John J. Flynn

Impacts of the Cretaceous Terrestrial Revolution and KPg extinction on mammal diversification.

Molecular phylogenetic analysis, calibrated with fossils, resolves the time frame of the mammalian radiation. Previous analyses of relations, divergence times, and diversification patterns among extant mammalian families have relied on supertree methods and local molecular clocks. We constructed a molecular supermatrix for mammalian families and analyzed these data with likelihood-based methods and relaxed molecular clocks. Phylogenetic analyses resulted in a robust phylogeny with better resolution than phylogenies from supertree methods. Relaxed clock analyses support the long-fuse model of diversification and highlight the importance of including multiple fossil calibrations that are spread across the tree. Molecular time trees and diversification analyses suggest important roles for the Cretaceous Terrestrial Revolution and Cretaceous-Paleogene (KPg) mass extinction in opening up ecospace that promoted interordinal and intraordinal diversification, respectively. By contrast, diversification analyses provide no support for the hypothesis concerning the delayed rise of present-day mammals during the Eocene Period.

Single origin of Malagasy Carnivora from an African ancestor.

The Carnivora are one of only four orders of terrestrial mammals living in Madagascar today. All four (carnivorans, primates, rodents and lipotyphlan insectivores) are placental mammals with limited means for dispersal, yet they occur on a large island that has been surrounded by a formidable oceanic barrier for at least 88 million years, predating the age of origin for any of these groups. Even so, as many as four colonizations of Madagascar have been proposed for the Carnivora alone. The mystery of the islands mammalian origins is confounded by its poor Tertiary fossil record, which leaves us with no direct means for estimating dates of initial diversification. Here we use a multi-gene phylogenetic analysis to show that Malagasy carnivorans are monophyletic and thus the product of a single colonization of Madagascar by an African ancestor. Furthermore, a bayesian analysis of divergence ages for Malagasy carnivorans and lemuriforms indicates that their respective colonizations were temporally separated by tens of millions of years. We therefore conclude that a single event, such as vicariance or common dispersal, cannot explain the presence of both groups in Madagascar.

Recent advances in South American mammalian paleontology.

Recently discovered deposits containing terrestrial mammal fossils, together with multidisciplinary studies of classical sequences, have yielded dramatic insights into the biotic and environmental history of South America. Notable advances include several new fossil primate taxa, an improved chronology of two major immigration events (caviomorph rodents and new world monkeys), documentation of the oldest mammalian faunas dominated by grazing taxa (which suggests that grasslands appeared at least 15 million years earlier than on other continents), evidence of early biogeographical provinciality within South America, and improved sampling of the best known Cenozoic tropical South American paleofauna.

Jurassic to Paleogene: Part 2 Paleogene geochronology and chronostratigraphy

Summary We present a revised Paleogene geochronology based upon a best fit to selected high temperature radiometric dates on a number of identified magnetic polarity chrons (within the late Cretaceous, Paleogene and Neogene) which minimizes apparent accelerations in sea-floor spreading. An assessment of first order correlations of calcareous plankton biostratigraphic datum events to magnetic polarity stratigraphy yields the following estimated magnetobiochronology of major chronostratigraphic boundaries: Cretaceous-Tertiary boundary (Chron C29R), 66.4 Ma; Paleocene-Eocene (Chron C24R), 57.8 Ma; Eocene-Oligocene (Chron C13R), 36.6 Ma; Oligocene-Miocene (Chron C6CN), 23.7 Ma. The Eocene is seen to have expanded chronologically (~ 21 m.y.) at the expense of the Paleocene (~ 9 m.y.) and is indeed the longest of the Cenozoic epochs. In addition, magnetobiostratigraphic correlations require adjustments in apparent correlations with standard marine stage boundaries in some cases (particularly in the Oligocene). Finally, we present a correlation between standard Paleogene marine and terrestrial stratigraphies.

The Tinguiririca Fauna, Chile: Biochronology, paleoecology, biogeography, and a new earliest Oligocene South American Land Mammal 'Age'

