Atractosteus simplex

Atractosteus simplex Temporal range: Early Eocene PreꞒ Ꞓ O S D C P T J K Pg N ↓
Fossil specimen, University of Wyoming
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Clade:	Ginglymodi
Order:	Lepisosteiformes
Family:	Lepisosteidae
Genus:	Atractosteus
Species:	†A. simplex
Binomial name
†Atractosteus simplex (Leidy, 1873)
Synonyms
Lepisosteus simplexLeidy, 1873

Atractosteus simplex (from simplex, Latin for "simple", likely referring to the smooth scales), the simplex gar ^[1] , is an extinct species of gar from the Early Eocene of western North America. It is known from many well-preserved specimens found in the famous Fossil Butte deposits of the Green River Formation in Wyoming, US. ^[2]

It was a close relative of the modern alligator gar (A. spatula), and one of two Atractosteus species known from Fossil Butte alongside the even larger A. atrox . It can be differentiated from the sympatric A. atrox by its lower number of lateral line scales and vertebrae, and reaching only 1 metre (3.3 ft) in length. ^{[1] [3]} It is the most abundant of the six gar species known from the Green River Formation, although even the 100-200 excavated specimens of this species are a minute percentage of the over 500,000 fossil fish specimens recovered from the formation. ^[1]

A. simplex was a highly predatory fish, with one fossil specimen preserving a young Diplomystus in its jaws. ^[1] Another specimen preserves coprolites in its mouth, representing the first instance of coprolites being found within a fossilized vertebrate's mouth. As gars are not known to engage in coprophagy, this is thought to likely represent an accidental ingestion or a consequence of taphonomy. ^[4]

The original type specimen is a skull fragment and some vertebrae recovered from the Bridger Formation, which Leidy (1873) named A.simplex, a name he also used for the well-preserved Green River Formation gars. However, this vertebra cannot be confidently assigned to A.simplex and may belong to A.atrox or Lepisosteus bemisi instead; for this reason, Eastman (1900) fixed the name to a more complete Green River specimen instead, which was treated as the "effective type" specimen. ^{[1] [2]}

References

1. Grande, Lance (2010). "An Empirical Synthetic Pattern Study of Gars (lepisosteiformes) and Closely Related Species, Based Mostly on Skeletal Anatomy. the Resurrection of Holostei". Copeia. 2010 (2A): iii–871. ISSN   0045-8511.
2. "PBDB Taxon". paleobiodb.org. Retrieved 2025-01-23.
3. Grande, Lance (2001), Gunnell, Gregg F. (ed.), "An Updated Review of the Fish Faunas From the Green River Formation, the World's Most Productive Freshwater Lagerstätten" , Eocene Biodiversity: Unusual Occurrences and Rarely Sampled Habitats, Boston, MA: Springer US, pp. 1–38, doi:10.1007/978-1-4615-1271-4_1, ISBN   978-1-4615-1271-4 , retrieved 2025-01-23
4. Frandsen, George; Godfrey, Stephen J. (2019). "A gar-bitten coprolite from the Eocene Green River Formation near Kemmerer, Wyoming, U.S.A" (PDF). The Ecphora. 34 (1): 3–4.