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Jamoytiiformes
''Jamoytius kerwoodi'' is an extinct species of primitive, eel-like jawless fish known from the Patrick Burn Formation in Scotland, dating to the Llandovery epoch of the Early Silurian period. Long thought of as a "basal anaspid," ''J. kerwoodi'' is now recognized as the best-known member of the Hyperoartian order (biology), order Jamoytiiformes. It had an elongated body, and is thought to have had, in comparison with relatives known from intact bodies like ''Euphanerops'', a dorsal fin and an anal fin near the rearmost third of its body. Earlier reconstructions depict the creature as having side-fins running the length of its body, starting from behind the branchial openings to the tip of its tail: new research demonstrates that such "fins" are actually deformations of the bodywall as the corpse was being squished post-burial. In life, ''J. kerwoodi'' resembled a lamprey with a very small mouth. Because the fossil had no teeth, teeth-like structures, nor suggestions of either in ...
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Jawless Fish
Agnatha (; ) or jawless fish is a paraphyletic infraphylum of animals in the subphylum Vertebrata of the phylum Chordata, characterized by the lack of jaws. The group consists of both extant taxon, living (Cyclostomi, cyclostomes such as hagfishes and lampreys) and Extinction, extinct clades (e.g. conodonts and Cephalaspidomorphi, cephalaspidomorphs, among others). They are sister taxon, sister to vertebrates with jaws known as gnathostomes, who evolution, evolved from jawless ancestors during the early Silurian by developing folding joint, articulations in the first pairs of gill arches. Sequencing, Molecular data, both from rRNA and from mtDNA as well as Embryology, embryological data, strongly supports the hypothesis that both groups of living agnathans, hagfishes and lampreys, are more closely related to each other than to Gnathostomata, jawed fish, forming the Class (biology), superclass Cyclostomi. The oldest fossil agnathans appeared in the Cambrian. Living jawless fish c ...
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Anaspidomorphi Genera
Anaspidomorphi (anaspidomorphs) is an extinct superclass of jawless fish. According to the newer taxonomy based on the work of Nelson, Grande and Wilson 2016 and van der Laan 2018, the phylogeny of Anaspidomorphi looks like this: * Superclass †Anaspidomorphi ** Order † Euphanerida *** Family † Euphaneropidae Woodward, 1900 ** Order †Jamoytiiformes Halstead-Tarlo, 1967 *** Family † Achanarellidae Newman, 2002 *** Family † Jamoytiidae White, 1946 ** Class †Anaspida Anaspida ("shieldless ones") is an extinct group of jawless fish that existed from the early Silurian period to the late Devonian period. They were classically regarded as the ancestors of lampreys, but it is denied in recent phylogenetic anal ... Janvier, 1996 non Williston, 1917 *** Order † Endeiolepidiformes Berg, 1940 **** Family † Endeiolepididae Stensio, 1939 *** Order † Birkeniiformes Stensiö, 1964 **** Family † Pharyngolepididae Kiær, 1924 **** Family † Pterygolepididae Obručhev, 1 ...
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Jamoytiiformes
''Jamoytius kerwoodi'' is an extinct species of primitive, eel-like jawless fish known from the Patrick Burn Formation in Scotland, dating to the Llandovery epoch of the Early Silurian period. Long thought of as a "basal anaspid," ''J. kerwoodi'' is now recognized as the best-known member of the Hyperoartian order (biology), order Jamoytiiformes. It had an elongated body, and is thought to have had, in comparison with relatives known from intact bodies like ''Euphanerops'', a dorsal fin and an anal fin near the rearmost third of its body. Earlier reconstructions depict the creature as having side-fins running the length of its body, starting from behind the branchial openings to the tip of its tail: new research demonstrates that such "fins" are actually deformations of the bodywall as the corpse was being squished post-burial. In life, ''J. kerwoodi'' resembled a lamprey with a very small mouth. Because the fossil had no teeth, teeth-like structures, nor suggestions of either in ...
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Basal (phylogenetics)
In phylogenetics, basal is the direction of the ''base'' (or root) of a phylogenetic tree#Rooted tree, rooted phylogenetic tree or cladogram. The term may be more strictly applied only to nodes adjacent to the root, or more loosely applied to nodes regarded as being close to the root. Note that extant taxa that lie on branches connecting directly to the root are not more closely related to the root than any other extant taxa. While there must always be two or more equally "basal" clades sprouting from the root of every cladogram, those clades may differ widely in taxonomic rank, Phylogenetic diversity, species diversity, or both. If ''C'' is a basal clade within ''D'' that has the lowest rank of all basal clades within ''D'', ''C'' may be described as ''the'' basal taxon of that rank within ''D''. The concept of a 'key innovation' implies some degree of correlation between evolutionary innovation and cladogenesis, diversification. However, such a correlation does not make a given ca ...
