Cenozoic Mammals Research Articles

Unique functional diversity during early Cenozoic mammal radiation of North America.

Mammals influence nearly all aspects of energy flow and habitat structure in modern terrestrial ecosystems. However, anthropogenic effects have probably altered mammalian community structure, raising the question of how past perturbations have done so. We used functional diversity (FD) to describe how the structure of North American mammal palaeocommunities changed over the past 66 Ma, an interval spanning the radiation following the K/Pg and several subsequent environmental disruptions including the Palaeocene-Eocene Thermal Maximum (PETM), the expansion of grassland, and the onset of Pleistocene glaciation. For 264 fossil communities, we examined three aspects of ecological function: functional evenness, functional richness and functional divergence. We found that shifts in FD were associated with major ecological and environmental transitions. All three measures of FD increased immediately following the extinction of the non-avian dinosaurs, suggesting that high degrees of ecological disturbance can lead to synchronous responses both locally and continentally. Otherwise, the components of FD were decoupled and responded differently to environmental changes over the last ~56 Myr.

Late Cenozoic Faunal and Ecological Change in Africa

Africa's fossil record of late Cenozoic mammals documents considerable ecological and evolutionary changes through time. Here, we synthesize those changes in the context of the mechanisms proposed to account for them, including bottom-up (e.g., climate change) and top-down (e.g., hominin impacts) processes. In doing so, we (a) examine how the incompleteness of the fossil record and the varied spatiotemporal scales of the evidence complicate efforts to establish cause-effect relationships; (b) evaluate hypothesized drivers of long-term ecological and evolutionary change, highlighting key unknowns; and (c) synthesize major taxonomic and functional trends through time (e.g., downsizing of faunal communities) considering the proposed drivers. Throughout our review, we point to unresolved questions and highlight research avenues that have potential to inform on the processes that have shaped the history of what are today the most diverse remaining large mammal communities on Earth.▪The study of late Cenozoic African mammal communities is intertwined with questions about the context, causes, and consequences of hominin evolution.▪The fossil record documents major functional (e.g., loss of megaherbivores) and taxonomic (e.g., rise of the Bovidae) changes over the past ∼7 Myr.▪Complexities inherent to the fossil record have made it difficult to identify the processes that drove ecological and evolutionary changes.▪Unanswered questions about the drivers of faunal change and the functioning of past ecosystems represent promising future research directions.

The ancestral morphology of lumbar vertebrae and its diversification in early Cenozoic mammals

The ancestral morphology of lumbar vertebrae and its diversification in early Cenozoic mammals

Per-Simper, An Innovative Method for Identifying Community Assembly Processes Within Modern, Recent, and Deep-Time Paleontological Assemblages

How biological communities are assembled is an old but lively debate, especially today, as the efficiency of conservation policies depend on our capacity to correctly identify the assembly processes at play within the species assemblages we aim to protect. The wide range of assembly modes, once seen as mutually exclusive hypothesis are now seen as part of a continuum where the opposite ends correspond to niche- and dispersal-assembly perspectives. Niche-assembled communities are closed and balanced with a stable taxonomic composition depending on deterministic processes when dispersal-assembled communities are open, in non-equilibrium state with constantly changing compositions depending on historical process and continuous dispersion between communities. The former must be protected by increasing habitat diversity and heterogeneity when the latter needing high connectivity to ensure dispersal between habitats. Protecting modern at-risk communities will require an understanding of how assembly processes have been affected by past climate change (both recent and ancient) or by the historical exploitation of ecosystems by humans. However, few methods exist that are capable of identifying assembly processes within paleontological datasets and producing time series at multiple scales due to missing information in the vast majority of the fossil record (e.g., abundance, environmental information, highly-resolved phylogeny) or due to limited precision of compatible methods (i.e. random vs. non-random patterns). The new PER-SIMPER method (and its associated DNCImper R package) can be used to identify and quantify the respective roles of niche and dispersal processes from the distribution of occurrences of extinct and extant species. Based on three modes of permutation of the occurrence matrix, I will illustrate PER-SIMPER with deep-time (e.g., trilobites), ancient (e.g. Cenozoic mammals) and modern datasets (e.g. small mountain mammals, host-flea assemblages).

