Evolution and Characteristics of EARLY Vertebrates and Chordates

Vertebrates

Animals with a backbone and complex nervous system.

Vertebrae

Skeletal elements enclosing the spinal cord.

Cambrian explosion

Period when vertebrates first appeared, around 541 mya.

Haikouella

Primitive vertebrate lacking a skull but with a brain.

Conodonts

Earliest vertebrates with mineralized skeletal elements.

Chordates

Animals with notochord, including vertebrates and some invertebrates.

Notochord

Flexible rod providing skeletal support in embryos.

Dorsal nerve cord

Develops into the central nervous system.

Pharyngeal slits

Grooves in pharynx for gas exchange or development.

Post-anal tail

Tail extending beyond the anus, provides propulsion.

Cephalochordata

Lancelets, retain chordate features as adults.

Urochordata

Tunicates, resemble chordates only in larval stage.

Myxini

Jawless vertebrates with rudimentary vertebrae.

Hagfishes

Jawless scavengers with cartilaginous skulls.

Lampreys

Parasitic jawless fish with cartilaginous segments.

Cyclostomes

Clade of living jawless vertebrates, includes hagfishes.

Acanthodians

Early jawed vertebrates from Silurian and Devonian periods.

Gnathostomes

Jawed vertebrates, including all modern bony fishes.

Placoderms

Extinct armored vertebrates, earliest gnathostomes.

Chondrichthyans

Cartilaginous fish lineage, includes sharks and rays.

Cloaca

Common chamber for digestive and reproductive tracts.

Oviparous

Eggs hatch outside the mother's body.

Ovoviviparous

Embryo develops in uterus, nourished by yolk.

Viviparous

Embryo develops in uterus, nourished by placenta.

Actinopterygii

Class of bony fish with ray-finned structures.

Osteichthyans

Majority of vertebrates with bony endoskeletons.

Operculum

Bony flap covering gills in bony fish.

Ray-finned fishes

Fishes with fins supported by flexible rays.

Lobe-fins

Fishes with muscular fins for swimming and walking.

Coelacanths

Ancient fish thought extinct, known as 'living fossils'.

Lungfish

Fish capable of breathing air using lungs.

Tetrapods

Vertebrates with four limbs and necks.