Native TN Herps: An Introduction

Evolutionary Framework and Systematics of Lepidosauria

• Paraphyly of Reptilia: Class Reptilia is historically defined as a paraphyletic grouping because traditional classifications exclude Aves (birds), despite birds sharing an immediate common ancestor with non-avian dinosaurs within the clade Archosauria.
• Lepidosauria Lineage: Lepidosaurs constitute a major diapsid subclass that contains two extant sister orders:
  • Rhynchocephalia: Represented today solely by the tuatara (Sphenodon), endemic to New Zealand.
  • Squamata: A highly diversified order comprising scaled reptiles: "lizards" (a paraphyletic assemblage of non-snake squamates) and snakes (Serpentes).
• Lepidosaurian Synapomorphies:
  • Keratinous, Overlapping Scales: An epidermal integumentary covering of beta-keratin scales that prevents cutaneous water loss and provides mechanical abrasion resistance.
  • Transverse Cloacal Opening: The external vent or cloacal slit is oriented horizontally (transversely across the body axis), contrasting with the longitudinal vent present in archosaurs (crocodilians and birds) and turtles.
  • Autotomy Planes in Caudal Vertebrae: Specialized cartilaginous or unossified fracture planes (autotomy septa) situated across individual tail vertebrae, allowing tail shedding (caudal autotomy) to evade predators.
• Squamate Synapomorphies:
  • Hemipenes: Paired male intromittent copulatory organs housed internally in the tail base posterior to the cloaca; only a single hemipenis is everted and engorged with blood during copulation.
  • Determinate Growth: Epiphyseal fusion of long bones occurs at reproductive maturity, terminating somatic elongation, unlike the indeterminate growth seen in tortoises and crocodilians.
• Temporal Fenestration and Cranial Evolution:
  • Ancestral Diapsid Skull: Characterized by two temporal fenestrae (infratemporal and supratemporal) bound by bony arcades.
  • Tuatara Skull Morphology: Tuatara display a fully diapsid skull configuration with an intact upper bar (postorbital-squamosal) and a secondarily present, robust lower temporal bar (jugal-quadratojugal/quadrate), which creates a rigid, non-kinetic skull.
  • Lizard Skull Morphology: Lizards have lost the lower temporal bar, creating an open lower temporal arcade that increases quadrate mobility (streptostyly) and cranial kinesis for grasping struggling prey.
  • Snake Skull Morphology: Snakes have lost both the upper and lower temporal bars, resulting in extreme cranial kinesis where the quadrate, squamosal, and maxillae articulate loosely via elastic ligaments, allowing ingestion of prey items significantly wider than the head.
• Integumentary Ecdysis:
  • Lizards: Typically undergo ecdysis (skin shedding) by sloughing off epidermis in patchy, broken pieces.
  • Snakes: Shed the cornified epidermal stratum corneum completely intact in a single, inverted, continuous piece from snout to tail.

Sauria (Lizards): Diversity and Native Tennessee Taxa

• General Lizard Characteristics:
  • Exhibit a wide range of adult body sizes and ecological specializations.
  • Many lineages are arboreal; others are adapted to terrestrial or burrowing niches.
  • Multiple lineages have independently evolved complete or partial limb reduction (e.g., legless lizards).
  • Diet is predominantly insectivorous across the majority of smaller species, though large monitor lizards and iguanines may be carnivorous or herbivorous.
• Lizard Diversity Across Global Clades:
  • Sceloporus olivaceus (Texas spiny lizard): Arboreal, heavily scaled phrynosomatid.
  • Phrynosoma cornutum (Texas horned lizard): Flattened, ant-specialized desert form with cranial horns.
  • Moloch horridus (Thorny devil): Convergent Australian agamid possessing moisture-collecting capillary body spines.
  • Basiliscus plumifrons (Green basilisk): Corytophanid adapted for bipedal aquatic locomotion.
  • Varanus gouldii (Racehorse goanna): Active predatory monitor lizard with high aerobic capacity.
  • Heloderma suspectum (Gila monster): Heavy-bodied venomous lizard possessing grooved mandibular teeth.
  • Furcifer oustaleti (Giant chameleon): Highly specialized zygodactylous arboreal hunter with ballistic tongue.