WOOD JAMS OR BEAVER DAMS? PLIOCENE LIFE, SEDIMENT AND LANDSCAPE INTERACTIONS IN THE CANADIAN HIGH ARCTIC

ABSTRACT During the mid-Pliocene (Zanclean, ca. ∼ 3.9 Ma), parts of the Canadian High Arctic experienced mean annual temperatures that were 14–22°C warmer than today and supported diverse boreal-type forests. The landscapes of this vegetated polar region left behind a fragmented sedimentary record that crops out across several islands in the Canadian Arctic Archipelago as the Beaufort Formation and correlative strata. Paleoecological information from these strata provides a high-fidelity window onto Pliocene environments, and prominent fossil sites yield unparalleled insights into Cenozoic mammal evolution. Significantly, many of the strata reveal evidence for life-sediment interactions in a warm-climate Arctic, most notably in the form of extensive woody debris and phytoclast deposits. This paper presents original field data that refines the sedimentological context of plant debris accumulations from the anactualistic High Arctic forests, most notably at the ‘Fyles Leaf Beds' and ‘Beaver Pond' fossil-bearing sites in the ‘high terrace deposits' of central Ellesmere Island. The former is a remarkably well-preserved, leaf-rich deposit that is part of a complex of facies associations representing lacustrine, fluvio-deltaic and mire deposition above a paleotopographic unconformity. The latter yields tooth-marked woody debris within a peat layer that also contains a rich assemblage of vertebrate and plant fossils including abundant remains from the extinct beaver-group Dipoides. Here we present sedimentological data that provide circumstantial evidence that the woody debris deposit at Beaver Pond could record dam-building in the genus, by comparing the facies motif with new data from known Holocene beaver dam facies in England. Across the Pliocene of the High Arctic region, woody debris accumulations are shown to represent an array of biosedimentary deposits and landforms including mires, driftcretions, woody bedforms, and possible beaver dams, which help to contextualize mammal fossil sites, provide facies models for high-latitude forests, and reveal interactions between life and sedimentation in a vanished world that may be an analogue to that of the near-future.

Do species factories exist? Detecting exceptional patterns of evolution in the mammalian fossil record.

A species factory refers to the source that gives rise to an exceptionally large number of species. However, what is it exactly: a place, a time or a combination of places, times and environmental conditions, remains unclear. Here we search for species factories computationally, for which we develop statistical approaches to detect origination, extinction and sorting hotspots in space and time in the fossil record. Using data on European Late Cenozoic mammals, we analyse where, how and how often species factories occur, and how they potentially relate to the dynamics of environmental conditions. We find that in the Early Miocene origination hotspots tend to be located in areas with relatively low estimated net primary productivity. Our pilot study shows that species first occurring in origination hotspots tend to have a longer average longevity and a larger geographical range than other species, thus emphasizing the evolutionary importance of the species factories.

Tectonic influence on Cenozoic mammal richness and sedimentation history of the Basin and Range, western North America.

Tectonic activity can drive speciation and sedimentation, potentially causing the fossil and rock records to share common patterns through time. The Basin and Range of western North America arose through widespread extension and collapse of topographic highlands in the Miocene, creating numerous basins with rich mammalian fossil records. We analyzed patterns of mammalian species richness from 36 to 0 million years ago in relation to the history of sediment accumulation to test whether intervals of high species richness corresponded with elevated sediment accumulation and fossil burial in response to tectonic deformation. We found that the sedimentary record of the Basin and Range tracks the tectonic evolution of landscapes, whereas species-richness trends reflect actual increased richness in the Miocene rather than increased fossil burial. The sedimentary record of the region broadly determines the preservation of the fossil record but does not drive the Miocene peak in mammalian species richness.

