''Terminonatator'' (meaning "last swimmer") is a

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 ...

elasmosaurid Elasmosauridae, often called elasmosaurs or elasmosaurids, is an extinct family of plesiosaurs that lived from the Hauterivian stage of the Early Cretaceous to the Maastrichtian stage of the Late Cretaceous period (c. 130 to 66 mya). The taxo ...

plesiosaur The Plesiosauria or plesiosaurs are an Order (biology), order or clade of extinct Mesozoic marine reptiles, belonging to the Sauropterygia. Plesiosaurs first appeared in the latest Triassic Period (geology), Period, possibly in the Rhaetian st ...

from the

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the more recent 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 ''cre ...

Saskatchewan Saskatchewan is a Provinces and territories of Canada, province in Western Canada. It is bordered on the west by Alberta, on the north by the Northwest Territories, on the east by Manitoba, to the northeast by Nunavut, and to the south by the ...

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 ...

. It is known from a skull and partial skeleton from a young adult, found in the

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. Campa ...

-age

Bearpaw Formation The Bearpaw Formation, also called the Bearpaw Shale, is a geologic formation of Late Cretaceous (Campanian) age. It outcrops in the U.S. state of Montana, as well as the Canadian provinces of Alberta and Saskatchewan, and was named for the Bear ...

near Notukeu Creek in Ponteix. ''Terminonatator'' is currently one of the youngest plesiosaurs from the

Western Interior Seaway The Western Interior Seaway (also called the Cretaceous Seaway, the Niobraran Sea, the North American Inland Sea, or the Western Interior Sea) was a large inland sea (geology), inland sea that existed roughly over the present-day Great Plains of ...

Description

''Terminonatator'' is based on RSM P2414.1, a skull and partially articulated incomplete skeleton found high in the Bearpaw Formation. Tamaki Sato, who named and described the specimen in

2003 2003 was designated by the United Nations as the International Year of Fresh water, Freshwater. In 2003, a Multi-National Force – Iraq, United States-led coalition 2003 invasion of Iraq, invaded Iraq, starting the Iraq War. Demographic ...

, used the genus name to emphasize its lateness in the fossil record, and the

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

epithet ''ponteixensis'' for Ponteix. Only one species has been described: the

type species In International_Code_of_Zoological_Nomenclature, zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the spe ...

''T. ponteixensis''. RSM P2414.1 appears to represent an adult, because the

neural arches Each vertebra (: vertebrae) is an irregular bone with a complex structure composed of bone and some hyaline cartilage, that make up the vertebral column or spine, of vertebrates. The proportions of the vertebrae differ according to their spinal ...

are fused to their

vertebra Each vertebra (: vertebrae) is an irregular bone with a complex structure composed of bone and some hyaline cartilage, that make up the vertebral column or spine, of vertebrates. The proportions of the vertebrae differ according to their spina ...

e, although incomplete fusion elsewhere indicates it was a young adult. It would have been small as an adult for an elasmosaurid, at only about long, up to if it had an extremely long neck like ''

Elasmosaurus ''Elasmosaurus'' () is a genus of plesiosaur that lived in North America during the Campanian stage of the Late Cretaceous period, at about 80.6 to 77million years ago. The first specimen was discovered in 1867 near Fort Wallace, Kansas, US, and ...

'' (which had 72 neck vertebrae). The skull as preserved is long, but is broken near the posterior end. Compared to other elasmosaurids, the snout was relatively short. Unlike other plesiosaurs, the

pineal foramen A parietal eye (third eye, pineal eye) is a part of the epithalamus in some vertebrates. The eye is at the top of the head; is photoreceptive; and is associated with the pineal gland, which regulates circadian rhythmicity and hormone production ...

in the roof of the skull was closed, and there were only nine teeth in 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 ...

ry bones that form the tip of the snout instead of ten, although this could be individual variation. The right jaw is better preserved than the left; at least 13 teeth were present in the right

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 ...

(the main tooth-bearing bone of the upper jaw), and 17 to 18 teeth were present in the right

dentary In jawed vertebrates, the mandible (from the Latin ''mandibula'', 'for chewing'), lower jaw, or jawbone is a bone that makes up the lowerand typically more mobilecomponent of the mouth (the upper jaw being known as the maxilla). The jawbone ...

, which held teeth in lower jaw. There was an unusually tall bony

process A process is a series or set of activities that interact to produce a result; it may occur once-only or be recurrent or periodic. Things called a process include: Business and management * Business process, activities that produce a specific s ...

on the coronoid, a bone of the lower jaw. Impressions of part of the

brain The brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It consists of nervous tissue and is typically located in the head (cephalization), usually near organs for ...

and other cranial nervous tissue were found in the

braincase In human anatomy, the neurocranium, also known as the braincase, brainpan, brain-pan, or brainbox, is the upper and back part of the skull, which forms a protective case around the brain. In the human skull, the neurocranium includes the calv ...

. The backbone is incomplete, but 51 neck, 17 back, four sacral, and 12 tail vertebrae were preserved. Over 150 pebbles, representing

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 ...

s, were found within the rib cage; the largest has a diameter of . The

shoulder The human shoulder is made up of three bones: the clavicle (collarbone), the scapula (shoulder blade), and the humerus (upper arm bone) as well as associated muscles, ligaments and tendons. The articulations between the bones of the shoulder m ...

and

pelvic girdle The hip bone (os coxae, innominate bone, pelvic bone or coxal bone) is a large flat bone, constricted in the center and expanded above and below. In some vertebrates (including humans before puberty) it is composed of three parts: the Ilium (bone) ...

are fragmentary. The

thigh bone The femur (; : femurs or femora ), or thigh bone is the only bone in the thigh — the region of the lower limb between the hip and the knee. In many four-legged animals the femur is the upper bone of the hindleg. The top of the femur fits in ...

was longer than the

upper arm The upper limbs or upper extremities are the forelimbs of an upright-postured tetrapod vertebrate, extending from the scapulae and clavicles down to and including the digits, including all the musculatures and ligaments involved with the should ...

, which is unusual for an elasmosaurid, and the right thigh bone was broken and healed. ''Terminonatator'' is significant because of its late age, its inclusion of a skull with most of a skeleton, and its nature as an elasmosaurid (the remains of short-necked plesiosaurs are more common in comparable rocks in Canada). The remains of comparable elasmosaurids are poorly preserved, and/or have poorly described skulls, making comparisons of this genus to other elasmosaurids difficult at this time.

References

{{Taxonbar, from=Q3984454 Elasmosauridae Late Cretaceous plesiosaurs of North America Cretaceous Saskatchewan Fossil taxa described in 2003 Sauropterygian genera

Description

See also

References