilopleuron pusillus, in 1879 renamed by Cope to Poekilopleuron minor; in 1887 Harry Govier Seeley made it a separate genus: Aristosuchus.[6] In 1883 W.A. Kiprijanow created a Poekilopleuron schmidti, of which the specific name honours Friedrich Schmidt[disambiguation needed], based on some indeterminate ribs and a sauropod metatarsal.[7] This chimaera is a nomen dubium. A much later named species is Poekilopleuron valesdunensis created by Ronan Allain in 2002.[8] In 2005 it was renamed Dubreuillosaurus.


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