Biology of the Reptilia: Laboratory 6: Lepidosauria (Sphenodontida and Squamata)

Lizard families within Sauria, specimens from underlined families were investigated in lab.

Introduction

There are two sister lineages within Eureptilia, Archosauromorpha (Lab 3 & 4) and Lepidosauromorpha.

Lepidosauria synapomorphies:
1) Transverse cloacal aperture (vent)

2) Notched tongue

3) Full body ecdysis

4) Imperforate columella (stapes)

5) Teeth are attached to the jaws

6) Pelvic bones fused in adults

7) Fracture planes or septa within caudal vertebrae

Within Lepidosauria are the Sphenodontida, made up of extant Tuatara & Rhynchocephalians; and the Squamata, made up of Sauria (lizards) and Serpentes (snakes).

Squamata is a very numerous and diverse group of reptiles. It consists of over 8,000 species that are found on every continent in the world (except Antarctica) and on most sub tropical and tropical islands. Because these reptiles are so widely spread throughout the world, they have each developed their own unique behaviors and characteristics to adapt to environments that are either hot or cold, wet or dry, freshwater or saltwater, etc.

Squamata synapomorphies:

1) Fused premaxillae

2) Fused parietals

3) Reduced nasals

4) Lack of vomerine teeth

5) Specialized joints between ulna-ulnare and radius-radiale

6) Specialized ankle joints

7) Well developed hemipenes

8) Saccular ovaries

9) Jacobson’s organ separated from nasal capsule.

10) Lacrimal duct joining the vomeronasal duct

11) Femoral and pre-anal glands

12) Egg tooth at hatching

Phylogeny & Diversity

The history of lizard systematics is a very controversial topic. Many argue over how large the families of the clade are, how inclusive family-level groups should be, whether or not to elevate some sub-families into families (for instance the subfamilies of Iguanidae), etc. As a result hypotheses have been presented based on molecular, morphological, and behavioral evidence and many different arrangements of the reptilian clade have been put forth. As of now, at least 19 families have been recognized, but there may be as many as 36.

“From an evolutionary perspective, it shouldn’t matter whether we recognize a group as a sub family or family, so long as we understand that the clades are real and that the relationships among them are real”

For Step 1 during lab, the anatomy of the skull in Varanus was observed. A handout was provided by Dr. Sheil which the dorsal, ventral, and lateral views for this genus. Observe the figure below and note the particular bones associated within each of the three views. This figure is for the species Varanus griseus.

See which bones you can identify on this varanid lizard skull.

Lizard Families

We should note that there are many families of lizards for the squamates. Although not all of these families were covered in lab, Step 2 examines the following families of lizards that were present in lab. For each family, make sure that you take note of the distribution along with some of their distinct characteristics which are presented below.

Agamidae

Distribution: Africa, Asia, Australia, and Tasmania

Draco volans, a gliding agamid

Characteristics: Small to large lizards which are covered by overlapping scales or granular, juxtaposed scales dorsally and ventrally. No osteoderms are present dorsally and ventrally on the trunk region. These species are limbed, where the pectoral girdle is t-shaped. Their tail is usually long and the tongue is covered dorsally with reticular papillae. The skull possesses paired nasals, postorbitals, squamosals, frontal, and parietal; the parietal foramen usually perforates the frontoparietal suture. They possess acrodont dentition.

Anguidae

(Looks like a snake when limbless, but this anguid is not a snake!)

Do you see the eyelids on this limbless Ophisaurus?

Distribution: Americas, Europe, Southwest Asia

Characteristics: These lizards can either be limbed or limbless which have tails that can be twice the length of their body. All of them are heavily armored with largely nonoverlapping scales and contain osteoderms on the trunk dorsally and ventrally. Ventrolateral folds are well developed in most anguidswhich allows for body expansion for breathing, feeding, and reproduction. The tongue bears papillae and lacks lingual scales which are associated near the tongue. The skull can have present or absent squamosals along with a fused parietal; the parietal perforates the parietal foramen. They possess pleurodont dentition.

