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Psammosteida
Psammosteida also called as Psammosteoidei is a suborder of pteraspidid heterostracan agnathans. The psammosteids had broad, flattened bodies, suggesting a predominantly benthic habit. The earliest unequivocal psammosteid is '' Drepanaspis'' of Early Devonian Germany, which is either included in the family Psammosteidae, or placed within its own family, Drepanaspididae. If the late Silurian/Early Devonian '' Weigeltaspis'' is a psammosteid, as opposed to being a traquairaspid, then that genus, instead, would be the oldest psammosteid. However, its placement within Heterostraci remains a matter of debate. Other notable psammosteids include '' Psammosteus'', and '' Obruchevia'', two genera of enormous species with dorsal shields around one meter in diameter. The Psammosteids were the only heterostracans to survive to the end of the Devonian, where they finally perish during the Hangenberg event The Hangenberg event, also known as the Hangenberg crisis or end-Devonian extinct ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Heterostraci
Heterostraci (Ancient Greek, ἕτερος+ὄστρακον "those itha different shell" i is pl. of -us is an extinct subclass of pteraspidomorph jawless vertebrate that lived primarily in marine and estuary environments. Heterostraci existed from the mid-Ordovician to the conclusion of the Devonian. Description and anatomy The Heterostracans differed from other Paleozoic agnathan taxa both in the arrangement and histology of their scales. Most heterostracans had two plates which form a large dorsal shield and a large ventral shield, and had series of scales arranged in various patterns on the sides of their bodies, the exact pattern differing from one group to another. In a few primitive forms, such as '' Lepidaspis'', the dorsal and ventral shields are composed of a mosaic of tiny scales. In most other known forms, though, these tiny scales have fused together to form the shield-plates. The scales of heterostracans are histologically distinct from other vertebrate ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pteraspidiformes
Pteraspidiformes is an extinct order of heterostracan agnathan vertebrates known from extensive fossil remains primarily from Early Devonian strata of Europe and North America, and from Upper Silurian Canada. Anatomy A pteraspidiform heterostracan has the cephalothorax enclosed in armor, formed from several plates, including dorsal, ventral, rostral, pineal plates, a dorsal spine derived from a scale, and a large, scale-covered tail. Many genera were benthic, others were apparently active swimming nekton.Botella, Hector, and Richard A. Farina. "Flow pattern around the rigid cephalic shield of the Devonian agnathan Errivaspis waynensis (Pteraspidiformes: Heterostraci)." Palaeontology 51.5 (2008): 1141-1150/ref> Delicate, finger-like components of the anterior end of the ventral plate forming the edges of the mouth suggest that pteraspidiform heterostracans were filter-feeding, filter-feeders that selectively filtered specific sized plankton from the water column.Purnell, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Heterostraci
Heterostraci (Ancient Greek, ἕτερος+ὄστρακον "those itha different shell" i is pl. of -us is an extinct subclass of pteraspidomorph jawless vertebrate that lived primarily in marine and estuary environments. Heterostraci existed from the mid-Ordovician to the conclusion of the Devonian. Description and anatomy The Heterostracans differed from other Paleozoic agnathan taxa both in the arrangement and histology of their scales. Most heterostracans had two plates which form a large dorsal shield and a large ventral shield, and had series of scales arranged in various patterns on the sides of their bodies, the exact pattern differing from one group to another. In a few primitive forms, such as '' Lepidaspis'', the dorsal and ventral shields are composed of a mosaic of tiny scales. In most other known forms, though, these tiny scales have fused together to form the shield-plates. The scales of heterostracans are histologically distinct from other vertebrate ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Psammosteidae
Psammosteidae is an extinct family of flattened, benthic heterostracan vertebrates that lived in marine and estuary environments in Europe, Russia & North America. They arose during the Early Devonian, with the first (and best) known genus, '' Drepanaspis'' from the Hunsrück lagerstätte. The Psammosteids were the only heterostracans that survived the Upper Frasnian extinction event during the Late Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, wher ..., dying out in the extinction event at the very end of the Devonian. Many of the Late Devonian genera, such as ''Psammolepis'', were among the largest heterostracans ever, growing to be at least 1.5 metres in width. References''Palaeos Vertebrates'' Devonian jawless fish Prehistoric jawless fish families Heterostraci F ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Weigeltaspis
