Author Archives: LS

Multis made it through, but most of the squamates scurried and slithered off…

New study looking at squamate (lizard and snake) extinction patterns across the K-Pg boundary. (It’s a really neat study, but they should have put ‘dinosaur’ in the title and it would have been a guaranteed Nature/Science hit!):

Longrich, N. R., Bhullar, B. A. S., & Gauthier, J. A. (2012). Mass extinction of lizards and snakes at the Cretaceous–Paleogene boundary. Proceedings of the National Academy of Sciences, 109(52), 21396-21401.

The Cretaceous–Paleogene (K-Pg) boundary is marked by a major mass extinction, yet this event is thought to have had little effect on the diversity of lizards and snakes (Squamata). A revision of fossil squamates from the Maastrichtian and Paleocene of North America shows that lizards and snakes suffered a devastating mass extinction coinciding with the Chicxulub asteroid impact. Species-level extinction was 83%, and the K-Pg event resulted in the elimination of many lizard groups and a dramatic decrease in morphological disparity. Survival was associated with small body size and perhaps large geographic range. The recovery was prolonged; diversity did not approach Cretaceous levels until 10 My after the extinction, and resulted in a dramatic change in faunal composition. The squamate fossil record shows that the end-Cretaceous mass extinction was far more severe than previously believed, and underscores the role played by mass extinctions in driving diversification.

Ian

Stop the Press!! – Ediacaran Life, on land!

Retallack, G. J., 2013: Ediacaran life on land.
–Nature: Vol. 493, #7430, pp. 89-92 [doi: 10.1038/nature11777]
http://dx.doi.org/10.1038/nature11777

Abstract:

Ediacaran (635–542 million years ago) fossils have been regarded as early animal ancestors of the Cambrian evolutionary explosion of marine invertebrate phyla, as giant marine protists and as lichenized fungi. Recent documentation of palaeosols in the Ediacara Member of the Rawnsley Quartzite of South Australia4 confirms past interpretations of lagoonal–aeolian deposition based on synsedimentary ferruginization and loessic texture. Further evidence for palaeosols comes from non-marine facies, dilation cracks, soil nodules, sand crystals, stable isotopic data and mass balance geochemistry. Here I show that the uppermost surfaces of the palaeosols have a variety of fossils in growth position, including Charniodiscus, Dickinsonia, Hallidaya, Parvancorina, Phyllozoon, Praecambridium, Rugoconites, Tribrachidium and ‘old-elephant skin’ (ichnogenus Rivularites). These fossils were preserved as ferruginous impressions, like plant fossils, and biological soil crusts of Phanerozoic eon sandy palaeosols. Sand crystals after gypsum and nodules of carbonate are shallow within the palaeosols, even after correcting for burial compaction. Periglacial involutions and modest geochemical differentiation of the palaeosols are evidence of a dry, cold temperate Ediacaran palaeoclimate in South Australia. This new interpretation of some Ediacaran fossils as large sessile organisms of cool, dry soils, is compatible with observations that Ediacaran fossils were similar in appearance and preservation to lichens and other microbial colonies of biological soil crusts, rather than marine animals, or protists.

Cheers!

–Mikko

Making sense of palaeoclimate sensitivity

Making sense of palaeoclimate sensitivity

A new approach for evaluating past climate sensitivity data has been developed by scientists to help improve comparison with estimates of long-term climate projections developed by the Intergovernmental Panel on Climate Change (IPCC).

http://www.bris.ac.uk/news/2012/8965.html

Paper can be found here:

http://www.nature.com/nature/journal/v491/n7426/full/nature11574.html

– Laura

Reconstructing the diversity of early terrestrial herbivorous tetrapods

Reconstructing the diversity of early terrestrial herbivorous tetrapods

Marianne R. Pearson, Roger B. J. Benson, Paul Upchurch, Jörg Fröbisch, Christian F. Kammerer

Terrestrial herbivorous tetrapods first appear in the fossil record during the Late Carboniferous (306.5 Ma). The diversification of herbivores is a key aspect of the transition to the modern trophic structure of terrestrial vertebrate ecosystems, because it allowed tetrapods to exploit terrestrial (i.e. non-aquatic) primary productivity. However, the palaeodiversity dynamics of the earliest terrestrial vertebrate herbivores have received relatively little attention, apart from a few studies that focus on specific clades. A new data set containing 287 species occurrences of herbivorous tetrapods including the major Palaeozoic and Early Triassic clades Anomodontia, Archosauromorpha, Bolosauridae, Captorhinidae, Caseidae, Cynodontia, Dinocephalia, Diadectomorpha, Edaphosauridae, Pareiasauria, Poposauroidea, Procolophonoidea, Rhynchosauria, Silesauridae and Therocephalia is used to analyse palaeodiversity from the Late Carboniferous to the Middle Triassic (~ 306.5 – ~ 236 Ma), taking into account the effects of potential sampling biases by using the number of tetrapod-bearing formations as a proxy. The results support a gradual increase in taxic diversity from the Late Carboniferous to the Wordian, followed by a dip in diversity during the Guadalupian (Middle Permian), and an increase to a peak in the Late Permian at the Wuchiapingian/Changhsingian boundary. Herbivorous tetrapods were strongly affected by the end-Permian mass extinction with both the herbivorous Pareiasauria and Captorhinidae becoming extinct and the observed number of anomodont species decreasing by up to 80%. The drop in observed diversity at the end Permian is dampened slightly because of the radiation of new herbivorous forms during the Early Triassic. A strong biological signal is apparent even after correcting for sampling.

http://www.sciencedirect.com/science/article/pii/S0031018212006347

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Laura

Diatryma, a gentle herbivore?

Footprints believed to have been made by the giant bird Diatryma indicate that it was a “gentle herbivore” and not a fierce carnivore.

http://www.bbc.co.uk/nature/20413665

http://onlinelibrary.wiley.com/doi/10.1111/j.1475-4983.2012.01195.x/abstract?isLogout=true

P.S. Note, the title of the original paper (Giant Eocene bird footprints from Northwest Washington, USA) gives no indication of *what* is the significance of the footprints, a similar case that was discussed in Kurten club during Mikko’s last news flash…

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Laura

Latest attempt on turtle affinities…

… although without fossils this time.

A Phylogenomic Approach to Vertebrate Phylogeny Supports a Turtle-Archosaur Affinity and a Possible Paraphyletic Lissamphibia

Fong JJ, Brown JM, Fujita MK, Boussau B

PLoS ONE 7(11): e48990. doi:10.1371/journal.pone.0048990

In resolving the vertebrate tree of life, two fundamental questions remain: 1) what is the phylogenetic position of turtles within amniotes, and 2) what are the relationships between the three major lissamphibian (extant amphibian) groups? These relationships have historically been difficult to resolve, with five different hypotheses proposed for turtle placement, and four proposed branching patterns within Lissamphibia. We compiled a large cDNA/EST dataset for vertebrates (75 genes for 129 taxa) to address these outstanding questions. Gene-specific phylogenetic analyses revealed a great deal of variation in preferred topology, resulting in topologically ambiguous conclusions from the combined dataset. Due to consistent preferences for the same divergent topologies across genes, we suspected systematic phylogenetic error as a cause of some variation. Accordingly, we developed and tested a novel statistical method that identifies sites that have a high probability of containing biased signal for a specific phylogenetic relationship. After removing putatively biased sites, support emerged for a sister relationship between turtles and either crocodilians or archosaurs, as well as for a caecilian- salamander sister relationship within Lissamphibia, with Lissamphibia potentially paraphyletic.

http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0048990

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Laura