Research Interests


I am interested in the evolution of mammalian dental and jaw morphology during the Mesozoic.  In particular, my research focuses on the origin(s) of tribosphenic mammals from more primitive groups during the Jurassic, and the evolution of terrestrial ecosystems through the Jurassic and into the Cretaceous.  The earliest members of modern mammal lineages (marsupials and placentals) are generally thought to have appeared at the very beginning of the Cretaceous.  However, discoveries of Middle Jurassic fossils displaying a surprising combination of advanced dentition and primitive jaws have led some to rethink the early history of modern groups.

The use of computed tomography (CT) has enabled investigation of novel features of some of the first Mesozoic mammal specimens ever collected, providing new data and allowing thorough redescription of important species.  Some questions that are central to my research are:
 Late Cretaceous sediments of the Kaiparowits Plateau, Utah



Are there transitional mammalian faunas in North America to fill the temporal and morphological gap between the Upper Jurassic Morrison Formation and units of Aptian-Cenomanian age (e.g., Cloverly, Antlers, and Cedar Mountain formations)?


Cifelli, R. L., Davis, B. M., and Sames, B. in press. Earliest Cretaceous mammals from the western United States. Acta Palaeontologica Polonica.
 
Earliest Cretaceous dryolestid from the Lakota Fm., South Dakota


Are the dentally advanced Middle Jurassic species and their relatives (the Australosphenida) functionally tribosphenic, and if so, is this acquisition homology or homoplasy?


Davis, B. M. 2011. Evolution of the tribosphenic molar pattern in early mammals, with comments on the "dual-origin" hypothesis. Journal of Mammalian Evolution 18: 227-244. (PDF)
 Early Cretaceous australosphenidan Ausktribosphenos

What does the morphology of the sister group to traditional tribosphenic mammals (the Peramura) tell us about dental homologies across the tribosphenic boundary?

Davis, B. M.
2012. Micro-computed tomography reveals a diversity of peramuran mammals from the Purbeck Group (Berriasian) of England. Palaeontology 55: 789-817.
(PDF)

 Early Cretaceous pretribosphenic mammal Peramus

Can any phylogenetic patterns be gleaned from the diversity of early, somewhat generalized tribosphenic mammals (such as the Early Cretaceous Trinity therians), and do they have any bearing on the early history of marsupials or placentals?


Fig. to R from: Davis, B. M. 2011. A novel interpretation of the tribosphenidan mammal Slaughteria eruptens from the Early Cretaceous Trinity Group, and implications for dental formula in early mammals. Journal of Vertebrate Paleontology 31: 676-683. (PDF)

Davis, B. M., Cifelli, R. L. and Kielan-Jaworowska, Z. 2008. Earliest evidence of Deltatheroida (Mammalia: Metatheria) from the Early Cretaceous of North America. In: Sargis, E. J. and Dagosto, M. (eds.), Mammalian Evolutionary Morphology: A Tribute to Frederick S. Szalay, 3-24. Springer, Dordrecht. (PDF)


 
Premolar replacement from CT data, Early Cretaceous therian Slaughteria


I also revised the systematics of a large, diverse family of Late Cretaceous, North American marsupials for my Masters thesis.  The Pediomyidae were among the most numerically dominant mammals in many faunas towards the end of the Cretaceous.  The principal genus, Pediomys, contained nine very diverse species, which I redistributed across a total of four genera.  The highly distinctive molar morphology which characterizes pediomyids may reflect a relationship with other taxa with purported ties to a South American faunal exchange. 

See:
  Davis, B. M. 2007. A revision of “pediomyid” marsupials from the Late Cretaceous of North America. Acta Palaeontologica Polonica 52: 217-256. (PDF)
 Late Cretaceous pediomyid marsupial Pediomys