Coccosteus

Coccosteus (from Greek: κόκκος kókkos, 'berry' and Greek: ὀστέον ostéon 'bone')^[1] is an extinct genus of arthrodire placoderm from the Devonian period. Its fossils have been found throughout Europe and North America. The majority of these have been found in freshwater sediments, though such a large range suggests that they may have been able to enter saltwater. It was a small placoderm, with Coccosteus cuspidatus measuring 29.6–39.4 cm (11.7–15.5 in) long.^[2]

Coccosteus Temporal range: Middle to Late Devonian, 393.3–359.3 Ma PreꞒ Ꞓ O S D C P T J K Pg N
C. cuspidatus specimen IVPP V19322, Paleozoological Museum of China
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	†Placodermi
Order:	†Arthrodira
Suborder:	†Brachythoraci
Family:	†Coccosteidae
Genus:	†Coccosteus Agassiz, 1843
Type species
Coccosteus cuspidatus Miller, 1841
Species
List Coccosteus canadensis Woodward, 1892 Coccosteus carbonarius M'Coy, 1848 Coccosteus chamberlini Bryant, 1932 Coccosteus cuspidatus Miller, 1841 (type) Coccosteus cuyahogae Claypole, 1998 Coccosteus decipiens Agassiz, 1841 Coccosteus disjectus Woodward, 1891 Coccosteus grossi Obrucheva, 1962 Coccosteus hercynius von Meyer, 1852 Coccosteus macromus Cope, 1892 Coccosteus markae Obrucheva, 1962 Coccosteus minor Miller, 1858 Coccosteus occidentalis Newberry, 1875 ? Coccosteus orvikui Gross, 1940 Coccosteus terranovae Obruchev, 1934

Description

Life reconstruction of C. cuspidatus

Like all other arthrodires, Coccosteus had a joint between the armor of the body and skull. It also had an internal joint between its neck vertebrae and the back of the skull, allowing for the mouth to be opened even wider. Along with the longer jaws, this allowed Coccosteus to feed on fairly large prey. The up-and-down movement of the skull also allowed for more water to be pumped through the gills. Possibly, the creature supplemented its diet with organic material filtered from mud using the gills. As with all other arthrodires, Coccosteus had bony dental plates embedded in its jaws, forming a beak. The beak was kept sharp by having the edges of the dental plates grind away at each other.^[3] Overall the creature looked similar to its gigantic cousin Dunkleosteus, save that its eyes were closer to the end of its snout than in its larger relative.

Phylogeny

C. cuspidatus restoration, shown attacking multiple Palaeospondylus

Coccosteus is the type genus for family Coccosteidae, which belongs to the clade Coccosteomorphi, one of the two major clades within Eubrachythoraci. The cladogram below shows the phylogeny of Coccosteus:^[4]

Eubrachythoraci

Coccosteomorphi Coccosteoidea Coccosteidae Millerosteus minor Coccosteus cuspidatus Dickosteus threiplandi Watsonosteus fletti Protitanichthys rockportensis Panxiosteidae Plourdosteus canadensis Panxiosteus ocullus Janiosteus timanicus Incisoscutoidea Harrytoombsia elegans Torosteus tuberculatus Torosteus pulchellus Mcnamaraspis kaprios Compagopiscis croucheri Trematosteus fontanellus Camuropiscidae Incisoscutum ritchiei Incisoscutum sarahae Rolfosteus canningensis Tubonasus lennardensis Fallacosteus turneri Camuropiscis laidlawi Latocamurus coulthardi Pachyosteomorphi

Species

C. cuyahogae reconstruction

• C. cuspidatus is the type species, and is an important index fossil in the continental Devonian sequence of northern Scotland deposited in the Orcadian Basin. It is only present at and below the Upper Eifelian Achanarras limestone level.^[5]

See also

• List of placoderms

References

1. Dean, Bashford (1895). Fishes, living and fossil. An outline of their forms and probable relationships. New York, London, Macmillan and Co. p. 228.
2. Engelman, Russell K. (2023). "A Devonian Fish Tale: A New Method of Body Length Estimation Suggests Much Smaller Sizes for Dunkleosteus terrelli (Placodermi: Arthrodira)". Diversity. 15 (3). 318. doi:10.3390/d15030318.
3. Palmer, D., ed. (1999). The Marshall Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals. London: Marshall Editions. p. 32. ISBN 978-1-84028-152-1.
4. Zhu, You-An; Zhu, Min; Wang, Jun-Qing (1 April 2016). "Redescription of Yinostius major (Arthrodira: Heterostiidae) from the Lower Devonian of China, and the interrelationships of Brachythoraci". Zoological Journal of the Linnean Society. 176 (4): 806–834. doi:10.1111/zoj.12356. ISSN 0024-4082.
5. Trewin, N.H.; Davison R.G. (1999). "Lake-level changes, sedimentation and faunas in a Middle Devonian basin-margin fish bed". Journal of the Geological Society. 156 (3): 535–548. Bibcode:1999JGSoc.156..535T. doi:10.1144/gsjgs.156.3.0535. S2CID 131241083. Retrieved 7 July 2012.