Phylogenetic Studies of Early Mammals                             return to Zhe-Xi Luo's main page

Estimating phylogenetic relationships of Mesozoic and extant mammals – Phylogenetic relationships are the roadmap to re-trace the pattern of evolution. Discoveries of numerous well-preserved skeletons of Mesozoic mammals in China (available through collaboration between the Carnegie Museum and Chinese Academy of Geological Sciences and Nanjing Institute of Geology and Palaeontology) made it possible to achieve a comprehensive sampling of nearly all osteological and dental features of the extinct Mesozoic mammals and the modern mammals. Comprehensive systematic dataset (supermatrix) can help to integrate both the extant and the Mesozoic mammals into a phylogeny (Refs. 8, 9, 10), to test the evolutionary hypotheses from molecular systematic datasets of modern mammals, with the fossil record of the Mesozoic (Fig. 4).

Divergence of Metatherian (marsupials) and Eutherias (placentals) mammals – A key event in early mammalian evolution is the divergence of placental and marsupial mammals. Placentals and marsupials dominated the Cenozoic biotasand make up 99% of all mammals living in the world today. But their histories can be traced at least to the Early Cretaceous. The collaborative studies by Chinese Academy of Geological Sciences and Carnegie Museum showed that Eomaia and Sinodelphys from the Lower Cretaceous of Liaoning are the most primitive fossils that can be unequivocally placed onto the placental lineage and the marsupial lineage (Fig. 5) (Refs. 11, 12). Their anatomic characteristics represent on the best approximation to the ancestral conditions from which the later placentals and marsupials have evolved.

(8) Kielan-Jaworowska, Zofia, Richard L. Cifelli, & Zhe-Xi Luo. 2004. Mammals from the Age of Dinosaurs - Origins, Evolution, and Structure. Columbia University Press, New York. Pp. i-xv; 1-630. (More information is available on the Web site for Columbia University Press).