Mekosuchinae

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Mekosuchinae
Temporal range: Eocene - Holocene, 56–0.003  Ma
Quinkana timara skull.jpg
Restoration of the skull of Quinkana timara at the Central Australian Museum
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Crocodilia
Clade: Mekosuchinae
Willis, Molnar & Scanlon, 1993
Type species
Mekosuchus inexpectatus
Balouet & Buffetaut, 1987
Genera

Mekosuchinae is an extinct clade of crocodilians from the Cenozoic of Australasia. They represented the dominant group of crocodilians in the region during most of the Cenozoic. [1] They first appear in the fossil record in the Eocene in Australia, and survived until the arrival of humans: in the Late Pleistocene in Australia and within the Holocene in the Pacific islands of Fiji, New Caledonia and Vanuatu.

Mekosuchine crocodiles are a diverse group. One of the last species, Mekosuchus inexpectatus from Holocene New Caledonia, may have been arboreal. [2] The early Miocene species Harpacochampsa camfieldensis may have resembled a false gharial. Another mekosuchine fossil, currently undescribed, has been found in Miocene deposits from New Zealand. One genus, Mekosuchus , managed to spread to the islands of the Pacific; it is believed to have island-hopped across the Coral Sea, moving first to a now submerged island known as Greater Chesterfield Island, then New Caledonia and onwards. In the Pleistocene, Quinkana was one of the top terrestrial predators of the Australian continent.

Mekosuchines underwent a drastic decline in post-Miocene Australia, with all genera, except for Quinkana and Paludirex (both perishing during the Quaternary extinction event) becoming extinct in Australia by the end of the Pliocene. After the demise of Quinkana and Pallimnarchus, the group survived on Vanuatu and New Caledonia until the arrival of humans, who are presumed to have driven them to extinction.

While historically considered to be true crocodiles (of the family Crocodylidae), modern research places them as an independent group within or closely related to Longirostres, which contains both crocodiles and gavialids. [1]

Phylogeny

Mekosuchus inexpectatus Mekosuchus inexpectans.JPG
Mekosuchus inexpectatus

Mekosuchinae is cladistically defined as a node-based taxon composed of the last common ancestor of Kambara implexidens , Mekosuchus inexpectatus , and all of its descendants. [3]

Mekosuchinae is traditionally thought to be included as a basal member Crocodyloidea, [4] although this is disputed. [5] A 2018 tip dating study by Lee & Yates simultaneously using morphological, molecular (DNA sequencing), and stratigraphic (fossil age) data established the inter-relationships within Crocodilia, [5] which was expanded upon in 2021 by Hekkala et al. using paleogenomics by extracting DNA from the extinct Voay . [6]

The below cladogram shows the results of the Lee and Yates study (2018), which placed Mekosuchinae outside of Crocodyloidea, as more basal than Longirostres (the combined group of crocodiles and gavialids). [5]

Crocodylia

Alligatoroidea Alligator white background.jpg

Prodiplocynodon

Asiatosuchus

"Crocodylus" affinis

"Crocodylus" depressifrons

"Crocodylus" acer

Brachyuranochampsa

Mekosuchinae

Australosuchus

Kambara taraina

Kambara implexidens

Kambara murgonensis

Kalthifrons

Pallimnarchus

Baru wickeni

Baru darrowi

Baru Alcoota

Bullock Creek taxon

Baru huberi

Volia

Mekosuchus

Trilophosuchus

Quinkana

Longirostres
Crocodyloidea

"Crocodylus" megarhinus

Crocodylidae Siamese Crocodile white background.jpg

Gavialoidea

extinct basal Gavialoids

Gavialidae

Gavialis Gavialis gangeticus (Gharial, Gavial) white background.jpg

Tomistoma Tomistoma schlegelii. white background.JPG

Other studies have recovered Mekosuchinae within Longirostres, belonging to Crocodyloidea, as shown in the alternative cladogram below. [1]

Anteophthalmosuchus epikrator

Theriosuchus pusillus

Susisuchidae

Bernissartia fagesii

Eusuchia

Hylaeochampsidae

Allodaposuchidae

Portugalosuchus azenhae

Crocodylia

Borealosuchus spp.

Alligatoroidea

Planocraniidae

Prodiplocynodon langi

'Crocodylus' affinis

'Crocodylus' depressifrons

Asiatosuchus germanicus

'Crocodylus' acer

Brachyuranochampsa eversolei

Longirostres
Gavialoidea

Kentisuchus spenceri

Megadontosuchus arduini

Gunggamarandu maunala

Dollosuchoides densmorei

Maomingosuchus petrolica

Harpacochampsa camfieldensis

Thecachampsa antiquus

'Tomistoma' cairense

Gavialidae

Crocodyloidea

'Crocodylus' megarhinus

Mekosuchinae

Kambara implexidens

Kambara taraina

Kambara murgonensis

Australosuchus clarkae

Kalthifrons aurivellensis

Mekosuchini

Trilophosuchus rackhami

Mekosuchus whitehunterensis

Mekosuchus sanderi

Baru wickeni

Baru darrowi

Paludirex gracilis

Paludirex vincenti

Quinkana meboldi

Quinkana fortirostrum

Quinkana timara

Crocodylidae

Related Research Articles

<span class="mw-page-title-main">Gavialinae</span> Subfamily of gharial crocodylians

Gavialinae is a subfamily of large semiaquatic crocodilian reptiles, resembling crocodiles, but with much thinner snouts. Gavialinae is one of the two major subfamilies within the family Gavialidae - the other being the subfamily Tomistominae, which contains the false gharial and extinct relatives.

