Systematics

I specialize in notoungulate systematics but have published studies on a variety of other South American mammals. Representative publications on various groups are summarized below with links to their full citations.

Notoungulates: Much of my research has focused typothere notoungulates, which include interatheres, archaeohyracids, mesotheres, and hegetotheres. Many of these papers have described new species and/or included a phylogenetic analysis of the group. In other papers, my colleagues and I have reported new occurrences of previously known species, described the species at a particular site, or analyzed variation within a particular sample. I have also been involved with studies of notoungulate ear regions using computed tomography (CT) scanning in order to discover features that may shed light on their evolutionary relationships.

Litopterns: We have collected some very nice specimens of macraucheniids from Quebrada Honda, Bolivia, and the research describing those remains was lead by a former undergraduate student of mine, Andy McGrath. In addition, Velizar Simeonovski’s life reconstructions of the two new species we named graced the cover of that issue of the Journal of Vertebrate Paleontology. Our paper on the gracile litopterns (proterotheriids) from Quebrada Honda was published a couple years later in Ameghiniana.

Xenarthrans: My first paper dealing with this group named a new species of glyptodont from Chucal, Chile. It is among the geologically oldest glyptodonts known from remains of the shell, skull, and skeleton, and we plan to eventually describe the ankle bones of this species. The same paper also discussed the armadillos from Chucal, which are only known from rather fragmentary remains. Similarly poor remains are addressed in our earlier summary of the fauna of Cerdas, Bolivia, along with an interesting partial lower jaw of the sloth Xyophorus. This specimen is noteworthy in being the geologically oldest representative of its family, Nothrotheriidae. Our second paper on Cerdas mentions a second sloth from this site that could be the oldest member of the megatheriid subfamily Megatheriinae. We have collected a variety outstanding armadillo, glyptodont, and sloth remains from Quebrada Honda, Bolivia and are working to clean and describe these specimens. An example of the beautiful material can be seen the paper we published on Megathericulus patagonicus, the megathere from that site.

Rodents: My first foray into rodent systematics was a paper on the rodents of Quebrada Honda, Bolivia that named two new species. Since then, I have continued to publish papers on the group, which is abundantly represented at many fossil sites. In 2012, I collaborated on a paper describing the oldest rodents in South America, which come from eastern Peru. The same year, other colleagues and I published a paper on the rodents of Tinguiririca, Chile, which were formerly the oldest rodents on the continent. Most recently, I published a paper describing remarkable remains of two new species of chinchillid rodents from northern Chile (Chucal) and Bolivia (Quebrada Honda and Nazareno) with colleagues from both of those countries. I am continuing to study additional rodent specimens from both Chucal and Quebrada Honda with students and colleagues.

Marsupials: South American meat-eating marsupials (sparassodonts) tend to be quite rare in the fossil record, but we have managed to find a few specimens in Chile and Bolivia. Two specimens from Chile represent new species; one of these was was named in 2018 (Chlorocyon phantasma) and the other was named in 2020 (Eomakhaira molossus). Both of these are relatively old species, from the late Eocene and early Oligocene, respectively. We have published three papers on sparassodonts from Quebrada Honda, Bolivia. The first paper described a new (but unnamed) species and analyzed the evolutionary relationships of the group. The second paper discussed new material of the most common species at the site, Acyon myctoderos, and the third paper named a new species, Australogale leptognathus, based on a very well-preserved partial lower jaw. Another group of marsupials from Bolivia we have studied are paucituberculatans, relatives of modern shrew-opossums (caenolestids). One paper we published suggested that two species of the genus Acdestis from southern Argentina actually represent males and females of a single species. The other paper named three new species of palaeothentids from Quebrada Honda, Bolivia and analyzed the evolutionary relationships within the group.