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Toyotamaphimeia

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Toyotamaphimeia
Temporal range: 0.8–0.1 Ma[1]
↓
 Pleistocene
Toyotamaphimeia machikanensis skeleton
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Clade: Archosauromorpha
Clade: Archosauriformes
Order: Crocodilia
Family: Gavialidae
Subfamily: Gavialinae
Genus: †Toyotamaphimeia
Aoki, 1983
Type species
†Toyotamaphimeia machikanensis
(Kobatake et al., 1965)
Other species
  • †T. taiwanicus Shikama, 1972 [2]
Synonyms
  • Tomistoma machikanensis

Toyotamaphimeia (Toyotama-hime from Mountain Machikane (ja:待兼山)) is a genus of extinct gavialid crocodylian which lived in Japan and Taiwan during the Pleistocene. A specimen recovered in 1964 at Osaka University during the construction of a new science building has been dated to around 430–380 thousand years old based on the stratum in which it was found.[3] Unassigned species from same genus is also known from Taiwan.[4] T. machikanensis was a fairly large crocodylian measuring approximately 6.3–7.3 metres (21–24 ft) long. Two species were named, T. machikanensis from Japan and T. taiwanicus from Taiwan, both originally described as members of the genus Tomistoma.

History and naming

Holotype material of Toyotamaphimeia, Scalebar = 20cm

The first bones belonging to Toyotamaphimeia were discovered on May 3, 1964, during the construction of a new school building on the grounds of Ôsaka University. A field survey was conducted shortly afterwards, confirming the presence of more fossils, however not yet identifying their crocodilian nature. Following the survey several digs were organized starting on 9 June 1964. The skull was found on September 17 during the second dig. A third excavation was held in December which yielded more material of Toyotamaphimeia as well as fossil shellfish, insects and plant remains. Finally a fourth excavation took place in January 1965. Following analysis of the fossils, the material was assigned to the genus Tomistoma and named Tomistoma machikanense.[5]

In 1983, 18 years after the initial discovery, the skull was redescribed and deemed different enough from Tomistoma to erect a new genus, Toyotamaphimeia creating the comb. nov. Toyotamaphimeia machikanensis. In turn Aoki also changed the species name from machikanense to machikanensis, as the new genus name was feminine. The generic name derives from Toyotama-hime, a goddess of Japanese mythology with the ability to change her appearance to that of a crocodile.[6] The species epithet means "from Mountain Machikane".[5]

Description

The holotype of Toyotamaphimeia is a nearly complete skeleton consisting of a skull, an entire cervical and dorsal series of vertebrae, various ribs, 33 osteoderms as well as almost half the bones of the limbs, hip region and pectoral girdle. Most of the tail past the 3rd cervical vertebra is missing,[7] making it difficult to determine the exact length of the animal. Estimates of the animal's total length range from approximately 6.3 to 7.3 metres (21 to 24 ft).[8]

Toyotamaphimeia's skull is triangular in shape and longirostrine. It's fairly large, measuring over 1 metre (3.3 ft) from the tip of the premaxillary to the posterior end of the parietal. Most of that length is taken up by the maxilla and the nasal bones penetrate the premaxilla dorsally, extending deep into the premaxilla to the level of the 3rd maxillary alveoli, but not coming in contact with the nares. The skulltable of the holotype is crushed and damaged just before the orbits. The dentaries are broken off at the anterior end and each preserves 10 alveoli. The absence of any grooves or confluence of alveoli suggests that the specimen is mature, which is consistent with its great size.[7][9]

Paleobiology

The holotype specimen (MOUF00001) preserves a series of pathologies described by Katsura in 2004. The mandible is broken off at the tip, the tibia and fibula have been fractured and healed and some of the osteoderms present preserve healing bite marks. The fact that these injuries healed is evidence that the animal survived for a while after being injured and Katsura suggests that they may have been the result of intraspecific fights, furthermore hypothesizing that this could mean the Osaka University specimen may have been a male.[9]

Although the holotype of Toyotamaphimeia is the first substantial and best preserved evidence of crocodilians in Japan, there are other remains found across the islands. The northernmost finds were made in the Iwate Prefecture (northern Honshu) while their range extends south to Nagasaki Prefacture (Kyushu Island).[10] At this latitude Toyotamaphimeia would have existed at the thermal limit of crocodilians.[11] The Ibaraki Formation, where the remains of Toyotamaphimeia have been found, is part of the Osaka Group, which consists of lacustrine and fluvial deposits of the Pliocene to Pleistocene. Specifically, the fossils belong to the Kasuri Tuff, which dates to the Chibanian age of the Pleistocene. Molluscs, pollen and plant fossils (species of lotus and water caltrop found in the Kasuri Tuff suggest a moderate climate. Toyotamaphimeia would have most likely coexisted in this area alongside Stegodon orientalis, Cervus kazusensis, Panthera youngi, Bubalus teihardi and Stephanorhinus. The pollen found in the region suggests a vegetation consisting of alders, beeches, pines and Cryptomeria (Japanese redwood).[7]

Phylogeny

Below is a cladogram based morphological studies comparing skeletal features that shows Toyotamaphimeia as a member of Tomistominae, related to the false gharial:[11]

