Ichthyoconodon
| Ichthyoconodon Temporal range: 145–139 Ma | |
|---|---|
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Subphylum: | Vertebrata |
| Class: | Mammalia |
| Order: | Eutriconodonta |
| Family: | Triconodontidae |
| Subfamily: | Alticonodontinae |
| Genus: | †Ichthyoconodon Sigogneau-Russell, 1995 |
| Type species | |
| Ichthyoconodon jaworowskorum Sigogneau-Russell, 1995 | |
Ichthyoconodon ("fish cone tooth") is an extinct genus of theriimorph mammal from the Lower Cretaceous of Morocco. Usually considered an eutriconodont, it is notable for its oceanic location and atypical shape, indicative of potentially unusual ecological niches; some researchers think that it may be the first marine mammal,[1] or part of a bizarre clade of flying mammals.[2]
Description
Ichthyoconodon is known primarily from isolated teeth from Anoual Syncline sediments of Morocco, in particular strata thought to date to the Berriasian. These teeth, mostly molars, possess many synapomorphies associated with triconodontid eutriconodonts, but its cusps are notoriously sharp for the group's standards and are rather specialised. They belong to animal in life possibly as large as a platypus.
Relationships
Ichthyoconodon has been found to be a eutriconodont, though the degree of speciation has been noted as being difficult to assess its status as such.[1] Rose et al. found some skepticism about a eutriconodont identity,[3] and some studies have suggested an identity not even as a mammal, but as a pterosaur,[4] but most recent phylogenetic studies favour a eutriconodont identity.[5][4][2]
The most recent phylogenetic studies favour a close relationship with Volaticotherium and Argentoconodon within the triconodontid clade Alticonodontinae.[2]
Ecology
Ichthyoconodon's teeth are located in marine deposits, alongside taxa like hybodontid sharks, ornithocheirid pterosaurs,[6] ray-finned fish and sea turtles, as well as several terrestrial taxa like theropods.[7] Unlike other mammal teeth, including other contemporary teeth such as those of Hahnodon, which show some degree of degradation, Ichthyoconodon teeth are not significantly modified, ruling out the possibility that the animal was carried over from river deposits. This means that the mammal either died in situ or was only carried over for a short distance.[1]
Because the teeth of Ichthyoconodon are rather sharp and convergent in some details to the teeth of piscivorous mammals like otters and seals, some researchers have suggested that it was a marine mammal. If this is the case, it is by far the earliest known mammal species to have adapted to live in the sea. The Jurassic and Cretaceous docodonts like Castorocauda and Haldanodon, Early Cretaceous monotremes and the Late Cretaceous Didelphodon have also specialised for an aquatic lifestyle, but Ichthyoconodon would have been the only known Mesozoic mammal to have foraged in the sea.
Alternatively, Ichthyoconodon may have been volant, based on its relationship with the gliding Volaticotherium and the possibly also volant Argentoconodon. The presence of Argentoconodon in South America, Volaticotherium in Asia and Ichthyoconodon in North Africa in such a relatively close span of time suggests that there may have been a clade of Jurassic-Early Cretaceous flying triconodonts.[2]
Either situation would have been exceptional for a Mesozoic mammal, further adding to the variety of ecological niches these animals occupied.
References
- 1 2 3 Sigogneau-Russell, Denise (1995). "Two possibly aquatic triconodont mammals from the Early Cretaceous of Morocco" (PDF). Acta Palaeontologica Polonica 40 (2): 149–162.
- 1 2 3 4 Gaetano, Leandro C.; Rougier, Guillermo W. (2011). "New materials of Argentoconodon fariasorum (Mammaliaformes, Triconodontidae) from the Jurassic of Argentina and its bearing on triconodont phylogeny". Journal of Vertebrate Paleontology 31 (4): 829–843. doi:10.1080/02724634.2011.589877.
- ↑ Rose, K.D., Cifelli, R.L. & Lipka, T.R. (2001) Second triconodont dentary from the Early Cretaceous of Maryland. Journal of Vertebrate Paleontology Volume 21. pp. 628–632.
- 1 2 Kielan-Jaworowska, R. L. Cifelli, and Z.-X. Luo. 2004. Mammals from the age of dinosaurs: Origins, evolution, and structure. Columbia University Press, New York 1-630 [R. Whatley/R. Whatley/R. Whatley]
- ↑ Mikko Haaramo (2007) Mikko's Phylogeny Archive. Acceso: 2 de noviembre de 2007.
- ↑ Wilton, Mark P. (2013). Pterosaurs: Natural History, Evolution, Anatomy. Princeton University Press. ISBN 0691150613.
- ↑ "Fossilworks: Gateway to the Paleobiology Database". fossilworks.org.