117 dinmore flora popular sci

7/29/2019 117 Dinmore Flora Popular Sci

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ThefossilfloraofDinmoreByDrStephenMcLoughlin


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40 Australian Age of Dinosaurs

Story and photos by Dr Stephen McLoughlin


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Twenty-one years ago, my firstfossil-hunting foray was to the sub-urbs of Ipswich. I had no field guide

describing where to find fossils, nogeological map, and no equipmentother than a rock hammer. All I knewwas that Ipswich was home to coalmines in Triassic strata, and wherethere was coal it was likely thered

be nice plant fossils. With an eye outfor coal mine tailings dumps, I drovearound the outskirts of Ipswich.

Through the course of the day Ifound several productive fossil sites

but the best I encountered on thatfirst fossil foray was undoubtedlythe Dinmore Claypit, also known as

the Roberts Street Claypit. This sitehas been actively quarried as a sourceof industrial clay since at least the1930s and has long been a favouritehaunt of fossil hunters. By the endof the day I had a car full of shaleslabs with beautiful imprints of leavesand stems. It is very satisfying thatsome of these now reside in museumswhere they are available for futuregenerations to study.

Throughout the two decades sincemy initial introduction to the DinmoreClaypit I have returned many times,sometimes with colleagues or stu-dents and sometimes to simply reac-quaint myself with this outstandingnatural resource. I quickly discoveredthat getting access to really good fos-sil material depends to a large extenton whether recent quarrying hasexposed fresh bedding surfaces of theshales. After long periods of exposureto the elements, the surface layers ofshale can become soft, bleached andfriable, reducing ones ability to findlarge cohesive slabs with preservation

Since it first opened in the early 1930s, the Dinmore Claypit at Ipswich, Queensland,

has been an important research and teaching destination for palaeontologists,

educators and students. Today, nearly 80 years later, the relevance of this unique

resource remains undiminished.

of fine vein details in the fossil leaves.Nevertheless, with a little digging, onecan always find excellent material at

Dinmore due to the sheer abundanceof fossils preserved. The fossils at themain Dinmore Claypit site are pre-served as impressions in thinly lami-nated pale grey or pink shale. Theseare simply imprints where all of theoriginal organic matter has weath-ered away leaving just an outline(such as the shape and veined patternof leaves) as indentations in the rock.In some cases, ground-waters havepercolated through the shales andon evaporating, have precipitated athin veneer of iron minerals over the

surface of the fossils. This also helps

accentuate some of the morphological

details of the leaves.

A little higher up the hill to the

south of the main claypit are old coalmine spoil dumps with large boulders

of dark grey siltstone and sandstone

that also contain Late Triassic plant

fossils. However, on these boulders

some of the fossils are preserved

as compressions, where the original

organic matter has been retained in

the rock and compressed to coaly

material. Both the grey shales in the

main claypit and the dark blocks

in the spoil dump derive from the

Blackstone Formation part of the

Ipswich Coal Measures.

Retaining coalified plant tissues,theseDicroidium leaves (right) preserved as compressions wereretrieved from coal mine spoildumps behind Dinmore Quarry.

Dicroidium leaves such asDicroidiumodontopteroides (opposite page) arecommon in the grey shales of the

Dinmore Claypit which form partof the Ipswich Coal Measures.


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The Fossil Flora

The Dinmore Claypit hosts an

extremely rich fossil flora dominated

by an extinct order of plants called

Corystospermales (also known as

Umkomasiales) that are recognised

by their distinctive fern-like forked

leaves. Corystosperms were the

dominant plants contributing to the

Triassic coal deposits of the SouthernHemisphere and the same species are

found right across the ancient super-

continent Gondwana, from South

America in the west to New Zealand in

the east. Several species ofDicroidiumoccur in the Dinmore deposit somewith small semicircular or lobed leaf-lets, others with long needle-like leaf-lets. Although the leaves look super-ficially like a fern, these plants didnot produce spores. Instead they pro-duced pollen and seeds. When the

various organs of the plant are founddispersed in the sediment, palaeobota-

nists assign the leaves to the genusDicroidium, the seed-bearing parts toUmkomasia, and the pollen-bearingparts to Pteruchus. Even the pollengrains are given a separate name

when found dispersed Falcisporites.Hence a single parent plant mighthave produced parts that are assignedto four or five names. But that is one

of the joys of palaeobotany work-ing out the jigsaw puzzle of dispersedparts to reconstruct the structure andecology of the whole plant.

