Miquel de Renzi

Cenozoic climate change influences mammalian evolutionary dynamics

Global climate change is having profound impacts on the natural world. However, climate influence on faunal dynamics at macroevolutionary scales remains poorly understood. In this paper we investigate the influence of climate over deep time on the diversity patterns of Cenozoic North American mammals. We use factor analysis to identify temporally correlated assemblages of taxa, or major evolutionary faunas that we can then study in relation to climatic change over the past 65 million years. These taxa can be grouped into six consecutive faunal associations that show some correspondence with the qualitative mammalian chronofaunas of previous workers. We also show that the diversity pattern of most of these chronofaunas can be correlated with the stacked deep-sea benthic foraminiferal oxygen isotope (δ18O) curve, which strongly suggests climatic forcing of faunal dynamics over a large macroevolutionary timescale. This study demonstrates the profound influence of climate on the diversity patterns of North American terrestrial mammals over the Cenozoic.

Constraint and adaptation in the evolution of carnivoran skull shape

Abstract The evolutionary history of the Order Carnivora is marked by episodes of iterative evolution. Although this pattern is widely reported in different carnivoran families, the mechanisms driving the evolution of carnivoran skull morphology remain largely unexplored. In this study we use coordinate-point extended eigenshape analysis (CP-EES) to summarize aspects of skull shape in large fissiped carnivores. Results of these comparisons enable the evaluation of the role of different factors constraining the evolution of carnivoran skull design. Empirical morphospaces derived from mandible anatomy show that all hypercarnivores (i.e., those species with a diet that consists almost entirely of vertebrate flesh) share a set of traits involved in a functional compromise between bite force and gape angle, which is reflected in a strong pattern of morphological convergence. Although the paths followed by different taxa to reach this “hypercarnivore shape-space” differ because of phylogenetic constraints, the morphological signature of hypercarnivory in the mandible is remarkably narrow and well constrained. In contrast, CP-EES of cranial morphology does not reveal a similar pattern of shape convergence among hypercarnivores. This suggests a lesser degree of morphological plasticity in the cranium compared to the mandible, which probably results from a compromise between different functional demands in the cranium (e.g., feeding, vision, olfactory sense, and brain processing) whereas the mandible is only involved in food acquisition and processing. Combined analysis of theoretical and empirical morphospaces for these skull data also show the lower anatomical disparity of felids and hyaenids compared to canids and ursids. This indicates that increasing specialization within the hypercarnivorous niche may constrain subsequent morphological and ecological flexibility. During the Cenozoic, similar skull traits appeared in different carnivoran lineages, generated by similar selection pressures (e.g., toward hypercarnivory) and shared developmental pathways. These pathways were likely the proximate source of constraints on the degree of variation associated with carnivoran skull evolution and on its direction.

Shell coiling in some larger foraminifera; general comments and problems

The logistic model provides a useful geometric description of coiling for larger Foraminifera. This model represents a spiral in polar coordinates by means of a logistic equation. The model describes the spires of the genera Alveolina, Nummulites , and Assilina very well. The logistic model is a consequence of allometric growth in these genera. The spires of Nummulites do not fit the logarithmic spiral model well, because the model does not accommodate ontogenetic change of form. Computer simulations using the logistic model also show the very different morphologies of the genus Alveolina . The model allows study of geometrical constraints on test form and of pathways followed by the evolution of the genus (or genera). The logistic model describes ontogenetic change in the organisms functional requirements. The main physiological requirements are nourishment, general exchanges of matter and energy with the environment, and light for the photosynthetic symbionts that live in the cytoplasm of these larger Foraminifera. All these functions require suitable area/volume ratios, that mandate changes of form during growth. The possible biological meaning of the parameters of the model is explored. The use of the more meaningful parameters is proposed in statistical multivariate studies.