4 key derived charactes of chordates?
- –a dorsal, hollow nerve cord
- –pharyngeal slits or clefts
- –and a muscular, post-anal tail.
orgins of tetrapods and identify some of their key derived traits
The first tetrapods descended from ancient lobe-finned fish: Skeletal structure of fins suggests that they could have assisted in movement on land. Oldest class of tetrapods, date back to late Devonian, about 365 million years ago. About 4000 species, only a remnant of the great Paleozoic radiation of labyrinthodonts, a subclass of primitive amphibians. Amphibians first appeared in the Paleozoic’s Devonian period, radiating extensively during the late paleozoic (Carboniferous period). Why did vertebrates come ashore? It may have been a need to escape drying water holes and to travel overland to others. Another reason could be the need to escape predation because the waters teemed with voracious fishes and the land was at first free of such perils. Or it may have been to exploit food (invertebrates).
- Origin of tetrapods: the ancestor of tetrapods may have resembled a lobe-finned fish.
3 key amniote adaptations for life on land?
–the amnion, chorion, yolk sac, and allantois
3 minor linageas of mammals. give example
- •Are egg-laying (or oviparous)
- •Only 2 species
- –Echidna (spiny anteater)
- Marsupials (kangaroos and allies):
- •Brief gestation, placenta forms
- •Embryo completes development in the marsupium (pouch)
- Placental mammals - Eutherians:
- –Young are nourished through a placenta.
- –Longer period of development in the womb.