Geology Home Page physical geology historical geology planetary gems
Roger Weller, geology instructor
The Devonian Period
Devonian world, of the Paleozoic Era from 410 to 360 million years ago was
teeming with a diversity of life. In the Devonian period, soft- bodied organisms
thrived in the shallow sea waters. There was an abundance of invertebrates like
crinoids, brachiopods and the fish were very diverse. The land supported the
first forests trees .The first seed bearing plants spread across the dry land,
and formed large forests. Also ferns, plants that were seedless, Vascular
Plants (Phylum Pterophyta) ferns; which mean they reproduce with no seeds but
with spore cells that falls to the ground and grow into an intergeneration
cycle, the sperm then fertilizes an egg cell from a neighboring plant. The
fertilized egg grows into a mature fern producing spores (in the brownish spots
on the underside of fern leaves) which are called sorus. Ferns and the first
trees began to cover the land.
Fern Life Cycle
The warm temperatures of the Devonian era was very beneficial for the plants and other living organisms Spiders and the first wingless insect found places to live on the trees.
The Rhynie Chert in Scotland is a Devonian silica deposit.
Fossils from the Rynie Chert were buried in short-lived freshwater deposits and underwent replacement of the organic material with silica, forming a chert deposit that preserved even details of the cells of the organisms. rhynie.html.
period marks the beginning of extensive land colonization by plants. With large
herbivorous land-animals not yet being present, large forests could grow and
shape the landscape. (www.newworldencyclopedia.org/entry/Devonian).
Early Devonian Marine Life:
Devonian freshwater faunas are also notable for the appearance of a variety of
small branchiopod crustaceans, including Conchostraca (clam shrimp), Anostraca
(fairy shrimp), Lipostraca and Acercostraca. The appearance of these swimming
icrocrustacean suggests stable stream flows. (www.newworldencyclopedia.org/entry/devonian)
During the Devonian period which is
also called the “Age of Fishes” fish’s lineage underwent major changes, Lobe-Fin
Fishes and Ray Fin Fishes Tetrapods appeared. This lobe – fins diversified
during these times together with the Acanthodians and the Placoderms reaching
their major changes and diversity in the Devonian Period. Most of the Placoderms
reached their diversification at this particular period. Sharks and Agnathans, a
polyphyletic group of jawless vertebrates also underwent considerable changes
and even major extinctions during the Devonian Period. Some of the marine life
that existed during the Devonian period were; corals, bryozoans, cephalopods,
trilobites crinoids and brachiopods which were all warm water organisms.
Agnathans a polyphyletic group of jawless vertebrates also undergo considerable
changes and even major extinctions during the Devonian period.
Devonian Period in the shallow warm sea waters lived crinoids along an
abundance of corals and brachiopods, Placoderms, and Euryptides. The
Placoderms were named because of the plate like armored body that covered its
head and torax, an ancient jawed fish together with the ostracoderm live and
hunted in these shallow waters. The eurypterids a Paleozoic group of
chelicerate arthropods ( jointed legs)Dolichopterus macrocheirus with the
length of 25 to 30 cm were called the sea scorpions and these fishes were
capable of breathing in and out of the water.
Another fish that lived in these waters was the Acanthodian. Acanthodians are among the earliest jawed vertebrates known. Fragmentary remains have been recovered from as early as the Upper Ordovician of North America and Lower Silurian of China. Their record extends about 160 million years to the Lower Permian. Diversity is greatest from the Upper Silurian through the Devonian. (www.Devoniantimes.com)
In this picture of the Devonian
Period the fishes are very distiguishable.
in the waters below, there are crinoids, members of phylum Echinodermata,
corals, brachiopods, which are considered benthic. Brachiopods dwell in the
bottom of the ocean, are inequalvalved and one shell is larger. They are
considered living fossils, and in our days, are rare but in abundance in the
Paleozoic Era. There are about 300 living species of brachiopods.The placoderms
(class Placodermiis) heavily armored fish that lived in fresh water and the
ocean and the sea scorpions, and are now extinct.
The work of the sponges and corals went on through the Devonian Period. They built some of the largest reefs in the world. Invertebrates grew well in Devonian seas too, so many new species developed. The ammonite is one of these. http://www.fossils-facts-and-finds.com/devonian_period.html
Atrypha was abundant in the Devonian Period.
Photo is copyright free for non-commercial educational uses.
Just credit photo to R.Weller/Cochise College.
Fossil courtesy of Dave Dechant.
Brachiopod Atrypha is an extinct brachiopod that lived during the Devonian Period about 370 million years ago. There about some two hundred brachiopods genera in the Devonian time
Picture of Brachiopods:
Photo is copyright free for non-commercial educational uses.
Credit photo to R.Weller/Cochise College and the Exhibit Museum of Natural History.
Model is on display at the Exhibit Museum of Natural History,University of Michigan, Ann Arbor
Picture below is “ The Placoderms”, one of the fishes that existed during early and late Devonian Period. Placoderms means “ plate” and derms means “skinned” in Greek
Devonian Ocean teeming with marine life.
The climate of the Early Devonian is strongly zonal, with a narrow equatorial tropical belt, broad subtropical arid zones extending to about 35 ° latitude,
and a temperate zones extending essentially to the poles. http://www.palaeos.org/Devonian
Accordingly, during the Devonian
period the climate was temperate, relatively warm and dry. There was a large
ocean and the climate was arid.
410 - 359.2 Million
Mean atmospheric O2 content over period duration ca. 15 Volume %
(75 % of modern level) Mean atmospheric CO2 content over period duration ca. 2200 8 times pre-industrial level)
Mean surface temperature over period duration ca. 20 °C
(6 °C above modern level)
Sea level (above present day) relatively steady around 180m, gradually falling to 120m through period (Devonian Climate.com).
Historically, the Devonian has been
regarded as largely warm and equable, with a disastrous drop in temperatures in
the Late Devonian leading to the mass extinctions.
The Devonian Period (named after
Devon, England) was a time of great tectonic activity.Laurasia and Gondwanaland
were convergent, meaning coming closer together, and in the early Devonian Era
the continent of Euramerica (Laurussia) was created when Laurentia and Baltica
collided. The paleogeography was dominated by the supercontinent of Gondwana to
the south, the continent of Siberia to the north, and the early formation of the
small supercontinent of Euramerica in between.
Early Devonian maps:
Exhibit Museum of Natural History,University of Michigan, Ann Arbor Michigan.
R.Weller/Cochise College. Fossil courtesy of Dave Dechant.