What is it? - 37 million year old fossil primate puzzles paleontologists

In the Fayum desert of northern Egypt, not too far from the banks of the Nile, the vestiges of ancient forests are preserved in the sand-covered strata. The fossils are ghosts of a vanished oasis in which prehistoric cousins of modern elephants wallowed in lush wetlands and a host of ancient primates scrambled through the trees, and despite being known as one of the world's best fossil sites for over a century paleontologists are continuing to discovery new species from the desert rock. The trouble is that not all these new species are easily classified.

Approximately 37 million years ago, around the middle of the Eocene, at least three branches of the primate family tree were represented in the forests of the Fayum. There were early anthropoids (members of the group containing monkeys and apes), adapiformes (lemur-like primates only distantly related to anthropoids), and "advanced" strepsirrhines (close relatives of the adapiformes and representatives of the group which contains lemurs, lorises, and bush babies today), together representing a diverse and disparate assemblage of primates living in the same place at the same time. Given this primate richness it might be expected that the announcement of a new Fayum primate would not be all that exciting - it would just be another name to add to the list as far as the public is concerned - but according to paleontologists Erik Seiffert, Elwyn Simons, Doug Boyer, Jonathan Perry, Timothy Ryan, and Hesham Sallam there is now evidence of a peculiar Fayum creature which may represent a previously unknown branch of primate evolution.

Named Nosmips aenigmaticus in honor of the famed paleontologist G.G. Simpson (Nosmips = anagram of Simpson) and its uncertain affinities, the new primate is so far only represented by a handful of isolated molars and premolars. This is even less than the researchers had when they described the lemur-like primate Afradapis last year, but there are some peculiarities of the Nosmips teeth which set it apart. The most obvious is that they are quite large compared to other primate teeth from the locality - the only other creatures from the site with teeth about the same size are rodents and extinct carnivores called creodonts, both of which have very different tooth shapes. It appears that Nosmips would have been the largest primate in the Fayum forest 37 million years ago.

Their large size is not the most puzzling aspect of the Nosmips teeth, though. Compared to the corresponding teeth of other fossil primates, the premolars of Nosmips are odd in that they are both elongated and are shaped more like molars than premolars. The presence of pits on the recovered teeth, as well, hints that Nosmips may have been eating hard foods such as seeds or fruits with pits, and overall it would seem that it had a specialized dentition representative of a diet different from that of other Fayum primates of its time, such as the leaf-eating Afradapis. If this is correct, the strange teeth of Nosmipis may be indicative of niche partitioning, a phenomenon seen in modern primates in which species living in the same forest feed on different foods and occupy different parts of the forest's vertical dimension as a result of competitive exclusion. While Afradapis would have been a specialized folivore, the authors of the new study propose that Nosmips was a more generalized feeder which dined on fruits, seeds, and insects.

Just how closely related Nosmips was to its neighbors is unclear. When the researchers compared 105 characteristics seen in the Nosmips teeth with as many as 361 characteristics seen across a wide swath of primates it did not comfortably fall within any known group. Depending on slight tweaks in the analysis Nosmips could be an anthropoid, an "advanced" strepsirrhine, or an adapiform - without more of the skeleton a definite assignment seems nearly impossible. At present it appears to be an odd, specialized offshoot of some earlier branching event among primates, and the fact that is shares some similarities with previous controversial taxa like Plesiopithecus does little to resolve the issue. Regardless of what Nosmips turns out to be, however, its discovery will surely help paleontologists better understand both the ecology of the Eocene Fayum forests and the fantastic radiation of primate types which existed during this time in earth's history.

Seiffert, E., Simons, E., Boyer, D., Perry, J., Ryan, T., & Sallam, H. (2010). A fossil primate of uncertain affinities from the earliest late Eocene of Egypt Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.1001393107