Cochise College            Student Papers in Geology

Geology Home Page                    physical geology  historical geology  planetary  gems

Roger Weller, geology instructor

Ellie Wilson
Historical Geology
Spring 2009


The Devonian Period

 The 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 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.  

Devonian Flora:      

     The Devonian 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. (

Early Devonian Marine Life:

 early devonian aquatic faunal development

     Early 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. (

 Devonian Marine Life:

 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.

vertebrate diversity over time

Devonian fishes:

Devonian fishes 

     Sharks and Agnathans a polyphyletic group of jawless vertebrates also undergo considerable changes and even major extinctions during the Devonian period.

      In the 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. (

In this picture of the Devonian Period the fishes are very distiguishable.

reconstructions of three acanthodians

     For example: 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 Devonian period  


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.


Brachiopod 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 Brachiopods


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

Devonian reef   


   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.



Devonian Climate:
The climate of the Early Devonian is strongly zonal, with a narrow equatorial tropical belt, broad subtropical arid zones extending to about 35 ° latitude,

U400_zonef.jpg (63413 bytes)
and a temperate zones extending essentially to the poles.

Accordingly, during the Devonian period the climate was temperate, relatively warm and dry.  There was a large ocean and the climate was arid.

390.jpg (120845 bytes)

410 - 359.2 Million Years Ago:

 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

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.

 Devonian Geography:

 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:


Works Cited

Exhibit Museum of Natural History,University of Michigan, Ann Arbor Michigan.


R.Weller/Cochise College

R.Weller/Cochise College. Fossil courtesy of Dave Dechant.