Amphibians and Reptiles Flashcards
What period did tetrapods evolve in?
Devonian (359-299 Ma)
What is the closest relative to tetrapods?
Lobe-finned fishes
What two extant groups of lobe-finned fishes are there?
- Actinistia - coelocanth Latmeria (2 species), symmetrical 3-lobed tail
- Dipnoi - lungfishes (3 genera)
What is the class of lobe-finned fishes called?
Sarcopterygii
Features of tetrapods
- Have limbs (not paired fins)
- Includes all modern amphibians and amniotes
- Ankle and wrist joints
- Fully developed pectoral girdle
- Pectoral girdle free from skull
- Discrete shaft of humerus
What were Panderichythys?
Extinct tetrapod-like organisms, fins had radial bones at the end of the fin skeletal structure which appeared to have 4 digits. No dorsal fin, lived in shallow water, dorsoventrally flattened, ready to walk
What was tiktaalik?
Intermediate between fish with fins and tetrapods with limbs, could go onto land.
Fish characteristics: scales, gills, fins
Tetrapods characteristics: eyes on top of skull, lungs, neck, ribs, fin skeleton, flat skull
What are Acanthostega and Ichthyostega?
Carnivore from Devonian of Greenland. Four limbs with well-developed digits. Dated to 395 million years ago
What groups does amphibians contain?
All extant salamanders, frogs and caecilians
What groups does amniotes contain?
All extant mammals, birds and reptiles
What was involved in the transition from aquatic lifestyle to terrestrial?
- Body support - in the water body doesn’t require limbs but on land it does
- Moving onto land means coping with gravity during locomotion
- Limbs have become larger and more differentiated
- Limb bones and joints become more robust
The 2 major trends aiding movement on land
- Pectoral girdle becomes dissociated from head skeleton to avoid pressure on skull and increase head mobility
- Limb girdles become more closely attached to the axial skeleton (vertebral column) - allows limbs to become support structures and transfers the forces to the axis
What was the change in locomotion in the transition from movement to land?
A switch from swimming to walking and running
Terrestrial locomotion harder on joints
Fin based swimming (lateral undulation) replaced by pushing off substrate
What were the changes made to limbs to transition from swimming to walking?
More robust
More differentiated
Switch from extrinsic to intrinsic limb musculature
What were the changes made to body shape to transition from swimming to walking?
Very hydrodynamic in fishes
A steady decrease in hydrodynamics in terrestrial forms
More elongate again in secondary aquatic forms
How did the form of respiration change during the transition from an aquatic to a terrestrial lifestyle?
Gills only -> gills and lungs -> lungs only
Decreased reliance on cutaneous respiration
Both gills and lungs ancestral as lungs arose from swim bladders
Ventilation increased in later tetrapods, powered by rib cage musculature
Amphibians still use cutaneous respiration
How did early terrestrial animals adapt to drier conditions?
Fish live in excess water
Amphibians live in moist environments
Excretion of concentrated urea conserves water
Mucous glands limit evaporation from amphibian bodies
Amphibians have behavioural adaptations that limit water loss
How did sensory systems change during the movement to land? 1. Hearing
Sound travels differently in air than denser water
Evolution of bony structures that better conduct vibrations to the inner ear
Lateral line system that detects water currents and vibrations disappears (mostly)
How did sensory systems change during the movement to land? 2. Feeding
Suction feeding prevalent in fishes
Jaws and tongue take more important role on land
Elaboration of tongue enables enhanced prey capture
3 major amphibian clades
Caecilians
Salamanders/newts
Frogs/toads
Caecilians
- Order Apoda ( part of larger clade Gymnophonia)
- Elongate without limbs of limb girdles
- Carnivorous, can grip prey and spin to process it
- 5-150 cm
- Body segmented by annular grooves, some species have scales
- Highly specialised for burrowing; heavily ossified compact skills, recessed mouths
- Some aquatic species have evolved fins
- Left lung is rudimentary
Where are caecilians found?
