| Comahuesaurus | |
|---|---|
 | |
| Skeletal reconstruction ofC. windhauseni based on several specimens including theholotype | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | †Sauropodomorpha |
| Clade: | †Sauropoda |
| Superfamily: | †Diplodocoidea |
| Family: | †Rebbachisauridae |
| Genus: | †Comahuesaurus Carballidoet al. 2012 |
| Type species | |
| Comahuesaurus windhauseni Carballidoet al. 2012 | |
Comahuesaurus (meaning "Comahue lizard", after the region in which it was found) is agenus ofsauropoddinosaur of the familyRebbachisauridae. It was found in theLohan Cura Formation inArgentina, and lived during the EarlyCretaceous (Aptian toAlbian). Thetype species isC. windhauseni, named for Anselmo Windhausen, who contributed significantly to the geological study ofPatagonia.[1]
Theholotype ofComahuesaurus, given the specimen numberMOZ-PV 6722, was discovered on the northern slope of a locality called Cerro Aguada del Leon in the south-central area of theNeuquén Basin, which corresponds to theLohan Cura Formation. It was originally assigned toLimaysaurus sp. by Leonardo Salgado and colleagues in 2004. Despite being referred to an existing genus, the authors remarked that there were significant enough anatomical differences to justify the possible naming of a new species.[2] The discovery and preparation of additional specimens from the same bone bed as the holotype led a team of authors, including José Luis Carballidoa, Leonardo Salgadob, Diego Pola, José Ignacio Canudod, and Alberto Garridoe, to describe the new material and create the new genusComahuesaurus to contain these remains.[1]
Theholotype ofComahuesaurus, MOZ-PV 6722, consists only of a singleneural arch from a vertebra of the lower-back. However, abundant additional material was discovered from the same bone bed, and the anatomy of these additional bones were used to diagnose the new species. The authors concluded they all belonged to a single taxon, but since the exact number of individuals preserved is not known, the holotype was restricted to the single bone originally reported by Salgado.[1]
Comahuesaurus is known from abundant material compared to other rebbachisaurids. Bones from at least three individuals were excavated from the type locality and they include: 37caudal vertebrae, three partialdorsal vertebrae, part of asternum, acoracoid, a complete righthumerus, part of anilium, a completepubis bone, fiveischia, two left and three rightfemora, part of atibia, and a leftfibula. Fragmentary remains of humeri, pubes, femora were also identified. The authors did not provide a full size estimate forComahuesaurus, but they did describe the humerus as being 67.5 cm (2.21 ft) long and the femur as being 113 cm (3.71 ft) long.[1]
The authors of its description distinguishedComahuesaurus from all otherrebbachisaurids by the followingautapomorphies: a thin keel on the bottom of the dorsal vertebrae, longprezygapophyses, several distinctivelaminae on the anterior dorsal vertebrae, well-developedfossae on the front caudal vertebrae, short transverse processes on the caudal vertebrae, a very robust humerus, a straight shaft of the ischium, and an unconstricted iliac peduncle.[1]
In their phylogenetic analysis, Carballidoet al. (2012) placedComahuesaurus in an intermediate position between basal rebbachisaurids such asHistriasaurus and the derived clade formed by subfamiliesRebbachisaurinae andLimaysaurinae. It shared the reduced hyposphene-hypantrum system that would characterize more derived rebbachisaurids, but hadn't yet completely lost this structure. That change would happen at some further point in the evolution of the clade, as it is so far only known to be fully absent inLimaysaurus and its close relatives. The cladogram shown in their description is shown below.[1]
| Rebbachisauridae |
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The bonebed which preserves all known remains ofComahuesaurus is believed to have been deposited rapidly in a single catastrophic event by an ephemeral river. This could have been a flash flood, a landslide, or some other natural disaster that buried and killed the individuals which would later be fossilized. TheLohan Cura Formation, where these remains were found, is composed mainly ofsiltstones andsandstones, which means the environment was likely heavily irrigated byrivers. This is further supported by the prevalence of a variety ofturtle fossils.[3] Remains from othersauropods are also common including the rebbachisauridLimaysaurus, themacronarianLigabuesaurus, and the enigmatic genusAgustinia. Pterosaur teeth belonging toornithocheiromorphs have also been found here.[4]
