Gogoselachus lynnbeazleyae: The first recorded Shark from the Late Devonian Gogo Formation of Western Australia.

The deepest evolutionary split in the jawed vertebrates (Gnathostomes) is that between the Sharks (Chondrichthyes) and Bony Fish (Osteichthyes), with all terrestrial vertebrates forming a subgroup within the bony fish. The skeletal structure of Sharks is quite different to that of other jawed vertebrates, with a skeleton comprised almost entirely of cartilage, which has little preservational potential. On the other hand Sharks produce new teeth and shed old ones throughout their lives, and in addition have a coating of mineralized scales with a tooth-like composition. These teeth and scales have excellent preservational potential, with the effect that Sharks have a very long and well documented fossil record, but that little is known of the anatomy of most fossil Sharks.

In a paper published in the journal PLoS One on 28 May 2015, a team of scientists led by John Long of the School of Biological Sciences at Flinders University, the Department of Earth and Marine Sciences at The Australian National University and Geosciences at Museum Victoria describe the first known Shark remains from the Late Devonian Gogo Formation of Western Australia.

The Gogo Formation is noted for the production of exceptional three-dimensionally preserved Fish skeletons within calcareous nodules which can be released by acid washing techniques which dissolve the calcareous matrix but leave the skeletal material intact. These Fish are thought to have lived on reefs but fallen into deep basins between reef fronts when they died, where oxygen deprived calcium rich water slowed decomposition and coated the skeletons in layers of calcite, which preserved them against deformation when subsequently buried by layers of sediment.

The specimen described by Long et al. comprises a set of disarticulated but clearly associated remains comprising both left and right Meckel's cartilages, nasal cartilage, ceratohyal, hyomandibula, basibranchial cartilage, both scapulocoracoids, and associated teeth and scales. This is described as Gogoselachus lynbeazleyae, where ‘Gogoselachus’ means Gogo-shark and ‘lynbeazleyae’ honours Lyn Beazley of the University of Western Australia for her ‘contribution to scientific progress in Western Australia’. The specimen is thought to be the first known acid-prepared mineralized Devonian Shark remains.

Preparation of Gogoselachus lynbeazleyae from the Gogo Formation, Western Australia. (A) Meckel's cartilage as exposed on collection, before acetic acid etching. (B) Specimen during early acid preparation. (C) Meckel's cartilages after full preparation, shown articulated in dorsal view. Long et al. (2015).

The cartilage of Gogoselachus lynbeazleyae is tessilated; that is to say it contains layers of small, mineralized plates, which added to the strength of the tissue without reducing its flexibility. Such tessilated cartilage is considered diagnostic of the Chondrichthys (Sharks and Rays) and has been found in specimens as ancient as the Early Devonian, however such tissues are rarely preserved in Devonian Sharks, as most known specimens are preserved in shale, a medium which does not tend preserve histological details. Interestingly the calcite present in the tesserae of Gogoselachus lynbeazleyae appear too be non-prismatic and are surrounded by a cartilage matrix with elongate lacunae, unlike the tesserae of modern Sharks which have fibrous connections between them.

Structure of Gogoselachus lynbeazleyae endoskeleton. (A–C) Gogoselachus calcified cartilage (A) SEM showing tessellate layout (B, C) horizontal section through tissue (D) transverse CT scan of right Meckel's cartilage. Scale bar is 0.1 mm in (C). Abbreviations: cp, cell processes; l, lacunae. Long et al. (2015).

See also…

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The demise of the Megashark.

The Giant Shark, Carcharocles megalodon, is one of the more charismatic creatures of the recent fossil record, a relative of modern Mackerel Sharks that is thought to have been able to reach about 18 m in length, known from the Middle Miocene to the end of the Pliocene, with some claims of the species persisting into the Pleistocene. It is interpreted to have had a life-style similar to the modern Great White Shark, which preys...

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Reconstructing cranial endocasts of Palaeozoic Ray-finned Fish.

Palaeontologists have been interested in the endocasts of vertebrate skulls (moulds of the interior of the skull made by sediment) since at least the nineteenth century, due to the possibility that these can reveal details of the animal’s brain. Unfortunately the brains of some vertebrates are very different to the skull cavities, with those of Sharks and Lungfish occupying as little as 1% of the available space, though in other groups, such as Birds and Mammals, the endocast records the shape of the brain far more accurately. Early Ray-finned Fish, Actinopterygians, are thought to fall into the latter category, and their endocasts have been studied extensively since the early 20^th century, although this has been problematic, as the best method available for most of that time has been to make serial sections of the skull, a destructive technique that can only be used on the most abundant of fossils, and which leaves only the palaeontologist’s notes and interpretation for examination by future generations of scientists.

