Vertebrate Evolution & Diversity

Trends in Animal Evolution



Symmetry none



radial



bilateral

Is there evidence that any of these



Pattern of gastrulation

trends have reversed over time?

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

What are exoskeletons made of? …endoskeletons?

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

 

Deuterostomia

Phylum Echinodermata

• “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)

4.

-evidence from anatomical comparisons

2.

 Segmentation: muscles 1.

 arranged in

segmented

blocks 3.

Most with an internal and jointed skeleton, differing from that of

echinoderms

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.

   

Subphylum Urochordata – tunicates

Sessile marine animals, some are colonial

How have the slits been

Filter-feed, using pharyngeal slits

adapted for filter feeding?

Animal encased in a

tunic

of cellulose-like CHO Larvae (c) presents all four chordate characteristics (“tail chordates”)

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

 Small, burrowing animals, marine     Sensory tentacles around mouth

– “lancelets”

Adults possess all four chordate traits (“head chordates”) Suspension feeders

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

Muscles arranged in “chevron” (<<<<<) around notochord

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)

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

• • • • •

Which adaptations enabled: better maneuvering in the environment?

more active lifestyle?

larger size?

terrestrial lifestyle?

reproduction independent of water?

Fig 34.7

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 Gnathostome

“jaw” KEY: yellow = fibrous c.t.

blue = bone green = notochord 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

Fig 34.10

Evolution of vertebrate jaws

Class Chondrichthyes: sharks and rays

Lungs

Lungs or lung derivatives:

•in most fishes developed into

swim bladder

(buoyancy)

What are the respiratory organs in fish?

•in other organisms, lungs function in

gas exchange

C. Actinopterygii ray-finned fishes

These diverse fish have a swim bladder; it permits neutral buoyancy Fig 34.12a

Legs

better locomotion in terrestrial and shallow water environments

What does “tetrapod” mean?

Does this adaptation mean a completely terrestrial lifestyle?

Fig 34.17

Amphibians – frogs, etc.

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

“Reptiles”

 Keratinized skin; lungs; internal fertilization Fig 34.24

Feathers

an adaptation for

thermal insulation

and

flight

      Feathers

Class Aves – birds

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