''Parvinatator'', from Latin, “parvus” little and “natator” swimmer, is an extinct

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

of small ichthyopterygian marine reptile that lived during the Early to Middle

Triassic The Triassic ( ) is a geologic period and system (stratigraphy), system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago (Year#Abbreviations yr and ya, Mya), to the beginning of the Jurassic Period 201.36 ...

. Its fossils have been found in

British Columbia British Columbia (commonly abbreviated as BC) is the westernmost province of Canada, situated between the Pacific Ocean and the Rocky Mountains. It has a diverse geography, with rugged landscapes that include rocky coastlines, sandy beaches, ...

Canada Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by tot ...

.Nicholls, 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).

Geological information

The only known Parvinatator fossil was located in an unknown horizon from the

Sulfur Mountain Formation The Sulphur Mountain Formation is a geologic formation of Early to Middle Triassic age. It is present on the western edge of the Western Canada Sedimentary Basin in the foothills and Rocky Mountains of western Alberta and northeastern British Col ...

in a

talus deposit Scree is a collection of broken rock fragments at the base of a cliff or other steep rocky mass that has accumulated through periodic rockfall. Landforms associated with these materials are often called talus deposits. Talus deposits typically h ...

, so its exact geological age is unknown. Best estimates place the fossil somewhere between the

Olenekian In the geologic timescale, the Olenekian is an age in the Early Triassic epoch; in chronostratigraphy, it is a stage in the Lower Triassic series. It spans the time between Ma and Ma (million years ago). The Olenekian is sometimes divided i ...

and

Ladinian The Ladinian is a stage and age in the Middle Triassic series or epoch. It spans the time between Ma and ~237 Ma (million years ago). The Ladinian was preceded by the Anisian and succeeded by the Carnian (part of the Upper or Late Triassic ...

age around 251-235 mya.Motani, R. (1999). Phylogeny of the Ichthyopterygia. Journal of Vertebrate Paleontology, 19:3, 473-496. Other small ichthyosaurs have been found nearby including

Grippia ''Grippia'' is a genus of early ichthyopterygian, an extinct group of reptiles that resembled dolphins. Its only species is ''Grippia longirostris''. It was a relatively small ichthyopterygian, measuring long and weighing . Fossil remains from ...

, Utatsusaurus, and Phalarodon.

Historical information / discovery

''Parvinatator wapitiensis'' was discovered in the Sulfur Mountain Formation in British Columbia, Canada, by Elisabeth Nicholls and Don Brinkman in 1995. The only fossil recovered of this genus is a partial skull and two forefins. 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.Motani, R. (1997). Phylogeny of the Ichthyosauria (Amniota: Reptilia) with special reference to Triassic forms. Ph.D. dissertation, University of Toronto, Toronto, Ontario, Canada.

Description and paleobiology

Based on analysis of tooth size relative to the skull width, Parvinatator is estimated to be less than 1 meter long, approximately the same size and general shape of other basal ichthyosaurs, although it is unknown if Parvinatator lacked a

dorsal fin A dorsal fin is a fin located on the back of most marine and freshwater vertebrates within various taxa of the animal kingdom. Many species of animals possessing dorsal fins are not particularly closely related to each other, though through c ...

like Utatsusaurus and Grippia. Also like other early ichthyosaurs, Parvinatator most likely used an eel-like lateral body movement for propulsion, known as

anguilliform Fish locomotion is the various types of animal locomotion used by fish, principally by swimming. This is achieved in different groups of fish by a variety of mechanisms of propulsion, most often by wave-like lateral flexions of the fish's body a ...

. Based on jaw size and tooth shape, Parvinatator is thought to have feed on small

fish Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of ...

and cephalopods similarly to other basal ichthyosaurs, as opposed to hard shelled organisms such as mollusks and

clam Clam is a common name for several kinds of bivalve molluscs. The word is often applied only to those that are edible and live as infauna, spending most of their lives halfway buried in the sand of the seafloor or riverbeds. Clams have two shel ...

s. Ichthyosaurs typically had large eyes suggesting they would hunt in the dark, either at night or in deep water. After the skull's dis-articulated

orbit In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as ...

was reconstructed, it matched the approximate shape and typical size of other ichthyosaurs eyes. Grippia1DB

Skull

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 the

squamosal The squamosal is a skull bone found in most reptiles, amphibians, and birds. In fishes, it is also called the pterotic bone. In most tetrapods, the squamosal and quadratojugal bones form the cheek series of the skull. The bone forms an ancestral co ...

quadratojugal The quadratojugal is a skull bone present in many vertebrates, including some living reptiles and amphibians. Anatomy and function In animals with a quadratojugal bone, it is typically found connected to the jugal (cheek) bone from the front and ...

, and a reduced supratemporal, a lack of contact between the prefrontal and

postfrontal The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, t ...

