Vertebrate Zoology Test #3

What are the major groups of Lepidosaurs?

Tuatara & Squamata

How many species of Tuatara are there?

1

How many species of lizards are there within Squamata?

>7,000 species

How many species of snakes are there within Squamata?

>4,000 species

True or False: Lepidosaurs are predominantly terrestrial.

True

What group did Tuataras diverge from?

Archosauria

When did Tuataras diverge from Archosauria?

~245 - 200 mya

True or False: Diversification of Lepidosaurs coincided with Arthropods.

True

Lepidosaur Synapomorphies

• Skin with overlapping scales

• Successive generations of epidermal cells are shed at intervals (skin shedding)

• Transverse cloacal slit (other tetrapods have longitudinal)

• Caudal vertebrae have autotomy planes in many species (allow the tail to be shed then regenerated)

Rhynchocephalia

Tuataras

How many natural populations are there of tuataras?

32

Photoreceptive pineal "eye"?

Not used for vision but possibly aids in regulating circadian rhythms or thermoregulation

What is the active body temperature of tuataras?

~6 degrees Celsius to 16 degrees Celsius

Synapomorphies of Squamates

• Determinate growth

• Males have hemipenes

• Skull modifications that allow for flexibility

Determinate Growth

Growth that stops at some genetically determined point, not continuously throughout life

What reproductive organ do male Squamates have?

Paired hemipenes

What is the purpose of the paired hemipenes?

Used during copulation

Frontal/parietal Bones

Meet and act as a hinge so the snout can flex upward

Quadrates

Flexibly attached and move during feeding

What 2 skull modifications allowed for flexibility in Squamates?

Frontal/parietal bones & Quadrates

Characteristics Specific to Lizards

• 4 limbs

• External ear openings

• Moveable eyelids

Body Form of Generalized Terrestrial Snakes

Elongated with long tails

• Lengths usually 10-15 times their body circumference

Body Form of Generalized Viper Snakes

Stout with body lengths only ~5 times their circumference

Body Form of Generalized Arboreal Snakes

Very slim with length usually 20-25 times their circumference

Body Form of Fossorial (burrowing) Snakes

Slim bodies but with short tails, usually reduced eyes and smooth scales

Body Form of Sea Snakes

Lack ventral scales, have laterally compressed bodies, flattened tails, valvular nostrils

Lateral Undulation (Serpentine) Movement

Body thrown into series of curves, each curve presses backward against substrate

Rectilinear Movement

Primarily used by heavy-bodied snakes

• Alternate sections of muscle contractions pull the snake forward while intervening sections rest (sometimes slightly lifted off the substrate)

• Slow, but effective even on smoother surfaces

Concertina Movement

Used in narrow passages or climbing trees

• Snake anchors posterior portion of body by pressing against walls (or around tree) then extends front part of body

• Forms new loops with anterior part and presses then releases posterior part

Sidewinding Movement

Used mainly by desert dwellers

• Snake raises body in loops, resting weight on 2-3 points as the only contact with the ground

• Loops brought forward through air and placed on ground with point of contact actually moving smoothly along body

Sit-and-Wait Lizards

Make short dashes from a perch to capture prey, then return to perch

Sit-and-Wait Snakes

Wait in ambush for prey to pass

• Muscles are not adapted for sustained motion, only short bursts

Wide Foraging Snakes and Lizards

Move nearly continuously looking into crevices, under leaves, etc.

• Snakes will often follow the same route and check sites where they have captured prey in the past

• Usually have better endurance than sit-and-wait but slower sprint speeds

• Rarer form of foraging, usually not fully active hunting

Constriction Method

Snake seizes prey with jaws and throws one or more body coils around prey

• Body loops press against adjacent loops

• Each time prey exhales, snake takes up slack and tightens until pressure stops prey’s heart

Opisthoglyphous

Species with one or more enlarged teeth near rear of maxillae and with smaller teeth in front

• Fangs can either be solid or with a venom groove

• Fangs do not engage until prey is deeper into the mouth

• Evolved in many colubrids

Proteroglyphous

Hollow fangs located at front of maxillae, often followed by several small solid teeth

• Fangs permanently erect, relatively short

• Evolved in snakes like elapids (cobras, mambas, etc.)

• Common ancestors likely had an ancestral venom-delivery system

Solenoglyphous

Hollow fangs are only teeth on maxillae, fangs rotate and are folded against roof of mouth when jaws closed

• Allows for long fangs that inject venom deeply into prey

• Evolved in pit vipers and true vipers

Venom

Complex mixture of proteins and polypeptides

• Enzymes break down connections between cells, destroy cell membranes, and break down muscle tissue

Neurotoxic

Harms the brain/nervous system

• Can be delivered without causing much pain

• Deadliest depending on amount injected

Hemotoxic

Disrupts blood clotting, impacting the cardiovascular system

• Additional degeneration of organs, tissue damage, internal bleeding

Cytotoxic

Severe pain by impairing tissues on molecular level leading to cell death

Myotoxic

Severe, instant muscular paralysis (sea snakes)

Crypsis

Being indistinguishable from surroundings/resembling object of no interest to predator

True or False: Crypsis is the first line of defense for Squamates.

