Cosmopolitodus planus

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Cosmopolitodus planus
Temporal range: Miocene
Isurus planus teeth.png
Cosmopolitodus planus upper teeth from Sharktooth Hill (the Temblor Formation)
Scientific classification edit
Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Superorder: Selachimorpha
Order: Lamniformes
Family: Lamnidae
Genus: †Cosmopolitodus
Species:
†C. planus
Binomial name
†Cosmopolitodus planus
(Agassiz, 1856)
Synonyms
  • Oxyrhina plana Agassiz, 1856
  • Isurus planus Jordan, 1907

Cosmopolitodus planus, also known as the hooked-tooth mako shark or hooked mako shark, is an extinct lamnid that lived during the Miocene epoch from 23 to 5 million years ago.[1] C. planus can be found only in marine deposits on the Pacific Rim, especially the west coast of the United States.[1][2] Teeth belonging to C. planus can reach lengths of 2.0 in (5.0 cm), and are often found in the Temblor Formation of Bakersfield, California.[3]

Description[]

Cosmopolitodus planus exists only around the Pacific Rim areas, including Australia, Japan, the eastern coast of Russia, Oregon, California, and Mexico,[1][2][4][5] while being most common in Southern California, especially at Sharktooth Hill near Bakersfield, California.[3] With teeth up to two inches long, C. planus would probably be around the size of a modern great white shark[6] and most likely preyed upon the fish, pinnipeds, and smaller cetaceans of its time.

Teeth[]

Cosmopolitodus planus teeth are somewhat similar to those of other mako sharks, especially the extinct species Cosmopolitodus hastalis and . Adult upper teeth are generally 2–4 cm long with an unserrated cutting edge and no lateral cusplets. True to its name, each tooth is "hooked", the point of which is shifted away from the middle axis, in the direction of the corners of the mouth. In this, the teeth of C. planus and I. desori differ from C. hastalis. I. desori teeth are much more heterodontic than C. planus and their roots are more uneven in thickness and shape, with more narrow builds and rounder lobes, somewhat making the appearance of a heart. But the crowns of the lower teeth of this species are described to be more straight and identical to the lower teeth of C. hastalis.[6][7] The hooked teeth, which probably would be efficient for gripping prey, would suggest a diet of smaller and medium-sized animals.

Classification[]

The hooked-toothed mako was initially believed to be a true mako shark under the genus Isurus, hence its colloquial name "mako." However, the species is now believed to be descended from the narrow-form of the broad-tooth "mako" Cosmopolitodus hastalis,[8] and its scientific name was thus reassigned to Cosmopolitodus planus in 2021.[9] However, the genus Cosmopolitodus itself is disputed, as some paleontologists argue that it should be a synonym of Carcharodon.[10]

References[]

  1. ^ a b c "Isurus planus, Shark-References". Retrieved 27 January 2016.
  2. ^ a b Yabumoto, Y. and Uyeno, T. (1994), Late Mesozoic and Cenozoic fish faunas of Japan. Island Arc, 3: 255–269. doi: 10.1111/j.1440-1738.1994.tb00115.x
  3. ^ a b Malchow, A. 2009. Miocene Shark Tooth Hill Locality, Kern County, California. Geological Society of America North-Central Section - 43rd Annual Meeting (2-3 April 2009)
  4. ^ Minch, John A.; Schulte, Kenneth C.; Hofman, George (1970). "A Middle Miocene Age for the Rosarito Beach Formation in Northwestern Baja California, Mexico". Geological Society of America Bulletin. 81 (10): 3149. doi:10.1130/0016-7606(1970)81[3149:AMMAFT]2.0.CO;2.
  5. ^ "Hooked Mako Isurus planus (Agassiz, 1856) from the Miocene of Sakhalin".
  6. ^ a b Cocke, Joe (2002). Fossil Shark Teeth of the World: A collector's guide.
  7. ^ Ciampaglio, C., Ricketts,D. Miocene Madness: Fossil Finder ID and Information Guide. Bakersfield, California. Buena Vista Museum of Natural History.
  8. ^ "Great White Sharks and Prehistoric White Sharks".
  9. ^ Yun, C. (2021). "A tooth of the extinct lamnid shark, Cosmopolitodus planus comb. noc. (Chondrichthyes, Elasmobranchii) from the Miocene of Pohang City, South Korea" (PDF). Acta Palaentologica Romaniae. 18 (1): 9–16. doi:10.35463/j.apr.2022.01.02.
  10. ^ Ehret, Dana J.; MacFadden, Bruce J.; Jones, Douglas S.; Devries, Thomas J.; Foster, David A.; Salas-Gismondi, Rodolfo (2012). "Origin of the white shark Carcharodon (Lamniformes: Lamnidae) based on recalibration of the Upper Neogene Pisco Formation of Peru". Palaeontology. 55 (6): 1139–1153. doi:10.1111/j.1475-4983.2012.01201.x.
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