| Lapparentosaurus | |
|---|---|
 | |
| Partial left femur | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | †Sauropodomorpha |
| Clade: | †Sauropoda |
| Clade: | †Gravisauria |
| Clade: | †Eusauropoda |
| Genus: | †Lapparentosaurus Bonaparte, 1986 |
| Species: | †L. madagascariensis |
| Binomial name | |
| †Lapparentosaurus madagascariensis Bonaparte, 1986 | |
Lapparentosaurus is agenus ofsauropoddinosaur from the MiddleJurassic. Itsfossils were found inMadagascar (Isalo III Formation). It contains one species,Lapparentosaurus madagascariensis. The genus and species were named by José Bonaparte in 1986. The classification ofLapparentosaurus is controversial, as it exhibits a combination of characteristics of basal sauropods andtitanosauriforms.
In 1895Richard Lydekker named a new species ofBothriospondylus,B. madagascariensis based on fossils found before 1894 byJoseph Thomas Last in theMajunga Basin in layers of theBathonian, theIsalo III Formation.[1] In a 1975 unpublished thesis, A. Ogier described a large amount of juvenile sauropod material, also from the Isalo III Formation, that he identified as more specimens ofBothriospondylus. In 1986,José Fernando Bonaparte considered the referral of all the Malagasy sauropod material toBothriospondylus to be unjustified, and due to the distinctiveness of the material described by Ogier, Bonaparte proposed the new genus and speciesLapparentosaurus madagascariensis for it. He designated two neural arches of dorsal vertebrae, MAA 91-92, as theholotype of his new species.[2] The generic name honoursAlbert-Félix de Lapparent.
Upchurch and colleagues considered Bonaparte's diagnosis ofLapparentosaurus to be inadequate, but accepted it as a valid taxon due to its unusual combination of characteristics oftitanosauriforms and basal sauropods.[3]
Much more abundant material has been referred, from at least three but perhaps as much as ten individuals from different growth stages. This includes vertebrae and limb elements but no skulls.Age determination studies performed using growth ring counts suggest that this sauropod took 31–45 years to reach sexual maturity[4] and was relatively fast-growing given the presence of a large amount of fibrolamellar bone.[5]
The phylogenetic position ofLapparentosaurus was long poorly understood. It exhibits an unusual combination of characters of both basal and derived sauropods.[3] It has been classified as a brachiosaurid or an indeterminate titanosauriform.[3] However, recent phylogenetic analyses have shown it to be a basal eusauropod, not closely related to brachiosaurids at all.[6] After many decades, Emilie Läng in 2008 recovered a traditionalCetiosauridae includingLapparentosaurus.[7] An in-depth revision in 2019 of the genus by Raveloson, Clark & Rasoamiaramana recovered a similar position withLapparentosaurus being part of a paraphyletic Cetiosauridae, also including a multitude of similar Middle Jurassic cetiosaurids such asChebsaurus,Ferganasaurus, andCetiosaurus.[8] This position is supported by the presence of two autapomorphies common on bothLapparentosaurus andCetiosaurus: a pyramid-shaped neural spine from the anterior dorsal vertebrae with tapering in shape or not flaring distally and loss of the spinodiapophyseal lamina on the dorsal vertebrae.[8]
All possible remains ofLapparentosaurus:
