Déjà vu: a reappraisal of the taphonomy of quarry VM4 of the Early Pleistocene site of Venta Micena (Baza Basin, SE Spain).

Venta Micena, an Early Pleistocene site of the Baza Basin (SE Spain), preserves a rich and diverse assemblage of large mammals. VM3, the main excavation quarry of the site, has been interpreted as a den of the giant hyaena Pachycrocuta brevirostris in the plain that surrounded the Baza palaeolake. Taphonomic analysis of VM3 has shown that the hyaenas scavenged the prey previously hunted by the hypercarnivores, transported their remains to the communal den, and consumed the skeletal parts according to their marrow contents and mineral density. In a recent paper (Luzón et al. in Sci Rep 11:13977, https://doi.org/10.1038/s41598-021-93261-1 , 2021), a small sample of remains unearthed from VM4, an excavation quarry ~ 350 m distant from VM3, is analysed. The authors indicate several differences in the taphonomic features of this assemblage with VM3, and even suggest that a different carnivore could have been the agent involved in the bone accumulation process. Here, we make a comparative analysis of both quarries and analyse more skeletal remains from VM4. Our results indicate that the assemblages are broadly similar in composition, except for slight differences in the frequency of megaherbivores, carnivores and equids according to NISP values (but not to MNI counts), the degree of bone weathering, and the intensity of bone processing by the hyaenas. Given that VM4 and VM3 were not coeval denning areas of P. brevirostris, these differences suggest that during the years when the skeletal remains were accumulated by the hyaenas at VM3, the rise of the water table of the Baza palaeolake that capped with limestone the bones was delayed compared to VM4, which resulted in their more in-depth consumption by the hyaenas.

Sixty-six million years along the road of mammalian ecomorphological specialization.

The fossil record of the large terrestrial mammals of the North American Cenozoic has previously been quantitatively summarized in six sequential episodes of faunal associations-"evolutionary faunas"-that correspond well with previously proposed qualitative "Chronofaunas." Here, we investigate the ecological spectrum of these faunas by classifying their major taxonomic components into discrete ecomorphological categories of diet, locomotion, and body size. To specifically address the potential influence of long-term climatic shifts on the ecomorphological composition of these faunas, we analyze via contingency tables and detrended correspondence analyses the frequency distribution of ecomorph types within faunas. We show that each evolutionary fauna has a unique, nonrandom association of ecomorphs, and we identify a long-term trend toward greater ecomorphological specialization over successive faunas during the past 66 My. Major vegetation shifts induced by climatic changes appear to underlie the ecomorphological dynamics of these six temporal associations that summarize Cenozoic North American mammalian evolutionary history.

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 (δ(18)O) 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.

Cranial shape transformation in the evolution of the giant panda (Ailuropoda melanoleuca).

In this study, landmark-based methods of geometric morphometrics are used for investigating the main aspects of cranial shape transformation in the evolution of the giant panda, Ailuropoda melanoleuca. Specifically, we explore if the highly derived cranial adaptations for bamboo feeding of the living panda were developed early in the panda's lineage. Results obtained show that the overall cranial morphologies of the oldest known panda, the "pygmy" Ailuropoda microta, and the late Pleistocene Ailuropoda baconi are both very similar to that of their closest living relative, A. melanoleuca, which agrees with a previous proposal based on qualitative criteria. However, we also describe several differences between the crania of A. microta, A. baconi, and A. melanoleuca, including the development of the postorbital process, the orientation of the occipital region, and the expansion of the braincase. As a result, the cranial morphology of A. microta shows a less specialized morphology toward a fibrous and durophagous diet compared to the giant panda. These results are confirmed by a comparative analysis of the dimensions of the upper teeth in bears, which has revealed differences in relative tooth size between A. microta and A. melanoleuca, most probably as a result of mosaic evolution. Therefore, we conclude that cranial shape did not remain essentially uniform in the Ailuropoda lineage, as previously thought, but underwent a number of changes during more than 2 Myr.

Switching between cooperation and competition in the use of extracellular glucose.

This paper addresses some questions related to the evolution of cooperative behaviors, in the context of energetic metabolism. Glycolysis can perform either under a dissipative working regime suitable for rapid proliferation or under an efficient regime that entails a good modus operandi under conditions of glucose shortage. A cellular mechanism allowing switching between these two regimes may represent an evolutionary achievement. Thus, we have explored the conditions that might have favored the emergence of such an accommodative mechanism. Because of an inevitable conflict for resources between individual interests and the common good, rapid and inefficient use of glucose is always favored by natural selection in spatially homogeneous environment, regardless of the external conditions. In contrast, when the space is structured, the behavior of the system is determined by its free energy content. If the fuel is abundant, the dissipative strategy dominates the space. However, under famine conditions the efficient regime represents an evolutionary stable strategy in a Harmony game. Between these two extreme situations, both metabolic regimes are engaged in a Prisoner's Dilemma game, where the output depends on the extracellular free energy. The energy transition values that lead from one domain to another have been calculated. We conclude that an accommodative mechanism permitting alternation between dissipative and efficient regimes might have evolved in heterogeneous and highly fluctuating environments. Overall, the current work shows how evolutionary optimization and game-theoretical approaches can be complementary in providing useful insights into biochemical systems.