VERTEBRATE ZOOLOGY
(VZ Lecture05 – Spring 2012 Althoff - reference PJH Chapter 3)

Radiation of Paleozoic Jawless Vertebrates:
__________________
•
Cover several distinct lineages
•
This “line” is extinct ( see Figs. 3-3, p46 & 3-4, p48
)
•
Characterized by presence of covering of dermal bone  carapace and/or smaller plates & scales ( see Fig. 3.7, p55
)
•
Jawless, probably feed on soft-bodied prey
•
Early demise probably linked to lowering of global sea levels during early Devonian that resulted in loss of coastal marine habitats
•
Extinction occurred in late Devonian

Pteraspids Cephalaspids

Fig. 3-3 p46 PJH

Transition from Jawless  _______ Vertebrates
Transition from Agnathous “condition” 
Gnathostome “condition”
•
Originally thought Gnathostomes radiated separately from the Agnathans…..
•
Now, recognized that Gnathostomes derived from Agnathans both in jaw development and other ways

1 st gill arch
AGNATHOUS CONDITON
1 st gill slit
1 st gill arch
GNATHOSTOME CONDITON
1 st gill slit
1 st gill arch

Jawed “condition” – greatest of all advances in vertebrates????
Jaws permitted ____________________________
•
Ability to grasp objects (food, mates, young, nesting materials, etc.)
•
Combined with teeth , ability to ___________, and/or ___________
•
______________ diet now possible

Transition from Jawless  Jawed Vertebrates
Transition from Agnathous “condition” 
Gnathostome “condition”

 Jaws that bear teeth

 Two sets of _________________ in the pectoral and pelvic regions

GENERALIZED “JAWED” VERTEBRATE
1
2.5
Fig. 3-9 p58 PJH
2

Generalized JAWED vertebrate
– ____ advancements
(numbering matches previous slide)

Jaws containing teeth

Pectoral and pelvic fins -- paired

.5
Jointed, brachial arches with internal gill rakers

Hypobrachial musculature: strong suction

Two distinct olfactory bulbs  two distinct nostrils

Original gill slit squeezed to form spiracle

Three semicircular canals in inner ear

Conus arteriosus: elastic reservoir in front of ventricle (i.e., heart)

Lateral line & spetum  dorsal from ventral portion

“elements” around the notochord & ribs

Generalized JAWED vertebrate
–other important developments
•
Presence of cerebellum & olfactory tract
•
Nervous system: insulating sheaths of myelin
(increased speed of nerve impulses), thicker spinal cord, nerves exiting the spinal column
•
Eyes have intrinsic musculature  accomodation of the lens
•
Sensory elements of lateral line covered by special scales
•
Distinct spleen, pancreas, and spiral valve within intestine
•
Gonads have distinct ducts to cloaca
•
Separate contractile proteins for muscles

Fins: Origin & Function
•
Probably originated from pre-jawed fishes that had
______________________ (that were immobile) — served same purpose (see below)
•
Function: ________ in 3dimensional space….water that is virtually incompressible. Force applied by one fin in one direction produces thrust in the opposite direction.
Tail fins —increased area—gives more thrust during propulsion
•
Advantages: _______________________________

Yaw
Pitch
Roll
Yaw
Pitch
Fig. 3-12 p62 PJH

Gnathosomes
CHONDRICHTHYANS
(cartilaginous fishes)
OSTEICTHYANS
(bony vertebrates)
Fig. 3-15p66 PJH

___________ Jawed Fishes (Paleozoic)
•
Placoderms – the armored fishes
•
Acanthodians – the stout-spined fishes

In summary: Jawless to Jawed Vertebrates
•
Step up in __________________ design
 Jaws: a) improved gill ventilation & bite prey
 Fins: improved locomotion/maneuverability
 True vertebrae
 Ribs
•
Step up in __________________ design
 Nerves: enclosed in myelinated shields
 Large, distinct cerebellum in hindbrain
 Two olfactory tracts
 Thicker spinal cord (with “gray matter”)
 Lateral line sensory system
 Third semicircular canal in inner ear

Gnathosomes
CHONDRICHTHYANS
(cartilaginous fishes)
OSTEICTHYANS
(bony vertebrates)
_____________