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

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 ...

arboreal Arboreal locomotion is the Animal locomotion, 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, but others are exclusively arboreal. Th ...

(tree-dwelling)

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 ( ...

that lived during the

Triassic The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest period ...

Period. 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 group first appeared about three hundred million years ago ...

reptiles known for their

prehensile tail A prehensile tail is the tail of an animal that has adapted to grasp or hold objects. Fully prehensile tails can be used to hold and manipulate objects, and in particular to aid arboreal creatures in finding and eating food in the trees. If the ta ...

s. ''Drepanosaurus'' was probably an

insectivore A robber fly eating a hoverfly An insectivore is a carnivorous animal or plant that eats insects. An alternative term is entomophage, which can also refer to the human practice of eating insects. The first vertebrate insectivores wer ...

, and lived in a coastal environment in what is now modern day Italy, as well as in a streamside environment in the midwestern United States.

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 (''pl''. ulnae or ulnas) is a long bone found in the forearm that stretches from the elbow to the smallest finger, and when in anatomical position, is found on the medial side of the forearm. That is, the ulna is on the same side of t ...

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 (or carpus) that connects the hand to the forearm. The term "carpus" is derived from the Latin carpus and the Greek καρπός (karpós), meaning "wrist". In human anatomy, th ...

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

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

. 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 ceratosaurian theropod dinosaur genus from the late Campanian-Maastrichtian (Late Cretaceous) of Argentina. The type and only species is ''N. leali''. Discovery and naming In the m ...

'' 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 se ...

''. 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 a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordate ...

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 Sacral may refer to: *Sacred, associated with divinity and considered worthy of spiritual respect or devotion *Of the sacrum The sacrum (plural: ''sacra'' or ''sacrums''), in human anatomy, is a large, triangular bone at the base of the spi ...

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 the ...

neural spines The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic ...

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

scapula The scapula (plural 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 eithe ...

was robust with a 70 degree bend. The

humerus The humerus (; ) 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 and ulna, and consists of three sections. The humeral upper extremity consists of a roun ...

and

radius In classical geometry, a radius ( : radii) of a circle or sphere is any of the line segments from its center to its perimeter, and in more modern usage, it is also their length. The name comes from the latin ''radius'', meaning ray but also the ...

were short, while the ulna was replaced by an

ulnare The triquetral bone (; also called triquetrum, pyramidal, three-faced, and formerly cuneiform bone) is located in the wrist on the medial side of the proximal row of the carpus between the lunate and pisiform bones. It is on the ulnar side of the ...

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 (plural pelves or pelvises) is the lower part of the trunk, between the abdomen and the thighs (sometimes also called pelvic region), together with its embedded skeleton (sometimes also called bony pelvis, or pelvic skeleton). The ...

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 (; ), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two bones in the leg below the knee in vertebrates (the other being the fibula, behind and to the outside of the tibia); it connects ...

and

fibula The fibula 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. Its upper extremity is ...

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: Greece 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 ...

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 Ne ...

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 polyphyletic group of 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 the English anatomis ...

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

monophyletic In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic gro ...

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

reptiles Reptiles, as most commonly defined are the animals in the Class (biology), class Reptilia ( ), a paraphyletic grouping comprising all sauropsid, sauropsids except birds. Living reptiles comprise turtles, crocodilians, Squamata, squamates (lizar ...

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 chameleon-like hands and feet to climb from branch to branch, as well as its long, prehensile tail, much like modern

monkeys Monkey is a common name that may refer to most mammals of the infraorder Simiiformes, also known as the simians. Traditionally, all animals in the group now known as simians are counted as monkeys except the apes, which constitutes an incomple ...

. 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 ( 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 ...

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

New Jersey New Jersey is a state in the Mid-Atlantic and Northeastern regions of the United States. It is bordered on the north and east by the state of New York; on the east, southeast, and south by the Atlantic Ocean; on the west by the Delaware ...

, in similar paleoenvironments.

References

External links