Thursday, October 18, 2007

The Family Tree of the Placental Mammals

In PNAS Genomics, biogeography, and the diversification of placental mammals
Among the placental mammals, phylogenetic branching events have been inferred by using either nucleotide sequence data (4–11) or rare insertion/deletion patterns (12–15). Many of the results recognize four primary eutherian groups: Afrotheria, Xenarthra, Laurasiatheria, and Euarchontoglires. Afrotherians (e.g., elephants, hyraxes, manatees, aardvarks, tenrecs, and allies) are a clade of mammals that originated in Africa, and whose extant members still mostly remain on that continent with the exception of Asian elephants and sirenians such as the Florida manatee. The Xenarthra includes the sloths, armadillos, and anteaters that today are restricted to South and Central America (although some Xenarthra, such as the nine-banded armadillo, have recently dispersed to North America). The Laurasiatheria (e.g., bats, eulipotyphlans, pangolins, carnivores, perrisodactyls, and cetartiodactyls) is a diverse clade including extant lineages that originated in the ancient northern continent of Laurasia. The Euarchontoglires includes the species from five living mammalian orders (e.g., primates, treeshrews, flying lemurs, rabbits, and rodents). This last group remains the most controversial, and a number of recent studies have suggested it is not valid (4, 6, 7).

The Human Visual System is Tuned for Animals

From this PNAS article: Category-specific attention for animals reflects ancestral priorities, not expertise
Visual attention mechanisms are known to select information to process based on current goals, personal relevance, and lower-level features. Here we present evidence that human visual attention also includes a high-level category-specialized system that monitors animals in an ongoing manner. Exposed to alternations between complex natural scenes and duplicates with a single change (a change-detection paradigm), subjects are substantially faster and more accurate at detecting changes in animals relative to changes in all tested categories of inanimate objects, even vehicles, which they have been trained for years to monitor for sudden life-or-death changes in trajectory. This animate monitoring bias could not be accounted for by differences in lower-level visual characteristics, how interesting the target objects were, experience, or expertise, implicating mechanisms that evolved to direct attention differentially to objects by virtue of their membership in ancestrally important categories, regardless of their current utility.

Where do Supernovas Come From?

In the preprint Constraining the Type Ia Supernova Progenitor: The Search for Hydrogen in Nebular Spectra the investigator looks for hydrogen emissions that are expected by theories of supernova formation. This signal has not been detected to date.