Abstract A new South American Land Mammal ‘Age’ (SALMA), the Tinguirirican, is formally established, based on an assemblage of at least 25 taxa from the Chilean Andes (and smaller correlative faunas from Argentine Patagonia) that lies near the Eocene–Oligocene transition. Tinguirirican faunas occur within a previously poorly sampled temporal interval, a significant gap in the SALMA succession, accounting for the very high percentage of taxa that are new. The Tinguirirican includes a suite of taxa not documented to co-occur elsewhere. It is defined by the first stratigraphic occurrences of taxa known elsewhere only from younger beds: caviomorph rodents; interatheriine interatheriids; an otherwise Deseadan and younger clade of notohippids, diagnosed by hypsodont lower incisors; the clade of archaeohyracids including those taxa more closely related to Archaeohyrax than to Pseudhyrax; leontiniids; and the clade of groeberiid marsupials stemming from the most recent common ancestor of Klohnia and Patagonia. Among its numerous noteworthy occurrences, the Tinguiririca Fauna includes the earliest rodents known from South America (documenting that caviomorphs had reached the continent near or before the Eocene/Oligocene boundary, with an African origin for the clade – based on preliminary phylogenetic analysis), an unusual diversity of therian species possessing a ‘gnawing’ dentition, and the world’s oldest mammalian herbivore assemblage dominated by species with hypsodont cheek teeth. The Tinguirirican assemblages indicate that Simpson’s ‘Second Faunal Stratum’ began considerably earlier (prior to the Deseadan) than previously thought. The stratotype sequence for the Tinguirirican SALMA assemblage in Chile has yielded high-precision 40Ar/39Ar radioisotopic dates, as have underlying non-fossiliferous beds. These indicate that the fauna is at least ∼31.5 Ma in age. While it potentially spans a range as large as 31–37.5 Ma or more, various lines of evidence hint that this SALMA is probably of short duration (possibly less than 2 m.y.). Body size distributions (cenograms), dental hypsodonty levels, and macroniche categories are employed to infer paleoenvironmental conditions for the Tinguiririca Fauna. Collectively, these analyses reveal some non-analog aspects of middle Cenozoic South American localities relative to modern systems; that an open, relatively dry habitat (with a mean annual rainfall of 1100 mm or less) was present at Tinguiririca, and that the most dramatic shift in Cenozoic South American paleoecology and paleoenvironment occurred between the Mustersan and Tinguirirican SALMAs. Additionally, the Tinguiririca Fauna is the first Cenozoic mammal assemblage dominated by hypsodont taxa (at levels dramatically higher than those of preceding times). The proportion of hypsodont taxa in modern assemblages correlates positively with the amount of open habitat, indicating that open habitat grassland/woodland environments flourished 15–20 million years earlier in South America than on other continents. Indeed, the Tinguiririca Fauna exhibits a proportion of hypsodont taxa exceeding even that seen in modern open habitats. Such faunas and habitats thus occur in very close proximity to the Eocene/Oligocene boundary and earliest Oligocene climatic ‘deterioration’, and their associated paleoclimatic and paleoenvironmental events. The mid-latitude Tinguiririca Fauna suggests complex biogeographic patterns during the early–middle Cenozoic – while it is decidedly ‘Patagonian’ in taxonomic composition, several members of the fauna hint at close affinities with lower latitude assemblages.

Brain-size evolution and sociality in Carnivora

Increased encephalization, or larger brain volume relative to body mass, is a repeated theme in vertebrate evolution. Here we present an extensive sampling of relative brain sizes in fossil and extant taxa in the mammalian order Carnivora (cats, dogs, bears, weasels, and their relatives). By using Akaike Information Criterion model selection and endocranial volume and body mass data for 289 species (including 125 fossil taxa), we document clade-specific evolutionary transformations in encephalization allometries. These evolutionary transformations include multiple independent encephalization increases and decreases in addition to a remarkably static basal Carnivora allometry that characterizes much of the suborder Feliformia and some taxa in the suborder Caniformia across much of their evolutionary history, emphasizing that complex processes shaped the modern distribution of encephalization across Carnivora. This analysis also permits critical evaluation of the social brain hypothesis (SBH), which predicts a close association between sociality and increased encephalization. Previous analyses based on living species alone appeared to support the SBH with respect to Carnivora, but those results are entirely dependent on data from modern Canidae (dogs). Incorporation of fossil data further reveals that no association exists between sociality and encephalization across Carnivora and that support for sociality as a causal agent of encephalization increase disappears for this clade.

The oldest known primate skeleton and early haplorhine evolution

Reconstructing the earliest phases of primate evolution has been impeded by gaps in the fossil record, so that disagreements persist regarding the palaeobiology and phylogenetic relationships of the earliest primates. Here we report the discovery of a nearly complete and partly articulated skeleton of a primitive haplorhine primate from the early Eocene of China, about 55 million years ago, the oldest fossil primate of this quality ever recovered. Coupled with detailed morphological examination using propagation phase contrast X-ray synchrotron microtomography, our phylogenetic analysis based on total available evidence indicates that this fossil is the most basal known member of the tarsiiform clade. In addition to providing further support for an early dichotomy between the strepsirrhine and haplorhine clades, this new primate further constrains the age of divergence between tarsiiforms and anthropoids. It also strengthens the hypothesis that the earliest primates were probably diurnal, arboreal and primarily insectivorous mammals the size of modern pygmy mouse lemurs.