Dicroidium leaves probably makeup 80 per cent of the individual plant

fossils at Dinmore and commonlyoccur in densely matted layers sug-gesting that the plants had a decidu-ous habit (dropping their leaves in thepolar autumn) a common strategy

Several species ofDicroidium occur in the Dinmoredeposit and include the lobe-leafleted Dicroidium odon-topteroides (above) and the long, needle-like leaflets ofDicroidium elongatum (left).Dicroidium leaves accountfor about 80 per cent of fossil plants at Dinmore andusually occur in dense matted layers, suggesting adeciduous habit.


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When leaves, seeds and pollen-bearing parts found dispersed

throughout a deposit cannot bedirectly linked to each other, theyare all given a different name. Itis therefore possible that a singleplant species can consist of severalorgans that bear different names.The name Umkomasia refers to theseed-producing parts of the plant -hence the name Umkomasia given tothis small seed organ (right). Pollenorgans are namedPteruchus withthis beautiful species (above) knownasPteruchus dubia. Leaves from theDinmore deposit associated with

these fossils are assigned to thegenusDicroidium.


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for plants living in strongly seasonalenvironments. However, there is also a

broad array of other plants preservedat Dinmore. Fern fronds and equi-setalean (horsetail) stems are presentin small numbers and several speciesof fan-shaped Ginkgo leaves are scat-tered through the deposit (see AAOD#8 Ginkgo in Australia). There are alsodistinctive strap-shaped leaves with

parallel veins calledHeidiphyllum thatbelong to the Voltziales, an extinctorder of conifers. Other extinct groupsof gymnosperms (seed-bearingplants) are also represented, includ-ing the Peltaspermales (Lepidopterisleaves and Antevsia pollen organs:Kannaskoppiales (Rhochipteris)Bennettitales (Pterophyllum leaves),possible cycads (Taeniopteris leaves),and some curious strap- or tongue-shaped leaves (Linguifolium) for whichwe do not yet have any firm ideas asto their affinities.

The Dinmore flora has many spe-cies and genera in common with thewell-studied Triassic floras of South

Africa, Argentina and Antarctica, butmuch less in common with florasfrom North America, Europe and Asia,thus contributing to the concept of awidespread but distinctive middle- tohigh-latitude Southern Hemisphere(Gondwanan) flora during this timeinterval.

The fan-shaped leaf ofGinkgo matatiensis, an ancient relativeof the Chinese maidenhair tree. Several species ofGinkgo leavesare scattered throughout the Dinmore Claypit.

Fossil leaves ofHeidiphyllum elongatum relics of an extinctorder of conifers, the Voltziales.

Ferns such as this foliage ofCladophlebissp. arerelatively uncommon in the Dinmore deposits.


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A leaf of the extinct gymnospermRhochipterisginkgoides.

Linguifolium tenison-woodsii, an unusual gymnospermleaf whose true affinities as yet remain obscure.

Pterophyllum multilineatum, a bennettitaleanleaf.

Pollen organ ofAntevsia sp. a seed-bearingpeltasperm from the Dinmore Claypit.

An elongate leaf of the gymnosperm Taeniopteris len-triculiformis a possible cycad.


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The Fossil Fauna

Beyond the plants, the Triassicshales exposed at Dinmore and near-

by Denmark Hill have also yieldeda few fossil insects and abundant

branchiopod crustaceans (spinicau-datans). In 2004 Peter Jell compileda comprehensive list of the insectsdescribed from the Australian fossilrecord. Although several new dis-coveries from around the continenthave been described subsequently, thispublication lists the significant dis-coveries from the rocks of the IpswichBasin and is a good starting point foranyone interested in pursuing furtherinvestigations of Australias Triassicinsects.