• Family Scincidae (Skinks):
  • Diagnostic Traits: Smooth, glossy, cycloid overlapping scales supported by osteoderms; small, streamlined, cylindrical bodies; poorly demarcated necks; and short, robust limbs.
  • Caudal Autotomy: Exhibit self-amputation of the tail via intravertebral fracture planes; the wriggling detached tail distracts predators while the lizard escapes, followed by cartilaginous regeneration.
  • Native Species — Common Five-Lined Skink (Plestiodon fasciatus):
  • Activity: Strictly diurnal foragers active in forest edge habitats, rotting logs, and rock piles.
  • Diet: Primarily insectivorous, consuming spiders, crickets, beetles, and other terrestrial arthropods.
  • Trophic Interactions: Frequently preyed upon by ophiophagous predators, notably kingsnakes (Lampropeltis).
  • Habitat Preference: Strongly prefers moist, humid microenvironments such as damp leaf litter, decayed wood, and shaded riparian borders.
  • Ontogeny: Juveniles possess bright metallic blue tails and five vivid yellowish-white dorsal longitudinal stripes against a jet-black ground color; adult males fade to uniform olive-brown with broadened reddish-orange jowls during the breeding season.

• Family Phrynosomatidae (North American Spiny Lizards):
  • Diagnostic Traits: Rough, pointed, heavily keeled/spiny dorsal scales giving a bristly texture; presence of pleurodont dentition.
  • Pleurodont Dentition: Teeth lack roots in individual sockets (thecodont) and are instead fused along the lingual (inner) side of the jawbone margins, shedding and replacing continually throughout life.
  • Native Species — Eastern Fence Lizard (Sceloporus undulatus):
  • Microhabitat: Highly arboreal and saxicolous; routinely seen climbing vertical pine tree trunks, split-rail wooden fences, and exposed sunlit rock outcrops.
  • Sexual Dimorphism: Marked ventral sexual dichromatism; adult males display intense, iridescent cyan-blue patches bordered by black on the lateral margins of the belly and across the throat, utilized in territorial display push-ups, whereas females display cryptic grayish-white venters with faint chevrons.

Serpentes (Snakes): Locomotion and Native Tennessee Families

• Anatomy and Cranial Features: Complete loss of pectoral and pelvic girdles (with minor vestigial spurs in primitive boids); limbless elongation; total loss of both the upper and lower temporal arcades enabling unilateral jaw movement and extreme cranial kinesis.
• Modes of Locomotion:
  • Lateral Undulation: The standard, most common mode of serpentine movement. Horizontal waves of muscular contraction pass along the body from anterior to posterior, pushing posteriorly and laterally against discrete physical contact points (rocks, vegetation, substrate irregularities).
  • Concertina Locomotion: Utilized in confined spaces such as narrow subterranean burrows or when climbing vertical channels. The snake anchors its posterior body by folding it into tight lateral S-curves against tunnel walls, pushes the anterior body forward, anchors the front, and pulls the rear forward in an accordion-like motion.
  • Rectilinear Locomotion: Typical of heavy-bodied snakes (such as large vipers and boids) traveling in straight paths. Waves of contraction move along the ventral musculature, lifting, advancing, and planting wide ventral scutes (gastrosteges) against the ground while the internal skeleton glides forward smoothly.
  • Sidewinding: Employed across low-friction or shifting substrates (such as loose desert sand or smooth mud). The body is propelled sideways via lateral S-loops that lift segments clear off the ground, ensuring only two moving contact points touch the substrate at any one time.
  • Aerial Gliding: Seen in arboreal colubrids such as the paradise flying snake (Chrysopelea paradisi), which flattens its ribs into a concave aerodynamic camber to generate lift while undulating in mid-air.

