? Ichthyostega Fossil range: Devonian
Scientific classification
Kingdom: Animalia Phylum: Chordata Superclass: Tetrapoda Order: Ichthyostegalia Family: Ichthyostegidae Genus: Ichthyostega Säve-Söderbergh, 1932
Species
I. stensioei I. watsoni I. eigili I. kochi

Ichthyostega (Greek: "fish roof") is an early tetrapod genus living in the Upper Devonian (Famennian) period, 367-362.5 million years ago, and the first to intermediate between fish and amphibians. Ichthyostega had legs but its limbs probably weren't used for walking as once believed, but were used instead to negotiate its way through the swamps of the time. == == Disambiguation: Devonian is sometimes used to refer to the Southwestern Brythonic language, and the people of the county of Devon are sometimes referred to as Devonians The Devonian is a geologic period of the Paleozoic era. ... Image File history File links Download high resolution version (1021x326, 19 KB)i draw it on macromedia flash October 2005 mateus zica File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Scientific classification or biological classification is how biologists group and categorize extinct and living species of organisms (as opposed to folk taxonomy). ... Binomial name Aptenodytes forsteri Gray, 1844 For other uses, see Animal (disambiguation). ... Typical Classes Subphylum Urochordata - Tunicatas Ascidiacea Thaliacea Larvacea Subphylum Cephalochordata - Lancelets Subphylum Myxini - Hagfishes Subphylum Vertebrata - Vertebrates Petromyzontida - Lampreys Placodermi (extinct) Chondrichthyes - Cartilaginous fishes Acanthodii (extinct) Actinopterygii - Ray-finned fishes Actinistia - Coelacanths Dipnoi - Lungfishes Amphibia - Amphibians Reptilia - Reptiles Aves - Birds Mammalia - Mammals Chordates (phylum Chordata) include the vertebrates, together with... Classes Synapsida Sauropsida Amphibia A tetrapod (Greek tetrapoda, four-legged) is a vertebrate animal having four feet, legs or leglike appendages. ... Groups See text. ... In biology, a genus (plural genera) is a taxonomic grouping. ... == == Disambiguation: Devonian is sometimes used to refer to the Southwestern Brythonic language, and the people of the county of Devon are sometimes referred to as Devonians The Devonian is a geologic period of the Paleozoic era. ... The Famennian Age is one of two ages in the Late Devonian Period. ... Atlantic herring, Clupea harengus: one of the most abundant species of fish in the world. ... For other uses, see Amphibian (disambiguation). ... A limb (from the Old English lim) is a jointed appendage of the human or animal body; a large or main branch of a tree; a representative, branch or member of a group or organization. ... Sheep walking along a road Walk redirects here. ... A freshwater swamp This article is about the wetland type (a landform). ...

History and systematics

Säve-Söderbergh, 1932a described four Ichthyostega species from the Upper Devonian of East Greenland and one species belonging to the genus Ichthyostegopsis, I. wimani. These species could be synonymous (in which case only I. stensioei would remain), because their morphological differences are not very pronounced. The species differ in skull proportions, skull punctuation and skull bone patterns. The comparisons were done on 14 specimens collected in 1931 by the Danish East Greenland Expedition. Additional specimens were collected between 1933 and 1955. Comparative anatomy is the study of similarities and differences in organisms. ... 1931 (MCMXXXI) was a common year starting on Thursday (link is to a full 1931 calendar). ...

The genus closely related to Acanthostega gunnari, also from East Greenland. Ichthyostega's skull seems more fish-like than that of Acanthostega, but its girdle (shoulder and hip) morphology seems stronger and better adapted to land-life. Ichthyostega also had more supportive ribs and stronger vertebrae with more developed zygapophyses. The first tetrapods (who probably didn't walk on land) were Elginerpeton and Obruchevichthys. Acanthostega Acanthostega gunnari is an extinct amphibian tetrapod species, among the first animals to have recognizable limbs. ... A girdle is a piece of womens underwear that replaced the corset in popularity and usage. ... The human rib cage. ... A diagram of a thoracic vertebra. ... A zygapophysis is process which sticks out of an end of a vertebra to lock with a zygapophysis on the next vertebra, to make the backbone more stable. ...

Characteristics

Ichthyostega was about 1.5 meter long and had seven digits on each hind foot. The exact number of digits on the hand is not yet known, but was probably about the same as on the foot. It had a fin containing fin rays on its tail.

