Thursday, February 23, 2012

Lab 5: Lepidosauria part 1: Sphenodontida & Sauria (Paluh and Harrington)

In this week’s lab we began looking at lepidosaurs. Lepidosauria includes the tuatara, lizards, and snakes. Some general characteristics of lepidosaurs include transverse vents, notched tongues, full-body ecdysis, imperforate collumellas, and fused pelvic bones. In lab, we focused exclusively on lizards, which are members of Squamata, the clade that includes lizards and snakes. Squamates generally have fused premaxillae, reduced nasals, fused parietals, no vomerine teeth, specialized wrist and ankle joints, well-developed hemipenes, Jacobson’s organs separated from the nasal capsule, and an egg tooth. In a phylogenetic context, snakes are derived lizards, and so Sauria, which once included only non-snake lizards, must be expanded to include Serpentes (snakes). With that said, it is still often useful to make a practical distinction between the “lizards” and snakes, and in this lab we focused exclusively on the non-snake lizards.

Varanus Skull Anatomy:

Pores and Caudal autotomy: Many lizards have glandular pores present anterior to the cloaca (precloacal pores) or on the underside on the hind leg (femoral pores). These pores are typically found on male lizards, and, if present, will be smaller in females than males of a species. Caudal autotomy (self-cutting) is a common defense mechanism in many saurians. If a predator attacks a lizard that is capable of caudal autotomy, it will purposely remove it's tail from it's body to distract the predator so it is able to escape.

Selected Lizard Families:

Family Agamidae (angleheads, calotes, dragon lizards, and allies; 2 subfamilies): Agamids are covered dorsally and ventrally by overlapping or granular and juxtaposed scales. Agamids lack osteoderms on the trunk. All species are limbed. Most species have moderately long to long tails that typically lack fracture planes (for autotomization). Agamids also possess acrodont teeth (teeth anchored to surface of jaw). We had a specimen of Draco from the subfamily Agaminae. Agamines are mostly terrestrial to semiarboreal that have diverse body shapes, including that of the unique gliding lizard, Draco. Agamines are primarily diurnal and most, if not all, are oviparous.

Family Chamaeleonidae (chameleons; 6 genera with 171 species): Chamaeleonids have laterally compressed bodies, prehensile tails, head casques covering their necks, and independently moveable eyes. In addition, their feet are xygodactylous, with the digits 1-2-3 and 4-5 fused in the manus and digits 1-2 and 3-4-5 fused in the pes. Tails are short to long and teeth are acrodont (Chamaeleonidae + Agamidae = Acrodontia). Chamaeleonids are primarily highly arboreal, and much of their morphology is adapted for an arboreal lifestyle. Chamaeleons tend to stalk their prey, moving in sync with movements of branches and leaves. They stalk prey, focus on it with both eyes, and then use their exceptionally long tongues to capture their prey and bring it back to the mouth. Chamaeleonids may be viviparous or oviparous.

Family Iguanidae (anoles, iguanas, and allies; 8 subfamilies): Iguanidae is a highly diverse family, and the lower-level taxonomy within this family is somewhat unresolved. Iguanids range from small to large. They may have large, overlapping, keeled scales or small, granular scales covering the body, with no osteoderms present on the trunk. Tails are usually moderately long to long, with fracture planes for caudal autotomy present. We examined specimens of the subfamilies Polychrotinae, Phrynosomatinae, Corytophaninae, and Iguaninae. Polychrotines are primarily arboreal and diurnal, and typically consume arthropod prey. Male polychrotines are typically larger than females. Phrynosomatines primarily dwell in arid environments and feed on arthropod prey. Most phrynosomatines are oviparous, but some are viviparous. Sceleoporus undulatus garmani, a lizard native to Ohio, is a member of Phrynosomatinae. Corytophanines are primarily arboreal, and are found in dry scrub forest to wet rain forest. Corytophanines are casque-headed, slender bodied, and have long limbs and tails. Corytophanines may be oviparous or viviparous. Iguanines are primarily large lizards and range from marine/rock-dweller to arboreal species. Iguanines are almost exclusively herbivorous, and all are oviparous.