• Family Viperidae (Vipers):
  • General Characteristics: Highly venomous snakes equipped with specialized hollow hypodermic fangs designed for deep tissue envenomation. Proteroglyphous dentition (permanently erect front fangs on shortened, fixed maxillae, as seen in elapids like mambas) contrasts with solenoglyphous dentition (long, foldable fangs mounted on highly mobile, rotating maxillae characteristic of vipers).
  • Subfamily Crotalinae (Pitvipers): Native venomous clade characterized by heat-sensing facial (loreal) pit organs situated bilaterally between the nostrils and eyes, sensitive to infrared thermal radiation for hunting endothermic mammalian prey.
  • Copperhead (Agkistrodon contortrix):
  • Camouflaged ambush predator possessing a dorsal pattern of alternating chestnut or russet hourglass-shaped crossbands on a pinkish-tan base.
  • Juveniles feature a bright sulfur-yellow or chartreuse tail tip used for caudal luring (wriggled like a caterpillar to entice small frogs and lizards into strike range).
  • Cottonmouth (Agkistrodon piscivorus):
  • Semiaquatic pitviper inhabiting wetlands, swamps, and river drainages.
  • Displays a defensive behavior when threatened: coils tightly, draws its head back, and gapes open its jaws to display the stark, brilliant-white lining of its buccal cavity.

• Family Colubridae (Colubrids):
  • Characteristics: The largest and most diverse snake family globally, comprising approximately $1{,}800$ species. The vast majority of species are nonvenomous aglyphous snakes (lacking specialized grooved or hollow fangs), though some rear-fanged opisthoglyphous forms exist.
  • Eastern Wormsnake (Carphophis amoenus): Small, secretive, fossorial colubrid with a smooth, glossy, uniform brown dorsum, bright pinkish-salmon venter, reduced eyes, and a sharp, spine-like tail tip used to gain leverage when burrowing through damp forest soils and decaying mulch.
  • Common Kingsnake (Lampropeltis getula): Powerful constrictor adorned with a black or dark chocolate ground color broken by white or pale-yellow chain-like bands; notable for its ophiophagous diet and physiological immunity to the hemotoxic venoms of sympatric pitvipers (copperheads, cottonmouths, rattlesnakes).
  • Eastern Hognose Snake (Heterodon platirhinos): Specialized amphibian hunter (toad-eater) with a distinctive sharply upturned rostral scale for unearthing burrowed toads. Known for complex defensive displays: neck flattening (spreading a cobra-like hood), loud hissing, mock strikes, followed by thanatosis (feigning death by rolling onto its back, writhing, gaping its mouth, defecating, and going limp).

Chelonia (Testudines): Turtle Anatomy and Native Families

• Unique Chelonian Bauplan:
  • Bony shell composed of a dorsal carapace (formed by the fusion of expanded ribs, thoracic vertebrae, and dermal bone) and a ventral plastron, connected laterally by bony bridges.
  • The pectoral and pelvic girdles are uniquely positioned inside the thoracic rib cage, an anatomical arrangement unique among tetrapods.
  • Completely toothless jaws covered by a sharp, keratinous horny sheath called the rhamphotheca.
  • Skull historically termed anapsid (lacking temporal fenestrae), though modern molecular and embryological phylogenies identify turtles as secondarily modified diapsid archosauromorphs.

• Family Chelydridae (Snapping Turtles):
  • Characteristics: Robust, heavily armored aquatic turtles characterized by massively oversized heads, powerful beaked jaws, long serrated tails, and a reduced, cruciform (cross-shaped) plastron.
  • Lack of Complete Retraction: Due to the combination of large head and limb girth and reduced plastral surface area, snapping turtles cannot retract their heads or limbs fully within the shell; defense relies on aggressive lunging strikes and biting.
  • Common Snapping Turtle (Chelydra serpentina): Widely distributed omnivore and scavenger found across diverse freshwaters; possesses a relatively smooth, dark carapace with saw-toothed marginal scutes and three low keels that wear smooth with age.
  • Alligator Snapping Turtle (Macrochelys temminckii): North America's largest freshwater turtle, reaching immense sizes; features a massive, hooked head, three prominent, raised, pyramid-shaped dorsal carapacial ridges, and a vermiform (worm-like) pink tongue appendage used in the water as a passive predatory lure.

