Early VertebratesPART I

VERTEBRATE ZOOLOGY (VZ Lecture04 – Spring 2012 Althoff - reference PJH Chapter 3)

PALEOZOIC (late Carboniferous Period)

Terrestrialnonamniotetetrapods

open water

shallow lake

lakemargin

upland

earlyamniote

12

3 4

5

Fig. 7-5 p165 PJH

The most conspicuous new features of early vertebrates vs. nonvertebrate chordates:

A ______________ end that….A) contained a tripartite brain that

was B) enclosed by a cartilaginous cranium C) containing sense organs

Newly acquired pharyngeal musculatureto draw water into the mouth and

over the gills _________________ …not for filter feeding (i.e, acquiring food).

Early vertebrates

• Fossil deposits, ~540 MYAA) Myllokumingia (see next slide), China B) Haikouichthys China, too—same deposits

• Small, fish-shaped, ~ 3 cm long

• _____________ present

• _____________ present

• BUT _____ evidence of bone or mineralized scales

• Dorsal fin and ribbonlike pairs of ventrolateralfins

Fig. 3-1 p44 PJH

Myllokumingia

Astrapis

MYOMERES

DORSAL FIN

VENTROLATERAL FIN

Next….bone fragments in fossil

• Fossil deposits: Australia, Bolivia, North America A) Astraspis (North America “version”)

• Large, fish-shaped, ~ 12 - 35 cm long

• Armored – close-fitting, polygonal bony plates

• Eye “protection”

• Torpedo-shaped

• Jawless

Fig. 3-1 p44 PJH

Myllokumingia

Astrapis

BONY PLATES/SCALES

EYEPROTECTION

Conodonts – “microfossils”

• _____________ elements of true vertebrates

• < 1mm long

• Composed of apartite = __________________ compound characteristic of vertebrate tissue

• Much like _____________ (making it uniquely vertebrate tissue)

• Complete impressions of conodont animals with the “conodont” elements arranged within the pharynx thus confirming they were true vertebrates

Fig. 3-2 p45 PJH

Clydagnathus

Idiognathus

CONODONTS

________ elements(anterior)

_________Elements(posterior)

http://earthnet-geonet.ca/images/dynamic/ranges/conodonts.jpg

Fig. 3-3 p46 PJH

Origin of Bone & Mineralized Tissue

• Origin of mineralized tissues still somewhat uncertain

• Earliest known types are _______________ in structure than mineralized tissues of living vertebrates

• ____________ basic units of mineralized tissue…tooth-like elements formed “____” the skin (in dermal layer…unlike mollusks), then overlaid by epidermis

• No cells in adult form….acellular

__________________ of Mineralized Tissue?

• Defensive structures against predator attacks

• Design of bony tissue resulted in more complex function that merely protection:system of pores and small projections suggest ____________________

• Protective against predators & insulating coating around ______________________ that increased detection of prey

or

• Subsequent advantage: ______________ & _______________ deposition and subsequent mobilization

Which happened first?

• Vertebrates evolved first in freshwater or first in marine ecosystems?

--some early thinking was that because ofvertebrate kidney clearly being anadvantage in freshwater, that mostearly evolution took place there

--now, thinking is that _________ was “fortuitously preadapted” for fresh-water exist….that withstanding, “early” evolution likely was in

_______ ecosystems.

Evidence of marine origin

• Earliest vertebrate __________ found in marine sediments (paleontological evidence)

• All nonvertebrate chordates and deuterostome invertebrates (starfish, sea urchins,

etc.) are exclusive marine forms (comparative physiological evidence) where ____________ in same concentrations as seawater

Extant (“still living”) Jawless Fishes

• Two representatives: _________ & __________

• No specialized reproductive ducts…eggs and sperm released into coelum

• Primitive handling of drainage from kidneys (no duct-work, more through pores)

• External fertilization of eggs

• Considered ________________ a subset of “Agnathans” = jawless fishes preceeding conodonts and ostracoderms—both of which are extinct groups.

Fig. 3-4 p48 PJH

Hagfishes

• Family: Myxinoidea

• Two major genera: Eptatretus and Myxine

• ~ 40 species

• ~ 0.5 m in length, elongated

• ________ scales

• ________ vertebrae

• Simple kidneys

• Eyes degenerate, covered with thick skin

• Tooth-like plates

• Found nearly worldwide (except polar regions)

• Primarily deep-sea, cold-water inhabitants

Hagfishes

• _________________ ….slime glands produce gelatinous mess that is a deterrent to predators. After threat gone, makes a knot to scrap off mass of mucus, then sneezes sharply to blow nasal passage clear.

• ______________ find food by sense of ______

• Also, use the “tying the knot” routine to brace themselves against their prey, mouth attaches to part of prey to tear off the flesh with pinching grasp….enough to expose soft coelomic cavity of prey.

• Digestion accomplished in a mucoid bag secreted by gut…nutrients diffuse out, then absorbed

Fig. 3-5 p49 PJH

Lampreys

• Family: Petromyzontoidea

• Two major genera: Petromyzon and Lampetra

• ~ 40 species

• ______ scales, up to 1 m in length

• ___ vertebrae, but “vertebral structures” (arculalia)that are ________________ skeletal

elements

• Kidneys – much _____________ over hagfishes, enables better regulation of ions,

water, and nitrogeneous waste…

• Exist in ___________ of salinities

• Found mostly in northern latitudes - temperate

• Most are _________________ live in sea/lake, breed in rivers or streams

Lampreys

• __________ on other fishes (usually bony fishes, but sometimes mammals = whales & porpoises)

• Attach to host by suction

• Oral gland secretes anticoagulant that prevents host’s blood from clotting

• Thus, bulk of lamprey’s diet is ___________ of the hosts

• _______, straight digestive tract…_______ “food”, _______ “digestion”

• Like many parasites, they don’t end up killing the host…only weaken them

Also see….Fig. 4-5 p30 FS

LAMPREYoral region

Tooth-like organs

(origin: ectoderm)

Lampreys

• Females produce hundreds to thousands of eggs, spawn with males after constructing a nest. Fertilized eggs get “surrounded” by larger rocks that create an eddy, dropping sediment over the eggs

• Adults die after breeding once

• Larvae hatch in about 2 weeks….known as Ammocoets, they float downstream, burrow in mud or sand and spend about the next ____ years as ______________________.

• Finally, metamorphosis into juvenile and become parasitic

Lampreys: Conservation Concern

• May have been indigenous to Lake Ontario….but not in any other Great Lakes until _________

• Devasting to sport and commercial fish populations in the Great Lakes—especially Lake Erie by the 1940s.

• Huge efforts in past 50-60 years to curb their numbers:

chemical lampricideselectrical barriers

mechanical weirs

Lake trout

Sea lamprey