Chamaelionidae

Note the acrodont teeth in this chameleon

Distribution: Africa, Middle East, Madagascar, southern Spain, India

Characteristics: Chameleons are unique for their laterally compressed bodies, prehensile tails, head casques covering their necks, and Xygodactylous feet where sets of digits are fused forming opposable fore-and hind feet. All of these species are limbed where the specialized pectoral girdle lacks an interclavicle and clavicles. Their tails are moderately short to long and the tongue is covered with reticular papillae dorsally.

Gekkota

The geckos examined in lab today involved three families in the subfamily Gekkota. Note the characteristics for each of these three families.

An example of a eublepharid gecko

Eublepharidae: Known as the eyelid geckos since they possess eyelids rather than spectacles! In particular, their feet lack modifications allowing them to climb.

Sphaerodactylidae: Known as the dwarf geckos, they possess well-developed limbs along with tiny juxtaposed scales. Adults are no larger than 60mm SVL Their eye is covered by a spectacle cover and do not possess eyelids.

One member of Sphaerodactylidae (top) and two members of Gekkonidae (middle and bottom)

Gekkonidae: Known as the house geckos, they possess well-developed limbs, and their eyes contain 14 scleral ossicles. They do not possess eyelids but do possess spectacle covers.

Helodermatidae

Distribution: Southwestern North America

Characteristics: Helodermatids are large lizards and are the only lizards with well-developed venom glands. The have broad, flattened heads along with robust bodies, short limbs, and heavy tails. They have thick skin, and their scales are slightly larger and squarish ventrally. Ventrally, the trunk contains osteoderms; the tongue bears papillae, and the parietal foramen is absent. They possess pleurodont dentition.

Skull cast displaying pleurodont dentition and synostotic fusion of dermal bones to skull

Pleurodonta

These lizards have been historically grouped into one large family named Iguanidae. This clade has recently been elevated to Pleurodonta and the historical subfamilies have been elevated to family level.

Inguanidae (prev. Iguaninae): In their skull, the lacrimal foramen is not enlarged, the jugal and squamosal are not in broad contact, Meckel’s cartilage in the mandible is fused. To determine sex, note that males possess femoral pores where the females do not.

Distribution: Americas from southwestern United States to south Brazil, West Indies, and west-central Pacific islands

Femoral pores on male iguanid

Corytophanidae: These lizards have pterygoid teeth, but no palatine teeth. Males have no femoral pores and adults are usually 90-200mm SVL.

Distribution: Southern Mexico to Northern South America

The long toes on the hind limb of this Basciliscus enable it to run on water.

Dactyloidae: This is the most speciose family within Pleurodonta, most species range between 40-80mm SVL. Males lack femoral pores and are usually larger than females.

Distribution: Southeastern US through Central South America and throughout West Indies

Scincidae

Distribution: Worldwide
Characteristics: The skinks are always covered with overlapping scales dorsally and ventrally. They can either possess limbs or be limbless externally. Their interclavicle is absent, so the clavicles are angular. Their tails are moderately long; tongue bears papillae; pleurodont dentition.

Teiidae

Distribution: The Americas (from northern U.S. to Chile and Argentina)
Characteristics: This family of whiptail lizards, tegus, and allies are small to large lizards that possess smaller scales on the dorsal and lateral views of the body compared to the ventral view. All of the species within this family have well-developed limbs along with a long, autonomous tail. The posterior edges of the lingual scales are smooth; teiids possess pleurodont dentition.

Two teiid lizards (top and middle) compared to a varanid lizard (bottom)

Varanidae

Distribution: Warm temperate and tropical Africa south of the Sahara
Characteristics: Family of the Kamoto Dragon (Varanus), most are moderate to large in size with thick skin containing numerous rows small scales circling the body. Their ventral scales are slightly larger than the dorsal scales. Varanids possess pleurdont dentition and a hemibaculum, a cartilaginous strut in each hemipenis.

Ohio Diversity

The final step in lab dealt with the Ohio diversity of lizards. Ohio only has two families and five species. Make sure you know the following families and species in Ohio for the exam!

Family: Phrynosomatidae

Sceloporous undulates garmani (Northern Fence Lizard)

THE DIFFERENCE BETWEEN MALE AND FEMALE PHRYNOSOMATIDS IS THAT MALES POSSESS FEMORAL PORES. NOTE THE DIFFERENCES FROM THE PICTURE SHOWN BELOW. (A = MALE, C= FEMALE)