Imogen Poole

Fossil Forests and Palaeoecology of the Cretaceous and Tertiary

Summary: Although considered to be a ‘traditional’ approach to palaeobotany, without background taxonomy and systematics, fossil plant material is of limited value to the more popular molecular and anatomical approaches. Therefore studies focusing on fossil plant identification provide the important foundation upon which results from integrated and high resolution studies can be based and thus become meaningful. I am interested in the analysis and development of morphological, anatomical and chemical characters of plants, in particular wood, as a tool for palaeoenvironmental/ ecological interpretations. The degree of variation within such structures coupled with and taphonomic bias always need to be considered when recontructing palaeoecology. Therefore my research concentrates not only on fossil material but also on recent material.. Studies of fossil material include Tertiary wood floras from southern England and Peru and the Cretaceous and Tertiary wood floras from Antarctica in addition to (geo)chemical studies of fossil and modern wood. These  interdisciplinary palaeobotanical studies are providing important information for the understanding of biodiversity and change and palaeoenvironments during the Cenozoic and Mesozoic in Europe and Gondwana. Such research often involves international collaboration.

1. Biodiversity & Palaeoecological reconstructions from angiosperm and conifer fossil wood floras



A. Antarctic Palaeoecology 


Studies of Late Cretaceous-Early Tertiary conifer and angiosperm woods from the Peninsula region of Antarctica.


Results from this work so far:

Field work in 1999 undertaken by invitation of the British Antarctic Survey enabled extensive new collections of silicified and calcified angiosperm and gymnosperm wood from the Peninsula region of Antarctica such as those featured below:


1. Fossil angiosperm wood belonging to one of the Nothofagaceae (southern beech) types. (Collected by R. Hunt 1999)

2. Fossil conifer wood from the Eocene of Antarctica belonging to the Araucariaceae (monkey puzzle tree family). (Collected by I.Poole 1999)

3. Exceptional preservation of this material can be illustrated by the pitting on these conifer tracheids. (From BAS collections)


Subsequent studies on this material conclude that the closest modern analogue to the Late Cretaceous-Early Tertiary Antarctic vegetation is the low to mid-altitudinal cool temperate rainforests of southern Chile (although similarities extend to the native forests of southern Australia). Floral associations found in the Antarctic fossil record actually occur today alongside one another in the virgin forests of Valdivia, South America. The environmental setting of both Cretaceous-Paleogene Antarctic Peninsula and modern Valdivian ecosystems is similar. The Peninsula was one of active subduction along the west coast with associated volcanism, much the same as that seen in the Andean chain today. Indeed the ecology of modern Valdivian forests is largely controlled by volcanic driven environmental disturbance.

Recent evidence from the rock record and fossil floras of 40 million years ago suggests that disturbance, rather than climate, was accountable for widescale vegetational changes. This can been summarised by the following diagram (Poole et al 2001):


Ecological changes seen in the geological and palaeobotanical record support the idea that changes in vegetation were determined by volcanic disturbance set against a backdrop of overall climate deterioration rather than simply climate change. Disturbance will probably be found to account for other major shifts of vegetation in other sites at different geological times across the Antarctic Peninsula which, until now, have been solely accounted for by climate change.

Climate changes of 7oC for the Maastrichtian, 4-8oC for the Palaeocene and 7-15oC for the Eocene inferred from fossil angiosperm wood (Francis and Poole 2002) need to be treated with great caution. Firstly, these ranges encompass many climate zones in the modern world. Secondly since the evolutionary states of the characters, used in formula used to calculate


mean annual precipitation and temperature (e.g. Weimann et al 1999), have not been widely investigated such that absences of certain characters or character states in these fossils may simply be due to the fact that they have not yet evolved! Thirdly, these formulae rely on large sample sizes, larger than we have yet studied. However, we are increasing our sample size of fossil material such that we will be able to understand more fully the state of wood anatomical character evolution in the Southern Hemisphere and thus be able to provide more rigorous climatic indications and enhance the validity of such a taxonomic independent approach.



