Revision of Discomesites and Estaingia (Trilobita) from the Lower Cambrian Cymbric Vale Formation, Western New South Wales: Taxonomic, Biostratigraphic and Biogeographic Implications

2005·6.2 MB·English

by  J R Paterson

Revision ofDiscomesites and Estaingia (Trilobita) from the
Lower Cambrian Cymbric Vale Formation, Western New
South Wales: Taxonomic, Biostratigraphic and Biogeographic
Implications
John R. Paterson
Centre for Ecostratigraphy and Palaeobiology, Department ofEarth and Planetary Sciences, Macquarie
NSW
University, 2109 ([email protected])
Paterson, J.R. (2005). Revision oiDiscomesites anA.Estaingia (Trilobita) from the LowerCambrian
CymbricVale Formation, westernNew SouthWales: taxonomic, biostratigraphic andbiogeographic
implications. Proceedings oftheLinnean Society ofNewSouth Wales 126, 81-93.
The taxonomy of Discomesites and Estaingia from the Lower Cambrian Cymbric Vale Formation
of western New South Wales is revised. Discomesites is regarded as a valid subgenus of Pagetides.
Pagetides (Discomesites)fragum is considereda seniorsubjective synonymofjR (D.) lunatulus. Pagetides
{Discomesites)spinosusfromthe ShackletonLimestone intheHolyoakeRange,TransantarcticMountains,
is considered to be ajunior subjective synonym off! {D.)fragum. Estaingia cerastes from the Cymbric
Vale Formation is considered to be synonymous with Hsuaspis cf H. bilobata from the Shackleton
Limestone. The Cymbric Vale Formation trilobite fauna is of late Early Cambrian (late Botoman) age,
equivalent to the Pararaiajaneae Zone of South Australia, based on correlation of the Syringocnema
favus archaeocyathan fauna. Absolute ages ofrecently dated tuffs from the Cymbric Vale and Billy Creek
Formations are questioned, based on new information regarding the stratigraphic position ofthe Cymbric
Vale Formation tuff in relation to archaeocyathan and trilobite biostratigraphy The co-occurrence of
Pagetides {Discomesites)fragum andEstaingia cerastes in the upper part ofthe Cymbric Vale Formation
andinthe ShackletonLimestonerepresentsthefirst species-levelcorrelationbetweenthe LowerCambrian
ofAustralia andAntarctica using trilobites. The distribution ofthese trilobite species, in association with
the Syringocnemafavus archaeocyathan fauna, provides supporting evidence thatAustralia andAntarctica
wereconnectedbyacontinuouscarbonate-detritalshelfduringthelateEarlyCambrian(mid-lateBotoman),
allowing faunal exchange between these regions.
Manuscriptreceived 2 June 2004, accepted forpublication 18 December2004.
KEYWORDS: Antarctica,Australia, biogeography, biostratigraphy, Botoman, Early Cambrian,
geochronology, Gondwana, New SouthWales, Trilobita.
Cymbric Vale Formation and stratigraphic position
INTRODUCTION
ofa recently dated tuffwithin the unit, allowing the
Cymbric Vale trilobite fauna to be placed in both a
Since the publication of Opik's (1975b) biostratigraphic and biogeographic context.
taxonomic study on the trilobites from the Lower The CymbricVale Formationis partoftheLower
CambrianCymbricValeFormation, severalimportant to early Middle Cambrian Gnalta Group, which
palaeontological and geochronological studies on the crops out in the Mt Wright area of western New
Early Cambrian ofAustralia andAntarctica, relevant South Wales (Fig. 1). The Gnalta Group comprises
to the Cymbric Vale Formation, have been published (in ascending order): the Mount Wright Volcanics,
(Kruse 1978, 1982; Debrenne and Kruse 1986; Cymbric Vale Formation and Coonigan Formation.
Bengtsonetal. 1990;ZhuravlevandGravestock 1994; The Lower Cambrian Mount Wright Volcanics and
Palmer and Rowell 1995; Jago et al. 1997; Jenkins overlying Cymbric Vale Formation are considered to
et al. 2002). The scope ofthis study is to revise the be conformable, based on common archaeocyathan
taxonomy oftwo key trilobite taxa from the Cymbric faunas (Kruse 1982). The uppermost beds of the
Vale Formation, Discomesites and Estaingia, as well CymbricVale Formation are disconformablyoverlain
as review the archaeocyathan biostratigraphy of the by the early Middle Cambrian 'first discovery
REVISION OF TRILOBITE GENERA D/SCOMESITES AND ESTAINGIA
carbonate rocks with abundant trilobites, molluscs,
brachiopods, eocrinoids and sponge spicules (Opik
1975b; Kruse 1982; Jago et al. 1997).
