Biology:False gharial

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Short description: Species of crocodilian

False gharial
Temporal range: Late Pleistocene - Recent, 0.1–0 Ma[1]
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Tomistoma schlegelii fg01.JPG
Captive false gharial in Berlin Zoo, Germany
CITES Appendix I (CITES)[2]
Scientific classification edit
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)
The range of the False gharial.png
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 specific name schlegelii honors Hermann Schlegel.[3][4]

Taxonomy

The scientific name Crocodilus (Gavialis) schlegelii was proposed by Salomon Müller in 1838 who described a specimen collected in Borneo.[5] In 1846, he proposed to use the name Tomistoma schlegelii, if it needs to be placed in a distinct genus.[6]

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.[7][8]

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.[9] 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.[10][11][12][13][14][15][7][16]

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.[17]

The below cladogram of the major living crocodile groups is based on molecular studies and shows the false gharial's close relationships:[11][14][15][7][16]

Crocodilia
Alligatoridae
Caimaninae
 
 

Caiman Caiman crocodilus llanos white background.JPG

 
 

Melanosuchus Melanosuchus niger white background.jpg

 
 
 

Paleosuchus Dwarf Caiman white background.jpg

 
 
Alligatorinae

Alligator Alligator white background.jpg

 
 
Longirostres
Crocodylidae
 

Crocodylus Siamese Crocodile white background.jpg

 
 
 

Mecistops Crocodylus cataphractus faux-gavial d'Afrique2 white background.JPG

 
 

Osteolaemus Bristol.zoo.westafrican.dwarf.croc.arp. white background.jpg

 
 
 
Gavialidae
 

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

 
 

Tomistoma Tomistoma schlegelii. white background.JPG

 
 
 
 

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:[7]

Gavialoidea
 
 
 
Gavialidae
 
 
 
 
 
 
 
 

Gharial

 
 

Gavialis bengawanicus†

 
 
 

Gavialis browni†

 
 
 

Gryposuchus colombianus†

 
 
 

Ikanogavialis†

 
 
 
 

Gryposuchus pachakamue†

 
 

Piscogavialis†

 
 
 
 

Harpacochampsa†

 
 
 
 
 

Toyotamaphimeia†

 
 

Penghusuchus†

 
 
 

Gavialosuchus†

 
 
 
 
 

Tomistoma lusitanicum†

 
 

False gharial

 
 
(crown group)
 

Tomistoma cairense†

 
 
 

Dollosuchoides†

 
 
 
 

Maroccosuchus†

 
 

Paratomistoma†

 
 
 
 

Kentisuchus†

 
(stem‑based group)

Characteristics

Close-up of a false gharial at the Tierpark Berlin
Skull of a false gharial 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.[18]

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.[9] 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).[19] Females have been recorded at lengths of up to 4 m (13 ft).[20] Males can grow up to 5 m (16 ft) in length and weigh up to 600 kg (1,300 lb).[21][22] 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.[23]

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).[24]

Distribution and habitat

False gharials are native to Peninsular Malaysia, Sarawak, and Indonesia (Sumatra, and Borneo), but were extirpated in Singapore, Vietnam, and Thailand. It is unclear if they remain in Java. Apart from rivers, they inhabit swamps and lakes.[2] The species is almost entirely found today in peat swamps and lowland swamp forests.[25] In the 1990s, information and sightings were available from 39 localities in 10 different river drainages, along with the remote river systems of Borneo.[citation needed]

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.[26]

Ecology and behaviour

Diet

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.[27] There is an eyewitness account of a false gharial attacking a cow in East Kalimantan.[25]

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.[9]

Reproduction

False gharials are mound-nesters. Females lay small clutches of 13 to 35 eggs per nest, and appear to produce the largest eggs of extant crocodilians. Sexual maturity in females appears to be attained around 2.5 to 3 m (8.2 to 9.8 ft), which is large compared to other crocodilians.[26]

It is not known when they breed in the wild or when the nesting season is. Once the eggs are laid, and construction of the mound is completed, the female abandons her nest. Unlike most other crocodilians, the young receive no parental care and are at risk of being eaten by predators, such as mongooses, tigers, leopards, and wild dogs. The young hatch after 90 days and are left to fend for themselves.[citation needed]

