VERTEBRATE ZOOLOGY
(VZ Lecture06 – Spring 2012 Althoff - reference PJH Chapters 5 & 6)
Aquatic Vertebrates
PART I
RATFISHES
SPOTTED RATFISH
__________________: The Cartilaginous Fishes
• Unlike their agnathan ancestors, this line of
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vertebrates has had a loss of bone….but not a
major “step back” as cartilage is lighter and
perhaps allows for easier maneuverability
Unlike their ancestors, they have some
senses and systems that have reached higher
levels than some other extant vertebrates
Two major groups:
Neoselachii: sharks, skates, & rays
Holocephali: ratfishes
RATFISHES
~ 30 species
Evolutionary History & Specializations
• Unlike today, most early Chondrichthyes were
found primarily in freshwater habitats
SHARKS
Bursiform: _______________________
Progressive “changes” in _________________
Progressive “changes” in _________________
CLADOSELACHE
Fig. 5-1a p103 PJH
Caudal fin: externally symmetrical,
________________________… resembles
extant sharks
Fig. 5-1a p103 PJH
CLADOSELACHE
Other features of early Chondrichthyans
• Skin:
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few scales (still!)…around the eyes, some
fins and within mouth behind teeth
These teeth-like scales had cusps of dentine
covered with enamel-like substances that
enveloped over a pulp core. These types of
scales known as _______________ scales.
Presence of ___________ claspers of some
Paleozoic sharks indicated _________ fertilization
Some groups had symmetrical, deeply forked
tails—in modern day sharks, this is characteristic
of fast swimming oceanic species
Tooth replacement: 2 “designs”
Extant shark
Edestoids
(early
chondrichthian)
Fig. 5-2 p104 PJH
Other notes on early Chondrichthyan teeth
• Several teeth in a “tooth whorl” were functional
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simultaneously for some species
Some had ___________ teeth…well-adapted
to crushing shelled prey
Some had _____________________ for
cutting and shearing
Early Mesozoic: ELASMOBRANCHS
• Further evolution of chondrichthyans impacted
•
____________ and ________________ systems
Prominent genus was Hybodus (Hybodont sharks)
key “improvement”: _____________dentition
Anterior teeth: sharp cusps
Posterior teeth: crushing surface
_______________ sharks
1
2
Fig. 5-3 p105 PJH
Mouth is _______, not “underslung”
like extant sharks
Hybodont Sharks: Advances in Pectoral &
Pelvic Fins
• More mobile than broad-based fins of Paleozoic
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sharks
Both pairs of fins supported on narrow stalks
formed on 3 narrow, platelike basal cartilages that
replaced long series of basals seen in earlier sharks
Such an arrangement allowed the fin to be rotated
to a different angle as the shark swam up or down
Musculature & flex of fins also permitted curving
from front to back and base to tip….________ fins,
thus, could produce a) more anterior lift, b) aid in
turning, and c) stabilize straight-line movement
1) Reduction in the ___________
2) _________ made of proteinaceous
flexible fin rays that extended to
margin of fin
1a
2a
1
2
Towards Extant Sharks:
Advances in Caudal Fin design/function
• Reduced hypochordal lobe
• Division of radials
• Addition of flexible ceratotrichia
Extant Sharks, Skates, & Rays:
• Arose during early Triassic (Mesozoic)
• Most conspicuous difference between most
members of early radiations and extant sharks is
the rostrum (snout) that _______________ the
ventrally positioned mouth in most forms
Sharks
Rays
Skates
Sharks
• ~ 360 species of pleurotremate elasmobranchs:
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sharks with gill openings on the side of the
head
~ 60 of these species are ______________ that
include the dogfish (next lab D/E)…usually live
in cold, deep water
~ 280 of these species are ___________: the
dominant carnivores of shallow, warm oceansex.
whale shark, mackerel shark (including great
white), and hammerhead sharks
Extant Sharks:
common characteristics
• Cartilaginous vertebral ________ with notochord
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fitting in depressions on opposing faces of adjacent
vertebrae: allows flex side-to-side
Intercalary plates protect the spinal cord above
and major arteries and view below the centra
Placoid scales have single cusp and single pulp
cavity…reduces
turbulence in flow
of water next to
body surface
Extant Sharks:
advanced sensory systems
• Extraordinary sensitivity of the neuromast organs
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and ampullae of Lorenzini (Chapter 4) to electrical
potentials and _________ temperature differences:
influences detection of water masses of
different temps….influencing likelihood of
finding prey species
Chemoreception: pick up concentrations of
chemicals in concentrations as low as ________
Vision: at low light levels is excellent. Due to ____rich retina and cells containing crystals of guanine
located in choroid layer = _________________
__________ brain, proportionately, than most other
fishes….helpful for processing sensory input
Extant Sharks: Jaws designed for
consumption of large food items
____________ jaw suspension: allows for
movably to side of the cranium
____________ jaw suspension: allows for multiple
jaw positions & protrusion of upper jaw….allowing
different feeding opportunities
Fig. 5-5 p110 PJH
Elasmobranchs: Reproductive Strategy is
broad ranged
Nourishment of Embryos
• ___________trophy: Greek = egg + nourishment
yolk supplies most of the
nourishment of the embryo
• ___________trophy: Greek = mother + nourishment
female reproductive tract
provides most of the
nourishment of the embryo
•
Elasmobranchs: Reproductive Strategy
Reduction in ___________________________
Most produce few young (2-14 vs. 2-11
million eggs for Atlantic cod)
Move from “external” to “internal” fertilization
with special “grasping structures” for copulation
Biennial reproduction (probably)
Many have eggs stay and hatch in oviduct
Some exhibit ________ …. others _________
Eggs develop outside
body…
Eventual “live” birth…