''Gunakadeit'' is an

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

thalattosaur Thalattosauria (Greek for "sea lizards") is an extinct order of prehistoric marine reptiles that lived in the middle to late Triassic period. Thalattosaurs were diverse in size and shape, and are divided into two superfamilies: Askeptosauroidea an ...

. It is known from a single species, ''Gunakadeit joseeae'', which is based on an articulated and mostly complete skeleton from the late

Triassic The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest period ...

(middle

Norian The Norian is a division of the Triassic Period. It has the rank of an age (geochronology) or stage (chronostratigraphy). It lasted from ~227 to million years ago. It was preceded by the Carnian and succeeded by the Rhaetian. Stratigraphic defi ...

) Hound Island Volcanics of

Alaska Alaska ( ; russian: Аляска, Alyaska; ale, Alax̂sxax̂; ; ems, Alas'kaaq; Yup'ik: ''Alaskaq''; tli, Anáaski) is a state located in the Western United States on the northwest extremity of North America. A semi-exclave of the U.S., ...

. ''Gunakadeit'' possessed a variety of features from the two major suborders of thalattosaurs, Askeptosauroidea and

Thalattosauroidea Thalattosauroidea is a superfamily of thalattosaurs, a Triassic group of marine reptiles. It was named in 1904 by paleontologist John Campbell Merriam to include the genus '' Thalattosaurus'' from California. Thalattosauroids are one of two gro ...

, and it is considered the most basal member of the latter group. Despite this, it is also the youngest known thalattosaur genus, with the group going extinct at the end of the Triassic. ''Gunakadeits basal position and relatively recent occurrence implies a 20-million-year

ghost lineage A ghost lineage is a hypothesized ancestor in a species lineage that has left no fossil evidence yet can be inferred to exist because of gaps in the fossil record or genomic evidence. The process of determining a ghost lineage relies on fossilized ...

connecting it to the rest of Thalattosauria. The skull ends in a sharply pointed and toothless tip like the askeptosauroid ''

Endennasaurus ''Endennasaurus'' is an extinct genus of thalattosaurian from the Upper Triassic of Italy. It was found in and named after the Endenna cave, composed of Zorzino Limestone in Lombardia.holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...

, UAMES 23258, was discovered by rare chance. It was discovered within the

intertidal zone The intertidal zone, also known as the foreshore, is the area above water level at low tide and underwater at high tide (in other words, the area within the tidal range). This area can include several types of habitats with various species o ...

off the coast of the Keku Islands, which is only exposed for a few days a year. On May 18, 2011, Jim Baichtal discovered a fossil poking out of the rock and he sent a picture to professional

palaeontologist Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of fossi ...

Patrick Druckenmiller Patrick S. Druckenmiller is a Mesozoic paleontologist, taxonomist, associate professor of geology, Earth Sciences curator, and museum director of the University of Alaska Museum of the North, where he oversees the largest single collection of A ...

. During June 2011, when low tides of under four feet were predicted again, the fossil was excavated. The descriptors chose to honour the Native American

Tlingit culture The culture of the Tlingit, an Indigenous people from Alaska, British Columbia, and the Yukon, is multifaceted, a characteristic of Northwest Coast peoples with access to easily exploited rich resources. In Tlingit culture a heavy emphasis is place ...

in the name of the new thalattosaur. The genus name ''Gunakadeit'' is a Tlingit word, referring to a sea monster in Tlingit mythology whose skin was worn by a young man to provide food to his village. The epithet, ''joseeae'', honours Gene Primaky's mother, Joseé Michelle DeWaelheyns. Primaky helped to excavate the holotype.

Description

Skull

The skull had a straight snout which ended in a sharply pointed tip somewhat reminiscent of the askeptosauroid ''

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. The t ...

from below and

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 b ...

and nasal from above. The

orbits 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 a p ...

were also very large; ''Guanakadeit'' is the only thalattosaur with orbits significantly larger than the portion of the skull behind them. 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 ...

is thin and has a unique shape in ''Gunakadeit'' compared to other thalattosaurs. It has an elongated forward branch which forms the entire lower edge of the orbit, an upper branch which slopes backwards rather than straight up, and a very short or absent rear branch. ''Gunakadeit'' also possesses a small and narrow

supratemporal fenestra 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, the ...

, which separates the wide

parietal bone The parietal bones () are two bones in the Human skull, skull which, when joined at a fibrous joint, form the sides and roof of the Human skull, cranium. In humans, each bone is roughly quadrilateral in form, and has two surfaces, four borders, an ...

from the elongated

supratemporal bone The supratemporal bone is a paired cranial bone present in many tetrapods and tetrapodomorph fish. It is part of the temporal region (the portion of the skull roof behind the eyes), usually lying medial (inwards) relative to the squamosal and latera ...

. The front of the lower jaw is straight and toothless, with both sides fused together into an extensive and pointed

symphysis A symphysis (, pl. symphyses) is a fibrocartilaginous fusion between two bones. It is a type of cartilaginous joint, specifically a secondary cartilaginous joint. # A symphysis is an amphiarthrosis, a slightly movable joint. # A growing together ...

. The rear of the jaw has a low and thick coronoid process and ends in an elongated, upturned retroarticular process. The lower jaw preserves many similar teeth with sharp, conical crowns. The teeth had long and flattened roots attached to the jaw bone via loose

pleurodont Pleurodont is a form of tooth implantation common in reptiles of the order Squamata, as well as in at least one temnospondyl. The labial (cheek) side of pleurodont teeth are fused (ankylosed) to the inner surface of the jaw bones which host them. T ...

implantation. ''Gunakadeit'' also has one of the most well-preserved

hyoid apparatus The hyoid apparatus is the collective term used in veterinary anatomy for the bones which suspend the tongue and larynx. It consists of pairs of stylohyoid, thyrohyoid, epihyoid and ceratohyoid bones, and a single basihyoid bone. The hyoid appara ...

known in thalattosaurs. The hyoid (as preserved) consists of a large rod, the ceratobranchial, which is lies adjacent to a large plate (the basihyoid) and is followed by several smaller and thinner rods (epibranchials).

