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Topic: Acanthostega

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	Coming Onto the Land (Site not responding. Last check: 2007-10-04)
		Acanthostega mixes the anatomy of a newt with the charm of a mutt.
		Acanthostega was a tetrapod, too, but at 360 million years old, it has a special distinction: aside from creatures suggested by a few older fossil fragments, it is the most primitive tetrapod known.
		Acanthostega, loping around underwater with a body prepared from head to foot for life on land, may be one of the strongest demonstrations that we humans owe our existence to preadaptation's unpredictable nature.
	www.mc.maricopa.edu /dept/d10/asb/anthro2003/origins/comingonto.html (5419 words)

	Acanthostega gunnari
		Acanthostega gunnari (Jarvik 1952) is one of a small but increasing number of genera of stem-tetrapods known from the Upper Devonian, which are providing an expanding view of the appearance of tetrapods and the origin of limbs with digits (Coates and Clack 1990, Clack and Coates 1995, Gould 1991, Pough et al.
		Clack, J.A. The neurocranium of Acanthostega gunnari and the evolution of the auditory region in tetrapods.
		Clack, J. 2003 A revised reconstruction of the dermal skull roof of Acanthostega, an early tetrapod from the Late Devonian.
	tolweb.org /tree?group=Acanthostega&contgroup=Terrestrial_Vertebrates (2041 words)

	Scientific American: Getting a Leg Up on Land (Site not responding. Last check: 2007-10-04)
		Acanthostega also drew attention to a formerly underappreciated part of early tetrapod anatomy: the inside of the lower jaw.
		Acanthostega showed that early tetrapods possessed a different dental plan: a small number of larger teeth on the outer row and a reduction in the size of the teeth populating the inner row--changes that probably accompanied a shift from feeding exclusively in the water to feeding on land or with the head above the water.
		And in contrast to fish, Acanthostega or other early tetrapods, Ichthyostega had spines on its vertebrae that changed direction along the spinal column, hinting that the muscles they supported were specialized for different jobs and that it moved in a unique fashion.
	www.sciam.com /print_version.cfm?articleID=000DC8B8-EA15-137C-AA1583414B7F0000 (4360 words)

	Coming Onto the Land - - science news articles online technology magazine articles Coming Onto the Land (Site not responding. Last check: 2007-10-04)
		In Acanthostega, however, the radius was about a third longer than the ulna--a kind of proportion found in lobe-finned fish and a hint that Acanthostega was the most primitive tetrapod yet found.
		Yet Acanthostega showed that the five-finger rule that these researchers assumed was absolute was actually very loose.) These eight fingers were sophisticated and multijointed, yet since they were attached to an insubstantial wrist, they were virtually useless for helping Acanthostega walk on land.
		Acanthostega, on the other hand, had a powerful, flexible tail with large fins running along the top and bottom of it.
	www.discover.com /issues/jun-95/features/comingontothelan523 (5527 words)

	Devonian Times - Acanthostega gunneri
		The skull roof of Acanthostega gunneri was first recovered from Famennian deposits (360 million years ago) in eastern Greenland in 1933, and was described and named in 1952 by Erik Jarvik.
		Acanthostega's small, fish-like nares (nostrils) were probably used only for smelling under water; air may have been brought to the lungs by gulping.
		Acanthostega has been recovered from river deposits, and the presence of well-articulated and minimally reworked remains indicate that it probably lived there.
	www.devoniantimes.org /Order/re-acanthostega.html (749 words)

	Fall'96Syllabus
		Among the most primitive early tetrapods is Acanthostega, from freshwater sediments deposited during the Late Devonian of Greenland (a cold and dry region today, but a warm, moist equatorial setting during the Devonian).
		As compared to rhipidistian fish (such as Eusthenopteron), a major development in Acanthostega is in the modification of bony fins to form a limb with digits (8 fingers were found on a preserved forelimb).
		It does not appear that any of the first terrestrial vertebrates were specialists for utilizing plants or insects as a potential food source, for they retain the relatively large body size and needle-like teeth of their rhipidistian ancestors, indicating a diet of fish (which are difficult to catch, but can generally be swallowed whole).
	ijolite.geology.uiuc.edu /00SummerClass/geo143/lectures/lect07.html (1083 words)