Antarctica 60 million years ago?

Similar vegetation is found today in temperate forests of Chile and Southern Australia (photo taken whilst on fieldwork in southern Australia)

Another important focus is that of biodiversity change from the Cretaceous to Tertiary. High latitude Cretaceous floras differ wildly from those at mid-latitudes. High latitude floras contained a diversity and abundance of certain plant groups that are either absent or ecologically unimportant in lower latitudes. One such example is the liverwort- and moss component. High latitude floras such as those of the Antarctic Peninsula or southeastern Australia contain up to 20% within-floral diversity whereas in mid-latitude floras they are rare or absent. Furthermore, certain groups seem to survive for longer at high latitudes than lower latitudes. The bennettites and other types of gymnosperm persist into the Late

Cretaceous (as recent as Santonian), yet are probably extinct from low latitudes by Albian times. Why plant groups such as these are more suited to extreme climatic conditions of warm polar latitudes is still unknown although the difference in composition is largely tied to one of the major biotic cataclysms in Earth History: The origin, radiation and diversification of flowering plants which had profound effects on the vegetation. Araucarian- (monkey puzzle trees) and podocarp conifers dominated the pre-angiosperm overstorey with rarer components including Ginkgo (maiden hair tree). The understorey contained abundant and diverse fern and bennettite communities. The angiosperms initially expanded into the understorey replacing the bennettites and ferns. During the ensuing 40 million years or so, up until the early Tertiary, angiosperms increased their advance to appropriate the mid- and overstorey niches. Ferns were able to make a comeback through exploiting new habitats created by angiosperms and consequently recovered in numbers. The conifers however were pushed further into increasingly unfavourable conditions resulting in their ultimate decline in numbers (Cantrill and Poole in press).


Angiosperm diversification brought colour, taste and smell to the Antarctic landscape through their flowers, seeds, fruits, leaves and bark. Evidence from the macrofossils record gives us a taste of what Gondwana might have been like: The presence of, amongst others, the Illiciaceae (or star anise) with flowers of red or yellow smelling of fish but with aniseed flavoured seeds and aromatic leaves used extensively in authentic eastern cuisine today. Bundles of conspicuous white and cream flowers, and seeds and wood tasting and smelling of pepper would have been indicative of the presence of the Winteraceae. The avocado pear family is represented by Sassafras with its pendulous bright yellow flowers set against pale green foliage that exudes an aroma reminiscent of fresh lemons and later turn to autumnal shades of orange and red. Members of the Monimiaceae were present with their edible fruits, and leaves and bark that produce aromatic oils, commercially exploited by the international perfume industry today. Canopies with breathtaking hues of yellow, red and orange would be accredited to the abundant Nothofagus (southern beech), a taxon today only found across austral landmasses but cultivated globally for their autumnal foliage.


Sadly, it should be noted that these fragile, primeval Valdivian forests, the only surviving representative of Antarctica’s Late Cretaceous-Early Tertiary vegetation, are being felled uncontrollably. The passing away of these forests will take with it the chance to further our understanding of the ecological diversity and dynamics. With that, an important legacy of a unique ecosystem that once existed some 80 - 40 million years ago in the southern high latitudes of Gondwana, will be lost forever.

Funding: This work was initiated as a NERC funded project but continues with the close collaboration from colleagues in the UK especially Dr David Cantrill at the British Antarctic Survey, U.K.





B. Lower Tertiary paratropical pyritised wood flora from southern England

A desolate beach in SE England today was once a subtropical paradise

Results from this work so far

The Eocene London Clay flora from southern England is a classic example of a boreotropical flora and represents one of the most varied, and the only diverse, flora from lower Eocene strata in Europe. The London Clay flora, with approximately 145 living and extinct genera placed in living families, shares similarities with smaller floras from this period in Europe and North America and suggests that a belt of similar vegetation may have extended across the Northern Hemisphere during the lower and early middle Eocene (Collinson, 1983).