Thefirst formal taxonomic studyofthe Early
Cambrian trilobites from the CymbricVale Formation
was by Opik (1975b). He recorded the trilobites
Dinesis aff. granulosus (Lermontova), Estaingia
bilobata Pocock, Strenax cerastes Opik, Strenax
(Sematiscus) fletcheri Opik, Serrodiscus daedalus
Opik, Meniscuchus menetus Opik, Discomesites
fragum Opik, Discomesites lunatulus Opik and
Pagetia sp. nov. Opik (1975b) correlated the Cymbric
Vale fauna with Daily's (1956) South Australian
faunal assemblages 9, 11 and 12, equivalent to the
PararaiajaneaeZoneofSouthAustralia(Bengtsonet
al. 1990), and to the Botoman Sanashtyk'gol Horizon
oftheAltay-Sayan region ofSiberia.
Jagoetal. (1997)recordedatrilobitefaunulefrom
a new locality within the Cymbric Vale Formation,
reassigning the species Estaingia bilobata Pocock
and Strenax cerastes Opik, originally documented by
Opik (1975b), to a single redefined species, Hsuaspis
cerastes (Opik), and also described Redlichia cf
ziguiensis Lin, a taxon previously unknown fi-om
the Cymbric Vale Formation. Jago et al. (1997) also
suggested that the Cymbric Vale trilobite fauna is of
late Early Cambrian (late Botoman) age.
BIOSTRATIGRAPHIC IMPLICATIONS
The taxonomic revision herein ofPagetides
Figure 1.Generalisedgeologicalmapofnorthwest-
(Discomesites) fragum Opik, 1975b and Estaingia
ernNewSouthWales,showinglocationofMtWright;
cerastes (Opik, 1975b) from the Cymbric Vale
modified from Shergold et al. (1982, text-fig. ID). Formation ofwestern New South Wales is based on
reexamination of Opik's (1975b) type material plus
limestone' of the Coonigan Formation (Roberts and additional collections housed at GeoscienceAustralia
Jell 1990). (Canberra) and provides the first direct interregional
The Cymbric Vale Formation attains a maximum correlationbetween the Lower Cambrian ofAustralia
m
thickness of 1900 and consists predominantly of andAntarctica using trilobites. Palmer(in Palmerand
interbeddedblue,greenandgrey-whitechertandgreen Rowell 1995) described a number ofEarly Cambrian
to brown tuff (Kruse 1982). Archaeocyath-bearing trilobiteassemblages, ranginginage fromAtdabanian
limestone lenses occur throughout the formation and to Toyonian(?), fi-om the Shackleton Limestone in
contain two distinct archaeocyathan faunas (Fig. 2): the Holyoake Range of the central Transantarctic
Fauna 1 (L96-L99) occurs in the upperMountWright Mountains. One of the Botoman assemblages
Volcanics and in the lower part ofthe Cymbric Vale ('Assemblage 3') contains the taxa Pagetides
Formation and is assigned an early Botoman age; (Discomesites) spinosus Palmer and Hsuaspis cf H.
Fauna 2 (LlOO-LlOl) occurs in the upper Cymbric bilobata(Pocock). ThesynonymyhereinofPagetides
Vale Formation and has been assigned a mid-late (Discomesites) spinosus with P. (D.) fragum, and
Botoman age (Kruse 1978, 1982; Zhuravlev and Hsuaspis cf. H. bilobata with Estaingia cerastes
Gravestock 1994; Kruseand Shi inBrocketal. 2000). permits direct correlation ofthe trilobite fauna from
The uppermost beds ofthe Cymbric Vale Formation the uppermost Cymbric Vale Formation with trilobite
consist ofwell-bedded lithic and feldspathic siltstone 'Assemblage 3' from the Shackleton Limestone.
and sandstone interbedded with impure iron-rich Unfortunately, further support for this correlation
82 Proc. Linn. Soc. N.S.W., 126, 2005
PATERSON
J.R.
South
c
(0 Australian Flinders Ranges
0) trilobite (South Australia)
zones
en
Mt Wright
NO
TOYON. (western New
ZONATION
South Wales)
1 -522.811.8Ma
(SL13) • •
Syringocnema § -2
P.janeae favus
1 beds
BOTOMAN
Cymbric
Vale
Formation
P.
bunyerooensis 517.8±2.1 Ma- y.y.y.y.y.y.y.y.y.y.y.y.yy -ic
(SL13) L99
P. tatei 525+8Ma L98 Fault to
11 A. huoi (SL13) LL9976
Mount
NO Wright
ATDABANIAN ZONATION Volcanics
Figure 2. Correlation diagram of tlie Lower Cambrian successions of Mt Wrigiit (western New South
Wales) and the Flinders Ranges (SouthAustralia). L96-L99 representFauna 1 and LlOO-LlOl represent
Fauna2ofKruse(1982).Tuffages:BiUyCreekFormation,522.8±1.8Ma(GravestockandShergold2001);
CymbricValeFormation, 517.8±2.1 Ma (Jenkins etal. 2002) and 525±8 Ma (Zhou andWhitford 1994).
based on similar archaeocyathan faunas from the correlation of the Cymbric Vale Formation with the
Cymbric Vale Formation (Kruse 1978, 1982) and the Lower Cambrian succession in South Australia. As
Shackleton Limestone (Debrerme and Kruse 1986) is noted by Kruse and Shi (in Brock et al. 2000), Fauna
complicated. Trilobites and archaeocyaths described 2 from the upper Cymbric Vale Formation can be
from the Shackleton Limestone were sampled from correlated with the mid-late Botoman Syringocnema
different localities in the Holyoake Range; see favus beds of the Adelaide Geosyncline (Fig. 2),
discussion by Palmer and Rowell (1995:4). Exposed based on five co-occurring species. Zhuravlev and
sections of Shackleton Limestone in the Holyoake Gravestock (1994, Table 2) have recorded the S.