- Moist forest soil, some in freshwater
- Tropical
- Approx 170 species, in 34 genera
Reproduction in caecilians
- Internal fertilisation
- Primitive caecilians are oviparous with aquatic eggs and larvae
- Some advanced caecilians are also oviparous, with direct development of terrestrial eggs
- The most advanced caecilians are viviparous and larvae have scraping teeth (shed at birth). They scrape epithelial lining of oviduct to obtain nutrients secreted by oviducal cells (matrotrophy)
Sensory systems of caecilians
- They have no ear openings
- Likely that they rely on retractable tentacles for sensing prey and mates
- Tentacles carry chemical cues from the environment to the nasal cavity
- Most have very small eyes; some species have the eye covered by skin
Newts and salamanders
- Order Urodela (in larger clade Caudata)
- Generalised morphology
- Possess a tail
- Some entirely aquatic, others terrestrial
- Limbs more or less equal length
- Terrestrial forms tend to walk side-to-side, bending body
Reproduction in newts and salamanders
- Eggs are laid in water where larvae hatch
- Eggs laid on land it in water
- Some go larval stage, others don’t
- Fertilisation is external in some, but mostly internal (without compilation)
- Males produce gelatinous spermatophores capped with sperm. Females pick up sperm with the cloaca, where sperm are stored. Eggs are fertilised as they pass through
- Eggs deposited either individually or in clumps
Features of axolotl
- Paedomorphosis (retention of larval features after maturity)
- Spends entire life in water, gills are retained
- Actually just a mole salamander that does not metamorphose in nature
- Neotony - animal is sexually mature whilst still in the larval state
Where are newts and salamanders found?
- Mainly in cooler northern temperate regions
- A few tropical and subtropical species in South America and Asia
- Approx 550 species
- 3 native UK species (palmate newt, smooth newt, great created newt)
Frogs and toads
- Order Anura (of larger clade Salientia)
- No tail but legs are always present in adults
- Highly adapted for locomotion
- Hindlimbs larger than forelimbs, webbed toes
Sensory adaptations of frogs and toads
- Foraging - carnivores which usually capture prey with long protrusions sticky tongue
- Visual and auditory communication important in breeding, often short-term, mass aggregations
- Often large vocal sacs that amplify make mating calls
Reproduction in frogs and toads
- Fertilisation is external except in a few species
- Most are oviparous with aquatic eggs and larvae
- Some are oviparous but with direct development of terrestrial eggs
- Some are viviparous (with lecithotrophy - embryo receives no nutrition other than the yolk originally contained within its egg)
- Many species exhibit bizarre forms of parental care
What are the four native species of UK frogs and toads?
- Common frog (Rana temporaria)
- Common toad (Bufo bufo)
- Natterjack toad
- Pool frog
Non-native UK species of frogs and toads
Midwife toad Yellow-bellied toad Painted frog European tree frog Australian green tree frog Marsh frog Edible frog American bullfrog African clawed toad
Where are frogs and toads found?
Worldwide distribution, except for extreme latitudes and arid environments
5420 species
When did the poison dart frog evolve and what is its Latin name?
Dendrobatidae (family)
Evolved 20-50 million years ago
Restricted to South America
When are where did Mantellidae evolve?
Family
Evolved 50 Ma
Restricted to Madagascar
When did Myobatrachidae evolve and where are they found?
Evolved 100 Ma
Restricted to Australia and Papua New Guinea
What is the Latin name for true toads and when did they evolve?
Bufonidae (family)
Evolved 50 million years ago
All continents except Australia
What is the Latin name of narrow-mouthed frogs and when did they evolve?
Microhylidae (family)
Evolved 70 Ma
On all continents except Australia
What percentage of amphibians live in forests?
82%
Causes of amphibian decline
- Enigmatic declining -reasons for decline not fully understood
- Disease
- Loss of habitat - deforestation
- Climate change - new temperature favours from pathogens
What chytrid fungi infects amphibians and causes lethal chytridiomycosis?
Batrachochytridium dendrobatidis
Infects the keratinised skin of amphibians. Symptoms prior to death include sloughing of skin and paralysis of hind legs
It has motile zoospores that swim in water and penetrate skin
Optimal temperature 17-25 degrees
What species of amphibians are resistant to chytrid fungi?
