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

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

of small ichthyopterygian

marine reptile Marine reptiles are reptiles which have become secondarily adapted for an aquatic or semiaquatic life in a marine environment. Only about 100 of the 12,000 extant reptile species and subspecies are classed as marine reptiles, including mari ...

that lived during the Early to Middle

Triassic The Triassic ( ; sometimes symbolized 🝈) is a geologic period and system which spans 50.5 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.4 Mya. The Triassic is t ...

. Its fossils have been found in

British Columbia British Columbia is the westernmost Provinces and territories of Canada, province of Canada. Situated in the Pacific Northwest between the Pacific Ocean and the Rocky Mountains, the province has a diverse geography, with rugged landscapes that ...

Canada Canada is a country in North America. Its Provinces and territories of Canada, ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, making it the world's List of coun ...

.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 in a talus deposit, 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 (geology), age in the Early Triassic epoch (geology), epoch; in chronostratigraphy, it is a stage (stratigraphy), stage in the Lower Triassic series (stratigraphy), series. It spans the time betw ...

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 around long. Fossil remains from Svalba ...

Utatsusaurus ''Utatsusaurus hataii'' is the earliest-known ichthyopterygian which lived in the Early Triassic period (c. 245–250 million years ago). It was nearly long with a slender body. The first specimen was found in Utatsu-cho (now part of Minamisa ...

, and Phalarodon.

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

ichthyosaur Ichthyosauria is an order of large extinct marine reptiles sometimes referred to as "ichthyosaurs", although the term is also used for wider clades in which the order resides. Ichthyosaurians thrived during much of the Mesozoic era; based on fo ...

s, although it is unknown if Parvinatator lacked a

dorsal fin A dorsal fin is a fin on the back of most marine and freshwater vertebrates. Dorsal fins have evolved independently several times through convergent evolution adapting to marine environments, so the fins are not all homologous. They are found ...

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 aquatic locomotion, swimming. This is achieved in different groups of fish by a variety of mechanisms of propulsion, most often by wave-like lateral flexions ...

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

fish A fish (: fish or fishes) is an aquatic animal, aquatic, Anamniotes, anamniotic, gill-bearing vertebrate animal with swimming fish fin, fins and craniate, a hard skull, but lacking limb (anatomy), limbs with digit (anatomy), digits. Fish can ...

and

cephalopod A cephalopod is any member of the molluscan Taxonomic rank, class Cephalopoda (Greek language, Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral symm ...

s similarly to other basal ichthyosaurs, as opposed to hard shelled organisms such as

mollusks Mollusca is a phylum of protostomic invertebrate animals, whose members are known as molluscs or mollusks (). Around 76,000 extant species of molluscs are recognized, making it the second-largest animal phylum after Arthropoda. The num ...

and

clam Clam is a common name for several kinds of bivalve mollusc. The word is often applied only to those that are deemed edible and live as infauna, spending most of their lives halfway buried in the sand of the sea floor or riverbeds. Clams h ...

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 (also known as orbital revolution) 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 ...

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 ancestra ...

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 postfrontal is a paired cranial bone found in many tetrapods. It occupies an area of the skull roof between and behind the orbits (eye sockets), lateral to the frontal and parietal bones, and anterior to the postorbital bone. The postfrontal ...

, as well as between the jugal and quadratojugal (which was previously identified as the squamosal). Other

diagnostic Diagnosis (: diagnoses) is the identification of the nature and cause of a certain phenomenon. Diagnosis is used in a lot of different academic discipline, disciplines, with variations in the use of logic, analytics, and experience, to determine " ...

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 o ...

surangular The surangular or suprangular 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 bone, angular, splenial and articular. It is o ...

, 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 ha ...

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 Temporal fenestrae are openings in the temporal region of the skull of some amniotes, behind the orbit (eye socket). These openings have historically been used to track the evolution and affinities of reptiles. Temporal fenestrae are commonly (al ...

or lower

zygomatic arch In anatomy, the zygomatic arch (colloquially known as the cheek bone), is a part of the skull formed by the zygomatic process of temporal bone, zygomatic process of the temporal bone (a bone extending forward from the side of the skull, over the ...

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 ve ...

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 mammals h ...

maxilla In vertebrates, the maxilla (: maxillae ) 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. The two maxil ...

and

nasal bone The nasal bones are two small oblong bones, varying in size and form in different individuals; they are placed side by side at the middle and upper part of the face and by their junction, form the bridge of the upper one third of the nose. Eac ...

, 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 found in and around a body of water, in contrast to land-based terrestrial ecosystems. Aquatic ecosystems contain communities of organisms—aquatic life—that are dependent on each other and on their environm ...

, although it was probably used for controlling pitch rather than locomotion. On the well preserved left forefin of ''Parvinatator'' the

ulna The ulna or ulnar bone (: ulnae or ulnas) is a long bone in the forearm stretching from the elbow to the wrist. It is on the same side of the forearm as the little finger, running parallel to the Radius (bone), radius, the forearm's other long ...

is reduced in both length and width and smaller than the

radius In classical geometry, a radius (: radii or radiuses) of a circle or sphere is any of the line segments from its Centre (geometry), center to its perimeter, and in more modern usage, it is also their length. The radius of a regular polygon is th ...

. 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 or phylogeny is a graphical representation which shows the evolutionary history between a set of species or Taxon, taxa during a specific time.Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, M ...

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 Ichthyosauriformes Olenekian first appearances Early Triassic reptiles of North America Middle Triassic reptiles of North America Fossils of Canada Paleontology in British Columbia Fossil taxa described in 1995