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A, Map showing Palaeozoic sedimentary basins in Western Australia, with reported Silurian vertebrate occurrences. B, Palaeogeographic globe maps ca. 420 Mya (after Li & Powell 2001, fig. 11), 1 ¼ Pendock 1A, 2 ¼ central Urals. C, stratigraphic column (metre depths indicated) of the Pendock 1A borehole; fish symbol indicates level yielding the studied sample (after Gorter et al.1994, figs 5, 7).
Source publication
A core sample from the offshore Pendock 1A well, Carnarvon Basin, Western Australia yielded microvertebrate residues at an horizon in the lower part of the Hamelin Formation, dated as late Silurian, ? Ludlow, based on associated conodonts. The fish fauna comprises loganelliiform thelodont scales, the ? stem gnathostome Aberrosquama occidens nov. ge...
Contexts in source publication
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... and stratigraphy Gorter et al. (1994, Fig. 5) illustrated the section in Pendock 1A, a petroleum exploration well in the Edel Platform, about 50 km offshore in the Carnarvon Basin (Fig. 1A, C). Conodont elements associated with the vertebrate remains in Core 6 part 2 were assigned by Gorter et al. (1994) to Ozarkodina confluens (Branson & Mehl 1933) at 7183-7192 feet (2190-2192.5 m) depth in the base of the Hamelin Formation, Dirk Hartog Group, presumed basal Gorstian (lower Ludlow) (Fig. 1C). However, O. confluens is a ...
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... 50 km offshore in the Carnarvon Basin (Fig. 1A, C). Conodont elements associated with the vertebrate remains in Core 6 part 2 were assigned by Gorter et al. (1994) to Ozarkodina confluens (Branson & Mehl 1933) at 7183-7192 feet (2190-2192.5 m) depth in the base of the Hamelin Formation, Dirk Hartog Group, presumed basal Gorstian (lower Ludlow) (Fig. 1C). However, O. confluens is a longranging late Silurian conodont known from the Ludlow through Pridoli elsewhere (e.g., Aldridge & Sch€ onlaub 1989, M€ arss & Mannik 2013, and specimens from Pendock 1A Core 6 are few; Gorter et al. (1994, fig. 13) illustrated only one element. Both the sparsity of conodont elements and the vertebrate ...
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... be remnants of an inner trabecular layer on the inner (acellular) base. The trabeculae of the middle cancellous layer in Sacabambaspis Gagnier, Blieck & Rodrigo, 1986 and Ritchieichthys are formed of cellular bone (Sansom et al. 2013), but the inner/basal layer in Sacabambaspis is acellular, and has a laminated structure ( Sansom et al. 2005, fig. 1c). In summary, differences between arandaspids and the type 2 element from Pendock 1A are: Sharpey's fibres are currently not considered to occur in any arandaspids ( Sansom et al. 2013), but these appear to be present in the Pendock 1A elements; the middle layer in arandaspids shows a honeycomb structure of open polygonal spaces (Young ...
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... the known Gondwanan Ordovician pteraspidomorphs are arandaspids, which are distinguished fig. 11), 1 ¼ Pendock 1A, 2 ¼ central Urals. C, stratigraphic column (metre depths indicated) of the Pendock 1A borehole; fish symbol indicates level yielding the studied sample (after Gorter et al.1994, figs 5, 7). histologically from other pteraspidomorphs by having cellular bone in the middle layer of the armour. In Laurentian Ordovician ...
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... et al. 2013). The structure of the basal layer in those forms is similar to that in the Pendock 1A type 2 fragments (Denison 1967, figs 12D, 22F). The same structure is also seen in postOrdovician heterostracan pteraspidomorphs (e.g., Gross 1961, figs 3E, 6D, 9C), with some taxa also showing 'oak-leaf' ornament (e.g., Traquairaspis: Gross 1961, fig. 1). However, no post-Ordovician pteraspidomorphs have been described from elsewhere in Australia ( Young 1981, Blieck & Turner 2003, with thelodonts and pituriaspids the only younger agnathans confirmed from this region. Further evidence is needed to clarify whether or not these probable pteraspidomorph fragments represent a Silurian ...
