296Tanner, L.H., Spielmann, J.A. and Lucas, S.G., eds., 2013, The Triassic System. New Mexico Museum of Natural History and Science, Bulletin 61.

A SYNTHESIS OF THE RICH GONDWANA TRIASSICMEGAFOSSIL FLORA FROM NYMBOIDA, AUSTRALIA

W.B. KEITH HOLMES1 AND H.M. ANDERSON2

1 Hon. Research Fellow, University of New England, Armidale, 46 Kurrajong Street, Dorrigo, NSW, Australia 2453, email: wbkholmes@hotmail.com;2 Hon. Palaeobotanist, BPI Palaeontology, University of Witwatersrand, Johannesburg, South Africa, email: hmsholmes@googlemail.com

Abstract—This synthesis of the Nymboida megafossil flora, based on a series of nine descriptive taxonomicpapers, provides the first comprehensive account of a Triassic fossil flora in Australia in the twenty-first century.From a fossil flora perspective the Nymboida Coal Measures, located southwest of the city of Grafton in northernNew South Wales, are highly significant as they are the source of the oldest commercial coal seams in the worldfollowing the "coal gap" after the disastrous Permian-Triassic extinction events. Similarity of the Nymboida florato the Kaihikuan floras of New Zealand suggests a Ladinian age. The previously active Coal Mine and ReserveQuarries, which lie in the Basin Creek Formation, have yielded over many years a very rich and diverse Triassicflora. To date a total of 58 genera, 105 species and another 28 forms that have insufficient detail preserved forspecific identification have been described. Due to a tectonic heating event during the Cretaceous, cuticles are notpreserved. The flora is particularly diverse in ferns (14 species) and fern-like fronds (23 species), whereasbryophytes and sphenophytes are rare. The Ginkgoopsida, which includes the so called seed-ferns and ginkgo-likeleaves, are rare (e.g., Rochipteris) to being among the dominant elements (e.g., Dicroidium, Sphenobaiera,Lepidopteris, Ginkgoites and Kurztiana) of the flora. Cycadophyta are very rare to rare with one species ofPseudoctenis being common. The Voltzialean conifer Heidiphyllum may occur in monotypic assemblages, as a co-dominant with the other common conifer Rissikia or with other common species. Among the leaves of uncertainclassification are Taeniopteris, with one common species, and other genera – Nilssonia, Linguifolium, Gontriglossaand Scoresbya – being rare to very rare.

INTRODUCTION

From a fossil flora perspective the Nymboida Coal Measures arehighly significant as they are the source of the oldest commercial coalseams in the world following the "coal gap" after the disastrous Permian-Triassic extinction events (Retallack et al., 2010). They are also impor-tant in having yielded over many years from two previously activequarries a very rich and diverse Triassic flora. A synthesis of the com-plete Nymboida megafossil flora is presented here for the first time.

GEOLOGICAL SETTING

The Nymboida Coal Measures (located south-west of the city ofGrafton, in northern New South Wales, Australia) were described andmapped during a study of the Clarence-Moreton Basin by McElroy(1963). They are now included in the Nymboida Subbasin (Fig. 1), whichlies unconformably below the Triassic to Late Cretaceous nonmarinesediments of the Clarence-Moreton Basin (O’Brien et al., 1994). TheDalmally Basalt, which lies below the Basin Creek Formation and abovethe Cloughers Creek Formation, has been radiometrically dated at 237 ±0.4 Ma (Retallack et al., 1993). Identical megafossil floras lie both aboveand below the Dalmally Basalt, thus indicating no significant time inter-val between the deposition of the two formations (Retallack et al., 1977).Using the recent time scale presented by Gradstein et al (2012), the ageof the Nymboida Flora falls on the Ladinian-Carnian boundary. Becausethe Nymboida flora exhibits closer similarity to the Kaihikuan floras ofNew Zealand (Retallack, 1987) rather than the typical Carnian floras ofthe Molteno (Anderson and Anderson, 2003) it is best assigned a Ladinianage.