	Acanthostega - Wikipedia, the free encyclopedia
		Acanthostega is an extinct tetrapod genus, among the first vertebrate animals to have recognizable limbs.
		The front foot of Acanthostega couldn't bend forward at the elbow, and thus couldn't be brought into a weight-bearing position, appearing to be more suitable for paddling or for holding on to aquatic plants.
		It had lungs, but its ribs were too short to give support to its chest cavity out of water, and it also had gills which were internal and covered like those of fish, not external and naked like those of some modern amphibians which are almost wholly aquatic.
	en.wikipedia.org /wiki/Acanthostega (291 words)

	So called Transition from fish to amphibians
		Acanthostega is at least based on a complete skeleton and clearly a distinct kind from others in the list.
		Acanthostega did have some fish like traits in the form of a fish-like vertebral skeleton, fin rays surrounding the tail fin, lacks of aneck joint, grooved gill bars, simple joints between limb elements, and a large bony cleithrum.
		Ichthyostega was a largely aquatic amphibian that was capable of waking on land this is known to occur in mammals such as seals.
	genesismission.4t.com /transition/fish-amphibians.html (649 words)

	IngentaConnect The dermal skull roof of Acanthostega gunnari, an early tetrapod ... (Site not responding. Last check: 2007-10-04)
		IngentaConnect The dermal skull roof of Acanthostega gunnari, an early tetrapod...
		The dermal skull roof of Acanthostega gunnari Jarvik is described in detail, giving new information on the anatomy, and new reconstructions of the skull in dorsal, lateral and occipital views, as well as sections through the skull at two points.
		This may be connected with having the lateral lines accommodated in tubes in Acanthostega rather than grooves, or some other property of the dermal bone in the later groups that reduced the need for stronger integration.
	www.ingentaconnect.com /content/rse/tes/2002/00000093/00000001/art00002 (299 words)

	Acanthostega
		Ichthyostega was an ancient extinct amphibian with four legs and a fish-like tail fin.
		There are many skeletal similarities between the fossils of these two animals, which strongly suggests that they have evolved from the same ancestoral forms.
		Different from Acanthostega, Ichthyostega had pelvic bones that connected the linbs to the spinal column (backbone), and the spinal column was able to support the body weight on land.
	www.sonic.net /~evolve/creation/acanthostega.htm (622 words)

	CC212: Transitional Tetrapods
		Tulerpeton, from estuarine deposits roughly the same age as Acanthostega and Ichthyostega, had six digits on its front limbs and seven on its rear limbs.
		Its shoulders were more robust than Acanthostega, suggesting it was somewhat less aquatic, and its skull appears to be closer to later Carboniferous amphibians than to Acanthostega or Ichthyostega.
		Coates, M. The Devonian tetrapod Acanthostega gunnari Jarvik: postcranial anatomy, basal tetrapod interrelationships and patterns of skeletal evolution.
	www.talkorigins.org /indexcc/CC/CC212.html (401 words)

	Pharyngula::Ichthyostega
		Acanthostega was a contemporary of Ichthyostega with a different lifestyle.
		Acanthostega, in contrast to Ichthyostega, had a laterally flexible trunk and appears better adapted for tail-propelled swimming.
		Coupled with differences in the dentition (recurved sectorial teeth in Ichthyostega, conical piercing teeth in Acanthostega) and body size (Ichthyostega is about 30% larger than Acanthostega), plus the fact that the two genera rarely occur together in the same locality within the Greenland sediments, this points to a clear ecological separation between these primitive tetrapods.
	pharyngula.org /index/weblog/comments/ichthyostega (748 words)

