New fossil hominins from the Upper Laetolil Beds, Laetoli, Tanzania.

New finds of fossil hominins from the Upper Laetolil Beds at Laetoli in northern Tanzania include associated right and left mandibular fragments and three isolated teeth. The specimens are described and compared with those previously collected from Laetoli, as well as with Australopithecus afarensis specimens from other localities in eastern Africa. The additional specimens contribute to a better understanding of the morphological and metrical variation among the hominins from Laetoli and provide the basis for critically reassessing the taxonomic status of A. afarensis. The Laetoli hominins are remarkably similar morphologically and metrically to those from Hadar, especially when considering their temporal and geographic separation, and together, they are justifiably included in a single species, A. afarensis. Consistent with their greater age, the Laetoli hominins retain several features that might be inferred to be more primitive than those from Hadar hominins, but there is insufficient justification to consider them chronomorphs within an anagenetically evolving lineage. The long-standing debate about whether Australopithecus anamensis and A. afarensis are conspecifics or time-successive members of a single anagenetically evolving lineage remains unresolved, but the current evidence is most consistent with a cladogenetic speciation event and the recognition of these two taxa as separate species.