Tuesday, February 28, 2012

Lab 5: Lepidosauromorpha: Matt Knestrick & Megan Thornhill


The group Lepidosauria is located within Eureptilia and is sister to the Archosauromorphs. The Lepidosaurs are represented by members of Sphenodontida (extant Tuataras), Sauria (lizards), and Serpentes (snakes). Some synapomorphies that tie these groups together include :

· A transverse cloacal opening

· A notched tongue

· Full-body ecdysis

· Imperperforate columella

· Teeth attached to jaws

· The pelvic bones in adults are fused

· Fracture planes (septa) in caudal vertebrae

The division of Lepidosauria containing both Serpentes (snakes) and Sauria (lizards) is called Squamata. Squamates can thrive in a wide variety of climates, elevations, environments, and habitats and are found on every continent except Antarctica. The members of Squamata are linked by over 50 synapomorphies, however, some of the most outstanding and most easily recognizable include a fused premaxillae, fused parietals, reduced nasals, and well developed hemipenes. They also have the presence of a Jacobson’s organ which is separated from the nasal capsule, they possess femoral and pre-anal glands and exhibit and egg tooth at hatching.

In order to better understand the synapomorphies of Squamata, a Varanus skull was examined. By doing this the examples of a fused premaxilla and parietals could be easily distinguished. As well as the lack of vomerine teeth, which is another synapomorphy that links the Squamates.

The following are examples of some of the families present in Sauria, this is by no means an exhaustive list and there is an ongoing debate to the exact number of families present in Sauria. This is due solely to the debate over some subfamilies being promoted to families. We were given examples of the following in lab:

Family: Agamidae

Distribution: Africa, Asia, Australia

Characteristics: Members of this family are covered in juxtaposed scales and lack osteoderms. All members are also limbed and have at least
moderately long tails. These lizards also posses acrodont dentition. The example in lab was from the Agaminae subfamily

Family: Anguidae

Distribution: Americas, Southwest and Southern Asia, and Europe
Characteristics: Members of this family vary greatly in size and the limb
condition of members of this family can range from fully limbed to reduced limbs to a lack of limbs.They exhibit large non-overlapping scales and have osteoderms
present ventrally and dorsally on the trunk region. Most members of this family show a longitudinal ventrolateral groove that allows for expansion of the body for reproduction, breathing, and feeding. This family express
pleurodont dentition and the example seen in lab was a member of the subfamily Anguinae. This specific genus had developed limblessness, and a longitudinal fold was clearly visible.

Family: Chamaelionidae

Distribution: Middle East, Africa, India, Southern Spain, Sri Lanka, and
Characteristics: Members of this family posses strong lateral compression, zygodactyl feet, and a prehensile tail. They also exhibit a parietal shield over their neck region as well as independently moving eyes. The dentition on this family is acrodont, and they possess reticular papillae on their tongues.

Family: Gekkonidae

Distribution: Tropics, South America, Africa, Western North America
Characteristics: Small granular scales cover members of this family both dorsally and ventrally. Other scale variations include large tubricles as well as defined papillae on their tongues. Caudal autonomy is common in this family. This is often paired with a large distracting tail used for fat and water storage. One characteristic seen in many members of this family is the presence of lamellae or ‘scansors’ on the feet used for climbing. They also express pleurodont dentition.

Family: Helodermatidae

Distribution: Southwestern North America south along the coast of the Mexican
Pacific toward Guatemala
Characteristics: Typically large lizards with well developed venom glands, but no system with which to inject prey. They have typically thick skin and large bead like granular scales. Physically they have rather flattened heads, robust bodies, and a short heavy tail. Among members of this family show no caudal autonomy and their tongues
have filamentous papillae. They spend most of their time underground except for mating, eating, and etc.

Family: Iguanidae

Distribution: Americas, Madagascar, west-central Pacific Islands
Characteristics: This family shows a wide range in size and diversity. This family is very sexually dimorphic. They are mainly opportunistic feeders, but occasionally exhibit a change in diet during different life stages. Four subfamilies were exhibited in lab, these were:

1. Polychrotinae: This subfamily contains 8 genera. In this subfamily the males are typically larger and possess a gular flap but no femoral pores.

2. Phrynosomatinae: This subfamily contains 10 genera including an Ohio species (Sceloporus undulates-Northern Fence Lizard). This subfamily is sexually dimorphic with the males showing femoral pores.

3. Corytophaninae: This subfamily contains 3 genera and extend from Southern Mexico to northern South America.

They possess a very long tail and males do not exhibit femoral pores, but the males to have frills/crests on their head and/or back.

4. Iguaninae: This subfamily contains 8 genera and have a huge distribution. In this family the adults are mainly herbivorous and the juveniles are very opportunistic feeders. They have large keeled scales, have pleurodont

dentition, and possess caudal autonomy.

Family: Scincidae

Distribution: Huge distribution (Nearly worldwide)

Characteristics: They exhibit smooth cycloid overlapping scales, and typically possess osteoderms. Show long to moderately long tails and some may exhibit reduced limbs. This family is highly speciated and there are both oviparous and viviparous examples in this family. This family is where many Ohio apecies are classified. These include:

· Scincella lateralis (Ground Skink)

· Eumeces fasciatus (Five-lined Skink)

Eumeces laticeps (Broad-headed Skink)

· Eumeces anthracinus (Northern Coal Skink)

Family: Teiidae

Distribution: Northern United States to Argentina and Chile

Characteristics: Possess small granular scales on the dorsal surface, but large rectangular scales ventrally. They have typically long tails and show caudal autonomy. The example seen in lab was from the subfamily Teiinae. The dentition of members of this family is also pleurodont.

Family: Varanidae

Distribution: Africa (warm temperate and tropical), Asia, and Australia

Characteristics: They are venomous lizards and lack caudal autonomy. Typically large with highly defined limbs. The ventral scales are generally visibly larger than those located on the dorsal surface. This is the family that the largest living lizard, the Komodo Dragon, belongs.

No comments:

Post a Comment