''Alexandronectes'' is a genus of

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 ...

, a type of long-necked marine reptile, that lived in the oceans of

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 ...

New Zealand New Zealand () is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and List of islands of New Zealand, over 600 smaller islands. It is the List of isla ...

. It contains one species, ''A. zealandiensis''. Fossils of ''Alexandronectes'' were found in the Conway Formation of Canterbury,Waipara River, M34/f1073
at

Fossilworks Fossilworks was a portal which provides query, download, and analysis tools to facilitate access to the Paleobiology Database, a large relational database assembled by hundreds of paleontologists from around the world. History Fossilworks was cr ...

.org which can be dated to the Early

Maastrichtian The Maastrichtian ( ) is, in the International Commission on Stratigraphy (ICS) geologic timescale, the latest age (geology), age (uppermost stage (stratigraphy), stage) of the Late Cretaceous epoch (geology), Epoch or Upper Cretaceous series (s ...

stage of the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

. Fossils of it were found around 1872 near the Waipara River, north of Christchurch, New Zealand. ''Alexandronectes'' belongs to the elasmosaurid subfamily Aristonectinae 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. A 2021 study used CT scans to create digital reconstructions of the holotype, and detected the

stapes The ''stapes'' or stirrup is a bone in the middle ear of humans and other tetrapods which is involved in the conduction of sound vibrations to the inner ear. This bone is connected to the oval window by its annular ligament, which allows the f ...

in the inner ear, marking the first time this bone has been found in an aristonectine. The study also found a recess in the floccular lobe of the cerebellum, which may have functioned to stabilize both the head and the retinal image of ''Alexandronectes''. This is the first occurrence of this feature in an elasmosaurid.

Fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserve ...

s of unknown animal were found in

, in a basin of middle Waipara River, on the north of Christchurch (possible coordinates 43°03’24’’ S, 172°34’52’’). Fossils lied between rock of the Conway Formation, built of soft, erosive, but massive dark gray mudstones and mud sandstones with intensive marks of

bioturbation Bioturbation is defined as the reworking of soils and sediments by animals or plants. It includes burrowing, ingestion, and defecation of sediment grains. Bioturbating activities have a profound effect on the environment and are thought to be a ...

and big spherical calcareous concretions from the end of

, from

. The rocks probably precipitated in the environment of small

oxygen Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...

capacity, in waters not stirred by strong current or waves. Previously in the rocks of aforementioned formation fossils of

Teleostei Teleostei (; Ancient Greek, Greek ''teleios'' "complete" + ''osteon'' "bone"), members of which are known as teleosts (), is, by far, the largest group of ray-finned fishes (class Actinopterygii), with 96% of all neontology, extant species of f ...

, shark teeth,

brachiopod Brachiopods (), phylum (biology), phylum Brachiopoda, are a phylum of animals that have hard "valves" (shells) on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear e ...

s, plant remains and

dinoflagellate The Dinoflagellates (), also called Dinophytes, are a monophyletic group of single-celled eukaryotes constituting the phylum Dinoflagellata and are usually considered protists. Dinoflagellates are mostly marine plankton, but they are also commo ...

s had been found, the latter used to date another ones. Aforementioned specimen was buried in a dinoflagellate ''A. acutulum'' layer. Fossils were found by Alexander McKay. A precise date he found them is not known, but according to Canterbury 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. Zfr 73 contained part of

mandible 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 i ...

with

quadrate bone The quadrate bone is a skull bone in most tetrapods, including amphibians, sauropsids ( reptiles, birds), and early synapsids. In most tetrapods, the quadrate bone connects to the quadratojugal and squamosal bones in the skull, and forms up ...

and

squamosal bone The squamosal is a skull bone found in most reptiles, amphibians, and birds. In fishes, it is also called the pterotic bone. In most tetrapods, the squamosal and quadratojugal bones form the cheek series of the skull. The bone forms an ancestral ...

, with preserved paroccipital process. Zfr 91 comprised part of cranium (big cranium, as Hiller and Mannering would point out later) comprising fragment of right

pterygoid bone The pterygoid is a paired bone forming part of the palate of many vertebrates, behind the palatine bone In anatomy, the palatine bones (; derived from the Latin ''palatum'') are two irregular bones of the facial skeleton in many animal specie ...

, basisphenoid bone,

basioccipital bone The basilar part of the occipital bone (also basioccipital) extends forward and upward from the foramen magnum, and presents in front an area more or less quadrilateral in outline. In the young skull, this area is rough and uneven, and is joined ...