Scattered amongst the leaf fossilsat Dinmore are small (about 5mmdiameter) circular or kidney-shaped

imprints that are commonly mis-

taken by first-time collectors as seeds.

Closer inspection with a hand lens

will reveal that these structures have

concentric growth rings and actually

represent the bi-valved shells of bran-

chiopod crustaceans (a group that

includes the modern brine shrimps).

These were formerly known as con-

chostracans until it was realized that

several quite distinct groups of crus-taceans had been lumped under this

banner. John Webb (now at Latrobe

University) published an article on

the Ipswich branchiopod crustaceans

in 1979 but there is much potential

for future work on this group since

they are relatively common in the

Dinmore deposit.

Even when the bodies of the inver-

tebrates are not preserved, we can still

recognise their presence in some cases

by the traces of their distinctive life

habits. For example, sparse trails in

the sediments attest to the presence

of a few small sediment-burrowing

invertebrates. Further, one conifer leaf

identified by palaeontologists Andrew

Rozefelds and Ian Sobbe in 1987 shows

the tell-tale evidence of a leaf-mining

invertebrate (probably either a small

insect or a mite). This fossil remainsone of the worlds oldest examples of

leaf mining in the fossil record.

To date, no vertebrate fossils have

been found at this site. This is a little

peculiar since the sediments are ideal

for preserving the remains of fish or

trackways. Perhaps the high-latitude

setting might explain the dearth of

vertebrate fossils, or perhaps we have

just not looked hard enough yet!

A bonus fossil deposit

Apart from the well-known and

abundant Triassic plant fossils, there is

another assemblage of much younger

plant remains in the same quarry at

Dinmore. These occur in soft clay-

stones that overlie the Triassic strata

in the northern half of the pit. Theseyounger deposits are of Paleogene age

(probably around 55 million years

old) and belong to the Redbank Plains

Formation. Due to their similar col-

our and lithology, these rocks can

easily be confused with the older

Triassic strata, but the fossil assem-

blages from the respective formations

are strikingly different. The fossils in

the Paleogene sediments are mostly

broad elliptical leaves of flowering

plants and include representatives of

families that one might recognise

in modern Australian moist forestsincluding members of the laurel fam-

ily (Lauraceae) and rainforest quan-

dongs (Elaeocarpaceae). A few ferns

are present including the climbing fern

Lygodium but conifers are surprising-

ly rare. Although a large assemblage

of fossils from this Paleogene deposit

has been collected and conserved in

the Queensland Museum, the full

composition of this flora has never

been described. The softer clays of

the Redbank Plains Formation meanthat exposures degrade very quickly,

and well-preserved fossils are usually

found only after fresh excavations are

made for industrial clays.

Shell of a branchiopod crustacean from the Dinmoreclaypit.

AHeidiphyllum leaf with evidence of leaf mining oneof the oldest such records on Earth.

An angiosperm leaf fromPalaeogene deposits at the DinmoreClaypit (right). At about 55 millionyears old, the fossils of theseflowering plants are preserved

in the Redbank Plains Formationwhich overlies the Triassic strataat Dinmore.


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The Ipswich Basin in perspective

The fossil-bearing beds at Dinmore

lie within the Ipswich Basin a small

fault-bound sedimentary basin in

southeast Queensland of Triassic age.

The Triassic (251200 million years

ago) is the first period of the Mesozoic

Era and saw the rise of the dinosaurs,

pterosaurs, large marine reptiles

and many new plant groups in theaftermath of the great end-Permian

extinction.

The Ipswich Basin is just one of

several small Triassic intermon-

tane sedimentary basins scattered

through eastern Australia including

the Tasmania Basin in Tasmania, five

small depressions that make up the

Leigh Creek basin complex in South

Australia, the Lorne Basin in New

South Wales, the Esk Trough span-

ning the Queensland-NSW border,

and the Tarong and Callide basins in

Queensland. Several of these basinshost commercial quantities of coal.

