When did birds become classified as reptiles?

Why is the skull of reptiles modified?

The skull of the reptiles is modified that gives the reptiles an efficient and powerful jaw action. The modification also makes the skull light. Following are the important characteristics of the animals belonging to Class Reptilia:

What is a primitive synapsid called?

Primitive synapsids are usually called pelycosaurs or pelycosaur-grade synapsids; more advanced mammal-like ones, therapsids. The non-mammalian members are described as mammal-like reptiles in classical systematics; they can also be called stem mammals or proto-mammals.

Why do reptiles have vacuities on their heads?

Generally in reptiles with big jaws and large head, the skull becomes too heavy for the neck to support it. Therefore vacuities or fossae developed in reptiles to lighten the skull and also to provide space for accommodating powerful jaw muscles.

How are snakes differentiated from other reptiles by their temporal openings?

They were differentiated from other reptiles by their distinctive temporal openings. These openings in the skull bones allowed the attachment of larger jaw muscles, hence a more efficient bite.

Are synapsids mammals or reptiles?

Note: Traditional classifications typically consider synapsids to be mammal-like, extinct reptiles ancestral to mammals. Cladistic classifications also consider these extinct forms ancestral to mammals but do not categorize them as reptiles.

What are the primitive and advanced groups of reptiles?

The mammal-like reptiles are traditionally divided into a primitive group and an advanced group, known respectively as pelycosaurs and therapsids. Pelycosaurs are a paraphyletic group of six primitive families of synapsids. 120 They were all rather lizard-like with sprawling gait and possibly horny scutes.

What type of Skull did the first reptiles have?

It was traditionally assumed that the first reptiles retained an anapsid skull inherited from their ancestors. This type of skull has a skull roof with only holes for the nostrils, eyes and a pineal eye.

What are the adaptations of reptiles for swallowing large objects?

Many reptiles developed joints (in addition to the hinge for the lower jaw) within the skull that permit the slight movement of one part relative to others. The capacity for such movement within the skull, called kinesis, enables an animal to increase the gape of the mouth and thus is an adaptation for swallowing large objects.

How did reptiles move away from water?

But several advances in lungs, bone structure, and egg composition enabled the earliest reptiles to move away from the water and populate the rest of the untapped ecological niches around the world. The first obvious signs of reptiles appeared in the fossil record some 310 to 320 million years ago.

How do snakes differ from other reptiles?

Snakes differ from other reptiles in being limbless and having a greatly elongated body and tail. Snakes also lack movable eyelids and external ear openings.

What is the difference between anapsid and synapsid skull?

[A] Anapsid skull – The most primitive form does not have any holes behind the orbit. All the first terrestrial animals had this kind of skull. Fish, amphibians and turtles still do. [B] Synapsid scull – One fenestra (hole) behind the orbit: includes all Pelycosaurs and all their decedents, Therapsids and mammals.

What do synapsids have in common with amniotes?

Unlike other amniotes, they have a temporal fenestra, an opening low in the skull roof behind each eye, leaving a bony arch beneath each; this accounts for their name. Primitive synapsids are usually called pelycosaurs or pelycosaur- grade synapsids.

Which reptiles have temporal fossa present high up on the skull?

These reptiles possess one temporal fossa present high up on the skull. Protosaurs, Nothosaurs, Placodonts showed this type of skull. The two largest groups among these were- Ichthyosaurs and Plesiosaurus.

How is the skull of a bird different from that of reptiles?

The skull represents an advance over that of reptiles in the relatively larger cranium with fusion of elements, made possible by the fact that birds have a fixed adult size. Birds differ from mammals in being able to move the upper mandible rather than the lower, relative to the cranium.

When did vertebrates first leave the water?

Although early amphibians had lumbered ashore in search of insects, vertebrates didn’t finally leave the water until later in the Paleozoic when the first reptiles evolved waterproof skin and an egg with membranes (amnion, chorion) to protect embryos from desiccation.

How do reptiles survive without water?

Specifically, changes in how reptiles reproduce, dry scaly skin and highly efficient kidneys all allow reptiles to thrive with very little water. Amphibians, such as frogs, have wet skin and are dependent on constant access to water to keep their bodies from drying out.

What is the difference between the Synapsida and mammals?

In traditional taxonomy, the Synapsida encompasses two distinct grades successively closer to mammals: the low-slung pelycosaurs have given rise to the more erect therapsids, who in their turn have given rise to the mammals.

What is the difference between a synapsid and euryapsid skull?

The euryapsid skull, characteristic of two reptile groups (ichthyosaurs and plesiosaurs), bears a supratemporal fenestra (Figure 1.9c), whereas the synapsid skull bears an infratemporal fenestra and is characteristic of synapsids (Figure 1.9d). Sign in to download full-size image FIGURE 1.9.

What are the sauropsid amniotes and synapsids?

The sauropsid amniotes include the reptiles and birds. Formally, this constitutes many different groups, but the sauropsid amniotes share many derived characteristics which separate them from the synapsids. The two groups evolved around the same time, from a common ancestor which was likely not terrestrial.

Which of the following animals have a common ancestor with reptiles?

The birds and the mammals have a common ancestor with the reptiles. It is the rule of the cladistic analysis that animals with most recent common ancestor must be placed in a particular taxon. Birds and mammals have common ancestor with reptiles.