Range are considerablythick (up to 200 m) and seem favus beds occurring in the Koolywurtie Member
to conform to a coherent stratigraphy; however, each of the Parara Limestone on Yorke Peninsula in the
section isboundedeitherby intenselydisturbedzones Stansbury Basin, and in the upper Ajax Limestone
offolding or faulting, orfields ofice orneve (Rowell (Ajax Mine and Mount Scott Range) and upper
et al. 1988:399; Rees et al. 1989:343). Sampling of Wilkawillina Limestone (Wilkawillina Gorge) in the
trilobites and archaeocyaths from disparate localities Arrowie Basin. Trilobites from coeval beds in the
in the Holyoake Range, coupled with the structural Flinders Ranges (Arrowie Basin) are representatives
complexity ofthe region, makes correlation between ofthe Pararaiajaneae Zone (Bengtson et al. 1990).
faunas difficult. While species-level correlation between the Cymbric
Documentation of archaeocyathan faunas Vale and Flinders Ranges trilobites is not possible,
from the Cymbric Vale Formation (Kruse 1978, generic similarities are evidentwiththe occurrence of
1982), and the development of a preliminary Early Serrodiscus andEstaingia inboth areas (Opik 1975b;
Cambrian archaeocyathan biozonation for Australia Bengtsonetal. 1990). SincetheCymbricValetrilobite
(ZhuravlevandGravestock 1994), hasallowedforthe fauna occurs in the uppermost part ofthe formation,
Proc. Linn. Soc. N.S.W., 126, 2005 83
RI-VISION OF TRILOBITH GENERA DISCOMESITES AND ESTAINGIA
stratigrapliically above archaeocyathan Fauna 2 (= S. Creek Formation tuff Furthermore, ages of the
fuviis beds), it is equivalent to the Puiaraia juncac Cymbric Vale and Billy Creek Formation tuffs using
Zone {sensii lato) or possibly even younger, thus the alternative QGNG standard yield dates of 531.8
supporting the late Botoman age suggested by Jago et ± 8 Ma and 529.6 ± 1.8 Ma respectively (Jago and
aI. (1997). Haines 1998), that better conform to archaeocyath
A dated felsic tuff from the Cymbric Vale and trilobite biostratigraphy.
Formation was recently re-calculatcd by Jenkins et
al. (2002) using the SL13 U-Pb SHRIMP method.
The tuffwas originally collected by Zhou (1992) and BIOGEOGRAPHIC IMPLICATIONS
subsequently dated by Zhou and Whitford (1994),
yielding an age of 525 ± 8 Ma (SL13). However, Jago (in Brock et al. 2000) noted that Early
Jenkins et al. (2002) produced an age of 517.8 ± 2.1 Cambrian trilobites from Australia have close faunal
Ma. Unfortunately, neither publication citing the age ties with other regions of East Gondwana, such as
of the Cymbric Vale tuff (Zhou and Whitford 1994; Antarctica, South and North China, Iran and India.
Jenkins et al. 2002) provided information about the However, Jago also demonstrated that faunal links
stratigraphic position of the tuff horizon, especially with distantly separated palaeogeographic regions
in regard to the local biostratigraphy. However, such as western Gondwana (e.g. Morocco), Laurentia
Zhou's (1992) unpublished PhD thesis does provide and Siberia are not uncommon. In discussing the
an Australian standard national grid reference for the biogeographic patterns of Early Cambrian trilobite
dated sample (i.e., 6332E; 65498N). Based on this faunas from Antarctica, Palmer (in Palmer and
grid reference and mapping by Zhou (1992, map 7) Rowell 1995:5) observed that 'Antarctic faunas do
and Kruse (1982, text-Fig. 2), the dated tuffappears not show any consistent similarity to faunas from
to have been collected in the vicinity of, or possibly any one geographic region ofthe rest ofGondwana'.