True

Aposematism

Use bright warning colors to advertise themselves as potentially dangerous

What squamate species often use aposematism?

Venomous species

Mimicry

Mimic the coloration of venomous counterparts in order to prevent predation

Batesian Mimicry

When a non-venomous/poisonous species mimics a venomous/poisonous species

What line of defense is deterrence used in?

Secondary

Bright Coloration as a Defense Mechanism

In some species on the underside of body that they only display when threatened

• Alerts predator that prey item is aware they are there and predator may move on to more unsuspecting prey

Spines as a Defense Mechanism

Can be effective deterrents if predator attacks

• Especially useful for species that seek shelter in crevices

• Make it difficult for predator to pull lizard from its retreat

Spraying as a Defense Mechanism

Squirting a terrible-smelling adhesive liquid from spines on tail

• Liquid can travel up to 50 cm and forms long sticky filaments

• Soil and debris stick to filaments and distract predator

Autonomy

Ability to break off part of the body and run off

Most Common Form of Autonomy in Squamates

Caudal Autonomy

Caudal Autonomy

Losing tail

Dermal Autonomy

Losing skin

What was venom evolved for in Squamates?

A Predatory Mechanism

How many cobra species have fang modification for making venom defensive?

~31 species

Courtship Behavior of Sit-and-Wait Species

Often use visual displays to communicate

Courtship Behavior of Widely Foraging Species

Use olfaction as primary sense for communication

What is hypothesized to be the ancestral reproductive mode for Squamates?

Oviparity

Number of Oviparous Squamates

~80%

Amount of Times Viviparity Evolved Within Squamates

>100

Advantages of Viviparity in Squamates

Female can use own thermoregulation to control embryo temperature

• May reduce time required for development

• Additionally useful for species living in colder climates

Disadvantages of Viviparity in Squamates

May lower reproductive output (female can only carry one clutch at a time)

• Mother agility is reduced as embryos grow, may be easier for predators to catch

• May spend more time hiding, possible to counteract this

Parental care can be observed in how many squamate species?

>100 species

Types of Parental Care Squamates Provide

• Nest defense

• Removal of dead eggs from clutch

• Egg brooding (coiling around eggs to protect and incubate them)

• Protection of newly-hatched offspring

How is genotypic sex determination (GSD) determined?

By genes inherited through sex chromosomes at the time of fertilization

How is environmental sex determination (ESD) determined?

By environmental factors

In temperature-dependent sex determination…

Hot temperatures result in males or females depending on the species

Chelonia

Include ONLY EXTANT turtles, tortoises, and terrapins

Testudines

Include Chelonia and EXTINCT relatives

Amount of turtle species

~361 species

What is unique about Chinlecheyls tenertesta?

A 215 million year old fossil that is considered a key intermediate fossil with ribs not fused to shell

What is the most distinctive feature of a testudine (turtle)?

The shell

Carapace

Dorsal part of shell

Description of the Carapace

• 5 central scutes bordered on either by 4 lateral scutes and with 10-12 marginal scutes on either side

Plastron

Ventral part of shell

Description of Plastron

• 6 paired scutes

Unique Factor of Testudine Inner Layer

Both pectoral and pelvic girdles enclosed by the rib cage

2 Extant Lineages of Testudine

Cryptodira & Pleurodira

Key Difference of Extant Lineages Cryptodira & Pleurodira

Head Retraction

Head Retraction of Cryptodira

• Retract head into shell by bending neck in a vertical S shape

• Enabled by multiple ginglymoidal joints

Head Retraction of Pleurodira

• Retract head by bending neck laterally

Testudine Lung Ventilation

• Lungs attached to carapace dorsally

• Ventrally, attached to viscera underlain by a sling (formed by abdominal muscles)

• Draw air by contracting muscles and increasing volume of the visceral cavity

  • Many are able to absorb/release oxygen and CO2 from the water through cloaca and pharynx

Approximately __ of the 361 species are Cryptodires

3/4

Part of the world that only has Cryptodires

Northern Hemisphere

Part of the world that only has Pleurodires

Freshwater habitats in Southern Hemisphere

Type of Shell Most Terrestrial Turtles Have

Domed Shells

Type of Carapace Most Aquatic Turtles Have

Low Carapaces

Another Specialization Sea Turtles Have

Modified Forelimb Flippers

Purpose of a Low Carapace

Allows for easier movement through water

What Do Softshell Turtles Have?

Reduced Shell Ossification

Ways Turtles Utilize Shells for Protection

1. Withdraw their head and legs when threatened by a predator

2. Some shells have flexible hinges (e.g., box turtles), allow for front or rear of shell to close

3. Use limbs to close gaps in the shell. Heavily scaled forelimbs and soles of feet

True or False: Most shells are crush-proof

True

Ways Testudines Communicate

Visual Signals, Olfactory Signals, & Tactile Signals

Visual Signals

• Color patterns on head and limbs may aid in species recognition

• Head bobbing during encounters between individuals

Olfactory Signals

From female, cloaca may indicate to males she is ready to breed

Tactile Signals

• Physical cues in the form of males ramming and biting each other during breeding season

• Males biting the heads of females prior to mating

Type of Reproduction All Turtles Have

Internal Reproduction