The wood forms a major constituent of this flora but has been studied comparatively little but the wood component reveal taxa, for example the Dipterocarpaceae, as yet unknown in the fruit and seed flora. Continued studies focusing on the wood component will help in understanding the composition of this boreotropical vegetation. Identifications of the wood flora include the Vitaceae, Sapindaceae, Platanaceae, Celastraceae, Pinaceae, Taxodiaceae and at least 6 fern types of which one is a polypodiaceous epiphyte.

Pyritised wood from the Southeast of England belonging to the Platanaceae (plane tree family)



All the records provide significant information concerning the diversity of the vegetation that covered southern England during the lower Eocene. Using the Nearest Living Relative approach, evidence from the wood flora supports a postulated paratropical environment similar to that of Indo-Malaysia today. Seasonality has been suggested from the presence of indistinct, or even absence, of growth rings in the wood which may be indicative of a more tropical, rather than a temperate, flora. However, growth ring data need careful analysis as growth rings can vary according to genera rather than climate (Détienne, 1989). Elements found in the wood flora also serve to illustrate that certain taxa, such as the Cercidiphyllaceae, were once widespread across the Northern Hemisphere in the geological past (Crane 1984). Inclusion of the taxonomic data from fossil wood, including studies of plant animal interactions as evidenced from frass and borings in the London Clay wood flora will contribute to a greater understanding of the biodiversity and prevailing climate in southern England and increase our knowledge concerning Lower Eocene boreotropical floras.


Funding: This work was initiated through NERC funding and continues through close collaboration with colleagues from the Jodrell Laboratory, Royal Botanic Gardens, Kew, U.K.





C. Late Tertiary tropical wood from the Amazon Basin, Peru


Results from this work so far:

Field work in 2001 enabled collections of mummified wood predominantly from fossil log jams (palisadas). Mummified tree trunks up to 2 m in diameter were excavated from these fossil log jams in sections dating back to the Miocene within the Manu National Park. Material of this age can be identified to genus level.


Miles Silman (leaft) and Pim van Bergen (right) standing by Miocene fossil tree trunks, many metres in length, being washed out of the river bank


These woods record details of past environments in both their anatomical structure and geochemical signatures. Palaeoecological reconstruction based on palynological evidence is very successful at demonstrating both dynamics and composition of individual tree communities in temperate floras. However, tropical forest communities are nearly an order of magnitude more diverse. Problems involving the non-appearance of important indicator species in the pollen spectra coupled with the fact that most tropical species are entomophilous (insect pollinated and therefore do not produce copious amounts of pollen), indicates that a combined palynological-macrofossil (e.g. wood) approach will provide the most representative data on community structure and dynamics. Coupling this data with evidence from the (more spatially biased) pollen flora and species diversity lists of the modern flora, vegetation composition and dynamics within the Rio Manu floodplain can be assesed in response to changing climate from Miocene to present.

            Taphonomic studies were undertaken on the modern log jams within the Manu River to (1) qualify the bias today which can then be compared with possible biases that might be found in the fossil material, and (2) determine the taxonomic composition and thus whether log jam material reflects the current vegetation along the Manu River. This data can then be used when interpreting and drawing conclusions from the fossil wood assemblages (also found in log jams). It was found that the wood content of the modern log jams are biased in favour of successional forest and does not represent the vegetation in the Manu reserve. The propagule assemblage however reflected a more regional bias. Only together could the natural vegetation be reflected in the dispersed assemblage and even then there were biases with regard to organ and crop size and density.


Funding: Grant from the Percy Sladen Memorial Fund and is being undertaken in close collaboration with Dr Miles Silman from Wake Forest University, North Carolina, U.S.A.


