Ikanogavialis Explained

Ikanogavialis is an extinct genus of gavialid 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.

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 of Venezuela, South America.

Additionally, a Pleistocene gavialoid found on Woodlark Island of Papua New Guinea was initially named Gavialis papuensis in 1905, but has since been proposed to be a member of Ikanogavialis,^[3] although the poor quality of the preserved material makes it difficult to determine.^[4]

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.^{[5] [6]} 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.^{[7] [8]} Ikanogavialis also existed with many other crocodilians in Venezuela during the late Miocene including the giant caiman Purussaurus and an extinct species of Melanosuchus.^[9]

"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.^[10]

Phylogeny

A phylogenetic analysis conducted in a 2007 study found Gryposuchinae to include the genera Aktiogavialis, Gryposuchus, Ikanogavialis, Piscogavialis, and Siquisiquesuchus. Below is a cladogram from the 2007 analysis showing the phylogenetic relationships of gryposuchines among gavialoids:^[11]

Alternatively, a 2018 tip dating study by Lee & Yates simultaneously using morphological, molecular (DNA sequencing), and stratigraphic (fossil age) data indicated that the members of Gryposuchinae may in fact be paraphyletic and rather an evolutionary grade towards Gavialis and the gharial, as shown in the cladogram below:^[12]

External links

• Ikanogavialis in the Paleobiology Database

Notes and References

1. Book: Langston . W. . Gasparini . Z. . 1997 . Crocodilians, Gryposuchus, and the South American gavials . Kay . R. F. . Madden . R. H. . Cifelli . R. L. . Flynn . J. J. . Vertebrate Paleontology in the Neotropics: The Miocene fauna of La Venta, Colombia . Washington, D.C. . Smithsonian Institution Press . 113–154 . 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 . Ameghiniana . 7 . Preliminary note on a new gharial Pliocene of Venezuela and a discussion of the South American gavials . 151–159 .
3. Martin . Jeremy E. . Buffetaut . Eric . Naksri . Wilailuck . Lauprasert . Komsorn . Claude . Julien . 18 September 2012 . Gavialis from the Pleistocene of Thailand and Its Relevance for Drainage Connections from India to Java . . 7 . 9 . e44541 . 10.1371/journal.pone.0044541 . 23028557 . 3445548 . 2012PLoSO...744541M . free.
4. 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 . . 9 . e12094 . 10.7717/peerj.12094 . 34567843 . 8428266 . free.
5. 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 .
6. 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 . 10.1017/S1477201906001829 . 84357359 .
7. 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 . 10.1007/BF02988368 . 84214781 .
8. Brochu . C. A. . Rincon . A. D. . 2004 . A gavialoid crocodylian from the Lower Miocene of Venezuela . Special Papers in Palaeontology . 71 . 61–78 .
9. 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 . 10.1017/S147720190600188X . 85950121 .
10. Molnar . R. E. . 1982 . A longirostrine crocodilian from Murua (Woodlark), Solomon Sea . Memoirs of the Queensland Museum . 20 . 675–685 .
11. Vélez-Juarbe . Jorge . Brochu, C.A. . Santos, H. . 2007 . A gharial from the Oligocene of Puerto Rico: transoceanic dispersal in the history of a non-marine reptile . Proceedings of the Royal Society B . 274 . 1615 . 1245–1254 . 10.1098/rspb.2006.0455 . 17341454 . 2176176.
12. 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 . . 285 . 1881 . 10.1098/rspb.2018.1071 . 30051855 . 6030529 . free.