LOCALITY INFORMATION AND PALAEOGEOGRAPHY

Almost all the described fossil plants of the Nymboida Flora havebeen collected from two quarries, which, although 5.3 km apart, arebelieved to have had a contemporaneous deposition (Holmes, 2000).

FIGURE 1. Map showing the Nymboida Subbasin as the inferred southernmostextension of the Esk Trough and the Nymboida District with location ofthe fossil-bearing quarries.

297The sedimentary sequences displayed at both the Coal Mine Quarry(Fig. 2) and the Reserve Quarry (Fig. 3) represent overbank floodingevents by a large meandering river on an alluvial floodplain with openstagnant lakes and swamplands. Spring-time flooding from snowmelt onthe highlands of the New England Fold Belt to the west would havetransported large quantities of sediment to the Nymboida Subbasin,which McElroy (1963) regarded as a ponded environment. The finelylaminated shales in the quarries are an indication of seasonal floodingevents. The irregular layers of coarse sandstone represent either highwater flooding or migration of the main stream across the floodplain. Thevarious types of preservation of plant material in the sediments indicateautochthonous to allochthonous deposits. The reconstruction (Fig. 4) ofthe Middle Triassic Nymboida flood plain as provided by Retallack(1977) suggests a wide range of habitats to support a very diverse flora.Thick beds of gray shales often contain numerous plant roots in situ,thus indicating fossil soil horizons. The presence of charcoal fragmentsin some sandstone beds indicates the occurrence of occasional fires inupland areas. Analysis of the paleopole position from paleomagneticdata (Anderson and Anderson, 1983; Scotese, 1994) indicates that theNymboida Subbasin was located at ca. 60° S. The proximity of thePaleo-Pacific Ocean would have had an ameliorating effect on daily andseasonal temperature fluctuations, thus creating a cool temperate cli-mate, with moisture not a limiting factor. Banks of fossil leaves thatoccur on numerous horizons suggest that at least some of the vegetation

was deciduous as an adaptation for coping with the low angle of sunlightand a long period of winter darkness.

THE NYMBOIDA MEGAFOSSIL FLORA

The presence of fossils plants in the Nymboida Coal Measureswas first noted by de Jersey (1958) with later descriptions based onlimited collections by Flint and Gould (1975), Retallack (1977), Retallacket al. (1977), Herbst (1977), Webb (1983, 2001) and Holmes (1987,1992).

Since 1966, the senior author and his family have made manycollecting trips to the Nymboida quarries. By 2013, their private collec-tion numbered over 2600 selected slabs with many displaying two ormore fossil plants. This is the most extensive and comprehensive collec-tion derived from two separate but contemporaneous Triassic localitiesin Australia. The large quantity of material collected allows for a greaterunderstanding of the range of variation within a “species” and morechance of identifying the very rare elements in the flora. However, somuch variation also introduces problems of identifying those fossil spe-cies that often show overlapping ranges with previously described spe-cies. Another extensive collection of plants from the Gondwana Triassicis from the Molteno Formation in South Africa by Anderson and Ander-son (1983, 1989, 2003, 2008), where they were the first to use paleo-gamma taxonomy and introduced the term “palaeodeme.” In brief, a“palaeodeme” is an assemblage of plant remains showing a normal distri-bution of variation, derived from a single assemblage and from a discretelithological unit. Unfortunately this approach is not applicable to thepresent Nymboida collections as the fossils have been derived from amiscellaneous collection of loose blocks dislodged from various horizonson the working quarry faces. However, the traditional alpha taxonomy,which works well for small limited collections of fossils, does not suitlarge collections showing much diversity in size and form of similarleaves. As a result leaf forms that show a wide range of variation are herereferred to as “species complexes,” basing the name on a previously-described species that represents the core of the complex.

