Crocodylus

Taxonomy

The generic name, Crocodylus, was proposed by Josephus Nicolaus Laurenti in 1768. Crocodylus contains 13–14 extant (living) species and 5 extinct species. There are additional extinct species attributed to the genus Crocodylus that studies have shown no longer belong, although they have not yet been reassigned to new genera.

Extant species

The 13–14 living species are:

Fossils

Crocodylus also includes six extinct species:

• † Crocodylus anthropophagus is an extinct crocodile from Plio-Pleistocene of Tanzania.
• † Crocodylus checchiai is an extinct crocodile from Late Miocene of Kenya.
• † Crocodylus falconensis is an extinct crocodile from Early Pliocene of Venezuela.
• † 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.
• † Crocodylus sudani is an extinct crocodile from the Late Pleistocene of Sudan.

Evolution

While taxonomists generally agree that the crown group of Crocodylus appeared ~16 - 14 million years ago, there is an ongoing debate discussing whether the genus has an African or Indo-Pacific origin. Proponents of the African origin point towards phylogenetic evidence suggesting that the most recent common ancestor of Crocodylus and its sister genus, Voay, diverged around 25 million years ago near the Oligocene/Miocene boundary. This theory is supported by the existence of closely related African genera Osteolaemus and Mecistops.

Proponents of the Indo-Pacific origin claim that the origin of the genus closely coincides with the appearance of the oldest known species, Crocodylus palaeindicus, in South Asia. Additionally, mitochondrial analysis consistently places Indo-Pacific species Crocodylus mindorensis, Crocodylus novaeguineae, and Crocodylus johnstoni in the basal-most clade of the genus. All known New World and African crocodylus species have a much more recent evolutionary origin. While the exact origins of the genus remain uncertain, the most recent common ancestor of the species likely utilized osmoregulatory adaptations, including lingual salt glands, to radiate across the tropics.

Phylogeny

A 2018 tip dating study by Lee & Yates simultaneously using morphological, molecular (DNA sequencing), and stratigraphic (fossil age) data established the inter-relationships within Crocodylidae. In 2021, Hekkala et al. were able to use paleogenomics, extracting DNA from the extinct Voay, to better establish the relationships within Crocodylidae, including the subfamilies Crocodylinae and Osteolaeminae. In 2023, Sales-Oliveira et al. suggested the relationships of recently recognised species (M. leptorhynchus, C. halli and the third Osteolaemus species).

The below cladogram shows the results of the 2021 study, with supplementary data from the 2023 study:

References

References

1. {{IRMNG. 1329411. ''Crocodylus''. 17 April 2022
2. (1768). "Specimen medicum, exhibens synopsin reptilium emendatam cum experimentis circa venena et antidota reptilium austriacorum". Joan. Thom. Nob. de Trattnern.
3. (2012). "A giant crocodile from the Plio-Pleistocene of Kenya, the phylogenetic relationships of Neogene African crocodylines, and the antiquity of ''Crocodylus'' in Africa". Journal of Vertebrate Paleontology.
4. (2019). "Divergent Morphology among Populations of the New Guinea Crocodile, ''Crocodylus novaeguineae'' (Schmidt, 1928) Diagnosis of An Independent Lineage and Description of A New Species.". Copeia.
5. {{EMBL species
6. (2021-04-27). "Paleogenomics illuminates the evolutionary history of the extinct Holocene "horned" crocodile of Madagascar, Voay robustus". Communications Biology.
7. (2019). "Trait-based range expansion aided in the global radiation of Crocodylidae". Global Ecology and Biogeography.
8. (2011). "A time-calibrated species tree of Crocodylia reveals a recent radiation of the true crocodiles". Evolution.
9. (2021-03-15). "Near-complete phylogeny of extant Crocodylia (Reptilia) using mitogenome-based data". Zoological Journal of the Linnean Society.
10. Lee, Michael S. Y.. (27 June 2018). "Tip-dating and homoplasy: reconciling the shallow molecular divergences of modern gharials with their long fossil". [[Proceedings of the Royal Society B]].
11. Sales-Oliveira, V.. (2023). "Cross‑species chromosome painting and repetitive DNA mapping illuminate the karyotype evolution in true crocodiles (Crocodylidae)". Chromosoma.