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Helix is a genus of large, air-breathing land snails native to the western Palaearctic and characterized by a globular shell. [1] [2] It is the type genus of the family Helicidae, and one of the animal genera described by Carl Linnaeus [3] at the dawn of the zoological nomenclature. Members of the genus first appeared in the fossil record ...
Somatohelix is a genus of curvilinear, spiralling tubular fossil, 2–7 mm wide and 3–14 cm long, from the Ediacaran deposites of the South Australia that was originally interpreted as a trace fossil; a larger amount of better-preserved material since facilitated its reconstruction as the remains of an organism of uncertain nature. [1]
The fossil record suggests that the population history of Xerocrassa geyeri is linked to palaeoclimate changes. [15] The latitudinal shifts of suitable habitat during Pleistocene across Europe, driven by climate change, were anticipated by Xerocrassa geyeri in the fossil record with remarkably short time lags. [ 15 ]
Tawuia describes a more sausage- or crescent-shaped fossil; Chuaria refers to more discoidal instances. The fossils are often preserved as organic compressions. They are considered to represent microbial structures; [ 1 ] some authors affiliate them with slime molds [ 1 ] Stratigraphically , they range from 1,630 million years ago [ 2 ] to the ...
The fossil history of this class goes back to the Late Cambrian. As of 2017 [update] , 721 families of gastropods are known, of which 245 are extinct and appear only in the fossil record, while 476 are currently extant with or without a fossil record.
Punctum minutissimum I. Lea, 1841 – but Helix minutissima may be considered as a synonym of Punctum pygmaeum [5] Punctum mokotoense Abdou & Bouchet, 2000; Punctum morseanum Pilsbry, 1902; Punctum nimbaense de Winter, 2017 † Punctum oligocaenicum Zinndorf, 1901; Punctum orphana (Heude, 1882) Punctum pallidum Connolly, 1922 [6] † Punctum ...
The pitch of a helix is the height of one complete helix turn, measured parallel to the axis of the helix. A double helix consists of two (typically congruent) helices with the same axis, differing by a translation along the axis. [3] A circular helix (i.e. one with constant radius) has constant band curvature and constant torsion. The slope of ...
Index fossils must have a short vertical range, wide geographic distribution and rapid evolutionary trends. Another term, "zone fossil", is used when the fossil has all the characters stated above except wide geographical distribution; thus, they correlate the surrounding rock to a biozone rather than a specific time period.