Vertebrates

egan lecture 22

What are trends we see in animal evolution?

symmetry

• none > radial > bilateral

gastrulation

• no blastopore > protostome

digestive system

• none > gastrovascular cavity > complete digestive system

body cavities

• none > acoelomate . psuedocoelomate > coelomate

segmentation

• none > segmented (arthropods and annelids)

skeletons

• none > hydrostatic > exoskeleton

What are some trends in deuterostomia?

symmetry

• none > radial > bilateral

gastrulation

• no blastopore > protostome > deuterostome

digestive system

• none > gastrovascular cavity > complete digestive system

body cavities

• none > acoelomate . psuedocoelomate > coelomate

segmentation

• none > segmented (chordates)

skeletons

• none > hydrostatic > exoskeleton > endoskeleton

What are deuterostomes defined by?

shared developmental patterns and deep genetic similarities among echinoderms, hemichordates, and chordates

What do deuterostomes share?

gene regulatory networks and early embryological traits

Where did diversification occur in deuterostomes?

cambrian marine ecosystems, with chordate traits emerging soon after major increases in ocean oxygenation

what three clades make up deuterostomia?

echinoderms, hemichordates, and chordates

What body plans make up echinoderms?

adult radial symmetry, unique water vascular system for locomotion

What body plan makes up hemichordates?

bilateral symmetry, worm-like body with gill slits

What body plan makes up chordates?

Notochord, dorsal nerve cord, pharyngeal gill slits

What trait mostly makes up echinoderms?

They are slow-moving or sessile marine animals

Echinoderms appear to have what?

radial symmetry with multiples of five

• symmetry is not truly radial

• larvae have bilateral symmetry

How are echinodermata’s body made up?

An endoskeleton of hard calcareous plates; most are prickly

water vascular system, a network of hydraulic canals, branches into tube feet that function in locomotion and feeding

What body makes up hemichordates?

a bilateral symmetry, worm-like body, hydrostatic skeleton, pharyngeal gill slits, post-anal tail

What do chordata share with hemichordata?

pharyngeal gill slits, post-anal tail

What are chordate innovations?

notochord - provided stiff but flexible support rod

dorsal hollow nerve cord allowed centralized control of movement and sensory processing, a step beyond nerve nets and ladder-like systems

pharyngeal slits enabled efficient filter feeding and eventually respiratory specialization

What is a vertebrae?

a jointed skeleton that runs along the main axis of the body, forming a series of hard segments

What kind of clade is deuterostomia?

monophyletic

What distinguishes vertebrate characters?

• a bony cranium that protects a well-developed brain

• pair of eyes

• distinctive mouth for food capture and ingestion

• internal skeleton commonly mineralized by calcium phosphate

What evolutions has vertebrate skeletons undergone?

cartilage endoskeelton

bone re-enforced cartilage in endoskeleton

replacement of cartilage with bony tissue

What does the vertebrae replace?

the notochord with a jointed support structure, enabling more powerful locomotion and larger body sizes

What did neural crest cells give rise to?

jaws, teeth, skull elements, and sensory structures

What are the earliest-branching and most diverse vertebrate?

Fish & jawless fish

How did jaws evolve?

from modified pharyngeal arches, allowing grasping, biting, and niche expansion into active predation

What produced major clades (think sharks)?

paired fins + enhanced gills + stronger axial skeletons

What major clades are produced by paired fins, etc.?

placoderms, chondrichthyans, osteichythans

Radiation occurred in what time period?

The Devonian (Age of Fishes), a greenhouse world with complex reef systems and expanding predator-prey dynamics

What are gnathostomes?

they have jaws (hinged structures) with teeth used to grip and slice foods

How may have jaws evolved?

by the modification of skeletal rods supporting pharyngeal gill slits

What monophyletic group includes sharks and rays?

Cartilaginous fishes, formally known as chondrichthyes

What group do majority of vertebrates fall under?

Osteichythans; nearly all of which have a bony endoskeleton

What evolutionary innovations do fish have?

Moveable elements in jaws to specialize and diversify feeding

A swim bladder — gas filled sac that controls buoyancy

Kidneys to regulate water balance over a range of salinity

What are sarcopterygii?

lobe-fins, they arose in the silurian period

have pectoral and pelvic fins have rod-shaped bones surrounded by thick layer of muscle

paired fins of fish has anatomical similarity to legs of tetrapods

How are lobe-fins equipped to conquer land?

strong, limb-like bones in paired fins, tetrapods radiated during the late Devonian

What did the fins of lobe-fins evolve into?

limbs and feet of tetrapods by 365 million years ago

What is the life cycle of amphibians?

aquatic larval stage with gills and terrestrial adult stage with lungs (amphibians must reproduce in water)

How do amphibians develop?

Where are amphibian eggs laid?

in water or moist environments — fertilization is external

What are amniotic eggs?

amniotic membranes + shell allowed embryos to develop away water, breaking amphibian dependence of moist environments

What did amniotic eggs allow?

full terrestrialization of vertebrates during the Carboniferous—Permian

What must happen before the eggshell is produced?

fertilized internally — it can exchange gases while retaining water and permit long development times

What are the extraembryonic membranes?

amnion — protects embryo and is a fluid-filled cavity that cushions against mechanical shock

yolk sac contains a stockpile of nutrients

allantois is a disposal sac for waste produced by embryo

chorion and the membrane of the allantois exchange gasses between embryo and air

Where did early amniotes live?

warm, moist areas then expanded into more diverse environments

How do reptiles display adaptations in drier environments?

Scales contain keratin to protect skin for desiccation and abrasion

lay shelled eggs on land

internal fertilization

Where did early reptiles diversify?

in the permian, after the permian-triassic extinction

Mesozoic greenhouse climate + open niches favored what?

large-bodied, fast-growing dinosaurs that dominated terrestrial ecosystems

What are some innovations of dinosaurs?

upright posture, efficient lungs, egg adaptations

What is the earliest reptile?

diapsids

What lineages compose diapsids?

turtles

lepidosaurs: living tuataras, lizards, snakes

archosaurs: living crocodilians, birds, extinct pterosaurs and dinosaurs

What do birds belong to?

a group of bipedal dinosaurs called theropods

What is the earliest known bird?

the archaeopteryx

What weight-saving adaptations improve bird flight?

no urinary bladder

only one ovary

small gonads

toothless mouths

bones with honeycombed internal structure

What are the four models for origin of flight?

running

wing-assisted running

wing-assisted incline running

wing-assisted climbing

when did fins of lobe-fins evolve into limbs and feet?

~365 mya

When did the earliest reptiles, diapsids, live?

310 mya