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''Keilhauia'' is a genus of
ophthalmosaurid Ophthalmosauridae is an extinct family of thunnosaur ichthyosaurs from the Middle Jurassic to the early Late Cretaceous (Bajocian - Cenomanian) worldwide. Almost all ichthyosaurs from the Middle Jurassic onwards belong to the family, until the e ...
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 ...
, a type of dolphin-like, large-eyed marine reptile, from the
Early Cretaceous The Early Cretaceous (geochronology, geochronological name) or the Lower Cretaceous (chronostratigraphy, chronostratigraphic name) is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 143.1 ...
shallow marine Slottsmøya Member of the
Agardhfjellet Formation The Agardhfjellet Formation is a Formation (geology), geologic formation in Svalbard, Norway. It preserves fossils dating back to the Oxfordian (stage), Oxfordian to Berriasian stages, spanning the Late Jurassic-Early Cretaceous boundary. The for ...
in
Svalbard Svalbard ( , ), previously known as Spitsbergen or Spitzbergen, is a Norway, Norwegian archipelago that lies at the convergence of the Arctic Ocean with the Atlantic Ocean. North of continental Europe, mainland Europe, it lies about midway be ...
,
Norway Norway, officially the Kingdom of Norway, is a Nordic countries, Nordic country located on the Scandinavian Peninsula in Northern Europe. The remote Arctic island of Jan Mayen and the archipelago of Svalbard also form part of the Kingdom of ...
. The genus contains a single species, ''K. nui'', known from a single specimen discovered in 2010 and described by Delsett ''et al.'' in 2017. In life, ''Keilhauia'' probably measured approximately in length; it can be distinguished by other ophthalmosaurids by the wide top end of its ilium and the relatively short ischiopubis (the fusion of the
ischium The ischium (; : is ...
and the pubis) compared to the
femur The femur (; : femurs or femora ), or thigh bone is the only long bone, bone in the thigh — the region of the lower limb between the hip and the knee. In many quadrupeds, four-legged animals the femur is the upper bone of the hindleg. The Femo ...
. Although it was placed in a basal position within the Ophthalmosauridae by
phylogenetic analysis In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical data ...
, this placement is probably incorrect.


Description

Judging by the partially preserved holotype specimen, ''Keilhauia'' has been estimated at based on comparisons to the related
ophthalmosaurid Ophthalmosauridae is an extinct family of thunnosaur ichthyosaurs from the Middle Jurassic to the early Late Cretaceous (Bajocian - Cenomanian) worldwide. Almost all ichthyosaurs from the Middle Jurassic onwards belong to the family, until the e ...
''
Cryopterygius ''Undorosaurus'' is an extinct genus of ophthalmosaurid ichthyosaur known from western Russia, Svalbard, and Poland. It was a large ichthyosaur, with the type species measuring long. Discovery and naming ''Undorosaurus'' was named by Vladimir ...
''. This specimen was probably mature or close to maturity at time of death, judging by the convex head of the
humerus The humerus (; : humeri) 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 (bone), radius and ulna, and consists of three sections. The humeral upper extrem ...
and the smooth texture of the humeral shaft.


