Isurus Explained

Isurus (meaning "equal tail")^[1] is a genus of mackerel sharks in the family Lamnidae, commonly known as the mako sharks. They are largely pelagic,^[2] fast predatory fish capable of swimming at speeds up to 50km/h.^{[3] [4]}

Fossil history and evolution

Although fossil teeth of Isurus have been reported from as early as the Late Cretaceous,^{[5] [6]} they are likely to be of a shark with a similar dentition, Cretoxyrhina; since at one point they were considered to be the same (now defunct) genus Oxyrhina,^[7] and modern referrals to Isurus in the Cretaceous are scant. The earliest appearance of Isurus proper seems to be during the Oligocene with Isurus desori.^{[8] [9]}

There has been much debate and speculation about the evolutionary origin and relationships between Isurus and its closest relatives, including the extant great white shark (Carcharodon carcharias). Molecular clock analyses place the last common ancestor of Isurus and Carcharodon between 43-60 million years ago during the Late Paleocene-Early Eocene.^[10] This insight should guide efforts to better resolve the fossil ancestry of both lineages, by providing a window of time in which to search for ancestor candidates.

Many fossil species of Lamnids have historically been placed under Isurus, which are now largely considered separate genera. These include species of Carcharodon (Cosmopolitodus) like C. hastalis, C. planus,^[11] species of Macrorhizodus,^{[12] [13]} Isurolamna,^{[14] [15]} and others.

Description

The two living species are the shortfin mako shark (I. oxyrinchus) and the longfin mako shark (I. paucus). They range in length from 2.5to, and have an approximate maximum weight of 680kg (1,500lb). They both have a distinctive blue-gray color scheme common among mackerel sharks.

Species

The genus contains these species:^[16]

• Isurus oxyrinchus (Rafinesque, 1810) (shortfin mako shark)^[17]
• Isurus paucus (Guitart-Manday, 1966) (longfin mako shark)^[18]
• †Isurus desori (Agassiz, 1843)
• †Isurus retroflexus (Agassiz, 1843)

See also

• Shortfin mako shark
• Longfin mako shark
• White sharks
• List of prehistoric cartilaginous fish
• Shark meat

Notes and References

1. Web site: Isurus paucus . 2023-05-24 . Discover Fishes . en-US.
2. McEachran, J.; Fechhelm, J.D. (1998). Fishes of the Gulf of Mexico, Vol. 1: Myxiniformes to Gasterosteiformes. Fishes of the Gulf of Mexico. Austin: University of Texas Press. p. 43. . . Retrieved 13 July 2021.
3. Peter Klimley . A. . Beavers . Sallie C. . Curtis . Tobey H. . Jorgensen . Salvador J. . 2002 . Movements and Swimming Behavior of Three Species of Sharks in La Jolla Canyon, California . Environmental Biology of Fishes . 63 . 2 . 117–135 . 10.1023/A:1014200301213 . 27883104. subscription .
4. Web site: May 23, 2023 . Shortfin Mako Shark . May 23, 2023 . ocean.si.edu.
5. J. B. Reeside. 1955. Revised interpretation of the Cretaceous section on Vermilion Creek, Moffat County, Colorado. Wyoming Geological Association Guidebook - 1955 85-88
6. R. Zangerl and R. E. Sloan. 1960. A new specimen of Desmatochelys lowi Williston: a primitive cheloniid sea turtle from the Cretaceous of South Dakota. Fieldiana: Geology 14(2):7-40
7. Book: Agassiz, Louis . Recherches sur les poissons fossiles ... . 1833 . Petitpierre . Neuchatel. 10.5962/bhl.title.4275 .
8. Andre Pharisat & Norbert Micklich (1998) Oligocene fishes in the western Paratethys of the Rhine Valley Rift System, Italian Journal of Zoology, 65:S1, 163-168,
9. Merle, D. & Baut, J.-P. & Ginsburg, L. & Sagne, C. & Hervet, S. & Carriol, R.-P. & Venec-Peyre, T. & Blanc-Valleron, M. & Mourer-Chauviret, C. & Arambol, D. & Viette, P. (2002). Découverte d'une faune de vertébrés dans l'Oligocène inférieur de Vayres-sur-Essonne (bassin de Paris, France) : biodiversité et paléoenvironnement. Comptes Rendus Palevol, 1(2), 111–116.
10. Martin, A. P. (1996). "Systematics of the Lamnidae and the Origination Time of Carcharodon carcharias Inferred from the Comparative Analysis of Mitochondrial DNA Sequences". In Klimley, A. P.; Ainley, D. G. (eds.). Great White Sharks: The Biology of Carcharodon carcharias. Academic Press. pp. 49–53. .
11. Ehret, D.J., Macfadden, B.J., Jones, D.S., DeVries, T.J., Foster, D.A. and Salas-Gismondi, R. (2012), Origin of the white shark Carcharodon (Lamniformes: Lamnidae) based on recalibration of the Upper Neogene Pisco Formation of Peru. Palaeontology, 55: 1139-1153.
12. White, E., 1956. The Eocene Fishes of Alabama. Bulletin of American Paleontology, 36 (no. 156): PRI. pp 122-152.
13. Glikman, L.S., 1964. Akuly paleogena i ikh stratigraphicheskoe znachenie. Akademii Nauk Soyuza Sovetskikh Sotsialisticheskikh Respublik, 1-228 Moscow.
14. Le Hon, H., 1871. Préliminaires d'un mémoir sur les poissons tertiaries de belgique. Brussels, pp. 1-15.
15. Leriche, M. 1905. Les poissons tertiaires de la Belgique. II. Les poissons éocènes. Mém. Mus. Roy. Hist. Natur. Belig., 11(3), p49-228.
16. http://www.fossilworks.org/cgi-bin/bridge.pl?a=taxonInfo&taxon_no=34613 Fossilworks
17. Smith, J.L.B. Sharks of the Genus Isurus Rafinesque, 1810. Ichthyological Bulletin; No. 6. Department of Ichthyology, Rhodes University, Grahamstown, South Africa
18. Tony Ayling & Geoffrey Cox, Collins Guide to the Sea Fishes of New Zealand, William Collins Publishers Ltd, Auckland, New Zealand 1982