''Megachirella'' is an

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

stem Stem or STEM may refer to: Plant structures * Plant stem, a plant's aboveground axis, made of vascular tissue, off which leaves and flowers hang * Stipe (botany), a stalk to support some other structure * Stipe (mycology), the stem of a mushro ...

- squamate that lived about 240 million years ago during the

Middle Triassic In the geologic timescale, the Middle Triassic is the second of three epochs of the Triassic period or the middle of three series in which the Triassic system is divided in chronostratigraphy. The Middle Triassic spans the time between Ma and ...

and contains only one known species, ''Megachirella wachtleri''. It is known from a partial

skeleton A skeleton is the structural frame that supports the body of an animal. There are several types of skeletons, including the exoskeleton, which is the stable outer shell of an organism, the endoskeleton, which forms the support structure inside ...

discovered in the

Dolomites The Dolomites ( it, Dolomiti ; Ladin: ''Dolomites''; german: Dolomiten ; vec, Dołomiti : fur, Dolomitis), also known as the Dolomite Mountains, Dolomite Alps or Dolomitic Alps, are a mountain range located in northeastern Italy. They form par ...

Northern Italy Northern Italy ( it, Italia settentrionale, it, Nord Italia, label=none, it, Alta Italia, label=none or just it, Nord, label=none) is a geographical and cultural region in the northern part of Italy. It consists of eight administrative regions ...

and was described in 2003.

Description

''Megachirella'' is known exclusively from a partial skeleton, preserved in anatomical connection. The find includes an almost complete

skull The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, the ...

, the front half of the body and part of the front legs. The skull, although devoid of the front part of the

snout A snout is the protruding portion of an animal's face, consisting of its nose, mouth, and jaw. In many animals, the structure is called a muzzle, rostrum, or proboscis. The wet furless surface around the nostrils of the nose of many mammals is c ...

, is rather robust and large; the neck is moderately elongated and the front legs are large and strong. The dimensions do not exceed in length, and the appearance is similar to that of a strong-legged lizard. Megachirella dorsal

Classification

Megachirella was discovered in the

Dont Formation Don't, Dont, or DONT may refer to: Films * ''Don't'' (1925 film), a 1925 silent comedy film * ''Don't'' (1974 film), a 1974 film about the monarch butterfly * ''Don't'', a fake trailer from the film ''Grindhouse'' (2007) Songs * "Don't" (Bill ...

of the area of

Braies Braies are a type of trouser worn by Celtic and Germanic tribes in antiquity and by Europeans subsequently into the Middle Ages. In the later middle ages they were used exclusively as undergarments. Braies generally hung to the knees or mid-c ...

, in

South Tyrol it, Provincia Autonoma di Bolzano – Alto Adige lld, Provinzia Autonoma de Balsan/Bulsan – Südtirol , settlement_type = Autonomous province , image_skyline = , image_alt ...

, and described in 2003. It was classified as a member of

Lepidosauromorpha Lepidosauromorpha (in PhyloCode known as ''Pan-Lepidosauria'') is a group of reptiles comprising all diapsids closer to lizards than to archosaurs (which include crocodiles and birds). The only living sub-group is the Lepidosauria, which contains ...

, the clade of

reptile Reptiles, as most commonly defined are the animals in the class Reptilia ( ), a paraphyletic grouping comprising all sauropsids except birds. Living reptiles comprise turtles, crocodilians, squamates (lizards and snakes) and rhynchocephalians ( ...

s that includes

lizard Lizards are a widespread group of squamate reptiles, with over 7,000 species, ranging across all continents except Antarctica, as well as most oceanic island chains. The group is paraphyletic since it excludes the snakes and Amphisbaenia alt ...

snake Snakes are elongated, Limbless vertebrate, limbless, carnivore, carnivorous reptiles of the suborder Serpentes . Like all other Squamata, squamates, snakes are ectothermic, amniote vertebrates covered in overlapping Scale (zoology), scales. Ma ...

s, the

tuatara Tuatara (''Sphenodon punctatus'') are reptiles endemic to New Zealand. Despite their close resemblance to lizards, they are part of a distinct lineage, the order Rhynchocephalia. The name ''tuatara'' is derived from the Māori language and m ...

and their closest extinct relatives, at the time. In particular, the

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 show some similarities, mainly in the skull, with some primitive forms such as the

Eolacertilia Eolacertilia ("dawn lizards") is an extinct clade of lepidosauriform diapsid reptiles known from the Late Permian to the Late Triassic. It is uncertain as to whether they are a natural group and it has been suggested that they form a "waste ba ...

. A

phylogenetics In biology, phylogenetics (; from Greek language, Greek wikt:φυλή, φυλή/wikt:φῦλον, φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary his ...

analysis in 2013 confirmed that it was a lepidosauromorph closely related to the

crown group In phylogenetics, the crown group or crown assemblage is a collection of species composed of the living representatives of the collection, the most recent common ancestor of the collection, and all descendants of the most recent common ancestor. ...

Lepidosauria The Lepidosauria (, from Greek meaning ''scaled lizards'') is a subclass or superorder of reptiles, containing the orders Squamata and Rhynchocephalia. Squamata includes snakes, lizards, and amphisbaenians. Squamata contains over 9,000 species, m ...

. A study in 2018, led by Tiago R. Simōes from the

University of Alberta The University of Alberta, also known as U of A or UAlberta, is a public research university located in Edmonton, Alberta, Canada. It was founded in 1908 by Alexander Cameron Rutherford,"A Gentleman of Strathcona – Alexander Cameron Rutherfor ...

, found that ''Megachirella'' was a stem-squamate, making it the oldest known member of the order Squamata, the order that includes

s and

amphisbaenia Amphisbaenia (called amphisbaenians or worm lizards) is a group of usually legless squamates, comprising over 200 extant species. Amphisbaenians are characterized by their long bodies, the reduction or loss of the limbs, and rudimentary eyes. As ...

ns (worm lizards). The study was conducted by performing high-resolution microfocus X-ray computed tomography (micro-CT) scans on the fossil specimen of ''Megachirella'' to gather detailed data about its

anatomy Anatomy () is the branch of biology concerned with the study of the structure of organisms and their parts. Anatomy is a branch of natural science that deals with the structural organization of living things. It is an old science, having its ...

. This data was then compared with a phylogenetic dataset combining the morphological and

molecular A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bioche ...

data of 129

extant Extant is the opposite of the word extinct. It may refer to: * Extant hereditary titles * Extant literature, surviving literature, such as ''Beowulf'', the oldest extant manuscript written in English * Extant taxon, a taxon which is not extinct, ...

(living) and extinct reptilian taxa. The comparison revealed ''Megachirella'' had certain features that are unique to squamates. The study also found that

gecko Geckos are small, mostly carnivorous lizards that have a wide distribution, found on every continent except Antarctica. Belonging to the infraorder Gekkota, geckos are found in warm climates throughout the world. They range from . Geckos ar ...

es are the earliest crown group squamates, not iguanians.

Paleobiology

Despite being found in marine deposits, the fossil of ''Megachirella'' shows no adaptation to aquatic life. On the contrary, characteristics like the strong front legs, the shape of the claws, the well-ossified carpus and the hollow ribs lead one to think that this animal was well adapted to a terrestrial lifestyle. The specimen was probably transported to a shallow coastal environment due to heavy storms after it died.

References

{{Taxonbar, from=Q16941205 Fossils of Italy Prehistoric lepidosauromorphs Prehistoric reptile genera