The descriptive taxonomy of the Holmes collections was com-menced with the publication of Part 1 in 2000, which described theBryophyta and Sphenophyta (Holmes, 2000) and was followed by eightother parts describing various sections of the flora (Holmes, 2001a,2003; Holmes and Anderson, 2005a, b, 2007, 2008, 2010, 2013). Unfor-tunately, due to a tectonic heating event during the Cretaceous (Russell,1994), cuticles are not preserved. Descriptions therefore are based on thegross morphology of the plant material, which is often exquisitely pre-served. Research for the above publications has revealed the presence inthe preserved flora of 58 genera, 105 species and another 28 forms thathave insufficient detail preserved for specific identification. Still to be

FIGURE 2. Coal Mine Quarry, Nymboida. Northeastern face showingoverlying massive sheet sandstone and crevasse splay deeply incised intothinly bedded gray shales, siltstones, thin coal seams and fossil soil horizons.

FIGURE 3. Reserve Quarry, Nymboida. Northern face with sheet sandstoneoverlying thin cyclic beds of sandstone, siltstone and coaly shales.

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described from the Nymboida collection are a few dispersed ovules andplant stems showing evidence of seasonal growth. A notable feature inthe Nymboida Flora is the absence of insect leaf damage. A singleundescribed beetle wing is the only evidence of the presence of insects.

A brief review of the Flora is given below, and two slabs showingtypical fossil plants are shown in Figures 5 and 6. A classified list of allthe taxa is provided in Appendix 1 for the two quarries. The classifica-tion follows broadly that of Anderson and Anderson (2007). Taxa withone or two collected specimens are listed as “very rare;” three to ten as“rare;” and those comprising ca. 1% or more of the collection are regardedas “common.”

All Type, illustrated and mentioned specimens previously de-scribed from the Nymboida collection are housed in the Australian Mu-seum, Sydney, New South Wales.

Bryophyta

Colonies of in situ thalloid plants occur rarely on some beddingplanes. They are most likely liverworts with a simple thallus and radiat-ing branches. In the absence of diagnostic characters, they are listed as“Thalloid fossil” sp. A and sp. B (Holmes, 2000).

Sphenophyta

Sphenophytes are rare. Horsetail swamp-like deposits, whichoccur in many Early and Late Triassic assemblages, are absent in theNymboida Flora. Characters observed on occasional leaf-bearing stemsand nodal diaphragms that have been collected have been placed in thegenera Zonulamites and Townroviamites to reflect significant differencesthat separate Gondwana and northern hemisphere Middle Triassicequisetalean genera (Holmes, 2000, 2001b). A unique scrambling or float-

ing sphenophyte Nymbolaria tenuicaulis, with pseudo-verticals of ellip-tic leaves radiating as bi-symmetrical pairs from slender ribbed stemswas recovered from a thin mud smear below a thick sandstone horizon.Sphenophyte fertile organs include strobili assigned to cf.Neocalamostachys sp. A and Nymbotheca verticillata, a stout axis bear-ing regularly spaced, stem-encircling discs bearing sessile sporangia onthe surface of each disc (Holmes, 2000).

Filicophyta

Fronds and frond fragments of ferns and fern-like plants compriseca 25% of the Nymboida collections and are among the most diverseelements of the flora. Leaf length ranges from a few centimeters(Micronymbopteris repens) to fronds over three meters long (Rhinipteriswalkomii) and similar to those of some extant tree ferns. Where sporan-gia-bearing material has been collected the ferns have been described ingenera in the Orders Marattiales with eight species; Filicales with fourspecies and Osmundales with two species (Holmes, 2001). For somespecies, e.g., Osmundopsis scalaris, their morphology is known fromalmost complete plants with both fertile and sterile fronds.

Twenty-three morphospecies have been described for forms with-out attached sporangia or associated fertile structures (Holmes, 2003).These are regarded as “fern-like foliage.” The largest genera areCladophlebis with six species; Nymbiella five species and Nymbopteristhree species. The remaining nine genera are all represented by a singlespecies.

