Updated 21 January 2005
Subphylum Vertebrata - survey chordates
(2-3 lineages of protochordates)
a.
small (1-3”), wormlike, marine, burrowing, sexually
dimorphic
b.
all chordate characters; notochord extends entire length;
similar circulatory and digestive systems to vertebrates
B.
Urochordata (slide 2)
a.
tunicates (“sea-squirts”), small, marine, brightly colored;
larvaceans (planktonic), adults sac-like (sessile filter feeders)
b.
chordate characters in larvae only (metamorphosis); notochord
confined to tail region
C.
Hemichordata (problematic) (slide 3)
a.
2 groups; acorn worms (sedentary burrowers), pterobranchs
(sessile filter feeders)
b.
no structures homologous to DHNC or notochord
c.
links to both chordates and echinoderms
What lineage is
the closest living relative of chordates?
-methodology:
compare fundamental embryonic development (conservative)
-2 groups
coelomates:
|
|
Deuterostomia |
Protostomia |
|
blastopore |
Anus |
Mouth |
|
Cleavage |
Indeterminant |
Determinant |
|
|
Radial |
Spiral |
|
Skeleton |
Mesoderm |
Ectoderm |
|
|
Chordates,
echinoderms |
Most everything
else |
Conclusion?
echinoderms closest living relatives (share common ancestor; not ancestral);
also similarities in larvae, mesoderm and coelom formation, blood proteins,
muscle chemistry
________________________________________________
Vertebrate Survey
Vertebrate diversity through geologic
time; (slide 4); recent
vertebrate species diversity
|
|
Known 1995 |
Projected 1995 |
Known 2000 |
|
Fishes |
20,000 |
40,000 |
23,250 |
|
Amphibians |
4500 |
6000 |
4780 |
|
Reptiles |
6400 |
7500 |
7800 |
|
Birds |
9100 |
950,000 |
9702 |
|
Mammals |
4000 |
4100 |
4675 |
Savage, J.M. 1995. Systematics and
the biodiversity crisis.
Bioscience 45:673-679.
Uetz, P. 2000. How many reptile
species? Herpetological
Review 31:13.
Important! Remember that Linnaean
groupings are determined by man for his convenience; they do not necessarily
reflect evolutionary history!
I. Pisces/Fish (primary aquatic;
non-amniote)
*Conodonta (slide 5)
A.
extremely common; mostly small, some up to 30 cm; no
appendages
B.
mineralized feeding apparatus
*Ostracoderms (slide 6)
A.
many fossils worldwide (extensive dermal armor); small minnow-sized;
no girdles or limbs (paired appendages derived from skin)
B.
2 lineages, relationships poorly known (bottom dwellers,
active swimmers)
Cyclostomes
(slide 7)
A. Elongate eel-like, median fins, no dermal
bone, rasping tongue (no true teeth); 2 lineages
1.
Scavenger; mucous glands; single median nostril
2.
Body fluids isotonic with sea water (physiologically like
invertebrates)
C.
Petromyzontiformes (lampreys)
1.
vertebrate parasites; ammocoetes larvae (filter feeder)
Superclass Gnathostomata - jawed
vertebrates
Class *Placodermi (“plate skin”);
slide 8
A.
Many fossils worldwide (heavily armored); little internal
bone; paired girdles and fins, jaws probably resulted in more active lifestyles
(cf ostracoderms)
B.
9 lineages (relationships poorly known), arthrodires best
known (up to 9m!)
C.
Evolutionary dead end (not closely related to either the
cartilaginous or bony fishes that replaced them!)
Class
Chondrichthyes (“cartilagenous fishes”); slide 9
A.
Subclass Elasmobranchii (“plate gill”) separate gill
openings (no operculum)
1.
No internal bone, reduced external bone (placoid scales);
pelvic claspers
2.
Teeth derived from scales (many fossils of shark teeth, but
little else)
3.
Large livers with buoyant oils; spiracle (reduced 1st
gill slit)
4.
Not primitive (younger than bony fish)
5.
4 lineages; sharks (active predators), up to 20m; rays
(bottom dwellers, mollusks, large pectoral fins)
B.
Subclass Holocephali
1.
Chimaeras (ratfish – tail)
2.
Large head, colorful, no scales, operculum
3.
Broad crushing teeth
Class *Acanthodii (“spiny forms”); slide 10
A.
Common, mostly small (minnow-sized, some up to 2 m)
B.
Up to 5 pair fins supported by spines
C.
No enamel on teeth; reduced dermal armor
Class
Osteichthyes (“bony fishes”)
Highly ossified
internal skeleton, reduced external bone (thin bony scales), pectoral girdle
connected to skull, swim bladder (in many)
A.
Subclass Actinopterygii (“ray finned fishes”)
a.
ganoine (form of enamel) in scales
b.
3 lineages; recent Polypterus (obligate air
breather), sturgeon (to 8m; roe) and paddlefish (plankton feeders); relicts of
an early radiation
2.
Superorder Neopterygii
b.
Amiiformes (bowfin) ganoine; relict of an early radiation; slide 11
c.
Teleostei (higher bony fishes)
1)
highly ossified (especially vertebrae); increased jaw
mobility; very thin bony scales (no ganoine)
2)
symetrical homocercal tail (cf heterocercal of many earlier
fishes) + swim bladder
3)
>40 recent orders (still radiating; most successful
recent vertebrates); diverse (slide 12)
4)
trends (primitive®advanced teleosts); cf trout and bass
a)
pelvic girdle moves forward
b)
greater ossification
c)
swim bladder loses connection with gut
d)
fin ray number reduced
e)
increased jaw mobility and protrusion: jaws shorten, maxilla
excluded from gape, lose teeth, premaxilla independently mobile (slide 13)
B.
Subclass Sarcopterygii (“fleshly finned fishes”)
1.
Superorder Crossopterygii (“lobefins”); slide 14
a.
not very diverse; important because one lineage
(*Rhipidistia) is thought to be ancestral to tetrapods