Gaviale

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Gaviale
Gharial (Gavialis gangeticus)

Gharial ( Gavialis gangeticus )

Systematics
Row : Land vertebrates (Tetrapoda)
without rank: Amniotes (Amniota)
without rank: Sauropsida
without rank: Archosauria
Order : Crocodiles (crocodilia)
Family : Gaviale
Scientific name
Gavialidae
Adams , 1854
Comparison of the skull shapes of recent crocodiles. At the top the only two recent longirostrine representatives Gangesgavial and Sundagavial, followed by the stenorostrine representatives of the Crocodylidae, Orinoco crocodile and armored crocodile. These include the mesorostrine and brevirostrine forms.
Sundagavial Tomistoma schlegelii

The Gaviale (Gavialidae) are a family of the crocodiles (Crocodylia). The only recent representative is traditionally the gharial ( Gavialis gangeticus ) living in Nepal and North India . The Sundagavial ( Tomistoma schlegelii ) native to Malaysia and western Indonesia is traditionally regarded as a member of the real crocodiles (Crocodylidae). The results of molecular genetic studies suggest, however, that gharial and sundagavial are more closely related than to any other recent crocodile. Therefore, the Sundagavial is now also taxonomically counted among the gavials.

features

Gaviale live semiaquatically and feed mainly piscivor . As an adaptation to fish hunting, their skulls are longirostrin , that is, their jaws are long and narrow. As a result, the mandibular symphysis, that is, the seam at the anterior end of the mandible where the tooth-bearing bones, the dentalia, meet, is extremely long in gavials and extends over about half the length of the mandible. As a result, the lower jaw is Y-shaped when viewed from below (ventral) or above (dorsal). The less specialized jaws of most crocodiles and alligators are relatively wide and the symphysis is limited to the foremost part of the lower jaw, so that the lower jaw is V- or U-shaped in a dorsal or ventral view. This shape of the snout is called mesorostrin or brevirostrin .

In addition, the jaws of the gaviale are equipped with a relatively large number of teeth. The Sundagavial has 76–84 teeth and the Gangesgavial 106–110 teeth. Crocodiles and alligators usually have significantly fewer teeth (between 64 and 82 depending on the species). The pointed conical teeth of the gaviale have a rather uniform size. This true homodontia is particularly pronounced in Gavialis . In the other crocodiles, the teeth all have the same shape, but sometimes show significant differences in size. This pseudoheterodontia is additionally accentuated by the undulation (festooning) of the jaw margins. Gaviale, on the other hand, have only slightly festooned jaw margins.

Longirostrine skulls are within the crocodiles in the broader sense (Crocodyliformes) but not a unique selling point of the gaviale. They occur convergent among other things in the extinct Teleosauriden ( Jura ).

Skulls that stand between the mesorostrine and longirostrine forms in terms of snout morphology, that is, that have a very narrow and only weakly festooned, but not significantly elongated snout and whose lower jaw is still more V-shaped than Y-shaped, are called stenorostrin designated. Recent representatives with stenorostrine skulls are the Orinoco crocodile ( Crocodylus intermedius ), the Australian crocodile ( Crocodylus johnstoni ) and the West African armored crocodile ( Mecistops cataphractus ), the latter sometimes also being classified as a longirostrine form.

Systematics and fossil record

The Gavialidae are one of the three recent families of the crocodiles (Crocodylia). Traditionally, they are considered to be more distantly related to real crocodiles (Crocodylidae) as well as to alligators and caimans (Alligatoridae) within the crocodiles . On this point, too, the results of molecular genetic studies contradict the traditional view. Instead, they suggest that the gavials are more closely related to the real crocodiles than to the alligators . Most current morphological studies, which also include fossil species, still come to results that support the traditional view. A comparative study of the ontogeny of recent crocodiles showed that the embryonic development of the Gharial differs fundamentally from that of the real crocodiles as well as that of the Sundagavial, with the embryonic development of the last two mentioned parallels. Another problem is that the fossil record of the Gavialoidea already begins with longirostrine forms such as Eothoracosaurus (Upper Cretaceous), while the Tomistominae only appear in the early Eocene (e.g. Kentisuchus ), at which point they are still stenorostrin. Only the geologically younger representatives of this subfamily are longirostrin.

