Paul Barrett's favourites

Paul Barrett is a researcher of dinosaurs and other fossil reptiles in the Department of Palaeontology at the Natural History Museum. His major research interests are centred on the evolutionary palaeobiology of dinosaurs and other extinct amniotes.

"Palaeontology is often regarded as a dry subject, with wizened curators hunched over dusty museum collections. However, recent papers in Biology Letters show that studying ancient life has major implications for those interested in many areas of biology, ranging from behaviour to molecular clocks and from conservation to phylogeny. The papers I have chosen show palaeontologists at the interface of many fields: applying new techniques to previously unanswerable questions and synthesizing information from fields as disparate as molecular phylogenetics, developmental biology and global change. The relevance of palaeontology to society has never been greater, as fossils provide the only direct evidence of biotic responses to past global change as well as being a direct window on to the processes that generated current levels of biodiversity."

All of Paul's selections are free to view.

  1. Origins of terrapins supported by fossil and genetic data

  2. The colour of fossil feathers

  3. Coordinated shifts to non-planktotrophic development

  4. Transitional fossils and the origin of turtles

Introduced delicacy or native species? A natural origin of Bermudan terrapins supported by
fossil and genetic data

"Parham et al.'s paper provides an elegant demonstration of how fossils can inform conservation strategies for extant species. Radiometric dates obtained from a sub-fossil diamondback terrapin showed that this species reached Bermuda prior to the human settlement of the island in the 17th Century. Genetic evidence indicates low levels of variation among the Bermudan terrapins and close similarity to diamondback populations in the southeastern USA. These results suggest that the Bermudan diamondback terrapins reached the island via a relatively recent natural transoceanic dispersal, facilitated by the Gulf Stream, and were not more recent human introductions, as had been proposed. Recognition of their native status implies that this small, threatened population should become a conservation priority for Bermudan authorities attempting to maintain the original biodiversity of their island."

Abstract
Humans have greatly altered the natural distribution of species, making it difficult to distinguish between natural and introduced populations. This is a problem for conservation efforts because native or introduced status can determine whether a species is afforded protection or persecuted as an invasive pest. Holocene colonization events are especially difficult to discern, particularly when the species in question is a naturally good disperser and widely transported by people. In this study, we test the origin of such a species, the diamondback terrapin (Malaclemys terrapin), on Bermuda using a combination of palaeontologic (fossil, radiometric and palaeoenvironmental) and genetic data. These lines of evidence support the hypothesis that terrapins are relatively recent (between 3000 and 400 years ago) natural colonizers of Bermuda. The tiny population of Bermudian terrapins represents the second naturally occurring non-marine reptile that still survives on one of the most densely populated and heavily developed oceanic islands in the world. We recommend that they should be given protection as a native species.

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The colour of fossil feathers

"Although palaeontologists can reconstruct the morphology of many organisms in great deal, one major aspect of their appearance has been conjectural: colour. Vinther et al. used energy dispersive X-ray analyses to investigate the ultrastructure of a banded fossil bird feather from the Lower Cretaceous of Brazil. This revealed the exceptional preservation of fossilized melanosomes, organelles that produce the pigment melanin, within the dark bands of the feather. These melanosomes were almost identical to those known in extant birds and allowed reconstruction of the original feather colours, which are likely to have been alternating bands of black and white. Application of these techniques to other fossil feathers of birds and dinosaurs is offering behavioural, ecological and species-specific insights into the uses of feathers prior to the evolution of flight, and the use of colour in intraspecific displays seems likely."

Abstract
Feathers are complex integumentary appendages of birds and some other theropod dinosaurs. They are frequently coloured and function in camouflage and display. Previous investigations have concluded that fossil feathers are preserved as carbonized traces composed of feather-degrading bacteria. Here, an investigation of a colour-banded feather from the Lower Cretaceous Crato Formation of Brazil revealed that the dark bands are preserved as elongate, oblate carbonaceous bodies 1-2 μm long, whereas the light bands retain only relief traces on the rock matrix. Energy dispersive X-ray analysis showed that the dark bands preserve a substantial amount of carbon, whereas the light bands show no carbon residue. Comparison of these oblate fossil bodies with the structure of black feathers from a living bird indicates that they are the eumelanin-containing melanosomes. We conclude that most fossil feathers are preserved as melanosomes, and that the distribution of these structures in fossil feathers can preserve the colour pattern in the original feather. The discovery of preserved melanosomes opens up the possibility of interpreting the colour of extinct birds and other dinosaurs.