2. Molecular palaeoclimatic interpretations from fossil plant remains


Results from this work so far: To date, stable carbon isotope analyses of marine carbonates and bulk organic carbon are often used as a basis for palaeoclimate reconstructions. In recent years the use of individual organic molecules has been gathering momentum allowing more precise distinctions between different sources contribution to the d13C signals. However, most of this research has focused on marine sourced organic matter or on molecules the origin of which is less unambiguous (i.e. alkanes). My current project is focusing on terrestrially derived fossil and modern wood using compound specific stable carbon isotope analyses to evaluate changes in past and palaeo- atmospheric CO2 concentrations. Combining molecular and bulk data for young (i.e. post Miocene) material chemical taphonomy (in terms of selective loss of certain moieties, e.g. polysaccharide or lignin) affect the bulk values. For older fossils internal chemical transformations cause additional isotopic shifts that are more ambiguous and are currently being studied.


Funding: This work is being financed by NWO/AWL and is undertaken in collaboration with colleagues in the Netherlands Institute for Sea Research (NIOZ) and at RING.


3. Natural variation in modern systems – understanding the signals locked within fossils


Acknowledging variation raises problems with regard to data interpretation, it hinders attempts to incorporate data from living organisms into computer generated models and above all it requires more interpretation (and imaginative?) deliberation to explain the data at hand. Variation is an integral part of organismal characteristics and has important implications for ecology, palaeoecology and evolutionary theory. Therefore maybe variation can be used to our scientific long term advantage and should now be recognised and discussed rather than simply ignored. My research takes into account variation and looks to determine the extent of variation such that the data obtained can be meaningful and conclusions regarding ecological systems through the geological past can be substantiated. This focus is incorporated into the above projects. An example of variation follows:




Variation in stomatal density in sun (a) and shade (b) leaves of Alnus glutinosa. Similar ranges can be seen with stomatal index. Range from light yellow with 100-120 stomata per mm2 to light purple >240 stomata per mm2 (Poole et al. 1996).


Poole I. (2002)

Systematics of Cretaceous and Tertiary Nothofagoxylon: Implications for Southern Hemisphere biogeography and evolution of the Nothofagaceae. Australian Systematic Botany (in press).

van Bergen P.F. and Poole I. (2002)

Stable carbon isotopes in wood: A clue to palaeoclimate? Palaeogeography, Palaeoclimatology, Palaeoecology (in press).

Cantrill D.J. and Poole I. (2002)

Cretaceous patterns of floristic change in the Antarctic Peninsula. Geological Society of London Special Publication (in press).

Francis J.E. and Poole I. (2002)

Cretaceous and Tertiary climates of Antarctica: evidence from fossil wood. Palaeogeography, Palaeoclimatology, Palaeoecology (in press).

Poole I. and Cantrill D.J. (2001)

Forest of the polar night. Geoscientist 11(9), 4-6.

Poole I. and Cantrill D.J. (2001)

Fossil woods from Williams Point Beds, Livingston Island, Antarctica: a Late Cretaceous southern high latitude flora. Palaeontology 44,1081-1112.

Poole I. and Davies C. (2001)

Glutoxylon Chowdhury (Anacardiaceae): the first known record of fossil wood from Bangladesh. Review of Palaeobotany and Palynology 113, 261-272.

Poole I. and Gottwald H. (2001)

Monimiaceae sensu lato, an element of Gondwanan polar forests: Evidence from the Late Cretaceous-early Tertiary wood flora of Antarctica. Australian Systematic Botany 14, 207-230.

Poole I.. Hunt R.J. and Cantrill D.J. (2001)

A fossil wood flora from King George Island: ecological implications for an Antarctic Eocene vegetation. Annals of Botany  88, 33-54.

van Bergen P.F. and Poole I. (2001)

Biasing the stable isotope record: The effect of chemical taphonomy on fossil plant remains. Terra Nostra 2001/3, 219-222.

van Bergen P.F. Poole I. Oglivey T. Capel C. and Evershed R.P. (2000)

Evidence for demethylation of syringyl moieties in archaeological wood using Pyrolysis/Gas Chromatography/Mass Spectrometry. Rapid Communications in Mass Spectrometry 14, 71-79.

Poole I. (2000)

Variation - Nature’s spanner or an unrecognised tool? Palaios Online 15, 1-2.