Family Gekkonidae (geckos and pygopodids; 4 subfamilies): Gekkonids are typically covered by small, granular scales periodically interrupted by tubercles, and lacking osteoderms on the trunk. Many gekkonids have scansors/lamellae present on their toe pads for climbing. The tail is typically moderately short to long. Teeth are pleurodont. Some gekkonids are elongated and snake-like (Pygopodinae). We observed specimens from the subfamilies Eublepharinae and Gekkoninae. Eublepharines are almost all terrestrial, nocturnal, insectivores that lay eggs in clutches of two. Gekkninae is a highly diverse group (more than 800 species), and have a variety of morphologies and ecologies. All gekkonines are oviparous, and most are insectivorous.

Family Teiidae (whiptail lizards, tegus, and allies; 2 extant subfamilies): Teiids have small, granular dorsal and lateral body scales, and large, rectangular, juxtaposed scales arranged in rows on the ventral surface of the body. They have no osteoderms on the trunk. They typically have long tails that have fracture planes for autotomization. We observed two specimens of Aspidoscelis from the subfamily Teiinae. Teiines have a streamlined body, long, whip-like tail, and long limbs. They are active at relatively high temperatures, and are active foragers that feed on arthropods. All teiines are oviparous, and some are parthenogenetic.

Family Scincidae (skinks; 2 subfamilies): Scincids are typically by overlapping scales that are underlain by osteoderms on the dorsal and ventral sides of the trunk. Some taxa have limb reduction that can be quite strong. Tails are moderately long to long, and many skinks have fracture planes for autotomization. We observed specimens of Plestiodon fasciatus, Plestiodon laticeps, and Scincella lateralis, all of which are Ohio-native species found in the subfamily Scincinae. Plestiodon anthracinus anthracinus is also native to Ohio and in Scincinae. Scincinae is a very diverse (~1200 species) and poorly resolved clade. As such, it is difficult to make generalities about the biology of scincines. Scincines are oviparous or viviparous, with some exhibiting the highest level of matrotrophy seen in reptiles.

Family Anguidae (alligator lizards, galliwasps, glass lizards, and allies; 4 subfamilies): Anguids are lizards that have small-well developed limbs or are limbless. They are heavily-armored with large, overlapping scales underlain by osteoderms on the trunk. Many anguids have a longitudinal, ventrolateral fold that allows for body expansion for breathing, feeding, and reproduction that might otherwise be limited by their armor. Most anguids have tails that have fracture planes for caudal autotomy. We observed a specimen of Ophisaurus from the subfamily Anguinae. Anguines are elongate, limbless lizards with ventrolateral folds. They are typically found in scrub or open habitats with dense ground coverage and typically prey on invertebrates.

Family Helodermatidae (gila monster and Mexican beaded lizard; 1 genus, Heloderma, with 2 species): Helodermatids have well-developed venom glands. They have stout, robust bodies, and are covered in rounded, bead-shaped scales. Ventrally, osteoderms are present on the trunk. Helodermatids are primarily crepuscular to nocturnal, and tend to spend most of their time in burrows when not foraging or searching for mates. They feed on a variety of mammals, birds, reptiles, eggs, and invertebrates.

Family Varanidae (monitors, goanna, and earless monitors; 2 subfamilies with one genus each; 64 species): Varanids are typically large lizards, and the largest extant lizard, Varanus komodoensis, is a varanid. The body is covered with small, circular scales with slightly larger scales on the ventral surface that resemble smaller versions of the ventral scales of teiids. Ventral osteoderms are present in some species. We observed a specimen of Varanus, the only genus in the subfamily Varaninae, which includes all varanids except for one. Varanines are primarily active predators with relatively small heads, long necks, and long, robust bodies. Smaller varanines prey primarily on small vertebrates and arthropods, while larger species may feed on fairly large vertebrates.

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