Rapoport effects are inconsistently demonstrated through time

A Rapoport effect is a pattern in which species' geographic range sizes increase toward the poles. Previous work suggested that Pleistocene glaciation caused the extinction of small-ranging species at higher latitudes, resulting in a Rapoport effect among North American mammals. If caused by glaciation, Rapoport effects should be apparent in Pleistocene Europe, where glaciers advanced relatively far south, but not in Asia, where glacial advance was much more limited. Variation in geographic range size in the fossil record of Cenozoic mammals of Europe was quantified, binning fossils into European land mammal ages. Next, the same was done for Cenozoic mammals of Asia, binning by Asian land mammal ages and China faunal ages. By requiring a minimum sample size of ten points to estimate range size, most time bins on either continent were too insufficiently sampled to assess Rapoport effects. A Rapoport effect was found for four of twelve European land mammal ages, but cooling was associated with only one Rapoport effect. A Rapoport effect was never recovered in Asia. After scrutinizing the evidence for North American Rapoport effects among fossil mammals, the overall evidence for glaciation driving Rapoport effects is scant. Support for glaciation causing Rapoport effects is questioned.

Mammaliaform extinctions as a driver of the morphological radiation of Cenozoic mammals

Adaptive radiations are hypothesized as a generating mechanism for much of the morphological diversity of extant species.1-7 The Cenozoic radiation of placental mammals, the foundational example of this concept,8,9 gave rise to much of the morphological disparity of extant mammals, and is generally attributed to relaxed evolutionary constraints following the extinction of non-avian dinosaurs.10-13 However, study of this and other radiations has focused on variation in evolutionary rates,4,5,7,14 leaving the extent to which relaxation of constraints enabled the origin of novel phenotypes less well characterized.15-17 We evaluate constraints on morphological evolution among mammaliaforms (mammals and their closest relatives) using a new method that quantifies the capacity of evolutionary change to generate phenotypic novelty. We find that Mesozoic crown-group therians, which include the ancestors of placental mammals, were significantly more constrained than other mammaliaforms. Relaxation of these constraints occurred in the mid-Paleocene, post-dating the extinction of non-avian dinosaurs at the K/Pg boundary, instead coinciding with important environmental shifts and with declining ecomorphological diversity in non-theriimorph mammaliaforms. This relaxation occurred even in small-bodied Cenozoic mammals weighing <100 g, which are unlikely to have competed with dinosaurs. Instead, our findings support a more complex model whereby Mesozoic crown therian evolution was in part constrained by co-occurrence with disparate mammaliaforms, as well as by the presence of dinosaurs, within-lineage incumbency effects, and environmental factors. Our results demonstrate that variation in evolutionary constraints can occur independently of variation in evolutionary rate, and that both make important contributions to the understanding of adaptive radiations.

A SHORT HISTORY OF PALEONTOLOGY IN TURKEY, PART II: PALEONTOLOGY IN THE REPUBLIC OF TURKEY

ABSTRACT Succeeding a period of wars and political turmoil, the reassuring policies of the new regime of Turkey positively influenced all branches of science, including geology which provided a basis for the earliest studies in paleontology, as it had done in the former Ottoman Turkey. Although most of the specialists were still foreigners during the early years of the republic, the government of Turkey under the leadership of Atatürk, rapidly established modern institutions in order to train native earth scientists and engineers of all sorts. Turkish paleontologists began to replace their foreign colleagues by the 1940s; and female Turkish paleontologists became especially prominent not only in the universities but also in the national geological surveys and mapping, and in fossil fuel exploration. Subsequent to their separation from departments of natural sciences, teaching fundamentals of paleontology was taken on by geology departments which, by the 1960s, started to evolve into departments of geological engineering. As a result, most Turkish paleontologists are geologists and most of them specialized either in micropaleontology or paleobotany. In contrast, paleontology of late Cenozoic mammals is dominated by graduates of anthropology programs.

