The origin of the latitudinal diversity gradient remains one of the most significant intellectual challenges in macroecology, yet the fossil record of the gradient remains poorly known. Research on…

The origin of the latitudinal diversity gradient remains one of the most significant intellectual challenges in macroecology, yet the fossil record of the gradient remains poorly known. Research on the gradient is critical to our understanding of "the biological and environmental factors leading to ... The potential distribution of complex life in the universe" (astrobiology: exobiology and evolutionary biology solicitation c.17, 2009) because the gradient is the fundamental spatial distribution of species over which all other patterns of diversity are overprinted. Recent work on the phanerozoic latitudinal diversity gradient of brachiopods has confirmed that the gradient is a time-invariant feature of brachiopod diversity, but that peak diversity has shifted northward through time, beginning in southern mid-latitudes in the early paleozoic and gradually moving to northern mid-latitudes at the present day. Changes in the steepness of the gradient over time were caused by the rise and fall of peak diversity rather than diversity at higher latitudes. These results challenge some of the major assumptions regarding the latitudinal diversity gradient: (1) that maximum diversity must be at or near the equator; (2) that changes in diversity at high latitudes control the steepness of the gradient; and (3) that the source of evolutionary novelty is some factor(s) intrinsic to the tropical environment. The recently uncovered brachiopod patterns BEG comparison with other taxa. The specific aims of this proposal are to: (i) reconstruct latitudinal diversity gradients for several key taxa using occurrence data from the paleobiology database; (II) determine the proximal controls of diversity gradients through time by reconstructing geographic patterns of origination rates, extinction rates, and geographic range shifts, and analyze how they interacted to produce the diversity gradient; (III) assess whether change in habitable area was the ultimate mechanism that produced and maintained fossil diversity gradients; (IV) produce sample-standardized diversity gradients to assess the impact of sampling and preservational bias, and explore methods of correcting for these biases; (v) determine whether present-day diversity maxima are displaced slightly north of the equator; and (VI) assess whether the degree of this displacement is related to a taxon's strength of cenozoic diversification. These aims are natural extensions of the recent work, which was limited to brachiopods. The proposed work will result in reconstructions of broad-scale, secular patterns of the latitudinal diversity gradient for multiple taxa and an analysis of its causal factors. These results will establish a baseline understanding of ancient latitudinal diversity gradients and provide the long-term historical context for the present-day latitudinal diversity gradient.