Palaeo Discussion Group - Dr Thomas Halliday, University of Birmingham - Title: Life in recovery: Immigration, Provincialism and Evolution in the Paleocene
Dr Thomas Halliday, University of Birmingham
Room G13/14, Life Sciences Building, University of Bristol
We are pleased to welcome Dr Thomas Halliday from the University of Birmingham, who will be leading the Palaeo Discussion Group.
Title: Life in recovery: Immigration, Provincialism and Evolution in the Paleocene
The Paleocene, the geological epoch lasting from 66 to 55 million years ago, is an ecologically and evolutionarily unique period of Earth history, offering a fantastic data set with which to study ecological patterns through deep time. It began with a mass extinction event, resulting in substantial faunal turnover, reorganisation of ecosystems, and a number of adaptive ecological radiations, including placental mammals. The world was a hothouse, with the modern continents at almost maximum separation and several epicontinental seas fragmenting the global landscape. The end of the Paleocene saw a temporary but rapid rise in global temperatures and a second faunal turnover, again particularly in mammals, resulting in global terrestrial faunas that, by and large, remain today.
All this makes the dense and diverse fossil record of Paleocene vertebrates, and comparisons with those from the earlier Cretaceous period and subsequent Eocene epoch, conducive to asking ecological questions in the context of deep time. How do mass extinctions affect biogeographic patterns? How do clades develop ecological diversity? The radiation of placental mammals can be demonstrated as a classic adaptive radiation; the increase in taxonomic diversity mirrored by expansions in niche-space occupation and revealing a period of morphological exploration followed by ecological specialisation.
At a broader scale, the use of networks in comparing faunal similarity within and between time bins reveals that, in the aftermath of the Cretaceous-Paleocene mass extinction, there was an increase in endemism and, uniquely from the Late Cretaceous through to the Eocene, a statistical relationship between the pairwise similarity of ecosystems and the geographic distance between them. The reason behind this for now remains unclear, whether this is a result of continental island effects with limited opportunity for long-distance dispersal, or a symptom of young clades whose distribution has not yet had time to become global. These analyses further confirm the increased frequency of significant faunal turnovers in the Cenozoic compared with remarkably stable Cretaceous genus and family distributions.
As well as opportunities, the ecology of extinct creatures can present challenges for interpreting the evolutionary history of a given group. The variation in distribution of species in geographic space, a fundamental of ecological work in the extant world, results in biases that impact palaeobiology. The very existence of our data is dependent on preservation, which is itself dependent on both ecological factors (sediment deposition and chemistry, biotic destruction of carcasses) and longer-term geological factors (subduction, erosion, metamorphism), and these factors vary in geological space and time. While species-area effects are frequently addressed in studies of environmental richness and diversity in the past, correcting for a structured lack of entire ecosystems is a challenge. In the case of placental mammals, immigration-driven faunal turnovers combined with spatial patchiness in preservation and poorly defined character matrices also affects our ability to place species in phylogenies.
All staff and students welcome.