Umkomasiaceae

At Nymboida the fragmentary or complete forked leaves attrib-uted to Dicroidium in the Family Umkomasiaceae are among the most

FIGURE 4. Reconstruction of the floodplain of the Nymboida Subbasin during mid Triassic time. From Retallack (1977).

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FIGURE 5. A fossil slab from Coal Mine Quarry showing numerous long leaves of Heidiphyllum elongatum and near the upper right two forked leaves ofDicroidium odontopteroides. Scale bar is 5 cm long.

FIGURE 6. A fossil slab from Coal Mine Quarry showing one large leaf (beyond the fork) of Dicroidium zuberi, a Sphenobaiera schenkii (upper right) anda few conifer-like leaves of Rissikia media. Scale bar is 5 cm long.

300commonly occurring plant remains. The extensive Nymboida collectionsreveal a range of intergrading forms that link the morphological charactersattributed to past described “species.” As in modern plants there arevarying degrees of morphological variation within a single species. Thedesignated “type” may not necessarily represent the midpoint in itsrange of variation. The problem is exacerbated in paleobotany wheremost taxa are described from dispersed plant organs. Following the taxo-nomic works on Dicroidium by Retallack (1977), Anderson and Ander-son (1983) and others, we endeavored to place well-preserved leavesinto previously published species while acknowledging the intergradingforms linking each “species.” Thus, in the Nymboida flora most materialof Dicroidium has been placed in five “species complexes” (Holmes andAnderson, 2005a). The single leaf of D. elongatum has probably beentransported from a drier environment as observed in the Benolong Flora(Holmes, 1982). It is closely similar in form to the specimens of attachedleaves from the Upper Triassic Ipswich Coal Measures (Anderson et al.,2008). A problematical frond has been described as ?D. nymboidensis.The affiliated fertile organs of the Dicroidium foliage are two species ofcomplete female strobili, Umkomasia distans and U. sessilis (Holmes,1987), together with dispersed ovules. Also present are incomplete malestrobili and dispersed microsporophylls of Pteruchus.

Peltaspermaceae

Lepidopteris leaves and fragments comprise ca. 3% of plants oncatalogued slabs. They show a great range of variation and have beendescribed in three “species complexes” with two distinct leaf forms asnew species (Holmes and Anderson, 2005b). The affiliated femalePeltaspermum and male Antevsia are each known only from two incom-plete strobili.

Kannaskoppiaceae

Although representatives of this family are rare, six new speciesof Rochipteris have been described (Holmes and Anderson, 2005b). Thepreservation of two species indicates the foliage is inserted on the stemeither as a close spiral or terminal whorl. The fertile organs Kannaskoppia(female) and Kannaskoppianthus (male), as occur in the Molteno (Ander-son and Anderson, 2003), have not yet been found at Nymboida.

Incertae sedis

Leaves of Kurtziana represent ca. 2% of the catalogued slabs andare sometimes found as the dominant leaf type on some bedding planes.They have been placed in two “species complexes” with “K. cacheutensiscomplex” being the more common (Holmes and Anderson, 2005b). Theaffiliated fertile organs of these leaves are as yet unknown in Gondwana.

Ginkgoaceae

Ginkgoites leaves with four species form ca 2.5% of the Nymboidacollection (Holmes and Anderson, 2007). Leaves of the “Ginkgoitesdenmarkensis complex” are very common and variable.

Hamshawviaceae

Sphenobaiera with seven species comprises ca 7.5% of theNymboida collection (Holmes and Anderson, 2007). Three of theSphenobaiera species are common, with “S. schenkii complex” beingdominant on certain bedding planes. Two pairs of female strobili,Hamshawvia distichos, affiliated with Sphenobaiera are preserved onone slab. Two species of the male strobili Stachyopitys are described.

