Molecular Biology and Genetics
Statistics of barcoding coverage
|Specimen Records:||55||Public Records:||54|
|Specimens with Sequences:||54||Public Species:||12|
|Specimens with Barcodes:||54||Public BINs:||13|
|Species With Barcodes:||12|
"Crocodylus" megarhinus is an extinct species of crocodile from the Eocene of Egypt. A partial skull was found by British paleontologist Charles William Andrews in the Fayum Depression. Andrews named Crocodylus megarhinus in 1905 on the basis of the holotype skull. A complete skull was also uncovered from Egypt in 1907 but was not recognized as "C." megarhinus until 1927.
"C." megarhinus shares many features with living crocodiles like the Nile crocodile (C. niloticus), including a robust triangular skull that is shorter than most other crocodiles. Similarities are also seen in the teeth of the two species. Like living crocodiles, "C." megarhinus has several constricted areas along the upper jaw that provide spaces for the teeth of the lower jaw when the mouth is closed. The proportions of "C." megarhinus and C. niloticus are so similar that American paleontologist Charles C. Mook considered it "very probable that C. megarhinus is a direct ancestor of C. niloticus."
A second Fayum crocodilian, "Crocodylus" articeps, was named alongside "C." megarhinus. Andrews distinguished "C." articeps from "C." megarhinus on the basis of its narrower snout, which is more similar to the Slender-snouted crocodile than the Nile crocodile. "C." articeps has recently been synonymized with "C." megarhinus, and may represent a less mature form in the species' population.
Although it has traditionally been described as a species of Crocodylus, "C." megarhinus has been placed outside the genus in many recent phylogenetic analyses. A new genus has not yet been erected for the species. "C." megarhinus is usually found to be a basal crocodyline outside the genus but still more closely related to it than the false gharial or mekosuchines. Below is a cladogram modified from Puértolas et al. (2011) showing its phylogenetic placement among crocodiles:
- Mook, C.C. (1927). "The skull characters of Crocodilus megarhinus Andrews". American Museum Noviates 289: 1–8.
- Brochu, C. A. (2000). "Phylogenetic relationships and divergence timing of Crocodylus based on morphology and the fossil record". Copeia 2000 (3): 657–673.
- Eduardo Puértolas, José I. Canudo and Penélope Cruzado-Caballero (2011). "A New Crocodylian from the Late Maastrichtian of Spain: Implications for the Initial Radiation of Crocodyloids". PLoS ONE 6 (6): e20011. doi:10.1371/journal.pone.0020011.
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- † Crocodylus anthropophagus is an extinct crocodile from Plio-Pleistocene of Tanzania.
- † Crocodylus checchiai is an extinct crocodile from Late Miocene of Kenya.
- † Crocodylus palaeindicus is an extinct crocodile the Miocene to the Pleistocene of southern Asia.
- † Crocodylus thorbjarnarsoni is an extinct crocodile from Plio-Pleistocene of Kenya.
The 13 living species are:
- American crocodile, Crocodylus acutus
- Slender-snouted crocodile, Crocodylus cataphractus - studies in DNA and morphology suggest this species may be more basal than Crocodylus and therefore belongs in its own genus, Mecistops.
- Orinoco crocodile, Crocodylus intermedius
- Freshwater crocodile, Crocodylus johnsoni
- Philippine crocodile, Crocodylus mindorensis
- Morelet's crocodile or Mexican crocodile, Crocodylus moreletii
- Nile crocodile or African crocodile, Crocodylus niloticus (the subspecies found in Madagascar is sometimes called the black crocodile)
- New Guinea crocodile, Crocodylus novaeguineae
- Mugger crocodile, marsh crocodile, or Indian crocodile, Crocodylus palustris
- Saltwater crocodile or estuarine crocodile, Crocodylus porosus
- Cuban crocodile, Crocodylus rhombifer
- Siamese crocodile, Crocodylus siamensis
- Desert crocodile, Crocodylus suchus
The cladogram below follows the topology from a 2012 analysis of morphological traits by Christopher A. Brochu and Glenn W. Storrs. Many extinct species of Crocodylus might represent different genera. C. suchus was not included, because its morphological codings were identical to these of C. niloticus. However, the authors suggested that it could be explained by their specimen sampling, and considered the two species to be distinct.
- Brochu, C. A.; Storrs, G. W. (2012). "A giant crocodile from the Plio-Pleistocene of Kenya, the phylogenetic relationships of Neogene African crocodylines, and the antiquity ofCrocodylusin Africa". Journal of Vertebrate Paleontology 32 (3): 587. doi:10.1080/02724634.2012.652324.
- McAliley, Willis, Ray, White, Brochu & Densmore (2006). Are crocodiles really monophyletic?—Evidence for subdivisions from sequence and morphological data. Molecular Phylogenetics and Evolution 39: 16-32.
- Brochu, C. A.; Njau, J.; Blumenschine, R. J.; Densmore, L. D. (2010). "A New Horned Crocodile from the Plio-Pleistocene Hominid Sites at Olduvai Gorge, Tanzania". PLoS ONE 5 (2): e9333. doi:10.1371/journal.pone.0009333. PMC 2827537. PMID 20195356. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2827537.
- Robert W. Meredith, Evon R. Hekkala, George Amato and John Gatesy (2011). "A phylogenetic hypothesis for Crocodylus (Crocodylia) based on mitochondrial DNA: Evidence for a trans-Atlantic voyage from Africa to the New World". Molecular Phylogenetics and Evolution 60: 183–191. doi:10.1016/j.ympev.2011.03.026.
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