Adaptations for land-life

Primitive amphibians like Ichthyostega and Acanthostega differed from animals like Crossopterygians (for instance Eusthenopteron or Panderichthys) in that although Crossopterygians had lungs, they used their gills as the primary means of acquiring oxygen. Ichthyostega probably used lungs as its primary means of breathing. Primitive amphibians had a special type of skin that helped them retain bodily fluids and deter desiccation, whereas Crossopterygians did not. Moreover, Crossopterygians used their body and tail to move about and their fins for balance while, Ichthyostega instead used its limbs for locomotion and its tail for balance. Subclasses Coelacanthimorpha - Coelacanths Dipnoi - Lungfishes Tetrapoda Sarcopterygii is traditionally the class of lobe-finned fishes, consisting of lungfish and coelacanths. ... Binomial name Eusthenopteron foordi Eusthenopteron foordi Whiteaves 1881 is a genus of lobe-finned fish which has attained an iconic status from its close relationships to tetrapods. ... Panderichthys Panderichthys is a 90-130 cm long fish from the Late Devonian period . ... The lungs flank the heart and great vessels in the chest cavity. ... gills of a Smooth Newt Gills inside of a tuna head In aquatic organisms, gills are a respiratory organ for the extraction of oxygen from water and for the excretion of carbon dioxide. ... General Name, Symbol, Number oxygen, O, 8 Chemical series Nonmetals, chalcogens Group, Period, Block 16, 2, p Appearance colorless Atomic mass 15. ... Diagram of the layers of human skin In zootomy and dermatology, skin is an organ of the integumentary system made up of a layer of tissues that protect underlying muscles and organs. ... Desiccation is the state of extreme dryness, or the process of extreme drying. ... With regard to living things, a body is the integral physical material of an individual, and contrasts with soul, personality and behavior. ... A Ring-tailed Lemur For other uses, see Tail (disambiguation). ... A fin is a surface used to produce lift and thrust or to steer while traveling in water, air, or other fluid media. ...

Late Devonian vertebrate speciation saw lobe-finned fish like Panderichthys having descendants such as Eusthenopteron which could breathe air in muddy shallows, then Tiktaalik whose limb-like fins could take it onto land, preceding the first tetrapod amphibians such as Acanthostega whose feet had eight digits, and Ichthyostega with developed limbs, negotiating weed-filled swamps. Lobe-finned fish evolved into Coelacanth species which survive to this day.

The adult animals were so big and heavy (1.5 m or 4 ft) and poorly adapted for terrestrial locomotion that there probably wouldn't have been much benefit to their being on land. However, the massive ribcage is made up of overlapping ribs -- and compared to their ancestors, the body has a stronger skeletal structure, a more advanced spine, and forelimbs with possibly enough power to pull the body from the water. These anatomical modifications are clearly evolved to handle the gravity experienced on land. The hindlimbs were smaller and so weak they couldn't have been able to bear the weight of an adult. Jennifer A. Clack suggests that Ichthyostega and relatives were spending time basking in the sun to raise their temperature, perhaps adopting a similar lifestyle to that of the marine iguana on Galapagos, seals or the Gharial -- mostly returning to water for food, to drink, to reproduce, or to cool down. In that case, they would need strong forelimbs to pull at least their anterior part out of the water, and a stronger ribcage and spine to support them while sunbathing on their abdomen like modern crocodiles. The juveniles, on the other hand, would have been able to move around on land much more easily. Image File history File links Fishapods. ... Image File history File links Fishapods. ... == == Disambiguation: Devonian is sometimes used to refer to the Southwestern Brythonic language, and the people of the county of Devon are sometimes referred to as Devonians The Devonian is a geologic period of the Paleozoic era. ... Vertebrata is a subphylum of chordates, specifically, those with backbones or spinal columns. ... Subclasses Coelacanthimorpha - Coelacanths Dipnoi - Lungfishes Tetrapoda Sarcopterygii is traditionally the class of lobe-finned fishes, consisting of lungfish and coelacanths. ... Panderichthys Panderichthys is a 90-130 cm long fish from the Late Devonian period . ... Binomial name Eusthenopteron foordi Eusthenopteron foordi Whiteaves 1881 is a genus of lobe-finned fish which has attained an iconic status from its close relationships to tetrapods. ... Binomial name Tiktaalik roseae Daeschler, Shubin & Jenkins, 2006 Tiktaalik (IPA pronunciation: ) is a genus of extinct sarcopterygian (lobe-finned) fishes from the late Devonian period, with many tetrapod-like features. ... Groups See text. ... Orders Subclass Labyrinthodontia- extinct Subclass Lepospondyli- extinct Subclass Lissamphibia   Anura   Caudata   Gymnophiona Amphibians (class Amphibia) are a taxon of animals that include all tetrapods (four-legged vertebrates) that do not have amniotic eggs. ... Acanthostega Acanthostega gunnari is an extinct amphibian tetrapod species, among the first animals to have recognizable limbs. ... Species Latimeria chalumnae Latimeria menadoensis Coelacanth (meaning hollow thorn, from the Greek coelia, κοιλιά (hollow) and acanthos, άκανθος (thorn)); IPA: ) is a species of fish and represents the oldest living lineage of jawed fish known to date. ... Jennifer A. Clack is a British expert in the theory of evolution. ... Binomial name Amblyrhynchus cristatus (Bell, 1825) The Marine Iguana (Amblyrhynchus cristatus) is a species of iguana that has the unique ability among modern lizards to live and forage in the sea. ... NASA Satellite photo of the Galápagos archipelago. ... Genera Monachus(Monk Seals) Mirounga(Elephant Seal) Lobodon(Crabeater Seals) Leptonychotes Hydrurga(Leopard Seals) Ommatophoca Erignathus(Bearded Seals) Phoca Halichoerus(Grey Seals) Cystophora(Hooded Seals) The true seals or earless seals are one of the three main groups of mammals within the seal suborder, Pinnipedia. ... Binomial name Gavialis gangeticus (Gmelin, 1789) // Taxonomy The gharial (Gavialis gangeticus) is the only surviving member of the family Gavialidae, a long-established group of crocodile-like reptiles with long, narrow jaws. ... Genera Crocodylus Osteolaemus Tomistoma See full taxonomy. ...

