| Antarctanax | |
|---|---|
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Archosauromorpha |
| Clade: | Archosauriformes |
| Genus: | †Antarctanax Peecook et al. 2019 |
| Type species | |
| †Antarctanax shackletoni Peecook et al. 2019 | |
Antarctanax is agenus of basalarchosauriform that during theTriassic lived inAntarctica. Thetype species isAntarctanax shackletoni. It was a reptile around the size of aniguana.[1]
During a paleontological expedition to theTransantarctic Mountains in 2010 and 2011, a small skeleton was discovered at theGraphite Peak.[1]
In 2019, the type speciesAntarctanax shackletoni was named and described by Brandon Robert Peecook, Roger Malcolm Harris Smith andChristian Alfred Sidor. The generic name combines a reference to Antarctica — itself derived from Greekanti, "opposite of", andarktikos, "of theBear" — with a Greekanax, "ruler", a reference to theArchosauria, the "Ruling Reptiles". Thespecific name honoursErnest Shackleton, the polar explorer who named theBeardmore Glacier which runs along the Graphite Peak.[1]
Theholotype,UWBM 95531, was found in a layer of the lowerFremouw Formation, which dates to the Early Triassic. It consists of a partial skeleton lacking the skull. It contains eight vertebrae of the neck or back, ribs, the left humerus, all five metatarsals of the left foot, phalanges, among them the claws, of the left foot, and the almost complete right foot. Apart from the feet, the skeleton is largely disarticulated. It represents an adult individual.[1]
Antarctanax was about the size of an iguana, 1.2 to 1.5 m (4 to 5 ft) long.[2]
The describing authors indicated a unique combination of traits that in themselves are not unique. These traits prove thatAntarctanax is a distincttaxon. The cervicodorsal vertebrae, those spanning the rear neck and front back, have per side alamina centrodiapophysealis anterior, a ridge running on the front underside of the side process towards the vertebral body. The cervicodorsal vertebrae have per side alamina prezygodiapophysealis, a ridge running from the side process to the front articulation process. The cervicodorsal vertebrae have per side alamina postzygodiapophysealis, a ridge running from the side process to the rear articulation process. The cervicodorsal vertebrae lack alamina centrodiapophyseal posterior, a ridge running on the rear underside of the side process towards the vertebral body. The neck vertebrae have no keels on the underside. The neck vertebrae have deep pits to the side of the base of theneural spine. The back vertebrae have deep pits to the side of the base of the neural spine. The fourthmetatarsal is more than 30% longer than the third metatarsal.[1]
Antarctanax was, within the largerArchosauromorpha, placed in the Archosauriformes. Acladistic analysis showed that it had a more derived position than theProterosuchidae. It was in apolytomy withFugusuchus andSarmatosuchus, all three forms being more basal thanCuyosuchus, theErythrosuchidae and theEucrocopoda.[1] The derived position ofAntarctanax indicates that several more basal archosauromorph groups must haveghost lineages dating back to theLate Permian.[2]
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