Paul E. Morse

Neocortical expansion is a key innovation of crown primates, although fossil evidence for how the neocortex has evolved remains elusive. We studied neocortical evolution using virtual brain endocasts from extant and Eocene-Miocene fossil primates. We found that neocortex size increased in parallel across crown primate clades, with rapid increases in tarsiers and anthropoids. Although the frontal lobe is commonly described as having expanded disproportionately in primates, we show that it evolved gradually, following a common pattern for allometric scaling. By contrast, nonfrontal neocortical regions underwent rapid increases relative to brain size in haplorhines. Neocortical expansion occurred in concert with increases in optic foramen area, suggesting that visual sensory inputs are functionally tied to modular evolution of the primate neocortex.

South American hystricognath rodents (Caviomorpha) are a dynamic and important group of mammals with a rich fossil record that spans nearly every continental ecosystem. The oldest records come from the Palaeogene of the Peruvian Amazonia. They are well‐documented in the Early Miocene assemblages from extratropical Patagonia. In this work, we describe the first Early Miocene caviomorph assemblage (AMD‐45) from the tropics that is both abundant and taxonomically rich, enabling us to evaluate early biogeographic patterns and dispersal events influencing this clade. Nine taxa belonging to the four caviomorph superfamilies, as well as a caviomorph incertae sedis are recognized. These rodents have brachydont and generalized molars ( Atalayamys incertum gen. et sp. nov., Matsigenkamys ericius gen. et sp. nov., Acarechimys manumanta sp. nov.), protohypsodont and more derived molars ( Ricardomys antiqua sp. nov., Manumys materdei gen. et sp. nov., Marianamys altadens gen. et sp. nov., Luantus silbamanta sp. nov. and Maquiamys precursor ), and even euhypsodont teeth ( Peruchinchilla prima gen. et sp. nov.). The AMD‐45 fauna represents a mix of generalized and derived taxa, with chinchilloids and pan‐octodontoids being the most taxonomically diverse and abundant. Comparison with other South American rodent assemblages supports the hypothesis that the equatorial tropics acted as a taxonomic incubator (long‐lasting lineages) and provides evidence for in situ evolution and migration waves. The AMD‐45 rodents also represent the oldest occurrence of high‐crowned caviomorphs in low‐latitude faunas, with the evolution of hypsodonty proposed to follow distinctive latitudinal and temporal trajectories.

Objectives: Maintaining effective and efficient occlusal morphology presents adaptive challenges for mammals, particularly because mastication produces interactions with foods and other materials that alters the geometry of occlusal surfaces through macrowear and/or catastrophic failure (i.e. “chipping”). Altered occlusal morphologies are often less effective for masticating materials of given diet—but not always—some species exhibit dental sculpting, meaning their dentitions are set up to harness macrowear to hone their occlusal surfaces into more effective morphologies (i.e. secondary morphologies). Here we show that dental sculpting is present in the folivorous Presbytis rubicunda of Borneo.Methods: Thirty‐one undamaged lower second molars of P. rubicunda exhibiting various stages of macroscopic wear were micro‐CT scanned and processed into digital surfaces. The surfaces were measured for convex Dirichlet normal energy (vDNE, a measure of surface sharpness), and degree of surface wear. Regression analyses compared surface sharpness with several measures of wear to test for the presence and magnitude of dental sculpting.Results: Positive correlations between the wear proxies and vDNE reveal that P. rubicunda wear in such a way as to become sharper, and therefore more effective chewing surfaces by exposing enamel‐dentine junctions on their occlusal surfaces and then honing these junctions into sharpened edges. Compared to another primate folivore in which increasing surface sharpness with macrowear has been demonstrated (i.e., Alouatta palliata), the worn surfaces are similarly sharp, but the dental sculpting process appears to be different.Discussion: The results presented here suggest that not only do some primates exhibit dental sculpting and the attendant secondary morphology, but that there appear to be multiple different morphological configurations that can achieve this result. P. rubicunda has thicker enamel and a more stereotyped wear pattern than A. palliata, although both show positive correlations of occlusal surface sharpness (vDNE) with various wear proxies. These findings shed light on the varied approaches for the maintenance of effective and efficient occlusal surfaces in primates.

Abilities of taxa to track suitable habitat under climate change is a concern in conservation biology. Projections that assume suitable habitat is limited to currently occupied biomes can produce underestimates of species viability. The geological record is a valuable source of data to test assumptions about habitat tracking because it archives past episodes of climate change. The Paleocene-Eocene Thermal Maximum (PETM) ~56 million years ago was an interval of rapid carbon release (millennial scale) and global warming (~5 C) that caused large geographic range shifts in Earth’s biota. Large, stratigraphically controlled fossil collections spanning the PETM in the Bighorn Basin, Wyoming, document first occurrence data for immigrant mammals and plants, providing evidence of geographic range shifts as well as changes in climate, flora and vegetation. If mammals tracked specific habitats, their intercontinental dispersal would imply continuity of biomes across Holarctica. In that case, intercontinental mammal and plant immigrants should appear concurrently. Instead, mammalian immigrants crossed high latitude belts of warm, temperate forest, then appeared in the Bighorn Basin during the warmest part of the PETM when plant fossils suggest a dry tropical forest. Warm temperate Eurasian plants are rare during the body of the PETM, but become abundant during the recovery, as climate became wetter. Floral change during the PETM recovery is not concurrent with change in mammalian community structure. Distinct patterns of mammalian and plant turnover suggest that mammals did not strictly track plant-defined habitats. Species may be capable of more flexible responses to rapid climate change than current models predict. Efforts that support movement and provide multi-latitudinal networks of protected areas should be prioritized as a viable means to help conserve some species in the face of climate change.

Sharks have cartilaginous skeletons, and each vertebra of their vertebral column contains a mineralized centrum that carries the loads generated during swimming.¹ The structure and mineralization of the centra enable shark vertebrae to survive enormous compressive strains of 3% to 8%² for millions of cycles of loading,³ despite the absence of a repair mechanism analogous to remodeling in bone. Diffraction has shown that the centra’s mineral is a bioapatite closely related to hydroxyapatite (hAp),^4,5 and is organized similarly to the bone.⁶

Interpreting the impact of climate change on vertebrates in the fossil record can be complicated by the effects of potential biotic drivers on morphological patterns observed in taxa. One promising area where this impact can be assessed is a high-resolution terrestrial record from the Bighorn Basin, Wyoming, that corresponds to the Paleocene–Eocene thermal maximum (PETM), a geologically rapid (~170 kyr) interval of sustained temperature and aridity shifts about 56 Ma. The PETM has been extensively studied, but different lines of research have not yet been brought together to compare the timing of shifts in abiotic drivers that include temperature and aridity proxies and those of biotic drivers, measured through changes in floral and faunal assemblages, to the timing of morphological change within mammalian species lineages. We used a suite of morphometric tools to document morphological changes in molar crown morphology of three lineages of stem erinaceid eulipotyphlans. We then compared the timing of morphological change to that of both abiotic and other biotic records through the PETM. In all three species lineages, we failed to recover any significant changes in tooth crown shape or size within the PETM. These results contrast with those documented previously for lineages of medium-sized mammals, which show significant dwarfing within the PETM. Our results suggest that biotic drivers such as shifts in community composition may have also played an important role in shaping species-level patterns during this dynamic interval in Earth history.