Morphological tree of recent crocodiles (after Brochu, 1999, 2003):

  Crocodiles  (crocodylia)  
  Brevirostres  
  Real crocodiles  (Crocodylidae)  

 Crocodylinae 


   

 Tomistominae 
 (only species: Sundagavial , Tomistoma schlegelii )



   

 Alligators  (Alligatoridae) 



   

 Gaviale (Gavialidae)  (only species: Gharial , Gavialis gangeticus )



Template: Klade / Maintenance / Style

Molecular tree of recent crocodiles (after Oaks, 2011):

  Crocodiles  (crocodylia)  


 Real crocodiles  (Crocodylidae) 


  Gaviale (Gavialidae)  

 Tomistominae   (only species: Sundagavial , Tomistoma schlegelii )


   

 Gavialinae  (only species: Gharial , Gavialis gangeticus )




   

 Alligators  (Alligatoridae) 



Template: Klade / Maintenance / Style
Skull and skull drawing by Gavialis cf. bengawanicus from the early Pleistocene of Thailand.
Skull of Gavialis browni from the early Pliocene of the Himalayan Molasses (Siwalik Group) of Pakistan.
Kentisuchus champsoides.jpg
Kentisuchus.jpg
Historical skull drawings of two specimens of Kentisuchus spenceri (early Eocene of England) from a compendium by Richard Owen , second half of the 19th century, shown under the names " Crocodilus champsoides " (above) and " Crocodilus toliapicus " (below). In the picture below, the dentalia lying close together in the entire front part of the lower jaw can be seen, the lower jaw being more V-shaped than Y-shaped, a typical characteristic of a stenorostrine skull.
Skull of Megadontosuchus arduini from the mid-Eocene of northern Italy.
Skull of "Gavialosuchus" americanus (alternatively Thecachampsa americana or T. antiqua ) from the late Miocene or early Pliocene of Florida, USA.
Reconstruction of the skeleton of Toyotamaphimeia machikanense from the mid-Pleistocene from Honshu , Japan.
Incomplete skull and lower jaw as well as extremity bones from “Tomistoma” petrolica , Upper Eocene of Guangdong , China.
Live reconstruction of Rhamphosuchus crassidens , a giant gavial from the Miocene of the Siwalik strata, North India, compared in size with a Ganges dolphin .

If fossil taxa are taken into account, the gavials are divided into three subfamilies: Gavialinae, Gryposuchinae and Tomistominae. The Gavialinae, to which the recent Gharial belongs, were found fossil mainly in Asia. Eogavialis from the Oligocene , however, comes from Africa. However, it is uncertain whether it is actually the earliest representative of the Gavialinae, or whether Eogavialis , still outside of the Gavialina, is at the base of the Gavialids. Representatives of this genus have also been found in marine deposits . The genus Gavialis appeared in the Miocene . Finds of Gavialis species on islands of Indonesia and Oceania suggest that they, unlike the Gharial, also lived in salt water or at least did not shy away from it.

The Gryposuchinae have no recent representatives. So far, they have only been found in South America and the Caribbean. They first appeared in the Oligocene and lived until the early Pliocene. Their fossils are also found in deposits from former coastal areas. Gryposuchus croizati was the largest species at over 10 meters in length.

Fossil tomistominae have been found in Africa, Europe, Asia, and North America. The oldest representatives come from the early Eocene. It is also assumed that the Tomistominae also lived in salt water and spread by crossing seas. Rhamphosuchus from India was the largest genus with an estimated 10–12 meters.

The following fossil species, including the Tomistominae, belong to the Gavialidae (according to Vélez-Juarbe, Brochu & Santos, 2007; Brochu & Storrs, 2012 and Martin & al., 2012):