<span class="mw-page-title-main">Gavialidae</span> Family of gharial crocodylians

Gavialidae is a family of large semiaquatic crocodilians with elongated, narrow snouts. Gavialidae consists of two living species, the gharial and the false gharial, both occurring in Asia. Many extinct members are known from a broader range, including the recently extinct Hanyusuchus. Gavialids are generally regarded as lacking the jaw strength to capture the large mammalian prey favoured by crocodiles and alligators of similar size so their thin snout is best used to catch fish, however the false gharial has been found to have a generalist diet with mature adults preying upon larger vertebrates, such as ungulates.

<i>Crocodylus</i> Genus of reptiles

Crocodylus is a genus of true crocodiles in the family Crocodylidae.

<i>Tomistoma</i> Genus of crocodilians

Tomistoma is a genus of gavialid crocodilians. They are noted for their long narrow snouts used to catch fish, similar to the gharial. Tomistoma contains one extant (living) member, the false gharial, as well as potentially several extinct species: T. cairense, T. lusitanicumT. coppensi, and T. dowsoni. However, these species may need to be reclassified to different genera as studies have shown them to be paraphyletic, for example: previously assigned species T. taiwanicus from Taiwan, is reclassified to the genus Toyotamaphimeia, and T. dowsoni should be excluded from Tomistoma based on phylogenetic analysis.

<i>Mekosuchus</i> Extinct genus of reptiles

Mekosuchus is a genus of extinct Australasian mekosuchine crocodilian. Species of Mekosuchus were generally small-sized, terrestrial animals with short, blunt-snouted heads and strong limbs. Four species are currently recognized, M. inexpectatus, M. whitehunterensis, M. sanderi and M. kalpokasi, all known primarily from fragmentary remains.

<span class="mw-page-title-main">Alligatoroidea</span> Superfamily of reptiles

Alligatoroidea is one of three superfamilies of crocodylians, the other two being Crocodyloidea and Gavialoidea. Alligatoroidea evolved in the Late Cretaceous period, and consists of the alligators and caimans, as well as extinct members more closely related to the alligators than the two other groups.

<i>Asiatosuchus</i> Extinct genus of reptiles

Asiatosuchus is an extinct genus of crocodyloid crocodilians that lived in Eurasia during the Paleogene. Many Paleogene crocodilians from Europe and Asia have been attributed to Asiatosuchus since the genus was named in 1940. These species have a generalized crocodilian morphology typified by flat, triangular skulls. The feature that traditionally united these species under the genus Asiatosuchus is a broad connection or symphysis between the two halves of the lower jaw. Recent studies of the evolutionary relationships of early crocodilians along with closer examinations of the morphology of fossil specimens suggest that only the first named species of Asiatosuchus, A. grangeri from the Eocene of Mongolia, belongs in the genus. Most species are now regarded as nomina dubia or "dubious names", meaning that their type specimens lack the unique anatomical features necessary to justify their classification as distinct species. Other species such as "A." germanicus and "A." depressifrons are still considered valid species, but they do not form an evolutionary grouping with A. grangeri that would warrant them being placed together in the genus Asiatosuchus.

<i>Planocrania</i> Extinct genus of reptiles

Planocrania is an extinct genus of eusuchian crocodyliforms from what is now China. Two species are currently known to belong to the genus.

Prodiplocynodon is an extinct genus of basal crocodyloid crocodylian. It is one of the only crocodyloids known from the Cretaceous and existed during the Maastrichtian stage. The only species of Prodiplocynodon is the type species P. langi from the Lance Formation of Wyoming, known only from a single holotype skull lacking the lower jaw.

<span class="mw-page-title-main">Crocodyloidea</span> Superfamily of crocodiles

Crocodyloidea is one of three superfamilies of crocodilians, the other two being Alligatoroidea and Gavialoidea, and it includes the crocodiles. Crocodyloidea may also include the extinct Mekosuchinae, native to Australasia from the Eocene to the Holocene, although this is disputed.

Rimasuchus is an extinct genus of crocodile from the Miocene of Egypt and possibly Libya. Only one species - Rimasuchus lloydi - is currently known. It was previously thought to be a species of Crocodylus, but is now thought to be more closely related to the modern African dwarf crocodiles (Osteolaemus).

<span class="mw-page-title-main">Gavialoidea</span> Superfamily of large reptiles

Gavialoidea is one of three superfamilies of crocodylians, the other two being Alligatoroidea and Crocodyloidea. Although many extinct species are known, only the gharial Gavialis gangeticus and the false gharial Tomistoma schlegelii are alive today, with Hanyusuchus having become extinct in the last few centuries.