A Review of the Mesozoic and Cenozoic Mammals of Mongolia

In Mongolia, fossil mammals are known from the Upper Jurassic, Lower and Upper Cretaceous, all series of the Paleogene and Neogene, as well as the Pleistocene. Over 335 new species and more than 185 new genera of fossil mammals (not including synonyms) were described from Mongolia up to the end of 2019. The most important results in the last hundred years of research, that most strongly influenced the development of mammal paleontology, have been: (1) the discoveries of extremely rich Paleogene and Neogene localities containing numerous fossils of various mammals by the Central Asian Expedition of the American Museum of Natural History (CAE AMNH) in 1922–1930, and subsequent expeditions; (2) the discovery and further study of the Late Cretaceous mammalian fauna by the CAE AMNH and the Mongolian Paleontological Expedition of the Academy of Sciences of the USSR (1946–1949), the Polish-Mongolian Paleontological Expedition (1963–1971) and the Joint Soviet-Mongolian (Russian-Mongolian) Paleontological Expedition (JSMPE, JRMPE); (3) the discovery by the JSMPE in the late 1960s–early 1970s of the Early Cretaceous Hoovor mammalian fauna, at the time of its discovery the most diverse and richest in Asia; (4) the obtaining by the JSMPE of a large amount of data on the early Paleogene, the most important stage in the evolution of mammals; (5) detailed biostratigraphic study of the Oligocene and the Lower Miocene mammal fossils of the Valley of Lakes, as part of the Austrian-Mongolian project (1995–2018).

The first duckbill dinosaur (Hadrosauridae: Lambeosaurinae) from Africa and the role of oceanic dispersal in dinosaur biogeography

The Late Cretaceous saw distinctly endemic dinosaur faunas evolve in the northern and southern hemispheres. The Laurasian continents of North America and Asia were dominated by hadrosaurid and ceratopsian ornithischians, with tyrannosaurs as apex predators. In Gondwanan communities, including Africa, South America, India and Madagascar, titanosaurian sauropods dominated as herbivores and abelisaurids as predators. These patterns are thought to be driven by the breakup of Pangaea and formation of seaways limiting dispersal. Here, we report a new lambeosaurine hadrosaurid, Ajnabia odysseus gen. et sp. nov., from the upper Maastrichtian of Morocco, North Africa, the first Gondwanan representative of a clade formerly thought to be restricted to Laurasia. The new animal shows features unique to Hadrosauridae and specifically Lambeosaurinae. Phylogenetic analysis recovers it within Arenysaurini, a clade of lambeosaurines previously known only in Europe. Biogeographic modelling shows that lambeosaurines dispersed from Asia to Europe, then to Africa. Given the existence of large, persistent seaways isolating Africa and Europe from other continents, and the absence of the extensive, bidirectional interchange characterizing land bridges, these patterns suggest dispersals across marine barriers, similar to those seen in Cenozoic mammals, reptiles, and amphibians. Dispersal across marine barriers also occurs in other hadrosaurid lineages and titanosaurian sauropods, suggesting oceanic dispersal played a key role in structuring Mesozoic terrestrial dinosaur faunas.

Eomakhaira molossus, A New Saber-Toothed Sparassodont (Metatheria: Thylacosmilinae) from the Early Oligocene (?Tinguirirican) Cachapoal Locality, Andean Main Range, Chile

Thylacosmiline sparassodonts (previously recognized as thylacosmilids) are among the most iconic groups of endemic South American Cenozoic mammals due to their distinctive morphology and convergent resemblance to saber-toothed placental carnivores. However, the early evolution of this group and its relationship to other sparassodonts remains poorly understood, primarily because only highly specialized Neogene taxa such as Thylacosmilus, Anachlysictis, and Patagosmilus are well known. Here, we describe a new Paleogene sparassodont, Eomakhaira molossus, from the Cachapoal locality of central Chile, the first sparassodont reported from early Oligocene strata of the Abanico Formation. Eomakhaira shares features with both Neogene thylacosmilines and Paleogene “proborhyaenids,” and phylogenetic analyses recover this taxon as sister to the clade of Patagosmilus + Thylacosmilus. This broader clade, in turn, is nested within the group conventionally termed Proborhyaenidae. Our analyses support prior hypotheses of a close relationship between thylacosmilines and traditionally recognized proborhyaenids and provide the strongest evidence to date that thylacosmilines are proborhyaenids (i.e, the latter name as conventionally used refers to a paraphyletic group). To reflect the internestedness of these taxa, we propose use of Riggs' (1933) original name Thylacosmilinae for the less inclusive grouping and Proborhyaenidae for the more inclusive one. Saber teeth arose just once among metatherians (among thylacosmilines), perhaps reflecting a developmental constraint related to nonreplacement of canines in metatherians; hypselodonty may have relaxed this potential constraint in thylacosmilines. The occurrence of Eomakhaira in strata of early Oligocene age from the Chilean Andes demonstrates that the stratigraphic range of thylacosmilines spanned almost 30 million years, far surpassing those of saber-toothed placental lineages.

