Recent animal phylogenies use molecular data and result in a different looking tree Tree built using protein or gene sequences Need to use a gene(s) that is found all animals Different genes give different results Genome sequencing has allowed the use of large amounts of molecular data

25_2 Molecular phylogeny suggests that key body transitions can occur repeatedly Changes to tree are in protostomes Body cavities appear to have evolved several times Suggest that mode of growth is a conserved characteristic

Traditional: - Emphasis on coelom - “Cumulative” relationship Molecular: - Emphasis on mode of growth - Chordates equally related to all protostomes Major group relations are the same - protostome relations change

Which tree do you think is correct? Why?

Animals are morphologically diverse but use many of the same genes to pattern their bodies Genes that regulate the expression of other genes (transcription factors) are highly conserved between animals Code body parts and regions that develop into morphologically diverse structures p.495

Cambrian explosion -Many animal phyla appear in the fossil record between MYA -Possible that evolution of modern phyla (and extinct phyla) was very rapid -Fossils from this time and before are rare, may be artifact of fossilization Extinct phylumTrace annelid fossil Arthropod - trilobite Chordate

Basal vertebrates - agnathans Fig 26_10 -No jaws -Initially no paired appendages -Radiated into several groups -Arose 500 MYA -Represented by 2 groups today, Lampreys and Hagfish

The evolution of jaws and paired appendages were key events in vertebrate evolution Fig 26_11 Paired fins allow greater control of movement Jaws allow grasping of prey, range of feeding behaviors

Jawed fishes radiated into several groups, survived by sharks and bony fish -Gnathostomes replaced most of the agnathan groups -Extinct early jawed fish had extensive skeletons, some were very large -Sharks and bony fish are hypothesized to be more efficient swimmers, able to out compete early gnathostomes during mass extinction events -Bony fish are a very successful group

Bony fish form 2 groups: “Ray-finned” and “Lobe-finned” fishes -Ray finned fishes are very diverse, no musculature in fins -Lobe finned fishes survived by 6 species, have muscles in fins Lobe finned fishes are the ancestors of terrestrial vertebrates (tetrapods)

Lobe finned fishes colonized land ~350 m.y.a. and gave rise to amphibians which dominated land for ~100 m.y. -Amphibians have legs, lungs, pulmonary vasculature -Survived by 3 groups (frogs, newts, cecilians) -Most living members require water for reproduction -Derived extinct members were fully terrestrial, large

Reptiles appeared ~300 M.Y.A. -Fully terrestrial with water-tight (amniotic) eggs -Anatomy could support fast movements (improved breathing mechanics, legs adapted for running) -Radiated into 3 groups: Pelycosaurs (extinct), Therapsids (became mammals), archosaurs (crocodiles, dinosaurs, birds) A Pelycosaur, early reptile

Archosaurs - Crocodiles and Birds, extinct forms include dinosaurs, pterosaurs, icthyosaurs…… Fig 26_19 Early archosaur Dinosaurs ~220 mya - 65 mya -Most diverse and successful group of land vertebrates -Survived by birds

Birds are the descendents of dinosaurs Archeopteryx - earliest known bird (~150 mya) -Birds arose from predatory dinosaurs ~150 mya -Share many of the same anatomical features (feathers) -Within a few million years had become much more “bird-like” (skeleton adapted for flight)

Therapsid reptiles became mammals -Mammals arose around the time of dinosaurs (220 mya) -Mammals were a relatively minor group until dinosaur extinction -Radiated, fill niches of dinosaurs -3 groups of mammals (monotremes, marsupials, placentals) All have hair, produce milk, have inner ear bones (derived from jaw) Typical early mammal

Fig 26_9 Age and relationships of extant vertebrates