In a paper published in the Journal of Paleontology in July 2014, Sam Giles and Matt Friedmann of the Department of Earth Sciences at the University of Oxford present the results of a study of two early Ray-finned Fishes made using computed tomographic X-ray scanning to build up a picture of the cranial endocasts without destroying the original skulls.

The first Fish selected was Mimipiscis toombsi, from the Late Devonian Gogo Formation of Western Australia. This species had its endocast studied by traditional methods by Brian Gardiner of King's College, London in the 1980s. The specimen chosen for this study came from the collection of the Natural History Museum in London, and comprises a 25 mm long by 15 mm with specimen, which was removed from its original matrix via acid preparation, and now has its dorsal surface preserved in a thick resin block. Although some original sediment remains and is preserved in the resin along with the skull, the brain cavity is largely devoid of infilling, creating a void space which shows up well in CT scans.

Photograph of the Mimipiscis toombsi used in the study as it is preserved. Giles & Friedmann (2014).

Giles and Friedmann found that the endocast of Mimipiscis toombsi was long and narrow, with elongate olfactory tracts. The forebrain comprises only 20% of the total length (25-30% is more typical) and is separated from the midbrain by a constriction. The forebrain is narrow, barely wider than the olfactory tracts, which diverge almost immediately after the olfactory bulbs, unlike the situation seen in most early Ray-finned Fish, where the two olfactory nerves share a common canal for most of their length. The midbrain is about twice the width of the forebrain, with poorly developed optic lobes. The hindbrain takes up about 60% of the length of the skull (50% is more typical).

Reconstruction of the endocast of Mimipiscis toombsi, in ventral view. (1) Three-dimensional rendering of endocast; (2) interpretive drawing of endocast. Anatomical abbreviations — bhc, buccohypophysial canal; b.oc.a, canal for branch of occipital artery; ccc, communication between cranial cavity andnotochordal canal; mcv,canal for middle cerebral vein; oof, otico-occipital fissure; opt.f, optic fenestra; spio, canal for spinooccipital nerve; s.v, saccus vasculosus; v.fon, vestibular fontanelle; I, canal for olfactory nerve; IV, canal for trochlear nerve; V, canal for trigeminal nerve; Vprof, canal for profundus nerve; VI, canal for abducens nerve; VII, canal for facial nerve;VIIlat, canal for lateralis branch of facial nerve; IX, canal forglossopharyngeal nerve; X, canal for vagus nerve. Giles & Friedmann (2014).

The second Fish chosen was Kentuckia deani, from the Early Carboniferous Stockdale Formation of Kentucky. Two specimens were examined, both from the collection of the Museum of Comparative Zoology at Harvard University. The first is 30 mm in length and preserved within a nodule, which has been broken in half to reveal the internal structure of the skull. The second is 15 mm in length and also within a nodule, which has been prepared so as to expose the upper surface of the skull.

(2) Kentuckia deani, 15 mm specimen; (3) Kentuckia deani, 30 mm specimen, part; (4) Kentuckia deani, 30 mm specimen, counterpart. Giles & Friedmann (2014).

Giles and Friedmann found that both endocasts of Kentuckia deani were less slender than that of Mimipiscis toombsi, with proportions closer to those of other, more familiar, ray finned fish. The forebrain makes up about 25% of the total length, with a single tract carrying both olfactory nerves for most of their length. The midbrain is twice the width of the forebrain, with well-developed optic lobes; the optic nerves also share a single opening. The hindbrain makes up about 50% of the total length.

Reconstruction of the endocast of Kentuckia deani, in left lateral view. (1) Three-dimensional rendering of endocast; (2) Interpretive drawing of endocast. The pocket of the lateral cranial canal has been ‘cut’ to avoid obscuring parts of the labyrinth. Anatomical abbreviations —acv, canal for anterior cerebralvein; aur, cerebellar auricle; c.c,crus commune; die, diencephalon; ica, canal for internal carotid artery; l.c.c, lateral cranial canal; sac, sacculus; s.su, sinus superior; s.v, saccus vasculosus; I, canal for olfactory nerve; III, canal for oculomotor nerve; IV, canal for trochlear nerve; V, canal for trigeminal nerve; VI, canal for abducens nerve; VII, canal for facial nerve; VIIlat, canal for lateralis branch of facial nerve. Dotted lines infigure indicate unresolved regions. Giles & Friedmann (2014).

See also…

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

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The pelvic girdles of two primitive boney fish from China.

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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; p.o.sc, 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; f.a.ps, 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. 

See also New species of Devonian Tetrapod from the northeast of Greenland, A novel Coelacanth from the Early Triassic of British Columbia, Live birth in a Middle Triassic Coelacanth, New Tetrapodomorph Fish from the Devonian of Nevada and Boney Fish on Sciency Thoughts YouTube.

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