Vertebrates

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Shark eggs are fertilized internally but embryos can develop in different ways:

Oviparous: eggs hatch outside the mother’s body.

Ovoviviparous: the embryo develops within the uterus and is nourished by the egg yolk.

Viviparous: the embryo develops within the uterus and is nourished through a yolk sac placenta from the mother’s blood.

The reproductive tract, excretory system, and digestive tract empty into a common cloaca.

Slide 24

The vast majority of vertebrates belong to a clade of gnathostomes called Osteichthyes.

Osteichthyes includes the bony fish and tetrapods.

They have a bony endoskeleton.

Aquatic osteichthyans are the vertebrates we informally call fishes.

Most fishes breathe by drawing water over gills protected by an operculum.

Fishes control their buoyancy with an air sac known as a swim bladder.

Slide 25

Anatomy of a trout - bony fish - Osteichthyes

Intestine

Adipose fin

(characteristic

of trout)

Cut edge

of operculum

Swim

bladder

Caudal

fin

Lateral

line

Urinary

bladder

Pelvic

fin

Anus

Dorsal fin

Spinal cord

Brain

Nostril

Gills

Kidney

Heart

Liver

Gonad

Anal fin

Stomach

Slide 26

Derived Characters of Tetrapods

Tetrapods have some specific adaptations:

Four limbs, and feet with digits

Ears for detecting airborne sounds.

In one lineage of lobe-fins, the fins became progressively more limb-like while the rest of the body retained adaptations for aquatic life.

For example, Acanthostega lived in Greenland 365 million years ago.

Slide 27

A Devonian era relative of tetrapods

Tetrapod

limb

skeleton

Bones

supporting

gills

Slide 28

Origin of Tetrapods

Ray-finned fishes

Coelacanths

Lungfishes

Eusthenopteron

Panderichthys

Tiktaalik

Elginerpeton

Metaxygnathus

Acanthostega

Ichthyostega

Hynerpeton

Amphibians

Greerpeton

Amniotes

PALEOZOIC

Carboniferous

Silurian

Devonian

Permian

0

265

280

295

310

325

340

355

370

385

400

415

430

Time (millions of years ago)

Slide 29

Amphibians

Amphibians (class Amphibia) are represented by about 6,150 species of organisms in three orders.

Amphibian means “both ways of life,” referring to the metamorphosis of an aquatic larva into a terrestrial adult.