Rodents

Abstract

New rodent specimens collected at Laetoli between 1998 and 2005 are described here. The material allows an updating and refinement of the previously published taxonomic lists, especially those for the Lower Laetolil Beds and the Upper Ndolanya Beds. The increased number of well-preserved cranial specimens allows the description of several new species and a better appreciation of the size and morphology of some Laetoli taxa compared to their southern and eastern African counterparts. This is especially the case for Saccostomus, for which the fossil record has recently been much improved. The new species described here include a small sciurid, two Gerbillinae, and a thryonomyid. Some species are newly recognized at certain localities, and Aethomys and Petromus are recorded for the first time at Laetoli. The distribution and stratigraphic range for Pedetes laetoliensis is extended, and it is now recorded in the Upper Ndolanya Beds. Similarly, Xerus janenschi is now identified in the Laetolil Beds. As in the previous study of the Laetoli rodents, important differences in species composition and diversity between the Upper Laetolil Beds and the Upper Ndolanya Beds are confirmed. These probably reflect differences in landscape. Compared to other Pliocene assemblages, the Laetolil Beds are characterized by a very unusual diversity of sciurids and the dominance of Saccostomus and Pedetes, but otherwise they compare well with other East African Mio-Pliocene rodent assemblages, such as those from the Omo Valley and Lemudong’o. The Laetoli assemblages are distinct from those of Lukeino, Chorora and Harasib 3, but could belong to the same faunal unit as Ibole (Manonga Valley). They also differ in some respects from those from Hadar and Pliocene South African sites. Few species are shared in common between the Laetolil Beds and Upper Ndolanya Beds, but it is uncertain whether this turnover is due to taphonomic or paleoclimatic factors. This contribution highlights the importance of Laetoli for understanding rodent evolution, as well as for its geographic position at the crossroads between East and South Africa.