Egg Layers Live on Land
- Amphibians retained vestiges of the life habit of predecessors
- Requirement to return to water for reproduction.
- Fertilized naked eggs develop fish-like larvae that use gills for respiration.
- Terrestrial Adaptations
- 3-chambered heart for better circulation
- More efficient lungs
- Limb and girdle structures modified to overcome body drag
- Spinal column developed into an interlocking set of sturdy but flexible bones
- Development of an ear structure
- Ichthyostegids
- Labyrinthodont amphibians (Late Dev. - Tr; EXTINCT) are coeval & possess same tooth
structure as Rhipidistians Sarcopterygii.
- Dev to Early Permfound in terrestrial e.o.d.'s
- Dev to Jr(?) known in marine settings
- Response to Environmental Stress?
- Seasonal aridity evidenced by red beds in East Greenland (site of Ichthyostega)
- Ephemeral landscape would favor rhipidistians with limbs.
- Dentition pattern reminiscent of carnivores.
- The Advent of the Reptiles
- Reproduction with protective amniotic egg in early Pennsylvanian.
- Early reptiles loosely grouped into the Captorhinids with several characteristics:
- Small stature with jaw structure with functional morphology for holding & chewing
- Swivel neck joint (double ball-and- socket articulation)
- Anapsid skull
- Early Reptile Diversification
- In the Permian Pelycosaurs ("sail-fin") becomes prominent
- Group is synapsids (one additional opening in cranium above jaw)
- Herbivores and carnivores
- Late Permian >20 families;
- Terminal Permian 20 families EXTINCT.
- Our Ancestral Mammals?
- Pelycosaurs possess several anatomical characters seen in mammalian skeletons
- Believed to be the ancestral stock of early mammal-like reptiles known as Therapsids.
- Permian to Triassic (EXTINCT)
- Therapsid Mammalian Characteristics
- Reduced number of bones in skull
- Enlargement of the lower jaw at the expense of more posterior jaw elements
- Double ball-and-socket articulation between neck and skull
- Primitive differentiation into incisors, canines, and cheek teeth
- Limb articulation into a more vertical alignment
- Ribs reduced in the neck and lumbar region