stratigraphically above, Kruse's (1982) localities L98 This appears to be true for any palaeogeographic
and L99 in the lower Cymbric Vale Formation (Fig. region when treating Early Cambrian trilobite faunas
2). as a whole, although by closely observing faunal
In light of the known stratigraphic position assemblages from specific time intervals, whether
of the dated Cymbric Vale tuff, there appears to be they be zones or stages, distinct biogeographic
an age discrepancy of dated tuffs from the Cymbric patterns often emerge (for example, see Theokritoflf
Vale Formation and the lower Billy Creek Formation 1979, 1985; Burrett and Richardson 1980; Alvaro
(Flinders Ranges), based on the correlation of the et al. 2003). Moreover, Alvaro et al. (2003:17) have
Syringocnemafavus beds. Gravestock and Shergold commentedthatintheLowerCambrian 'the ideal ofa
(2001) reported a SHRIMP age of 522.8 ± 1.8 Ma globalbiostratigraphyandpalaeobiogeographysuffers
from a tuff within the lower Billy Creek Formation from both a relatively limited diversity of trilobites
using the same standard (SL13) used by Jenkins et and their pronounced endemism. Furthermore, the
al. (2002) to re-calculate the Cymbric Vale tuff. distribution of trilobites is...strongly controlled by
This means that the "older" (522.8 Ma) Billy Creek facies, so that even a precise interregional con"elation
Formation tuff occurs stratigraphically above the is difficult'.
Syringocnemafavus beds in the Flinders Ranges, and The occurrence of Pagetides {Discomesites)
the "younger" (517.8 Ma) Cymbric Vale tuff occurs fragum and Estaingia cerastes, in addition to the
stratigraphically below archaeocyathan Fauna 2 (= Syringocnema favus archaeocyathan fauna, in the
S. favus beds) in western New South Wales (Fig. Cymbric Vale Formation (Gnalta Shelf) and the
2). This discrepancy implies that the age of the tuff Shackleton Limestone (Holyoake Range) provides
horizon in the Cymbric Vale Formation or Billy supporting evidence that a continuous continental
Creek Formation is erroneous, or perhaps both ages shelf connected southeastern Australia and the
are incorrect. This age discrepancy may be related to Transantarctic Mountains during the Early Cambrian
the standard used, since the reliability of the SL13 (Rowell and Rees 1991; Courjault-Rade et al. 1992;
standard has been questioned in recent years (see WronaandZhuravlev 1996;Veeversetal. 1997;Brock
Jago and Haines 1998 for detailed discussion). It is et al. 2000; Veevers 2000). The palaeogeographic
interestingto notethatthe original ageoftheCymbric distance between the Gnalta Shelfand the Holyoake
Vale tuff of 525 ± 8 Ma, calculated using the SL13 Range is estimated to be around 2500 km (Brock
standard (Zhou and Whitford 1994; Jago and Haines et al. 2000, Fig. 8), although the shelf may have
1998), is more in accord with the archaeocyath and extended as far as King George Island, implying a
trilobite biostratigraphy and the age of the Billy length ofover 6500 km. Courjault-Rade et al. (1992,
84 Proc. Linn. Soc. N.S.W., 126, 2005
PATERSON
J.R.
Fig. 2) have suggested that throughout the Early and Laurie 2004) and from the Minaret Formation,
Cambrian, and indeedtheMiddle andLate Cambrian, Ellsworth Mountains, WestAntarctica (Shergold and
a continuous carbonate-detrital shelf connected Webers 1992).
Australia andAntarctica. The widespread dominance The position ofAustralia and Antarctica during
of the Syringocnema favus fauna in Australia and the Cambrian, coupled with the persistence of
Antarctica during the mid-late Botoman coincides carbonate deposition in Australia and Antarctica
withaglobalhighsealevel, allowingfaunal exchange throughout the Cambrian, indicates thatthese regions
between these regions (Zhuravlev and Gravestock remained within the tropical Carbonate Development
1994; Wrona and Zhuravlev 1996; Gravestock and Zone (30 ± 5° north and south latitudes) (McKerrow
Shergold 2001). This strong faunal link between et al. 1992; Courjault-Rade et al. 1992; Brock et
Australia and Antarctica during the Botoman is al. 2000; Li and Powell 2001). Hence migration of
also supported by conspecific occurrences of small trilobite species between Australia and Antarctica
shelly fossils (SSF), such as Eiffelia araniformis was not inhibited by a latitudinal thermocline during
(Missarzhevskiy), Chancelloria racemifundis the Cambrian. However, this does not explain the
Bengtson,HalkieriaparvaConwayMorris,Dailyatia lack of conspecific occurrences of Early Cambrian
ajax Bischoff, Lapworthella fasciculata Conway trilobites between Australia and Antarctica, although
Morris and Bengtson, HyoUthellus micans (Billings), one may argue that a paucity ofdata fromAntarctica
HyoUthelliis filiformis Bengtson, Byronia? bifida could be responsible. Moreover, there is a distinct
Wrona, and Aetholicopalla adnata Conway Morris, absence ofconspecific occurrences between western
fromglacialerraticsofKingGeorgeIsland,Antarctica New South Wales (Gnalta Shelf) and SouthAustralia
(Wrona 2004) and the Parara, Wilkawillina andAjax (Adelaide Geosyncline). One possible explanation
Memmema
Limestones and Kulpara and Formations for the absence of conspecific occurrences of Early
in South Australia (Bengtson et al. 1990; Gravestock Cambrian trilobites between South Australia and
etal. 2001). Antarctica is the presence ofa tectonic barrier during
The carbonate-detrital shelfconnectingAustralia this time, i.e., the Kanmantoo Trough (Haines and
and Antarctica may have persisted until at least the Flottmann 1998; Flottmann et al. 1998). The Early
early Late Cambrian (Idamean), based on other Cambrian palaeogeographic relationship between
conspecific occurrences of benthic, shelf-dwelling the eastern Arrowie Basin (eastern South Australia)
polymerid trilobites and other biotas. For example, and the Gnalta Shelf(western New South Wales) is,
Holmer et al. (1996) described an Early Cambrian however, poorly understood. Various studies (e.g.,
Ungulate brachiopod faunule, containing Eoobohis Cook 1988; Gravestock and Hibburt 1991; Scheibner
aff. E. elatus (Pelman), Karathele napuru (Kruse) and Basden 1998; Zang 2002) have inferred
and Vandalotreta djagoran (Kruse), from the glacial connection between the eastern Arrowie Basin
erratics of King George Island, Antarctica. These and the Gnalta Shelf via a common seaway. While
same brachiopod species have been documented correlation ofthe Syringocnemafavus beds provides
from the Toyonian (latest Early Cambrian) Wirrealpa supporting evidence for a cormected seaway during
and Ramsay Limestones in South Australia (Brock the late Early Cambrian (mid-late Botoman), there
and Cooper 1993; Gravestock et al. 2001), and early may have been some form ofgeographic barrier that
Middle Cambrian units in the Northern Territory: inhibited trilobite migration between these regions.
