Ikanogavialis

Ikanogavialis is an extinct genus of gryposuchine gavialoid crocodilian. Fossils have been found in the Urumaco Formation in Urumaco, Venezuela and the Solimões Formation of Brazil. The strata from which remains are found are late Miocene in age, rather than Pliocene as was once thought.[1] A possible member of this genus survived into the Late Holocene on Muyua or Woodlark Island in Papua New Guinea.

Ikanogavialis
Temporal range: Late Miocene; possibly Late Pleistocene/Holocene
if "Gavialis" papuensis is part of the genus
~11.6–5.3 Ma
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Crocodilia
Family: Gavialidae
Subfamily: †Gryposuchinae
Genus: †Ikanogavialis
Sill 1970
Species

Description

Ikanogavialis had a dorsoventrally deep snout and a distinctive notch between the dentary and maxillary alveoli.[2] The external nares projected anterodorsally from the rostrum. This can be seen as a plesiomorphic characteristic in crocodilians, but given that the earliest gavialoids possessed dorsally projecting external nares, this feature can be seen as having been a reversal from the gavialoid apomorphy back to the crocodilian plesiomorphy rather than having been directly obtained from an early crocodilian ancestor.

Species

The type species of Ikanogavialis is I. gameroi. It was named in 1970 from material found from the Urumaco formation. A Pleistocene gavialoid named Gavialis papuensis from Murua also known as Muyua or Woodlark Island, part of Papua New Guinea (erroneously considered part of the Solomon Islands in some sources), bears some vague similarities with Ikanogavialis and was referred to the genus in 1999,[3] along with other slender-snouted forms from the Neogene of South America and Africa.

Paleobiology

Ikanogavialis may have lived in a coastal paleoenvironment along with other gavialids such as Gryposuchus. The strata of the Urumaco formation were deposited in both marine and fluvial settings, although it is unclear to which portion both genera belong.[4][5] Other gavialoids such as Siquisiquesuchus and Piscogavialis are known to have lived in coastal environments, and it is likely that extant freshwater gavialoids such as Gavialis may have originated from these coastal forms.[6][7] Ikanogavialis also existed with many other crocodilians in Venezuela during the late Miocene including the giant caiman Purussaurus and an extinct species of Melanosuchus.[8]

"Gavialis"/Ikanogavialis papuensis was similarly fully marine, having been found in association with sea turtles and sirenians. It represents the youngest fully marine crocodilian to date.[9]

Notes and references
  1. Langston, W.; Gasparini, Z. (1997). "Crocodilians, Gryposuchus, and the South American gavials". In Kay, R. F.; Madden, R. H.; Cifelli, R. L.; Flynn, J. J. (eds.). Vertebrate Paleontology in the Neotropics: The Miocene fauna of La Venta, Colombia. Washington, D.C.: Smithsonian Institution Press. pp. 113–154. ISBN 1-56098-418-X.
  2. Sill, W. D. (1970). "Nota preliminar sobre un nuevo gavial del Plioceno de Venezuela y una discusion de los gaviales sudamericanos" [Preliminary note on a new gharial Pliocene of Venezuela and a discussion of the South American gavials]. Ameghiniana. 7: 151–159.
  3. Rauhe, M.; Frey, E.; Pemberton, D. S.; Rossmann, T. (1999). "Fossil crocodilians from the Late Miocene Baynunah Formation of the Emirate of Abu Dhabi, United Arab Emirates: osteology and palaeoecology". In Whybrow, P. J.; Hill, A. (eds.). Fossil vertebrates of Arabia. New Haven: Yale University Press. pp. 163–185. ISBN 0-300-07183-3.
  4. Linares, O. J. (2004). "Bioestratigrafia de la fauna de mamiferos de las Formaciones Socorro, Urumaco y Codore (Mioceno Medio–Plioceno Temprano) de la region de Urumaco, Falcon, Venezuela". Paleobiologia Neotropical. 1: 1–26.
  5. Sánchez-Villagra, M. R.; Aguilera, O. A. (2006). "Neogene vertebrates from Urumaco, Falcón State, Venezuela: diversity and significance". Journal of Systematic Palaeontology. 4 (3): 213–220. doi:10.1017/S1477201906001829.
  6. Kraus, R. (1998). "The cranium of Piscogavialis jugaliperforatus n. gen., n. sp. (Gavialidae, Crocodylia) from the Miocene of Peru". Paläontologische Zeitschrift. 72 (3–4): 389–406. doi:10.1007/BF02988368.
  7. Brochu, C. A.; Rincon, A. D. (2004). "A gavialoid crocodylian from the Lower Miocene of Venezuela". Special Papers in Palaeontology. 71: 61–78.
  8. Aguilera, O. A.; Driff, D.; Bocquentin-Villanueva, J. (2006). "A new giant Purussaurus (Crocodyliformes, Alligatoridae) from the Upper Miocene Urumaco Formation, Venezuela". Journal of Systematic Palaeontology. 4 (3): 221–232. doi:10.1017/S147720190600188X.
  9. Molnar, R. E. (1982). "A longirostrine crocodilian from Murua (Woodlark), Solomon Sea". Memoirs of the Queensland Museum. 20: 675–685.
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