Uplift of Anatolia

The Cenozoic history of the Anatolian Plateau is investigated using the distribution of the last Cenozoic marine strata, the ages of Neogene continental sediments and magmatic rocks, and thermochronology. In central and northern Anatolia, the youngest marine sediments are of Middle Eocene age and show that the region has been above the sea level since ca. 41 Ma. The preservation of marine Eocene sequences over large regions and widespread distribution of Neogene continental sediments point to minor erosion or subsidence, except in the Miocene core complexes, and indicate average surface uplift or subsidence rates of less than 0.05 km/Myr since 41 Ma. The Cenozoic mammal ages point to widespread continental deposition on the Anatolian Plateau from Early Miocene ca. 22 Ma to the present, and a similar pattern of semicontinuous magmatism has been observed in Anatolia since ca. 23 Ma. New thermochronological data from central Anatolia to west of Ankara have indicate a major exhumation phase during the Paleocene and Early Eocene, followed by minor uplift and/or subsidence. Miocene exhumation is restricted to the core complexes, such as the Kazdag Massif. The Anatolian Plateau has been a land area since 41 Ma and was characterized by continental sedimentation and volcanism in the last 22 Myr. In this period, subsidence and uplift were balanced so that central Anatolia was maintained above sea level. In contrast, its southern mountainous margin, the Taurides, is free of Neogene magmatism and has undergone a fast uplift above sea level since 8 Ma ca. 0.3 km/Myr . These differences indicate that the uplift of Anatolia cannot be ascribed to a single mechanism. Flat subduction, followed by mantle upwelling under Anatolia in the post-Middle Eocene period, maintained the region above the sea level, whereas the Late Miocene rupture of the subducting eastern Mediterranean oceanic slab have induced fast uplift of the Taurides.

Perissodactyl diversities and responses to climate changes as reflected by dental homogeneity during the Cenozoic in Asia.

Cenozoic mammal evolution and faunal turnover are considered to have been influenced and triggered by global climate change. Teeth of large terrestrial ungulates are reliable proxies to trace long‐term climatic changes due to their morphological and physicochemical properties; however, the role of premolar molarization in ungulate evolution and related climatic change has rarely been investigated. Recently, three patterns of premolar molarization among perissodactyls have been recognized: endoprotocrista‐derived hypocone (type I); paraconule–protocone separation (type II); and metaconule‐derived pseudohypocone (type III). These three patterns of premolar molarization play an important role in perissodactyl diversity coupled with global climate change during the Cenozoic in Asia. Those groups with a relatively higher degree of premolar molarization, initiated by the formation of the hypocone, survived into Neogene, whereas those with a lesser degree of molarization, initiated by the deformation of existing ridges and cusps, went extinct by the end of the Oligocene. In addition, the hypothesis of the “Ulan Gochu Decline” is proposed here to designate the most conspicuous decrease of perissodactyl diversity that occurred in the latest middle Eocene rather than at the Eocene–Oligocene transition in Asia, as conventionally thought; this event was likely comparable to the contemporaneous post‐Uintan decline of the North American land fauna.

Fantastic beasts and what they ate: Revealing feeding habits and ecological niche of late Quaternary Macraucheniidae from South America

The extinction of the Quaternary megafauna stands out among the evolutionary history of Cenozoic mammals. In South America, nearly 80% of the megamammals went extinct, including the native ungulates Macrauchenia patachonica and Xenorhinotherium bahiense. Little is known about the causes of the macraucheniids’ extinction and their paleobiology. Here, we have reconstructed the dietary habits of M. patachonica and X. bahiense using enamel microwear and occlusal enamel index analyses, and also inferred their niches using species distribution modeling and stable isotope paleoecology, in addition to enamel microwear and occlusal enamel index data. We found that both macraucheniids had grazer-feeding habits, although their environmental requirements were different. M.patachonica could live in colder temperatures and arid, subtropical/temperate ecosystems, while X. bahiense was adapted to warmer temperatures and more humid, semi-arid tropical environments. Thus, despite similar feeding habits, these macraucheniids had distinct environmental requirements and ecological niches, which might explain the disjunction in the South American records.

