''Ancistronychus'' is an

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

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 ...

drepanosaur 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 ...

from the

Late Triassic The Late Triassic is the third and final epoch (geology), epoch of the Triassic geologic time scale, Period in the geologic time scale, spanning the time between annum, Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch a ...

Petrified Forest National Park Petrified Forest National Park is a national park of the United States in Navajo and Apache counties in northeastern Arizona. Named for its large deposits of petrified wood, the park covers about , encompassing semi-desert shrub steppe as wel ...

in the

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 ...

Arizona Arizona is a U.S. state, state in the Southwestern United States, Southwestern region of the United States, sharing the Four Corners region of the western United States with Colorado, New Mexico, and Utah. It also borders Nevada to the nort ...

. The

type Type may refer to: Science and technology Computing * Typing, producing text via a keyboard, typewriter, etc. * Data type, collection of values used for computations. * File type * TYPE (DOS command), a command to display contents of a file. * ...

and only known species is ''Ancistronychus paradoxus'', from

Ancient Greek Ancient Greek (, ; ) includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Greek ...

to mean "unexpected fishhook claw" due to its characteristic hooked shape. ''Ancistorhynchus'' is only known from a collection of isolated large claws from its second fingers, a distinctive trait of other derived drepanosaurs. ''Ancistorhynchus'' is characteristic amongst drepanosaurs by the strongly hooked shape of its claw, which is shorter in height and broader than those of ''

Drepanosaurus ''Drepanosaurus'' (; "sickle lizard") is a genus of arboreal (tree-dwelling) reptile that lived during the Triassic Period. It is a member of the Drepanosauridae, a group of diapsid reptiles known for their prehensile tails. ''Drepanosaurus'' wa ...

'', and is flat at its tip. The claw is also cleft at its tip, a trait found in living animals that use their claws for digging, such as moles and

pangolins Pangolins, sometimes known as scaly anteaters, are mammals of the order Pholidota (). The one extant family, the Manidae, has three genera: ''Manis'', '' Phataginus'', and '' Smutsia''. ''Manis'' comprises four species found in Asia, while ''P ...

, by providing a larger attachment area for the keratin sheath of the claw. Likewise, functional analyses of its claws compared to other drepanosaurs and various living animals indicates that ''Ancistronychus'' used its large claw for digging underground, perhaps even for burrowing.

References

Drepanosauromorpha Late Triassic reptiles of North America Fossil taxa described in 2019 Prehistoric reptile genera {{Triassic-reptile-stub