Skull and axial skeleton

Although only a small portion of the snout is known, it seems to be taller than that of ''
Aegirosaurus ''Aegirosaurus'' is an extinct genus of platypterygiine ophthalmosaurid ichthyosaurs known from the late Jurassic and early Cretaceous of Europe. It was originally named as a species of '' Ichthyosaurus''. Discovery and species Originally des ...
'', instead being more similar to those of ''Cryopterygius'' and ''
Caypullisaurus ''Caypullisaurus'' is an extinct genus of platypterygiine ophthalmosaurid ichthyosaur from the Late Jurassic to the Early Cretaceous (Tithonian and Berriasian stages) of Argentina. Its holotype was collected from the Vaca Muerta Formation of C ...
''. A shallow groove that housed blood vessels, known as the
nutrient foramen All bones possess larger or smaller foramina (openings) for the entrance of blood-vessels; these are known as the nutrient foramina, and are particularly large in the shafts of the larger long bones, where they lead into a nutrient canal, which ext ...
, is visible on the side of the jaw. About ten teeth are preserved; they are conical, narrow at the tip, and slightly curved. It is difficult to estimate the exact number of vertebral segments that were present in front of the
sacrum The sacrum (: sacra or sacrums), in human anatomy, is a 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 of the pelvic cavity, ...
; the preserved
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 individual shops are all owned by individual franchisees. The chain has three ...
suggest that there are at least 43. This is more than the 42 in '' Athabascasaurus'', the 41 in ''
Nannopterygius ''Nannopterygius'' (meaning "small wing/flipper" in Greek) is an extinct genus of ophthalmosaurid ichthyosaur that lived during the Middle Jurassic to the Early Cretaceous (Callovian to Berriasian stages). Fossils are known from England, Kazakhsta ...
'', and the 37 in ''
Platypterygius americanus ''Platypterygius'' is a historically paraphyletic genus of platypterygiine ichthyosaur from the Cretaceous period. It was historically used as a wastebasket taxon, and most species within ''Platypterygius'' likely are undiagnostic at the genus o ...
'', but less than the 46 in ''Platypterygius australis'' and the 50 or more in ''Cryopterygius'', ''Aegirosaurus'', and ''Platypterygius platydactylus''. The posterior
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 vertebra (anatomy), vertebrae of intermediate size between the ce ...
are wider and taller than those near the front, and their front and rear faces are rounded. The first few caudal vertebrae are the proportionally tallest and widest of all the vertebrae, but the vertebrae quickly become shorter vertically prior to the bend in the tail that supported the tail fluke. Each
neural spine 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 ...
is about the same length as the underlying centrum, which is similar to ''Cryopterygius'' but not ''
Ophthalmosaurus ''Ophthalmosaurus'' (Greek ὀφθάλμος ''ophthalmos'' 'eye' and σαῦρος ''sauros'' 'lizard') is a genus of ichthyosaur known from the Middle-Late Jurassic. Possible remains from the earliest Cretaceous, around 145 million years ago, a ...
'' (in which they are proportionally longer in the posterior cervical vertebrae). Similar to ''
Gengasaurus ''Gengasaurus'' is an extinct genus of ophthalmosaurid ichthyosaur from the Jurassic. The type and only species, ''Gengasaurus nicosiai'', was named in 2017, after the locality of Genga, Marche. It lived in Italy about 152 million years ago. His ...
'', the first few neural spines are taller than the corresponding centra, but then decrease in height gradually. The tops of the neural spines, which are the thinnest parts of the bones, are straight, instead of being notched like ''Cryopterygius'' or ''Platypterygius australis''. The ribs are shaped like a
figure eight Figure 8, figure of 8, figure eight, or Figure of Eight may refer to: * 8 (number), in Arabic numerals Geography * Figure Eight Island, North Carolina, United States * Figure Eight Lake, Alberta, Canada * Figure-Eight Loops, feature of the Hi ...
in cross section near their top ends, but this is less obvious closer to the bottom; such a morphology is typical among ophthalmosaurids, except for ''
Acamptonectes ''Acamptonectes'' is a genus of ophthalmosaurid ichthyosaurs, a type of dolphin-like marine reptiles, that lived during the Early Cretaceous around 130 million years ago. The first specimen, a partial adult skeleton, was discovered in Speeton, ...
'' and ''
Mollesaurus ''Mollesaurus'' is an extinct genus of large ophthalmosaurine ichthyosaur known from northwestern Patagonia of Argentina. Etymology ''Mollesaurus'' was named by Marta S. Fernández in 1999 and the type species is ''Mollesaurus periallus''. T ...
''. The dorsal ribs are around long, while the first few caudal ribs are only long.


