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Topic: Placoderm

	Palaeos Vertebrates 60.000 Placoderm Overview
		The placoderms are among the most ancient of jawed fish, and, along with the Acanthodii, the only class of (gnathostomes) to become completely extinct.
		Most placoderms were quite small, about 10 or 15 cm in length, but one specialized group of carnivorous types, Dinichthyidae included a few genera reached 4 to 9 meters in length, making them the largest carnivore of the Devonian.
		The placoderms were seemingly little affected by the extinction at the end of the Frasnian Age, yet the group dwindled during the Famennian and died out at the Devonian/Carboniferous boundary, without leaving any descendents.
	www.palaeos.com /Vertebrates/Units/Unit060/060.000.html (654 words)

	Introduction to the Placodermi
		Placoderms bore heavy bony armor on the head and neck, often with an unusual joint in the dorsal armor between the head and neck regions; this joint apparently allowed the head to move upwards as the jaw dropped downwards, creating a larger gape.
		In a sense, placoderms represent an "early experiment" in the evolution of jawed fish; they radiated into a number of body shapes and ecological niches, which were occupied by other fish lineages after the extinction of the placoderms.
		Placoderms survived until the very end of the Devonian, and their extinction appears to have been quite sudden, but its causes are still unknown.
	www.ucmp.berkeley.edu /vertebrates/basalfish/placodermi.html (823 words)

	Placodermi - Palaeos
		Placoderms were one of the first jawed fish, their jaws likely evolving from the first of their gill arches.
		Most placoderms were quite small, about 10 or 15 cm in length, but one specialized group of carnivorous types, Dinichthyidae included a few genera reached 4 to 9 meters in length, making them the largest animals of their time, and the most fearsome.
		The first appearance of Silurian placoderm fossils, in China, show the fishes already differentiated into Antiarchs and Arthrodires, along with the other, more primitive groups; 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.
	www.palaeos.org /Placoderm?title=Placoderm&redirect=no (574 words)

	Your group:Fossil Groups: SciComms 04-05: Earth Sciences (Site not responding. Last check: 2007-10-29)
		Placoderms were early jawed fish that lived in the Silurian and Devonain (439-362 Mya).
		The name placoderm means 'plated skin' and refers to the dermal armour of large plates that covered the head and trunk region of the majority of the taxa in the Class Placodermi.
		Although placoderms have been recorded from the Silurian of China, they do not become widespread until the Devonian, when they briefly became one of the most successful groups of fishes before their extincion in the end Devonian mass extinctinon event.
	palaeo.gly.bris.ac.uk /Palaeofiles/Fossilgroups/Placodermi/index.html (252 words)

	Placodermi - EvoWiki (Site not responding. Last check: 2007-10-29)
		The first appearance of late Silurian placoderm fossils, in China, show the fishes already differentiated into Antiarchs and Arthrodires, along with the other, more primitive groups; 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.
		It was originally thought that the placoderms went extinct due to competition from the first bony fish, as well as the early sharks, due to a combination of the supposed inherent superiority of the bony fish and sharks, as well as the presumed sluggishness of the placoderms themselves.
		Many other placoderm specialists suspected that Stensio was trying to shoehorn placoderms into a relationship with sharks, but with more fossil specimens found, especially the exceptionally well-preserved fossils from the Gogo Reef formation in Australia, Stensio's theory of sharks and placoderms as sister groups is accepted as fact.
	wiki.cotch.net /index.php?title=Placoderm&redirect=no (646 words)

	Carr (Site not responding. Last check: 2007-10-29)
		Analysis at the level of substage is critical for the recognition of placoderm subclade diversity patterns.
		The current temporal and taxonomic resolution of individual placoderm taxa is sufficient to provide a clear picture of diversity independent of the level of resolution selected for screening data.
		This event may have reduced the numbers of placoderms sufficiently to provide a "window of opportunity" for the early radiation of actinopterygians and chondrichthyans.
	www.mnhn.fr /publication/geodiv/g95n1a4.html (627 words)

	Placoderm fossil localities (Site not responding. Last check: 2007-10-29)
		The great diversity of fishes found in these deposits are excellently preserved because of the lack of later geological activity that kept the region free of large crustal movements which usually deform and compress fossils of this age.
		Placoderm fossils are also notably found in the Old Red Sandstone outcrops of Scotland.
		In Canada placoderm fossils have been found in marine deposits of the Escuminac Formation of Miguasha, Quebec.
	hoopermuseum.earthsci.carleton.ca /placoderms/seventh.html (97 words)

	DIADIST databases-glossary
		The placoderm or "true" desmids are different from saccoderms in that their cells consist of two halves with a more complex wall structure and a fairly elaborate pore system.
		The two halves, which are referred to as semicells, are separated either by suture lines (in the Archidesmidiinae, Fig.2) or by a well-defined constriction referred to as the isthmus (in the Desmidiinae, Fig.3).
		While saccoderm desmids usually exhibit simple cylindrical symmetries, the placoderms are diverse in their morphologies, and symmetry is often complicated.
	rbg-web2.rbge.org.uk /DIADIST/glossary.htm (420 words)

