Early VertebratesPART II

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

• Originally thought Gnathostomes radiated separately from the Agnathans…..

• Now, recognized that Gnathostomes derived from Agnathans both in jaw development and other ways

Transition from Agnathous “condition” Gnathostome “condition”

GNATHOSTOME CONDITON

AGNATHOUS CONDITON

1st gill arch

1st gill slit

1st gill arch

1st gill arch

1st gill slit

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

Jaws that bear teeth

Two sets of _________________ in the pectoral and pelvic regions

Transition from Agnathous “condition” Gnathostome “condition”

Fig. 3-9 p58 PJH

GENERALIZED “JAWED” VERTEBRATE

1

2

2.5

Generalized JAWED vertebrate – ____ advancements(numbering matches previous slide)

Jaws containing teeth

Pectoral and pelvic fins -- paired

Jointed, brachial arches with internal gill rakers

Hypobrachial musculature: strong suction

Two distinct olfactory bulbstwo 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 & spetumdorsal from ventral portion

“elements” around the notochord & ribs

.5

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 musculatureaccomodation 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 3-dimensional 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: _______________________________

Fig. 3-12 p62 PJH

Pitch

Yaw Pitch

YawRoll

Gnathosomes

Fig. 3-15p66 PJH

CHONDRICHTHYANS(cartilaginous fishes)

OSTEICTHYANS(bony vertebrates)

___________ Jawed Fishes (Paleozoic)

• Placoderms – the armored fishes

• Acanthodians – the stout-spined fishes

• Step up in __________________ design

• Step up in __________________ design

In summary: Jawless to Jawed Vertebrates

Jaws: a) improved gill ventilation & bite preyFins: improved locomotion/maneuverability True vertebraeRibs

Nerves: enclosed in myelinated shieldsLarge, distinct cerebellum in hindbrain Two olfactory tractsThicker spinal cord (with “gray matter”)Lateral line sensory systemThird semicircular canal in inner ear

GnathosomesCHONDRICHTHYANS(cartilaginous fishes)

OSTEICTHYANS(bony vertebrates)

_____________