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.

Multituberculate and other mammal hair recovered from Palaeogene excreta.

Evidence of hair from several extinct mammals has been recovered from a rich accumulation of fossil excrement from the Late Palaeocene beds of Inner Mongolia, China. This highly unusual and previously undocumented depositional occurrence consists of hundreds of mammalian carnivore coprolites (fossil faeces) and a lesser number of probably raptorial bird regurgitalites (fossil pellets). The fossil hair occurs as impressions and natural casts in the extremely fine-grained, calcareous matrix that cements the skeletal remains within these faecal structures and preserves even the cuticular scale pattern on individual hair. Hair from at least four mammalian taxa, most notably the multituberculate Lambdopsalis bulla, has been identified. This record constitutes the first tangible evidence that, along with monotremes and therian mammals, multituberculates were hirsuite, and lends support for the presence of this mammalian feature in the most recent common ancestor of these three groups.

An Early Miocene anthropoid skull from the Chilean Andes.

Partly because of their poor fossil record, the relationships of neotropical platyrrhine monkeys to other groups of primates and to each other remain perhaps the most poorly known for any major primate clade. Here we report the discovery of a complete platyrrhine skull from the Andes of central Chile, by far the best preserved Tertiary primate cranium from South America. This find, coupled with recent phylogenetic analyses of higher groups of anthropoid primates, has the potential to revise substantially our understanding of platyrrhine interrelationships, indicating, among other points, significant modification to reconstruction of the ancestral platyrrhine morphotype and a likely African origin for New World monkeys. A 40Ar/39Ar radioisotopic date directly associated with the skull indicates an Early Miocene age, marking the first report of South American mammals of this age from outside Argentine Patagonia. Finally, this discovery demonstrates the enormous potential of vastly distributed, but virtually untapped, Andean volcaniclastic deposits to yield further insights into the origin and diversification of South American primates.

Primitive fossil rodent from Inner Mongolia and its implications for mammalian phylogeny.

The evolutionary origin of rodents is obscured by the group's sudden and highly transformed first appearance in the fossil record in the latest Paleocene. We report here the discovery of nearly complete dental remains of an extraordinary new primitive rodent from strata of transitional Paleocene-Eocene age in Inner Mongolia, China. The strikingly conservative morphological features of this taxon, Tribosphenomys minutus, gen. et sp. nov., substantially modify previous ideas about the ancestral rodent morphotype, which in turn has important implications for understanding the origin of rodents and their relationship to other eutherian mammals. This new fossil, in conjunction with recent morphological and molecular evidence confirming rodent monophyly, indicates the need for a reassessment of phylogenetic affinities among gliriform eutherians. Our results indicate a sister-group position of the new taxon to other rodents, and support the alliance of lagomorphs (rabbits) and rodents (cohort Glires). They also suggest that paraphyly of an extinct assemblage, the 'Eurymylidae', and reveal an unexpectedly complex pattern of character evolution near the ancestry of Rodentia.

Skeleton of the Oldest Known Pinniped, Enaliarctos mealsi.

A nearly complete skeleton of the archaic pinniped Enaliarctos, found in late Oligocene or early Miocene rocks (approximately 23 million years old) of California, provides new evidence on the origin of pinnipeds. Enaliarctos retains many primitive features expected in the hypothesized common ancestor of pinnipeds. Skeletal modifications seen in Enaliarctos document swimming adaptations and indicate that pinnipeds primitively used the axial skeleton and both fore and hindflippers as sources of propulsion. Elongate hindlimbs with prominent bony processes (reflecting powerful musculature) suggest that Enaliarctos was more active on land than modern pinnipeds.

Amino acid sequence versus morphological data and the interordinal relationships of mammals.

To a large extent, the mutual affinities of the mammalian orders continue to puzzle systematists, even though comparative anatomy and amino acid sequencing offer a massive data base from which these relationships could potentially be adduced. In the present paper the consistency index--the number of character states less the number of characters in a data set, divided by the total number of changes in the character states on a cladogram--was used to examine the relative resolving powers of recently published morphological and molecular-sequence data. Consistency indices were calculated for previously published alpha crystallin A chain and myoglobin amino acid-sequence cladograms and for four original amino acid-sequence cladograms (alpha crystallin A, myoglobin, and alpha and beta hemoglobin); these were found to be comparable to the consistency indices of morphologically based cladograms. Qualitative comparisons between the morphologically based and molecularly based trees were also made; only moderate congruence between the two was observed. Moreover, there was a general lack of congruence between the cladograms specified by each of the four proteins. Amino acid-sequence and morphological data agreed on the placement of edentates as an early eutherian offshoot and on the grouping of hyracoids, proboscideans, and sirenians. Otherwise there was only limited congruence: morphology strongly supported the grouping of lagomorphs and rodents and the alliance of pholidotes and edentates, but sequence analyses did not. The placement of tubulidentates differed widely among proteins. Morphology indicated the close association of sirenians with proboscideans; proteins suggested a pairing of sirenians with hyracoids. Sequence data did not identify many (morphologically well-diagnosed) orders as monophyletic (e.g., Lagomorpha).(ABSTRACT TRUNCATED AT 250 WORDS)