The biological screw joint is a naturally occurring form of the

screw joint A screw joint is a one-Degree of freedom (mechanics), degree-of-freedom kinematic pair used in mechanisms. Screw joints provide single-axis translation by utilizing the threads of a lead screw to provide such translation. This type of joint is ...

, a mechanical device that combines rotational movement with single-axis translation. Alexander Riedel of the State Museum of Natural History Karlsruhe and Thomas van de Kamp of the

Karlsruhe Institute of Technology The Karlsruhe Institute of Technology (KIT; german: Karlsruher Institut für Technologie) is a public research university in Karlsruhe, Germany. The institute is a national research center of the Helmholtz Association. KIT was created in 2009 w ...

discovered it in specimens of '' Trigonopterus oblongus'', a

weevil Weevils are beetles belonging to the Taxonomic rank, superfamily Curculionoidea, known for their elongated snouts. They are usually small, less than in length, and Herbivore, herbivorous. Approximately 97,000 species of weevils are known. They b ...

found in Papua.

Discovery

Anatomical examination was made for specimens of the weevil species '' Trigonopterus oblongus'', provided by the Karlsruhe State Museum of Natural History, using a microtomograph at the Institute of Synchrotron Radiation (ANKA) of

. The analysis revealed that the weevils had a

nut Nut often refers to: * Nut (fruit), fruit composed of a hard shell and a seed, or a collective noun for dry and edible fruits or seeds * Nut (hardware), fastener used with a bolt Nut or Nuts may also refer to: Arts, entertainment, and media Com ...

-and- screw system for the

hip In vertebrate anatomy, hip (or "coxa"Latin ''coxa'' was used by Celsus in the sense "hip", but by Pliny the Elder in the sense "hip bone" (Diab, p 77) in medical terminology) refers to either an anatomical region or a joint. The hip region is ...

- leg joint.

Mechanism

The mechanism has been described as "rotational movement combined with a single-axis translation". The arthropod hip–leg joint consists of two parts – the coxa (or the hip) and the trochanter (or the head of the arthropod leg femur). The coxa, in the case of weevils, resembles a nut, and it has a thread running along its inner surface with an angular span of 345°. The trochanter resembles the screw. It is rod-shaped with a large external spiral flange, having an angular span of 410°, in excess of a full circle, which functions as a thread. When the leg muscles of a beetle are stretched, the screw turns. Though the screw-thread provide for very large angular rotation, the front legs of weevils are capable of rotating by 90°, while their hind legs can rotate by 130°. The weevils are just long and can fold their legs below their body. The joint is just in size. Before this was discovered, all known hip-leg joints have been based on either the

ball and socket joint The ball-and-socket joint (or spheroid joint) is a type of synovial joint in which the ball-shaped surface of one rounded bone fits into the cup-like depression of another bone. The distal bone is capable of motion around an indefinite number o ...

system for hip-leg connections, as in humans, as

hinge A hinge is a mechanical bearing that connects two solid objects, typically allowing only a limited angle of rotation between them. Two objects connected by an ideal hinge rotate relative to each other about a fixed axis of rotation: all other ...

s or as saddle joints. The discovery is the first ever instance of a musculoskeletal nut-and-screw system in the animal kingdom.

Evolution

The screw-and-nut system has been found to be present in all 15 weevils examined by the scientists and appears to be a hitherto unknown anatomical feature of weevils. It has been estimated that weevils evolved this system about 100 million years ago. It is surmised that the development of this feature provided additional flexibility which permitted weevils to improve their climbing abilities, helped them keep steady when at rest, and to give a stronger leverage for piercing by 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 ...

References

{{Reflist, 32em Cryptorhynchinae Insect anatomy

Discovery

Mechanism

Evolution

See also

References