Tanaocrossus Explained

Tanaocrossus (Ancient Greek for "outstretched fringe", referring to its distinctive dorsal fin) is an extinct genus of primitive freshwater ray-finned fish that inhabited southwestern and eastern North America during the Late Triassic period. It contains a single known species, T. kalliokoskii, known from the United States, with indeterminate species also known.^{[1] [2]}

It is primarily known from the Norian to Rhaetian of the Chinle Formation of Colorado and Utah.^{[3] [4] [5]} Indeterminate remains are known from the Dockum Group of Texas and New Mexico (Bull Canyon Formation).^[6] A single fragmentary but distinctive fossilized fin from the earlier Carnian-aged Doswell Formation of Virginia, which shares the genus's distinctive fin rays, was long the only record from the eastern United States, but a partial specimen was also later identified from the Manassas Sandstone.^{[4] [7]}

Morphologically, it can be easily distinguished from other co-occurring fishes by its highly elongated dorsal fin that stretches across its body. Its taxonomic affiliations have long been enigmatic since its description due to its unusual morphology.^[4] More recent studies have found it to be a scanilepiform, an enigmatic order of fish which were later found to most likely be basal cladistians, which would make it a distant relative of modern bichirs.^{[8] [9]} A 2008 study questioned this assignment and instead reclassified it to the Perleidiformes, but this has been disputed by later studies.^{[10] [11]}

It was likely a slow-moving fish that inhabited quiet waters, with its dorsal fin allowing for undulation while swimming.

References

1. Web site: PBDB Taxon . 2024-09-19 . paleobiodb.org.
2. Schaeffer . Bobb . 1967 . Late Triassic fishes from the western United States . Bulletin of the AMNH . 135 . 6.
3. Book: Heckert . Andrew B. . Vertebrate Paleontology in Arizona: Bulletin 29 . Lucas . Spencer G. . 2005 . New Mexico Museum of Natural History and Science . en.
4. Schaeffer . Bobb . McDonald . Nicholas G. . 1978 . Redfieldiid fishes from the Triassic-Liassic Newark Supergroup of eastern North America. Bulletin of the AMNH ; v. 159, article 4 . Bulletin of the American Museum of Natural History . 159 . 4 . 131–173.
5. Gibson . Sarah Z. . 2016-09-22 . Schubert . Michael . Redescription and Phylogenetic Placement of †Hemicalypterus weiri Schaeffer, 1967 (Actinopterygii, Neopterygii) from the Triassic Chinle Formation, Southwestern United States: New Insights into Morphology, Ecological Niche, and Phylogeny . PLOS ONE . en . 11 . 9 . e0163657 . 10.1371/journal.pone.0163657 . 1932-6203 . 5033578 . 27657923 . free.
6. Romano . Carlo . Koot . Martha B. . Kogan . Ilja . Brayard . Arnaud . Minikh . Alla V. . Brinkmann . Winand . Bucher . Hugo . Kriwet . Jürgen . 2016 . Permian-Triassic Osteichthyes (bony fishes): diversity dynamics and body size evolution (supplementary material) . Biological Reviews of the Cambridge Philosophical Society . 91 . 1 . 106–147 . 10.1111/brv.12161 . 1469-185X . 25431138.
7. Weems . Robert E. . 2018 . A SYNOPSIS OF THE VERTEBRATE FAUNA FROM THE CULPEPER BASIN (UPPER TRIASSIC-LOWER JURASSIC, MARYLAND AND VIRGINIA) . New Mexico Museum of Natural History and Science Bulletin . 79 .
8. Xu . Guang-Hui . Gao . Ke-Qin . 2011 . A new scanilepiform from the Lower Triassic of northern Gansu Province, China, and phylogenetic relationships of non-teleostean Actinopterygii: EARLY TRIASSIC SCANILEPIFORM FROM CHINA . Zoological Journal of the Linnean Society . en . 161 . 3 . 595–612 . 10.1111/j.1096-3642.2010.00645.x.
9. Giles . Sam . Xu . Guang-Hui . Near . Thomas J. . Friedman . Matt . 2017 . Early members of 'living fossil' lineage imply later origin of modern ray-finned fishes . Nature . en . 549 . 7671 . 265–268 . 10.1038/nature23654 . 28854173 . 1476-4687.
10. Milner . Andrew . Spears . Sarah . Olsen . Paul . 2008 . NEW SPECIMENS OF TANAOCROSSUS (ACTINOPTERYGII, PERLEIDIFORMES) FROM THE LATE TRIASSIC CHINLE FORMATION OF THE WESTERN UNITED STATES . Society of Vertebrate Paleontology.
11. Xu . Guang-Hui . Gao . Ke-Qin . Finarelli . John A. . 2014-06-07 . A revision of the Middle Triassic scanilepiform fish Fukangichthys longidorsalis from Xinjiang, China, with comments on the phylogeny of the Actinopteri . Journal of Vertebrate Paleontology . en . 34 . 4 . 747–759 . 10.1080/02724634.2014.837053 . 0272-4634.