Pre-Younger Dryas megafaunal extirpation at Rancho La Brea linked to fire-driven state shift

An update on Aenocyon dirus in the interior of North America: new records, radiocarbon dates, ZooMS spectra, and isotopic data for an iconic late Pleistocene carnivore

Aenocyon dirus played a crucial role as a predator in late Quaternary megafaunal communities throughout southern North America. This article presents two new occurrences of the species from southwest Iowa on the eastern Great Plains, updates the Peccary Cave record in the southern Ozark Highlands, and amends the fossil record of the species. In southern North America, there are 166 occurrences of A. dirus, spanning Marine Isotope Stage (MIS) 2-19, with at least two-thirds (n = 112) of the occurrences dating to MIS 2-3 (11,600-57,000 cal B.P.). A. dirus fossils are found across this region, with notable concentrations in California, Florida, the Ozark Highlands, and broadly across the southern Great Plains. Consideration of Canis specimens from the lead region (covering contiguous parts of Illinois, Wisconsin, and Iowa) previously identified as Canis mississippiensis (and sometimes synonymized with A. dirus or C. lupus) reveals they are actually C. lupus. The terminal extinction of A. dirus occurred sometime after 12,800 cal B.P. The Iowa finds, consisting of a radius and a partial cranium, are the first records for the state. Zooarchaeology by mass spectrometry confirms these records, as well as the Peccary Cave record, are A. dirus, as opposed to C. lupus. The Iowa specimens are directly dated to 29,040-28,410 cal B.P. and 14,325-14,075 cal B.P., while Peccary Cave is dated to 25,350-21,405 cal B.P. These results place A. dirus in the interior of southern North America before, during, and after the Last Glacial Maximum (26,500-19,000 cal B.P.). Stable nitrogen isotope (δ15N) values of bone collagen from the younger of the two Iowa records suggest this individual did not regularly compete for prey with Smilodon fatalis during the Bølling-Allerød Chronozone (14,640-12,850 cal B.P.). To the south, at Peccary Cave, considerations of prey size, prey abundance, and isotopic data strongly suggest Platygonus compressus was the focal prey species.

Identification of fossil juniper seeds from Rancho La Brea (California, USA): drought and extirpation in the Late Pleistocene

Juniperus spp. are keystone shrubs in western North America and important climatic indicators in paleo-records. However, a lack of taxonomic resolution among fossil species limits our ability to track past environmental changes. Plant macrofossils at Rancho La Brea (RLB) allow for reconstructions of juniper occurrence to species across 60 000 yr. We use microscopy, image analysis, species distribution modeling (SDM), and radiocarbon dating to identify an unknown Juniperus species at RLB and put it into chronological context with fossil Juniperus californica at the site to infer past environmental conditions. We identify the unknown taxon as Juniperus scopulorum Sargent, 1897. The Pleistocene occurrence of this species in California expands its known distribution and documents its extirpation. Temporal ranges of the two fossil junipers alternate, revealing a pattern of differential climatic sensitivity throughout the end of the Pleistocene. Occurrence patterns suggest sensitivity to temperature, moisture availability, and the presence of two mega-droughts at c. 48-44.5 ka and c. 29.3-25.2 ka. Extirpation of both taxa by c. 13 ka is likely driven by climate, megafaunal extinction, and increasing fire. The extirpation of fossil junipers during these past climatic events demonstrates vulnerability of juniper species in the face of global change.

The late-Quaternary megafauna extinctions: Patterns, causes, ecological consequences and implications for ecosystem management in the Anthropocene

Across the last ~50,000 years (the late Quaternary) terrestrial vertebrate faunas have experienced severe losses of large species (megafauna), with most extinctions occurring in the Late Pleistocene and Early to Middle Holocene. Debate on the causes has been ongoing for over 200 years, intensifying from the 1960s onward. Here, we outline criteria that any causal hypothesis needs to account for. Importantly, this extinction event is unique relative to other Cenozoic (the last 66 million years) extinctions in its strong size bias. For example, only 11 out of 57 species of megaherbivores (body mass ≥1,000 kg) survived to the present. In addition to mammalian megafauna, certain other groups also experienced substantial extinctions, mainly large non-mammalian vertebrates and smaller but megafauna-associated taxa. Further, extinction severity and dates varied among continents, but severely affected all biomes, from the Arctic to the tropics. We synthesise the evidence for and against climatic or modern human (Homo sapiens) causation, the only existing tenable hypotheses. Our review shows that there is little support for any major influence of climate, neither in global extinction patterns nor in fine-scale spatiotemporal and mechanistic evidence. Conversely, there is strong and increasing support for human pressures as the key driver of these extinctions, with emerging evidence for an initial onset linked to pre-sapiens hominins prior to the Late Pleistocene. Subsequently, we synthesize the evidence for ecosystem consequences of megafauna extinctions and discuss the implications for conservation and restoration. A broad range of evidence indicates that the megafauna extinctions have elicited profound changes to ecosystem structure and functioning. The late-Quaternary megafauna extinctions thereby represent an early, large-scale human-driven environmental transformation, constituting a progenitor of the Anthropocene, where humans are now a major player in planetary functioning. Finally, we conclude that megafauna restoration via trophic rewilding can be expected to have positive effects on biodiversity across varied Anthropocene settings.

Quantifying the effects of exceptional fossil preservation on the global availability of phylogenetic data in deep time

Fossil deposits with exceptional preservation ("lagerstätten") provide important details not typically preserved in the fossil record, such that they hold an outsized influence on our understanding of biodiversity and evolution. In particular, the potential bias imparted by this so-called "lagerstätten effect" remains a critical, but underexplored aspect of reconstructing evolutionary relationships. Here, we quantify the amount of phylogenetic information available in the global fossil records of 1,327 species of non-avian theropod dinosaurs, Mesozoic birds, and fossil squamates (e.g., lizards, snakes, mosasaurs), and then compare the influence of lagerstätten deposits on phylogenetic information content and taxon selection in phylogenetic analyses to other fossil-bearing deposits. We find that groups that preserve a high amount of phylogenetic information in their global fossil record (e.g., non-avian theropods) are less vulnerable to a "lagerstätten effect" that leads to disproportionate representation of fossil taxa from one geologic unit in an evolutionary tree. Additionally, for each taxonomic group, we find comparable amounts of phylogenetic information in lagerstätten deposits, even though corresponding morphological character datasets vary greatly. Finally, we unexpectedly find that ancient sand dune deposits of the Late Cretaceous Gobi Desert of Mongolia and China exert an anomalously large influence on the phylogenetic information available in the squamate fossil record, suggesting a "lagerstätten effect" can be present in units not traditionally considered lagerstätten. These results offer a phylogenetics-based lens through which to examine the effects of exceptional fossil preservation on biological patterns through time and space, and invites further quantification of evolutionary information in the rock record.