Individual evidence

  1. ↑ John Harshman, Christopher J. Huddleston, Jonathan P. Bollback, Thomas J. Parsons, Michael J. Braun: True and false gharials: a nuclear gene phylogeny of crocodylia. Systematic Biology. Vol. 52, No. 3, 2003, pp. 386-402, doi : 10.1080 / 10635150390197028
  2. ↑ Axel Janke, Anette Gullberg, Sandrine Hughes, Ramesh K. Aggarwal, Ulfur Arnason: Mitogenomic Analyzes Place the Gharial ( Gavialis gangeticus ) on the Crocodile Tree and Provide Pre-K / T Divergence Times for Most Crocodilians. Journal of Molecular Evolution. Vol. 61, No. 5, 2005, pp. 620–626, doi : 10.1007 / s00239-004-0336-9 (free full text: Researchgate )
  3. ↑ Ray E. Willis, L. Rex McAliley, Erika D. Neeley, Llewellyn D. Densmore III: Evidence for placing the false gharial ( Tomistoma schlegelii ) into the family Gavialidae: Inferences from nuclear gene sequences. Molecular Phylogenetics and Evolution. Vol. 43, No. 3, 2007, pp. 787-794, doi : 10.1016 / j.ympev.2007.02.005
  4. ↑ Ray E. Willis: Transthyretin Gene (TTR) Intron One Elucidates Crocodylian Relationships. Molecular Phylogenetics and Evolution. Vol. 53, No. 3, 2009, pp. 1049-1054, PMC 2787865 (free full text)
  5. ↑ a b c Jamie R. Oaks: A time-calibrated species tree of Crocodylia reveals a recent radiation of the true crocodiles. Evolution. Vol. 65, No. 11, 2011, pp. 3285-3297, doi : 10.1111 / j.1558-5646.2011.01373.x
  6. ↑ a b Christopher W. Walmsley, Peter D. Smits, Michelle R. Quayle, Matthew R. McCurry, Heather S. Richards, Christopher C. Oldfield, Stephen Wroe, Phillip D. Clausen, Colin R. McHenry: Why the Long Face ? The Mechanics of Mandibular Symphysis Proportions in Crocodiles. PLoS ONE. Vol. 8, No. 1, 2013, e53873, doi : 10.1371 / journal.pone.0053873 .
  7. ↑ Richard Owen: Odontography; or, a treatise on the comparative anatomy of the teeth; their physiological relations, mode of development, and microscopic structure, in the vertebrate animals. Volume I: Text. Hippolyte Baillière, London 1840–1845, p. 285 ff. ( BHL )
  8. ↑ L. Rex McAliley, Ray E. Willis, David A. Ray, P. Scott White, Christopher A. Brochu, Llewellyn D. Densmore III: Are crocodiles really monophyletic? - Evidence for subdivisions from sequence and morphological data. Molecular Phylogenetics and Evolution. Vol. 39, No. 1, 2006, pp. 16-32, doi : 10.1016 / j.ympev.2006.01.012 .
  9. ↑ P. Piras, P. Colangelo, DC Adams, A. Buscalioni, J. Cubo, T. Kotsakis, C. Meloro, P. Raia: The Gavialis - Tomistoma debate: the contribution of skull ontogenetic allometry and growth trajectories to the study of crocodylian relationships . In: Evolution & Development . Vol. 12, No. 6, 2010, pp. 568-579. doi : 10.1111 / j.1525-142X.2010.00442.x .
  10. ↑ Christopher A. Brochu: Phylogenetics, Taxonomy, and Historical Biogeography of Alligatoroidea. Society of Vertebrate Paleontology Memoir. Vol. 6 (Journal of Vertebrate Paleontology, Vol. 19, Supplementum No. 2), 1999, pp. 9-100, doi : 10.1080 / 02724634.1999.10011201
  11. ↑ Christopher A. Brochu: Phylogenetic Approaches Toward Crocodylian History. Annual Review of Earth and Planetary Sciences. Vol. 31, 2003, pp. 357-397, doi : 10.1146 / annurev.earth.31.100901.141308
  12. ↑ J. Velez-Juarbe, CA Brochu, H. Santos: A gharial from the Oligocene of Puerto Rico: transoceanic dispersal in the history of a non-marine reptile . In: Proceedings of the Royal Society B . Vol. 274, No. 1615, 2007, pp. 1245-1254. doi : 10.1098 / rspb.2006.0455 . PMID 17341454 . PMC 2176176 (free full text).
  13. ↑ CA Brochu, GW Storrs: A giant crocodile from the Plio-Pleistocene of Kenya, the phylogenetic relationships of Neogene African crocodylines, and the antiquity of Crocodylus in Africa . In: Journal of Vertebrate Paleontology . Vol. 32, No. 3, 2012, p. 587. doi : 10.1080 / 02724634.2012.652324 .
  14. ^ JE Martin, E. Buffetaut, W. Naksri, K. Lauprasert, J. Claude: Gavialis from the Pleistocene of Thailand and Its Relevance for Drainage Connections from India to Java . In: PLoS ONE . Vol. 7, No. 9, 2012, p. E44541. doi : 10.1371 / journal.pone.0044541 .
  15. ↑ Stéphane Jouve: A new basal tomistomine (Crocodylia, Crocodyloidea) from Issel (Middle Eocene; France): palaeobiogeography of basal tomistomines and palaeogeographic consequences. Zoological Journal of the Linnean Society. Vol. 177, No. 1, 2016, pp. 165-182, doi : 10.1111 / zoj.12357