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Coordinated shifts to non-planktotrophic development in spatangoid echinoids during the Late
Cretaceous

"Insights into developmental mechanisms are usually derived from observations on model organisms in the laboratory, but palaeontological data can provide a unique source of information on the evolution of ontogeny that is inaccessible to developmental biologists. The tests of spatangoid echinoids (sea urchins) preserve direct evidence of their larval development, allowing differentiation of fossil taxa with planktotrophic or non-planktotrophic strategies. Mapping this information onto a phylogeny of Cretaceous spatangoids revealed that non-planktotrophy (the reliance on yolk reserves in the egg, in contrast to planktonic feeding) evolved separately on five occasions, with each of these transitions taking place in a narrow time interval close to the end of the Cretaceous Period. This coincidence in timing suggests a common environmental factor was responsible for driving this developmental change. One candidate would be the increased climatic seasonality that occurred at the end of the Cretaceous, which might have led to more variability in the availability of planktonic food supply. "

Abstract
Despite widespread interest in the interplay between evolutionary and developmental processes, we still know relatively little about the evolutionary history of larval development. Many clades exhibit multiple shifts from planktotrophic (feeding) to non-planktotrophic (non-feeding) larval development. An important question is whether these switches are scattered randomly through geological history or are concentrated in particular intervals of time. This issue is addressed using the Cretaceous spatangoid sea urchins, which are unusual in that larval strategy can be determined unambiguously from abundantly fossilized adult tests. Using a genus-level phylogeny, we identify five clades of non-planktotrophic taxa, each of which first appears in the fossil record in the Campanian or Maastrichtian (the final two Cretaceous stages). No examples of non-planktotrophy have been identified in any of the earlier stages of the Cretaceous. This strongly suggests that shifts to non-planktotrophic development are clustered in certain episodes of geological history, and this, in turn, implies that extrinsic factors operating at these times are responsible for driving shifts in developmental strategy.

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Transitional fossils and the origin of turtles

"The origin of turtles remains a highly contentious area, as the unusual anatomy of the group obscures their relationships with other amniotes. Recent molecular and morphological phylogenetic analyses have postulated that turtles and tortoises are close relatives of diapsid reptiles (lizards, crocodiles, birds and their allies), but other evidence continues to support alternative positions within the amniote tree of life. Lyson et al. (2010) breathe new life into an old hypothesis that the enigmatic parareptile Eunotosaurus, from the Permian of South Africa, is a key taxon for understanding the evolution of the turtle bauplan. Adding Eunotosaurus to early amniote phylogenies results in the removal of turtles from Diapsida and their inclusion in an otherwise extinct clade of basal reptiles, the Parareptilia. This result has major implications for the evolution of the distinctive turtle shell, suggests that turtles were primitively terrestrial animals and implies that some key divergence dates used to calibrate molecular phylogenies require reappraisal."

Abstract
The origin of turtles is one of the most contentious issues in systematics with three currently viable hypotheses: turtles as the extant sister to (i) the crocodile-bird clade, (ii) the lizard-tuatara clade, or (iii) Diapsida (a clade composed of (i) and (ii)). We reanalysed a recent dataset that allied turtles with the lizard-tuatara clade and found that the inclusion of the stem turtle Proganochelys quenstedti and the 'parareptile' Eunotosaurus africanus results in a single overriding morphological signal, with turtles outside Diapsida. This result reflects the importance of transitional fossils when long branches separate crown clades, and highlights unexplored issues such as the role of topological congruence when using fossils to calibrate molecular clocks.

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Read other board member favourites

See selections of papers compiled by other Biology Letters board members.

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