Postcrania

The neck is very short, formed by only four

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 ...

. The 28

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 ...

have tall neural spines, which become pointed and bent backwards closer to the hip. There were three

sacral vertebrae The sacrum (plural: ''sacra'' or ''sacrums''), in human anatomy, is a large, triangular bone at the base of the spine that forms by the fusing of the sacral vertebrae (S1S5) between ages 18 and 30. The sacrum situates at the upper, back part ...

, although these were similar to the dorsals and had unusually thin sacral ribs. Caudals (tail vertebrae) had narrow and fairly elongated

chevrons Chevron (often relating to V-shaped patterns) may refer to: Science and technology * Chevron (aerospace), sawtooth patterns on some jet engines * Chevron (anatomy), a bone * ''Eulithis testata'', a moth * Chevron (geology), a fold in rock lay ...

and neural spines at the base of the tail, which diminished in size further down the tail. The tip of the holotype's tail is missing, so ''Gunakadeit'' had more caudals than the 23 preserved in the skeleton.

Ribs The rib cage, as an enclosure that comprises the ribs, vertebral column and sternum in the thorax of most vertebrates, protects vital organs such as the heart, lungs and great vessels. The sternum, together known as the thoracic cage, is a semi- ...

were single-headed and weakly curved, overlying several sets of extremely thin and numerous

gastralia Gastralia (singular gastralium) are dermal bones found in the ventral body wall of modern crocodilians and tuatara, and many prehistoric tetrapods. They are found between the sternum and pelvis, and do not articulate with the vertebrae. In these ...

. The

interclavicle An interclavicle is a bone which, in most tetrapods, is located between the clavicles. Therian mammals ( marsupials and placentals) are the only tetrapods which never have an interclavicle, although some members of other groups also lack one. In th ...

had uniquely extensive lateral processes (side branches), which connected to very long and robust

clavicles The clavicle, or collarbone, is a slender, S-shaped long bone approximately 6 inches (15 cm) long that serves as a strut between the shoulder blade and the sternum (breastbone). There are two clavicles, one on the left and one on the right ...

. The

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 ...

and

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 ...

were smaller and less unusual in their proportions. 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 ...

was simple and flattened. Its widest point was near the shoulder, unlike askeptosauroids. 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 ...

is thick and curved, though not as short as the similarly-shaped radius of ''

Xinpusaurus ''Xinpusaurus'' is an extinct genus of thalattosaur from the Late Triassic of Guanling in Guizhou, China. Several species have been named since 2000: the type species ''X. suni'' along with the species ''X. bamaolinensis'' and ''X. kohi''. A 201 ...

''. It was slightly shorter than the humerus and similar in length to the robust, tapering

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 ...

. The wrist and hand are poorly preserved, but there appears to be at least two

carpals The carpal bones are the eight small bones that make up the wrist (or carpus) that connects the hand to the forearm. The term "carpus" is derived from the Latin carpus and the Greek καρπός (karpós), meaning "wrist". In human anatomy, th ...

and four fingers. The posterodorsal process (upper rear branch) of the ilium tapers to a point, a shape otherwise unknown in thalattosaurs. A bone tentatively identified as the pubis is large, wide, and lacks an obturator foramen (a hole present in other thalattosaur hips). 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 with ...

is fairly simple and widens towards the knee. The

fibula The fibula or calf bone is a leg bone on the lateral side of the tibia, to which it is connected above and below. It is the smaller of the two bones and, in proportion to its length, the most slender of all the long bones. Its upper extremity is ...

is very short, as is the tibia which has a uniquely convex inner edge. At least six tarsals and five toes were present, although most bones of the foot are poorly preserved.

Classification

phylogenetic analysis In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...

found ''Gunakadeit'' to be the most basal member of

, a suborder of the marine reptile

order Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of d ...

Thalattosauria Thalattosauria (Greek for "sea lizards") is an extinct order of prehistoric marine reptiles that lived in the middle to late Triassic period. Thalattosaurs were diverse in size and shape, and are divided into two superfamilies: Askeptosauroidea ...

. Its placement within Thalattosauroidea is supported by various aspects of the postcrania, such as the shape of the

, and tail vertebrae. However, it also retained several askeptosauroid-like features of the skull such as a low coronoid process and a straight, pointed jaw without much variation in tooth shape. These traits are likely to be

plesiomorphic In phylogenetics, a plesiomorphy ("near form") and symplesiomorphy are synonyms for an ancestral character shared by all members of a clade, which does not distinguish the clade from other clades. Plesiomorphy, symplesiomorphy, apomorphy, and ...

("primitive") for thalattosaurs as a whole, so they are more likely to signify that ''Gunakadeit'' was a basal thalattosauroid rather than an askeptosauroid. The following cladogram illustrates the result of the analysis, after the exclusion of several unstable and fragmentary thalattosaurs ('' Agkistrognathus'' and several unnamed taxa represented by specimens TMP 88.99.21 and SMNS 90568):

References

{{Taxonbar, from=Q85764861 Thalattosaurs Norian life Late Triassic reptiles of North America Paleontology in Alaska Fossil taxa described in 2020 Prehistoric reptile genera