The Tarong, Callide and Leigh Creek

coal measures, in particular, current-

ly contribute major coal resources

to the generation of electricity inQueensland and South Australia. Theformation of coal requires the accu-mulation of thick quantities of peatin swampy environments wherein theorganic matter builds up in oxygen-deprived soils faster than microbescan break it down. This generallyrequires a very wet environment and

continuous subsidence. Later burial

by sediments compresses the peatand, combined with geothermal heat-ing, converts it to coal.

All of these sedimentary basinsdeveloped at the tail end of a majorphase of mountain building in east-ern Australia when the landmass (atthat time still attached to the otherSouthern Hemisphere continents) wasactively colliding with the ancientPacific Plate. At that time, the eastern

Australian margin might have beenreminiscent of the modern Andeanand Rocky Mountain margins of the

Americas, with high mountains sepa-rated by deep valleys and local lakesystems accumulating sediments.

All of this occurred while eastern

Australia was situated much closer to

the South Pole as determined by thepalaeomagnetic signature imprintedin the rocks of that time. Hence,the eastern Australian Triassic florasprobably developed under a cool andgenerally moist climate.

Because these basins were accu-mulating sediments at differenttimes through the Triassic, the fossilsobtained from these deposits collec-

tively allow us to build up a pictureof the progressive changes in the veg-etation through the early Mesozoic ofeastern Australia. Few fossil leaf flo-ras of this age have yet been studiedfrom Western Australian basins butthe fossil spore-pollen record of thosewestern basins has been well studiedas an aid to petroleum exploration. Aregular turnover of species is evidentthroughout the Australian Triassicand there are some regional differ-ences in the composition of the floras,

but the major plant groups are rep-resented throughout the continent.The Ipswich Basin provides a windowinto the floras of the early and mid-dle parts of the Late Triassic (around226203 million years ago).

The Ipswich Basin is one of several smallTriassic intermontane sedimentary basins(right) that developed at the end of a major

mountain building phase when Australia still attached to the supercontinentGondwana was colliding with theancient Pacific Plate. The subsequentformation of deep valleys between mountainranges, combined with a cool moistenvironment and dense vegetation, led tothe accumulation of thick peat beds, andseveral of the sedimentary basins formedunder these circumstances host commercialquantities of coal. Comprehensive miningoperations in what is known today as theIpswich Coal Measures have now beencarried out at Dinmore (above).

Image courtesy Trade Alliance


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A Teaching ResourceGiven its proximity to Ipswich and

Brisbane and its relatively easy access

and generally safe setting for collect-ing, the Dinmore Claypit has long

been used as a teaching site for school

and university palaeontologicalexcursions with access being allowed

by the operators, Claypave, on appli-cation. The close preservation of two

fossil deposits of greatly differentage allows teachers to point out the

dramatic turnovers that Australias

vegetation has experienced in the past230 million years. Indeed, most of thegenera that are so abundantly repre-sented in the Late Triassic Blackstone

Formation assemblage did not survivebeyond the end-Triassic mass extinc-

tion 200 million years ago one ofthe big five mass-extinction events

in Earths history.The Blackstone Formation deposits

are also a useful resource for explain-ing the differences between the depo-

sitional environments of various sedi-mentary rocks. Whereas some expo-

sures of the Blackstone Formationin the Ipswich district reveal thicksandstones with cross-bedding and

large fossil logs typical of depositionwithin the major river channels that

meandered across the landscape inthe Triassic, the deposits at DinmoreClaypit are thinly laminated shalescontaining finely preserved delicatefoliage and aquatic crustaceans, allfeatures indicating they were laiddown in much quieter floodplain lakeenvironments.

Further, the differences between thefossils of the coal mine spoil dumps(compressions) and those of the mainclaypit (impressions) offer an oppor-tunity for teachers to explain theprocesses behind the varying styles of

fossil preservation. Elsewhere in theIpswich Basin, stem and root castsand permineralised (silicified) logs canalso be found, which teachers can useto elaborate on the multiple waysthat plants can be fossilised.

