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False gharial

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False gharial
Temporal range: Late Pleistocene - Recent, 0.1–0 Ma[1]
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Captive false gharial in Berlin Zoo, Germany
CITES Appendix I (CITES)[2]
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Clade: Archosauromorpha
Clade: Archosauriformes
Order: Crocodilia
Family: Gavialidae
Subfamily: Tomistominae
Genus: Tomistoma
Müller, 1846
Species:
T. schlegelii
Binomial name
Tomistoma schlegelii
(Müller, 1838)
Range of the false gharial
Synonyms

Pseudogavialis schlegelii

The false gharial (Tomistoma schlegelii), also known by the names Malayan gharial, Sunda gharial and tomistoma is a freshwater crocodilian of the family Gavialidae native to Peninsular Malaysia, Borneo, Sumatra and Java. It is listed as Endangered on the IUCN Red List, as the global population is estimated at around 2,500 to 10,000 mature individuals.[2]

The species name schlegelii honors Hermann Schlegel.[3][4]

Characteristics

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Gembira Loka Zoo
Los Angeles Zoo
Skull at the Zoological Museum of the Zoological Institute of the Russian Academy of Sciences, St. Petersburg

The false gharial is dark reddish-brown above with dark brown or black spots and cross-bands on the back and tail. Ventrals are grayish-white, with some lateral dark mottling. Juveniles are mottled with black on the sides of the jaws, body, and tail. The smooth and unornamented snout is extremely long and slender, parallel sided, with a length of 3.0 to 3.5 times the width at the base. All teeth are long and needle-like, interlocking on the insides of the jaws, and are individually socketed. The dorsal scales are broad at midbody and extend onto the sides of the body. The digits are webbed at the base. Integumentary sensory organs are present on the head and body scalation. Scales behind the head are frequently a slightly enlarged single pair. Some individuals bear a number of adjoining small keeled scales. Scalation is divided medially by soft granular skin. Three transverse rows of two enlarged nuchal scales are continuous with the dorsal scales, which consist of 22 transverse rows of six to eight scales, are broad at midbody and extend onto the sides of the body. Nuchal and dorsal rows equals a total of 22 to 23 rows. It has 18 double-crested caudal whorls and 17 single-crested caudal whorls. The flanks have one or two longitudinal rows of six to eight very enlarged scales on each side.[5]

The false gharial has one of the slimmest snouts of any living crocodilian, comparable to that of the slender-snouted crocodile and the freshwater crocodile in slenderness; only that of the gharial is noticeably slimmer.[6] Three mature males kept in captivity measured 3.6 to 3.9 m (12 to 13 ft) and weighed 190 to 210 kg (420 to 460 lb), while a female measured 3.27 m (10.7 ft) and weighed 93 kg (205 lb).[7] Females are up to 4 m (13 ft) long.[8] Males can grow up to 5 m (16 ft) in length and weigh up to 600 kg (1,300 lb).[9] The false gharial apparently has the largest skull of any extant crocodilian, in part because of the great length of the slender snout. Out of the eight longest crocodilian skulls from existing species that could be found in museums around the world, six of these belonged to false gharials. The longest crocodilian skull belonging to an extant species was of this species and measured 84 cm (33 in) in length, with a mandibular length of 104 cm (41 in). Most of the owners of these enormous skulls had no confirmed (or even anecdotal) total measurements for the animals, but based on the known skull-to-total length ratio for the species they would measure approximately 5.5 to 6.1 m (18 to 20 ft) in length.[10]

Three individuals ranging from 2.9 to 4.05 m (9 ft 6 in to 13 ft 3 in) in length and weighing from 79 to 255 kg (174 to 562 lb) had a bite force of 1,704–6,450 N (383–1,450 lbf).[11]

Taxonomy

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Compared to the Indian gharial.

