Onchopristis

Onchopristis is a genus of extinct giant sclerorhynchoid (a sawfish-like chondrichthyan) from the Lower Cretaceous to Upper Cretaceous of North America, North Africa, Brazil, and New Zealand. It had an elongated snout lined laterally with barbed "teeth", or denticles.[2][3]

Onchopristis
Temporal range: Albian–Maastrichtian
Tooth of O. numidus from the Tegana Formation, of the Kem Kem Beds
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Order: Rajiformes
Suborder: †Sclerorhynchoidei
Genus: †Onchopristis
Stromer, 1917[1]
Type species
†Gigantichthys numidus
Haug, 1905
Species
  • †O. numidus (Haug, 1905)
  • †O. dunklei McNulty & Slaugter, 1962
Synonyms[2]

Taxonomy

Despite formerly being classified within a family of extinct sawfish-like rays known as Sclerorhynchidae,[4] phylogenetic analyses indicate that Ischyrhiza, Schizorhiza, and Onchopristis form a distinct clade that groups closer with the extant family Rajidae, which contains the true skates, possibly rendering the suborder Sclerorhynchoidei paraphyletic.[5]

Description
Life restoration with the contemporary Mawsonia/Axelrodichthys

The rostrum, or snout, was around 1–2 metres (3.3–6.6 feet) long,[6] lined with barbed "teeth" or denticles. In the type species, O. numidus, each tooth had one barb, but in O. dunklei there were two to five barbs on each tooth, and two to three in O. d. praecursor.[2] This sclerorynchid was about 5–6 metres (16.4–19.7 feet) long.[6]

Denticle comparison with other sawfish and sclerorhynchid species, (O. numidus in red and O. dunklei in green)

Paleobiology

As with the modern sawfish, Onchopristis' eyes were on top of its head, to spot predators rather than prey, and its mouth and gills were under its body. The rostrum most likely would have had electroreceptors to detect food in the water below them like most modern sharks and some rays. Onchopristis may have raked through the riverbed to find and then eat prey.[7]

Predators

It is thought that some species of Onchopristis may have migrated up rivers to breed. At the height of the breeding season, piscivores like Spinosaurus aegyptiacus may have preyed upon the them.[8]

References
  1. Stromer, E. (1917). "Ergebnisse der Forschungsreisen Prof. E. Stromers in den Wüsten Ägyptens: Wirbeltier-Reste der Baharije-Stufe (unterstes Cenoman)". Abhandlungen der Königlich Bayerischen Akademie der Wissenschaften, Math.-naturwiss. Abt., N.F. 28 (8): 1–28. |chapter= ignored (help)
  2. Keyes, I.W. (1977). "Records of the northern hemisphere Cretaceous Sawfish genus Onchopristis (order batoidea) from New Zealand". New Zealand Journal of Geology and Geophysics. 20 (2): 263–272. doi:10.1080/00288306.1977.10420706.
  3. Medeiros, Manuel Alfredo; Lindoso, Rafael Matos; Mendes, Ighor Dienes; Carvalho, Ismar de Souza (2014-08-01). "The Cretaceous (Cenomanian) continental record of the Laje do Coringa flagstone (Alcântara Formation), northeastern South America". Journal of South American Earth Sciences. 53: 50–58. Bibcode:2014JSAES..53...50M. doi:10.1016/j.jsames.2014.04.002. ISSN 0895-9811.
  4. "Fossilworks: Sclerorhynchidae". fossilworks.org. Retrieved 2020-10-17.
  5. Villalobos‐Segura, Eduardo; Underwood, Charlie J.; Ward, David J. "The first skeletal record of the enigmatic Cretaceous sawfish genus Ptychotrygon (Chondrichthyes, Batoidea) from the Turonian of Morocco". Papers in Palaeontology. n/a (n/a). doi:10.1002/spp2.1287. ISSN 2056-2802.
  6. This huge ancient sawfish had harpoons on its face
  7. Scott, C. (2012). Planet Dinosaur: The Next Generation of Killer Giants. Firefly Books. pp. 72–73. ISBN 978-1-77085-049-1.
  8. www.bbc.co.uk https://www.bbc.co.uk/programmes/p00kgk6n. Retrieved 2020-08-15. Missing or empty |title= (help)


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