Basal Chordates — The Earliest Members of the Phylum Chordata
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Cast of Pikaia gracilens is a well known member of the Phylum Chordata, but diverged before the origin of true vertebrates. It has a notochord and segmented muscles like other members of the phylum.
Taxonomy: Phylum Chordata
Burgess Shale, British Columbia, Canada
Middle Cambrian Period, 508 Ma
Chicago Field Museum
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Group of Yunnanozoon lividum, an early stem-vertebrate, sometimes known as Haikouella lanceolata.
Taxonomy: Phylum Chordata
China
Early Cambrian, Period, 520 Ma
Chicago Field Museum
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Tully Monster fossil, Tullimonstrum gregarium. This species has long puzzled scientists with its strange probosis ending in a pincer-like structure, eyes at the ends of stalks, tail fin, and segmented muscles. Recently, detailed studies of some specimens have suggested that it may be a vertebrate related to modern lampreys (jawless, unarmored fish). This view is not without its dissenters, however. Three examples are shown.
Taxonomy: Chordata?; Vertebrata?; Cyclostomata?; Petromyzontiformes?
Mazon Creek, IL
Middle Pennsylvanian Epoch, Carboniferous Period
Chicago Field Museum
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Life model of a Tully Monster, Tullimonstrum gregarium. This model may be oriented upside down.
Taxonomy: Chordata?; Vertebrata?; Cyclostomata?; Petromyzontiformes?
Mazon Creek, IL
Middle Pennsylvanian Epoch, Carboniferous Period
Wyoming Dinosaur Center, Thermopolis
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Ostracoderms — Armored Jawless Fishes
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Oostracoderm is an informal name for various primitive jawless fishes with dermal (skin) armor. Although their armor plates were bone, their internal skeleton was cartilage.
Cast of Protaspis transversa.
Taxonomy: Vertebrata: "Ostracodermi": Pteraspidomorphi: Heterostraci: Pteraspidida
Wyoming
Devonian Period
Denver Museum of Science & Nature
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Cardipeltis bryanti fossil.
Taxonomy: Vertebrata: "Ostracodermi": Pteraspidomorphi: Heterostraci: Cardipeltidae
Wyoming
Devonian Period
Chicago Field Museum
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Cast of Drepanaspis gemuendenensis.
Taxonomy: Vertebrata: "Ostracodermi": Pteraspidomorphi: Heterostraci: Psammosteidae
Germany
Early Devonian Period, 400 Ma
Wyoming Dinosaur Center
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Cast of Drepanaspis sp.
Taxonomy: Vertebrata: "Ostracodermi": Pteraspidomorphi: Heterostraci: Psammosteidae
Germany
Devonian Period
Chicago Field Museum
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Fossil Pteraspis crouchi head shield.
Taxonomy: Vertebrata: "Ostracodermi": Pteraspidomorphi: Heterostraci: Pteraspididae
Herefordshire, England
Devonian Period
Chicago Field Museum
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Life model of Jamoytius kerwoodi.
Taxonomy: Ostracodermi; Anaspsida
Silurian Period
Museum of Ancient Life, Utah
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Life model of Drepanaspis gemuendenensis.
Taxonomy: Ostracodermi; Heterostraci; Pteraspidiformes
Early Devonian Period; Europe
Wyoming Dinosaur Center
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Life model of Protaspis transversa.
Taxonomy: Ostracodermi; Heterostraci; Pteraspidiformes
Early Devonian Period; Montana
Museum of Ancient Life, Utah
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Life model of Cephalaspis powriei.
Taxonomy: Ostracodermi; Osteostraci; Antiarchi
Early Devonian Period, Scotland
Museum of Ancient Life, Utah
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Life model of Pteraspis sp.
Taxonomy: Ostracodermi; Heterostraci; Pteraspidiformes
Early Devonian Period; Europe
Wyoming Dinosaur Center
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Placoderms — Armored Jawed Fishes
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In addition to having movable jaws, placoderms differed from their ostacoderm ancestors in having 2 sets of paired fins. Their armor was mostly restricted to the head and midbody.
Pterichthyodes milleri.
Taxonomy: Vertebrata: Placodermi; Antiarchi; Pterichthyodidae
Scotland
Early Devonian Period, 400 ma
Wyoming Dinosaur Center
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Bothriolepis canadensis was a benthic (bottom dwelling) feeder. The back half of the fish lacked armor and was thus not preserved.
Taxonomy: Vertebrata: Placodermi; Antiarchi; Bothriolepididae
Ontario, Canada
Late Devonian Period, 365 Ma
Black Hills Institute Museum, South Dakota
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A trio of Bothriolepis canadensis.
Taxonomy: Vertebrata: Placodermi; Antiarchi; Bothriolepididae
Quebec, Canada
Devonian Period
Chicago Field Museum
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Bothriolepis canadensis with 3-dimensionally preserved armor.
Taxonomy: Vertebrata: Placodermi; Antiarchi; Bothriolepididae
Quebec, Canada
Devonian Period
Chicago Field Museum
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Coccosteus cuspidatus was a pelagic predator. Note the preservation of the internal skeleton (vertebral column and fin rays) in addition to the dermal armor.
Taxonomy: Vertebrata: Placodermi; Arthrodira; Coccosteidae
Scotland
Middle Devonian Period, 385 Ma
Wyoming Dinosaur Center
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Coccosteus decipiens fossil.
Taxonomy: Vertebrata: Placodermi; Arthrodira; Coccosteidae
Scotland
Devonian Period
Chicago Field Museum
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Dunkleosteus terrelli (cast of skull) was the largest predator on earth up to that time, reaching 8 m long. It lacked true teeth but had large, sharp bony plates lining its jaws.
Taxonomy: Placodermi; Arthrodira
Cuyahoga Co., OH
Middle Devonian Period
Denver Museum of Science & Nature
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Life model of Coccosteus sp.
Taxonomy: Placodermi; Arthrodira
Middle-late Devonian Period
Wyoming Dinosaur Center
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Life model of Gemuendina stuertzi.
Taxonomy: Placodermi; Rhenanida
Early Devonian Period; Europe
Wyoming Dinosaur Center
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Life model of Pterichthyodes sp.
Taxonomy: Placodermi; Antiarchi
Europe
Devonian Period
Wyoming Dinosaur Center
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Life model of Bothriolepis sp.
Taxonomy: Placodermi; Antiarchi
Late Devonian Period
Wyoming Dinosaur Center
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Life model of Bothriolepis sp.
Taxonomy: Placodermi; Antiarchi
Late Devonian Period
Museum of Ancient Life, Utah
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Life model of Ctenurella sp. This species was viviparous (live-bearing).
Taxonomy: Placodermi; Ptyctodontida
Late Devonian Period; Germany
Museum of Ancient Life, Utah
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