Last Wednesday… began our final phylum - Chordata
Arthropoda
Nematoda
Rotifera
Annelida
Mollusca
Nemertea
Platyhelminthes
Ectoprocta
Phoronida
Brachiopoda
Chordata
Echinodermata
Cnidaria
Ctenophora
Silicarea
Calcarea
“Radiata”
“Porifera”
Deuterostomia
Lophotrochozoa
Ecdysozoa
Bilateria
Eumetazoa
Metazoa
Ancestral colonial
flagellate
A taxon within the Deuterostomia, and the Bilateria…
After describing chordate characters, looked at
Cephalochordata & Urochordata
- do share defining chordate characters...
Chordate Phylogeny
Also introduced ‘Craniates’ (vague hierarchical rank)
– have a ‘head’ w. skull, more regulatory genes, gill slits &
neural crest cells
Class Myxini - Hagfishes
Predators of invertebrates & scavenge on dead
vertebrates in deep, cold marine waters
- about 30 spp.
- cartilaginous skull &
small brain but no jaws
or vertebrae
- ‘teeth’ of keratin
- small eyes, ears & single
nostril
- have lateral line system for detecting vibrations in water
& sensory tentacles
Famous for slime
production…
- but also (over)fished for
‘eelskin’ and meat
hagfish slime scone
-next step… evolution of vertebral column
Subphylum Vertebrata
Earliest vertebrates prob.
sometime in Cambrian
- initially some skeletal
elements above notochord
protecting nerve cord,
later replacing notochord
& surrounding nerve cord
- more gene duplication
(Dlx family) may have
allowed greater
complexity
Class Petromyzontida - Lampreys
About 40 spp. in marine & fresh water
- parasites of fish, attach with round sucking mouth
No jaws, but rasping teeth
on tongue create hole
Larvae are suspension
feeders in streams
Have notochord with
covering, plus cartilages
along nerve cord (no collagen)
Sea lampreys invaded the Great Lakes, feed on trout,
whitefish, etc.
Next characters… jaws & mineralized skeleton
Gnathostomes have true jaws,
hinged structures that enable
them to grasp food firmly
- jaws thought to have evolved by
modification of the arches that
previously supported anterior
pharyngeal gill slits.
- remaining gill slits no longer
required for suspension feeding
& remained as main site of
respiratory gas exchange.
Gill slits
Cranium
Mouth
Skeletal rods
More Gnathostome Characteristics
Another duplication of the Hox genes (now 4 clusters)
& other developmental genes
- forebrain enlarged, associated with enhanced vision
& smell
- mineralized axial skeleton, shoulder girdle, & 2 sets of
paired appendages
Gnathostomes appear in fossil record in mid-Ordovician,
about 470 MYA, & steadily diversified
Bothriolepis - Devonian
Dunkleosteus - Devonian
Class Chondrichthyes - Sharks & rays
Basking Shark
Manta Ray
Spotted Ratfish
Fairly diverse, w. about 460+ sharks,
460 rays & 30 chimeras
- many predators, but filter feeders
too
Shark & Ray Characteristics
Skeletons (mostly) cartilaginous, although ancestors
had mineralized skeleton
- well developed jaws, paired fins, streamlined
bodies, dorsal fin for stability
- water flow over gills
maintained by swimming,
or by pumping of
mouth/pharynx if still
- well-developed sight & smell,
also lateral line system &
electrical field detectors
Shortfin Mako
Next group is ‘Osteicthyes’, known traditionally as
‘the bony fishes’, but includes tetrapods …& us!
- a key character is lungs or derivative (e.g. swim bladder)
Class Actinopterygii – Ray-finned Fishes
Actinopterygii - Characteristics
About 27,000 spp., make up > half of all vertebrates
- throughout oceans, but 40% occur in fresh water
- most have bony (ossified) skeleton w. calcium phosphate
matrix
- skin usually with thin, flat bony scales (vs. tooth-like
scales of sharks)
- fins supported by long,
semiflexible rays
- mucus covering reduces drag,
prevents infection
- respire with 4-5 pairs of gills
in chamber w. protective
flap: operculum
Bluegill
Dorsal fin
Adipose fin
(characteristic of
trout)
Swim bladder
Spinal cord
Nostril
Cut edge of
operculum
Caudal
fin
Brain
Gills
Gonad
Heart
Urinary
Anus bladder
Liver
Kidney
Stomach
Pelvic fin
Anal fin
Lateral
line
Intestine
Body plan of a typical ray-finned fish – trout
Most have swim bladder for buoyancy (off digestive tract)
- originally, & often still, functioned as simple lung
‘Lobe-fins’ - Sarcopterygii
Originally referred to as lobe-finned fish, but
includes tetrapods now
- originated as aquatic forms in Devonian
- short linear bones & thick muscles support base
of fins, could be useful for moving in shallows
Eusthenopteron
Two aquatic classes of ‘lobe-fins’ survive:
1) Class Actinistia - coelacanths & relatives
Known from Devonian fossils, 2 spp. discovered off
Comoros Islands (1938) & Indonesia (1999)
- large deep-water predators
- move limbs alternately when swimming
2) Class Dipnoi - lungfishes
Six spp., in Australia, Africa (4), & South America
- live in rivers & swamps, African spp. at least must
use lungs
- some estivate in mud burrow in dry season
African lungfish
Next… evolution of limbs with feet
Tetrapods
Evolution of limbs that could support weight
about 365 MYA, e.g. Acanthostega
- still basically aquatic,
w. gills, tail fin, etc.