Forelimb and pectoral girdle

In ''Keilhauia'', the
scapula The scapula (: 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 either side ...
has a relatively straight blade that was broadened at its front end into a fan-like
acromion process In human anatomy, the acromion (from Greek: ''akros'', "highest", ''ōmos'', "shoulder", : acromia) or summit of the shoulder is a bony process on the scapula (shoulder blade). Together with the coracoid process, it extends laterally over the shou ...
. This process is less prominent than that of ''Acamptonectes'' and ''
Sveltonectes ''Sveltonectes'' (meaning "agile swimmer" in Greek) is an extinct genus of platypterygiine ophthalmosaurid ichthyosaurs known from Ul’yanovsk region, western Russia. History of discovery ''Sveltonectes'' is known from the holotype Royal Belgi ...
'', instead being more similar to that of ''Cryopterygius'', ''Platypterygius hercynicus'', and '' Sisteronia''. The scapula formed more of the
glenoid The glenoid fossa of the scapula or the glenoid cavity is a bone part of the shoulder. The word ''glenoid'' is pronounced or (both are common) and is from , "socket", reflecting the shoulder joint's ball-and-socket form. It is a shallow, pyrif ...
than the
coracoid A coracoid 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 present as part of the scapula, but this is n ...
; like ''Sveltonectes'' but unlike ''Cryopterygius'', the glenoid does not extend onto the bottom face of the scapula. The ''de facto'' blade of the scapula was widest near the middle, and angled slightly downwards; like ''Acamptonectes'' but unlike all other ophthalmosaurids, the blade has a relatively uniform thickness along its entire length. The
clavicle The clavicle, collarbone, or keybone is a slender, S-shaped long bone approximately long that serves as a strut between the scapula, shoulder blade and the sternum (breastbone). There are two clavicles, one on each side of the body. The clavic ...
, which is not fused to other elements in the
pectoral girdle The shoulder girdle or pectoral girdle is the set of bones in the appendicular skeleton which connects to the arm on each side. In humans, it consists of the clavicle and scapula; in those species with three bones in the shoulder, it consists o ...
, bears a thickened process on its frontal bottom edge which points towards the midline of the torso. This process is relatively short, square-shaped from the front, and bordered by a rim on its back edge. In most other ophthalmosaurids, this same process is more finger-like, although some specimens of ''Ophthalmosaurus'' have similar processes. The back part of the clavicle gradually narrows into a curved point, as in ''Ophthalmosaurus'', ''
Baptanodon ''Baptanodon'' is an ichthyosaur of the Late Jurassic period (160-156 million years ago), named for its supposed lack of teeth (although teeth of this genus have since been discovered). It had a graceful long dolphin-shaped body, and its jaws we ...
'', and '' Janusaurus''. The
coracoid A coracoid 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 present as part of the scapula, but this is n ...
is a kidney-shaped bone that is about as long as it is wide, compared to ''Cryopterygius'', ''Nannopterygius'', and ''Sveltonectes'', where it is not as wide proportionally. Like ''Ophthalmosaurus'' and ''
Arthropterygius ''Arthropterygius'' is a widespread genus of ophthalmosaurid ichthyosaur which existed in Canada, Norway, Russia, and Argentina from the late Jurassic period and possibly to the earliest Cretaceous. Description ''Arthropterygius'' appears to h ...
'', the coracoid bears a prominent notch on its front edge; it also bears a ridge on the frontal part of its midline, like ''Ophthalmosaurus'' and ''Acamptonectes'', but unlike ''Caypullisaurus'' and ''Platypterygius australis''. Its
articular facets A joint or articulation (or articular surface) is the connection made between bones, ossicles, or other hard structures in the body which link an animal's skeletal system into a functional whole.Saladin, Ken. Anatomy & Physiology. 7th ed. McGraw- ...
with the scapula and glenoid are clearly separate, as in ''Sveltonectes'' but not ''Acamptonectes''. The former is only about 45% of the latter in length; this figure is 50% in ''Cryopterygius'', and the two facets are effectively the same length in ''Janusaurus''. There are two prominent processes on the
humerus The humerus (; : humeri) 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 (bone), radius and ulna, and consists of three sections. The humeral upper extrem ...
. The longer, less prominent, and more ridge-like of these is the dorsal process. This process is remarkably short compared to other ophthalmosaurids, being less than half of the length of the humeral shaft, a condition also seen in ''
Undorosaurus ''Undorosaurus'' is an extinct genus of ophthalmosaurid ichthyosaur known from western Russia, Svalbard, and Poland. It was a large ichthyosaur, with the type species measuring long. Discovery and naming ''Undorosaurus'' was named by Vladimir ...
'' and ''Aegirosaurus''; in ''Ophthalmosaurus'', ''
Brachypterygius ''Brachypterygius'' (meaning ″short wing/paddle″ in Greek) is an extinct genus of platypterygiine ophthalmosaurid ichthyosaur known from the Late Jurassic of England.McGowan, C. & Motani, R. ''Ichthyopterygia''. In Sues, H.-D. (ed.) Handbook ...
'', '' Paraophthalmosaurus'', and ''Cryopterygius'', the process reaches the midpoint of the humerus, while it is even longer in ''Arthropterygius'', ''Platypterygius americanus'', ''Platypterygius australis'', and ''Platypterygius hercynicus''. The other process is the deltopectoral crest, which is similarly small among ophthalmosaurids (i.e. less than half of the shaft length) in the same manner as ''Arthropterygius'', ''Platypterygius hercynicus'', and ''Janusaurus''; it is about half of the shaft length in ''Ophthalmosaurus'', and is almost as long as the entire shaft in ''Sisteronia'', ''Acamptonectes'', and ''Platypterygius americanus''. At the midpoint of the humeral shaft, the bone is mildly constricted, being approximately 20% narrower than the maximum width. The bottom end of the humerus is larger than the top end; it bears three articular facets, with one for the preaxial accessory element (the smallest of the three), one for 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 ...
(the tallest of the three), and one for 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 ...
(which forms an angle of 120° with the radial facet). ''Sveltonectes'', ''Nannopterygius'', ''Platypterygius hauthali'', and ''Platypterygius platydactylus'' all only have two; ''
Maiaspondylus ''Maiaspondylus'' is an extinct genus of platypterygiine ophthalmosaurid ichthyosaurs known from Northwest Territories of Canada, the Cambridge Greensand of England and the Voronezh Region of Russia. Description ''Maiaspondylus'' is known from ...
'', ''Aegirosaurus'', ''Brachypterygius'', and ''Platypterygius americanus'' also have three, but the second facet articulates with a different bone; ''Cryopterygius'' has two on the left humerus and three on the right; and ''Platypterygius australis'' and ''Platypterygius hercynicus'' have up to four facets.


