''Drepanosaurus'' (; "sickle lizard") is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

arboreal Arboreal locomotion is the locomotion of animals in trees. In habitats in which trees are present, animals have evolved to move in them. Some animals may scale trees only occasionally (scansorial), but others are exclusively arboreal. The hab ...

(tree-dwelling)

reptile Reptiles, as commonly defined, are a group of tetrapods with an ectothermic metabolism and Amniotic egg, amniotic development. Living traditional reptiles comprise four Order (biology), orders: Testudines, Crocodilia, Squamata, and Rhynchocepha ...

that lived during the

Triassic The Triassic ( ; sometimes symbolized 🝈) is a geologic period and system which spans 50.5 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.4 Mya. The Triassic is t ...

Period Period may refer to: Common uses * Period (punctuation) * Era, a length or span of time *Menstruation, commonly referred to as a "period" Arts, entertainment, and media * Period (music), a concept in musical composition * Periodic sentence (o ...

. It is a member of the Drepanosauridae, a group of

diapsid Diapsids ("two arches") are a clade of sauropsids, distinguished from more primitive eureptiles by the presence of two holes, known as temporal fenestrae, in each side of their skulls. The earliest traditionally identified diapsids, the araeosc ...

reptiles known for their

prehensile tail A prehensile tail is the tail of an animal that has Adaptation (biology), adapted to grasp or hold objects. Fully Prehensility, prehensile tails can be used to hold and manipulate objects, and in particular to aid arboreal creatures in finding and ...

s. ''Drepanosaurus'' was probably an

insectivore file:Common brown robberfly with prey.jpg, A Asilidae, robber fly eating a hoverfly An insectivore is a carnivore, carnivorous animal or plant which eats insects. An alternative term is entomophage, which can also refer to the Entomophagy ...

, and lived in a coastal environment in what is now modern day

Italy Italy, officially the Italian Republic, is a country in Southern Europe, Southern and Western Europe, Western Europe. It consists of Italian Peninsula, a peninsula that extends into the Mediterranean Sea, with the Alps on its northern land b ...

, as well as in a streamside environment in the southwestern

United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...

Description

''Drepanosaurus'' is known to have a huge claw on the "index finger" (digit II) of each hand along with the tail claw. The skull of ''Drepanosaurus'' has never been found and is still unknown; however, the skull of ''Drepanosaurus'' was likely similar to other drepanosaurs, such as ''Megalancosaurus''. ''Megalancosaurus skull was approximately the same size as its enlarged claws, and had a bird-like jaw and head shape. The forelimb of ''Drepanosaurus'' is highly modified compared to other vertebrates. Its

ulna The ulna or ulnar bone (: ulnae or ulnas) is a long bone in the forearm stretching from the elbow to the wrist. It is on the same side of the forearm as the little finger, running parallel to the Radius (bone), radius, the forearm's other long ...

was modified into a robust, crescent-shaped site for muscle attachment. The elongated

carpal The carpal bones are the eight small bones that make up the wrist (carpus) that connects the hand to the forearm. The terms "carpus" and "carpal" are derived from the Latin carpus and the Greek καρπός (karpós), meaning "wrist". In huma ...

bone functionally replaced the ulna. Additional forelimb musculature would have attached to the

withers Withers are the ridge between the shoulder blades of an animal, typically a quadruped. In many species, this ridge is the tallest point of the body. In horses and dogs, it is the standard place to measure the animal's height. In contrast, catt ...

. The animal's second digit bore a large claw, reminiscent of those found in dinosaurs such as ''

Noasaurus ''Noasaurus'' ("Northwestern Argentina lizard") is a genus of Ceratosauria, ceratosaurian theropod dinosaur from the Maastrichtian (Late Cretaceous) of Argentina. The Type species, type and only species is ''N. leali''. The fragmentary holotype s ...

'' and ''

Baryonyx ''Baryonyx'' () is a genus of theropod dinosaur which lived in the Barremian stage of the Early Cretaceous period, about 130–125 million years ago. The first skeleton was discovered in 1983 in the Smokejack Clay Pit, of Surrey, England, in ...

''. However, it is more likely that ''Drepanosaurus'' used its claw like the modern pygmy anteater, tearing through bark and insect nests to find

invertebrate Invertebrates are animals that neither develop nor retain a vertebral column (commonly known as a ''spine'' or ''backbone''), which evolved from the notochord. It is a paraphyletic grouping including all animals excluding the chordata, chordate s ...

prey. Some researchers have forwarded the more far-fetched proposal that the claw was used to excavate burrows, but this is not unanimously agreed upon. The dorsal neural spine humps of ''Drepanosaurus'' are much taller along all succeeding spines reaching down to the sacrum. Sacral and anterior

caudal Caudal may refer to: Anatomy * Caudal (anatomical term) (from Latin ''cauda''; tail), used to describe how close something is to the trailing end of an organism * Caudal artery, the portion of the dorsal aorta of a vertebrate that passes into th ...

neural spines Each vertebra (: vertebrae) is an irregular bone with a complex structure composed of bone and some hyaline cartilage, that make up the vertebral column or spine, of vertebrates. The proportions of the vertebrae differ according to their spinal ...