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... between the openings on the surface of the base and the 'neck'. Sharpey's fibre bundles penetrate the base in several different orientations: as 'cones' radiating from the base apex, inverted 'hemispheres', and a 'column' from the apex to the centre of the basal surface, building an overall structure reminiscent of that in many acanthodian scales (Burrow 2001, fig. 5). In ground thinsections, cross-cutting of these variously oriented bundles lead to complicated patterns of fibre traces (Fig. 5C, ...
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... some resemblance to those of Nostolepis gracilis Gross, 1947 from the Pridoli of the Baltic and north German erratics, but the crown of the latter have parallel, thin, constantwidth ridges extending the length of the crown, separated by wide grooves which usually have large pore openings, with Strangewebbe filling most of the crown (Gross 1971, fig. ...
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... bone fragments from the same sample are also assigned to Andreolepis sp. aff. A. petri because of their resemblance to fragments of the dermal bone of A. hedei (Janvier 1978, fig. 1D) and A. petri (M€ arss 2001, pl. 2.4) as well as younger actinopterygians. The fragments from the Pendock 1A sample have a basal layer separated from the ornamented layer by a vascular layer (Fig. 7L-N). The ornament comprises noncontiguous, elongated, grooved tubercles or short ridges (Fig. 7M, N). One broken element (Fig. 7O) appears ...
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... This type of scale lacks the diagnostic features of flank scales. Chen et al. (2012, fig. 3) designated the latter scales as type 1; Pendock 1A scales in Fig. 6F-H, ? K fit this form. The rhombic Pendock 1A scale with a minimal depressed field and free field covering nearly the whole outer surface (Fig. 7I, J) corresponds to the Chen et al. Type 2 (2012, fig. 3) from the precaudal region. The small diamond-shaped Pendock 1A scale (Fig. 7E) with a wide depressed field on all four sides corresponds to Chen et al. Type 9 (2012, fig. 3), which they interpreted as being a mid-ventral ...
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... smooth, so these fragments are only assigned to Vertebrata indet. (see below). The hollow structure of the ornament ridges on Andreolepis sp. aff. A. petri dermal bone (Fig. 7P) is reminiscent of that in scales (and presumably dermal bone) of the Late Devonian Mimipiscis toombsi Gardiner & Bartram, 1977 from the Gogo Formation, Western Australia (Gardiner 1984, fig. ...
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... from Aberrosquama, but it lacks a large base and triangular-shaped crown, two of the distinguishing features of that taxon. The other fragment with a horseshoe-shaped tubercle (Fig. 9C, D) differs in having a very thin base. In the Devonian, tubercles of this shape are found on many sarcopterygian scales and bones. However, M€ arss (1997, pl. 3, fig. 15, 19) referred dermal bone fragments with horseshoe-shaped tubercles from the Kaugatuma or Ohesaare Stage (Pridoli) of the East Baltic to an undetermined ...
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... rare vertebrate microremains that have been recovered from the Silurian of Western Australia show possible affinities with middle to late Silurian assemblages from Iran and northern Eurasia (Fig. 1B), which are also from shallow marine to evaporitic deposits, and differ markedly from those of a similar age in southeastern Australia ( Burrow et al. 2010). Although considered that the few vertebrate microremains from the Yaringa 1 borehole in the Carnarvon Basin were comparable with those from Pendock 1A, on re-examination we ...
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... closely related to the Pendock 1A Andreolepis, has only previously been recorded from the upper Ludlow or lower Pridoli of the central Urals. These similarities between a Ludlow fauna from Western Australia and upper Ludlow-Pridoli faunas of northern Europe is surprising, in light of most palaeogeographic reconstructions (e.g., Li & Powell 2001, fig. 11; Fig. 1B) that show both regions in tropical latitudes but with the East Gondwanan (Australian) terrane far to the east of Baltica, and with the North and South China blocks and the LB-Siberian terrane scattered between them. (However, note that longitude is not fixed in palaeogeographic ...
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