Water was also still a requirement, because the jelly-like eggs of the earliest terrestrial tetrapods couldn't survive out of water, so reproduction could not occur without it. Water was also needed for their larvae and external fertilization. Most land-dwelling vertebrates have since developed two methods of internal fertilization; either direct as seen in all amniotes and a few amphibians, or indirect for many salamanders by placing a spermatophore on the ground which then is picked up by the female salamander. Look up jelly in Wiktionary, the free dictionary. ... An average Whooping Crane egg is 102 mm long, and weighs 208 grams In some animals, an egg (Latin ovum) is the zygote, resulting from fertilization of the ovum. ... For other uses, see Reproduction (disambiguation) Reproduction is the biological process by which new individual organisms are produced. ... Categories: Biology stubs ... Living subgroups Class Synapsida    Class Mammalia(mammals) Class Sauropsida    Anapsida        Testudines(turtles)    Diapsida        Lepidosauria           Squamata(lizards& snakes)           Sphenodontida(tuatara)        Archosauria           Crocodilia(crocodiles)           Class Aves(birds) The amniotes are a microphylum of vertebrates that have an amnion during embryonic development. ... Suborders Cryptobranchoidea Salamandroidea Sirenoidea Salamander is the common name applied to approximately 500 amphibian vertebrates with slender bodies, short legs, and long tails (order Caudata or Urodela). ... A spermatophore is a capsule or mass created by males of various invertebrate species, containing spermatozoa and transferred in entirety to the female during sex. ...

Ichthyostegoids (Elginerpeton, Acanthostega, Ichthyostega,...) were "succeeded" by temnospondyls and anthracosaurs, such as Eryops, an amphibian that truly developed the ability to walk on land. There is a gap of 20-30 million years between both groups. This gap, a classic in vertebrate paleontology, is known as Romer's Gap, after the American paleontologist Alfred Sherwood Romer. In 2002 a 350 million year old fossil named Pederpes finneyae was found. Binomial name Eryops megacephalus Cope, 1882 Eryops (AR-ee-ops) meaning drawn-out face because most of its skull was in front of its eyes (Greek eryein = drawn-out + ops = face) is a genus of extinct, semi-aquatic amphibian found primarily in the Permian-aged Admiral Formation of Archer County... Vertebrata is a subphylum of chordates, specifically, those with backbones or spinal columns. ... A paleontologist carefully chips rock from a column of dinosaur vertebrae. ... Romers Gap is an example of a gap in the fossil record. ... Alfred Sherwood Romer (December 28, 1894 _ November 5, 1973) was an American paleontologist and comparative anatomist and a specialist in vertebrate evolution. ... For the Cusco album, see 2002 (album). ...

See also

• Prehistoric amphibian
• Prehistoric life

Prehistoric amphibians are various amphibians that lived before recorded history. ... Prehistoric life is a term used to refer to diverse organisms that inhabited Earth from the origin of life about 3. ...

External links

• Excellent site on early tetrapods
• Course site
• Course site
• First Four-Legged Animals Inched Along

References

Blom, H. (2005) — Taxonomic Revision Of The Late Devonian Tetrapod Ichthyostega from East Greenland. Palaeontology, 48, Part 1:111–134

Westenberg, K. (1999) — From Fins to Feet. National Geographic, 195, 5:114–127