| Albertonectes | |
|---|---|
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| Holotype skeleton (TMP 2007.011.0001) | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Superorder: | †Sauropterygia |
| Order: | †Plesiosauria |
| Superfamily: | †Plesiosauroidea |
| Family: | †Elasmosauridae |
| Subfamily: | †Elasmosaurinae |
| Genus: | †Albertonectes Kuboet al.,2012 |
| Type species | |
| †Albertonectes vanderveldei Kuboet al., 2012 | |
Albertonectes (meaning 'Alberta swimmer') is anextinctgenus of largeplesiosaurs that lived in North America during theCampanianstage of theLate Cretaceous period, at around 73.5 million years ago. The only knownspecies isA. vanderveldei, described in 2012 from an almost complete postcranial skeleton discovered in 2007 nearLethbridge, in theprovince ofAlberta, Canada. Although currently only documented from theholotype, a possible second specimen was discovered in 2015 in the same locality.
With a maximum length estimated at 12.1 metres (40 ft),Albertonectes is the longest knownelasmosaurid. Like the other representatives of this group, it has a streamlined body with paddle-like limbs, a short tail, a small head, and an extremely long neck. The neck alone is estimated at around 7 meters (23 ft) long, makingAlbertonectes one of the animals with the longest known necks. It is also thevertebrate with the greatest number ofcervical vertebrae identified to date, 76, ahead of its close relativeElasmosaurus.
The first known specimen ofAlbertonectes was discovered in 2007 near theSt. Mary River, near the town ofLethbridge, in southernAlberta,Canada. It was discovered unexpectedly by an excavator duringammolite mining carried out by the companyKorite International Ltd. At the initial moment of the discovery, the excavator accidentally broke part of the fossils coming from the middle of the animal'strunk, including an unknown quantity ofgastroliths (stomach stones). A large part of these fossils have since been noted as lost, and due to the unique character of the specimen as well as its excellent preservation, it was subsequently decided to leave it as is and not to remove any elements found there.[1][2] This specimen, since housed at theRoyal Tyrrell Museum of Palaeontology and numbered as TMP 2007.011.0001, consists of an almost complete and articulated skeleton of a largeplesiosaur, but theskull is missing. More precisely, it includes 132 vertebrae from theatlas-axis complex to fused tip of thetail vertebrae, a completepectoral but an incompletepelvic girdle, almost complete forelimbs and hindlimbs, disarticulatedribs, anabdominal rib, and at least 97 associatedgastroliths. The skeleton also preserves two teeth coming from thelamniformsharkSqualicorax, the few traces of grooves present on the leftcoracoid indicating that the specimen would have beenscavenged after its death.Stratigraphically, the skeleton was exhumed in an area dating from the middle of the lateCampanian of theBearpaw Formation, a period located around 73.5 million years ago. In 2012, Japanese paleontologist Tai Kubo and his Canadian colleagues Mark T. Mitchell and Donald M. Hendersondescribed the specimen as theholotype of a newgenus andspecies ofelasmosaurid namedAlbertonectes vanderveldei. The genus nameAlbertonectes comes from Alberta, in reference to theprovince where the animal was discovered, and from theAncient Greek wordνηκτός (nêktós, "swimmer"). Thespecific name is named in honor of Rene Vandervelde, the founder of the Korite International, the gem-mining company that discovered the holotype.Albertonectes represents the first significantly complete plesiosaur to be discovered in the Bearpaw Formation, as well as the second elasmosaurid to be identified in the same formation afterTerminonatator in 2003.[1]
On November 9, 2015, it was reported to the Royal Tyrrell Museum that some articulated vertebrae were discovered in conditions similar to those previously mentioned, still near Lethbridge. Subsequently, more vertebrae were discovered by Korite workers, but due to the particularly difficult conditions in winter, the recovery of the fossils had to be done quickly. The fossils recovered consist of a partial skeleton preserving avertebral column running from the base of the neck to the base of the tail, followed by a few articulated and disarticulated ribs. The discovery was made official the following year by Canadian paleontologistDarren H. Tanke via a summary, in which he referred this specimen ascf.Albertonectes.[3]
Albertonectes has the longest neck of anyelasmosaur ever discovered, which reached up to 7 metres (23 ft). The holotype, missing the skull, measures at 11.2 metres (37 ft) from theatlas-axis complex to the tip of the tail, suggesting a total body length of 11.6 metres (38 ft) with the skull.[1] In 2024, Henderson estimated its total body length up to 12.1 metres (40 ft) and its total body mass around 4.8 metric tons (5.3 short tons).[2]
Albertonectes is alsounique among otherelasmosaurids in having 76 neck vertebrae, a record number among elasmosaurids (and vertebrates as a whole).[4]Callawayasaurus with a similar count of 56 lacks the dumbbell-shaped articular faces that are present on the vertebrae ofVegasaurus. Additional traits rarely seen in other elasmosaurids include: a tapered front-side projection on thepubis that extends to the side beyond theacetabulum, a longitudinal ridge on the side of most neck vertebrae up to cervical 69, aclavicular arch that is wider than the adjacent front edge of thescapula, the lack of pectoral and pelvic bar, a tip of the tail that is made of seven fused tail vertebrae, and a slenderhumerus with a width-to-length ratio of 0.56, among other traits.