Acanthostega
Now many fossils
known of
transitional forms
between
lobe-finned fish
& tetrapods
Tetrapoda - the tetrapods
Tetrapods have feet with digits,
transfer muscular forces to
ground
Pelvic girdle fused to vertebral
column, allowing transfer of
forces to body
Neck to allow head to move
separately from body
No pharyngeal clefts in adults,
ears adapted for airborne sounds
Class Amphibia
Present day amphibians are highly specialized groups
not necessarily very similar to early tetrapods
- most dependent on H2O
at least part of life, or
in moist habitats
- moist skin important for
gas exchange, some
lack lungs
- skin may also be toxic
to varying degrees
Cobalt Poison Dart Frog
(b) The tadpole is
an aquatic
herbivore with
a fishlike tail and
internal gills.
(a) The male grasps the female, stimulating her to
release eggs. The eggs are laid and fertilized in
water. They have a jelly coat but lack a shell and
would desiccate in air.
(c) During metamorphosis, the
gills and tail are resorbed, and
walking legs develop.
Amphibian: ‘both lives’ - metamorphosis
- most species breed, develop as larvae in fresh water
but typically terrestrial as adults
Eastern Red-backed Salamander
Southern Gastric Brooding Frog
Exceptions to standard life cycle fairly numerous,
& sometimes bizarre…
Order Urodela - Salamanders
Over 600 spp., many in
eastern US
- some entirely aquatic, but
often live on land as
adults, or sometimes
throughout life
On land, most walk with
side-to-side bending of
body, may resemble
movement of early
terrestrial tetrapods.
Spotted Salamander
Order Anura – Frogs &Toads
By far largest order, w. > 6,000 spp., worldwide except
many ocean islands, cold climates
- specialized for hopping
on land (legs, urostyle)
but swim well too
- catch insects with sticky
tongue (attached in
front)
American Toad
Golden Mantella
Many species toxic, & may have aposematic
coloration (warning colors, easy to recognize &
learn)
Order Apoda - Caecilians
About 190 species, legless & nearly blind
- short tentacles on front of
head
- reduction of legs evolved
secondarily
- superficially resemble
big earthworms, most
burrow in moist soil in
tropical forests
- some South American
spp. live in ponds &
streams
Bannan Caecilian
The Amniotes
Amniota consists of mammals, turtles, crocodilians,
birds, tuataras & squamates (lizards & snakes), plus
many extinct groups
Extraembryonic membranes
Allantois. The allantois is a disposal
sac for certain metabolic wastes produced by the embryo. The membrane
of the allantois also functions with
the chorion as a respiratory organ.
Chorion. The chorion and the membrane of the
allantois exchange gases between the embryo
and the air. Oxygen and carbon dioxide diffuse
freely across the shell.
Yolk sac. The yolk sac contains the
yolk, a stockpile of nutrients. Blood
vessels in the yolk sac membrane transport
nutrients from the yolk into the embryo.
Other nutrients are stored in the albumen (“egg white”).
Amnion. The amnion protects
the embryo in a fluid-filled
cavity that cushions against
mechanical shock.
Embryo
Amniotic cavity
with amniotic fluid
Yolk (nutrients)
Albumen
Shell
Amniotic Egg - major derived trait
Amniotic egg allowed life
completely on land
- shell retains water, but
allows gas exchange
Great Tinamou eggs
Eggs of birds calcareous,
of most ‘reptiles’ more
leathery
Leatherback Turtle
hatching
- most mammals have lost
shell & retain egg in
uterus
echidna ‘puggle’
Other amniote traits...
- evolved less permeable skin with keratin & scales
(lost in mammals & only on legs of birds)
- lungs almost exclusively for respiration &
increasing use of rib cage to ventilate lungs
- adopted more elevated stance than earlier tetrapods
Komodo
Dragon
Saurischians
Dinosaurs
Lepidosaurs
Archosaurs
Synapsids
Diapsids
Reptiles
Ancestral
amniote
An Amniote Phylogenetic Tree
Class Testudinia - Turtles
Highly distinctive group - shell formed by bony
shields fused to vertebrae, ribs, clavicles, &
covered with horny scutes
- over 300 species, most associated
with water but some in arid areas
- respiration in water aided by
cloaca (common excretory &
reproductive opening) or pharynx
- relationships
uncertain, but
perhaps closer
to crocs &
birds
Ornate Box Turtle
Green Sea Turtle