• Family Emydidae (Pond and Box Turtles):
  • Characteristics: Diverse, primarily semiaquatic family displaying marked sexual dimorphism (e.g., males frequently possess elongated foreclaws for courtship titillation, concave plastrons, and longer tails with more distal vents). Prominently exploited and traded globally in the commercial pet market.
  • Pond Slider (Trachemys scripta): Highly common basking turtle; subspecies T. s. elegans (Red-eared slider) is recognized by prominent crimson-red postorbital stripes flanking both sides of the head.
  • Northern Map Turtle (Graptemys geographica): Semiaquatic riverine turtle featuring an olive carapace decorated with intricate, yellowish contour-map-like lines, a pronounced dorsal midline keel, and broad crushing alveolar surfaces on female jaws adapted for molluscivory.
  • Eastern Box Turtle (Terrapene carolina carolina): Fully terrestrial emydid featuring a high-domed carapace and a specialized transverse plastral hinge that allows the anterior and posterior plastral lobes to pull shut flush against the carapace, encasing the head and limbs within a sealed bone chamber.

• Family Kinosternidae (Mud and Musk Turtles):
  • Characteristics: Small body sizes typically ranging from $4\text{--}6\text{ in}$ ($10\text{--}15\text{ cm}$). Possess paired Rathke's glands along the bridge that exude a foul-smelling, yellowish musk secretion when handled or threatened.
  • Plastral Differentiation Between Genera:
  • Kinosternon (Mud turtles): Characterized by a well-developed, hinged plastron (typically containing two functional transverse hinges) that permits partial closure of the shell openings.
  • Sternotherus (Musk turtles): Characterized by a significantly reduced, fused plastron with minimal or single incomplete cartilaginous hinging, leaving soft tissues around the legs exposed.
  • Common Musk Turtle / "Stinkpot" (Sternotherus odoratus): Features an arched, dark brown dome often coated in algae, two light yellow horizontal stripes along the face and neck, sensory barbels on the chin/throat, and an offensive musk defense.
  • Eastern Mud Turtle (Kinosternon subrubrum): Smooth, dome-shaped carapace lacking prominent keels, with a large double-hinged plastron.

• Family Trionychidae (Softshell Turtles):
  • Native Species — Spiny Softshell (Apalone spinifera):
  • Morphology: Carapace lacks peripheral keratinous scutes; instead, it consists of a flattened, flexible, rubbery-margined disk covered in leathery skin. The anterior leading edge of the carapace is lined with small, sharp, conical spines or tubercles.
  • Ecology & Behavior: Fast, benthic ambush predators that bury themselves entirely under sand or silt in riverbeds, using an elongated, tubular snout ("snorkel nose") to breathe at the water surface while keeping the body concealed.
  • Physiology: Highly vascularized buccopharyngeal mucosa and skin allow cutaneous and pharyngeal respiration under water for extended intervals.

Lissamphibia: Systematics and Anuran Diversity

• Class Amphibia / Subclass Lissamphibia Shared Characteristics:
  • Moist, Permeable, Scaleless Skin: Epidermis lacks keratinized dermal scales; heavily supplied with mucous glands (preventing desiccation) and granular/poison glands (secreting toxins); primary site of cutaneous respiration.
  • Pedicellate Teeth: Each tooth consists of a crown and base (pedicel) made of dentine, separated by a distinct uncalcified ring of collagenous fibrous tissue.
  • Biphasic Life History / Metamorphosis: Typically involves an aquatic, gill-bearing larval stage that metamorphoses into an air-breathing terrestrial/semiaquatic adult.
  • Carnivorous Diet: Post-metamorphic adults are obligate predatory carnivores feeding primarily on insects and other invertebrates.
• Phylogenetic Relationships in Lissamphibia:
  • Order Gymnophiona (Caecilians): Limbless, fossorial, or aquatic amphibians. Diagnostic apomorphies include a sensory tentacle on the snout and an interhyoid muscle used to close the lower jaw.
  • Clade Batrachia: Monophyletic sister group pairing Caudata (salamanders) and Anura (frogs), defined by synapomorphies in skull osteology and extensive molecular sequence divergence.
  • Order Anura (Frogs and Toads):
  • Urostyle: Fused post-sacral caudal vertebrae forming a rigid rod that stabilizes the pelvic girdle against the shock of leaping.
  • Loss of Adult Tail: Caudal vertebrae resorbed during metamorphic climax.
  • Tibiofibula: Fusion of the tibia and fibula bones in the lower hindlimb to withstand the mechanical strains of saltation (jumping).
  • Tympanum: External circular auditory membrane specialized for receiving airborne acoustic signals and vocalizations.

