''Kawanectes'' (meaning "Kawas swimmer") is a genus of

elasmosaurid Elasmosauridae is an extinct family of plesiosaurs, often called elasmosaurs. They had the longest necks of the plesiosaurs and existed from the Hauterivian to the Maastrichtian stages of the Cretaceous, and represented one of the two groups of ...

plesiosaur, a type of long-necked marine reptile, that lived in the marginal marine ( estuarine) environment of

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', ...

Patagonia Patagonia () refers to a geographical region that encompasses the southern end of South America, governed by Argentina and Chile. The region comprises the southern section of the Andes Mountains with lakes, fjords, temperate rainforests, and g ...

. It contains one species, ''K. lafquenianum'', described in 2016 by O'Gorman.

Description

At in body length and in body mass, ''Kawanectes'' was small for an elasmosaurid. It belongs to the "non-elongated" group of elasmosaurids, meaning that its cervical vertebrae are not extremely lengthened, neither do they show great variability in length. The MCS specimen preserves 15 cervical vertebrae and 15

dorsal vertebrae In vertebrates, thoracic vertebrae compose the middle segment of the vertebral column, between the cervical vertebrae and the lumbar vertebrae. In humans, there are twelve thoracic vertebrae and they are intermediate in size between the cervical ...

, while the holotype preserves 10 caudal vertebrae; the true number of cervical and caudal vertebrae is unknown due to the incompleteness of the specimens. A combination of traits can be used to distinguish ''Kawanectes'' from all other elasmosaurids: the

centra Centra is a convenience shop chain that operates throughout Ireland. The chain operates as a symbol group owned by Musgrave Group, the food wholesaler, meaning the stores are all owned by individual franchisees. The chain has three different ...

of the vertebrae are wider than they are long; the projections known as the parapophyses on the caudal vertebrae are knob-like; the ischium and pubis form a "bar" of bone that encloses two diamond-shaped openings; the ratio between the length of the humerus and the

femur The femur (; ), or thigh bone, is the proximal bone of the hindlimb in tetrapod vertebrates. The head of the femur articulates with the acetabulum in the pelvic bone forming the hip joint, while the distal part of the femur articulates wit ...

is unusually high (1.2); the end of the humerus bears a backward projection of bone which forms an articulating surface; and the capitulum of the femur, which likewise forms an articulating surface, is strongly

convex Convex or convexity may refer to: Science and technology * Convex lens, in optics Mathematics * Convex set, containing the whole line segment that joins points ** Convex polygon, a polygon which encloses a convex set of points ** Convex polytop ...

. Although ''Kawanectes'' is similar to the somewhat-larger '' Vegasaurus'', its bones clearly represent that of an adult due to the fusion in the vertebrae, the proportions of its cervical vertebrae are the same as ''Vegasaurus'' (if ''Vegasaurus'' was an older ''Kawanectes'', its cervical vertebrae would be longer, as with other elasmosaurids), and ''Vegasaurus'' does not have a pelvic bar (since the pelvic bar is absent in juvenile elamosaurids but present in adults, the emergence then disappearance of the pelvic bar contradicts a hypothetical growth sequence), suggesting that ''Vegasaurus'' is not the adult form of ''Kawanectes''.

Discovery and naming

''Kawanectes'' is known from the "Bentonitas Patagonicas" quarry in

Rio Negro Province Rio or Río is the Portuguese, Spanish, Italian, and Maltese word for "river". When spoken on its own, the word often means Rio de Janeiro, a major city in Brazil. Rio or Río may also refer to: Geography Brazil * Rio de Janeiro * Rio do Sul, a ...

Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...

. This quarry belongs to the Middle Member of the

Allen Formation The Allen Formation is a geological formation in Argentina whose strata date back to the Late Cretaceous (middle Campanian to early Maastrichtian.Salgado et al., 2007 Dinosaur remains are among the fossils that have been recovered from the formati ...

, which dates to the

late Campanian The Campanian is the fifth of six ages of the Late Cretaceous Epoch on the geologic timescale of the International Commission on Stratigraphy (ICS). In chronostratigraphy, it is the fifth of six stages in the Upper Cretaceous Series. Campanian ...

Early Maastrichtian The Maastrichtian () is, in the ICS geologic timescale, the latest age (uppermost stage) of the Late Cretaceous Epoch or Upper Cretaceous Series, the Cretaceous Period or System, and of the Mesozoic Era or Erathem. It spanned the interval fro ...

of the

. Three specimens are known: the holotype, MLP 71-II-13-1, which consists of various parts of the

axial skeleton The axial skeleton is the part of the skeleton that consists of the bones of the head and trunk of a vertebrate. In the human skeleton, it consists of 80 bones and is composed of six parts; the skull (22 bones), also the ossicles of the middle ...

along with a

, a humerus, an ilium, and a foot bone; MCS PV 4, which again consists of various axial bones in addition to a

scapula The scapula (plural scapulae or scapulas), also known as the shoulder blade, is the bone that connects the humerus (upper arm bone) with the clavicle (collar bone). Like their connected bones, the scapulae are paired, with each scapula on eith ...

