Amniote origins and Lepidosauria (Tuataras and Squamata) Flashcards
Amniote Origins and Diversification
- Tetrapods that are NOT amphibians
Why/how did they evolve?? - Late carboniferous; 312 mya
- Via Anthracosaurs (Reptilliomorphs)
2 early diversifications: - *Synapsids (to mammals)
- *Sauropsids -> *Diapsids (to reptiles & birds)
The Mesozoic was “The Age of Reptiles” - Dinosaurs!
Truly terrestrial
The Early Split
- *Synapsids (mammals) & *Sauropsids (birds/reptiles)
- Diverged very early in Amniote evolution (312-306 mya)
- e.g. *Protoclepsydrops (early fossil synapsid - 1st known?) & *Paleothyris (early sauropsid) both from Joggins Fossil cliffs in NS!
Amniotes Synapomorphies
- Amniotic egg
- Thicker and more waterproof skin
- Rib ventilation of the lungs
Enclosing “the Pond”
- The *amnion is an *extraembryonic membrane that encloses a *fluid-filled cavity – i.e., *“the pond”
- Embryonic development occurs in the *amnion (larger & faster too)
- Most evolved a *shelled egg that did not depend on water!!
- *Protective & *semipermeable, (allows gasses, limits water loss) - Paleozoic amniote diversification gave rise to all *nonavian reptiles, birds, & mammals
- Amniotic Egg
- All amniotes have eggs with *4 extraembryonic membranes
1. *Chorion (O2/CO2)
2. * Allantois (O2/CO2, waste)
3. *Amnion (fluid, cushion)
4. *Yolk sac (food) - Better protection & nourishment
- Thicker & More Waterproof Skin
- Mostly gas-proof; cannot breathe through the skin
- Keratinized (scales, hair, feathers, claws…)
- Rib Ventilation of the Lungs
- Anamniote: “Mouth breather”
- Mouth/throat muscular contraction & expansion
- *Pushing air into lungs
- *Positive pressure ventilation - Amniote: Aspiration
- Rib/muscular contraction & expansion
- *Sucking air into lungs
- *Negative pressure ventilation
- Jaws
- Jaws efficiently designed for applying *crushing or gripping force to prey
- Move from fast closure/suction feeding to *large muscles to grip and chew
- E.g., Pliosaurs!
Skulls: Holes for Jaw Musculature
*Anapsids (ancestral)
- Have a skull with *no temporal opening behind the orbits
- E.g. ancestral, and secondarily derived in turtles (truly diapsids)
*Diapsids
- Skull has “two pairs of temporal opening (fenestra)
- one pair below the cheeks and another above
- Gave rise to all other traditional “reptiles” and to birds
- e.g., dinosaurs, snakes, lizards, crocodiles
- Turtles appear anapsid, but secondarily lost diapsid condition
Amniotes Synapomorphies
- Amniotic egg
- Thicker and more waterproof skin
- Rib ventilation of the lungs
- Thicker and More Waterproof Skin
- Mostly gas-proof; Cannot breath through the skin
- Karatinised (scales, hair, feathers, claws)
- Rib Ventilation of the Lungs
Anamniote: “Mouth breather”
- Mouth/throat muscular contraction and expansion
- Pushing air into lungs
- Positive pressure ventilation
Amniote: Aspiration
- Rib/muscular contraction & expansion
- Sucking air into lungs
- Negative pressure ventilation
Anamniotes vs Amniotes
- Jaws Efficiently Designed for Applying Crushing or Gripping Force to Prey
- Move from fast closure/suction feeding to large muscles to grip and chew
- e.g., Pliosaurs
Skulls: Holes for Jaw Musculature
- Anapsid skull (ancestral)
- Skull with no temporal opening behind orbits
- E.g., ancestral; secondarily derived in turtles (lost diapsid condition) - Synapsid skull
- Single pair of temporal openings (fesetra)
- E.g., Mammals & early mammal-like reptiles - Diapsid skull
- Two pairs of temporal openings (fenestra)
- Gave rise to all other “reptiles” and birds
- E.g., dinosaurs, snakes, lizards, crocodiles
- Efficient and versatile Circulatory System (4-chambered heart)
Amphibian: 3-chambered heart
Amniote: 4-chambered heart
- Incomplete ventricle separation in some “reptiles” is handy for hibernation (winter) or estivation (summer)
- Efficient Strategies for Water Conservation (Uric Acid, Salt Glands)
Kidneys and urinary bladder adaptive for life on land
- Water mostly reabsorbed
- Mammals; kidney most efficient; urine made of urea
- “Reptiles” & birds: urine voided as semi-solid paste of uric acid
- Some reptiles need to excrete salt via salt glands!
