Biology:Voay

Short description: Extinct genus of reptiles

Voay Temporal range: Late Pleistocene, 0.1–0.01 Ma PreЄ Є O S D C P T J K Pg N ↓ Divergence estimates suggest Oligocene origin
Skull, American Museum of Natural History
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Clade:	Archosauromorpha
Clade:	Archosauriformes
Order:	Crocodilia
Family:	Crocodylidae
Subfamily:	Crocodylinae
Genus:	†Voay Brochu, 2007
Type species
†Voay robustus (Grandidier & Vaillant, 1872)
Synonyms
Crocodylus robustus Grandidier & Vaillant, 1872

Voay is an extinct genus of crocodile from Madagascar that lived during the Late Pleistocene to Holocene, containing only one species, V. robustus. Numerous subfossils have been found, including complete skulls, noted for their distinctive pair of horns on the posterior, as well as vertebrae and osteoderms from such places as Ambolisatra and Antsirabe. The genus is thought to have become extinct relatively recently. It has been suggested to have disappeared in the extinction event that wiped out much of the endemic megafauna on Madagascar, such as the elephant bird and Malagasy hippo, following the arrival of humans to Madagascar around 2000 years ago. Its name comes from the Malagasy word for crocodile.

Description

Reconstruction of V. robustus

One unusual feature of V. robustus that distinguishes it from other crocodilians is the presence of prominent "horns" extending from the posterior portion of the skull. They are actually the posterolaterally extended corners of the squamosal bone. Other related crocodilians such as Aldabrachampsus also had similar bony projections, although in Aldabrachampsus these projections were more like crests than horns. Another diagnostic characteristic is the near-exclusion of the nasals from the external naris. It had a shorter and deeper snout than the extant Crocodylus niloticus, as well as relatively robust limbs. The osteoderms had tall keels and were dorsally symmetrical with curved lateral margins, running the entire length of the postcranial body.

V. robustus would have measured around 3.5–4 m (11–13 ft) long and weighed about 170 kg (370 lb). These estimates suggest that V. robustus was the largest predator to have existed in Madagascar in recent times. Its size, stature, and presumed behavior is similar to the modern Nile crocodile (Crocodylus niloticus). Because V. robustus shared so many similarities with the Nile crocodile there must have been a great deal of interspecific competition for resources between the two crocodile genera if they were to have coexisted with one another. It has recently been proposed that the Nile crocodile only migrated to the island from mainland Africa after V. robustus had become extinct in Madagascar. However, this was subsequently disproved after some Crocodylus specimens from Madagascar were found to be at least 7,500 years old and contemporaneous with Voay.

Phylogenetics

When V. robustus was first described in 1872, it was originally assigned to the genus Crocodylus. It was later found to morphologically have had more in common with the extant Osteolaemus, or dwarf crocodile, than Crocodylus. Some features it shared with Osteolaemus include a depressed pterygoid surface that forms a choanal "neck" on the palate. Because it was not close enough to be placed in the same genus as the dwarf crocodile, it was assigned to the new genus in 2007. Before this reassignment, the species was considered by some to be synonymous with Crocodylus niloticus. However, this was most likely due to a misinterpretation of remains from the living C. niloticus with V. robustus and the poor description of the original material from which the species was described. In contrast to the morphological similarities with Osteolaemus, a 2021 study using paleogenomics found Voay to be a sister group to Crocodylus, with both genera diverging in the mid-late Oligocene; this indicates that the apparent similarities with Osteolaemus are likely due to convergent evolution.

The below cladogram shows the results of the latest study:

Crocodylidae

Osteolaeminae     Mecistops cataphractus West African slender-snouted crocodile     Euthecodon†         Brochuchus†       Rimasuchus†       Osteolaemus osborni Osborn’s dwarf crocodile     Osteolaemus tetraspis Dwarf crocodile           Crocodylinae   Voay†   Crocodylus       Crocodylus anthropophagus†     Crocodylus thorbjarnarsoni†         Crocodylus palaeindicus†     Crocodylus Tirari Desert†               Crocodylus johnstoni Freshwater crocodile       Crocodylus novaeguineae New Guinea crocodile     Crocodylus mindorensis Philippine crocodile           Crocodylus porosus Saltwater crocodile       Crocodylus siamensis Siamese crocodile     Crocodylus palustris Mugger crocodile               Crocodylus checchiai†     Crocodylus falconensis†         Crocodylus suchus West African crocodile       Crocodylus niloticus Nile crocodile         Crocodylus moreletii Morelet's crocodile     Crocodylus rhombifer Cuban crocodile         Crocodylus intermedius Orinoco crocodile     Crocodylus acutus American crocodile

(crown group)

References

Wikidata ☰ Q22113584 entry