Vertebrate Evolution & Diversity

Trends in Animal Evolution Symmetry none  radial  bilateral Pattern of gastrulation no blastopore  protostome  deuterostome Digestive system None  gastrovascular cavity  complete digestive system Body cavities acoelomate  pseudocoelomate  eucoelomate Segmentation none  segmented  fused segments Skeletons none  hydrostatic  exoskeleton  endoskeleton Is there evidence that any of these trends have reversed over time? What are exoskeletons made of? …endoskeletons? Consider animals with endoskeletons…Do they demonstrate evidence of segmentation? Describe the relationship.

Deuterostomia Phylum Echinodermata Phylum Chordata “spiny skinned” water vascular system What is this vascular system used for? Phylum Chordata named for the notochord What features of embryonic development are shared by members of these two groups? Do all chordates have a vertebral column?

Phylum Chordata (chordates) -evidence from anatomical comparisons Segmentation: muscles arranged in segmented blocks Most with an internal and jointed skeleton, differing from that of echinoderms 2. 1. 3. 4. Where is the notochord located, relative to the digestive tube and nerve cord? What is its function? Where is the nerve cord located in most non-chordate animals? What is the pharynx? How are these slits specialized in aquatic organisms? Describe the advantage of a muscular, post-anal tail.

Subphylum Urochordata – tunicates Sessile marine animals, some are colonial Filter-feed, using pharyngeal slits Animal encased in a tunic of cellulose-like CHO Larvae (c) presents all four chordate characteristics (“tail chordates”) How have the slits been adapted for filter feeding? Do you find evidence of segmentation in the larval form? Fig 34.3 What is the term used to describe the change in body form here?

Subphylum Cephalochordata – “lancelets” Small, burrowing animals, marine Adults possess all four chordate traits (“head chordates”) Suspension feeders Muscles arranged in “chevron” (<<<<<) around notochord Sensory tentacles around mouth How is the mouth modified to support this method of feeding? 2 cm Fig 34.4

The Origin of Vertebrates Cephalochordates are the closest living relatives of modern vertebrates. Larval urochordate exhibiting paedogenesis* cephalochordate ? * Early sexual maturity. Recall that genes that control development have played a major role in evolution (pg. 478)

? ancestral vertebrates, @ 530 mya The fossil record suggests an intermediate stage between cephalochordates and vertebrates, that lacks a cranium, but has eyes. Haikouella Some fossils from the same period exhibit all of the vertebrate characteristics. Myllokunmingia ? ancestral vertebrates, @ 530 mya

Fig 34.1 Fig 34.6 “Craniates” Neural crest: Unique group of embryonic cells that develop into various structures, including skeletal elements like the skull. Note that not all craniates have a vertebral column.

Phylogeny of Craniates Fig 34.7 Phylogeny of Craniates Which adaptations enabled: better maneuvering in the environment? more active lifestyle? larger size? terrestrial lifestyle? reproduction independent of water? Describe the blood circulatory adaptations that also support a more vigorous lifestyle.

Craniates The endoskeletons of craniates are made of cartilage or a combination of cartilage and bone (mineralized tissue). How are these tissues related in embryonic development? Hagfish Jawless fishes Lamprey KEY: yellow = fibrous c.t. blue = bone green = notochord Gnathostome “jaw” Adapted from Tree of Life web site, available at http://tolweb.org/tree?group=Craniata

Class Myxini – hagfish All marine. Mostly bottom-dwelling scavengers Slime glands along the sides for defense Cartilaginous skeleton; no jaws, no teeth, no appendages, no spine Mostly blind, well-developed sense of smell Why are hagfishes considered the most primitive of the craniates? Fig 34.8

Fig 34.1 Vertebrates Rigid spine of cartilage or bone gives support and anchors muscles better than the notochord.

C. Cephalaspidomorphi – lampreys Marine and freshwater environments Clamp round mouth onto flank of live fish, use rasping tongue to penetrate skin and ingest blood Cartilaginous skeleton, including spine No paired appendages, no jaws Fig 34.9

Jaws & Appendicular skeleton Jaws and mineralized teeth: firmly grip and slice food items, eat prey that had been inaccessible Paired appendages (fins): accurate maneuvering in aquatic environments

Evolution of vertebrate jaws Fig 34.10 Evolution of vertebrate jaws Class Chondrichthyes: sharks and rays Gill arches evolved into jaws (and inner ear bones)

Lungs Lungs or lung derivatives: in most fishes developed into swim bladder (buoyancy) in other organisms, lungs function in gas exchange What are the respiratory organs in fish?

C. Actinopterygii - ray-finned fishes These diverse fish have a swim bladder; it permits neutral buoyancy Marine and freshwater environments. -Ossified skeleton, skin often covered by flattened, bony scales. -Skin glands secrete a mucus that reduces drag during swimming. -Lateral line system and jaws; fins mainly supported by flexible rays. -A protective flap called the operculum covers the gills. -A variety of feeding mechanisms. -Part of the “bony fishes”. Fig 34.12a

Legs better locomotion in terrestrial and shallow water environments What does “tetrapod” mean? Does this adaptation mean a completely terrestrial lifestyle?

Amphibians – frogs, etc. Fig 34.17 Aquatic and terrestrial environments. -Ossified skeleton. -Moist skin, legs (secondarily lost in some species) and lungs (usually). -Skin glands secrete distasteful or poisonous mucus as a protection against predators. -Mostly carnivores. -Frogs, toads, salamanders, and newts. Still tied to water for reproduction, most abundant in damp habitats. -Many go through a metamorphosis.

Amniotes extraembryonic membranes (including the amnion) bring the aquatic environment onto land! enables completion of their life cycle on land first appeared in mammal-like reptile Do these animals demonstrate other adaptations to life on land?

Amniotic egg Fig 34.19

Keratinized skin; lungs; internal fertilization “Reptiles” Keratinized skin; lungs; internal fertilization Fig 34.24

Feathers an adaptation for thermal insulation and flight

Class Aves – birds Feathers Light and hollow skeleton; - other flight adaptations Legs and wings, most species move by flying Amniote egg with a shell Mouth developed into a beak A variety of feeding mechanisms

Bird flight Fig 34.26

Milk provides the ability to adequately nourish offspring

Mammalia – mammals Hair Mammary glands in the females to provide milk to young Legs lost in some (marine mammals) Amniote embryo, but does not develop a shell Variety of feeding mechanisms

Which vertebrate characteristic is most responsible for their success in relatively dry environments? Lungs and feathers were most important. That makes me best at taking advantage of the “dry” environment! The amniote egg was the most important adaptation to life on land. Nobody would have gotten anywhere without my cranium! Wait a minute! I can fly…I think it’s the ability to provide milk to offspring.

Summary General traits of reviewed phyla, subphyla and classes Important evolutionary trends in body plan: Endoskeleton: Echinoderms Notochord, nerve cord, tail, pharyngeal slits: Chordates Cranium, brain development, neural crest cells: Craniates Vertebral column: Vertebrates Jaws, 2 sets of paired appendages, mineralized skeleton and teeth: Chondrichthyes (sharks and rays) Lungs or lung-derivatives: Osteichthyes (bony fishes) Legs: Amphibians Amniote egg: Mammals, turtles, snakes and lizards, birds Feathers: Birds Milk: Mammals These trends helped animals adapt to different environments or exploit the same environment in a different manner