The Chordata

Chapter 34

Chordate characteristics

Figure 34.1 Clades of extant chordates

Subphylum Cephalochordata: the lancelet Branchiostoma

Subphylum Cephalochordata: lancelet anatomy

Pikaia, the Burgess-shale chordate, with evident somites

Primitive chordates suggest first steps in their evolution ---

Figure 34.1 Clades of extant chordates

tunicates

The hagfish: a skull of cartilage and primitive eyes, but no jaw, no vertebrae

Figure 34.1 Clades of extant chordates

Figure 34.9 A sea lamprey

Origin of the jaw: transformation of skeletal rods accompanying gills

Figure 34.11 Cartilaginous fishes (class Chondrichthyes): Great white shark (top left), silky shark (top right), southern stingray (bottom left), blue spotted stingray

(bottom right)

Figure 34.12a Ray-finned fishes (class Actinopterygii): yellow perch

Figure 34.12b Ray-finned fishes (class Actinopterygii): long-snouted sea horse

Figure 34.13 Anatomy of a trout, a representative ray-finned fish

Figure 34.1 Clades of extant chordates

Figure 34.7 Phylogeny of the major groups of extant vertebrates

Figure 34.18 A coelocanth (Latimeria), the only extant lobe-finned genus

Figure 34.15 The origin of tetrapods

Figure 34.16 Skeleton of Acanthostega, a Devonian tetrapod fish

Transitional tetrapods -- feet in place but gills and tail with fin

Figure 34.17 Amphibian orders: Newt (left), frog (right)

Figure 34.18 “Dual life” of a frog (Rana temporaria)

Figure 34.22 A hatching reptile

Figure 34.24 Amniotic egg

Amnion: cushioning chamber for embryo

Chorion: gas exchange to exterior

Allantois: disposal sac

A phylogeny of amniotes

Figure 34.24 Extant reptiles: Desert tortoise (top left), lizard (top right), king snake (bottom left), alligators (bottom right)

Figure 25.16  Building a phylogenetic tree of dinosaurs

Figure 34.23 A phylogeny of amniotes

Figure 34.27x Archaeopteryx

Pelvises:Left, a saurischian carnivoreCenter, an ornithischian herbivoreRight, Archaeopteryx

Figure 34.27 Archaeopteryx, a Jurassic bird-reptile

Figure 34.28b Cretaceous theropod dinosaurs with putative feathers from Chinese sediments: Caudipteryx

Figure 34.29 A small sample of birds: Blue-footed boobies (top left), male peacock (top right), penguins (bottom left), perching bird (bottom right)

Figure 34.23 A hypothetical phylogeny of amniotes

Figure 34.32 Evolution of the mammalian jaw and ear bones

Figure 34.36 Hypothetical cladogram of mammals

Figure 34.32 Evolutionary convergence of marsupial and eutherian (placental) mammals

Figure 34.34 Prosimians:Lemurs

A phylogenetic tree of primates

The Cenozoic

Fig. 24.40: A timeline for some selected hominin species:

Australopithecus afarensis and the Laetoli footprints

3.24 mya 3.5 mya

The Cenozoic

Closeup --- Late Cenozoic

Fig. 24.40: A timeline for some selected hominin species:

Neanderthal and human

Mitochondrial DNA phylogeny for Homo sapiens and H. neanderthalis

HUMAN MIGRATIONS

Secondary contact between the last Neanderthals and humans