The First Record of a Miocene Terrestrial Mammal (Astrapotheria: Uruguaytheriinae) from Northern Coastal Peru

Astrapotheres were a clade of unusual early to middle Cenozoic herbivorous mammals endemic to South America. Neogene astrapotheres were large, tusked mammals that probably had a short proboscis and may have preferred mesic lowland habitats; they were widespread during the early Miocene, became restricted to the tropics during the middle Miocene, and apparently did not persist into the late Miocene. The geologically youngest astrapotheres pertain to the subfamily Uruguaytheriinae, and in this report, we describe a partial uruguaytheriine astrapothere cranium with well-preserved postcanine dentition that we identify as Granastrapotherium cf. snorki. This specimen was collected from fluviolacustrine strata in the Tumbes Region of extreme northwestern Peru that likely pertain to the Zorritos Formation. At present, the temporal range of Granastrapotherium snorki is restricted to the late middle Miocene (Serravallian Age; ca. 13.6–12.8 Ma), which suggests a similar age for the fossil-bearing sediments of the upper Zorritos Formation. The fossil locality, which is ca. 25 km southwest of the city of Tumbes, is ca. 1,000 km distant from other sites in Peru and Colombia where G. snorki has been recorded and extends the geographic range of the species westward more than 550 km. We estimate the body mass of G. snorki at 1,800–2,500 kg based on head-body length of 3.75 m; this is lower than dentition-based body mass estimates but still suggests G. snorki was the largest terrestrial mammal in South America at the time.

Dome-headed, small-brained island mammal from the Late Cretaceous of Romania

The island effect is a well-known evolutionary phenomenon, in which island-dwelling species isolated in a resource-limited environment often modify their size, anatomy, and behaviors compared with mainland relatives. This has been well documented in modern and Cenozoic mammals, but it remains unclear whether older, more primitive Mesozoic mammals responded in similar ways to island habitats. We describe a reasonably complete and well-preserved skeleton of a kogaionid, an enigmatic radiation of Cretaceous island-dwelling multituberculate mammals previously represented by fragmentary fossils. This skeleton, from the latest Cretaceous of Romania, belongs to a previously unreported genus and species that possesses several aberrant features, including an autapomorphically domed skull and one of the smallest brains relative to body size of any advanced mammaliaform, which nonetheless retains enlarged olfactory bulbs and paraflocculi for sensory processing. Drawing on parallels with more recent island mammals, we interpret these unusual neurosensory features as related to the island effect. This indicates that the ability to adapt to insular environments developed early in mammalian history, before the advent of therian mammals, and mammals with insular-related modifications were key components of well-known dwarfed dinosaur faunas. Furthermore, the specimen suggests that brain size reduction, in association with heightened sensory acuity but without marked body size change, is a novel expression of the island effect in mammals.

Scaling of species diversity and body mass in mammals: Cope’s rule and the evolutionary cost of large size

Equations are constructed describing the inverse correlation of species diversity and body mass in extant and Cenozoic mammals. Cope’s rule, the tendency for many mammal clades to increase in body size through time, through phyletic change in single lineages or turnover within species groups, is interpreted as a probability function reducing diversity potential as a tradeoff for ecological/evolutionary gains. The inverse rule predicts that large species in clades will be less diverse than smaller species and, unless origination rates remain high among smaller clade members, clades conforming to Cope’s rule will decline in diversity, moving towards extinction. This proposition is evaluated in the Cenozoic histories of five North American mammal clades; cotton rats, felids, canids, hyaenodontids, and equids. Diversity potential of different size classes within the 3.75 million year phyletic history of the muskrat, Ondatra zibethicus, is also examined. A corollary prediction of the inverse rule, that large species should have longer durations (species lifespans) than small species, is unresolved. Successful clades maintain small size or a significant number of smaller species relative to clade average size. The potential loss of unique extant large mammal species justifies the conservation effort to protect them. The similarity of scaling exponents of species diversity to mass around a slope of -1.0 suggests that species diversity is correlated with home range size, the latter related to the probability of population fragmentation.

A survey of Cenozoic mammal baramins

A survey of Cenozoic mammal baramins