Parvinatator
| Parvinatator Temporal range:
| |
|---|---|
Scientific classification
| |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Superorder: | †Ichthyopterygia |
| Family: | †Parvinatatoridae McGowan and Motani, 2003 |
| Genus: | †Parvinatator Nicholls and Brinkman, 1995 |
| Type species | |
| †Parvinatator wapitiensis Nicholls and Brinkman, 1995
| |
Parvinatator,from Latin, “parvus” little and “natator” swimmer, is an extinctgenusof smallichthyopterygianmarine reptilethat lived during the Early to MiddleTriassic.Its fossils have been found inBritish Columbia,Canada.[1]
Geological information
[edit]The only known Parvinatator fossil was located in an unknown horizon from theSulfur Mountain Formationin atalus deposit,so its exact geological age is unknown. Best estimates place the fossil somewhere between theOlenekianandLadinianage around 251-235 mya.[2]Other small ichthyosaurs have been found nearby includingGrippia,Utatsusaurus,andPhalarodon.
Discovery
[edit]Parvinatator wapitiensiswas discovered in the Sulfur Mountain Formation in British Columbia, Canada, byElisabeth Nichollsand Don Brinkman in 1995. The only fossil recovered of this genus is a partial skull and two forefins.[1]The skull has been tectonically deformed, partially dis-articulated and broken with the posterior section rotated forward into the orbit. The left forefin is well preserved with only minor overlapping and breakage, while the right forefin is heavily overlapped and broken.[3]
Description and paleobiology
[edit]Based on analysis of tooth size relative to the skull width, Parvinatator is estimated to be less than 1 meter long,[2]approximately the same size and general shape of otherbasalichthyosaurs,although it is unknown if Parvinatator lacked adorsal finlike Utatsusaurus and Grippia. Also like other early ichthyosaurs, Parvinatator most likely used an eel-like lateral body movement for propulsion,[4]known asanguilliform.Based on jaw size and tooth shape, Parvinatator is thought to have feed on smallfishandcephalopodssimilarly to other basal ichthyosaurs, as opposed to hard shelled organisms such asmollusksandclams.[3]Ichthyosaurs typically had large eyes suggesting they would hunt in the dark, either at night or in deep water.[5]After the skull's dis-articulatedorbitwas reconstructed, it matched the approximate shape and typical size of other ichthyosaurs eyes.[3]
Skull
[edit]The fossil of the skull is small, measuring approximately 15 cm in width by 10 cm in height. The skull had been dis-articulated, broken and tectonically deformed, but was reconstructed by Ryosuke Motani, leading to several differences from Nicholls and Brinkman's original description, including; the presence of thesquamosal,quadratojugal,and a reduced supratemporal, a lack of contact between theprefrontalandpostfrontal,as well as between thejugaland quadratojugal (which was previously identified as the squamosal).[3]Otherdiagnosticcharacteristics of the Parvinatator skull are as follows:
- The retroarticular process, composed of thearticular,surangular,andangular,is present and well developed. This is suggested to be aderived traitfor all ichthyosaurs.[1][6]
- The quadratojugal is high and narrow, laterally covering thequadrate.[7][6]
- The jugal and quadratojugal have a deep notch between them, agreeing with the lack of a lowertemporal fenestraor lowerzygomatic archas in all other ichthyosaurs.[7][6]
- Thepostorbitalis enlarged and overlaps the jugal along the posterior of the orbit, forming a natural articulation point.[8][3]
- The orbit is oval in shape, being longer than tall.[3]
- The external naris is enclosed by thepremaxilla,maxillaandnasal bone,separate from a well developedlacrimal.[1][6]
Forefin
[edit]
Unlike some basal ichthyosaurs,Parvinatator's forefin appears well adapted foraquatic life,although it was probably used for controllingpitchrather thanlocomotion.[9]On the well preserved left forefin ofParvinatatortheulnais reduced in both length and width and smaller than theradius.Several bones ofdigits4 and 5 are fused together as well.[1][3]
Phylogeny
[edit]There is some disagreement about the exact location ofParvinatatoramong its relatives. The followingphylogenyby Motani placesParvinatatorwithUtatsusaurusas basal ichthyopterygians but not true ichthyosaurs.[2]
| Ichthyopterygia |
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However, according to Maisch and Matzke in 2000,Parvinatatoris a true ichthyosaur and more derived thanUtatsusaurusandGrippia.[10]
| Ichthyosauria | |
See also
[edit]References
[edit]- ^abcdeNicholls, E. & Brinkman, D. (1995). A new ichthyosaur from the Triassic Sulphur Mountain formation of British Columbia. Sarjeant WAS (ed.): Vertebrate fossils and the evolution of scientific concepts: 521–535 London (Gordon & Breach).
- ^abcMotani, R. (1999). Phylogeny of the Ichthyopterygia. Journal of Vertebrate Paleontology, 19:3, 473-496.
- ^abcdefgMotani, R. (1997). Phylogeny of the Ichthyosauria (Amniota: Reptilia) with special reference to Triassic forms. Ph.D. dissertation, University of Toronto, Toronto, Ontario, Canada.
- ^Motani, R., You, H., & Mcgowan, C. (1996). Eel-like swimming in the earliest ichthyosaurs. Nature, 382, 347-348.
- ^Motani, R.; Rothschild, B.M.; Wahl, W. (1999). "Large eyes in deep diving ichthyosaurs".Nature.402:747.
- ^abcdMaisch, M. (2010). Phylogeny, systematics, and origin of the Ichthyosauria – the state of the art. Palaeodiversity, 3, 151–214.
- ^abMaisch, M.W. & Matzke, A.T. (2002). The skull of a large Lower Triassic ichthyosaur from Spitzbergen and its implications for the origin of the Ichthyosauria. Lethaia, 35, 250–256.
- ^Cuthbertson, R. S., Russell, A. P., & Anderson, J. S. (2013). Cranial morphology and relationships of a new grippidian (Ichthyopterygia) from the Vega-Phroso Siltstone Member (Lower Triassic) of British Columbia, Canada. Journal of Vertebrate Paleontology, 33, 831-847.
- ^McGowan, C. (1973). "Differential growth in three ichthyosaurs:Ichthyosaurus communis,I. breviceps,andStenopterygius quadriscissus(Reptilia, Ichthyosauria) ".Life Sciences ContributionsRoyal Ontario Museum.93:1–21.doi:10.5962/bhl.title.52086.
- ^Maisch, M.W.; Matzke, A.T. (2000). "The Ichthyosauria".Stuttgarter Beitrage zur Naturkunde, Serie B (Geologie und Palaontologie).298:1–159.