Pest species
Cane toads
American bullfrogs
African clawed frogs
Amphibian adaptations for thermal regulation
- Ectothermic - body temperature matches that of the environment
- Metabolic heat produced is small and easily lost
- Raised temperature enables faster metabolism (eg digestion), but remaining cool enables long periods without food
- Behavioural thermal regulation
- To reduce water loss, some bask in water, others only do it briefly, helped with a dark skin colour
What species of amphibian bathes on slopes then moves to shade?
Anaxyrus debilis
How do amphibians prevent overheating?
They undergo evaporative cooling
eg the cane toad (Bufo marinus)
What temperatures can frogs and toads live between?
3-35.7 degrees Celsius
What temperatures can salamanders live between?
-2 to 30 degrees Celsius
Amphibian physical adaptations related to water economy
- Water is 70-80% of body mass
- Adults do not drink
- Water exchanged through skin and in lungs - cutaneous respiration
- Amphibians restricted to moist environments
- Skin delicate, small amount of keratin, abundant mucus glands
- Aquatic species - extremely dilute urine
- Terrestrial species - nitrogenous waste excreted as urea or utica acid to preserve water
- Urinary bladder can serve as water store
- Water uptake can be highly efficient
Amphibian behavioural adaptations to avoid water loss
- Avoid exposure to the sun
- Hide in moist shelters
- Live in locations with water availability (streams, ponds)
- Reduce surface area by compacting resting posture
- Aggregate to reduce exposed surface area
Amphibian adaptations for prey detection and capture
- Larvae do not compete with adults for resources
- Often tadpoles herbivorous, planktivorous (filter-feeding) or opportunistic omnivores
- Adults always carnivorous, eating arthropods and annelids
- Vision primary method of prey detection, but lateral line persists in larvae - hearing and ground vibrations also important in some species
- Prey items in anurans and urodeleans usually caught with sticky tongue. Tongue can be propelled by muscular activity, or a flip-type action
What adaptation in lungless salamanders helps them to catch prey?
The lung muscles have evolved into powerful muscles that project an elongated tongue forward
Amphibian predators
- Amphibians have huge diversity of predators and pathogens
- Eggs - arthropods, leeches
- Larvae - arthropods, fishes, turtles, wading birds
- Adults - birds, snakes, spiders, crabs, fishes, turtles, amphibians, mammals
Amphibian adaptations to avoid predation
- Frogs communicate with ripples
- They have concealing colours and shapes for camouflage
- Disruptive colours break up the outline of the animal, so it doesn’t conform to the search image of the predator. A mid-dorsal line is present in many anurans
- Confusing colours delay or prevent the prey-capture instinct of many predators
- Enlarged body when predators approach, making them appear to big for the predator to handle
- Pretend to be something bigger - some amphibians have bizarre skin colouration
- Aposemic colouration - use of bright colouration by amphibians with physical or chemical defenders as a warning to predators, animals learn to avoid them
Why do frogs only respond to ripples from far away?
Frogs communicate with ripples in water. They only respond if ripples come from far away, not too close to them. This is because there is a bat that responds to echolocation from aquatic surfaces and can hunt frogs from their ripples
What adaptation does the false-eyed frog have?
Its rear end is designed to look like the eyes of a large predator
What does amphibian colour provide information on?