	tech (Site not responding. Last check: 2007-10-04)
		Ichthyostega and acanthostega seem to be an ancient variety of amphibians, with the perceived “fish-like affinities” being overemphasized (salamanders and other amphibians share many transitory aquatic features during their lifetime, with no more evidence to prove their hypothetical fish ancestry.
		In the case of ichthyostega and acanthostega, they hypothetically had to have received their new land-adapted appendages, fingers and all, with all of the appropriate systems to manipulate and utilize them to the utmost, so as to “survive as the fittest”.
		I might add that the fossil remnants of Ichthyostega and Acanthostega are rather fragmentary themselves, missing certain aspects of the skeletal structure, and missing the ever-so-vital soft tissue and muscle remnants (acanthostega limb is extremely fragmented.
	www.calarts.edu /~shockley/tech.html (4050 words)

	Publications (Site not responding. Last check: 2007-10-04)
		Clack, J. 1998 The neurocranium of Acanthostega gunnari and the evolution of the otic region in tetrapods.
		Clack, J. Acanthostega gunnari, a Devonian tetrapod from Greenland; the snout, palate and ventral parts of the braincase, with a discussion of their significance.
		Clack, J. 1992 The stapes of Acanthostega gunnari and the role of the stapes in early tetrapods.
	theclacks.org.uk /jac/publications.htm (1279 words)

	Yet another 'missing link' fails to qualify (Site not responding. Last check: 2007-10-04)
		However, Acanthostega was a fully formed and fully functional four-legged amphibian, with four legs and not four fins, in some respects not unlike amphibians such as salamanders and newts.
		Acanthostega is not the first fossil to be called a mosaic, a creature that has characteristics common to two or more other types of creatures.
		The fossil record has so far revealed many types of fish, some of which have bones in their fin lobes, serving a useful purpose as in the coelacanth (long believed to be an extinct ancestor of land animals, until it was found alive and well).
	www.answersingenesis.org /creation/v15/i3/missinglink.asp (2432 words)

	Fall'96Syllabus
		As compared to Eusthenopteron and Panderichthys, a major development in Acanthostega is in the modification of bony fins to form a limb with digits (8 fingers were found on a preserved forelimb).
		Bones on the interior of the skull and hip girdle are channeled, suggesting that in life they harbored blood vessels which would have connected to a set of internal gills that were reduced as compared to osteolepiforms, but still functional.
		It does not appear that any of the first terrestrial vertebrates were specialists for utilizing plants or insects as a potential food source, for they retain the relatively large body size and needle-like teeth of the sarcopterygians, indicating a diet of fish (which are difficult to catch, but can generally be swallowed whole).
	ijolite.geology.uiuc.edu /00FallClass/geo143/lect/lect12.html (1075 words)

	ChrisAuman.com - An Experiment
		The drying out of the coal swamps during the latest Carboniferous and again at the end of the Early Permian diminished many of the environments of these Paleozoic amphibians, with the result that many types died out, and they were supplanted by reptiles.
		This spiracle is a transitional organ that led, through evolution, to the development of the stirrup bone, one of the three bones (stirrup, hammer, and anvil) in the human inner ear.
		Acanthostega has extremely tetrapod-like limbs, feet (with a few extra fingers), and a pelvic girdle.
	www.chrisauman.com (1996 words)

	DEVONIANO Tetrápodes 1
		Acanthostega é um tetrápode conhecido do devoniano superior da groelândia que está proporcionando uma visão do aparecimento dos tetrápodes e da origem dos membros com dígitos.
		As relações filogenéticas do acanthostega permanecem não resolvidas, pendente a uma análise da cladística completa, entretanto tentativas provisórias têm sugerido que foi um dos vertebrados com dedos mais antigos.
		O acanthostega possuía brânquias e costelas muito mal desenvolvidas o que indica que provavelmente era um animal de vida aquática.
	www.geocities.com /historiadaterra/devacan.html (138 words)

