Vertebrate Evolution & Vertebrate Evolution & DiversityDiversity

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 endoskeletonWhat are exoskeletons made of? …endoskeletons?

Consider animals with endoskeletons…Do they demonstrate evidence of segmentation? Describe the relationship.

Is there evidence that any of these trends have reversed over time?

Deuterostomia Phylum Echinodermata

• “spiny skinned”• water vascular systemWhat is this vascular system

used for?

Phylum Chordata• named for the notochordWhat 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

1.

1. Where is the notochord located, relative to the digestive tube and nerve cord? What is its function?

2. Where is the nerve cord located in most non-chordate animals?3. What is the pharynx? How are these slits specialized in aquatic

organisms?4. Describe the advantage of a muscular, post-anal tail.

2.

3.4.

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”)

Fig 34.3

How have the slits been adapted for filter feeding?

Do you find evidence of segmentation in the larval form?

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

Fig 34.4

How is the mouth modified to support this method of feeding?

2 cm

The Origin of VertebratesCephalochordates 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)

The fossil record suggests an intermediate stage between cephalochordates and vertebrates, that lacks a cranium, but has eyes. Haikouella Haikouella

Myllokunmingia

? ancestral vertebrates, @ 530 mya

Some fossils from the same period exhibit all of the vertebrate characteristics.

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.

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

Adapted from Tree of Life web site, available at http://tolweb.org/tree?group=Craniata

KEY:

yellow = fibrous c.t.

blue = bone

green = notochord

Hagfish

Lamprey

Gnathostome

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?

Jawless fishes

“jaw”

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

Fig 34.8

Why are hagfishes considered the most primitive of the craniates?

Vertebrates

Fig 34.1

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 and mineralized teeth: firmly grip and slice food items, eat prey that had been inaccessible

Paired appendages (fins): accurate maneuvering in aquatic environments

Jaws & Appendicular

skeleton

Fig 34.10

Evolution of vertebrate

jaws

Class Chondrichthyes: sharks and rays

Lungs or lung derivatives:•in most fishes developed into swim bladder (buoyancy)

•in other organisms, lungs function in gas exchange

Lungs

What are the respiratory organs in fish?

These diverse fish have a swim bladder; it permits neutral buoyancy

Fig 34.12a

C. Actinopterygii - ray-finned fishes

better locomotion in terrestrial and shallow water environments

Legs

What does “tetrapod” mean?

Does this adaptation mean a completely terrestrial lifestyle?

Fig 34.17

Amphibians – frogs, etc.

•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

Amniotes

Do these animals demonstrate other adaptations to life on land?

Fig 34.19

Amniotic egg

Fig 34.24

“Reptiles” Keratinized skin; lungs; internal fertilization

an adaptation for thermal insulation and flight

Feathers

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

Fig 34.26

Bird flight

provides the ability to adequately nourish offspring

Milk

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?

Nobody would have gotten

anywhere without my cranium!

Lungs and feathers were most important. That makes me best at taking advantage of the “dry”

environment!

Wait a minute! I can fly…I think it’s

the ability to provide milk to

offspring.

The amniote egg was the most

important adaptation to life

on land.

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