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   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:
- to reconstruct the evolutionary history and adaptive patterns
of South American primates and other mammals;
- 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
- to use anatomy and niche structure of modern mammals as a
means to reconstruct the evolution of mammalian niche structure
in the Neotropics.
A full publication list may be found on the Rio Gallegos website.
The following publications over the past five years relate
to the above themes:
Primate evolution in South America
1997 Fleagle, J. G., R. F. Kay, and M. R. L. Anthony. Fossil
New World monkeys. In R. F. Kay, R. H. Madden, R. L. Cifelli
and J. J. Flynn (eds.), Vertebrate Paleontology in the Neotropics,
pp. 473-495. Smithsonian Institution Press, Washington,
D. C.
1997 Meldrum, D. J., and R. F. Kay Nuciruptor rubricae,
a new pitheciin seed predator from the Miocene of Colombia. Am.
J. Phys. Anthrop. 102:407-427.
1997 Kay, R. F., R. H. Madden, R. L. Cifelli, and J. J. Flynn.
Vertebrate Paleontology in the Neotropics. Smithsonian
Institution Press, Washington, D.C.
1998 Kay, R. F., D. Johnson, and D. J. Meldrum A new pitheciin
primate from the middle Miocene of Argentina. Am. J. Primat.
45:317-336.
2001 Kay, R. F., B. A. Williams, and F. Anaya. The adaptations
of Branisella boliviana, the earliest South American Monkey.
In J. M. Plavcan, R. F. Kay, W. L. Jungers and C. van Schaik
(eds.), Reconstructing Behavior in the Primate Fossil Record,
pp. . Plenum Publishing Corporation, New York.
Geochronology and paleoecology
1997 Kay, R. F., R. H. Madden, R. L. Cifelli, and J. J. Flynn.
Vertebrate Paleontology in the Neotropics. Smithsonian
Institution Press, Washington, D.C.
1997 Kay, R. F., and R. H. Madden Mammals and rainfall: paleoecology
of the middle Miocene at La Venta (Colombia, South America).
J. Hum. Evol. 32:161-199.
1997 Kay, R. F., R. H. Madden, C. Van Schaik, and D. Higdon
Primate species richness is determined by plant productivity:
implications for conservation. Proc. Natl. Acad. Sci. (USA)
94:13023-13027.
1998 Kay, R. F., B. J. MacFadden, R. H. Madden, H. Sandeman,
and F. Anaya. Revised age of the Salla beds, Bolivia, and its
bearing on the age of the Deseadan South American Land Mammal
'Age'. J. Vert. Paleon. 18:189-199.
1999 Kay, R. F., R. Madden, M., M. G. Vucetich, A. A. Carlini,
M. M. Mazzoni, G. H. Ré, M. Heizler, and H. Sandeman.
Revised age of the Casamayoran South American land Mammals 'Age'--
climatic and biotic implications. Proc. Natn. Acad. Sci (US).
1999 Kay, R. F., R. H. Madden, M. Mazzoni, M. G. Vucetich,
G. Ré, M. Heizler, and H. Sandeman. The oldest Argentine
primates: first age determinations for the Colhuehuapian South
American Land Mammal 'Age'. Am. J. Phys. Anthro. Supplement
28:166.
Primate Anatomy -- Implications for Phylogeny
and Adaptations
A major theme of my work is to improve our understanding of
two related topics:
- the phylogeny of primates based (principally) on anatomical
evidence; and
- inferring the adaptations of extinct primates based mainly
on cranial and dental evidence.
The following publications relate to these two themes:
Phylogeny
1995 Williams, B. A., and R. F. Kay The taxon Anthropoidea
and the crown clade concept. Evol. Anthrop. 3:188-190.
1997 Kay, R. F., C. F. Ross, and B. A. Williams Anthropoid
Origins. Science 275:797-804.
1998 Ross, C. F., B. A. Wiilliams, and R. F. Kay Phylogenetic
analysis of anthropoid relationships. Journal of Human Evolution
35:221-306.
Adaptation
1995 Ungar, P. S., and R. F. Kay The dietary adaptations of
European Miocene catarrhines. Proc. Nat. Acad. Sci. (USA)
92:5479-5481.
1998 Kay, R. F., M. C. Cartmill, and M. Balow The hypoglossal
canal and the origin of human vocal behavior. Proc. Natl.
Acad. Sci. (USA) 95:5417-5419.
2000 Kay, R. F., and E. C. Kirk Osteological evidence for
the evolution of activity pattern and visual acuity in Primates.
American Journal of Physical Anthropology 113:1-28.
2000 Williams, S. H., and R. F. Kay. A comparative test of
competing adaptive explanations for hypsodonty in ungulates and
rodents. Programa y Resúmenes, Evolución Neotropical
del Cenozoico:46.
2000 Kay, R. F., and E. C. Kirk Osteological evidence for
the evolution of activity pattern and visual acuity in Primates.
American Journal of Physical Anthropology 113:235-262.
2001 Plavcan, J. M., R. F. Kay, W. L. Jungers, and C. van
Schaik. Reconstructing Behavior in the Primate Fossil Record.
Plenum Publishing Company, New York.
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).
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