Hindlimb and pelvic girdle

The ilium of ''Keilhauia'' is rather short compared to that of other ophthalmosaurids; ''Aegirosaurus'' is the only other ophthalmosaurid that possibly approaches ''Keilhauia'' in this respect. The side of the ilium directed towards the back of the body is concave, like ''Ophthalmosaurus'', ''Athabascasaurus'', and ''Janusaurus'', with the curve being more pronounced in the latter two. The
acetabulum The acetabulum (; : acetabula), also called the cotyloid cavity, is a wikt:concave, concave surface of the pelvis. The femur head, head of the femur meets with the pelvis at the acetabulum, forming the Hip#Articulation, hip joint. Structure The ...
, on the lower end of the ilium, is thickened relative to the rest of the bone, and does not bear any distinct articular facets. Autapomorphically, the top end of the ilium is 1.5 times the width of the acetabular end. The
ischium The ischium (; : is ...
and the pubis are fused together into a single, continuous, solid trapezoid-shaped element known as the ischiopubis, with the wider edge (1.4 times the width of the other end, which is shorter proportionally than that of ''Aegirosaurus'', ''Janusaurus'', ''Ophthalmosaurus'', and ''Athabascasaurus'') being at the midline of the body. This complete fusion is also seen in ''Janusaurus'', ''Sveltonectes'', ''Athabascasaurus'', ''Aegirosaurus'', ''Caypullisaurus'', and possibly ''Platypterygius australis''; meanwhile, ''Ophthalmosaurus'', ''Cryopterygius'', ''Undorosaurus'', and ''Paraophthalmosaurus'' retain a small hole in the ischiopubis. The probable portion of the ischiopubis that represents the pubis is thicker than the rest of the bone. Also uniquely among ophthalmosaurids, this fused element is shorter than the
femur The femur (; : femurs or femora ), or thigh bone is the only long bone, bone in the thigh — the region of the lower limb between the hip and the knee. In many quadrupeds, four-legged animals the femur is the upper bone of the hindleg. The Femo ...
. Both ends of the femur of ''Keilhauia'' are approximately the same width, with the middle of the femoral shaft being slightly narrower. The top end was slightly thicker than the rest of the bone along its front rim. Like ''Arthropterygius'' but unlike ''Ophthalmosaurus'', the femoral dorsal and ventral processes were rather reduced. At the bottom end, there are two facets, one for the
tibia The tibia (; : tibiae or tibias), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two Leg bones, bones in the leg below the knee in vertebrates (the other being the fibula, behind and to the outsi ...
and one for the
fibula The fibula (: fibulae or fibulas) 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. ...
; this is typical of ophthalmosaurids, but ''Platypterygius hercynicus'', ''Platypterygius americanus'', ''Platypterygius australis'', and ''Paraophthalmosaurus'' all have three. Both facets in ''Keilhauia'' were roughly the same length, and the fibular facet was directed slightly to the back, forming an angle of 120° with the tibial facet.