• Family Ranidae (True Frogs):
  • Characteristics: Widest worldwide distribution of any amphibian family; includes species spanning an exceptionally broad size range; characterized by smooth skin, long powerful hind limbs, webbed feet, and well-developed tympana.
  • American Bullfrog (Lithobates catesbeianus):
  • Largest native ranid in North America.
  • Lacks dorsolateral folds running down the back; instead, a distinct raised glandular fold curves tightly around the posterior margin of the massive tympanum down to the shoulder.
  • In adult males, the tympanum diameter is substantially larger than the diameter of the eye.
  • Pickerel Frog (Lithobates palustris):
  • Characterized by two parallel rows of distinct, squarish or rectangular dark brown spots aligned down the dorsal area between prominent yellow-tinged dorsolateral folds.
  • Features vivid, bright yellow or orange wash coloration on the inner concealed surfaces of the hind legs.
  • Southern Leopard Frog (Lithobates sphenocephalus):
  • Characterized by rounded, irregularly positioned dark dorsal blotches, a pointed snout, unbroken pale dorsolateral folds, and a prominent round white spot situated in the center of the tympanum.

• Family Bufonidae (True Toads):
  • Characteristics: Primarily terrestrial; possess dry, thickened, heavily glandular "warty" skin; relatively short hind limbs adapted for hopping rather than leaping.
  • Parotoid Glands: Large paired cutaneous glands situated behind the eyes that synthesize and exude toxic steroid-based bufotoxins when attacked.
  • Native Species — American Toad (Anaxyrus americanus): Warty-skinned terrestrial toad featuring typically 1 to 2 large warts within each of the largest dark dorsal spots; chest usually mottled with dark pigment.

• Family Microhylidae (Narrow-mouthed Toads):
  • Native Species — Eastern Narrow-Mouthed Toad (Gastrophryne carolinensis):
  • Habits: Highly secretive, nocturnal, and fossorial; adapted for eating ants and termites.
  • Cranial & Sensory Morphology: Completely lack external visible tympana; head is sharply pointed with a tiny mouth and narrow snout.
  • Body Shape: Plump, pear-shaped, squat body.
  • Transverse Skin Fold: Possesses a distinct, mobile transverse groove/fold of skin directly posterior to the eyes, which can be pulled forward to wipe ants and debris from the eye sockets when foraging underground.

Caudata: Salamander Diversity and Ecology

• Family Plethodontidae (Lungless Salamanders):
  • Characteristics: The largest and most diverse family of salamanders globally, comprising over $500$ species. Evolutionarily distinguished by the complete loss of lungs across all life stages; respiration is entirely non-pulmonary, occurring via gas exchange across the vascularized skin (cutaneous respiration) and the epithelial lining of the throat/mouth (buccopharyngeal pumping).
  • Nasolabial Grooves: A unique pair of narrow glandular slits running from the nostrils down to the upper lip margin, functioning to draw non-volatile liquid chemical cues into the olfactory epithelium via capillary action.
  • Spotted Dusky Salamander (Desmognathus conanti): Robust, semiaquatic stream-dwelling plethodontid; has an enlarged, pale diagonal stripe running from the eye down to the jaw angle, muscular hind limbs larger than forelimbs, and a keeled tail.
  • Long-Tailed Salamander (Eurycea longicauda): Slender, yellowish-orange salamander possessing an exceptionally long, slender tail comprising roughly $60\%$ of total body length, decorated with irregular vertical black bars creating a "herringbone" pattern along the caudal margins.
  • Cave Salamander (Eurycea lucifuga): Bright orange to reddish-orange body peppered with small, distinct, irregular black spots; specialized troglophilic habits, living in the twilight zones of limestone cave entrances and cool spring seeps.

