Week 5: Stages of Vertebrate Evolution

Phylogenies: Trees of Life Linnaeus: Linnaean System of Classification Based on similarity of traits Hierarchical: –Kingdom –Phylum –Class –Order –Family –Genius –Species K ings P lay C hess O n F ine G rained S and K eep P ots C lean O r F amily G et S ick

Kingdom:Animal Phylum:Cordate (Sub Phylum Vertebrate) Class:Mammal Order:Primate Family:Hominid (Super Family Hominoid) GeniusHomo SpeciesSapiens Humans are:

Inheritance or Convergence? Homologous = Similar because of common decent (share a recent common ancestor) – Inheritance. Analogous = Similar because of adaptation to the same or similar environmentally stable problem (Bird and Bat wings) - Convergence.

Phylogenies use homologous structures (traits) and must avoid analogous structures Present Past

YesNo Derived Trait Analogous Trait Ancestral Trait (last common ancestor) (convergence) (common ancestor of all 3)

Using Overall Similarity of Traits Leads to the Wrong Family Tree

Using Similarity of Derived Traits Leads to the Correct Family Tree

Systematics: the study that distinguishes ancestral from derived traits Ancestral Traits Appear earlier in embryonic development –Ontology recapitulates phylogeny Appear earlier in the fossil record –Older traits Seen in out-groups –If a trait is absence in one species but seen in other more distant lineages (tails)

Cordates Solid Notochord (no longer solid in humans) –Bilateral symmetry –Cephalization (head) –Tails –Endoskeleton –Three layer construction Ectoderm Mesoderm Endoderm Dorsal Nerve cord (spinal cord) Brachial arches (gills in fish, seen in embryonic development in people)

Vertebrates Bony Vertebral Column (backbone) Cranium (skull) Three part brain Olfactory organs (smell) Eyes Skin Internal Organs

Fish to Amphibian to Reptile Our Fish Heritage –Adaptive radiation associated with new niches created by higher levels of Oxygen in the environment (age of fish, Paleozoic 245 to 545 mya). –Backbones may have been an adaptation associated with swimming –Some early fish became larger and evolved skeletons, perhaps to avoid predation, –Evolved jaws to become predators Earlier fish had larger throats to suck up water with food in it (like filter feeders today) –Evolved fins for stability in water

Our Amphibian Heritage –Some fresh water fish evolved fleshy lobed fins (2 front & 2 back) to support their bodies out of water Adaptation to move from pond to pond –New theory is that lobed fins are adaptations to mangrove swamps which have lots of vegetation and roots to hide in but created difficulty for moving through, strong fleshy lobed fins allow for wiggling and pulling and pushing your way through this environment. –Air bladder evolve into lungs that allow early amphibians to live on land Adaptation for avoiding predators Opens up new niche (land plants and insects)

–Amphibians retain: Egg laying in water Free swimming stage of development with gills and fins – Living on land (no buoyancy) selects for changes in skeletons Thicker to support wait Limbs for walking Modern Amphibians stayed in early niche Close to water Insect eating

Our Reptilian Heritage –Age of Reptiles (Mesozoic Era, 245 to 264 mya) –Adaptive Radiation for new land niche Adaptations include: –No longer need to return to water to lay eggs –Egg with amniotic structure (hard shell & yoke) »Development of nesting (nest guarding) behaviors –No swimming stage (babies look like adults) –Dry skin –Internal fertilization »Development of mating behaviors

Our Mammalian Heritage –Age of Mammals (Cenozoic, 70 mya) –Adaptive Radiation into what niche? Maybe not special niche but vacated niche Reproductive advantage –Mammalian Adaptations Faster –Limbs moved under the body to get belly off the ground Warm blooded (endothermic), better circulatory system (heart) Hetrodontic (different teeth with different specializations Live Birth Lactation (parenting) Hair Good ears (inter ear) Better Brain (we will elaborate much more on this later in the course)