Radiation of Reptiles Flashcards
Reptiles had a major adaptive radiation that continued into _____________________
Mesozoic - 2525 to 66 mya (“Age of Reptiles”)
- Insects offered strong prey base
- Advantages provided by amniote novelties in terrestrial habitats
Scales in reptiles
Keratinized
Derived from EPIDERMIS
Feathers and hair are derived from reptilian scales
Scales in “bony fishes”
Derived from DERMIS (dermal scales)
Ganoid, cycloid, ctenoid
Independently evolved scales NOT homologous to teeth
Placoid scales in Chondrichthyes
Derived from EPIDERMIS and DERMIS
HOMOLOGOUS to teeth
Lepidosauria: Rhynchocephalia
Tuatara (Sphenodon)
Sister lineage to Squamata
ONE extant species (MONOTYPIC order)
Now only live on small islands off of main islands of New Zealand
Insectivorous and cernivorous
Can function at temperatures in the single digits (C)
12-15 month incubation of eggs
~20years to sexual maturity
Lifespan of at least 60 years (possibly >120 years)
“Living fossil”
-Remnant species from a diverse Mesozoic group (~20 genera)
Diversity of extinct forms
Carnivores, herbivores and marine forms
Lepidosauria: Squamata - HISTORICAL CLASSIFICATION
Lizards (Lacertilia)
- > 6500 species
- PARAPHYLETIC (when snakes and/or amphisbaenians not included)
Snakes (Serpentes)
->3700 species
Amphisbaenians (Amphisbaenia)
- Worm lizards
- > 195 species
Lepidosauria: Squamata - CURRENT VIEW
Snakes, Lizards, and Amphisbaenians are all in one clade
Lepidosauria: Squamata - Synapomorphies
Hemipenes: Paired intromittent organ (NOT a true penis)
Cranial kinesis: Significant movement of different parts of skull relative to each other (joints in skull)
Lepidosauria: Squamata - Charasterics
Integument periodically shed (lepidosayr synapomorphy)
Tail autotomy:
- Lost in snakes and some lizards
- Lepidosaur synapomorphy
Viviparity has evolved many times in squamates (perhaps over 80 times)
Protection of developing young from predation
Provides opportunity to invade certain habitats
- Marine environment
- High latitudes and altitudes: i.e. cold regions
Squamata: “Lacertilia”
Lizards
Huge size range
Paraphyletic group
Includes SMALL and LARGE specimens
Most insectivorous
Some specialists on specific insect prey (e.g. ants)
Herbivory common in larger species
Some carnivorous on large prey
Tail autotomy
- Fracture planes WITHIN VERTEBRAE
- -Fracture plane: Zone of weakness within each caudal vertebra; if the tail grabbed by predator, it fractures WITHIN the vertebra (intravertebra)
Limblessness evolved many times (CONVERGENT EVOLUTION: snakes and MANY lizard lineages)
2 major categories of prey capture:
- Clade Iguania: Use tongue to capture prey
- Other lineages: Use jaws to capture prey
Squamata: “Lacertilia”: Chameleons
One family of lizards
Color/pattern changes used in communication
Projectile tongues
Squamata: Amphisbaenia
Limbless (except one family with front limbs)
One lung (Left lung)
Fossorial (digging/burrowing habit)
Robust AKINETIC skull used as burrowing organ
Eat mostly invertebrates
Squamata: Serpentes
~10cm to nearly 10m
Occupy huge range of habitats
Lack limbs
-None with pectoral girdle but some with vestiges of pelvic girdle
Lack external and middle ear
Eyelids fued into spectacle
One lung dominant (Right lung)
- OPPOSITE of amphisbaenians
- May not be a reason for this, just what worked for them
Various predatory strategies
- Seize and eat prey alive
- Constriction (CARDIAC INTERFERENCE)
- Venomous (<15% of snakes)
- -Venom immobilizes prey (reduces risk to snake)
- -Venom can begin digestion from the inside out
Thermal sense organ in snakes
- Infrared (i.e. heat) receptors evolved several times
- Most developed in pit vipers: pit organ between nostril and eye on each side
- Pit organ paired: Snake can sense directionality of heat
- Used to track endothermic prey and aim strikes
- Can differentiate temperature differences to 0.003C
ALL carnivorous
Feeding specializations:
- Extremely cranial kinesis
- Paired joints on each side of head increase gape
- Mandibular symphysis only soft tissues: mandibles move independently to ingest prey
Evolution of Serpentes
2 major hypotheses origin of snakes
- Fossorial ancestor
- -Eye morphology suggests that at one time sight was reduced (consistent with fossorial habit)
- -Most basal extant snakes are burrowers
- Aquatic ancestor
- -Suggests that snakes evolved from marine ancestor
- -Snake fossil found in Israel had hindlimbs, kinetic skull, and was marine
Giant Extinct Snake
Titanoboa cerrejonesis
Found in Columbian coal mine (8 speciments)
Dated to ~60mya
Estimated at 13m (42’) and 1135kg (~2500 lbs): typical size
Largest extant snake (green anaconda) to 6m (20’) and 250kg (550lbs): Exceptional size for an anaconda
