Richard F. Kay
I have two areas of research. The first encompasses the evolution of primates and mammalian faunal evolution, especially in South America. The second is the use of primate anatomy to reconstruct the phylogenetic history and adaptations of living and extinct primates, especially Anthropoidea.
Click here to visit my Web site on paleontological research in the Rio Gallegos area of Argentina.
Evolution of Primates and of Mammalian Faunas in South America
For the past several years, I have been engaged in research in Argentina, Colombia, and Bolivia with three objectives:
1. to reconstruct the evolutionary history and adaptive patterns of South American primates and other mammals;
2. to establish a more precise geologic chronology for the mammalian faunas between the late Eocene and middle Miocene (between about 36 and about 15 million years ago); and
3. to use anatomy and niche structure of modern mammals as a means to reconstruct the evolution of mammalian niche structure in the Neotropics.
Primate Anatomy -- Implications for Phylogeny and Adaptations
A major theme of my work is to improve our understanding of two related topics:
1. the phylogeny of primates based (principally) on anatomical evidence; and
2. inferring the adaptations of extinct primates based mainly on cranial and dental evidence.
Plans for Future Research
Plans for research over the next 3-5 years are embodied in two projects. One is a particularly important site called the Gran Barranca in Patagonian Argentina that spans the Eocene-Oligocene transition, a period of particularly significant climatic change. The other project concentrates more particularly on recovery of early SA primate fossils at several localities in Argentina and Bolivia.
Tracing Climate Change in the Eocene-Oligicene interval
This research is a study terrestrial biotic change in Patagonia through the Eocene-Oligocene transition (EOT). The end of the Eocene and the beginning of the Oligocene mark an important change in world climate from latitudinally more uniform, warmer, and more equable conditions to climates characterized by more latitudinal variation, cooler temperatures and more seasonality, i.e., when world climate transitioned from 'greenhouse' to 'icehouse'. The causes of this change are complex but involved regional tectonic activity as well as reorganized oceanic circulation. The timing and biotic impact of the change has been studied in the continental records of North America, Europe and Asia and shows a response to both local and global influences. As yet, however, no sequence of continental mammals and plants for the Eocene-Oligocene transition has been studied in the Southern Hemisphere. Recent revision of the ages of rock units and biotas in Patagonia has demonstrated that the Sarmiento Fm at Gran Barranca at 45° South in Patagonian Argentina spans the late Eocene through early Oligocene interval. In fact, this is the only known continental vertebrate and plant sequence so far identified from the Southern Hemisphere that spans this interval. The formation contains an as-yet inadequately sampled, but certainly rich, sequence of mammalian faunas and plant microfossils. Preliminary analysis of the mammalian herbivores suggests that dramatic changes occurred over a comparatively short interval of geologic time. The same sedimentary interval contains plant microfossils that document important change in the plant communities. Pilot data from mammalian tooth enamel suggest that these events occurred within the context of increasingly arid and more seasonal environments. The precise timing and nature of this biotic change, and its relation to the marine and Northern Hemisphere changes, will remain obscure until more fossils are collected in a more highly resolved temporal framework.
In this collaborative research undertaking, the geochronology of the Sarmiento Fm at Gran Barranca will be further refined using radiometric dating, chemical identification of tephra, and paleomagnetism. Stratigraphically-controlled collections will be made of vertebrates and plant microfossils. Climate change and its impact on the biota will be assessed 1) using biogeochemical analysis of stable oxygen isotopes in fossil mammalian tooth enamel; 2) by documenting changes in mammalian community structure (richness, origination and extinction rates, and ecological morphology); and 3) by documenting changes in vegetation and floral composition from the study of phytoliths. These three independent lines of evidence in a refined geochronologic framework will then be compared with similar evidence from continental sequences in the Northern Hemisphere and oceanic climatic data to improve our understanding of the timing and character of climatic change in continental high latitudes during this temporal interval.
Recovery of the earliest primates from South America
This field project has two objectives: to recover fossil primates in middle Tertiary rocks in Argentina and Bolivia and to place known and new specimens within a more refined chronological framework. Recovery of older primates from South America (SA), and of cranial and postcranial remains of known early platyrrhines will contribute important new information to the adaptive profile of the earliest platyrrhines. New material will shed light on the phylogenetic status of African Paleogene anthropoids, one of which may be the platyrrhine sister-taxon. Also, new remains of fossil primates will help to refine hypotheses about the origins of the modern families and subfamilies of platyrrhines, all of which trace back to an early Miocene (~17-21 Ma) common ancestor. Finally, new fossil primates may further constrain the time of entry of platyrrhines into South America.
We will collect in four areas: 1) the late Oligocene Salla beds of Bolivia which yield the oldest known South American primates, and the upper units of that formation which are well exposed, fossiliferous, but little-explored, and represent the late Oligocene; 2) a newly discovered late Oligocene locality (~25 Ma) in the southern Altiplano of Bolivia; 3) Patagonian early Miocene sites that contain primates and other small mammals; and 4) later Eocene sites in Patagonia and northern Argentina with small mammals and favorable paleoclimate that are presently inadequately sampled. Each of three years of research involves two field seasons-one in Patagonia and one in Bolivia and/or NW Argentina.
The research plan concentrates on recovery of more specimens of primates where they are already documented to occur-two field seasons at Salla, Bolivia (~26 Ma), and two seasons at the Colhuehuapian level of the Gran Barranca (~20-22 Ma). The Salla primates are the oldest known from South America but at present are represented only by teeth and jaws. Three Colhuehuapian-age localities in Patagonia (Gaiman, Sacanana, and Gran Barranca); represent the next oldest occurrence of primates in SA (Las Lañas in Chile is a fourth). Of these, Gran Barranca yields more specimens than any other site of comparable age and, as a quarry site, offers the most promise for the recovery of relatively complete material.
Efforts will then be made to recover primates at sites where conditions are promising and recovery would be scientifically important. The collecting plan is informed by refinements in the time scale of SA mammal evolution. We have published the first dates for Eocene mammalian faunas from SA showing that the Casamayoran SA Land Mammal Age (SALMA), hitherto thought to represent the early Eocene, is actually late-middle to late Eocene. Thus unexpectedly, at least some Casamayoran sites are similar in age to the earliest anthropoid-rich Egyptian sites and fall within a time interval when anthropoid primates most likely entered SA. Three sites within the temporal interval from ~37 to ~25 Ma have small mammals in sufficient abundance to be screen washed and quarried. These sites are known to have favorable paleoclimate (equable temperatures, humid, and forested) judging from known faunas and regional geologic settings. They are the Casamayoran sites at Gran Barranca and Curandera (~37 Ma), the Mustersan site at Antofagasta de la Sierra, the Deseadan site at La Flecha (~25-29 Ma) and Bolivian sites at Toloma and Pululos on the southern Altiplano (~25 Ma).
Publications