That the amphibian is poisonous to those who eat it
An indication of social status - brighter males respond to calls faster
Amphibian adaptations to compete for a mate
- Many species exhibit sexual dimorphism, but the female is usually bigger than the male
- In species where the male is bigger, there is competition between males for mates. These species have weapons used in combat e.g. spines on the upper jaw of the moustache toad, teeth on lower jaw of the tusked frog
Amphibian parental care - foam nest tree frogs
Build nests overhanging water made of air bubbles, incorporating leaves and twigs. When larvae hatch, they fall into water below
Amphibian parental care - midwife toads
Female expels a strand of eggs, make fertilises externally then carries the string of eggs around his legs. Warts on his back give off strong smelling poison, the protects both the adult and larvae from predators. Then males leave tadpoles to develop in small temporary pools
Amphibian parental care - Rheobatrachus
- Incubate the larval stages in their stomach
- Only two species ever found
- Extinct in the mid 1980s
Amphibian parental care - poison frogs
Eggs laid in temporary pools, such as holes in trees. Adults then move them by carrying them on their back
Amphibian parental care - marsupial frogs
Possess a dorsal brood pouch. Eggs are fertiliser then incubated in a pouch on the lower back. Eggs are next to vascular tissue, providing oxygen. Eventually fully formed eggs are released
Amphibian parental care - Nectophyrnoides
The only roads that do not lay true eggs. Fertilisation is internal, and eggs develop in the oviducts of the female. When the yolk is used up, the tadpoles feed on ‘uterine milk’ secreted by the oviduct
Amphibian parental care - caecilians
At least 2 brooding caecilians provide additional food for their young. Young caecilians have evolved teeth capable of tearing skin from mother’s body, providing nutrition
Xenopus - extreme amphibian adaptations
- Family Pipidae
- Habitats: lakes, swamps, ditches, dams
- Adult diet: any live arthropods and fish of manageable size, may scavenge dead animals, cannibalistic
- Tadpoles diet: filtered feeders
- Almost exclusively aquatic, but can tolerate extreme conditions
- Overland migration: enables colonisation of new habitats in absence of waterways
Xenopus sensory perception
- Adaptations for olfaction in air and water
- Eyes adapted for vision in air
- Auditory system designed for sound perception in water
- Lateral line system persists in Xenopus - can detect depth, currents and vibrations through changes in water pressure
Xenopus adaptations for dry periods
- Can aestivate (live in prolonged state of dormancy) for over 6 months in mud
- Excretion of toxic ammonia switches to urea in dry periods, and is excreted when water returns
- Can survive without food for 1 year
- Metabolism slows to conserve energy
Xenopus defences against predation
- Skin contains toxins distasteful (or lethal) to other animals
- Potent anti-bacterial secretions that kill bacteria by perforating membranes
- Shoaling - an anti-predatory tactic
- Predators: birds and fish
Extreme adaptations of Spadefoot toad
- Scaphiopodidae (family)
- Two genera: Spea and Scaphiopus
- Dry habitats
- Rains fall in July-August, dormant late-August to early July
- Hibernate 1 meter underground
- Bury themselves with hard skin on their heels
- Toads can survive 2 years without rain
- Urinary bladder serves as water store
- Skin delicate and permeable - enables water absorption from soil when buried
- During hibernation nitrogenous wastes concerted to urea and stored in tissues - maintains osmotic flow of water from drier soils
Spadefoot toad reproductive adaptations
- Breed on first night when rain falls
- Eggs laid in pools, and tadpoles undergo fast metamorphosis 9-10 days after eggs laid
- Tadpoles feed on organic materials in pond
- Adults active in pools at night, and at dawn bury themselves in shallow burrows to avoid heat of day
- Adults feed on large abundance of desert invertebrate during the rains
Example of phenotypic plasticity in spadefoot toads
When ponds have high density of tadpoles, they undergo morphological shift (large jaws) and become cannibalistic rather than omnivorous - they can then reach metamorphosis much more quickly
What is the amniotic egg?
- Amniotic eggs have ‘aquatic environment’ within the egg
- No larval stage
Form of amniotic eggshell in birds
Calcareous
Form of amniotic eggshell in reptiles
Leathery and flexible
Form of amniotic egg in mammals
Eggshell gone (mostly), embryo develops within mother’s body
Four extra-embryonic memebranes
- Amnion - membranous sac that surrounds embryo for protection
- Chorion - outer membrane: surrounds embryo and yolk sac, allows gas exchange between embryo and air
- Allantois - outgrowth of hindgut - storage for nitrogenous wastes
- Yolk - surrounds yolk (nutrient supply), extensive blood supply to embryo
Potential disadvantages of shelled eggs
- Air is more thermally variable than water
- Must have internal fertilisation
- Usually requires more parental care
- Relatively expensive to produce - fewer shelled eggs can be produced
By 285 million years ago, what amniote groups had evolved?
Parareptiles and turtles (Anapsids)
Diapsids
Synapsids
What are the three skull types, distinguished by the number of openings (fenestra) in the skull?
1 Anapsids = no openings
- Synapsids = one opening
- Diapsids = two openings
What are parareptiles?