	The Fish, Part II: The Chondrichthyans
		In "The Fish, Part I," I mentioned that the fish are divided into four groups: the ostracoderms, the placoderms, the chondrichthyans, and the osteichthyans.
		The chondrichthyan fish are also known as the cartilaginous fish, as their skeletons are made entirely of cartilage, with the exception of their teeth and jaws.
		The chondrichthyans originated from the placoderms, and lost both their armour and their bony skeletons.
	www.suite101.com /article.cfm/4003/24454 (416 words)

	Palaeos Vertebrates 140.040 Sarcopterygii: Orbits: Fossils
		The problem may stem from Basden and Young's use of placoderms as the model model.
		seen, the placoderm orbit is unique because of the approximately 45° clockwise rotation of the muscle origins.
		We prefer a reconstruction which resembles the case of sharks and coelacanths, is not completely at odds with the apparent geometry in placoderms, makes mechanical sense, and keeps appropriate symmetry between the dorsal and ventral halves of the orbit -- at least until the next basal gnathostome braincase is described.
	www.palaeos.com /Vertebrates/Units/140Sarcopterygii/140.040.html (687 words)

	Placoderm body (Site not responding. Last check: 2007-10-29)
		Placoderms had heavy armour that covered their head and thorax.
		The head and trunk shields of most placoderms were articulated by bony joints.
		Placoderms lacked teeth but biting or grinding structures are often found in the dermal bones lining their mouths.
	hoopermuseum.earthsci.carleton.ca /placoderms/fourth.html (172 words)

	Palaeontology - Late Devonian fauna from the Hunter Siltstone near Grenfell, New South Wales
		The fishes preserved in this fauna are largely disarticulated so that the material recovered is separate placoderm plates, bones, scales toothplates, etc. This represents a very different mode of preservation than seen in the Canowindra fauna, signalling transport after death in moving water, perhaps a river or stream.
		A fourth placoderm, Grenfellaspis branagani, is unusual in having its ventral trunk region largely open (i.e., Covered with skin), while in most other placoderms, this part of the trunk is covered in bony plate.
		Biogeographic relationships of the Grenfell fauna and eastern Australia during the Late Devonian were largely based on the distribution of the Sinolepidae.
	www.austmus.gov.au /palaeontology/field_sites/grenfell.htm (556 words)

	palaeontology > placoderm (Site not responding. Last check: 2007-10-29)
		Placoderm Base of the United States Submarine Veterans contact point for Base membership upcoming...
		The placoderm fish Coccosteus cuspidatus Miller ex Agassiz from the Middle Devonian Old Red Sandstone of Scotland.
		The name "placoderm" is from the Greek and...
	www.fossilien.in /palaeontology/placoderm.cgi (144 words)

	Mark-Kurik (Site not responding. Last check: 2007-10-29)
		Rhenanids, though rather poorly known placoderm fishes, are quite widely distributed.
		Mark-Kurik, E. Contribution to the correlation of the Emsian (Lower Devonian) on the basis of placoderm fishes.
		A new buchanosteid arthrodire (placoderm fish) from the Early Devonian of the Ural Mountains.
	sds.uta.edu /sds18/Mark_Kurik.htm (396 words)

	Dunkleosteus - Wikipedia, the free encyclopedia
		The largest of the genus grew to around 8 to 10 m (27 to 33 feet) long, and were probably the top predators of their time.
		Although Placoderms only existed for 60 million years, their mark on the fossil record is quite visible.
		The Placoderms died out in the late Devonian for reasons that are still not well understood.
	en.wikipedia.org /wiki/Dunkleosteus (747 words)

	Home
		Placoderms occupied a wide range of ecological roles.
		Some placoderm detritus feeders had greatly expanded box-shaped thoracic armor and pectoral fins enclosed in arthropod-like armor as well.
		Placoderm diversity was greatly reduced by an extinction event in the Late Devonian.
	www.geol.umd.edu /~jmerck/honr219d/notes/11.html (1479 words)

	Geotimes - April 2003 - Devonian Dentistry
		During the Devonian, 350 million years ago, a group of armored fishes known as placoderms roamed the seas.
		Although placoderms radiated into a wide variety of ecological niches, they survived only 50 million years, reaching a sudden and complete collapse at the end of the Devonian.
		Says Coates: “Without a good phylogeny of placoderm relationships, can we be certain that the teeth are independently derived?” Smith and colleagues plan to re-examine placoderm phylogenetics to resolve this question.
	www.agiweb.org /geotimes/apr03/NN_dentistry.html (321 words)