The Dinmore Claypit is even poten-tially an important site for environ-mental science and urban planningstudents to discuss the managementand competing interests of extractiveindustries, recreation and sites of sci-entific significance within a suburbansetting. To date, only minor plannedre-vegetation work has been carriedout on disused parts of the claypitsite. However, should the well-inten-tioned actions of local authorities andpublic interest groups seek to entirely

rehabilitate the site in the future, thena very valuable research and teaching

asset could be placed at risk. In a simi-

lar manner, the Haig Street Quarry in

western Ipswich, another important

Triassic palaeontological site, is now

a formally designated environmental

park and is off-limits for further fossil

collecting.

Future Research

Although fossils from the Dinmore

Claypit and surrounding areas havebeen studied for over 100 years, there

is great potential for future research at

this site. Some key studies of the com-

position of the Ipswich Basin Triassic

flora include those of Shirley (1898),

Walkom (1917), Jones and de Jersey

(1947), Hill et al. (1965), Pattemore

and Rigby (2005) and Anderson and

Anderson (2008). Despite these stud-

ies, there have been few investigations

into the palaeoenvironments and pal-

aeoecology of the fossil biota. Because

the strata in the quarry dip at only a

shallow angle, the Dinmore Claypit isone of the few sites where it should

be possible to expose large areas of

a single bedding surface and under-

take a detailed quantitative survey


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Issue 10 49

of a Triassic plant assemblage. Fewsuch studies have been undertaken

anywhere on Earth for rocks of this

age. Furthermore, the relatively flat-

lying beds at Dinmore could be pro-

gressively removed to reveal floristic

changes through the vertical succes-

sion of strata. A detailed investigation

integrating the floristic aspects and

sedimentology of the site would be a

fine project for some keen student of

palaeontology.

Another aspect of the fossil biota

that has been little investigated is the

role of insect-plant interactions in

the Triassic high-latitude forests. We

have no modern analogues for the

polar forests that flourished during

the warm Mesozoic era. Today, tem-

peratures are too extreme for plant

life at the poles. Hence, our under-

standing of how complex forest eco-

systems dealt with a peculiar climatic

regime involving mild temperatures

yet six-monthly alternations of sun-

light and darkness must come from

either greenhouse experiments or a

thorough understanding of the fos-sil record. The recognition of leafmining was a novel discovery atDinmore, but there is great potentialfor assessing the roles of other stylesof insect-plant interaction in the LateTriassic biota (e.g., external leaf feed-ing, piercing-and-sucking behaviour,seed predation, wood boring, galling,pollen feeding, and egg laying withinplant tissues).

We look to the school teachingcommunity to inspire students atan early age to take up an interest

in palaeontology and other aspectsof natural history. Sites such as theDinmore Claypit offer an invaluableresource for teachers to offer a uniquefossil-collecting experience for stu-dents. Further, we await a keen newgeneration of university undergradu-ate and postgraduate palaeontologystudents to take on thechallenges of inves-tigating the palae-oecology of therich Dinmorefossil biota.

The Author

Steve McLoughlin completed his PhD in thepalaeobotany of Permian floras at The Universityof Queensland in 1990. He has subsequentlyundertaken research and teaching at the University ofWestern Australia, University of Melbourne and theQueensland University of Technology. Steve is now asenior curator in the Department of Palaeobotany atthe Swedish Museum of Natural History, Stockholm.

Further reading: For more information on the fossils at Dinmore, go to: http://www.nrm.se/english/researchandcollections/researchdivision/palaeobotany/collections/databases/traustralia/trdinmore.13332.html

A trail of first-year University of Queensland geology students follow thewell beaten path of many young people before them as they investigatethe coal-bearing strata of the Blackstone Formation at Dinmore (left). Thethick sandstones at the top of this old mine represent ancient river channeldeposits, whereas the dark shales below represent lake and swampdeposits rich in plant fossils. The unbridled enthusiasm of QueenslandUniversity of Technology geology students digging for plant fossils atDinmore (above) demonstrates the importance of this outstanding depositand its unparalleled significance as an educational resource for students.

117 dinmore flora popular sci

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