Crocodylidae

Based on morphological studies of extinct taxa, the tomistomines (including the living false gharial) were long thought to be classified as crocodiles and not closely related to gavialoids.[12] 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).[13][14][15][16][17][18][19]

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 Toyotamaphimeia as a gavialid, related to both the gharial and the false gharial:[18]

Gavialidae

References

  1. ^ 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.
  2. ^ Cho, Y.-Y.; Tsai, C.-H. (2023). "Crocodylian princess in Taiwan: Revising the taxonomic status of Tomistoma taiwanicus from the Pleistocene of Taiwan and its paleobiogeographic implications". Journal of Paleontology: 1–14. doi:10.1017/jpa.2023.36.
  3. ^ "Valuable Specimen which Osaka University Possesses". Archived from the original on 2005-03-06.
  4. ^ Ito, Ai; Aoki, Riosuke; Hirayama, Ren; Yoshida, Masataka; Kon, Hiroo; Endo, Hideki (2018). "The Rediscovery and Taxonomical Reexamination of the Longirostrine Crocodylian from the Pleistocene of Taiwan". Paleontological Research. 22 (2): 150–155. doi:10.2517/2017PR016. ISSN 1342-8144. S2CID 134961600.
  5. ^ a b Kobatake, N.; Chiji, N.; Ikebe, N.; Ishida, S.; Kamei, T.; Nakaseko, K.; Matsumoto, E. (1965). "Discovery of Crocodile Fossil from the Ôsaka Group". National Science Museum Monographs. 4 (2): 49-58. doi:10.4116/jaqua.4.49.
  6. ^ Aoki, R. (1983). "A new generic allocation of Tomistoma machikanense, a fossil crocodilian from the Pleistocene of Japan". Copeia. 1983 (1): 89–95. doi:10.2307/1444701. JSTOR 1444701. S2CID 87351884.
  7. ^ a b c Kobayashi, Y.; Tomida, Y.; Kamei, T.; Eguchi, T. (2006). ""Anatomy of a Japanese tomistomine crocodylian, Toyotamaphimeia machikanensis (Kamei et Matsumoto, 1965), from the middle Pleistocene of Osaka Prefecture: the reassessment of its phylogenetic status within Crocodylia"". National Science Museum Monographs (35).
  8. ^ Iijima, M.; Kubo, T. (2020). "Vertebrae-Based Body Length Estimation in Crocodylians and Its Implication for Sexual Maturity and the Maximum Sizes". Integrative Organismal Biology. 2 (1). obaa042. doi:10.1093/iob/obaa042.
  9. ^ a b Katsura, Yoshihiro (2004-06-01). "Paleopathology of Toyotamaphimeia machikanensis (Diapsida, Crocodylia) from the Middle Pleistocene of Central Japan". Historical Biology. 16 (2–4): 93–97. doi:10.1080/08912963400015041. ISSN 0891-2963. S2CID 84758037.
  10. ^ Taruno, H. (1999). "A fossil crocodile from Nagareki Town, Kishiwada City". Excavation Report on a Fossil Crocodile from Nagareki Town, Kishiwada City: 1-36.
  11. ^ a b 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. 496: 346–360. Bibcode:2018PPP...496..346I. doi:10.1016/j.palaeo.2018.02.002. ISSN 0031-0182.
  12. ^ 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.
  13. ^ Harshman, J.; Huddleston, C. J.; Bollback, J. P.; Parsons, T. J.; Braun, M. J. (2003). "True and false gharials: A nuclear gene phylogeny of crocodylia" (PDF). Systematic Biology. 52 (3): 386–402. doi:10.1080/10635150309323. PMID 12775527.
  14. ^ Gatesy, Jorge; Amato, G.; Norell, M.; DeSalle, R.; Hayashi, C. (2003). "Combined support for wholesale taxic atavism in gavialine crocodylians" (PDF). Systematic Biology. 52 (3): 403–422. doi:10.1080/10635150309329. PMID 12775528.
  15. ^ Willis, R. E.; McAliley, L. R.; Neeley, E. D.; Densmore Ld, L. D. (June 2007). "Evidence for placing the false gharial (Tomistoma schlegelii) into the family Gavialidae: Inferences from nuclear gene sequences". Molecular Phylogenetics and Evolution. 43 (3): 787–794. doi:10.1016/j.ympev.2007.02.005. PMID 17433721.
  16. ^ Gatesy, J.; Amato, G. (2008). "The rapid accumulation of consistent molecular support for intergeneric crocodylian relationships". Molecular Phylogenetics and Evolution. 48 (3): 1232–1237. doi:10.1016/j.ympev.2008.02.009. PMID 18372192.
  17. ^ 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). Claessens, Leon (ed.). "Insights into the ecology and evolutionary success of crocodilians revealed through bite-force and tooth-pressure experimentation". PLOS ONE. 7 (3): e31781. Bibcode:2012PLoSO...731781E. doi:10.1371/journal.pone.0031781. PMC 3303775. PMID 22431965.
  18. ^ a b 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.
  19. ^ 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.
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