Tindall Limestone, Daly Basin (Kruse 1990); Firstly, it is important to note that the Cymbric Vale
Montejinni Limestone of the Wiso Basin and Gum Formation trilobites occur stratigraphically above
Ridge Formation of the western Georgina Basin the S. favus beds and that during their temporal
(Kruse 1998); and the Top Springs Limestone, separation the palaeogeography between the eastern
northern Georgina Basin (Kruse 1991). The latest Arrowie Basin and the Gnalta Shelfmay have altered
Middle Cambrian {Glyptagnostus stoUdotus Zone) significantly, severing ties between these regions.
trilobite species Rhodonaspis longiila Whitehouse There are two possible palaeogeographic barriers
has been recorded from the Georgina Limestone, that may have hindered migration ofEarly Cambrian
Glenormiston, Queensland, Australia (Whitehouse trilobites between the eastern Arrowie Basin and the
1939;Opik1963)andintheSpursFormation,Northern Gnalta Shelf: (1) the Mount Wright Volcanic Arc
Victoria Land, Antarctica (Jago and Cooper 2001). situated immediately to the west ofthe Gnalta Shelf;
Furthermore, the early Late Cambrian (Idamean) and (2) an inferred trough situated to the west ofthe
trilobite species Protemnites magnificans Shergold Mount Wright Volcanic Arc (Scheibner and Basden
and Webers has been recorded from the Dolodrook 1998, Fig. 14.6). A small outcrop of the Lower-
Riverlimestones,easternVictoria,Australia(Paterson Middle Cambrian Teltawongee beds, considered by
Proc. Linn. Soc. N.S.W., 126, 2005 85
REVISION OF TRILOBITE GENERA DISCOMESITES AND ESTA/NGIA
Mills (1992) to be coeval with the Gnalta Group, Discussion
occurs at the northern end ofthe Mount Wright Block Palmer's (in Palmer and Rowell 1995) treatment
at Nundora. The Tcltawongee beds are thought to and diagnosis of Discomesites as a subgenus of
have been deposited as a turbidite slope-trough facies Pagetides is supported here.
(Mills 1992). Scheibnerand Basden (1998) suggested
that the Tcltawongee beds might extend beneath the Pagetides (Discomesites)fragum Opik. 1975b
large thickness of Devonian sediments within the Fig. 3A-K, Fig. 4A-J
Bancannia Trough, situated to the west ofthe Gnalta
Shelf. This inferred trough would have created an Discomesitesfragum Opik, 1975b:32, PI. 5, Figs
oceanic barrier between the eastern Arrowie Basin 1-8.
and the Gnalta Shelf. Discomesites lunatulus Opik, 1975b:34, PI. 6, Figs
Wrona (2004) observed that Lower Cambrian 1-4.
horizons in Australia and Antarctica that contain Neopagetina sp., Rowell et al. 1989, p. 14, Fig. C.
very similar faunas correspond with transgressive Pagetides {Discomesites) spinosus Palmer in Palmer
episodes that occurred during the early Botoman, and Rowell, 1995:7, Fig. 7.
late Botoman and middle Toyonian (Gravestock
and Shergold 2001; Gravestock et al. 2001). Wrona Material
(2004:52) suggested that several isolated basins 13 cranidia, 8 pygidia; CPCl3176-13179 [Type
might have existed along the East Antarctic craton material of Discomesites fragum], CPC13ISO-
and that those basins 'connected only during the IS183 [Type material oiDiscomesites lunatulus] and
most prominent transgressions, thus allowing faunal CPC37623-37635 [New topotype material from Site
exchange'. Alvaro et al. (2003) suggestedthat species A ofOpik (1975b)].
migration of Cambrian trilobites along the western
Gondwanan margin coincides with transgressive Discussion
episodes and subsequent connection ofneighbouring The characters that Opik (1975b) used
platforms. This also appears to have been the case to differentiate Discomesites fragum from D.
in influencing trilobite migration patterns along the lunatulus can be explained by ontogenetic variation,
eastern Gondwanan margin, especially between defomaation,preservationormisinterpretation. Opik's
Australia andAntarctica. differential characters include: ornamentation, length
of the occipital spine, pygidial shape and number of
pygidial axial rings.