• Family Ambystomatidae (Mole Salamanders):
  • Characteristics: Heavy-bodied, stout terrestrial salamanders with broad, blunt heads, robust limbs, prominent costal grooves, and granular defensive skin glands that produce viscous, noxious secretions along the tail and dorsum. Terrestrial adults possess functioning internal lungs; spend most of the year subterranean (fossorial) in small mammal burrows, emerging in mass breeding migrations to fishless vernal pools during late winter rains.
  • Spotted Salamander (Ambystoma maculatum): Slate-black to bluish-gray ground color patterned with two irregular, longitudinal rows of bright yellow or orange rounded spots extending from the head onto the tail tip.
  • Eastern Tiger Salamander (Ambystoma tigrinum): One of North America's largest terrestrial salamanders; robust build with olive, yellow, or brassy-tan blotches, spots, and irregular crossbands against a dark brown/black ground color.

• Subfamily Pleurodelinae (Newts, Family Salamandridae):
  • Characteristics: Skin is rougher, more granular, and lacks the prominent lateral costal grooves characteristic of ambystomatids and plethodontids; adults exhibit marked secondary returns to aquatic environments for breeding and foraging.
  • Triphasic Life History: Exhibit an uncommon complex ontogenetic pathway:
  1. Aquatic larval stage with external gills.
  2. Terrestrial juvenile stage known as the eft (subadult).
  3. Secondarily aquatic breeding adult stage.
  • Native Species — Eastern / Red-Spotted Newt (Notophthalmus viridescens):
  • Red Eft Stage: Immature terrestrial stage that spends $1\text{--}4\text{ years}$ on the forest floor; exhibits aposematic (warning) bright orange to crimson skin embedded with potent tetrodotoxin (TTX) neurotoxins to deter predators, accented with a row of black-bordered red dorsal spots.
  • Adult Stage: Returns permanently or seasonally to ponds, wetlands, and vernal pools; transforms to an olive-green dorsal coloration with a yellow belly covered in small black flecks, retains the red dorsal ocelli spots, and adult males develop broad, laterally compressed tail fins and cornified nuptial pads on their hind legs for aquatic mating.

Questions & Discussion

• Question 1: What anatomical and morphological features separate turtles (Chelonia/Testudines) from snakes and lizards (Squamata)?
  • Bony Shell: Presence of a two-part bony armor shell (carapace and plastron) derived from fused thoracic vertebrae, expanded dorsal ribs, and dermal ossifications.
  • Internal Limb Girdles: Unlike squamates (where the scapula and pelvic girdles sit exterior or adjacent to the thoracic cage), turtles have the pectoral and pelvic girdles situated anatomically inside the rib cage.
  • Lack of Teeth (Keratinous Rhamphotheca): Squamates possess pleurodont or acrodont teeth mounted directly on jawbones; turtles lack all teeth and instead possess a sharp, keratinous beaked covering (rhamphotheca).
  • Temporal Cranial Architecture: Squamates have modified diapsid skulls characterized by either the loss of the lower temporal bar (lizards) or both temporal bars (snakes), creating high cranial kinesis. Turtles exhibit a solid or emargination-modified skull that lacks typical temporal fenestrae.
  • Absence of Hemipenes: Male turtles possess a single, median ventral penis contained in the floor of the cloaca, rather than the paired, eversible hemipenes found in squamates.
• Question 2: Why have these unique characteristics evolved in turtles?
  • Predator Defense: The bony, enclosed shell provides primary mechanical protection against predators, allowing retraction of vital organ systems and, in hinged forms (Terrapene, Kinosternon), complete sealing from external attack.
  • Subterranean and Burrowing Anchoring: Evolutionary transitions in stem turtles indicate that initial expansion of the ribs served to stabilize the torso and provide mechanical anchoring for powerful forelimb digging while excavating burrows.
  • Structural and Hydrodynamic Rigidity: The fused shell provides structural rigidity that shields the internal organs from underwater hydrostatic pressure changes in benthic aquatic habitats and acts as an efficient hydrodynamic shield during swimming.