Discovery and naming

Excavations led by the Spitsbergen Mesozoic Research Group from 2004 to 2012 recovered 29
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 ...
specimens from outcrops of the Slottsmøya Member
lagerstätte A Fossil-Lagerstätte (, from ''Lager'' 'storage, lair' '' Stätte'' 'place'; plural ''Lagerstätten'') is a sedimentary deposit that preserves an exceptionally high amount of palaeontological information. ''Konzentrat-Lagerstätten'' preserv ...
, which belongs to the greater
Agardhfjellet Formation The Agardhfjellet Formation is a Formation (geology), geologic formation in Svalbard, Norway. It preserves fossils dating back to the Oxfordian (stage), Oxfordian to Berriasian stages, spanning the Late Jurassic-Early Cretaceous boundary. The for ...
, on the island of
Spitsbergen Spitsbergen (; formerly known as West Spitsbergen; Norwegian language, Norwegian: ''Vest Spitsbergen'' or ''Vestspitsbergen'' , also sometimes spelled Spitzbergen) is the largest and the only permanently populated island of the Svalbard archipel ...
,
Svalbard Svalbard ( , ), previously known as Spitsbergen or Spitzbergen, is a Norway, Norwegian archipelago that lies at the convergence of the Arctic Ocean with the Atlantic Ocean. North of continental Europe, mainland Europe, it lies about midway be ...
,
Norway Norway, officially the Kingdom of Norway, is a Nordic countries, Nordic country located on the Scandinavian Peninsula in Northern Europe. The remote Arctic island of Jan Mayen and the archipelago of Svalbard also form part of the Kingdom of ...
. These outcrops likely date to the
Tithonian In the geological timescale, the Tithonian is the latest age (geology), age of the Late Jurassic Epoch and the uppermost stage (stratigraphy), stage of the Upper Jurassic Series. It spans the time between 149.2 ±0.7 annum, Ma and 143.1 ±0.6 (mi ...
-
Berriasian In the geological timescale, the Berriasian is an age/ stage of the Early/Lower Cretaceous. It is the oldest subdivision in the entire Cretaceous. It has been taken to span the time between 143.1 ±0.6 Ma and 137.05 ± 0.2 (million years ago) ...
based on
ammonite Ammonoids are extinct, (typically) coiled-shelled cephalopods comprising the subclass Ammonoidea. They are more closely related to living octopuses, squid, and cuttlefish (which comprise the clade Coleoidea) than they are to nautiluses (family N ...
biostratigraphy Biostratigraphy is the branch of stratigraphy which focuses on correlating and assigning relative ages of rock strata by using the fossil assemblages contained within them.Hine, Robert. "Biostratigraphy." ''Oxford Reference: Dictionary of Biology ...
. From these, the new genera and species '' Cryopterygius kristiansenae'', '' Palvennia hoybergeti'', and '' Janusaurus lundi'' have previously been described. Four ichthyosaur specimens were prepared at the
University of Oslo The University of Oslo (; ) is a public university, public research university located in Oslo, Norway. It is the List of oldest universities in continuous operation#Europe, oldest university in Norway. Originally named the Royal Frederick Univ ...
and subsequently described in 2016; they include PMO 222.655, the holotype of ''Keilhauia'', discovered from the Berriasian portions of the Slottsmøya Member in 2010. This articulated partial skeleton, which was preserved lying on its left side, consists of part of the snout, the dorsal and anterior caudal vertebrae, the right forelimb and
pectoral girdle The shoulder girdle or pectoral girdle is the set of bones in the appendicular skeleton which connects to the arm on each side. In humans, it consists of the clavicle and scapula; in those species with three bones in the shoulder, it consists o ...
, the majority of the pubic girdle, and both of the
femora 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 ...
. Since all of the cervical vertebrae and parts of the dorsal vertebrae are missing, it is difficult to assign precise numberings to the existing dorsal vertebrae. The other three described specimens were PMO 222.670 and PMO 227.932, both discovered in 2011; and PMO 222.662, discovered in 2007. The genus name ''Keilhauia'' honours the Norwegian geologist Baltazar Mathias Keilhau, who conducted an expedition to Spitsbergen in 1827. Meanwhile, the species name ''nui'' is derived from the acronym of the environmental organization
Natur og Ungdom Natur og Ungdom (NU) which translates to Nature and Youth, also known in English as Young Friends of the Earth Norway, is a Norwegian youth environmental protection organisation. It is the only environmentalist youth organisation in Norway. 7, ...
, the fiftieth anniversary of which occurred in 2017.


