| Nasakia | |
|---|---|
Scientific classification  | |
| Kingdom: | Animalia |
| Clade: | Lophophorata |
| Phylum: | Brachiopoda |
| Class: | † Obolellata |
| Order: | † Naukatida |
| Family: | † Tomteluvidae |
| Genus: | † Nasakia |
| Species: | †N. thulensis |
| Binomial name | |
| †Nasakia thulensis Streng et al 2016 | |
Nasakia is a genus of Naukatid brachiopod known from Cambrian strata. There is a species called Nasakia thulensis. [1]
The Ordovician is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period 485.4 million years ago (Mya) to the start of the Silurian Period 443.8 Mya.
Craniata is a class of brachiopods originating in the Cambrian period and still extant today. They have calcitic inarticulated shells that are subcircular in outline. This class of brachiopods has an unsupported lophophore and is always attached to a hard substrate in the fossil record. This hard substrate is usually another brachiopod. The plicae from the host brachiopod will then appear within the shell of the craniata.
The Cambrian–Ordovician extinction event occurred approximately 488 million years ago (m.y.a.). This early Phanerozoic Eon extinction event eliminated many brachiopods and conodonts, and severely reduced the number of trilobite species. The Period in the Cambrian extinction in which most of the extinction occurred was the Caerfai Period.
Linguliformea is a subphylum of inarticulate brachiopods. These were the earliest of brachiopods, ranging from the Cambrian into the Holocene. They rapidly diversified during the Cambrian into the Ordovician, but most families became extinct by the end of the Devonian.
Brachiopods, phylum Brachiopoda, are a group of lophotrochozoan animals that have hard "valves" (shells) on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear end, while the front can be opened for feeding or closed for protection. Two major groups are recognized, articulate and inarticulate. The word "articulate" is used to describe the tooth-and-groove features of the valve-hinge which is present in the articulate group, and absent from the inarticulate group. This is the leading diagnostic feature (fossilizable), by which the two main groups can be readily distinguished. Articulate brachiopods have toothed hinges and simple opening and closing muscles, while inarticulate brachiopods have untoothed hinges and a more complex system of muscles used to keep the two valves aligned. In a typical brachiopod a stalk-like pedicle projects from an opening in one of the valves near the hinges, known as the pedicle valve, keeping the animal anchored to the seabed but clear of silt that would obstruct the opening.
The origin of the brachiopods is uncertain; they either arose from reduction of a multi-plated tubular organism, or from the folding of a slug-like organism with a protective shell on either end. Since their Cambrian origin, the phylum rose to a Palaeozoic dominance, but dwindled during the Mesozoic.
The Kirengellids are a group of problematic Cambrian fossil shells of marine organisms. The shells bear a number of paired muscle scars on the inner surface of the valve.
Acrothyra gregaria is a species of gregarious brachiopod known from the Middle Cambrian Burgess Shale. 253 specimens of Acrothyra are known from the Greater Phyllopod bed, where they comprise 0.5% of the community.
Obolella is a genus of Cambrian brachiopods.
Stenothecoida is a taxon of bivalved fossils from the Early to middle Cambrian period. They look a bit like brachiopods or bivalve molluscs.
Mobergella is a millimetric Lower Cambrian shelly fossil of unknown affinity, usually preserved in phosphate and particularly well known from Swedish strata, where it is diagnostic of lowermost Cambrian rocks. Originally interpreted as a monoplacophoran, the circular, cap-shaped shell resembles a hyolith operculum, with concentric rings on its upper surface, and seven pairs of internal muscle scars. It is never found in association with a conch, and its affinity therefore remains undetermined. Nevertheless, its heavy musculature does seem to indicate that it functioned as an operculum.
Mickwitziids are a Cambrian group of shelly fossils with originally phosphatic valves, belonging to the Brachiopod stem group, and exemplified by the genus Mickwitzia – the other genera are Heliomedusa and Setatella. The family Mickwitziidae is conceivably paraphyletic with respect to certain crown-group brachiopods.
Askepasma is an extinct genus of brachiopods which existed in what is now Australia and southern China during the Lower Cambrian.
Discinida is an order of brachiopods comprising the extant superfamily Discinoidea, and the extinct superfamilies Botsfordioidea (early—mid-Cambrian) and Acrotheloidea. It represents a sister taxon to the Lingulids, and is possibly paraphyletic with respect to the Acrotretoids.—or the acrotretids are paraphyletic with respect to it. The group displays a broad range of shell structures, some of which incorporate substantial organic or silicified components.
Acrotheloidea is a superfamily of Discinid brachiopods, alternatively ascribed to the lingulids—for a discussion of discinid taxonomy, see Discinida.
Strophomenata is an extinct class of brachiopods in the subphylum Rhynchonelliformea.
Micrina is an extinct genus of tommotiids with affinities to brachiopods.
Lingulellotretidae is an extinct family of brachiopods, with an extended pseudointerarea, including some soft-shelled representatives.
Kutorginates are early rhynchonelliform brachiopods.
Alisina is a Cambrian genus of Obolellid brachiopod from which soft tissue is known.
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