SYSTEMATIC PALAEONTOLOGY Opik (1975b) distinguished Discomesites
fragum from D. hinatidus by its dense granulose
Specimens come from the Commonwealth ornament; however, this difference is the result of
Palaeontological Collection (prefix CPC) housed at either ontogenetic variation and/or preservation.
Geoscience Australia, Canberra. Firstly, it is important to note that specimens of D.
lunatulus are considerably smaller than those of D.
fragum. The type series cranidia oiD. lunatulus range
OrderAGNOSTIDA Salter, 1864 between 2.6-2.9 mm (n=2) in length (sag.), whereas
Suborder EODISCINA Kobayashi, 1939 the type series cranidia ofD. fragum range between
Family EODISCIDAE Raymond, 1913 3.4-4.1 mm (n=3) in length (sag.). This correlation
Genus PAGETIDES Rasetti, 1945 between size and ornamentation can also be observed
mm
inpygidia ofDiscomesites. Smallerpygidia (<2.7
Type species in length) appear to lack the granulose ornamentation
Pagetides elegans Rasetti, 1945, Early (Fig. 4C-H, J), whereas larger pygidia clearly show
Cambrian, Sillery Formation, Quebec, Canada. dense granulation (Fig. 4A-B, I). It is also worth
mentioning that some specimens of Discomesites
Subgenus DISCOMESITES Opik, 1975b that lack granulose ornamentation, including those of
D. lunatulus, have a coating of 'desert varnish" (iron
Type species oxide), while others appear to have been indurated
Discomesites fragum Opik, 1975b, Early or partially silicified. It is therefore possible that the
Cambrian, Cymbric Vale FoiTnation, Mt. Wright, difference in ornamentation may havebeen causedby
western New South Wales, Australia. weathering or diagenesis.
The differentiation ofDiscomesites species
86 Proc. Linn. Soc. N.S.W., 126, 2005
PATERSON
J.R.
€?*:-^
__.._.. '"-.
._^^M
iMis' ''SiaS^
jtfp ""
'''-,11|
^r
m m^1
w^^
A
^^^^^^^ffVv" m
j-lV,' j|
^^^^t^^-^ ** '3HI»»-'.'- I^Bf^-''- ^a
p
1
Figure 3. Pagetides (Discomesites)fragum Opik, 1975b. All scale bars = 1 mm. A, CPC13177, holotype
cranidium, dorsal view, stereo pair; B, CPC13176, cranidium, dorsal view; C, CPC13178, latex cast
of partial cranidium, dorsal view; D, CPC13180, holotype cranidium oi Discomesites lunatulus Opik,
1975b, dorsal view; E, CPC13181, cranidium, dorsal view; F, CPC37623, cranidium, dorsal view;
G, CPC37627, cranidium, dorsal view; H, CPC37628, cranidium, dorsal view; I, CPC37632, cra-
nidium, dorsal view; J, CPC37635, cranidium, dorsal view; K, CPC37629, cranidium, dorsal view.
Proc. Linn. Soc. N.S.W., 126, 2005 87
RHVISION Ol" TF<ll,()BITF^ GENERA DISCOMESITES AND ESTAINGIA
Figure 4. Pagetides (Discomesites) fragum Opik, 1975b. A, CPC13179, latex cast of pygid-
ium, dorsal view, stereo pair, scale bar = 1 mm; B, CPC37631, pygidium, dorsal view, scale
bar = 1 mm; C-D, CPC13182, pygidium, dorsal and posterior views, scale bars = 1 mm; E-F,
CPC13183, pygidium, dorsal and posterior views, scale bars = 0.5 mm; G-H, CPC37624, py-
gidium, dorsal and oblique posterolateral views, scale bars = 0.5 mm; I, CPC37630, pygidium,
dorsal view, scale bar = 1 mm; J, CPC37626, partial pygidium, dorsal view, scale bar = 1 mm.
based on occipital spine length appears to have specimens. Opik illustrated only two pygidia of D.
been exaggerated by Opik (1975b). He described lunatulus, of which only one (CPC13183) has a
the occipital spine of D. lunatulus as 'slender and complete axis preserved. Examination of pygidium
relatively long'. However, specimens ofDiscomesites CPC13183 reveals the presence of only six distinct
that have a preserved occipital spine, including the axial rings and a terminal piece. It is likely that Opik
holotype ofD.fragum, show no significant difference misinterpreted the change in slope at the base ofthe
in size and shape to that of the holotype of D. axial node on the terminal piece as an axial fiirrow.
