Sunday 24 March 2013

A new species of Lungfish from the Late Devonian of northwest Australia.

Lungfish are an ancient group of Vertebrates more closely related to the Tetrapods (terrestrial Vertebrates) than to other groups of Fish. They get their name from their ability to breath air, which is useful in anoxic or seasonal waters; all modern species are freshwater and most can no longer use their gills to extract oxygen from water, though ancient Lungfish are known to have originated in fully marine waters. The group have a fossil record dating back to at least the Devonian, and were one of the most numerous Fish groups in the Palaeozoic.

In a paper published in the journal Palaeontology on 9 January 2012, Alice Clement of the Research School of Earth Sciences at the Australian National University in Canberra describes a new species of Lungfish from the Late Devonian Gogo Formation of northern Western Australia.

The Gogo Formation is a Fossil Lagerstätte in the Kimberly Region of Western Australia. It is noted for its diverse fish fauna, which are preserved in limestone concretions, and recovered by slowly dissolving  the concretions in weak acid. The deposits were laid down in anoxic lagoons behind algal reefs in the Late Devonian.

The location and outcrop distribution of the Gogo Formation. Clement (2012).

The new species of Lungfish is described from a single specimen from a limestone concretion from the Long Wells Area. It is placed in the genus Rhinodipterus, which has previously only been known from Europe and Russia, and given the specific name kimberleyensis, meaning 'from Kimberly'.

The skull of Rhinodipterus kimberlyensis in dorsal (A & B) and lateral (C & D) views. B & D are interpretive drawings based upon A & C. Abbreviations: A, skull roof bone A; art.c.r, articulation surface for cranial ribs; art.mnd, articulation surface for mandible; B, skull roof bone B; f.a.orb, foramen for orbital artery; ft.hy, hyomandibular facet; gr.op, groove for ophthalmic superficialis nerve VII; gr.v.jug, groove for jugular vein; hy.sp, facet for hyosuspensory ligament; I, skull roof bone I; J, skull roof bone J; L, skull roof bone L; med.cav, median cavity; n.I, foramen for olfactory nerve I; n.II, foramen
for optic nerve II; n.X, foramen for vagus nerve X; olf, olfactory canals I; orb, position of orbit;, orbital sensory canal pores; p.l, pit line; pr.I, posterior projection of I bone; psph, parasphenoid; qu, quadrate; sc, scales; sp.occ, spino-occipital nerve foramen; t.p, tooth plate; X, skull roof bone X; Y1, skull roof bone Y1; Y2, skull roof bone Y2; Z, skull roof
bone Z. Arrow indicates midline. Clement (2012).

Rhinodipterus kimberlyensis appears to have been a long snouted fish, with limited dentition and oral a mouth that did not open to a very high angle. This implies that it was probably a suction feeder targeting soft-bodied prey. This is a common strategy among modern Fish, and is also the primary feeding method in Walruses.

The skull of Rhinodipterus kimberlyensis in ventral (A & B) anterior (C)  and anterioventral (D) views. B is an interpretive drawing based upon A. Abbreviations: art.c.r, articulation surface for cranial ribs; cr.dl, dorsolateral cristae; cr.m, median crista; crp, corpus of parasphenoid; dent, dentine; ec.cav, extracranial space; ext, anteromedial extension of pterygoid and prearticular tooth plates; ext, anteromedial extension of pterygoid and prearticular tooth plates; f.a.ic, foramen for internal carotid artery; f.a.occ, foramen for occipital artery; f.a.orb, foramen for orbital artery;, foramen for efferent pseudobranchial artery; gr.op, groove for ophthalmic superficialis nerve VII; gr.v.jug, groove for jugular vein; med.cav, median cavity;  n.X, foramen for vagus nerve X; olf, olfactory canals I; psph, parasphenoid; pt, pterygoid; stk, stalk of parasphenoid; t.p, tooth plate; t.r, tooth row. 

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