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The Mackenzie Mountains are a Canadian mountain range forming part of the Yukon-Northwest Territories boundary between the Liard and Peel rivers. The range is named in honour of Canada's second prime minister, Alexander Mackenzie. Nahanni National Park Reserve and Nááts'ihch'oh National Park Reserve are in the Mackenzie Mountains.
Heterostraci is an extinct subclass of pteraspidomorph jawless vertebrate that lived primarily in marine and estuary environments. The first identifiable heterostracans appear in the fossil record during the Early Silurian, and all, save for the Psammosteids, became extinct by the start of the late Devonian. This last group of heterostracans died out in the extinction event at the end of the Devonian.
Paleontology or palaeontology is the study of prehistoric life forms on Earth through the examination of plant and animal fossils. This includes the study of body fossils, tracks (ichnites), burrows, cast-off parts, fossilised feces (coprolites), palynomorphs and chemical residues. Because humans have encountered fossils for millennia, paleontology has a long history both before and after becoming formalized as a science. This article records significant discoveries and events related to paleontology that occurred or were published in the year 2004.
Furcacauda is a genus of thelodontid agnathan from the Lower Devonian of Canada, and is the type genus of the order Furcacaudiformes. Furcacaudiform thelodontids were deep water jawless vertebrates with symmetrical fork and lobed-finned tails and scales smaller than typical loganellid and nikoliviid thelodonti scales. Furcacaudiform thelodonts are noted as having a laterally compressed body, large anterior eyes, slightly posterior, lateral, and vertical to a small mouth, and a condensed curved row of branchial openings (gills) directly posterior to the eyes. Many but not all had laterally paired fins. Wilson and Caldwell also note the presence of a caudal peduncle and a long caudal fin made of two large lobes, one dorsal and one ventral separated by 8 to 14 smaller intermediate lobes, giving the appearance of a striated half-moon shaped tail resembling the tail of a heterostracan. A large square cavity within the gut connecting a small intestine to an anal opening lead many to believe that it is this genus that exhibits the first vertebrate stomach. According to Wilson and Caldwell their discovery, based on sediment infillings of fossils of the Furcacauda heintze, gives credence to the evolutionary development of stomach before jaws.
Superciliaspis is an extinct genus of jawless fish which existed in what is now the Northwest Territories of Canada during the Lochkovian age. Originally identified as a species of Cephalaspis by Dineley and Loeffler in 1976, it was reassigned to Superciliaspis gabrielsi by Adrain and Wilson in 1994.
Lechriaspis is an extinct genus of poraspid heterostracan agnathan known from the Early Devonian of northern Utah, western United States.
Poraspis is an extinct genus of heterostracan. Fossils are found in Late Silurian and Early Devonian marine strata of Norway, Canada and the United States.
Ariaspis is an extinct genus of cyathaspidiform heterostracan agnathan. Fossils are found in marine strata of Canada and Europe from the late Silurian period until its extinction during the Early Devonian. A new species, A. arctata, was described by David K. Elliott and Sandra Swift in 2010.
Capitaspis is an extinct genus of cyathaspidine cyathaspidid heterostracan jawless vertebrate known from the Late Silurian Somerset Island Formation of the Northwest Territories, Canada. It contains a single species, Capitaspis giblingi. It is most closely related to Pionaspis.
Kiangsuaspis nankingensis is an extinct phyllocarid crustaceans from Late Silurian China. It was originally described in 1962 by Kiang P'an as an incomplete ventral plate of a cyathaspidid heterostracan agnathan with a unique pattern of raised, sculptured tubercles that fuse together into anastomosing ridges. In 1984, Jiang P'an then reappraised it as a ceratiocaridid crustacean.
Panamintaspis snowi is an extinct species of pteraspidid heterostracan agnathan which existed during the early Middle Devonian period of Death Valley, California. Fossils are found in Late Emsian-aged marine strata of the Lost Burro Formation. P. snowi strongly resembles Pteraspis, though while it was originally described as a member of the same family, Pteraspididae, a recent phylogenetic reassessment of the order Pteraspidiformes places P. snowi within the paraphyletic family "Protopeteraspidae," as the sister taxon of the suborder Pteraspidoidei.
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.
Cyathaspidiformes is an extinct order of heterostracan vertebrates known from extensive fossil remains primarily from Silurian to Early Devonian strata of Europe, and North America, and from Early Devonian marine strata of Siberia.
Cyathaspididae is an extinct family in the heterostracan order Cyathaspidiformes.
Ctenaspidae is a family of extinct cyathaspidiform heterostracan agnathans in the suborder Cyathaspidida.
Anchipteraspididae is an extinct family of heterostracan vertebrates restricted to Late Silurian and Early Devonian strata of Arctic Canada.
References
- ↑ David K. Elliott & David L. Dineley (1985). "A new heterostracan from the Upper Silurian of Northwest Territories, Canada". Journal of Vertebrate Paleontology . 5 (2): 103–110. doi:10.1080/02724634.1985.10011848. JSTOR 4523034.
- ↑ David K. Elliott & David L. Dineley (1991). "Additional information on Alainaspis and Boothiaspis, cyathaspidids (Agnatha: Heterostraci) from the Upper Silurian of Northwest Territories, Canada". Journal of Paleontology . 65 (2): 308–313. doi:10.1017/S0022336000020540. JSTOR 1305766.
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