Antarctanax
Triassic archosauriform reptile from Antarctica.
Antarctanax is a basal archosauriform reptile from the Triassic of Antarctica, roughly iguana-sized. Its only known species is *Antarctanax shackletoni*.
**Discovery and naming** A small skeleton was uncovered at Graphite Peak during a 2010–2011 expedition to the Transantarctic Mountains. In 2019, Brandon Robert Peecook, Roger Malcolm Harris Smith, and Christian Alfred Sidor named and described the species. The genus name combines “Antarctica” (from Greek *anti*, “opposite of,” and *arktikos*, “of the Bear”) with Greek *anax*, “ruler,” a nod to the Archosauria (“Ruling Reptiles”). The species name honors polar explorer Ernest Shackleton, who named the Beardmore Glacier near Graphite Peak. The holotype, UWBM 95531, came from a lower Fremouw Formation layer dating to the Early Triassic. It includes eight neck or back vertebrae, ribs, a left humerus, all five left foot metatarsals, left foot phalanges (including claws), and a nearly complete right foot. Aside from the feet, the skeleton is mostly disarticulated. The individual was an adult.
**Description** The authors identified a unique combination of traits, none individually unique, that distinguish *Antarctanax* as a valid taxon. In the cervicodorsal vertebrae (spanning the rear neck and front back), each side has a *lamina centrodiapophysealis anterior*—a ridge on the front underside of the side process toward the vertebral body. Each side also has a *lamina prezygodiapophysealis* (ridge from side process to front articulation process) and a *lamina postzygodiapophysealis* (ridge from side process to rear articulation process). These vertebrae lack a *lamina centrodiapophysealis posterior* (ridge on the rear underside of the side process toward the vertebral body). Neck vertebrae have no keels on their undersides but do have deep pits beside the neural spine base; back vertebrae also have deep pits beside the neural spine base. The fourth metatarsal is more than 30% longer than the third.
**Phylogeny** Within Archosauromorpha, *Antarctanax* falls under Archosauriformes. A cladistic analysis places it more derived than Proterosuchidae, in a polytomy with *Fugusuchus* and *Sarmatosuchus*. These three are more basal than *Cuyosuchus*, Erythrosuchidae, and Eucrocopoda.
Quick Facts
- Taxon
- Antarctanax
- Type Species
- †Antarctanax shackletoni
- Type Species Authority
- Peecook et al. 2019
Facts from the source article.
Lore & Background
During a paleontological expedition to the Transantarctic Mountains in 2010 and 2011, a small skeleton was discovered at Graphite Peak. In 2019, the type species Antarctanax shackletoni was named and described by Brandon Robert Peecook, Roger Malcolm Harris Smith and Christian Alfred Sidor. The generic name combines a reference to Antarctica with Greek anax, 'ruler', a reference to the Archosauria. The specific name honours Ernest Shackleton, the polar explorer who named the Beardmore Glacier which runs along Graphite Peak.
Reader's Guide
Antarctanax is significant as a basal archosauriform from the Early Triassic of Antarctica, a region that was then part of Gondwana. Its description in 2019 added to the known diversity of early archosauriforms and helped clarify phylogenetic relationships within Archosauriformes. A cladistic analysis placed Antarctanax in a polytomy with Fugusuchus and Sarmatosuchus, more derived than Proterosuchidae but more basal than Erythrosuchidae and Eucrocopoda. This derived position indicates that several more basal archosauromorph groups must have ghost lineages dating back to the Late Permian. The unique combination of vertebral traits, such as the presence of specific laminae and the absence of others, confirms it as a distinct taxon. Its discovery underscores the importance of Antarctic fossil sites for understanding the early Mesozoic radiation of reptiles.
Did You Know?
- Antarctanax was a reptile around the size of an iguana.
- The holotype was discovered during a 2010–2011 expedition to the Transantarctic Mountains at Graphite Peak.
- The specific name shackletoni honors polar explorer Ernest Shackleton.
- The fourth metatarsal of Antarctanax is more than 30% longer than the third metatarsal.
More in Fossils of Antarctica 1-24
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