The scientific name Crocodilus (Gavialis) schlegelii was proposed by Salomon Müller in 1838 who described a specimen collected in Borneo.[12] In 1846, he proposed to use the name Tomistoma schlegelii, if it needs to be placed in a distinct genus.[13]

The genus Tomistoma potentially also contains several extinct species like T. cairense, T. lusitanicum, T. taiwanicus, and T. coppensi. However, these species may need to be reclassified to different genera as evidence suggests they may be paraphyletic.[14][15]

Close-up of a false gharial at the Tierpark Berlin

The false gharial's snout broadens considerably towards the base and so is more similar to those of true crocodiles than to the gharial (Gavialis gangeticus), whose osteology indicated a distinct lineage from all other living crocodilians.[6] However, although more morphologically similar to Crocodylidae based on skeletal features, recent molecular studies using DNA sequencing consistently indicate that the false gharial and by inference other related extinct forms traditionally viewed as belonging to the crocodylian subfamily Tomistominae actually belong to Gavialoidea and Gavialidae.[16][17][18][19][20][21][14][22]

Fossil dorsal plates of "Tomistoma" calaritanus

Fossils of extinct Tomistoma species have been found in deposits of Paleogene, Neogene, and Quaternary ages in Taiwan, Uganda, Italy, Portugal, Egypt and India, but nearly all of them are likely to be distinct genera due to older age compared to the false gharial.[23]

The below cladogram of the major living crocodile groups is based on molecular studies and shows the false gharial's close relationships:[17][20][21][14][22]

Crocodilia

The following cladogram shows the false gharial's placement within the Gavialidae; it is based on a tip dating study, for which morphological, DNA sequencing and stratigraphic data were analysed:[14]

Gavialoidea
(stem-based group)

Distribution and habitat

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The false gharial is native to Peninsular Malaysia and the islands of Borneo and Sumatra; it is locally extinct in Singapore, Vietnam and Thailand.[2] It inhabits peat swamps and lowland swamp forests.[24]

Prior to the 1950s, Tomistoma occurred in freshwater ecosystems along the entire length of Sumatra east of the Barisan Mountains. The current distribution in eastern Sumatra has been reduced by 30-40% due to hunting, logging, fires, and agriculture.[25] The population has been estimated to comprise less than 2,500 mature individuals as of 2010.[24]

Ecology and behaviour

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Diet

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Until recently, very little was known about the diet or behaviour of the false gharial in the wild. Details are slowly being revealed. In the past, the false gharial was thought to have a diet of only fish and very small vertebrates, but more recent evidence indicates that it has a generalist diet despite its narrow snout. In addition to fish and smaller aquatic animals, mature adults prey on larger vertebrates, including proboscis monkeys, long-tailed macaques, deer, water birds, and reptiles.[26] There is an eyewitness account of a false gharial attacking a cow in East Kalimantan.[24]

The false gharial may be considered an ecological equivalent to Neotropical crocodiles such as the Orinoco and American crocodiles, which both have slender snouts but a broad diet.[6]

Reproduction

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The false gharial is a mound-nester. Females lay small clutches of 13–35 eggs per nest and appear to produce the largest eggs of living crocodilians. They attain sexual maturity at a length of around 2.5 to 3 m (8 ft 2 in to 9 ft 10 in), which is large compared to other crocodilians.[25] Courtship coincides with periods of rainfall in November to February and from April to June.[7]

Conflict

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In 2008, a 4-m female false gharial attacked and ate a fisherman in central Kalimantan; his remains were found in the gharial's stomach. This was the first verified fatal human attack by a false gharial.[26] However, by 2012, at least two more verified fatal attacks on humans by false gharials had occurred indicating perhaps an increase of human-false gharial conflict possibly correlated to the decline of habitat, habitat quality, and natural prey numbers.[27]

Threats

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Juveniles at the Bronx Zoo, with an Arrau turtle.

