Vertebrate Evolution

1
Vertebrate Evolution Diversity
2
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? Con
sider animals with endoskeletonsDo they
demonstrate evidence of segmentation? Describe
the relationship.
3
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?

4
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.

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.

5
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?
6
Subphylum Cephalochordata lancelets

• Small, burrowing animals, marine
• Adults possess all four chordate traits (head
  chordates)
• Suspension feeders
• Muscles arranged in chevron (ltltltltlt) around
  notochord
• Sensory tentacles around mouth

How is the mouth modified to support this method
of feeding?
Fig 34.4
2 cm
7
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)
8
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, _at_ 530 mya
9
Craniates
Fig 34.1
Fig 34.6
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.
10
Phylogeny of Craniates
Fig 34.7

• 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.

11
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?groupCraniata
12
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
13
Vertebrates
Fig 34.1
Rigid spine of cartilage or bone gives support
and anchors muscles better than the notochord.
14
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
15
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
16
Evolution of vertebrate jaws
Fig 34.10
Class Chondrichthyes sharks and rays
17
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?
18
C. Actinopterygii - ray-finned fishes
These diverse fish have a swim bladder it
permits neutral buoyancy
Fig 34.12a
19
Legs
better locomotion in terrestrial and shallow
water environments
What does tetrapod mean? Does this adaptation
mean a completely terrestrial lifestyle?
20
Amphibians frogs, etc.
Fig 34.17
21
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?
22
Amniotic egg
Fig 34.19
23
Reptiles

• Keratinized skin lungs internal fertilization

Fig 34.24
24
Feathers
an adaptation for thermal insulation and flight
25
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

26
Bird flight
Fig 34.26
27
Milk
provides the ability to adequately nourish
offspring
28
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

29
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 flyI think its the
ability to provide milk to offspring.
30
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