Mesozoic mammals are rare and known mostly from Northern continents. The PI has made a unique collection of Mesozoic and early Tertiary mammals from South America (SA) that includes exquisitely preserved cranial and postcranial material, as well as isolated teeth, mandibles, and ear regions. These fossils represent a dramatic improvement in the quality of specimens and an increase of more than 500% in the total number of known SA Mesozoic mammals. The new materials range in age from the Middle Jurassic (170MY) to the early Paleocene (58MY) from five different localities in Patagonia, Argentina, and include the first record of mammals (with some new groups) for the early Late Cretaceous (Turonian) in Gondwana. This collection represents the best evidence to date for tackling the Mesozoic/early Paleocene diversification of Mammalia in SA and its impact on mammalian evolution. The proposal will produce detailed descriptions of the new specimens and will generate a comprehensive morphological data matrix including all major relevant Mesozoic mammals surveying all major traditional character systems (dental, cranial, and postcranial) in addition to new data such as enamel microstructure and Computer Tomography. The impact of different subsets of fossil data on evolutionary histories will be analyzed and compared with molecular data to explore agreements and discrepancies. The new data will provide additional insight into the early evolution of mammals. This project will have as an important component the training of a graduate student and the participation of undergraduates in research opportunities. Casts of the specimens will be donated to major collections, and an exhibit will be prepared for routing to multiple museums and similar institutions. Information on the results and general popular information will be made available via the web, while more technical data and illustrations will also be accessible on-line via MORPHOBANK. The PI and students plan to participate in science education programs open to students of every level, but with an emphasis on K-12 teachers following the success of recent projects organized by the Kentucky Academy of Sciences.
The goals of this proposal were to describe and study early mammals from the Mesozoic (approximately between 250 and 65 million years ago) of South America and the importance that they have in understanding the evolution of mammals. All Mesozoic mammals are rare, only a few hundred forms are known, but those from the southern continents are even scarcer and therefore even more important. The bulk of our understanding of early mammalian evolution is based on a body of knowledge that has been slowly amassed from the northern continents (mostly Europe and North America and to a lesser degree Asia). Mammals from the southern continents in general and those from South America in particular are very different, dramatically changing our overall picture of the early mammals. Our project discovered new specimens in the field and reported on others previously discovered by the PI and associates. We recognized a new group of mammals we called Meridiolestids, from Meridio, meaning south; these mammals were shrew sized, and only distantly related to modern marsupials and placentals, but they were relatively abundant during the Cretaceous of South America and apparently not present in the northern continents. Meridiolestids appear to have been broadly distributed throughout the continent and through time; the oldest known is about 95 million years old, but surprisingly we identified the youngest as an enigmatic mammal from the Miocene of Patagonia that is only 16 million years old. This Miocene meridiolestid , Necrolestes, was discovered in the late eighteen hundreds but remained a puzzling creature until we recognized its affinities with another from the Cretaceous of Patagonia that we had described earlier during this project. This key mammal which led us to the recognition of the meridiolestids is about 95 million years old and was dubbed by us as Cronopio dentiacutus; it is represented by relatively complete skulls which greatly add to its usefulness to disentangle mammalian relationships. Cronopio represents a mammalian form which has no close parallel among living forms; it is small with a long narrow snout, very long canine teeth, large eye sockets, and the skull is rounded, bulbous. Cronopio vaguely resembles the "saber tooth squirrel" of a popular set of animated movies and as such had great press coverage, but Cronopio is not "saber tooth" and only very distantly related to squirrels! Its discovery and the ties with the much younger Necrolestes meant that the great extinction event at the end of the Cretaceous, probably related in part to the fall of a large meteorite, had a very different impact on the faunas of the southern continents than on those of the northern. Archaic linages like the meridiolestids are all but extinct in the northern continents after the Cretaceous, but we have recorded a relatively non-traumatic transition in South America, where not only mammals but amphibians and reptiles of Cretaceous origin continue to be present during the Paleogene. The mammals we studied from older Jurassic rocks do not show the provincialism of the later Cretaceous Meridiolestids; the earlier forms appear to be part of a global fauna were small mammals from South America share close ties with those from China and North America, probably reflecting more interconnected land masses; this is particularly true of a series of forms known as triconodonts. Others, the australosphenidans, are more enigmatic and likely related to the origin of modern mammals. Our results were framed in a rigorous phylogenetic framework for which we produced several large scale, freely accessible, data matrices for the study of the taxa of interest. We also participated in a variety of projects addressing complementary goals on some other groups of mammals used as a reference for the study of archaic Mesozoic forms. Most importantly among those projects were the publication of a global phylogeny and data matrix investigating the time, origin, and sequence of events leading to the radiation of placental mammals, and studies on basal metatherians and marsupials. Additionally, during this project we published on other vertebrate groups found in the same deposits as the mammals we were studying to have a broad understanding of the ecological community in which those mammals evolved and thrived. During this period a Ph.D. and a M.S. were trained and successfully graduated; other graduate, undergraduate and professional students participated in research, lab rotations and data gathering during this period. The results of the project were disseminated to graduate level courses, honors courses, popular talks, and schools (at all levels). The PI and the Senior Personnel actively sought to interact with minorities and participated in outreach opportunities to showcase the research in progress. Some of the outreach activities were conducted at the home institutions of the researchers, or other academic institutions, but others were developed and tailored for the isolated communities where the fossils were collected.