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Fossil Taxa Described In 1946
A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved in amber, hair, petrified wood and DNA remnants. The totality of fossils is known as the ''fossil record''. Though the fossil record is incomplete, numerous studies have demonstrated that there is enough information available to give a good understanding of the pattern of diversification of life on Earth. In addition, the record can predict and fill gaps such as the discovery of ''Tiktaalik'' in the arctic of Canada. Paleontology includes the study of fossils: their age, method of formation, and evolutionary significance. Specimens are sometimes considered to be fossils if they are over 10,000 years old. The oldest fossils are around 3.48 billion years to 4.1 billion years old. Early edition, published online before print. The ob ...
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Silurian Animals Of Europe
The Silurian ( ) is a geologic period and system spanning 23.5 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the Devonian Period, Mya. The Silurian is the third and shortest period of the Paleozoic Era, and the third of twelve periods of the Phanerozoic Eon. As with other geologic periods, the rock beds that define the period's start and end are well identified, but the exact dates are uncertain by a few million years. The base of the Silurian is set at a series of major Ordovician–Silurian extinction events when up to 60% of marine genera were wiped out. One important event in this period was the initial establishment of terrestrial life in what is known as the Silurian-Devonian Terrestrial Revolution: vascular plants emerged from more primitive land plants, dikaryan fungi started expanding and diversifying along with glomeromycotan fungi, and three groups of arthropods (myriapods, arachnids and hexapods) became full ...
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Synapomorphy
In phylogenetics, an apomorphy (or derived trait) is a novel Phenotypic trait, character or character state that has evolution, evolved from its ancestral form (or Plesiomorphy and symplesiomorphy, plesiomorphy). A synapomorphy is an apomorphy shared by two or more taxon, taxa and is therefore Hypothesis#Scientific hypothesis, hypothesized to have evolved in their most recent common ancestor. ) In cladistics, synapomorphy implies Homology (biology), homology. Examples of apomorphy are the presence of Terrestrial locomotion#Posture, erect gait, fur, Evolution of mammalian auditory ossicles, the evolution of three middle ear bones, and mammary glands in mammals but not in other vertebrate animals such as amphibians or reptiles, which have retained their ancestral traits of a Terrestrial locomotion#Posture, sprawling gait and lack of fur. Thus, these derived traits are also synapomorphies of mammals in general as they are not shared by other vertebrate animals. Etymology The word ...
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Chordate
A chordate ( ) is a bilaterian animal belonging to the phylum Chordata ( ). All chordates possess, at some point during their larval or adult stages, five distinctive physical characteristics ( synapomorphies) that distinguish them from other taxa. These five synapomorphies are a notochord, a hollow dorsal nerve cord, an endostyle or thyroid, pharyngeal slits, and a post- anal tail. In addition to the morphological characteristics used to define chordates, analysis of genome sequences has identified two conserved signature indels (CSIs) in their proteins: cyclophilin-like protein and inner mitochondrial membrane protease ATP23, which are exclusively shared by all vertebrates, tunicates and cephalochordates. These CSIs provide molecular means to reliably distinguish chordates from all other animals. Chordates are divided into three subphyla: Vertebrata (fish, amphibians, reptiles, birds and mammals), whose notochords are replaced by a cartilaginous/ bony axia ...
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Rhuddanian
In the geologic timescale, the Rhuddanian is the first age of the Silurian Period and of the Llandovery Epoch. The Silurian is in the Paleozoic Era of the Phanerozoic Eon. The Rhuddanian Age began 443.8 ± 1.5 Ma and ended 440.8 ± 1.2 Ma (million years ago). It succeeds the Hirnantian Age (the last age of the Ordovician Period) and precedes the Aeronian Age. GSSP The GSSP for the Silurian is located in a section at Dob's Linn, Scotland, in an artificial excavation created just north of the Linn Branch Stream. Two lithological units ( formations) occur near the boundary. The lower is the Hartfell Shale ( thick), consisting chiefly of pale gray mudstone with subordinate black shales and several interbedded meta-bentonites. Above this is the thick Birkhill Shale, which consist predominantly of black graptolitic shale with subordinate gray mudstones and meta-bentonites. The name is given after Cefn-Rhuddan Farm, Llandovery in Carmarthenshire, Wales Wales ( ) is a Co ...
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