Alkaidia

Alkaidia Temporal range: Barremian–Cenomanian PreꞒ Ꞓ O S D C P T J K Pg N
Fossil of A. sumralli
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Echinodermata
Class:	Asteroidea
Order:	Forcipulatida
Family:	†Terminasteridae
Genus:	†Alkaidia Blake & Reid, 1998
Type species
†Alkaidia sumralli Blake & Reid, 1998
Other species
†A. megaungula Ewin & Gale, 2020

Alkaidia is an extinct genus of sea stars which lived in the western Tethys Ocean from the Barremian to Cenomanian stages of the Cretaceous period. It was first described in 1998, and two species are currently assigned to it. The type species, A. sumralli, is known from both complete and fragmentary specimens collected in Texas, and fossils of an earlier species, A. megaungula, have been found in Morocco.

Discovery and naming

The fossilized remains of Alkaidia were first described by paleontologists Daniel B. Blake and Robert Reid, III in a 1998 publication describing some Albian-aged starfish fossils from north-central Texas. The authors determined that over 50 specimens (some complete and other fragmentary) originating from the Washita Group represented a new genus and species which they named Alkaidia sumralli. The generic name references Alkaid, a star in the constellation Ursa Major, while the specific name honors Colin Sumrall, who discovered and prepared some of the specimens, including the holotype. A complete specimen (1786TXI) found in deposits of the Del Rio Formation at Waco Dam Quarry was designated as the holotype, and was placed in the Texas Memorial Museum. Some additional fragments from the same locality and from the Paw Paw Formation were designated as paratypes.[1]

A second species of Alkaidia was described in 2020 by paleontologists Timothy A. M. Ewin and Andrew S. Gale based on material originating from the Taba Starfish Bed of the Barremian-aged Taboulouart Formation in Morocco and purchased from commercial fossil collectors. This species was named Alkaidia megaungula, the specific name meaning "large hoof" in Greek and referencing the large terminal ossicle of this species, which resembles a hoof. The studied specimens are well-preserved and represent numerous individuals of various growth stages, allowing an ontogenetic series to be shown.[2]

References

1. Blake, Daniel B.; Reid, Robert (1998). "Some Albian (Cretaceous) asteroids (Echinodermata) from Texas and their paleobiological implications". Journal of Paleontology. 72 (3): 512–532. Bibcode:1998JPal...72..512B. doi:10.1017/S002233600002429X. JSTOR 1306650. S2CID 131483454.
2. Ewin, Timothy A. M.; Gale, Andrew S. (September 2020). "Asteroids (Echinodermata) from the Barremian (Lower Cretaceous) of the Agadir Basin, west Morocco". Journal of Paleontology. 94 (5): 931–954. doi:10.1017/jpa.2020.20. ISSN 0022-3360.