The false gharial is threatened by habitat loss in most of its range due to the drainage of freshwater swamps and conversion for commercial plantation of oil palms.[2] It is also hunted for its skin and meat, and its eggs are often harvested for human consumption.[26] Population surveys carried out in the mid 2000s indicated that the distribution of individuals is spotty and disconnected, with a risk of genetic isolation.[28] Some population units in unprotected areas do not bear viable breeding adults.[29]

Conservation

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The false gharial is listed on CITES Appendix I.[2]

Steps have been taken by the Malaysian and Indonesian governments to prevent its extinction in the wild. There are reports of some populations rebounding in Indonesia, yet with this slight recovery, mostly irrational fears of attacks have surfaced amongst the local human population.[26]

References

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  1. ^ Rio, J.P. & Mannion, P.D. (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. ^ a b c d e f Shaney, K.; Shwedick, B.; Simpson, B.K.; Pine, A.; Sideleau, B. & Stevenson, C. (2023). "Tomistoma schlegelii". IUCN Red List of Threatened Species. 2023: e.T21981A214287051. Retrieved 11 December 2023.
  3. ^ Müller, S. (1838). "Waarnemingen over de Indische Krokodillen en Beschrijving van eene nieuwe Soort". Tijdschrift voor Natuurlijke Geschiedenis en Physiologie (in Dutch). 5: 61–87.
  4. ^ Beolens, B.; Watkins, M. & Grayson, M. (2011). "Tomistoma schlegelii". The Eponym Dictionary of Reptiles. Baltimore: Johns Hopkins University Press. p. 235. ISBN 978-1-4214-0135-5.
  5. ^ Brazaitis, P. (2001) A Guide to the Identification of the Living Species of Crocodilians. Science Resource Center, Wildlife Conservation Society
  6. ^ a b c Piras, P.; Colangelo, P.; Adams, D. C.; Buscalioni, A.; Cubo, J.; Kotsakis, T. & Raia, P. (2010). "The Gavialis–Tomistoma debate: the contribution of skull ontogenetic allometry and growth trajectories to the study of crocodylian relationships". Evolution & Development. 12 (6): 568−579. doi:10.1111/j.1525-142X.2010.00442.x. PMID 21040423. S2CID 8231693.
  7. ^ a b Mathew, A.; Ganesan, M.; Majid, R. A. & Beastall, C. (2011). Breeding of False Gharial, Tomistoma schlegelii, at Zoo Negara, Malaysia (PDF). Zoo Negara. Archived from the original (PDF) on 2018-01-27. Retrieved 2012-06-13.
  8. ^ Milàn, J. & Hedegaard, R. (2010). "Interspecific variation in tracks and trackways from extant crocodylians". New Mexico Museum of Natural History and Science Bulletin. 51: 15.
  9. ^ Ahmad, A. A.; Dorrestein, G. M.; Oh, S. J. W. Y.; Hsu, C. D. (2017). "Multi-organ metastasis of fibrolamellar hepatocellular carcinoma in a Malayan Gharial (Tomistoma schlegelii)". Journal of Comparative Pathology. 157 (2): 80–84. doi:10.1016/j.jcpa.2017.06.007. PMID 28942308.
  10. ^ Whitaker, R. & Whitaker, N. (2008). "Who's got the biggest?" (PDF). Crocodile Specialist Group Newsletter 27 (4): 26−30.
  11. ^ 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. Bibcode:2012PLoSO...731781E. doi:10.1371/journal.pone.0031781. PMC 3303775. PMID 22431965.
  12. ^ Müller, S. (1838). "Waarnemingen over de Indische Krokodilen en beschrijving eene nieuwe soort". Tijdschrift Vorr Naturrlijke Geschiendes en Physiologie. 5: 61–87.
  13. ^ Müller, S. (1846). "Über den Charakter der Thierwelt auf den Inseln des indischen Archipels, ein Beitrag zur Naturgeschichte". Archiv für Naturgeschichte. 12: 109–128.