<span class="mw-page-title-main">Tomistominae</span> Subfamily of reptiles

Tomistominae is a subfamily of crocodylians that includes one living species, the false gharial. Many more extinct species are known, extending the range of the subfamily back to the Eocene epoch. In contrast to the false gharial, which is a freshwater species that lives only in southeast Asia, extinct tomistomines had a global distribution and lived in estuaries and along coastlines.

<span class="mw-page-title-main">Brevirostres</span> Taxon of reptiles

Brevirostres is a paraphyletic group of crocodilians that included alligatoroids and crocodyloids. Brevirostres are crocodilians with small snouts, and are distinguished from the long-snouted gharials. It is defined phylogenetically as the last common ancestor of Alligator mississippiensis and Crocodylus niloticus and all of its descendants. This classification was based on morphological studies primarily focused on analyzing skeletal traits of living and extinct fossil species, and placed the gharials outside the group due to their unique skull structure, and can be shown in the simplified cladogram below:

<i>"Crocodylus" affinis</i> Species of reptile (fossil)

"Crocodylus" affinis is an extinct species of crocodyloid from the Eocene of Wyoming. Fossils were first described from the Bridger Formation by American paleontologist Othniel Charles Marsh in 1871. Marsh described the species, along with every other species of crocodyloid in the Bridger Formation, under the genus Crocodylus. The known specimen of "Crocodylus" affinis is a skull found at Grizzly Buttes, Wyoming, measuring 13 inches in length on the upper surface. Recent phylogenetic studies of crocodyloids show that "C." affinis is not a species of Crocodylus, but a genus has not yet been erected to include the species. Other Bridger species such as Crocodylus clavis and Brachyuranochampsa zangerli have been synonymized with "C." affinis.

<i>"Crocodylus" acer</i> Extinct species of reptile

"Crocodylus" acer is an extinct species of crocodyloid from the Eocene of Utah. A single well preserved skull was described by paleontologist Edward Drinker Cope in 1882 and remains the only known fossil of the species. It was found from the Wasatchian-age Green River Formation. "C." acer had a long, narrow snout and a low, flattened skull.

"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.

Crocodylus palaeindicus is an extinct species of crocodile from southern Asia. C. palaeindicus lived from the Miocene to the Pliocene. It may be an ancestor of the living Mugger crocodile.

Tomistoma cairense is an extinct species of gavialoid crocodilian from the Lutetian stage of the Eocene era. It lived in North East Africa, especially Egypt. Remains of T. cairense have been found in the Mokattam Formation, in Mokattam, Egypt. Tomistoma cairense did not have a Maxilla process within their lacrimal gland, whereas all extant (living) crocodilians do.

<span class="mw-page-title-main">Longirostres</span> Clade of crocodilians

Longirostres is a clade of crocodilians that includes the crocodiles and the gavialids, to the exclusion of the alligatoroids. Defined in 2003 by Harshman et al., Longirostres is a crown group defined phylogenetically as including the last common ancestor of Crocodylus niloticus and Gavialis gangeticus and all of its descendants.

References

  1. 1 2 3 Ristevski, Jorgo; Weisbecker, Vera; Scanlon, John D.; Price, Gilbert J.; Salisbury, Steven W. (February 2023). "Cranial anatomy of the mekosuchine crocodylian Trilophosuchus rackhami Willis, 1993". The Anatomical Record. 306 (2): 239–297. doi:10.1002/ar.25050. ISSN   1932-8486. PMC   10086963 . PMID   36054424.
  2. Naish, Darren (13 May 2009). "The small, recently extinct, island-dwelling crocodilians of the south Pacific". Tetrapod Zoology. ScienceBlogs. Retrieved 27 November 2010.
  3. Rio, Jonathan P.; Mannion, Philip D. (6 September 2021). "Phylogenetic analysis of a new morphological dataset elucidates the evolutionary history of Crocodylia and resolves the long-standing gharial problem". PeerJ . 9: e12094. doi: 10.7717/peerj.12094 . PMC   8428266 . PMID   34567843.
  4. Stein, Michael D.; Yates, Adam; Hand, Suzanne J.; Archer, Michael (2017). "Variation in the pelvic and pectoral girdles of Australian Oligo–Miocene mekosuchine crocodiles with implications for locomotion and habitus". PeerJ. 5: e3501. doi: 10.7717/peerj.3501 . PMC   5494174 . PMID   28674657.
  5. 1 2 3 Michael S. Y. Lee; Adam M. Yates (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 . 285 (1881). doi: 10.1098/rspb.2018.1071 . PMC   6030529 . PMID   30051855.
  6. Hekkala, E.; Gatesy, J.; Narechania, A.; Meredith, R.; Russello, M.; Aardema, M. L.; Jensen, E.; Montanari, S.; Brochu, C.; Norell, M.; Amato, G. (2021-04-27). "Paleogenomics illuminates the evolutionary history of the extinct Holocene "horned" crocodile of Madagascar, Voay robustus". Communications Biology. 4 (1): 505. doi: 10.1038/s42003-021-02017-0 . ISSN   2399-3642. PMC   8079395 . PMID   33907305.