Conflict

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.[27] 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.[28]

Threats

The false gharial is threatened with extinction throughout most of its range due to the drainage of its freshwater swamplands and clearance of surrounding rainforests. The species is also hunted frequently for its skin and meat, and the eggs are often harvested for human consumption.[27]

Conservation

The false gharial is listed on CITES Appendix I.[2] Currently population surveys indicate that while the false gharial is not for the most extirpated from areas it used to inhabit, the distribution of individuals is much more spotty than the previously more connective distribution, putting the animals at risk of genetic isolation.[29] In large part, the isolation of false gharials is due to extremely extensive habitat destruction and disturbance within the species' area of distribution, few areas outside of legally protected areas are likely to bear viable breeding populations.[30]

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.[27] Yayasan Ulin (The Ironwood Foundation) is currently attempting to manage a wetland area in East Kalimantan, which is known to contain the false gharials.[31]

References

  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. PMID 34567843. 
  2. ↑ 2.0 2.1 2.2 2.3 2.4 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. https://www.iucnredlist.org/species/21981/214287051. Retrieved 11 December 2023. 
  3. ↑ Müller, S. (1838). "Waarnemingen over de Indische Krokodillen en Beschrijving van eene nieuwe Soort" (in nl). Tijdschrift voor Natuurlijke Geschiedenis en Physiologie 5: 61–87. https://archive.org/stream/tijdschriftvoorn05amst#page/n81/mode/2up. 
  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. ↑ Müller, S. (1838). "Waarnemingen over de Indische Krokodilen en beschrijving eene nieuwe soort". Tijdschrift Vorr Naturrlijke Geschiendes en Physiologie 5: 61–87. https://archive.org/details/tijdschriftvoorn05amst/page/n81/mode/2up. 
  6. ↑ Müller, S. (1846). "Über den Charakter der Thierwelt auf den Inseln des indischen Archipels, ein Beitrag zur Naturgeschichte". Archiv für Naturgeschichte 12: 109–128. https://archive.org/details/archivfrnaturg46berl/page/n131/mode/2up. 
  7. ↑ 7.0 7.1 7.2 7.3 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. PMID 30051855. 
  8. ↑ Iijima, M.; Momohara, A.; Kobayashi, Y.; Hayashi, S.; Ikeda, T.; Taruno, H.; Watanabe, K.; Tanimoto, M. et al. (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. doi:10.1016/j.palaeo.2018.02.002. Bibcode: 2018PPP...496..346I. https://www.sciencedirect.com/science/article/pii/S0031018217311124. 
  9. ↑ 9.0 9.1 9.2 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. 
  10. ↑ 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. 
  11. ↑ 11.0 11.1 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. 
  12. ↑ 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. 
  13. ↑ 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. doi:10.1016/j.ympev.2007.02.005. PMID 17433721. 
  14. ↑ 14.0 14.1 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. 
  15. ↑ 15.0 15.1 Erickson, G. M.; Gignac, P. M.; Steppan, S. J.; Lappin, A. K.; Vliet, K. A.; Brueggen, J. A.; Inouye, B. D.; Kledzik, D. et al. (2012). "Insights into the ecology and evolutionary success of crocodilians revealed through bite-force and tooth-pressure experimentation". PLOS One 7 (3): e31781. doi:10.1371/journal.pone.0031781. PMID 22431965. Bibcode: 2012PLoSO...731781E. 
