Appendix: Palynology of clastic rocks of the Walker Volcanics at
Coppings Crossing
Five subsamples from ostracod-bearing localities were analysed for chitinozoan
microfossils using the standard palynological techniques of Paris (1981). All samples
yielded an abundant, identical and monospecific assemblage of Angochitina cf.
Angochitina echinata Eisenack, 1931, totalling many thousands of specimens (Fig. 8).
Unfortunately, and likely due to the geological setting and associated volcanics, the
specimens are poorly preserved.
A suite of morphologically similar species of Angochitina exists in other
middle Llandovery to lower Pridoli sedimentary deposits, encompassing A.
longicollis, A. echinata, A. elongata and A. milleri. Discriminating these taxa is
challenging when fossil preservation is poor. The Angochitina specimens from
Copping Crossing have abundant, relatively long spines that at times branch distally
and are spread evenly over the entire surface of the vesicles. The specimens most
resemble A. echinata, mainly based on morphometric criteria (Fig. 9); the total length
of the specimens is between 100 and 200 m, and they conform to published
measurements by Eisenack (1931: 140<L<160 m) and Laufeld (1974: 150<L<200
m). The Australian specimens lack the granular surface texture described by Laufeld
(1974), and hence are left in open nomenclature.
Published specimens of Angochitina longicollis generally have longer
dimensions (L = 160-290 m; Eisenack 1959) than the specimens from Coppins
Crossing, and also have shorter and slightly aligned spines. A. elongata is more
slender. A. milleri is equally slender as A. elongata but has more complex
ornamentation. Despite these differences, and although their morphometry suggests
they are Angochitina cf. echinata, a potential attribution of the Australian specimens
to A. longicollis or even A. elongata cannot be excluded, given the poor preservation
of (the surface ornamentation of) the specimens.
Angochitina echinata ranges from the mid Gorstian Stage, Ludlow Series, into
the earliest Pridoli Series (Verniers et al. 1995), and this is the biostratigraphical age
assignment suggested for the Coppins Crosssing material based on the available
chitinozoan data. However, as indicated, the taxonomic assignment is uncertain, and
attributions to other species, such as A. longicollis, cannot be fully excluded. The
presence of A. longicollis would point to an older age, as it ranges from the Telychian
Stage, Llandovery Series, into the Sheinwoodian Stage, Wenlock Series. Angochitina
elongata has more or less the same range as A. echinata. In addition, it should be
pointed out that taxonomic comparisons and range correlations are over a long
distance, to the type Ludlow area in the UK (Sutherland 1994), Gotland (Laufeld
1974), the wider Baltic (Eisenack 1931) and N. Gondwana (Paris 1981). Comparative
material from Australia or nearby sites does not exist, adding to the uncertainty. In
summary, based on chitinozoan data, the samples provide a biostratigraphical age
within the interval of the Telychian to Ludfordian stages, suggesting the GorstianLudfordian interval of the Ludlow Series as the most likely assignment. Nevertheless,
as noted in the main body of the text, most stratigraphical and palaeontological lines
of evidence, including that from graptolites, point to a late Wenlock Homerian age for
the ostracod-bearing localities.
Eisenack, A. 1931. Neue Mikrofossilien des baltischen Silurs, I. Paläontologisches
Zeitschrift, 13, 74–118.
Eisenack, A. 1959. Neotypen baltischer Silur-Chitinozoen und neue Arten. Neues
Jahrbuch für Geologie und Paläontologie. Abhandlungen, 108, 1–20.
Laufeld, S. 1974. Silurian Chitinozoa from Gotland. Fossils and Strata, 5, 1–130.
Paris, F. 1981. Les Chitinozoaires dans le Paléozoïque du sud-ouest de l'Europe.
Mémoires de la Société géologique et minéralogique de Bretagne, Université de
Rennes, Rennes, 26, 1–497.
Sutherland, S. J. E. 1994. Ludlow chitinozoans from the type area and adjacent
regions. Monographs of the Palaeontographical Society, 148, 1–124.
Verniers, J., Nestor, V., Paris, F., Dufka, P., Sutherland, S. J. E. & Van Grootel, G.
1995. A global Chitinozoa biozonation for the Silurian. Geological Magazine, 132,
651–666.
Supplemental figures
Figure 8. Chitinozoan Angochitina cf. echinata, Coppins Crossing, Australia; Walker
Volcanics, Wenlock Series, lower Silurian. A, CPC 42063, Specimen 2; B, CPC
42063, Specimen 13; C, CPC 42064, Specimen 8; D, CPC 42064, Specimen 12; E,
CPC 42064, Specimen 17. All figures are SEM photographs.
Figure 9. Morphometry of chitinozoans from Coppings Crossing compared to
dimensions of selected published Silurian angochitinids. L = total length; D =
maximum diameter (Paris 1981). The Australian specimens best fit the dimensions of
A. echinata Eisenack, 1931 (n.b. only the total length of the specimens from the
assemblage containing the holotype is given in Eisenack 1931, 1959).