  14. ^ a b c d Lee, M. S. Y.; Yates, A. M. (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.
  15. ^ Iijima, M.; Momohara, A.; Kobayashi, Y.; Hayashi, S.; Ikeda, T.; Taruno, H.; Watanabe, K.; Tanimoto, M.; Furui, S. (2018). "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.
  16. ^ Densmore, L. D.; Owen, R. D. (1989). "Molecular Systematics of the Order Crocodilia". American Zoologist. 29 (3): 831–841. doi:10.1093/icb/29.3.831.
  17. ^ a b 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". Systematic Biology. 52 (3): 386–402. doi:10.1080/10635150309323. PMID 12775527.
  18. ^ Gatesy, J.; Amato, G.; Norell, M.; DeSalle, R.; H. C. (2003). "Combined support for wholesale taxic atavism in gavialine crocodylians". Systematic Biology. 52 (3): 403–422. doi:10.1080/10635150309329. PMID 12775528.
  19. ^ Willis, R. E.; McAliley, L. R.; Neeley, E. D.; Densmore, L. D. (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. Bibcode:2007MolPE..43..787W. doi:10.1016/j.ympev.2007.02.005. PMID 17433721.
  20. ^ a b Gatesy, J.; Amato, G. (2008). "The rapid accumulation of consistent molecular support for intergeneric crocodylian relationships". Molecular Phylogenetics and Evolution. 48 (3): 1232–1237. Bibcode:2008MolPE..48.1232G. doi:10.1016/j.ympev.2008.02.009. PMID 18372192.
  21. ^ a b 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. Bibcode:2012PLoSO...731781E. doi:10.1371/journal.pone.0031781. PMC 3303775. PMID 22431965.
  22. ^ a b Hekkala, E.; Gatesy, J.; Narechania, A.; Meredith, R.; Russello, M.; Aardema, M. L.; Jensen, E.; Montanari, S.; Brochu, C.; Norell, M.; Amato, G. (2021). "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. PMC 8079395. PMID 33907305.
  23. ^ "Fossilworks: Tomistoma". Fossilworks. Archived from the original on 2021-12-12. Retrieved 2021-12-17.
  24. ^ a b c Bezuijen, M.R.; Shwedick, B.M.; Sommerlad, R.; Stevenson, C.; Steubing, R.B. (2010). "Tomistoma Tomistoma schlegelii" (PDF). In Manolis, S.C.; Stevenson, C. (eds.). Crocodiles. Status Survey and Conservation Action Plan. Darwin: Crocodile Specialist Group. pp. 133−138.
  25. ^ a b Bezuijen, M.R.; Webb, G.J.W.; Hartoyo, P.; Samedi; Ramono, W.S.; Manolis, S.C. (1998). "The False Gharial (Tomistoma schlegelii) in Sumatra" (PDF). Crocodiles. Proceedings of the 14th Working Meeting of the Crocodile Specialist Group. Gland, Switzerland and Cambridge, UK: IUCN. The World Conservation Union. pp. 10–31.
  26. ^ a b c d Rachmawan, D.; Brend, S. (2009). "Human-Tomistoma interactions in central Kalimantan, Indonesian Borneo" (PDF). Crocodile Specialist Group Newsletter. 28 (1): 9–11.
  27. ^ Sideleau, B.; Britton, A. R. C. (2012). "A preliminary analysis of worldwide crocodilian attacks" (PDF). Crocodiles. Proceedings of the 21st Working Meeting of the IUCN-SSC Crocodile Specialist Group. Gland, Switzerland: IUCN Crocodile Specialist Group. pp. 111–114.
  28. ^ Stuebing, R. B.; Bezuijen, M. R.; Auliya, M. & Voris, H. K. (2006). "The current and historic distribution of Tomistoma schlegelii (the False Gharial) (Müller 1838) (Crocodylia, Reptilia)"". The Raffles Bulletin of Zoology. 54 (1): 181–197.
  29. ^ Rödder, D.; Engler, J.O.; Bonke, R.; Weinsheimer, F. & Pertel, W. (2010). "Fading of the last giants: an assessment of habitat availability of the Sunda gharial Tomistoma schlegelii and coverage with protected areas". Aquatic Conservation: Marine and Freshwater Ecosystems. 20 (6): 678–684. Bibcode:2010ACMFE..20..678R. doi:10.1002/aqc.1137.
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