Cycadopsida

True cycad leaves in the Order Cycadales comprise ca 4% of thetotal collection (Holmes and Anderson, 2008). The majority of the leavesare placed in ten species in the genus Pseudoctenis and are very rare torare with one species being common. Others are placed in two species of

Ctenis and a form with serrate pinnae in Moltenia sparsispinosa. Nofertile material has been found.

Bennettitopsida

A bennettiatalean form is placed in Halleyoctenis brachypinnata(Holmes and Anderson, 2008). It is possible that some of the generaplaced in incertae sedis may belong here.

Incertae sedis

Due to the absence of cuticular details or affiliated fertile organsthe taxonomic position of the following material is uncertain. Strap-likeleaves with parallel lateral venation have been placed in two species eachin the genera Nilssonia and Taeniopteris and spatulate forms in twospecies of Linguifolium (Holmes et al, 2010). Leaves with variouslyanastomosing lateral venation have been placed in four species of thegenus Gontriglossa. An outstanding specimen of G. grandis shows aterminal branch bearing 10 leaves in a whorl or close spiral (Holmes,1992; Holmes et al., 2010). A large leaf bifurcating into irregular lobeswas described as a new species (Holmes et al, 2010) in the genusScoresbya, whose species were known previously mainly from the Ju-rassic of the Northern Hemisphere.

Pinopsida

Fragments and complete leaves of the Voltzialean coniferHeidiphyllum elongatum form ca 1% of the preserved Nymboida floraand are often found associated with Dicroidium and other commonlyoccurring species. However, it also is preserved as monotypic assem-blages. During working operations at the Reserve Quarry one such bed-ding plane of over 300 square meters was exposed, suggesting the au-tumn leaf fall from a mono-specific deciduous forest. Foliage shoots ofthe podocarp Rissikia media are common, often in association withleaves of Heidiphyllum elongatum. A few Rissikianthus (male) andRissikistrobus (female) cones are associated with the foliage shoots butare lacking in details for specific identification (Holmes and Anderson,2013).

Gnetopsida

One possible species of Yabeiella has been recorded. However,probably some of the leaves now placed in incertae sedis, e.g., in thegenus Taeniopteris, will prove to belong here.

CONCLUSIONS

The Nymboida Flora is comparable with the megafloras from theMiddle Triassic Toogoolawah Group of the Esk Trough in the northernClarence-Moreton Basin (Walkom, 1924) and the Moolayember Forma-tion of the Bowen Basin (Playford et al., 1982) of Queensland. However,as the flora from the Esk Trough is in need of a modern update and theone from Moolayember is based on a limited collection from one locality,detailed comparisons are difficult. Numerous papers have been pub-lished on Gondwana Triassic floras, but in the absence of comprehensivedescriptions of the complete floral assemblages one cannot make usefulcomparisons with the Nymboida Flora.

This synthesis of the Nymboida megafossil flora, based on aseries of nine descriptive taxonomic papers, provides the first compre-hensive account of a Triassic fossil flora in Australia in the twenty-firstcentury. Furthermore, the Nymboida Coal Measures are highly signifi-cant as they are the source of the oldest commercial coal seams in theworld following the "coal gap" after the disastrous Permian-Triassicextinction events. Continuous collection from the once active quarries,over some 40 years, has yielded an extensive range of the common leavesand many of the rare elements of the flora. To date a total of 58 genera,105 species and 28 forms have been described. The common genera suchas Asterotheca, Cladophlebis, Dicroidium, Sphenobaiera, Lepidopteris,

301Ginkgoites, Kurztiana, Pseudoctenis, Heidiphyllum, Rissikia andTaeniopteris are found in other Gondwana Triassic floras, but many oftheir species are unique and among the very rare finds they are often theonly occurrence known in the world.

ACKNOWLEDGMENTS

We thank Spencer Lucas, Greg Retallack and Lawrence Tanner forcomments on an earlier version of the manuscript.

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303APPENDIX

A classified list of the plant taxa from the Nymboida Coal Mine and Reserve.

304

305