Chordata

Urochordata

Craniata

Conodonts

Pterapsidamorphi

Cephalaspidomorphi

Gnathostomata

Acanthodii

Sarcopterygii

Actinopterygii

• larval "tadpole" stage which shows pharyngeal slits and arches,
• dorsal hollow nerve cord,
• notochord and post-anal muscular (unsegmented) tail.
• Adults of most members are sessile filter feeders with an expanded pharynx

• lack all traces of vertebrae, i.e., a backbone

• Early speculation that Conodonts formed their own phylum
• More recent fossil discoveries suggest Conodonts are true Chordates
• V-shaped muscle bundles
• Suggestion of a notochord
• Raylike fin elements
• Possibly related to the lineage that gave rise to hagfishes

• possess at least a simple backbone of neural arches
• presence of a cartilaginous (and often bony) head skeleton;
• relatively large brain plus a unique set of sensory and motor cranial nerves;

• much disagreement about the relationships of these jawless fishes
• first known vertebrates
• acellular dermal armor consisting of enamel, dentine, and bone
• occur first in marine deposits, then freshwater

Class Pteraspidomorphi (aka Diplorhina = possess two external nares)

• jawless filter feeders
• Possibly related to hagfishes

• 6 families, 50 genera recognized
• evolutionary trends in group toward reducing dermal armor
• development of lateral projections

• Covered with denticles rather than bony plates
• Hypocercal tail
• Some thelodonts deep bodied, had stomach

• Appear in the fossil record 100 million years after Pteraspids
• Cellular dermal armor (bone)
• Internal fin musculature
• Ossification of endoskeleton
• Development parallels lampreys (growing larval form metamorphoses to adult of fixed size)

• Six families - c. 100 species

II. Gnathostomata (monophyletic group of jawed vertebrates)

• Kill and grasp prey
• Reduce size of prey
• Move things e.g. nest building
• protection

Where did jaws come from? No intermediates between jawless and jawed fishes in the fossil record.

• Hypothesized to have arisen from 1^st (anterior) branchial arch
• Presence of adductor muscle to close mouth (ventillation expensive)
• Modified into palatoquadrate (upper jaw) and Meckel's cartilage (lower jaw)
• Palatoquadrate fused to neurocranium (autostylic attachment)
• 2^nd branchial arch (hyomandibular) modified to attach jaw to neurocranium (hyostylic)

• sister to all other gnathostomes
• Occur first in marine deposits, then freshwater
• Reduction in dermal armor
• 8-9 orders , 30 families, 50 genera
• include Dunkleosteus with craniovertebral joint
• possibly pelvic claspers

• Early fossils restricted to teeth, scales, and spines (Ceratotrichia - unseqmented, epidermal origin)
• Cartilagenous skeleton
• Single ventral nostrils on each side of head
• Pelvic fins modified as claspers
• Hybodontiformes - possible ancestors of modern sharks and rays hyostylic jaw attachment
• Tooth replacement a key feature that offered advantages over other gnathostomes

Appeared in fossil record 440 MYA

Two rows of ventral paired fins, each preceded by a spine

Fin-fold theory of paired fin origin

• Bony operculum
• Three otoliths
• Branchiostegal rays
• (super)Class Osteichthyes
• ossification of bone
• Scales
• Lepidotrichia fin ray are of dermal origin, probably derived from scales

• fins with bony, leg like supports
• swimbladder involved in respiration

• Three-lobed (diphycercal tail)
• External nostrils, no Choana

• African and South American lungfishes
• Extremely conservative in their evolution
• First indication of pulmonary artery

• Lobed fins - series of bony elements that link fins to pelvic/pectoral girdle
• Autostylic jaw suspension (like terrestrial vertebrates)
• Teeth have complex foldings of enamel

• Fins become limbs

• scales - reduction in heaviness
• branchiostegal rays - developed from bones in the floor of the mouth
• swimbladder - trend toward use primarily as a hydrostatic organ
• jaws - separation of premaxilla and maxilla, sliding of maxilla - suction feeding