The principles of classification and a classification of mammals. Bulletin of the AMNH ; v. 85

Bones of recent mammals in the Amboseli Basin, southern Kenya, exhibit distinctive weathering characteristics that can be related to the time since death and to the local conditions of temperature, humidity and soil chemistry. A categorization of weathering characteristics into six stages, recognizable on descriptive criteria, provides a basis for investigation of weathering rates and processes. The time necessary to achieve each successive weathering stage has been calibrated using known-age carcasses. Most bones decompose beyond recognition in 10 to 15 yr. Bones of animals under 100 kg and juveniles appear to weather more rapidly than bones of large animals or adults. Small-scale rather than widespread environmental factors seem to have greatest influence on weathering characteristics and rates. Bone weathering is potentially valuable as evidence for the period of time represented in recent or fossil bone assemblages, in- cluding those on archeological sites, and may also be an important tool in censusing populations of animals in modern ecosystems.

Taphonomic and Ecologic Information Form Bone Weathering

The precise hierarchy of ancient divergence events that led to the present assemblage of modern placental mammals has been an area of controversy among morphologists, palaeontologists and molecular evolutionists. Here we address the potential weaknesses of limited character and taxon sampling in a comprehensive molecular phylogenetic analysis of 64 species sampled across all extant orders of placental mammals. We examined sequence variation in 18 homologous gene segments (including nearly 10,000 base pairs) that were selected for maximal phylogenetic informativeness in resolving the hierarchy of early mammalian divergence. Phylogenetic analyses identify four primary superordinal clades: (I) Afrotheria (elephants, manatees, hyraxes, tenrecs, aardvark and elephant shrews); (II) Xenarthra (sloths, anteaters and armadillos); (III) Glires (rodents and lagomorphs), as a sister taxon to primates, flying lemurs and tree shrews; and (IV) the remaining orders of placental mammals (cetaceans, artiodactyls, perissodactyls, carnivores, pangolins, bats and core insectivores). Our results provide new insight into the pattern of the early placental mammal radiation.

/pdf/molecular-phylogenetics-and-the-origins-of-placental-mammals-umiq1pgg63.pdf

Molecular phylogenetics and the origins of placental mammals

To discover interordinal relationships of living and fossil placental mammals and the time of origin of placentals relative to the Cretaceous-Paleogene (K-Pg) boundary, we scored 4541 phenomic characters de novo for 86 fossil and living species. Combining these data with molecular sequences, we obtained a phylogenetic tree that, when calibrated with fossils, shows that crown clade Placentalia and placental orders originated after the K-Pg boundary. Many nodes discovered using molecular data are upheld, but phenomic signals overturn molecular signals to show Sundatheria (Dermoptera + Scandentia) as the sister taxon of Primates, a close link between Proboscidea (elephants) and Sirenia (sea cows), and the monophyly of echolocating Chiroptera (bats). Our tree suggests that Placentalia first split into Xenarthra and Epitheria; extinct New World species are the oldest members of Afrotheria.

http://science.sciencemag.org/content/sci/339/6120/662.full.pdf

The Placental Mammal Ancestor and the Post–K-Pg Radiation of Placentals

During the Paleocene-Eocene Thermal Maximum (PETM), ∼56 Mya, thousands of petagrams of carbon were released into the ocean-atmosphere system with attendant changes in the carbon cycle, climate, ocean chem- istry, and marine and continental ecosystems. The period of carbon release is thought to have lasted <20 ka, the duration of the whole event was ∼200 ka, and the global temperature increase was 5-8 ◦ C. Terrestrial and marine or- ganisms experienced large shifts in geographic ranges, rapid evolution, and changes in trophic ecology, but few groups suffered major extinctions with the exception of benthic foraminifera. The PETM provides valuable insights into the carbon cycle, climate system, and biotic responses to environmental change that are relevant to long-term future global changes.

https://www.whoi.edu/fileserver.do?id=136084&pt=2&p=148709

The Paleocene-Eocene Thermal Maximum: A Perturbation of Carbon Cycle, Climate, and Biosphere with Implications for the Future

In the tradition of G. G. Simpson's classic work, Kenneth D. Rose's The Beginning of the Age of Mammals analyzes the events that occurred directly before and after the mysterious K-T boundary which so quickly thrust mammals from obscurity to planetary dominance. Rose surveys the evolution of mammals, beginning with their origin from cynodont therapsids in the Mesozoic, contemporary with dinosaurs, through the early Cenozoic, with emphasis on the Paleocene and Eocene adaptive radiations of therian mammals. Focusing on the fossil record, he presents the anatomical evidence used to interpret behavior and phylogenetic relationships. The life's work of one of the most knowledgeable researchers in the field, this richly illustrated, magisterial book combines sound scientific principles and meticulous research and belongs on the shelf of every paleontologist and mammalogist.

