Devonian : Life in the Devonian Seas

Leaf and wood of Archaeopteris.
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Placoderm
Ammonite
Shark
Brachiopods
Trilobites
Centipede
Lobe-finned fish
Amphibian skull

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Life in the Devonian Seas
Invertebrate and plant life teemed in the vast ocean that covered much of the globe. Ammonoid cephalopods first appeared in the Early Devonian, along with siliceous sponges. Brachiopods (which arose in the Cambrian) reached their maximum diversity as did hundreds of rugose coral species. Extensive reef-building produced some of the largest reef complexes in Earth’s history. Trilobites are also known from this time, but most groups had disappeared by the end of the Devonian, leaving only a select few genera to continue on through the Carboniferous and Permian.

The first radiation of vertebrates with jaws (gnathostomes) occurred during the Devonian, which is why it is sometimes known as the “Age of Fishes.” Although they first appeared in the Silurian, spiny acanthodians and armored placoderms reached their peak diversity during the Devonian and began to dwindle in numbers later in the Paleozoic. Some, like the giant Dunkleosteus, reached nearly three meters in length and were menacing marine predators. Placoderms had no teeth, instead relying on self-sharpening bony plates in their jaws that performed the function of teeth. Chondrichthyan (cartilaginous) fishes, such as sharks, were Ordovician survivors that thrived during the Devonian. A few shark scales have been dated to the Late Ordovician, but the earliest shark teeth are Early Devonian, and the first relatively modern-looking sharks had evolved by the Middle Devonian. The first true bony fishes (osteichthyans) appear as well, as both lobe-finned (sarcopterygians) and ray-finned (actinopterygians) forms. The lobe-finned fish are of particular interest because they gave rise to the first land vertebrates, around 360 million years ago.

Overview | Life in the Devonian Seas | Terrestrial Habitats Conquered
The Devonian Extinction | Climate and Tectonics during the Devonian

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cephalopod

Any mollusk of the class Cephalopoda, which includes squids, octopus, and ammonites. They are characterized by the tentacles attached to their heads.

sponge

Any member of the phylum Porifera, which are multicellular, colonial, aquatic invertebrates. Sponges are among the simplest multicellular animals, and they are known as fossils throughout the Phanerozoic.

brachiopod

Any member of a phylum of marine invertebrate animals called Brachiopoda. Brachiopods are sessile, bivalved organisms, but are more closely related to the colonial Bryozoa than the bivalved mollusks. Brachiopod diversity peaked in the Paleozoic, but some species survive.

rugose coral

Any member of an extinct order (Rugosa) of corals that take their name from the wrinkled ridges on their thecae. They range from Ordovician to Early Triassic and were major reef builders in the late Paleozoic.

reef

A ridge or mound-like structure, usually of calcium carbonate, built by the accumulation of skeletons of sessile marine organisms, dominantly corals in the present day. At different times in the geological past, reefs have been built by a variety of groups of organisms, including cyanobacteria and clams. Reefs provide important habitat for many species of marine organisms.

trilobite

Any member of Trilobita, an extinct class of marine arthropods. Trilobites are known from the Cambrian to the Permian. They had segmented, oval-shaped bodies and were the first animals to have complex eyes (similar to the compound eyes in modern insects).

Carboniferous

The fifth of six periods constituting the Paleozoic Era, from about 362 to 298 million years ago. In North America, the Carboniferous is divided in to the Mississippian and Pennsylvanian periods. Their mutual boundary is around 323 mya.

vertebrate

Any member of the chordate group Vertebrata, which are characterized by a spinal column or backbone.

gnathostome

Any member of the superclass Gnathostomata. All jawed vertebrates are gnathostomes, the first of which evolved in the Middle Devonian.

acanthodian

Any member of an extinct order (Acanthodia) of fish called placoderms that were characterized by bony fins. Acanthodians are among the earliest known fish with jaws.

placoderm

Any member of the extinct vertebrate group Placodermi. These were the earliest jawed fish and are known for bony armor on their heads and necks.

bony fish

The common name for the class Osteichthyes, fish that have bony rather than cartilaginous skeletons.

lobe-finned fish

Common name for members of the class Sarcopterygii. Lobe-finned fishes are osteichthyans (bony fishes) with fleshy lobe-shaped fins that are like the limbs of terrestrial animals.

ray-finned fish

Any member of the class Actinopterygii. Ray-finned fishes are osteichthyans (bony fishes) that have webbed fins supported by bony spines.