Placodermi
Conservation status: Fossil
Fossil range: Early/Mid
Silurian - Late Devonian |
![](./modules/Fish-MM/images/200px-PlacodermiZICA.png)
|
Scientific classification |
Kingdom: |
Animalia
|
Phylum: |
Chordata
|
Subphylum: |
Vertebrata
|
Infraphylum: |
Gnathostomata
|
Class: |
Placodermi
McCoy, 1848 |
|
Orders |
Antiarchi †
Arthrodira †
Petalichthyida †
Phyllolepida †
Ptyctodontida †
Rhenanida †
Acanthothoraci †
?Pseudopetalichthyida †
?Stensioellida † |
The Placodermi are armoured prehistoric fishes
known from fossils dating from the late Silurian to the end
of the Devonian Period. Their head and thorax were covered
by articulated armoured plates and the rest of the body was
scaled or naked. Placoderms were among the first of the
jawed fish, their jaws likely evolving from the first of
their gill arches. There are studies that attribute to the
Placodermi the first development of teeth. The first
identifiable Placoderms evolved in the late Silurian; they
disappeared in the Late Devonian extinctions. The first
appearance of late Silurian placoderm fossils, in China,
show the fishes already differentiated into Antiarchs and
Arthrodires; apparently Placoderm diversity originated
long before the Devonian, somewhere in the middle Silurian,
though earlier fossils of basal Placodermi, have yet to be
discovered in these particular strata.
The earliest studies of placoderms were published by
Louis Agassiz, in his five volumes on fossil fishes, 1833 –
1843. The work of Dr. Erik Stensiö, at the Swedish Museum of
Natural History, Stockholm, from the late 1920s established
the details of placoderm anatomy, and identified them as
true jawed fishes related to sharks.
External links
References
- Janvier, Philippe. Early Vertebrates Oxford,
New York: Oxford University Press, 1998.
ISBN 0-19-854047-7
- Long, John A. The Rise of Fishes: 500 Million
Years of Evolution Baltimore: The John Hopkins
University Press, 1996.
ISBN 0-8018-5438-5