	Science News Online (5/22/99): Out of the Swamps
		Acanthostega lurked in shallow waters of coastal swamps.
		The squat humerus of Acanthostega, however, would have baffled a poor dog because it didn't narrow at its middle.
		At the heart of Carroll's theory lies the amniote egg, which has a series of membranes not present in the simpler eggs of frogs and salamanders.
	www.sciencenews.org /sn_arc99/5_22_99/bob1.htm (2412 words)

	TRANITIONAL FORMS: Fish to Amphibians
		The stapes, the bone which eventually became part of the hearing apparatus in tetrapods was still used for ventilation of the gills (Clack,1989, p.
		Acanthostega and Ichthyostega would only have been able to bend their hands slightly (Monastersky, 1999, p.
		This creature has a primitive stapes, the bone used in hearing and it resembles that of Acanthostega rather than those of the later amphibians.
	home.entouch.net /dmd/transit.htm (1530 words)

	EvolutionTheLie.com: The fossil record of ‘early’ tetrapods: evidence of a major evolutionary transition? (Site not responding. Last check: 2007-10-04)
		Acanthostega is also much more completely known as a result of material collected by the 1987 expedition, including the first postcranial remains.
		Clack, J.A., Acanthostega gunnari, a Devonian tetrapod from Greenland; the snout, palate and ventral parts of the braincase, with a discussion of their significance, Meddelelser om Grønland: Geoscience 31:1–24, 1994.
		Clack, J.A., The neurocranium of Acanthostega gunnari Jarvik and the evolution of the otic region in tetrapods, Zoological Journal of the Linnean Society 122:61–97, 1998.
	www.evolutionthelie.com /arguments/naturalSelection/earlyTetrapod.aspx (4739 words)

	Evolution -- Tetrapod Transitionals (Site not responding. Last check: 2007-10-04)
		Once upon a time there was Acanthostega and Ichthyostega and......well, not much else for millions of years.
		In Acanthostega and Ichthyostega, the metatarsals are not clearly differentiated, and in Tulerpeton, if correctly interpreted, they are cylindrical but include some interarticulations.
		Clack, J. The Neurocranium of Acanthostega gunnari and the Evolution of the Otic Region in Tetrapods.
	hometown.aol.com /darwinpage/tetrapods.htm (1432 words)

	amphibian (Site not responding. Last check: 2007-10-04)
		The limbs of these ancient fish are supposed to have been the raw material to have given rise to the “later” amphibians which possessed several digits (fingers) on both their front and hind limbs.
		Ichthyostega and acanthostega, the amphibians in this scenario, were also equally as interesting,.......just as how modern day amphibians go through some sort of strange, metamorphic process in their life cycle, seemingly transforming into another creature altogether.
		It would also strengthen this case more if it could be shown that both ichthyostega and acanthostega were, in fact, the same animal, with one being in either the earlier or latter stages of amphibian metamorphosis (since they were apparently amphibians, although even this could be wrong).
	www.calarts.edu /~shockley/amphibian.html (1245 words)

	Late Devonian Carboniferous amphibians Xenacanthus eusthenopteron Ichthyostega acanthostega crassigyrnius eogryrinius
		The spread of land based plants especially trees made fresh water environments attractive to early vertebrates.
		It is often pictured climbing out of the water, but its fins could only have moved slightly back and forth: the shoulder girdle would not have supported the body on land.
		Acanthostega, found in Greenland,was a relatively good swimmer and also able to move slowly on land.
	www.dinosaurcollector.150m.com /carboniferous.html (455 words)

	Devonian Times - Recent Findings
		Since it was essentially contemporaneous with the apparently more terrestrial Ichthyostega, Acanthostega, like modern-day dolphins and whales, may have secondarily lost the skeletal features needed for life on land.
		The unexpected characteristics of Acanthostega have led to reinterpretations of Ichthyostega by Per Ahlberg, Jennifer Clack and Michael Coates.
		Ichthyostega forelimbs were more robust than those of Acanthostega and were probably able to lift the front half of the body.
	www.devoniantimes.org /Order/new-order.html (989 words)

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