Classification

In 2017, ''Keilhauia'' was referred to the clade
Ophthalmosauridae Ophthalmosauridae is an extinct family of thunnosaur ichthyosaurs from the Middle Jurassic to the early Late Cretaceous (Bajocian - Cenomanian) worldwide. Almost all ichthyosaurs from the Middle Jurassic onwards belong to the family, until the ex ...
. This was on account of it bearing an
articular facet A joint or articulation (or articular surface) is the connection made between bones, ossicles, or other hard structures in the body which link an animal's skeletal system into a functional whole.Saladin, Ken. Anatomy & Physiology. 7th ed. McGraw- ...
on the
humerus The humerus (; : humeri) 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 (bone), radius and ulna, and consists of three sections. The humeral upper extrem ...
for the attachment of an anterior accessory element (a specialized limb bone that ichthyosaurs gained), as well as its forelimb elements lacking notches on their front edges. A
phylogenetic analysis In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical data ...
likewise recovered ''Keilhauia'' as an ophthalmosaurid. Its specific relationships within the ophthalmosaurids, however, were difficult to elucidate due to the lack of cranial material. Thus, the authors considered the basal placement of ''Keilhauia'' in the below phylogenetic tree somewhat suspect (a similar problem occurs for ''
Undorosaurus ''Undorosaurus'' is an extinct genus of ophthalmosaurid ichthyosaur known from western Russia, Svalbard, and Poland. It was a large ichthyosaur, with the type species measuring long. Discovery and naming ''Undorosaurus'' was named by Vladimir ...
'', which was also placed basally despite having a forelimb similar to ''
Cryopterygius ''Undorosaurus'' is an extinct genus of ophthalmosaurid ichthyosaur known from western Russia, Svalbard, and Poland. It was a large ichthyosaur, with the type species measuring long. Discovery and naming ''Undorosaurus'' was named by Vladimir ...
''). ''Keilhauia'' can be distinguished from its contemporaries by various characters. Unlike ''Cryopterygius'', 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 ...
r facet of the
humerus The humerus (; : humeri) 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 (bone), radius and ulna, and consists of three sections. The humeral upper extrem ...
is angled backwards, and there is no opening in the fused ischiopubis. ''Janusaurus'' has comparatively more robust humeri and more strongly-developed dorsal and ventral processes on the
femur The femur (; : femurs or femora ), or thigh bone is the only long bone, bone in the thigh — the region of the lower limb between the hip and the knee. In many quadrupeds, four-legged animals the femur is the upper bone of the hindleg. The Femo ...
. Additionally, the
autapomorphies In phylogenetics, an autapomorphy is a distinctive feature, known as a derived trait, that is unique to a given taxon. That is, it is found only in one taxon, but not found in any others or outgroup taxa, not even those most closely related to ...
, or traits unique to this genus, provide further evidence for its distinctness.


Paleobiology

A statistical analysis of
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 ...
ian proportions conducted in the description of ''Keilhauia'' showed that, throughout their evolutionary history, ichthyosaurs did not significantly reduce the relative size of their ilium, but their
femora 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 ...
did become proportionally longer relative to their
humeri The humerus (; : humeri) 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 ...
. ''Keilhauia'' has a small
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) ...
as well as a small humerus and femur, but it falls within the normal range of variation between
parvipelvia Parvipelvia (Latin for "little pelvis" - ''parvus'' meaning "little" and ''pelvis'' meaning "pelvis") is an extinct clade of euichthyosaur ichthyosaurs that existed from the Late Triassic to the early Late Cretaceous (middle Norian to Cenomanian ...
n ichthyosaurs.