hmatuhis. Therefore occipital spine length does not Therefore, based on the evidence above, D. lunatulus
appear to be a reliable diagnostic character. is herein considered a junior subjective synonym of
PygidialcharacteristicsusedbyOpik(1975b) D.fragum.
todistinguishspeciesoiDiscomesitescanbeattributed Palmer (in Palmer and Rowell 1995:7)
to preservation ormisinterpretation. Opik (1975b:32) distinguished the Antarctic species Discomesites
differentiated D. fragum from D. lunatulus by its spinosus from Australian species of Discomesites
'relativelybroadpygidiumwithsixaxialannulations', based on the 'presence ofaxial spines on the thoracic
and stated that the latterspecies possesses seven axial and pygidial segments and of distinct nodes on the
rings. Firstly, tectonic deformation offossils from the pygidial margin'. Examination of Opik's (1975b)
Cymbric Vale Formation is relatively common; see type material of Discomesites, in addition to new
for example, specimens illustrated by Opik (1975b, topotype material from the Cymbric Vale Formation,
PI. 1, Figs 4-5; PI. 2, Fig. 1). The larger pygidium of reveals that smaller pygidia of Discomesites (<2.3
D. lunatulus illustrated by Opik (1975b, PI. 6, Fig. mm sagittal length) have axial rings bearing short,
3) (see Fig. 4C-D for dorsal and posterior views) median axial nodes or spines (Fig. 4E-H, J). Larger
has clearly been laterally compressed, thus appears pygidia have less conspicuous axial nodes; in some
to be narrower (tr.). This was, in fact, noticed by cases the nodes appear to be absent (Fig. 4A-D, I),
Opik (1975b:35) in his comments on the illustrated implying that axial nodes vary ontogenetically. The
88 Proc. Linn. Soc. N.S.W., 126, 2005
PATERSON
J.R.
pygidia of Discomesites spinosus illustrated by in which the name Hsuaspis was first mentioned
Palmer and Rowell (1995, Fig. 7.2-7.3) conform to (Zhang et al. 1957; Zhang 1957) did not satisfy the
this ontogenetic pattern, being less than 2.5 mm in ICZN criteria for availability, thus Hsuaspis must
length (sag.). be considered nomen nudum in both publications.
The presence of marginal nodes opposite Therefore Hsuaspis became available in Lu et al.
the pleural furrows on the pygidium ofDiscomesites (1965), ayearafteritssynonymEstaingiawaserected
spinosus appears to be a rather dubious diagnostic by Pocock (1964).
character. Marginal nodes are not clearly delineated
onthepygidiaillustratedbyPalmerandRowell(1995, Estaingia cerastes (Opik, 1975b)
A
Fig. 7.2-7.3).Apygidiumof /w«a^w/w5(CPC13183) Fig. 5A-K
andanassociatedunnumberedpygidiumdisplaywhat
appearto be faintmarginal nodes opposite the pleural Strenax cerastes Opik, 1975b:14, PI. 2, Figs 1-6.
fiarrows. However, this character does not seem to Strenax {Sematiscus)fietcheri Opik, 1975b:16, PI. 3,
be consistent in all pygidia ofDiscomesites from the Figs 1-2.
Cymbric Vale Formation. Estaingia bilobata Pocock, Opik 1975b:11, PI. 1,
Palmer(inPalmerandRowell 1995:7) noted Figs 1-7.
that the Australian species of Discomesites have 'a Bergeroniellus sp., Rowell et al. 1989, p. 14, Fig. A.
slight posterior deflection ofthe inner margin ofthe Hsuaspis cf. H. bilobata Pocock, Palmer in Palmer
[anterior cranidial] border on the axial line'. This is andRowelll995:16, Fig. 12.
certainlytrueforthemajorityofDiscomesitescranidia Hsuaspis cerastes (Opik), Jago et al. 1997:71, Fig.
from the Cymbric Vale Formation, although there is 2B-L,Fig. 3.
a great deal of variation, and some cranidia do not
display this deflection at all (Fig. 3E, I, J). Therefore, Material
D. spinosus is herein considered a junior subjective 11 cranidia, 3 librigenae, 5 pygidia; CPC13152-
synonym ofD.fragum. 13158 [Opik's (1975b) illustrated material of
Estaingiabilobata], CPC13159-13163 [Typematerial
ofStrenaxcerastes], CPC13164 [Holotype cranidium
Order REDLICHIIDARichter, 1932 of Strenax (Sematiscus) fietcheri] and CPC37636-
Suborder REDLICHIINA Richter, 1932 37641 [New material from SiteA ofOpik (1975b)].
