Reptile Anatomy

파충류샵 Reptiles share the general pattern of vertebrates with a bony skull, a long spinal cord and ribs. The skin is dry and covered with scales that are keratinized.

파충류샵

Like birds and mammals, reptiles have a kinetic skull that allows them to move their upper jaw/beak to widen the gape during feeding. They also have a quadrate bone that articulates loosely with the mandible and can move rostrally to increase the gape.

Skull

A reptile skull is shaped differently than the mammal skull. Mammals have a large opening called a temporal fenestra behind each eye that provides space for more attachment of jaw muscles. This is why mammals have a stronger bite than reptiles. Reptiles have a much simpler skull with less fusion and looser connections between the bones. This enables snakes to move their mouths around large prey.

The crocodile skull is an example of this type of skull. The superior temporal vacuity is guarded by the parietal and squamosal bones above and by the postorbital and quadratojugal below. This makes the skull lighter and gives the jaw muscles greater strength.

Reptiles have a number of joints within their skulls that allow for slight movement of one part of the skull relative to another, a process called kinesis. This allows them to increase the size of their mouths in order to swallow larger prey items. These joints also enable them to move their heads from side to side, an important ability for hunting. This type of head movement is not found in mammals, but does occur in a few groups of dinosaurs that gave rise to reptiles and mammals.

Scales파충류샵

Scales are the external covering of reptiles and function in two basic ways: protection and locomotory support. Unlike the skin of mammals and amphibians, scales do not contain glands. They are made of a hard substance called keratin, which is formed through cycles of growth and resorption.

There are many different types of scales in reptiles, each with a distinct appearance. For example, frills (also known as elongated scales) are seen on the back of iguanas. Other scales, such as those on the limbs of crocodiles, show only minor overlapping and are characterized by narrow hinge regions that include hard, cornified b-keratinized epidermis. These scales, known as ctenoid scales, have the same functions of protection and locomotory support (1).

Some scales have keels, which increase the rigidity of the scale and enhance the ability to climb. For example, the toe pads of anoles and geckos feature specialized surfaces that help them grip the ground. Scales are also a vital part of the reptile’s protection from sunlight. Thick layers of keratin reduce water loss and keep the animal from becoming overheated.

Skin

Reptiles have dry skin with a layer of heavily keratinized scales that helps to prevent water loss. This reflects their commitment to a terrestrial existence, as opposed to aquatic ones like amphibians.

The scales are arranged in a way that is specific to the species, and their shape and position can help scientists identify the animal without dissection. On the head, horny plates called scutes form a shield-like structure whose shape and number varies between family, genus, and species.

In addition to scales, the skin is lined with mucous glands that reduce water loss and can also help to protect against parasites. Many reptiles use camouflage to hide from predators, and the coloring of their skin can be used for other purposes as well – for example, some geckos have patches on their tails that mimic moss, which is a potential food source for them. Other reptiles release pheromones from their skin that can be used for territorial marking, breeding, or danger signaling. They can also use their skin to absorb heat or reflect light.

Teeth

Though mammal teeth get all the press, squamate reptiles (the ancestors of snakes and lizards) have unique and striking teeth as well. Their tooth shape, location, and dental implantation are more diverse than in any other amniote group.

In fact, a team of researchers led by Michael Caldwell, a UofA professor in the Department of Biological Sciences, used thin sections and CT scans to examine fossil jaw specimens from Cretaceous-era Priosphenodon. These fossils revealed tooth enamel that is not prismatic but a more complex arrangement of incremental lamellae, characterized by the presence of cylindrical groups of crystallites whose orientation varies regularly. This gives the enamel a pseudo-prismatic appearance when seen between crossed nicols of a polarizing microscope.

The Priosphenodon teeth also reveal an unexpected pattern of tooth replacement and acrodont vs. pleurodont tooth formation in this unique reptile. The team’s analysis of gene expression patterns during tooth odontogenesis in P. vitticeps, along with the comparison to similar patterns in mouse and mammal teeth, confirms that the key tooth formation regulator Sox2 is involved in the initiation of replacement acrodont teeth in Priosphenodon.

Ears

Although a reptile lacks the outer ears that mammals have, it has an inner ear structure that can detect sound vibrations. This unique feature is called “bone conduction hearing” and allows a reptile to sense sounds in their environment.

In lizards, the middle ear is coupled with the tympanic membrane via a single bone called the stapes. Its inner end is fitted inside the oval opening of the tympanic membrane and its outer end has a cartilage cap that comes into contact with the tympanic membrane. Laser vibrometry measurements of tympanic membrane responses to free-field sound show that the lizard middle ear is highly directional within a 2 kHz range, with up to 40 dB difference in response to ipsilateral and contralateral stimulation (Christensen-Dalsgaard et al., 2005).

The middle ear also contains a columella connecting the tympanic membrane with the eardrum. This is likely to have evolved independently in lepidosaurs (lizards and snakes) and archosaurs (crocodiles, dinosaurs including birds).