, as well as between the

jugal The jugal is a skull bone found in most reptiles, amphibians and birds. In mammals, the jugal is often called the malar or zygomatic. It is connected to the quadratojugal and maxilla, as well as other bones, which may vary by species. Anatomy ...

and quadratojugal (which was previously identified as the squamosal). Other

diagnostic Diagnosis is the identification of the nature and cause of a certain phenomenon. Diagnosis is used in many different disciplines, with variations in the use of logic, analytics, and experience, to determine " cause and effect". In systems engin ...

characteristics of the Parvinatator skull are as follows: * The retroarticular process, composed of the

articular The articular bone is part of the lower jaw of most vertebrates, including most jawed fish, amphibians, birds and various kinds of reptiles, as well as ancestral mammals. Anatomy In most vertebrates, the articular bone is connected to two oth ...

surangular The suprangular or surangular is a jaw bone found in most land vertebrates, except mammals. Usually in the back of the jaw, on the upper edge, it is connected to all other jaw bones: dentary, angular, splenial and articular. It is often a mu ...

, and angular, is present and well developed. This is suggested to be a

derived trait In phylogenetics, an apomorphy (or derived trait) is a novel character or character state that has evolved from its ancestral form (or plesiomorphy). A synapomorphy is an apomorphy shared by two or more taxa and is therefore hypothesized to have ...

for all ichthyosaurs.Maisch, M. (2010). Phylogeny, systematics, and origin of the Ichthyosauria – the state of the art. Palaeodiversity, 3, 151–214. * The quadratojugal is high and narrow, laterally covering the quadrate.Maisch, 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. * The jugal and quadratojugal have a deep notch between them, agreeing with the lack of a lower

temporal fenestra An infratemporal fenestra, also called the lateral temporal fenestra or simply temporal fenestra, is an opening in the skull behind the orbit in some animals. It is ventrally bordered by a zygomatic arch. An opening in front of the eye sockets ...

or lower

zygomatic arch In anatomy, the zygomatic arch, or cheek bone, is a part of the skull formed by the zygomatic process of the temporal bone (a bone extending forward from the side of the skull, over the opening of the ear) and the temporal process of the zygo ...

as in all other ichthyosaurs. * The

postorbital The ''postorbital'' is one of the bones in vertebrate skulls which forms a portion of the dermal skull roof and, sometimes, a ring about the orbit. Generally, it is located behind the postfrontal and posteriorly to the orbital fenestra. In some ...

is enlarged and overlaps the jugal along the posterior of the orbit, forming a natural articulation point. * The orbit is oval in shape, being longer than tall. * The external naris is enclosed by the

premaxilla The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammal has ...

maxilla The maxilla (plural: ''maxillae'' ) in vertebrates is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. T ...

and

naris A nostril (or naris , plural ''nares'' ) is either of the two orifices of the nose. They enable the entry and exit of air and other gasses through the nasal cavities. In birds and mammals, they contain branched bones or cartilages called turbi ...

, separate from a well developed lacrimal.

Forefin

Unlike some basal ichthyosaurs, Parvinatator's forefin appears well adapted for

aquatic life An aquatic ecosystem is an ecosystem formed by surrounding a body of water, in contrast to land-based terrestrial ecosystems. Aquatic ecosystems contain communities of organisms that are dependent on each other and on their environment. The tw ...

, although it was probably used for controlling pitch rather than

locomotion Locomotion means the act or ability of something to transport or move itself from place to place. Locomotion may refer to: Motion * Motion (physics) * Robot locomotion, of man-made devices By environment * Aquatic locomotion * Flight * Locomo ...

. On the well preserved left forefin of Parvinatator the

ulna The ulna (''pl''. ulnae or ulnas) is a long bone found in the forearm that stretches from the elbow to the smallest finger, and when in anatomical position, is found on the medial side of the forearm. That is, the ulna is on the same side of t ...

is reduced in both length and width and smaller than the

radius In classical geometry, a radius ( : radii) of a circle or sphere is any of the line segments from its center to its perimeter, and in more modern usage, it is also their length. The name comes from the latin ''radius'', meaning ray but also the ...

. Several bones of digits 4 and 5 are fused together as well.

Phylogeny

There is some disagreement about the exact location of ''Parvinatator'' among its relatives. The following

phylogeny A phylogenetic tree (also phylogeny or evolutionary tree Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, MA.) is a branching diagram or a tree showing the evolutionary relationships among various biological spe ...

by Motani places ''Parvinatator'' with ''Utatsusaurus'' as basal ichthyopterygians but not true ichthyosaurs. However, according to Maisch and Matzke in 2000, ''Parvinatator'' is a true ichthyosaur and more derived than ''Utatsusaurus'' and ''Grippia''.Maisch, M.W.; Matzke, A.T. (2000). "The Ichthyosauria". ''Stuttgarter Beitrage zur Naturkunde, Serie B (Geologie und Palaontologie)''. 298: 1–159.

References

{{Taxonbar, from=Q7141334 Fossils of Canada Triassic ichthyopterygians Paleontology in British Columbia Olenekian first appearances Ichthyosauromorph genera Early Triassic reptiles of North America