Superfamily ELLIPSOCEPHALOIDEAMatthew,
1887 Discussion
Family ESTAINGIIDAE Opik, 1975a The revision of Estaingia cerastes from
Genus ESTAINGIAPocock, 1964 the Cymbric Vale Formation has been previously
documented by Jago et al. (1997) and will only be
Type species briefly discussed here. Jago et al. (1997) noted
EstaingiabilobataPocock, 1964,EarlyCambrian, that specimens of E. bilobata illustrated by Opik
Emu Bay Shale, Kangaroo Island, SouthAustralia. (1975b) do not belong to this species because Opik's
specimens possess a longer (sag.) glabella (relative
Discussion to cranidial length) and show a marked forward
Jell (in Bengtson et al. 1990:310) originally expansion ofthe glabella, whereas the type cranidia
regardedEstaingia and Zhuxiella asjunior subjective of£. bilobata illustrated by Pocock (1964) display a
synonymsofHsuaspis.Thissynonymywassupported shorter (sag.) glabella that either tapers anteriorly or
in subsequent studies by Palmer and Rowell (1995), has a slight waist. Nedin and Jenkins (1999, Fig. 4)
Nedin (1995), Jago et al. (1997) and Nedin and have documentedthe difference in glabella length (or
Jenkins (1999). Jell (in Bengtson et al. 1990) also preglabellar field) between specimens ofE. bilobata
suggested that Strenax may be regarded as a junior and E. cerastes. Nedin and Jenkins (1999) have also
subjective synonym of Pseudichangia. Jago et al. demonstrated that E. bilobata and E. cerastes can
(1997) supported Jell in synonymising Strenax with be differentiated based on cranidial length/width
Pseudichangia, but considered both genera to be ratios. Jago et al. (1997) also suggested that Opik's
junior synonyms ofHsuaspis. Recently, Jell (in Jell specimens of E. bilobata and Strenax cerastes are
and Adrain 2003:334) discovered a nomenclatural likely to represent the same species based on the
error between the synonymous genera Estaingia variation displayed in Opik's illustrated specimens
and Hsuaspis. Jell noted that Estaingia should be and those illustrated by Jago et al. (1997). Therefore,
considered the senior name because the publications in placing Strenax in synonymy with Hsuaspis, Jago
Proc. Linn. Soc. N.S.W., 126, 2005 89
REVISION OF TRILOBITE GENERA DISCOMESITES AND ESTAINGIA
Figure 5. Estaingia cerastes (Opik, 1975b). A, CPC13159, latex cast of holotype cranidium of Stre-
nax cerastes, dorsal view, scale bar = 5 mm; B, CPC13152, cranidium, dorsal view, scale bar = 5
mm; C, CPC13156, cranidium, dorsal view, scale bar = 5 mm; D, CPC13157, pygidium, dorsal
view, scale bar = 2.5 mm; E, CPC13158, latex cast of pygidium, dorsal view, scale bar = 2.5 mm; F,
CPC37638, pygidium, dorsal view, scale bar = 2.5 mm; G, CPC13153, cranidium, dorsal view, scale
bar = 5 mm; H, CPC37637, cranidium, dorsal view, scale bar = 2.5 mm; I, CPC37636, cranidium,
dorsal view, scale bar = 2.5 mm; J, CPC13164, latex cast of holotype cranidium of Strenax (Sematis-
cus)fletcheri, dorsal view, scale bar = 1 mm; K, CPC37641, librigena, dorsal view, scale bar = 2.5 mm.
et al. (1997) reassigned E. bilobata and S. cerastes Jago et al. (1997:71) based this interpretation on the
described by Opik (1975b) from the Cymbric Vale fact that the Antarctic specimens 'have a glabella of
H
Formation to a single species, Hsuaspis cerastes, similar length to occipitospina as well as a similar
reassigned herein to Estaingia cerastes (Opik). Jago preglabellarmedianridge [=plectrum] TheAntarctic
'.
etal. (1997:71) alsonotedthattheholotype cranidium specimens do appearto have a shorter (sag.) glabella,
of Strenax (Sematisciis) fletcheri Opik, 1975b 'is similarto E. bilobata andE. occipitospina, compared
clearly an immature specimen which should not be to that of£. cerastes. However, it is important to note
the basis of a new taxon'. The holotype of Strenax that the Antarctic cranidia are considerably smaller
(Sematiscus)fletcheri is considered herein ajuvenile (sagittal length: 3.8-5.6 mm) than the large holaspid
specimen (sagittal length: 3.0 mm) and junior cranidia of E. cerastes (sagittal length: 11-18 mm)
subjective synonym ofEstaingia cerastes. illustrated by Opik (1975b) and Jago et al. (1997).
Jago et al. (1997) suggested that specimens Smaller cranidia of E. cerastes (Opik 1975b, PI. 3,
of Hsuaspis cf. H. bilobata described by Palmer Figs 1-2; Jago et al. 1997, Fig. 2K) ofsimilar size to
(in Palmer and Rowell 1995) from the Shackleton the Antarctic cranidia show similar glabella lengths.
Limestone in the Transantarctic Mountains may Therefore the glabella of E. cerastes appears to
belong to Hsuaspis {=Estaingia) occipitospina, become longer (sag.) relative to the cranidial length
originally described by Jell (in Bengtson et al. 1990). during ontogeny; a trend also observed by Jago et al.
90 Proc. Linn. Soc. N.S.W., 126, 2005