- Large, stocky quadrupeds
- Plates on skin
- Died out by 200 million years ago
Features of turtles
Chelonians (order)
Approx 300 species
Sea turtles have evolved enlarged forelimbs
Carnivorous and herbivorous
Anatomy of turtles (Chelonians)
Box-like shell, fused to the vertebrae, clavicles and ribs
1. Top shell: carapace
2. Bottom shell: plastron
Plastron evolved before carapace
Two suborders of extant chelonians:
- Cryptodires: hidden nick turtle - next retracts in ‘S’ shape into shell, most living turtles
- Pleurodires: side-necked turtles - neck folds sideways but doesn’t retract into shell, few species)
What are the four lineages of diapsids?
1) Lepidosaurs (lizards and snakes)
2) Archsaurs (crocodilians, pterosaurs and dinosaurs)
3) Plesiosaurs (extinct)
4) Ichthyosaurs (extinct)
What are the Lepidosaurs?
- Two living orders: tuatara and squamata
- Largest group of non-avian reptiles
- Primarily terrestrial tetrapods, with some secondarily aquatic species
- Scale covered skin, relatively impermeable to water, ouster layer is shed at intervals
- Reduction of loss of limbs is common
Features of Tuatara (Sphenodontia)
- Evolved 220 million years ago
- Lizard-like, but skull is heavier
- Fossil evidence shows they were globally distributed, present in many continents, but now only 2 species in New Zealand
- Nocturnal, live in cool habitats, low body temperature compared to most lizards
- Live in burrows
- Dependent on seabirds for food - eat arthropods attracted by guano
- Slow reproduction - breed once every 4 years
- Temperature-dependent sex determination - more males due to warmer climate
Features of Squamata (lizards / snakes)
- Evolved 240 million years ago
- Approx 8000 species
- Worldwide distribution
- 16mm-3 metres
- Highly kinetic skulls
- Scaly skin
- Limb reduction
What are the advantages of limb reduction?
Moving through small openings
Helps with moving across sand, through tall grass and for burrowing
6 indigenous UK species of squamata
Smooth snake Grass snake (Natrix natrix) Added Sand lizard Common lizard Slow worm
Features of crocodilians
- Alligators and crocodiles
- Earliest fossils 84 Ma
- 23 extant species
- Confined to tropical/subtropical waters
3 crocodilian families
- Alligatoridae
- Crocodylidae
- Gavialidae - gharial and false gharial
Crocodilian adaptations
- Crocodiles and gharials have modified salivary glands on their tongue, for excreting excess salt (marine adaptation)
- Alligators and caimans have them, but non-functioning (freshwater adaptation)
- All crocodilians swallow stones (gastroliths) to act as ballast (for stability) and aid prey digestion
- Two stomachs, the first muscular to ground prey, the second acidic, so they can digest feathers, bones and horn
What is more important for reproductive isolation of reptiles, habitat or long-term isolation?
Habitat
What are the declines observed in the density of both amphibians and snakes over what time period?
1970-2005
75% decline
Why are the locations and descriptions of new reptile species often not disclosed?
Illegal pet traders find the animals, endangering them
What areas do reptiles have specialised adaptations in?
Respiration Thermal regulation Locomotion Reproduction Prey capture Predator avoidance Communication
What areas do amphibians have specialised adaptations in?
Thermal regulation Water economy Prey detection and capture Defence against predators Competition for mates Parental care
Reptile thermal regulation adaptations
- Ectothermic - body temperature matches that of the environment
- Can regulate metabolic heat derived from oxidation of food to sustain body warmth and a constant body temperature - in large species this can be a significant heat source
- Lizard basking in sun may have higher body temperature than mammal, and must shade to avoid overheating
How many extant reptile species are there in how many orders?
8200 species
- Tuatara
- Chelonia
- Crocodilia
- Squamata
Reptile respiration adaptations
- All reptiles have lungs
- In snakes left lung reduced or absent
- Respiratory ventilation using rib movements
- Some aquatic or semi-aquatic reptiles use skin for respiration when submerged e.g. file snakes, sea snakes and soft-shelled turtles
How do turtles respire (they cannot use ribs to ventilate lungs)?
