''Alexandronectes'' is a genus of elasmosaurid plesiosaur, a type of long-necked marine reptile, that lived in the oceans of

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger 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 ''creta'', ...

New Zealand New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 List of islands of New Zealand, smaller islands. It is the ...

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

Fossilworks Fossilworks is 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 cre ...

.org which can be dated to the Early

Maastrichtian The Maastrichtian () is, in the ICS geologic timescale, the latest age (uppermost stage) of the Late Cretaceous Epoch or Upper Cretaceous Series, the Cretaceous Period or System, and of the Mesozoic Era or Erathem. It spanned the interv ...

stage of the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...

. 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 animals 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 foot ...

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 The flocculus (Latin: ''tuft of wool'', diminutive) is a small lobe of the cerebellum at the posterior border of the middle cerebellar peduncle anterior to the biventer lobule. Like other parts of the cerebellum, the flocculus is involved in moto ...

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 preserved ...

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 pr ...

and big spherical calcareous concretions from the end of

, from

. The rocks probably precipitated in the environment of small

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as we ...

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

Teleostei Teleostei (; Greek ''teleios'' "complete" + ''osteon'' "bone"), members of which are known as teleosts ), is, by far, the largest infraclass in the class Actinopterygii, the ray-finned fishes, containing 96% of all extant species of fish. Tele ...

, shark teeth,

brachiopod Brachiopods (), phylum Brachiopoda, are a phylum of trochozoan 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 end, ...

s, plant remains and

dinoflagellate The dinoflagellates (Greek δῖνος ''dinos'' "whirling" and Latin ''flagellum'' "whip, scourge") are a monophyletic group of single-celled eukaryotes constituting the phylum Dinoflagellata and are usually considered algae. Dinoflagellates are ...

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 anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bon ...

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 uppe ...

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 co ...

, 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 () are two irregular bones of the facial skeleton in many animal species, located above the uvula in the ...

, 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 t ...

, 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, 7 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 s ...

''. Of the ones assumed valid nowadays one can mention '' Kaiwhekea'', 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 elasmosaurid 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. Polycotylids first appeared during the Albian stage of the Early Cretaceous, before becoming abundant and widespread during the early Late Cretaceou ...

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 to ...

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'' and '' Kaiwhekea'', taller than '' Aristonectes'' one, but lower than those of '' Kaiwhekea''. 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 articulation between the temporal bone of the skull above and the mandible below; it is from these bones that it ...

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 resebmling ''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'' one. Kaiwhekea NT small

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) or Tasmantis, is an almost entirely submerged mass of continental crust that subsided after breaking away from Gondwanaland 83–79 million years ago.Gurnis, M., Hall, C.E., and Lavier, L.L ...

, a land mass that broke away from

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

Gondwana Gondwana () was a large landmass, often referred to as a supercontinent, that formed during the late Neoproterozoic (about 550 million years ago) and began to break up during the Jurassic period (about 180 million years ago). The final st ...

in late Cretaceous epoch and contained areas of what is nowadays New Zealand. Researchers classified that animal in elasmosaurid family and Aristonectinae subfamily. They conducted a filogenetic analysis, concerning 24 plesiosaur genera and 91 traits. It resulted in a ''strict consensus'' trees, according to which closest kin of ''Alexandronectes'' was '' Kaiwhekea''.

References

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