are very low, if present at all, and neural spines are elongated, showing expanded dorsal margins after those areas. The

scapula The scapula (: scapulae or scapulas), also known as the shoulder blade, is the bone that connects the humerus (upper arm bone) with the clavicle (collar bone). Like their connected bones, the scapulae are paired, with each scapula on either side ...

was robust with a 70 degree bend. The

humerus The humerus (; : humeri) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius (bone), radius and ulna, and consists of three sections. The humeral upper extrem ...

and

radius In classical geometry, a radius (: radii or radiuses) of a circle or sphere is any of the line segments from its Centre (geometry), center to its perimeter, and in more modern usage, it is also their length. The radius of a regular polygon is th ...

were short, while the ulna was replaced by an ulnare and shifted to the elbow, taking a disc-like form. This skeletal configuration change is thought to have adapted as a result of the large claw on digit II requiring a large muscle in order to operate. The

pelvis The pelvis (: pelves or pelvises) is the lower part of an Anatomy, anatomical Trunk (anatomy), trunk, between the human abdomen, abdomen and the thighs (sometimes also called pelvic region), together with its embedded skeleton (sometimes also c ...

was large with the pubis forming the majority of the ventral portion. The hind limbs of ''Drepanosaurus'' were much larger than the forelimbs, with the

tibia The tibia (; : tibiae or tibias), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two Leg bones, bones in the leg below the knee in vertebrates (the other being the fibula, behind and to the outsi ...

and

fibula The fibula (: fibulae or fibulas) or calf bone is a leg bone on the lateral side of the tibia, to which it is connected above and below. It is the smaller of the two bones and, in proportion to its length, the most slender of all the long bones. ...

being broadly separated. Drepanosaurus unguicaudatus tail

Discovery and classification

Discovered in northern Italy in 1979, ''Drepanosaurus'' was named by Giovanni Pinna, a paleontologist and museologist. The species name is ''Drepanosaurus unguicaudatus''. It is derived from the

Greek Greek may refer to: Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group *Greek language, a branch of the Indo-European language family **Proto-Greek language, the assumed last common ancestor of all kno ...

for "sickle lizard." Only one incomplete adult specimen has been found. Another partial specimen of ''Drepanosaurus'' was found in New Mexico's

Chinle Formation The Chinle Formation is an Upper Triassic continental geological formation of fluvial, lacustrine, and palustrine to eolian deposits spread across the U.S. states of Nevada, Utah, northern Arizona, western New Mexico, and western Colorado. In ...

in 2016. ''Drepanosaurus'' is part of the clade Drepanosauridae, which is nested in the larger clade

Drepanosauromorpha Drepanosaurs (members of the clade Drepanosauromorpha) are a group of extinct reptiles that lived between the Carnian and Rhaetian stages of the late Triassic Period, approximately between 230 and 210 million years ago. The various species of dre ...

. Drepanosauromorphs are sometimes considered part of the group

Protorosauria Protorosauria is an extinct, likely paraphyletic group of basal archosauromorph reptiles from the latest Middle Permian ( Capitanian stage) to the end of the Late Triassic ( Rhaetian stage) of Asia, Europe and North America. It was named by t ...

which may or may not be a natural group (i.e.,

monophyletic In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria: # the grouping contains its own most recent co ...

). In any case, it is clear that drepanosaurs are

reptiles Reptiles, as commonly defined, are a group of tetrapods with an ectothermic metabolism and Amniotic egg, amniotic development. Living traditional reptiles comprise four Order (biology), orders: Testudines, Crocodilia, Squamata, and Rhynchocepha ...

Paleobiology

''Drepanosaurus'' is hypothesized to have been an

, using the claws on the second digits to lift bark and dig into crevices and grooves on trees to find insects. It has been suggested that ''Drepanosaurus'' was also a digging animal, and could use the clawed tail as a tool for unearthing insects. However, it is not thought that ''Drepanosaurus's'' tail was flexible enough to be used for digging, especially since many characteristics point to an

lifestyle.

Paleoecology

Being only in length, ''Drepanosaurus'' likely spent its time in trees using its clawed hands and feet to climb from branch to branch, as well as its

, much like a

chameleon Chameleons or chamaeleons (Family (biology), family Chamaeleonidae) are a distinctive and highly specialized clade of Old World lizards with 200 species described as of June 2015. The members of this Family (biology), family are best known for ...

. The claw on the tip of the tail may have also been used to grip branches. ''Drepanosaurus'' is much larger than its relatives, more than double the length of ''Megalancosaurus''. Most drepanosaurs are thought to be tree-dwelling insectivores with similar body structures to ''Drepanosaurus'', except for minor differences usually dealing with forelimb configuration and head shape disparities. ''Drepanosaurus'' inhabited forests in what is now

northern Italy Northern Italy (, , ) is a geographical and cultural region in the northern part of Italy. The Italian National Institute of Statistics defines the region as encompassing the four Northwest Italy, northwestern Regions of Italy, regions of Piedmo ...

. Relatives have been found in other parts of Italy and New Mexico, as well as

New Jersey New Jersey is a U.S. state, state located in both the Mid-Atlantic States, Mid-Atlantic and Northeastern United States, Northeastern regions of the United States. Located at the geographic hub of the urban area, heavily urbanized Northeas ...

, in similar paleoenvironments.

References

External links