Thursday, 20 October 2016

Brachiopods from the Late Cretaceous of South Island, New Zealand.

Brachiopods are Lophophorate animals related to Bryozoans and Phoranid Worms. They are superficially similar to Bivalve Molluscs, with a filter feeding animal living between two opposed shells, but their internal structure is quite different with a lophophore (net-like organ) being extruded to capture planktonic prey rather than the siphon of Bivalves which lets them pump in water and strain it for food. This, along with a different muscle structure used to seal the shell whch makes Brachiopods more vulnerable to predators such as Starfish, has led to the Brachiopods being less ecologically successful than the Bivalves in most environments, so that while Brachiopods dominated many Palaeozoic benthic ecosystems and are still extant today, they were progressively replaced in many environments by their Mollusc rivals during the Mesozoic, and by the end of the Cretaceous were uncommon members of invertebrate communities.

In a paper published in the Records of the Canterbury Museum on 29 September 2016, Norton Hiller of the Department of Geological Sciences at the University of Canterbury and the Canterbury Museum, describes a new species of Brachiopod from an exposure of the Mead Hill Formation on the foreshore at Kaikoura in North Canterbury on South Island, New Zealand. The fossils were discovered during a field trip by the Geological Society of New Zealand in 2005, made to make that organizations 50th anniversary, and were part of the first collection of macro-invertebrate fossils collected from the Mead Hill Formation, a collection that also included Sponges, Echinoid spines, and a possible Belemnite.

The new species is named Gowanella capralis, where 'Gowanella' refers to the Gowan Hill Farm, on whose land the specimens were found, and 'capralis' is a Latin word for a marsh, implying land fit only for the grazing of Goats, a reference to the marshy gully where the specimens were found. The species is described from six complete shells, two lose dorsal valves and two broken ventral valves. The shells are ventribiconvex, which is to say each half of the shell is convex, with the two halves separated by a raised median line (a common bodyplan in Brachiopods) and roughly hexagonal in outline, with a short beak and short robust teeth on the ventral valve.

Gowanella capralis. (A−D) First specimen, complete shell in dorsal (A), ventral (B), anterior (C), and lateral (D) views. (E) Second specimen, juvenile complete shell in dorsal view. (F−I) Third specimen, complete shell in dorsal (F), ventral (G), lateral (H), and anterior (I) views. (J−M) Fourth specimen, complete shell in dorsal (J), anterior (K), lateral (L), and ventral (M) views. (N) Fifth specimen, dorsal valve in interior view. (O) Sixth specimen, dorsal valve in interior view. (P-R) Seventh specimen, complete shell in dorsal (P), lateral (Q), and anterior (R) views. Hiller (2016).

Hiller also records a second type of Brachiopod from the Mead Hill deposits, though the shells of these Brachiopods are less well preserved so they are not formally described as a new species. There are ten of these Brachiopods, all conjoined valve pairs all deformed by crushing and tectonic deformation. They are subcircular in outline and have narrow, erect beaks.

 Second Mead Hills Brachiopod. (A-C) First specimen, complete shell in dorsal (A), lateral (B), and ventral (C), views. The exaggerated curvature of the ventral valve is due to tectonic distortion. (D-F) Second specimen, complete shell in dorsal (D), ventral (E), and lateral (F), views. The thin shell at the growth margins of both these specimens has been broken off. (G) Third specimen, complete shell in anterior view showing broken anterior end with portion of the loop visible (arrowed). Hiller (2016).

See also... elegans: An Early Cambrian Lophophorate Animal with affinities to Brachiopods and Phoronids.                   Lophophorates are animals which feed using a...
Brachiopods (or Lampshells) superficially resemble Bivalve Molluscs, though they are not closely related. They were abundant in the seas of the Palaeozoic, often dominating benthic faunas, but today are comparatively rare, and seldom seem outside the... tissue preservation in Linguloid Brachiopods from the Early Ordovician Fenxiang Formation of Hubei Province, China.                                                  

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