  16. ↑ 16.0 16.1 Hekkala, E.; Gatesy, J.; Narechania, A.; Meredith, R.; Russello, M.; Aardema, M. L.; Jensen, E.; Montanari, S. et al. (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. PMID 33907305. 
  17. ↑ "Fossilworks: Tomistoma". Fossilworks. http://www.fossilworks.org/cgi-bin/bridge.pl?a=taxonInfo&taxon_no=38460. 
  18. ↑ Brazaitis, P. (2001) A Guide to the Identification of the Living Species of Crocodilians. Science Resource Center, Wildlife Conservation Society
  19. ↑ Mathew, A., Ganesan, M., Majid, R. A., & Beastall, C. (2011). Breeding of False Gharial, Tomistoma schlegelii, at Zoo Negara, Malaysia. Zoo Negara. http://www.zoonegaramalaysia.my/RPFalseGharial.pdf. 
  20. ↑ Milàn, J.; Hedegaard, R. (2010). "Interspecific variation in tracks and trackways from extant crocodylians". New Mexico Museum of Natural History and Science Bulletin 51: 15–2. 
  21. ↑ Shaney, Kyle and Shwedick, Bruce and Simpson, Boyd and Stevenson, Colin and Sideleau, B (2019). Tomistoma Tomistoma schlegelii (4 ed.). Crocodiles: Status, Survey and Conservation Action Plan. http://www.iucncsg.org/365_docs/attachments/protarea/29250d3a4c25ac44646a45ccf2aeebdc.pdf. 
  22. ↑ Ahmad, A. A.; Dorrestein, G. M.; Oh, S. J. W. Y.; Hsu, C. D. (1 August 2017). "Multi-organ Metastasis of Fibrolamellar Hepatocellular Carcinoma in a Malayan Gharial (Tomistoma schlegelii)" (in en). Journal of Comparative Pathology 157 (2): 80–84. doi:10.1016/j.jcpa.2017.06.007. ISSN 0021-9975. PMID 28942308. https://www.sciencedirect.com/science/article/pii/S0021997517301408. 
  23. ↑ Whitaker, R. and Whitaker, N. (2008). "Who's got the biggest?". Crocodile Specialist Group Newsletter 27 (4): 26−30. http://www.iucncsg.org/365_docs/attachments/protarea/907d4ded022a4ddefe525f89ee64b150.pdf. 
  24. ↑ Erickson, G. M.; Gignac, P. M.; Steppan, S. J.; Lappin, A. K.; Vliet, K. A.; Brueggen, J. A.; Inouye, B. D.; Kledzik, D. et al. (2012). "Insights into the ecology and evolutionary success of crocodilians revealed through bite-force and tooth-pressure experimentation". PLOS ONE 7 (3): e31781. doi:10.1371/journal.pone.0031781. PMID 22431965. Bibcode: 2012PLoSO...731781E. 
  25. ↑ 25.0 25.1 Bezuijen, M.R., Shwedick, B.M., Sommerlad, R., Stevenson, C. and Steubing, R.B. (2010). "Tomistoma Tomistoma schlegelii". in S.C. Manolis. Crocodiles. Status Survey and Conservation Action Plan. Darwin: Crocodile Specialist Group. pp. 133−138. 
  26. ↑ 26.0 26.1 Bezuijen, M.R., Webb, G.J.W., Hartoyo, P., Samedi, Ramono, W.S., Manolis, S.C. (1998) "The False Gharial (Tomistoma schlegelii) in Sumatra". In: Crocodiles. Proceedings of the 14th Working Meeting of the Crocodile Specialist Group, IUCN. The World Conservation Union, Gland, Switzerland and Cambridge, UK. Pp. 10–31.
  27. ↑ 27.0 27.1 27.2 27.3 Rachmawan, D.; Brend, S. (2009). "Human-Tomistoma interactions in central Kalimantan, Indonesian Borneo". Crocodile Specialist Group Newsletter 28 (1): 9–11. http://www.iucncsg.org/365_docs/attachments/protarea/CSG%20-e8b500ff.pdf. 
  28. ↑ Sideleau, B.; Britton, A. R. C. (2012). "A preliminary analysis of worldwide crocodilian attacks". Crocodiles. Proceedings of the 21st Working Meeting of the IUCN-SSC Crocodile Specialist Group. Gland, Switzerland: IUCN Crocodile Specialist Group. pp. 111–114. 
  29. ↑ 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.
  30. ↑ 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, 20(6), 678-684.
  31. ↑ "Siamese Crocodile Conservation Case Study | the Mohamed bin Zayed Species Conservation Fund". http://www.speciesconservation.org/projects/Siamese-Crocodile/309. 

External links

Wikidata ☰ Q242464 entry



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