University of Tasmania

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Palaeobiogeography, extinctions and evolutionary trends in the Cunoniaceae : a synthesis of the fossil record

posted on 2023-05-27, 00:48 authored by Barnes, Richard Wayne
The fossil record of the flowering plant family Cunoniaceae is comprehensively examined and reviewed using detailed studies of the morphology of extant Cunoniaceae with new macrofossil species described from Australian Cainozoic sediments. Eleven of the 26 extant Cunoniaceae genera are represented in the macrofossil record and include leaves and leaf fragments, foliar cuticle and reproductive structures. These occur almost exclusively in Australian fossil deposits and range from Late Paleocene to Quaternary in age. Cunoniaceae fossil pollen is widely documented across the Southern Hemisphere but is less informative due to the low taxonomic resolution of its identification. Leaf and infructescence macrofossils from five Cainozoic deposits in south-eastern Australia are indistinguishable from the extant species Callicoma serratifolia which is now restricted to eastern Australia. The first macrofossil of Codia, C. australiensis, is described from Western Australia, and has affinities with the juvenile foliage of at least one extant Codia species which is now endemic to New Caledonia. Two new fossil species of Ceratopetalum are described from fruits, C. westermannii (late Early-Late Miocene) and C. maslinensis (Middle Eocene) and the identification of two others previously described, C. priscum (Middle Miocene) and C. wilkinsonii (Late Eocene-Early Oligocene), is supported. Fossil Eucryphia capsules are described for the first time, E. reticulata (Early Oligocene) and E. sp. `LRR1' (Early Oligocene), in addition to new species based on leaf macrofossils, E. leaensis (entire margin, Early Oligocene) and E. mucronata (serrate margin, ?Latest Eocene-Early Oligocene). The previously identified E. aberensis has been located at the early Oligocene Little Rapid River, making this the first Eucryphia species to be located in more than a single deposit. This species has both serrate and entire margins. Early Pleistocene leaves from Tasmania are conspecific with the two extant species, E. lucida and E. milliganii ssp. milliganii. The identification of E. falcata (Late Paleocene; Lake Bungarby) is supported. Macrofossils and the fossil pollen record show that some genera had a different or more widespread distribution in Australia during the Cainozoic, with two genera (Weinmannia and Codia) having become extinct from the continent. A reduction in vegetation disturbance regimes (e.g. volcanism, uplifting, landslips) or changes in climate, including increasing cold, frost, dryness, seasonality, or some combination of these, may be implicated in these generic extinctions, although the cause of others remains unidentified. Many extant genera (Schizomeria, Vesselowskya, Callicoma, Ceratopetalum, Acsmithia, Codia) had evolved by the Early Oligocene or earlier (Eucryphia, Late Paleocene; Weinmannia, ?latest Eocene-Early Oligocene), perhaps with generic diversification more or less complete by the Early Cainozoic. A late Cretaceous origin of the family is possible, and may account for its widespread distribution on nearly all Southern Hemisphere landmasses, although long-distance dispersal events are required to explain some geographic disjunctions. Foliar evolution has occurred at different rates within the Cunoniaceae. Within Eucryphia there has been an evolutionary trend towards simple leaves with entire margins and well developed peltiform cuticular extensions. These evolutionary trends and apparent adaptations are consistent with those proposed to have occurred within other prominent Cainozoic Australian rainforest genera, including a reduction in leaf size and increased protection of stomata. In contrast, the leaf form in Callicoma has remained relatively unchanged since the Early Oligocene which may be due to its paedomorphic origin from an ancestor shared with its sister taxon Codia. A reduction in the flower size of two genera (Acsmithia and Schizomeria) provides support to the hypothesis that within some Cunoniaceae there has been a shift from entomophily to partial or exclusive anemophily. Petally in one extant and two fossil species of Ceratopetalum shows that petally was once more widespread in the genus. Secondary loss of petals may have been in response to fruit specialisation or a change in pollinator vector. Infructescences of Callicoma indicate that the genus has not changed florally since the Early Oligocene.


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Copyright 1999 the Author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s). Thesis (Ph.D.)--University of Tasmania, 1999. Includes bibliographical references

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