Paleoecology

The Slottsmøya Member of the
Agardhfjellet Formation The Agardhfjellet Formation is a Formation (geology), geologic formation in Svalbard, Norway. It preserves fossils dating back to the Oxfordian (stage), Oxfordian to Berriasian stages, spanning the Late Jurassic-Early Cretaceous boundary. The for ...
, from which ''Keilhauia'' is known, consists of a mix of
shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of Clay mineral, clay minerals (hydrous aluminium phyllosilicates, e.g., Kaolinite, kaolin, aluminium, Al2Silicon, Si2Oxygen, O5(hydroxide, OH)4) and tiny f ...
s and
siltstone Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility. Although its permeabil ...
s. It was deposited in a shallow marine environment, near a patch of deeper
marine sediment Marine sediment, or ocean sediment, or seafloor sediment, are deposits of insoluble particles that have accumulated on the seafloor. These particles either have their origins in soil and Rock (geology), rocks and have been Sediment transport, ...
. The seafloor, which was located about below the surface, seems to have been relatively dysoxic, or oxygen-poor, although it was periodically oxygenated by clastic sediments. Despite this, near the top of the member, various diverse assemblages of invertebrates associated with
cold seep A cold seep (sometimes called a cold vent) is an area of the ocean floor where seepage of fluids rich in hydrogen sulfide, methane, and other hydrocarbons occurs, often in the form of a brine pool. ''Cold'' does not mean that the temperature ...
s have been discovered; these include
ammonite Ammonoids are extinct, (typically) coiled-shelled cephalopods comprising the subclass Ammonoidea. They are more closely related to living octopuses, squid, and cuttlefish (which comprise the clade Coleoidea) than they are to nautiluses (family N ...
s, lingulate brachiopods,
bivalves Bivalvia () or bivalves, in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of aquatic molluscs (marine and freshwater) that have laterally compressed soft bodies enclosed by a calcified exoskeleton consis ...
, rhynchonellate brachiopods, tubeworms,
belemnoids Belemnoids are an extinct group of marine cephalopod, very similar in many ways to the modern squid. Like them, the belemnoids possessed an ink sac, but, unlike the squid, they possessed ten Cephalopod arm, arms of roughly equal length, and no t ...
,
tusk shell Scaphopoda (plural scaphopods , from Ancient Greek σκᾰ́φης ''skáphē'' "boat" and πούς ''poús'' "foot"), whose members are also known as tusk shells or tooth shells, are a class (biology), class of shelled Marine life, marine inve ...
s,
sponge Sponges or sea sponges are primarily marine invertebrates of the animal phylum Porifera (; meaning 'pore bearer'), a basal clade and a sister taxon of the diploblasts. They are sessile filter feeders that are bound to the seabed, and a ...
s,
crinoid Crinoids are marine invertebrates that make up the class Crinoidea. Crinoids that remain attached to the sea floor by a stalk in their adult form are commonly called sea lilies, while the unstalked forms, called feather stars or comatulids, are ...
s,
sea urchin Sea urchins or urchins () are echinoderms in the class (biology), class Echinoidea. About 950 species live on the seabed, inhabiting all oceans and depth zones from the intertidal zone to deep seas of . They typically have a globular body cove ...
s,
brittle star Brittle stars, serpent stars, or ophiuroids (; ; referring to the serpent-like arms of the brittle star) are echinoderms in the class Ophiuroidea, closely related to starfish. They crawl across the sea floor using their flexible arms for locomot ...
s,
starfish Starfish or sea stars are Star polygon, star-shaped echinoderms belonging to the class (biology), class Asteroidea (). Common usage frequently finds these names being also applied to brittle star, ophiuroids, which are correctly referred to ...
,
crustacean Crustaceans (from Latin meaning: "those with shells" or "crusted ones") are invertebrate animals that constitute one group of arthropods that are traditionally a part of the subphylum Crustacea (), a large, diverse group of mainly aquatic arthrop ...
s, and
gastropods Gastropods (), commonly known as slugs and snails, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, freshwater, and from the land. Ther ...
, numbering 54 taxa in total. Outside of the cold seeps, many of these invertebrates were also present in abundance. Besides ''Keilhauia'', 16 other
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 ...
specimens are also known from the Slottsmøya Member. These include the three that were described alongside it, as well as the type and only specimens of '' Cryopterygius kristiansenae'', '' Palvennia hoybergeti'', and '' Janusaurus lundi''. Additionally, 21
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 ...
ian specimens are also known from the site, including two belonging to the large '' Pliosaurus funkei'', three to '' Colymbosaurus svalbardensis'', and one each to '' Spitrasaurus wensaasi'' and '' S. larseni''. Many of these specimens are preserved in three dimensions and partially in articulation; this is correlated with high abundance of organic elements in the sediments they were buried in, as well as a lack of invertebrates locally.


References

{{Taxonbar, from=Q28744991 Early Cretaceous ichthyosaurs Ichthyosaurs of Europe Berriasian life Cretaceous Norway Fossils of Svalbard Agardhfjellet Formation Fossil taxa described in 2017 Ichthyosauromorph genera