Turtle lungs connected to visceral muscles, that contract to force viscera against lung to expel air. Other muscles pull viscera back, expanding lungs.
In aquatic turtle tissues (mucous membranes) lining the mouth are capable of extracting oxygen from water
Some turtles have highly vascularised sacs off the cloaca that allow gas exchange from water
How does temperature affect the longevity of reptiles?
- Ectothermy - variable body temperature allows survival on low/sporadic food input, and a low metabolic rate
- Turtles can live for over 100 years
- Snakes can live for over 30 years
- Also associated with slow reproduction - overharvesting can lead to extinction
Distributions of reptiles
- Ectothermy excludes them from cold environments
- Reptiles most common in warm dry environments
- Nitrgoenous waste excreted primarily is utica acid (aids water conservation)
- Body surface covered by horny scales, skin provides a barrier to water loss, few cutaneous glands, not involved in respiration
Reptile adaptations to aid locomotion
- Limbs and girdles that support the body from underneath
- Many reptiles now have bipedal walking and running
- Lizards show very rapid locomotion
What Genus of reptiles have webbed feet to increase surface area, acting like a parachute?
Flying geckos
Ptychozoon sp.
What genus of reptiles have flaps of skin along their ribs that can be extended into ‘wings’ by elongating it’s ribs?
Gliding lizards
Draco sp.
What reptile lineages have evolved leglessness?
Snakes
Slowworms
Worm lizards
What is the advantage of leglessness for reptiles?
- Allows movement through small spaces and through vegetation
- Burrowing
- Very efficient movement
- Allows cooling for defence, thermoregulation and prey constriction
- Aboreal lifestyle: allows weight to be spread evenly across branches
4 methods of undulation in snakes
- Lateral undulation
- Sidewinding
- Concertina
- Rectilinear
What is lateral undulation?
Movements left and right coupled with posterior moving waves push against contact points in the environment
Most common form of movement
What is sidewinding?
A modified lateral undulation, and good where solid contact points are absent. Different parts of the body touch the substrate at different times
What is concertina (form of locomotion)
Used in tunnels. Latter half of body grips the tunnel wall while anterior stretches, and then vice versa
What is rectilinear (form of locomotion)?
No lateral movement. Belly scales are lifted and pulled forward before being placed down and the body pulled over them. Used by large pythons and boas
Adaptations of fully aquatic sea snakes?
- Sea snakes have flattened, paddle-like tails that increase swimming efficiency
- Nostrils with valves that exclude water
- Highly venomous, many with aposematic colouration
Adaptations of gecko feet
Adhesion between tips of setae and substrate linked to van der Waal’s forces (electrical intermolecular attractions)
Reproductive adaptations of marine turtles
- All turtles oviparous
- Marine turtle females excavate nests in sand
- No parental care
- Embryonic development usually 40-60 days
- Advantage for simultaneous hatching: predator satiation
Nesting adaptations of alligators
- Nest constructed from layers of aquatic vegetation
- Rotting vegetation warms eggs
- Females lay above water level (eggs can drown)
- Female guards eggs until hatching (65 days)
- Nestlings make grunting noises
- Females carry young to waters edge, and protect them against predators
Predatory adaptations of crocodilians
- Crocodiles have secondary palate (shelf in roof of mouth separating nasal and mouth passages). Enables prey to be held without water entering the respiratory tract
- Crocodilians have dermal pressure receptors (bundles of nerve fibres that respond to slight disturbances in surface waters). It is therefore possible to detect predators and prey in darkness
- Crocodiles have them on almost every scale in the body, while alligators and caimans only have them on their jaws
What is the vomeronasal / Jacobson’s organ?
- Snake tongue collects odour particles, then withdraws
- Transfers particles into olfactory chamber - processed by the Jacobson’s organ
- Sensitive to compounds with high molecular weight
- Can detect chemicals with the nostrils
- Use nostrils (olfaction) for long-range and Jacobson’s organ (volmerofaction) for short-range sensing
Features of snake jaws
- They do not detach (permanently hinged)
- Not joined by a rigid symphysis, have elastic ligament that allows them to spread apart
- Important as food manipulation by limbless animals is difficult
What is lizard prey size restricted by?