The Beginning of the Age of Mammals

True primates appeared suddenly on all three northern continents during the 100,000-yr-duration Paleocene–Eocene Thermal Maximum at the beginning of the Eocene, ≈55.5 mya. The simultaneous or nearly simultaneous appearance of euprimates on northern continents has been difficult to understand because the source area, immediate ancestors, and dispersal routes were all unknown. Now, omomyid haplorhine Teilhardina is known on all three continents in association with the carbon isotope excursion marking the Paleocene–Eocene Thermal Maximum. Relative position within the carbon isotope excursion indicates that Asian Teilhardina asiatica is oldest, European Teilhardina belgica is younger, and North American Teilhardina brandti and Teilhardina americana are, successively, youngest. Analysis of morphological characteristics of all four species supports an Asian origin and a westward Asia-to-Europe-to-North America dispersal for Teilhardina. High-resolution isotope stratigraphy indicates that this dispersal happened in an interval of ≈25,000 yr. Rapid geographic dispersal and morphological character evolution in Teilhardina reported here are consistent with rates observed in other contexts.

/pdf/rapid-asia-europe-north-america-geographic-dispersal-of-1f5afnzyvx.pdf

Rapid Asia–Europe–North America geographic dispersal of earliest Eocene primate Teilhardina during the Paleocene–Eocene Thermal Maximum

The Clarkforkian Land-Mammal Age and Mammalian Faunal Composition Across the Paleocene-Eocene Boundary

The subfamily Anaptomorphinae contains the oldest and most generalized members of the tarsier-like primates and is the basal group of the extinct family Omomyidae. The best and most continuous record of anaptomorphine history is from rocks of early Eocene (Wasatchian) age in the Bighorn Basin of northwest Wyoming where eight genera and 14 species are recognized. Three of these species are new (Teilhardina crassidens, Tetonius matthewi, Absarokius metoecus), and four other new species are described from elsewhere (Tetonius mckennai, Absarokius gazini, A. australis, Strigorhysis huerfanensis). Teilhardina tenuicula and Absarokius nocerai are new combined forms. Absarokius noctivagus is considered to be a synonym of A. abbotti, and Mckennamorphus is a synonym of Pseudotetonius. The evolution of dental characters in three principal morphologic clades of anaptomorphines from the Bighorn Basin is documented with the aid of numerous new specimens (75% of the sample is new) and with precise stratigraphic data. These major clades are Teilhardina–Anemorhysis, Tetonius–Pseudotetonius, and Absarokius. In each of these clades, evolution appears to have occurred gradually. In the first two clades it was mainly anagenetic, although each one included a minor branching event. In Absarokius, evolution was instead characterized by cladogenesis followed by continued (and continual) anagenetic change in each of the new lines. Anagenetic gradual evolution produced the new genus Pseudotetonius (from Tetonius) and possibly Anemorhysis (from Teilhardina). Similarly, the Absarokius metoecus lineage probably gave rise to late Wasatchian–early Bridgerian Strigorhysis. Evolution from Tetonius to Pseudotetonius has been clarified by establishment of five arbitrary stages of evolution (Tetonius–Pseudotetonius intermediates). Estimates of relative proportions of time represented by paleosols in different parts of the Willwood section suggest that cladogenetic speciation in Absarokius was almost certainly more rapid than anagenesis in Tetonius–Pseudotetonius. Anagenetic character evolution and speciation in the anaptomorphine primates was typified first by increase, then decrease in variability, which resulted in measurable apomorphic morphologic change. Cumulation of changes of this sort created more extensive differences of importance at the species and genus levels. Introduction of changing character states and their tempo was staggered temporally, and new characters (and new taxa) are least separable from their antecedent states when they first appear. This evidence is in sharp contrast to predictions of the punctuated equilibria model of evolution. Because the emergence of diagnostic characters occurs gradually (in evolutionary terms) and not all at once (in temporal terms), and because diagnostic characters are the essence of the diagnosis (and thereby taxonomy), the implications of gradual evolution for both systematic paleontology and biostratigraphy are profound. Stasis exists in the evolution of individual characters over certain periods, but this study offers no evidence supporting either organismic stasis or even stasis in the dental evolution of the Anaptomorphinae over a period of about 4.8 million years.

/pdf/patterns-of-dental-evolution-in-early-eocene-anaptomorphine-2iamg38kz3.pdf

Patterns of Dental Evolution in Early Eocene Anaptomorphine Primates (Omomyidae) from the Bighorn Basin, Wyoming

Among the most interesting mammalian dental specialization is the mandibular 'tooth comb' or 'tooth scraper' that evolved independently in certain primates and other mammals. Its occurrence is most widely known in lemurs and lorises, where it is comprised of the long, slender, procumbent incisors (one or two pairs) and incisiform canines (Fig. 1). In non-primates to canines are not incorporated into the comb. Some tree shrews (Tupaiidae) possess a tooth comb consisting of the four central incisors, and some early Tertiary arctocyonid condylarths had a similar structure composed of all six lower incisors. The extant flying lemurs (Dermoptera: Cynocephalus) also have a dental 'comb' but it is very different from the ones already mentioned, consisting of two pairs of pectinate incisors, each tooth modified into a comb with as many as 15 tines. This condition, although sometimes said to be similar to that in lemurs, is unique to Cynocephalus. One of the principal functions of the tooth comb in primates is to comb the fur, and we present here indirect evidence that condylarths used this structure in the same way, millions of years before tooth combs evolved in prosimians. We also show that the comb-like incisors of Cynocephalus, contrary to popular belief, probably do not function to comb the fur.

Function of the mandibular tooth comb in living and extinct mammals

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