''Weigeltaspis'' is a genus of extinct heterostracan agnathan fish known from the Late Silurian and Early Devonian periods. Fossils are known primarily from Early Devonian-aged marine strata of Europe and Canada. Fragments and disarticulated plates of what may be of ''Weigeltaspis'' are known from Late Silurian-aged marine strata of Arctic Canada. Rare articulated fossils, plus the overall anatomy of its plates suggest the living animals were, at least superficially, similar to psammosteids, some authorities, such as Tarlo, place them within Psammosteida.Tarlo, Halstead. "LB t1965) Psammosteiformes tAgnatha)—A review with descriptions of new material from the Lower Devonian of Poland, II. Systematic Part." Palaeontologia Polonica 15: 168. Pages 20-21 Because the ornamentation on the plates and scales are very similar to the ornamentation seen on the plates and scales of '' Traquairaspis'' to the point of constant confusion, other authorities follow the lead of Obruchev, and pl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Drepanaspis
''Drepanaspis'' (from el, δρεπάνη 'sickle' and el, ἀσπίς 'shield') is an extinct genus of primitive jawless fish from Early Devonian marine strata of Europe. ''D. gemuendenensis'', of the Hunsrück lagerstätte is the best known, and most thoroughly studied species, as it is known from several articulated specimens. Description ''Drepanaspis'' was a flattened creature with a heavily armored body, superficially ray Ray may refer to: Fish * Ray (fish), any cartilaginous fish of the superorder Batoidea * Ray (fish fin anatomy), a bony or horny spine on a fin Science and mathematics * Ray (geometry), half of a line proceeding from an initial point * Ray (g ...-like in appearance. Its mouth faced upwards, unlike most other Heterostracans, which had downward-facing mouths. It also had small, widely spaced eyes. It is presumed to have foraged the ocean floor for food. This frying-pan-shaped fish may have been the ancestor of the giant, meter-long, meter-wide P ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Traquairaspis
''Traquairaspis'' is a genus of extinct heterostracan agnathan fish known from the Silurian and Early Devonian periods. It is predominantly known from Late Silurian fluvial deposits from Wales and England: some species were also found in shallow water marine environment in Canada and North America. The head-shield and body armor of most species form an almond shape. Plates have a distinctive ornamentation of tubercles: this ornamentation is very similar to the plate ornamentation of the heterostracan ''Weigeltaspis''. This similarity of ornamentation creates much confusion over the taxonomical placement of ''Weigeltaspis'', in addition to confusion over whether or not an isolated plate is of ''Traquairaspis'', or of ''Weigeltaspis''.Tarlo, Halstead. "LB t1965) Psammosteiformes tAgnatha)—A review with descriptions of new material from the Lower Devonian of Poland, II. Systematic Part." Palaeontologia Polonica 15: 168. Pages 20-21 The generic name honors Ramsay Heatley Traqu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Devonian Extinctions
The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, where rocks from this period were first studied. The first significant adaptive radiation of life on dry land occurred during the Devonian. Free-sporing vascular plants began to spread across dry land, forming extensive forests which covered the continents. By the middle of the Devonian, several groups of plants had evolved leaves and true roots, and by the end of the period the first seed-bearing plants appeared. The arthropod groups of myriapods, arachnids and hexapods also became well-established early in this period, after starting their expansion to land at least from the Ordovician period. Fish reached substantial diversity during this time, leading the Devonian to often be dubbed the Age of Fishes. The placoderms began dominating al ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Devonian Jawless Fish
The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, where rocks from this period were first studied. The first significant adaptive radiation of life on dry land occurred during the Devonian. Free-sporing vascular plants began to spread across dry land, forming extensive forests which covered the continents. By the middle of the Devonian, several groups of plants had evolved leaves and true roots, and by the end of the period the first seed-bearing plants appeared. The arthropod groups of myriapods, arachnids and hexapods also became well-established early in this period, after starting their expansion to land at least from the Ordovician period. Fish reached substantial diversity during this time, leading the Devonian to often be dubbed the Age of Fishes. The placoderms began dominating al ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hangenberg Event
The Hangenberg event, also known as the Hangenberg crisis or end-Devonian extinction, is a mass extinction that occurred at the end of the Famennian stage, the last stage in the Devonian Period (roughly 358.9 ± 0.4 million years ago). It is usually considered the second-largest extinction in the Devonian Period, having occurred approximately 13 million years after the Late Devonian mass extinction (Kellwasser event) at the Frasnian-Famennian boundary. The Hangenberg event was an anoxic event marked by a layer of black shale, and it has been proposed to have been related to a rapid sea-level fall from the last phase of the Devonian Southern Hemisphere glaciation. It has also been suggested to have been linked to an increase in terrestrial plant cover. That would have led to increased nutrient supply in rivers and may have led to eutrophication of semi-restricted epicontinental seas and could have stimulated algal blooms. However, support for a rapid increase in plant cover at the e ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
