Search results
Results from the WOW.Com Content Network
Phylogenetic analyses distribute the features that developed along the tetrapod stem and display a stepwise process of character acquisition, rather than abrupt. [1] The complete transition occurred over a period of 30 million years beginning with the tetrapodomorph diversification in the Middle Devonian (380 myr).
The evolution of tetrapods began about 400 million years ago in the Devonian Period with the earliest tetrapods evolved from lobe-finned fishes. [1] Tetrapods (under the apomorphy-based definition used on this page) are categorized as animals in the biological superclass Tetrapoda, which includes all living and extinct amphibians, reptiles, birds, and mammals.
The upper limbs or upper extremities are the forelimbs of an upright-postured tetrapod vertebrate, extending from the scapulae and clavicles down to and including the digits, including all the musculatures and ligaments involved with the shoulder, elbow, wrist and knuckle joints. [1]
In typical early tetrapod posture, the upper arm and upper leg extended nearly straight horizontal from its body, and the forearm and the lower leg extended downward from the upper segment at a near right angle. The body weight was not centered over the limbs, but was rather transferred 90 degrees outward and down through the lower limbs, which ...
A forelimb or front limb is one of the paired articulated appendages attached on the cranial end of a terrestrial tetrapod vertebrate's torso. With reference to quadrupeds, the term foreleg or front leg is often used instead. In bipedal animals with an upright posture (e.g. humans and some other primates), the term upper limb is often used.
Polydactyly in early tetrapod aquatic animals, such as in Acanthostega gunnari (Jarvik 1952), one of an increasing number of genera of stem-tetrapods known from the Upper Devonian, which are providing insights into the appearance of tetrapods and the origin of limbs with digits. It also occurs secondarily in some later tetrapods, such as ...
The coronoid process is a bony projection that extends upwards from the upper surface of the lower jaw behind the tooth row. This process serves as an attachment site for muscles that close the jaw; a higher coronoid process increases the lever arm of these muscles, and thus the bite force. [43] [26] (see Figure here) cranial kinesis
The "sprawling" posture is the most primitive, and is the original limb posture from which the others evolved. The upper limbs are typically held horizontally, while the lower limbs are vertical, though upper limb angle may be substantially increased in large animals.