| Alexandronectes | |
|---|---|
 | |
| Life restoration | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Superorder: | †Sauropterygia |
| Order: | †Plesiosauria |
| Superfamily: | †Plesiosauroidea |
| Family: | †Elasmosauridae |
| Subfamily: | †Aristonectinae |
| Genus: | †Alexandronectes Oteroet al., 2016 |
| Species: | †A. zealandiensis |
| Binomial name | |
| †Alexandronectes zealandiensis Oteroet al., 2016 | |
Alexandronectes is a genus ofelasmosauridplesiosaur, a type of long-necked marine reptile, that lived in the oceans ofLate CretaceousNew Zealand. It contains one species,A. zealandiensis.[1] Fossils ofAlexandronectes were found in theConway Formation of Canterbury,[2] which can be dated to the EarlyMaastrichtian stage of theCretaceous. Fossils of it were found around 1872 near the Waipara River, north of Christchurch, New Zealand.[3]
Alexandronectes belongs to the elasmosaurid subfamilyAristonectinae based on the pterygoid structure and an A-shaped squamosal arch. However, it differs from other aristonectines in its smaller skull, different paroccipital processes, and different mandibular glenoid.[1] A 2021 study used CT scans to create digital reconstructions of the holotype, and detected thestapes in the inner ear, marking the first time this bone has been found in an aristonectine. The study also found a recess in thefloccular lobe of the cerebellum, which may have functioned to stabilize both the head and the retinal image ofAlexandronectes. This is the first occurrence of this feature in an elasmosaurid.[3]
Fossils of unknown animal were found inNew Zealand,[1] in a basin of middleWaipara River, on the north of Christchurch (possible coordinates 43°03'24 S, 172°34'52). Fossils lied between rock of theConway Formation, built of soft, erosive, but massive dark gray mudstones and mud sandstones with intensive marks ofbioturbation and big spherical calcareous concretions from the end ofCretaceous,[4] fromMaastrichtian.[1] The rocks probably precipitated in the environment of smalloxygen capacity, in waters not stirred by strong current or waves. Previously in the rocks of aforementioned formation fossils ofTeleostei, shark teeth,brachiopods, plant remains anddinoflagellates had been found, the latter used to date another ones. Aforementioned specimen was buried in a dinoflagellateA. acutulum layer.[4]
Fossils were found by Alexander McKay. A precise date he found them is not known, but according toCanterbury Museum catalog it had to be before 1888. The specimen was cataloged as M Zfr 73 and CM Zfr 91. It comprised two elements of cranium.[1] Zfr 73 contained part ofmandible withquadrate bone andsquamosal bone, with preserved paroccipital process. Zfr 91 comprised part of cranium (big cranium, as Hiller and Mannering would point out later) comprising fragment of rightpterygoid bone,basisphenoid bone,basioccipital bone, crushed rights squamosal bone and quadrate bone.[4] Initially these specimens were thought to originate from different individuals.[1]
The situation changed with publication of paper by Hiller and Mannering in 2004 in a journal published by Canterbury Museum, where the fossils had been transported to. Researches concluded that both cranial fragments had originated from the same individual, a big plesiosaur.[4] Indeed, as Oteroet al. had found, fragments in debate comprises complelemtary cranial parts, their sizes have corresponding sizes, there are no overlapping elements and the mineralisation level is the same. What is more, a way the bones had been damaged by crushing, erosion and disintegration was the same.[1] Hiller & Mannering compared the specimen to sympatricMauisaurus haasti, however, in a systematic chapter of their paper they described the specimen as simply unidentified Elasmosauridae.[4]
Mentioned paper put the specimen in rich fauna of New Zealand late Cretaceous plesiosaurs, seven species of which had been described earlier, besides part of them becomingnomina dubia.[1] Of the ones assumed valid nowadays one can mentionKaiwhekea, described in 2002 and classified by Cruickshanket al. to theCryptoclididae family,[5] and later doAristonectidae[6] (degraded subsequently toAristonectinae),[1] andTuarangisaurus belonging toelasmosaurid family,[7] but not to Aristonectinae,[1] and finallyMauisaurus, described by Hector yet in 19th century. Besides, in New Zealand unidentified fossils ofPolycotylidae andPliosauroidea were found.[1]
However, the discussed specimen distinguished from plesiosaurs known before due to earlier unobserved combination of characteristics. Its cranium was a bit shorter and narrower than these belonging toAristonectes andKaiwhekea, taller thanAristonectes one, but lower than those ofKaiwhekea. Anarticular surface of atemporomandibular joint was rounded, thick and somewhat similar to observed inKaiwhekea. Asquamosal bone had dorsal process pointed posterolaterally, it made A-shaped recess. According to Oteroet al., this is one more trait resemblingKaiwhekea, however, they found a difference in stouter dorsal rami. On the other side, paroccipital process does not resemble its homologous counterparts in other Aristonectinae in the matter of size, as it is shorter and more corpulent. Its distal end is widened dorsoventrally and flattened axially, with its dorsal surface concave and convex ventral one. It can be compared toLibonectes one.[1]
In 2016 Otero, R. A., O'Gorman, J. P., Hiller, N., O'Keefe, F. R. & Fordyce, R. E. published inJournal of Vertebrate Paleontology a paper titled Alexandronectes zealandiensis gen. et sp. nov.,a new aristonectine plesiosaur from the lower Maastrichtian of New Zealand, making a formal description of a new plesiosaur genus and species. The generic name honors Alexander McKay, who discovered its bones. It this genus a single species was put, namelyAlexandronectes zealandiensis. Its specific epithet appeals tomicrocontinent ofZealandia, a land mass that broke away fromsupercontinentGondwana in late Cretaceous epoch and contained areas of what is nowadays New Zealand.[1]
Researchers classified that animal inelasmosaurid family andAristonectinae subfamily. They conducted a phylogenetic analysis, concerning 24 plesiosaur genera and 91 traits. It resulted in astrict consensus trees, according to which closest kin ofAlexandronectes wasKaiwhekea.[1]
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