Inferring the physiological regimes of extinct vertebrates: methods, limits and framework.

What can we know of the physiological regimes of ancient vertebrates? Essential to the exploration of this question are several epistemological tools: (i) a phylogenetic framework for interpreting whole animals and individual tissues, (ii) reliable knowledge of variation in populations and among climates and geographies, (iii) an understanding of phenotypic variation during ontogeny and between sexes, and (iv) a sense of the patterns of body size change, both phyletically and ontogenetically. Palaeobiologists are historically bound to a dichotomous set of terms developed long ago to describe the relatively depauperate living vertebrate fauna. This system sees only binary categories of five major groupings: the 'cold-blooded' fishes, amphibians, and reptiles, and the 'warm-blooded' birds and mammals. The integration of histoanatomical data with patterns of size, growth and phylogeny provides an opportunity to re-imagine not only vertebrate palaeophysiology, but vertebrate physiology in general. Here, we discuss how four 'signals' or 'influences' on bone tissues-phylogeny, ontogeny, mechanics and environment-can help to address these questions. This article is part of the theme issue 'Vertebrate palaeophysiology'.

Measuring Biodiversity and Extinction-Present and Past.

How biodiversity is changing in our time represents a major concern for all organismal biologists. Anthropogenic changes to our planet are decreasing species diversity through the negative effects of pollution, habitat destruction, direct extirpation of species, and climate change. But major biotic changes-including those that have both increased and decreased species diversity-have happened before in Earth's history. Biodiversity dynamics in past eras provide important context to understand ecological responses to current environmental change. The work of assessing biodiversity is woven into ecology, environmental science, conservation, paleontology, phylogenetics, evolutionary and developmental biology, and many other disciplines; yet, the absolute foundation of how we measure species diversity depends on taxonomy and systematics. The aspiration of this symposium, and complementary contributed talks, was to promote better understanding of our common goals and encourage future interdisciplinary discussion of biodiversity dynamics. The contributions in this collection of papers bring together a diverse group of speakers to confront several important themes. How can biologists best respond to the urgent need to identify and conserve diversity? How can we better communicate the nature of species across scientific disciplines? Where are the major gaps in knowledge about the diversity of living animal and plant groups, and what are the implications for understanding potential diversity loss? How can we effectively use the fossil record of past diversity and extinction to understand current biodiversity loss?

Narrative and "Anti-narrative" in Science: How Scientists Tell Stories, and Don't.

Narratives are common to all branches of science, not only to the humanities. Scientists tell stories about how the things we study work, develop, and evolve, and about how we come to be interested in them. Here I add a third domain (Secularity) to Gould's two "non-overlapping magisteria" of Science and Religion, and I review previous work on the parallels in elements between story-telling in literature and science. The stories of each domain have different criteria for judging them valid or useful. In science, especially historical sciences such as biology and geology, particular scientific methods and approaches both structure and test our narratives. Relying on the narrative assumptions of how certain processes, such as natural selection, are supposed to work is treacherous unless they are tested by appropriate historical patterns, such as phylogeny, and rooted in the process of natural mechanisms. The structure of scientific explanation seen in peer-reviewed papers and grant proposals obscures true narrative within a formulaic sequence of "question, methods, materials" and so on that is quite different from the classic narrative of folk-tales and novels, producing an "anti-narrative" that must be "un-learned" before it can be communicated to non-scientists. By adopting some of the techniques of classic story-telling, scientists can become more effective in making our ideas clear, educating the public, and even attracting funding.

Measuring and Comparing Extinction Events: Reconsidering Diversity Crises and Concepts.

To understand our present diversity crisis, it is natural to look to past crises for parallels and indicators. This is difficult because the present crisis is unlike the "Big Five" of the past: it is mostly terrestrial (with an increasing marine component), involves widespread habitat destruction and alteration of climate, and is largely anthropogenic, with confounding effects of differences in loss of diversity among continents and the difficulty of separating anthropogenic extinctions from natural Pleistocene and post-Pleistocene extinctions. In contrast, the "Big Five" crises of the geologic record are mainly marine (in the first two, no land vertebrates existed), and because marine taxa outnumber terrestrial taxa by a margin of about 25:1, global analyses of diversity crises have tended to lump together all phyla and environments. As a result, terrestrial evidence has been "swamped" statistically by the marine data. Both synchroneity and causality of terrestrial and marine events have usually been assumed, but without decisive data. Terrestrial vertebrate faunas do not seem to have been suddenly and catastrophically affected at the ends of the Permian, the Triassic, and the Cretaceous; rather, the pattern generally seems to be of steady turnover and replacement of groups and sometimes of slow decline. Here I suggest a revision of the concept of "mass extinction," which has no definitional limits on the application of the term with respect to duration, geography, ecology, or taxa affected. Unusual drops in taxonomic diversity have traditionally focused on increases in extinction rates, with scarce consideration of origination rates and their interplay with extinction rates. Analyses of hypothesized diversity crises should be operationally and situationally defined and statistically normalized through the histories of taxa and biotas, and should explicitly include both origination and extinction rates. The term "mass extinctions" would be usefully replaced by "diversity crises." These parameters require not absolute numerical (or percentage) limits but situational ones.

ROM mapping of ligamentous constraints on avian hip mobility: implications for extinct ornithodirans.

Studies of soft tissue effects on joint mobility in extant animals can help to constrain hypotheses about joint mobility in extinct animals. However, joint mobility must be considered in three dimensions simultaneously, and applications of mobility data to extinct taxa require both a phylogenetically informed reconstruction of articular morphology and justifications for why specific structures' effects on mobility are inferred to be similar. We manipulated cadaveric hip joints of common quail and recorded biplanar fluoroscopic videos to measure a 'ligamentous' range of motion (ROM), which was then compared to an 'osteological' ROM on a ROM map. Nearly 95% of the joint poses predicted to be possible at the hip based on osteological manipulation were rendered impossible by ligamentous constraints. Because the hip joint capsule reliably includes a ventral ligamentous thickening in extant diapsids, the hip abduction of extinct ornithodirans with an offset femoral head and thin articular cartilage was probably similarly constrained by ligaments as that of birds. Consequently, in the absence of extraordinary evidence to the contrary, our analysis casts doubt on the 'batlike' hip pose traditionally inferred for pterosaurs and basal maniraptorans, and underscores that reconstructions of joint mobility based on manipulations of bones alone can be misleading.