Prehistoric Models: Early Chordates

Chordata are animals that possess a notochord (a flexible rod formed of a material similar to cartilage), a dorsal nerve cord, pharyngeal slits, and a post-anal tail. For simplicity I have included the infraphylum Agnatha meaning “without jaws“. Agnatha are more commonly referred to as jawless fish in the phylum Chordata, subphylum vertebrata.

Kingdom: Animalia – Phylum: Chordata – Family: Pikaiidae – Genus: Pikaia

(extinct primitive chordata)

Cambrian Period

Genus and Species: Pikaia gracilens “Pika Peak”
Pronounced: Pik-ay-ah
Named by: Charles Walcott, 1911
Classification: Phylum: Chordata – Family: Pikaiidae
Time: Middle Cambrian Period
Locality: Canada, British Columbia – Burges Shale
Size: 38 millimeters or 1.5 inches
Diet: Unknown

Agnathajawless fish”

Domain: Eukaryota – Kingdom: Animalia – Phylum: Chordata – Infraphylum: Agnatha – Class: Pteraspidomorphi – Subclass: Heterostraci – Order: Pteraspiformes – Suborder: Pteraspidoidei – Family: Pteraspididae

(heterostracan vertebrates)

Devonian Period

Genus: Pteraspis ‭”Wing shield‭”
Pronounced: Teh-rass-pis
Species:P. crou chi, P. rostratus, P. stensioei
Named by: Agassiz – 1835
Classification: Phylum: Chordata – Infraphylum: Agnatha – Class: Pteraspidomorphi – Subclass: ‬Heterostraci – Order:‭ ‬Pteraspidiformes – Family:‭ ‬Pteraspidae
Known locations: Europe, particularly Belgium and Britain
Time period: Early to Middle Devonian (Lochkovian to Emsian)
Size: 20‭ ‬centimetres long
Diet: Carnivore

Domain: Eukaryota – Kingdom: Animalia – Phylum: Chordata – Infraphylum: Agnatha – Clade: Cephalaspidomorphi – Class: Osteostraci

(osteostraci meaning: “bony shells”)

Late Silurian to End Devonian

Genus: Cephalaspis‭ “Head shield‭”
Pronounced: Seff-ah-lass-pis
Species: C.‭ ‬lyelli
Named By: Louis Agassiz‭ ‬-‭ 1835 or ‬1846‭
Classification: Phylum: Chordata – Infraphylum: Agnatha – Class: ‬Osteostraci
Size: Approximately‭ ‬20‭ ‬to‭ ‬30‭ ‬centimetres long.
Known locations: Western Europe.‭ ‬North America
Time period: Early Devonian (Lochkovian to Emsian)
Diet: Carnivore/bottom feeder

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