Paratomistoma Explained

Paratomistoma (meaning "next to or near Tomistoma") is an extinct monospecific genus of gavialoid crocodylian. It is based on the holotype specimen CGM 42188, a partial posterior skull and lower jaw discovered at Wadi Hitan, Egypt, in Middle Eocene-age rocks of the Gehannam Formation. The skull is unfused but considered morphologically mature. Paratomistoma was named in 2000 by Christopher Brochu and Philip Gingerich; the type species is P. courti in honor of Nicholas Court, who found CGM 42188. They performed a phylogenetic analysis and found Paratomistoma to be a derived member of Tomistominae, related to the false gharial. It may have been a marine or coastal crocodilian.^[1]

Below is a cladogram based morphological studies comparing skeletal features that shows Paratomistoma as a member of Tomistominae:^[2]

Based on morphological studies of extinct taxa, the tomistomines were long thought to be classified as crocodiles and not closely related to gavialoids.^[3] However, recent molecular studies using DNA sequencing have consistently indicated that the false gharial (Tomistoma) (and by inference other related extinct forms in Tomistominae) actually belong to Gavialoidea (and Gavialidae).^{[4] [5] [6] [7] [8] [9] [10]}

Below is a cladogram from a 2018 tip dating study by Lee & Yates simultaneously using morphological, molecular (DNA sequencing), and stratigraphic (fossil age) data that shows Paratomistoma as an early-diverging gavialoid, more basal than the last common ancestor to both the gharial and the false gharial:^[9]

Notes and References

1. Brochu . Christopher A. . Gingerich, Philip D. . 2000 . New tomistomine crocodylian from the Middle Eocene (Bartonian) of Wadi Hitan, Fayum Province, Egypt . Contributions from the Museum of Paleontology . 30 . 10 . 251–268 .
2. Iijima. Masaya. Momohara. Arata. Kobayashi. Yoshitsugu. Hayashi. Shoji. Ikeda. Tadahiro. Taruno. Hiroyuki. Watanabe. Katsunori. Tanimoto. Masahiro. Furui. Sora. 2018-05-01. Toyotamaphimeia cf. machikanensis (Crocodylia, Tomistominae) from the Middle Pleistocene of Osaka, Japan, and crocodylian survivorship through the Pliocene-Pleistocene climatic oscillations. Palaeogeography, Palaeoclimatology, Palaeoecology. en. 496. 346–360. 10.1016/j.palaeo.2018.02.002. 2018PPP...496..346I. 0031-0182.
3. Brochu . C.A. . Gingerich, P.D. . 2000 . New tomistomine crocodylian from the Middle Eocene (Bartonian) of Wadi Hitan, Fayum Province, Egypt . University of Michigan Contributions from the Museum of Paleontology . 30 . 10 . 251–268.
4. 12775527 . 2003 . Harshman . J. . True and false gharials: A nuclear gene phylogeny of crocodylia . Systematic Biology . 52 . 3 . 386–402 . Huddleston . C. J. . Bollback . J. P. . Parsons . T. J. . Braun . M. J. . 10.1080/10635150309323 . free . 2021-06-30 . 2022-10-09 . https://ghostarchive.org/archive/20221009/http://si-pddr.si.edu/bitstream/handle/10088/6275/2003C_Harshman_et_al.pdf . dead .
5. Gatesy . Jorge . Amato, G. . Norell, M. . DeSalle, R. . Hayashi, C. . 2003 . Combined support for wholesale taxic atavism in gavialine crocodylians . Systematic Biology . 52 . 3 . 403–422 . 10.1080/10635150309329. 12775528 . free .
6. Willis . R. E. . McAliley . L. R. . Neeley . E. D. . Densmore Ld . L. D. . Evidence for placing the false gharial (Tomistoma schlegelii) into the family Gavialidae: Inferences from nuclear gene sequences . 10.1016/j.ympev.2007.02.005 . Molecular Phylogenetics and Evolution . 43 . 3 . 787–794 . June 2007 . 17433721.
7. Gatesy . J. . Amato . G. . 2008 . The rapid accumulation of consistent molecular support for intergeneric crocodylian relationships . Molecular Phylogenetics and Evolution. 48 . 3 . 1232–1237 . 10.1016/j.ympev.2008.02.009. 18372192.
8. Erickson, G. M.. Gignac, P. M.. Steppan, S. J.. Lappin, A. K.. Vliet, K. A.. Brueggen, J. A.. Inouye, B. D.. Kledzik, D.. Webb, G. J. W. . 2012 . Insights into the ecology and evolutionary success of crocodilians revealed through bite-force and tooth-pressure experimentation . PLOS ONE . 7 . 3 . e31781 . 10.1371/journal.pone.0031781. Claessens. Leon. 2012PLoSO...731781E . 22431965 . 3303775. free.
9. 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 . . 285 . 1881 . 10.1098/rspb.2018.1071 . 30051855 . 6030529 . free.
10. 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 . en . 4 . 1 . 505 . 10.1038/s42003-021-02017-0 . 33907305 . 8079395 . 2399-3642 . free.