Albertonectes is known from a mature individual, as suggested by the fusedneural spines and most cervical ribs to their centra, and by the only partial connection between thetrochanter and the capitulum (head) of thefemur, seen in TMP 2007.011.0001. Other observation also support an adult age, e.g. rough and wrinkled vertebral surfaces as well as well-developed facets and articulations on itswrist andankle bones.[1]
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The single known specimen ofAlbertonectes preservesgastroliths, 97 of which are exposed and visible. These poked out of the dorsal side of the body between the ribs, as the animal had come to lie down on the seabed on its back some time after death, the gastroliths moving into the present position through gravity as the body decayed. The largest of the visible gastroliths weighed an estimated 1.13 kg. Gastroliths were generally either disc-shaped or spherical; the former would've come from beaches and the latter from river mouths. All were composed ofchert, as is the case with several other species of plesiosaurs. It is hypothesized that chert stones are specifically sought out by plesiosaurs as gastroliths for their hardness and durability.[2]
In their original 2012 description, Kubo and colleagues argued that assigningAlbertonectes to the Elasmosauridae would be problematic in the absence of cranial material, as the skull provides key diagnostic features for newly described species. Nevertheless, many other elasmosaurids, including thetype genusElasmosaurus, are known primarily from postcranial remains, and numerous previouscladistic analyses have shown that more than one-third of the characters used are postcranial. To determine thephylogenetic affinities ofAlbertonectes, the authors coded it into a data matrix originally created by Tamaki Sato in 2002. They recovered it in a relatively basal position within the Elasmosauridae, although the exclusion of cranial characters increased the number of unresolvedpolytomies.[1] In the official description of the related genusVegasaurus, published in 2015, Argentine paleontologist José P. O’Gorman and colleagues adopted the modified topology proposed by Kuboet al. (2012). In this analysis,Albertonectes occupied a more derived position, within aclade that also includedFutabasaurus andMauisaurus[5]—the latter since recognized as anomen dubium in a paper published two years later.[6]
In 2016, Chilean paleontologist Rodrigo A. Otero established thesubfamily Styxosaurinae to include four genera:Terminonatator,Styxosaurus,Albertonectes, andElasmosaurus. Members of this group are primarily characterized by having more than 60 cervical vertebrae. Within the subfamily,Albertonectes andElasmosaurus form a derived branch that includes the only known representatives with more than 70 cervical vertebrae.[7] In another analysis published the following year, American paleontologist Danielle J. Serratos and her colleagues did not resolve the position ofElasmosaurus, but noted that the Styxosaurinae could be synonymous with the Elasmosaurinae if the type genus indeed belongs to the group.[8] In 2020, O’Gorman formally synonymized the Styxosaurinae with the Elasmosaurinae based on the inclusion ofElasmosaurus within the clade, and also provided a list of diagnostic features defining it.[9] The followingcladogram follows Otero (2016),[7] with clade names following O’Gorman (2020):[9]
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