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Carcharocles chubutensis
#1
Carcharocles chubutensis

Temporal range: Oligocene-Early Pliocene ~28–5 Ma 

Scientific classification
Kingdom:  Animalia
Phylum:  Chordata
Class:  Chondrichthyes
Order:  Lamniformes
Family:  †Otodontidae
Genus:  †Carcharocles
Species:  Carcharocles chubutensis  Agassiz, 1843

Carcharocles chubutensis, meaning "glorious shark of Chubut", from Ancient Greek: κλέϝος (kléwos) “glory/fame” + καρχαρίας (karkharías) “shark”, is an extinct species of prehistoric megatoothed sharks in the genus Carcharocles, that lived during Oligocene, Miocene, and Pliocene epochs, approximately 28 – 5 million years ago. This shark is considered to be a close relative of the famous prehistoric megatoothed shark, C. megalodon. However, as is the case with C. megalodon, the classification of this species is disputed.

Taxonomy
As is the case with other known megatoothed sharks, the genus of C. chubutensis remains in dispute. The Swiss naturalist Louis Agassiz first identified this shark as a species of Carcharodon in 1843. In 1906, Ameghino renamed this shark as C. chubutensis. In 1964, shark researcher, L. S. Glikman recognized the transition of Otodus obliquus to C. auriculatus. In 1987, shark researcher, H. Cappetta reorganized the C. auriculatus - C. megalodon lineage and placed all related megatoothed sharks along with this species in the genus Carcharocles. Finally, the complete Otodus obliquus to C. megalodon progression became clear and has since gained the acceptance of many shark researchers.
Within the Carcharocles lineage; C. chubutensis is the succeeding species of C. angustidens and is followed by C. megalodon. In short, C. chubutensis is considered a possible ancestor of C. megalodon. However, due to its co-existence with C. megalodon during the Miocene and Pliocene epochs, it is regarded as a morpho-species.

Size
Carcharocles chubutensis was larger than C. angustidens. Teeth of C. chubutensis can approach 130 millimetres (5.1 in) in slant height (diagonal length), which according to a size estimation method proposed by Gottfried at al, in 1996, indicate a 12.2 m (40 ft) long specimen.

Paleoecology
Paleontological research suggests that this species may have changed habitat preferences through time, or it may have had enough behavioral flexibility to occupy different environments at different times.

Diet
Carcharocles chubutensis was likely an apex predator and commonly preyed upon fish, sea turtles, cetaceans (e.g. whales), and sirenids.

Fossil record
This species is also known from fossil teeth and some fossilized vertebral centra. Shark skeletons are composed of cartilage and not bone, and cartilage rarely gets fossilized. Hence, fossils of C. chubutensis are generally poorly preserved. Although the teeth of C. chubutensis are morphologically similar to teeth of C. megalodon, they are comparatively slender with curved crown, and with presence of lateral heels feebly serrated. Fossils of this species have been found in North America, South America, Africa, and Europe.



Journal Reference:
Victor J. Perez et al, The transition between Carcharocles chubutensis and Carcharocles megalodon (Otodontidae, Chondrichthyes): lateral cusplet loss through time, Journal of Vertebrate Paleontology(2019). DOI: 10.1080/02724634.2018.1546732

ABSTRACT
The teeth of two megatooth macro-predatory shark species (Carcharocles chubutensis and Carcharocles megalodon; Otodontidae, Chondrichthyes) occur within the Miocene Chesapeake Group of Maryland, U.S.A. Definitive separation between all the teeth of Carcharocles chubutensis and Carcharocles megalodon is impossible because a complex mosaic evolutionary continuum characterizes this transformation, particularly in the loss of lateral cusplets. The cuspleted and uncuspleted teeth of Carcharocles spp. are designated as chronomorphs because there is wide overlap between them both morphologically and chronologically. In the lower Miocene Beds (Shattuck Zones) 2–9 of the Calvert Formation (representing approximately 3.2 million years, 20.2–17 Ma, Burdigalian) both cuspleted and uncuspleted teeth are present, but cuspleted teeth predominate, constituting approximately 87% of the Carcharocles spp. teeth represented in our sample. However, in the middle Miocene Beds 10–16A of the Calvert Formation (representing approximately 2.4 million years, 16.4–14 Ma, Langhian), there is a steady increase in the proportion of uncuspleted Carcharocles teeth. In the upper Miocene Beds 21–24 of the St. Marys Formation (representing approximately 2.8 million years, 10.4–7.6 Ma, Tortonian), lateral cusplets are nearly absent in Carcharocles teeth from our study area, with only a single specimen bearing lateral cusplets. The dental transition between Carcharocles chubutensis and Carcharocles megalodon occurs within the Miocene Chesapeake Group. Although this study helps to elucidate the timing of lateral cusplet loss in Carcharocleslocally, the rationale for this prolonged evolutionary transition remains unclear.

https://www.tandfonline.com/doi/full/10....18.1546732
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  • Claudiu Constantin Nicolaescu
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How much would a 12.2m shark weigh? 20 to 30 tons?
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