, crushed rights squamosal bone and quadrate bone. Initially these specimens were thought to originate from different individuals. Mauisaurus BW

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. Indeed, as Otero ''et 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. Hiller & Mannering compared the specimen to sympatric '' Mauisaurus haasti'', however, in a systematic chapter of their paper they described the specimen as simply unidentified Elasmosauridae. 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 becoming ''

nomina dubia In binomial nomenclature, a ''nomen dubium'' (Latin for "doubtful name", plural ''nomina dubia'') is a scientific name that is of unknown or doubtful application. Zoology In case of a ''nomen dubium,'' it may be impossible to determine whether a ...

''. Of the ones assumed valid nowadays one can mention ''

Kaiwhekea ''Kaiwhekea'' () is an extinct genus of plesiosaur from the Late Cretaceous (Maastrichtian age) of what is now New Zealand. History of discovery The holotype was discovered in 1983 by Gary Raper, an amateur fossil collector, at the base of a ...

'', described in 2002 and classified by Cruickshank ''et al.'' to the

Cryptoclididae Cryptoclididae is a family of medium-sized plesiosaurs that existed from the Middle Jurassic to the Early Cretaceous. They had long necks, broad and short skulls and densely packed teeth. They fed on small soft-bodied preys such as small fish and ...

family, and later do Aristonectidae (degraded subsequently to Aristonectinae), and '' Tuarangisaurus'' belonging to

family, but not to Aristonectinae, and finally '' Mauisaurus'', described by Hector yet in 19th century. Besides, in New Zealand unidentified fossils of

Polycotylidae Polycotylidae is a family of plesiosaurs from the Cretaceous, a sister group to Leptocleididae. They are known as false pliosaurs. Polycotylids first appeared during the Albian stage of the Early Cretaceous, before becoming abundant and widesprea ...

and

Pliosauroidea Pliosauroidea is an extinct clade of plesiosaurs, known from the earliest Jurassic to early Late Cretaceous. They are best known for the subclade Thalassophonea, which contained crocodile-like short-necked forms with large heads and massive toot ...

were found. 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 to ''

Aristonectes ''Aristonectes'' (meaning "best swimmer") is an extinct genus of large elasmosaurid plesiosaurs that lived during the Maastrichtian stage of the Late Cretaceous. Two species are known, ''A. parvidens'' and ''A. quiriquinensis'', whose fossil ...

'' and ''

'', taller than ''

'' one, but lower than those of ''

''. An

articular surface 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- ...

of a

temporomandibular joint In anatomy, the temporomandibular joints (TMJ) are the two joints connecting the jawbone to the skull. It is a bilateral Synovial joint, synovial articulation between the temporal bone of the skull above and the condylar process of mandible be ...

was rounded, thick and somewhat similar to observed in ''Kaiwhekea''. A

had dorsal process pointed posterolaterally, it made A-shaped recess. According to Otero ''et al.'', this is one more trait resembling ''Kaiwhekea'', 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 to ''

Libonectes ''Libonectes'' is an extinct genus of sauropterygian reptile belonging to the plesiosaur order. It is known from specimens found in the Britton Formation of Texas (USA) and the Akrabou Formation of Morocco, which have been dated to the lower Turo ...

'' one.

In 2016 Otero, R. A., O'Gorman, J. P., Hiller, N., O'Keefe, F. R. & Fordyce, R. E. published in ''Journal 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, namely ''Alexandronectes zealandiensis''. Its specific epithet appeals to

microcontinent Continental crustal fragments, partly synonymous with microcontinents, are pieces of continents that have broken off from main continental masses to form distinct islands that are often several hundred kilometers from their place of origin. Caus ...

Zealandia Zealandia (pronounced ), also known as (Māori language, Māori) or Tasmantis (from Tasman Sea), is an almost entirely submerged continent, submerged mass of continental crust in Oceania that subsided after breaking away from Gondwana 83� ...

, a land mass that broke away from

supercontinent In geology, a supercontinent is the assembly of most or all of Earth's continent, continental blocks or cratons to form a single large landmass. However, some geologists use a different definition, "a grouping of formerly dispersed continents", ...

Gondwana Gondwana ( ; ) was a large landmass, sometimes referred to as a supercontinent. The remnants of Gondwana make up around two-thirds of today's continental area, including South America, Africa, Antarctica, Australia (continent), Australia, Zea ...

in late Cretaceous epoch and contained areas of what is nowadays New Zealand. Researchers classified that animal in

family and Aristonectinae subfamily. They conducted a phylogenetic analysis, concerning 24 plesiosaur genera and 91 traits. It resulted in a ''strict consensus'' trees, according to which closest kin of ''Alexandronectes'' was ''

''.

References

{{Taxonbar, from=Q52984900 Elasmosauridae Late Cretaceous plesiosaurs Cretaceous reptiles of Oceania Campanian life Fossils of New Zealand Fossil taxa described in 2016 Sauropterygian genera