The correlated evolution of Runx2 tandem repeats, transcriptional activity, and facial length in Carnivora

SUMMARY To assess the ability of protein‐coding mutations to contribute to subtle, inter‐specific morphologic evolution, here, we test the hypothesis that mutations within the protein‐coding region of runt‐related transcription factor 2 (Runx2) have played a role in facial evolution in 30 species from a naturally evolving group, the mammalian order Carnivora. Consistent with this hypothesis, we find significant correlations between changes in Runx2 glutamine–alanine tandem‐repeat ratio, and both Runx2 transcriptional activity and carnivoran facial length. Furthermore, we identify a potential evolutionary mechanism for the correlation between Runx2 tandem repeat ratio and facial length. Specifically, our results are consistent with the Runx2 tandem repeat system providing a flexible genetic mechanism to rapidly change the timing of ossification. These heterochronic changes, in turn, potentially act on existing allometric variation in carnivoran facial length to generate the disparity in adult facial lengths observed among carnivoran species. Our results suggest that despite potentially great pleiotropic effects, changes to the protein‐coding regions of genes such as Runx2 do occur and have the potential to affect subtle morphologic evolution across a diverse array of species in naturally evolving lineages.

A radiation of arboreal basal eutherian mammals beginning in the Late Cretaceous of India

Indias Late Cretaceous fossil mammals include the only undisputed pre-Tertiary Gondwanan eutherians, such as Deccanolestes. Recent studies have suggested a relationship between Deccanolestes and African and European Paleocene adapisoriculids, which have been variably identified as stem euarchontans, stem primates, lipotyphlan insectivores, or afrosoricids. Support for a close relationship between Deccanolestes and any of these placental mammal clades would be unique in representing a confirmed Mesozoic record of a placental mammal. However, some paleogeographic reconstructions place India at its peak isolation from all other continents during the latest Cretaceous, complicating reconstructions of the biogeographic history of the placental radiation. Recent fieldwork in India has recovered dozens of better-preserved specimens of Cretaceous eutherians, including several new species. Here, we incorporate these new specimens into an extensive phylogenetic analysis that includes every clade with a previously hypothesized relationship to Deccanolestes. Our results support a robust relationship between Deccanolestes and Paleocene adapisoriculids, but do not support a close affinity between these taxa and any placental clade, demonstrating that Deccanolestes is not a Cretaceous placental mammal and reinforcing the sizeable gap between molecular and fossil divergence time estimates for the placental mammal radiation. Instead, our expanded data push Adapisoriculidae, including Deccanolestes, into a much more basal position than in earlier analyses, strengthening hypotheses that scansoriality and arboreality were prevalent early in eutherian evolution. This comprehensive phylogeny indicates that faunal exchange occurred between India, Africa, and Europe in the Late Cretaceous-Early Paleocene, and suggests a previously unrecognized ∼30 to 45 Myr “ghost lineage” for these Gondwanan eutherians.

New evidence for late mesozoic-early Cenozoic evolution of the Chilean Andes in the upper Tinguiririca valley (35 °S), central Chile

Abstract New geologic, paleontologic and isotopic geochronometric results from the Termas del Flaco region in the upper Tinguiririca River valley in central Chile demand considerable revision of the accepted geotectonic history of the Andean Main Range in this region. A diverse, transitional Eocene-Oligocene aged, land-mammal fauna was recovered from several sites in volcaniclastic sediments of the Coya-Machali (=Abanico) Formation. Major results of our study include: 1) The 1000 + m thick studied deposits, previously attributed to the Cretaceous Colimapu Formation, belong to the Coya-Machali (=Abanico) Formation. Radioisotopic data from levels immediately above (31.5 Ma) and below (37.S Ma) the fossiliferous horizon indicate a latest Eocene to early Oligocene age for the basal part of the formation and the fauna contained in it. 2) The fossiliferous unit rests with slight angular offset on different Mesozoic units: “Brownish-red Clastic Unit” (BRCU) and Banos del Flaco Formation; in a limited area it also overlies a white tuff dated at 104 Ma. 3) The contacts just discussed (none of which is attributable to faulting), demonstrate the existence of two, or possibly three, unconformities in the region. 4) Sedimentological criteria argue against reference of the BRCU to the Colimapu Formation, and imply correlation of the former unit to basal levels with in the late Cretaceous Neuquen Group of western Argentina. 5) The Coya-Machali Formation, previously viewed as representing the western volcanic equivalent of Riogrdndico Supercycle deposits of western Argentino, is likely coeval to much younger units in that region such as the Agua de la Piedra Formation. 6) Paleomagnetic results from the fossil producing horizon indicate about 20 ° of post-early Oligocene, counterclockwise rotation. 7) Fossil mammals from the Coya-Machali Formation near Termas del Flaco represent a distinct biochronologic interval not heretofore clearly recognized from elsewhere on the continent. This new fauna helps fill the long recognized post-?middle Eocene, pre-late Oligocene faunal hiatus between the Mustersan and Deseadan South American Land Mammal Ages (SALMA). In addition, it records the earliest known presence of rodents in South America and otherwise differs strongly from the enigmatic Divisaderan SALMA.