Poole I. (2000)

Fossil angiosperm wood anatomy: its role in the reconstruction of biodiversity and palaeoenvironment. Botanical Journal of the Linnean Society 134, 361-381.

Poole I.. Cantrill D.J., Hayes P. and Francis J.E. (2000)

The fossil record of Cunoniaceae: new evidence from Late Cretaceous wood of Antarctica. Review of Palaeobotany and Palynology 111, 127-144.

Poole I. and Francis J.E. (2000)

The first record of fossil wood of Winteraceae from the Upper Cretaceous of Antarctica. Annals of Botany 85, 307-315.

Poole I., Gottwald H. and Francis J.E. (2000)

Illiciaceae, an element of Gondwanan polar forests? Late Cretaceous and Early Tertiary woods of Antarctica. Annals of Botany 86, 421-432.

Poole I., Lawson T., Weyers J.D.B. and Raven J.A. (2000)

Effect of elevated CO2 on the stomatal distribution and leaf physiology of Alnus glutinosa (L.) Gaertn.. New Phytologist 145, 511-521.

Poole I. and Lloyd, G.E. (2000)

A new SEM technique for observing pyritised plant material. Review of Palaeobotany and Palynology 112, 287-295.

Poole I. and Page C. (2000)

A fossil fern indicator of epiphytism in a Tertiary flora. New Phytologist. 148, 117-125.

Poole I.. Richter H. and Francis J.E. (2000)

Gondwanan origins for Sassafras (Lauraceae): evidence from Late Cretaceous fossil wood of Antarctica. International Association of Wood Anatomists Journal 21, 463-475.

Poole I. and Wilkinson H.P. (2000)

Early Eocene vines of Southeast England. Botanical Journal of the Linnean Society 133, 1-26.

Poole I. (1999)

The presence and absence of growth ring structures in fossil twig wood: some possible explanations. In The Evolution of Plant Architecture. Eds A.R. Hemsley & M. Kurman. Royal Botanic Gardens, Kew, pp. 205-219.

Poole I. and Francis J.E. (1999)

The first record of fossil atherospermataceous wood from the upper Cretaceous of Antarctica. Review of Palaeobotany and Palynology 107, 97-107.

Poole I. and Francis J.E. (1999)

Reconstruction of Antarctic palaeoclimates using angiosperm wood anatomy. In: Proceedings of the 5 EPPC, Acta Palaeobotanica supplement 2 173-179.

Poole I. and Kürschner W. (1999)

Stomatal density and index: the practice. In: Fossil Plants and Spores: modern techniques Eds Jones T.P. & Rowe N.P. Geological Society London, pp. 257-260.

Poole I. and Wilkinson H.P. (1999)

A celastraceous twig from the London Clay (Eocene) of Southeast England. Botanical Journal of the Linnean Society 129, 165-176.

Lockheart M., Poole I., van Bergen P.F. and Evershed R. (1998)

Leaf carbon isotope compositions and stomatal characters: important considerations for palaeoclimate reconstructions. Organic Geochemistry 29, 1003-1008.

Poole I. (1996)

Conifer twigs from the London Clay (Eocene) of Southeast England. Review of Palaeobotany and Palynology 94, 25-37.

Poole I. Weyers J.D.B. Lawson T. and Raven J.A. (1996)

Variations in stomatal density and index: implications for palaeoclimatic reconstructions. Plant, Cell and Environment 19, 705-712.

Poole I. (1994)

Twig wood anatomical characters as palaeoecological indicators. Review of Palaeobotany and Palynology 81, 33-52.

Poole I. (1993)

A dipterocarpaceous twig from the Eocene London Clay Formation of Southeast England. Special Papers in Palaeontology 49, 155-163.

Poole I. (1992)

Pyritized twigs from the London Clay, Eocene, of Great Britain. Tertiary Research 13, 71-85.

Poole I. and Wilkinson H.P. (1992)

Two sapindaceous woods from the London Clay (Eocene) of Southeast England. Review of Palaeobotany and Palynology 75, 65-75.