Salt Glands (“Reptiles”)
- Nasal glands:
- Lizards (also marine birds); under nasal passage/above orbit - Salivary gland
- sea snakes, under tongue - Lacrimal gland
- sea turtles; tear ducts - Lingual gland
- crocodiles; on tongue
- A more Complex Nervous System
“Lizard brain”: Bigger cerebrum and cerebellum
- Better integration of sensory info & control of muscles
- Some lizards and snakes can “see” UV and infrared lights
- Lizards and snakes have Jacobsone’s organ
- Olfactory in the roof of mouth transmitted from the tongue
Classification of Non-Avian “Reptiles”
Diapsida
- Lepidosauria
- Squamata (snakes + lizards)
- Sphenodonta (Tuatara)
- Testudines (Turtles)
- Archosauria
- Crocodilia
- Dinosaurs, led to birds
Lepidosaur Synapomorphies:
- Overlapping keratinous scales (from epidermis)
- Transverse cloacal slit (longitudinal in the other tetrapods)
- Automise tails (may or may not grow back)
Clade Sphanodonta (AKA Rhynchocephalia)
- Tuataras
- 200 mya
- “Living Fossil”
- 1 remnant sp (Sphenodon punctatus)
- Lizard-like, with no external ears
- New Zealand; lives in burrows
- Slow growing: may live to 77 yrs
- Skull is nearly identical to diapsid skulls of 200 mya!!
- A well-developed media parietal/pineal eye buried beneath its skin, function is unknown
Order Squamata
- “Lizards” & snakes
- 95% of living reptiles
- Diapsid skull mods
- Lazard fossils in Permian; radiated in Cretaceous
- Snake fossils in Jurassic; highly modified
- Synapomorphy:
- Males with hemipenes (Bilateral penis; only one used is copulation)
Squamata Skulls: Diapsis w. Lost Bone(s)
- Permitting evolution of the mobile kinetic skull with moveable joints
- Joints in the palate and across the roof of the skull permit the snout to be tilted up
- Squamates seize and manipulate prey; they close the jaw with force
- Flexible Braincase
- Extreme skull mobility of snakes lead to major diversification!
Order Squamata -> “Lizards”
Typical “Lizards”
- 7000+ spp.
- Small, mostly insectivores, mods for climbers, some legless
- Moveable eyelids
- External ear openings
- Hot & dry regions
- Ectothermic
- e.g., geckos, iguanids, skinks, monitors, chameleons, glass lizards, worm lizards
“Lizards” -> Geckos
- Geckos
~1500 spp; small & agile
- usually nocturnal; excellent night/colour binocular vision; vocal
- Climbers- adhesive toe pads covered in micro hairs
- Can even walk on ceilings!
“Lizards” -> Iguanids
- Iguanids
~700 spp.
- Include many New World lizards as well as the only marine lizards (Galapagos)
- Small scales, crest on back and tail (elongated scales), large dewlap
“Lizards” -> Chameleons
- Chameleons
- 150+ spp.
- Arboreal (climbing) lizards of Africa and Madagascar
- Many have projectile tongues
- Zygodactylous feet, prehensile tail, binocular vision, colour change
“Lizards” -> Skinks
- Skinks
- 1500+ species
- No visible neck
- Smooth shiny scales
- Small legs (sometimes lost)
Squamate Lizards
- Monitor Lizards
~80 spp. - The only venomous lizrds
- Typically large and carnivorous
- e.g., Komodo dragon: largest lizard
- Thought most closely related to snakes
Order Squamata -> Suborder Serpentes
~4000+ spp.; the snakes (extreme modified squamates)!
- Evolved in the Cretaceous from burrowing lizards
- Limbless
- No pectoral or pelvic girdles, short wide vertebrae (undulatory), many ribs (Columnal rigidity/lateral stress)
- No eyelids (Clear scale cover), no external ears
- How to eat without limbs?: Venom, teeth, a crazy kinetic skull, and construction
Snake Skull and jaws
- Bones not all connected
- Kinetic skull!
Sensory Systems
- Most have poor vision
- except tree snakes (binocular vision)
- No external ears
- Unique sensing organs!
- e.g., Jacobson’s organ (olfactory via forked tongue)
- e.g., temperature-sensing pit organs (pit vipers, pythons, rattlesnakes)
A Nasty Bite
Most snakes are venomous
- **Poisonous = inhaled or ingested
- **Venom = injected
Injected in modified saliva through fangs
- Hollow or grooved
- Primary for predation; self-defense secondary
The “Deadliest” snake
- Inland Taipan (AKA “Fierce Snake”)
- Central East America
- Based on unit of venom (single drop = kill 100 humans)
- rarely bites - minimal human deaths! - Saw-Scaled Viper
- Africa, Middle East, Sri Lanka, Pakistan
- V. aggressive, more deaths/yr than all other snakes combined
Not Just Venom!
Constriction
- Prey squeezed & dies from asphyxiation/cardiac arrest
- E.g., Boa constrictors, anacondas, pythons
Snake Reproduction
Internal fertilization
- Hemipene: grooves, hooks and spines!
- Oviparity, ovoviviparity (e.g., vipers), viviparity (e.g. boa constrictor, anaconda)
- Most abandon eggs, some make nests (e.g., king cobra), coil around (e.g., python)