	Placoderm showcase (Site not responding. Last check: 2007-10-29)
		The armoured sharks - Placodermi - were a numerous group of fish which had developed real jaws.
		In many Placoderms, the head and front part of the body was covered by a strong armour of rigid and fused bony plates.
		The Placoderms had paired pectoral and pelvic fins.
	www.toyen.uio.no /palmus/galleri/montre/english/m_panserhai_e.htm (126 words)

	InfoHub - View Single Post - Cowralepis - A Placoderm Fish
		Cowralepis mclachlani was a fish species that lived during the Middle Devonian.
		The placoderms were the first known fishes with jaws.
		Placoderms appeared in the late part of the Silurian and died out in the late portion of the Devonian.
	www.infohub.com /forums/showpost.php?p=22290&postcount=1 (85 words)

	InfoHub - View Single Post - Arctolepis - A Placoderm Fish of the Devonian
		Arctolepis was a Placoderm fish that lived during the Devonian period (416-359 million years ago).
		The Arthrodira placoderms had flexible joints between the armor that covered the head and part of the body.
		The placoderms went extinct at the end of the Devonian.
	www.infohub.com /forums/showpost.php?p=30327&postcount=1 (194 words)

	InfoHub - View Single Post - Gemuendina - A Placoderm Fish of the Devonian
		Gemuendina was a placoderm fish of the Devonia period (416-359 million years ago).
		Gemuendina was not as heavily armored as many other placoderms.
		In this way it was different from Arctolepis (a placoderm of the Arthrodira order), which had a single sharp plate for biting.
	www.infohub.com /forums/showpost.php?p=30328&postcount=1 (186 words)

	Devonian Times - Turrisaspis elektor
		A new species of groenlandaspid placoderms, Turrisaspis elektor, is one of the two most numerous fossil vertebrates at Red Hill.
		Turrisaspis elektor is smaller (about 20 cm in length) than a similar new Red Hill placoderm, Groenlandaspis pennsylvanica.
		It can readily be distinguished from its larger relative by its narrow and tall median dorsal plate (a dermal skeletal element that resembles the dorsal fins in more familiar fishes).
	www.devoniantimes.org /who/pages/turrisapsis.html (253 words)

	mac (Site not responding. Last check: 2007-10-29)
		The placoderms (meaning 'plated skin) were a group of fish characterised by bony armour covering the head and trunk.
		The placoderms flourished in the Devonian period after which they became extinct.
		It is the only placoderm with annular cartilage that provides evidence of a link to all sharks as a group.
	www.sdps.wa.edu.au /Celebration/mac.html (94 words)

	Palaeontology - Zerina Johanson
		Johanson, Z. Vascularization of the osteostracan and antiarch (Placodermi) pectoral fins: Similarities, and implications for placoderm* relationships.
		Johanson, Z. The clavobranchialis musculature in sarcopterygian fishes, and contribution to osteichthyan feeding and respiration.
		Johanson, Z. and Smith, M. Placoderm* Fishes, Pharyngeal Denticles and the Vertebrate Dentition.
	www.amonline.net.au /palaeontology/staff/johanson.htm (742 words)

	Gogo reef Formation: Lagerstätten Catalogue: University of Bristol (Site not responding. Last check: 2007-10-29)
		The placoderm fish Mcnamaraspis was approximately 25 cm long and, like other placoderms, had a bony head shield which was joined to the 'shark'-like body (Fig.
		The Mcnamaraspis skull exhibits annular cartilage preserved in the snout, which has never been observed in other placoderm specimens.
		This facilitated the entrance of water over its olfactory organs and hence its sense of smell was acute.
	palaeo.gly.bris.ac.uk /Palaeofiles/Lagerstatten/Gogo/fauna.html (126 words)

	Untitled Document (Site not responding. Last check: 2007-10-29)
		Adding a placoderm to polarize (code) the character states
		Observed characters in Placoderm outgroup, compared to 3 original taxa:
		Cladistic coding of character states, based on Placoderm outgroup:
	www.eeb.uconn.edu /courses/245_01/Lec10_outline.htm (266 words)

	Devonian Times - Groenlandaspis pennsylvanica
		Groenlandaspis pennsylvanica is one of two new species of groenlandaspid placoderms found at Red Hill.
		Known from a total of 27 isolated trunk plates, it apparently was uncommon at the site.
		Questions or comments should be sent to Dennis Murphy at
	www.devoniantimes.org /who/pages/groenlandapsis.html (187 words)

	Placoderm Base Website (Site not responding. Last check: 2007-10-29)
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	g.msn.com /9SE/1?http://ussvi-placoderm.org/31801/index.html?sessionidkey=sessionidval&&DI=6244&IG=e8a2efdaea3f4b1890825daf3cb7345b&POS=4&CM=WPU&CE=4&CS=AWP&SR=4 (232 words)

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