Skeletomuscular Advances In Reptiles 

what skeletomuscular advances occurred in reptiles?

Some major advances occurred in the skeletomuscular status as they evolved from amphibians. 

Significant advancements in the skeletomuscular system aimed at enhancing the overall condition of amniotes began to emerge even within reptilian-like amphibians. 

( a ) Development of limb bones and girdles :

The gephyrostegid labyrinthodonts, characterized by their small size and agility, are likely to have been direct ancestors to the earliest known reptiles, specifically the romeriid captorhinomorphs. 

Over time, limb bones and girdles developed increased power, accompanied by a more intricate appendicular musculature that spread across the trunk muscles. 

( b ) Advanced pelvic anchorage :

In contrast to amphibians, which possess only a single sacral vertebra, reptiles evolved a pelvic girdle that articulates with a sacrum comprised of two to five fused vertebrae, featuring short sacral ribs. This enhanced pelvic anchorage facilitated better support and greater propulsion from the hind limbs.

( c ) Adoption of bipedality :

Unlike the lateral splayed legs of salamanders, reptilian limbs evolved to rotate, positioning the elbows backwards and the knees forward. 

Although cotylasaurs and mammal-like reptiles maintained a quadrupedal stance, early archosaurs adopted bipedalism, as did various dinosaur descendants, including birds, which can effectively be regarded as "feathered dinosaurs." 

Even quadrupedal dinosaurs exhibited traits indicative of ancestral bipedality, characterized by powerful hind legs and a body structure where the back was typically highest at the pelvis, tapering down to smaller forequarters.

( d ) Neck flexibility :

Amphibians possess only one cervical vertebra, whereas reptiles feature multiple cervical vertebrae that articulate freely, enhancing neck flexibility. The mobility of the head improved significantly as the first two vertebrae evolved into a ring-shaped atlas, which connected with cranial processes known as occipital condyles. 

The axis, bearing an anteriorly directed process, enables side-to-side head movement through the rotation of the atlas upon the axis.

( e )  Temporal fossae :

Diagram : Evolution of temporal fossae in reptiles 

Temporal fossae emerged in most reptiles and were subsequently inherited by mammals and birds. A key distinction between reptilian-like amphibians and amphibian-like reptiles is that the latter possess a subdivided jaw-closing musculature, which includes the pterygoideus and temporalis portions, with the latter extending upward from the posterior aspect of the jaw. 

In bony fishes as well as primitive amphibians and reptiles, the dermocramium, formed from dermal bone, creates a solid roof over the originally cartilaginous neurocranium, confining the jaw musculature to the space between the two structures. 

The development of one or two pairs of large openings (temporal fossae) through the dermocramium allowed the temporalis muscle to extend onto the outer surface, facilitating its considerable expansion and improving the mechanics of chewing.

 While cotylosaurs and turtles lack these fossae, similar openings evolved independently across various other reptilian lineages, establishing a foundation for the recognition of distinct subclasses.