''Kawanectes'' (meaning "Kawas swimmer") is a genus of elasmosaurid plesiosaur, a type of long-necked marine reptile, that lived in the marginal marine (

estuarine An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environmen ...

) 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 ...

. 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 In tetrapods, cervical vertebrae (singular: vertebra) are the vertebrae of the neck, immediately below the skull. Truncal vertebrae (divided into thoracic and lumbar vertebrae in mammals) lie caudal (toward the tail) of cervical vertebrae. In ...

are not extremely lengthened, neither do they show great variability in length. The MCS specimen preserves 15 cervical vertebrae and 15 dorsal vertebrae, while the holotype preserves 10

caudal vertebrae The spinal column, a defining synapomorphy shared by nearly all vertebrates, Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic ...

; 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 of the vertebrae are wider than they are long; the projections known as the parapophyses on the caudal vertebrae are knob-like; the

ischium The ischium () form ...

and pubis form a "bar" of bone that encloses two diamond-shaped openings; the ratio between the length of the

humerus The humerus (; ) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius and ulna, and consists of three sections. The humeral upper extremity consists of a roun ...

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 ''Vegasaurus'' is an extinct genus of elasmosaurid plesiosaur known from the Late Cretaceous (early Maastrichtian stage) Snow Hill Island Formation of Vega Island, Antarctic Peninsula. It contains a single species, ''Vegasaurus molyi''. Descr ...

'', 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,

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, t ...

. 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 to Early Maastrichtian 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 middl ...

along with a

, a

, an

ilium Ilium or Ileum may refer to: Places and jurisdictions * Ilion (Asia Minor), former name of Troy * Ilium (Epirus), an ancient city in Epirus, Greece * Ilium, ancient name of Cestria (Epirus), an ancient city in Epirus, Greece * Ilium Building, a ...

, 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 eithe ...

, 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 pre ...

, 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 wes ...

and

pubes Pubic hair is terminal body hair that is found in the genital area of adolescent and adult humans. The hair is located on and around the sex organs and sometimes at the top of the inside of the thighs. In the pubic region around the pubis bon ...

, part of a foot, and 389 gastroliths; 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 ''Trinacromerum'' is an extinct genus of sauropterygian reptile, a member of the polycotylid plesiosaurs. It contains two species, ''T. bentonianum'' and ''T. kirki''. Specimens have been discovered in the Late Cretaceous fossil deposits of what ...

'',

polycotylid 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. ...

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 "unispe ...

''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 Creta ...

, 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.

Paleoecology

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

and the contemporary La Colonia Formation) contains all three major lineages of Late Cretaceous plesiosaurs: non-

aristonectine 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 fami ...

elasmosaurids (''Kawanectes''), aristonectine elasmosaurids ('' Aristonectes''), and polycotylids (''

Sulcusuchus ''Sulcusuchus'' is a genus of polycotylid plesiosaur from the Late Campanian of Argentina. Description The type species ''Sulcusuchus erraini'' was named in 1990 by Zulma Brandoni de Gasparini and Luis Spalletti. It was at first considered t ...

''). 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