Residual presence of pectoral girdle (absent in snakes)
How do snakes use infrared?
- Some snakes detect minute changes in the infrared spectrum (heat)
- Used for locating endothermic prey
- Pit organs are located in ‘pits’ in the skin, between the nostril and eye
- They can detect prey even if it is standing still
- Some rattlesnakes can detect changes as small as 0.003 degrees Celsius
Venom as an adaptation
- Helps dead with large prey
- Helps capture prey by immobilisation
- Helps digestion through protease enzymes
- Complex mixture of proteins produced by special oral glands (modified saliva glands)
- Injected quickly, then reptile withdraws to safety
- Some neurotoxic (death after paralysis of respiratory muscles)
- Others haemolytic (breakdown of blood cells)
- Some act on cell membrane function
What reptiles is venom present in?
Glia monster Beaded lizard Advanced snakes Iguana (Iguanidae) Monitor lizards (Varanidae)
Where do gene expression profiles indicate venom glands are derived from?
Pancreatic origins
Reptile adaptations to predator avoidance
- Most lizards shed tail when grasped by a predator - caudal anatomy
- Often the tail will continue to wriggle, to distract the predator allowing escape
- But tail loss reduces escape performance, running speed and stability when jumping
- Also diverts energy from reproduction into tail regrowth
- It can also reduce male social status and access to mates
Reptile adaptations to aid camouflage
- Mc1r gene has a role in melanin production. Allele frequencies of this gene differ between sand and soil populations
- Mimicry - the non-venomous milk snake mimics the aposematic venomous coral snake
Reptilian adaptations for sexual selection
- Many reptilian sexually selected traits - colour, head size, male ornaments (spurs, drills, dewlaps)
- Chameleons change colour rapidly between submissive (camouflaged) and dominant (colourful) - signals used to attract mates and intimidate other males
What group did the dinosaurs evolve alongside?
The Crurotarsi (clade within reptilia)
What clade were dinosaurs part of?
Orthinodira
When did most Crurotarsi go extinct?
In a mass extinction at the end of the Triassic period (206 million years ago)
Dinosaur diversity
- Persisted throughout the Mesozoic
- Most genera present near the K-T boundary (65 million years ago)
- Over 1000 species described, many may be synonyms
- 500 reliable species
What were the two dinosaur clades? How are they distinguished?
- Ornithischia - bird-hipped
- Saurischia - lizard-hipped
Distinguished by the pelvic girdle/hip
Features of Ornithischia
- All were herbivorous
- Variety of four-legged and bipedal species
- Rare prior to the Jurassic, but common thereafter
Features of Saurischia
-Contains two major lineages, the bipedal carnivores (Theropods) and the quadrupedal long-necked herbivores (Sauropodomorphs)
Which lineage do Aves belong to?
Therapod lineage (Saurischia)
3 dinosaur thermoregulation hypotheses
- Endothermic (like mammals and birds)
- Ectothermic (raised body temperature primarily by basking and regulating temperature through behaviour)
- Inertial homeothermy (maintain a body temperature, but that temperature is dependent on mass. Larger individuals = smaller surface area)
How do we determine the colour of dinosaur feathers?
Melanosomes used to determine feather colour of extinct animals - the shape of fossilised melanosomes is different for each colour
How is the body temperature of dinosaurs determined? What was determined about dinosaur body temperature?
From growth rates (from bones) and known effects of temperature on animal growth rates, the temperature of dinosaurs can be estimated.
Smaller dinosaurs ectothermic, but larger species warmer - supports inertial homeothermy
Theories of dinosaur extinction
- Meteor impact - 180km crater at Chicxulub in Mexico. Asteroid may have been 10km wide. Microtektites in crater wall dated back to 65 million years ago. Global deposits of iridium (common in asteroids). Would have caused sudden temperature drop.
- Massive volcanic eruption - Deccan Traps (India). Massive volcanic eruptions (over 800,000 years). Aerosols and dust would have blocked photosynthesis and had a greenhouse effect leading to temperature rises
What would these disasters have effected?
- Ecology
- Direct - physiological
- Embryonic development
- Sex ratios