, part of a

coracoid A coracoid (from Greek κόραξ, ''koraks'', raven) is a paired bone which is part of the shoulder assembly in all vertebrates except therian mammals (marsupials and placentals). In therian mammals (including humans), a coracoid process is prese ...

, both sets of

ischia Ischia ( , , ) is a volcanic island in the Tyrrhenian Sea. It lies at the northern end of the Gulf of Naples, about from Naples. It is the largest of the Phlegrean Islands. Roughly trapezoidal in shape, it measures approximately east to west ...

and pubes, part of a foot, and 389

gastrolith A gastrolith, also called a stomach stone or gizzard stone, is a rock held inside a gastrointestinal tract. Gastroliths in some species are retained in the muscular gizzard and used to grind food in animals lacking suitable grinding teeth. In oth ...

s; and MUC Pv 92, which also contains axial elements along with a femur, two foot bones, and fragments of the limb girdles. Initially recognized as a species of '' Trinacromerum'', polycotylid affinities were later rejected for ''"T." lafquenianum''. O'Gorman named the new

monotypic genus In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unispec ...

''Kawanectes'' for ''"T." lafquenianum'' in 2016. The name combines ''Kawa'', which refers to the Kawas Sea, an ancient ocean that covered Patagonia from the Campanian to the

Danian The Danian is the oldest age or lowest stage of the Paleocene Epoch or Series, of the Paleogene Period or System, and of the Cenozoic Era or Erathem. The beginning of the Danian (and the end of the preceding Maastrichtian) is at the Cretace ...

, and Greek ''nectes'', which means "swimmer". The original specific name, ''lafquenianum'', is the

Mapuche The Mapuche ( (Mapuche & Spanish: )) are a group of indigenous inhabitants of south-central Chile and southwestern Argentina, including parts of Patagonia. The collective term refers to a wide-ranging ethnicity composed of various groups who s ...

word for "sea".

Classification

In 2016, a phylogenetic analysis found that ''Kawanectes'' was a close relative to, but not a member of, the

Aristonectinae Aristonectinae is a clade of plesiosaurs in the family Elasmosauridae. It includes the Late Cretaceous plesiosaurs ''Aristonectes'' and '' Kaiwhekea'', traditionally grouped with the Late Jurassic ''Tatenectes'' and ''Kimmerosaurus'' in the famil ...

Paleoecology

With the discovery of ''Kawanectes'', the plesiosaurian fauna of the Kawas sea (which spans both the

and the contemporary

La Colonia Formation The La Colonia Formation is a geological formation in Argentina whose strata date back to the Late Cretaceous. Dinosaur remains are among the fossils that have been recovered from the formation.Weishampel et al., 2004, pp.600-604 Originally thou ...

) contains all three major lineages of Late Cretaceous plesiosaurs: non- aristonectine

elasmosaurids Elasmosauridae is an extinct family of plesiosaurs, often called elasmosaurs. They had the longest necks of the plesiosaurs and existed from the Hauterivian to the Maastrichtian stages of the Cretaceous, and represented one of the two groups of p ...

(''Kawanectes''), aristonectine elasmosaurids (''

Aristonectes ''Aristonectes'' (meaning 'best swimmer') is an extinct genus of plesiosaur from the Late Cretaceous Paso del Sapo Formation of what is now Argentina, the Quiriquina Formation of Chile and the Lopez de Bertodano Formation of Antarctica. The ...

''), and

polycotylids Polycotylidae is a family of plesiosaurs from the Cretaceous, a sister group to Leptocleididae. Polycotylids first appeared during the Albian stage of the Early Cretaceous, before becoming abundant and widespread during the early Late Cretaceous ...

('' Sulcusuchus''). This is unusual, since these formations represent continental-to-marginal marine environments (i.e. not open ocean). These plesiosaurs appear to be generally smaller than their open-ocean counterparts at adult size.

References

{{Taxonbar, from=Q28432499 Elasmosaurids Late Cretaceous plesiosaurs Campanian life Maastrichtian life Plesiosaurs of South America Late Cretaceous reptiles of South America Cretaceous Argentina Fossils of Argentina Allen Formation Fossil taxa described in 2016 Sauropterygian genera