LH 4 sample from efossils
Laetoli Hominid 4 was discovered by Mary Leakey in 1974. Among other important traits, it serves as the type specimen for Australopithecus afarensis!
When they first described it, Leakey and colleagues noted that “presence of a C/P3 diastema, inclined symphyseal axis, bulbous anterior corpus, and low placement of the mental foramen on the adult mandible”. Originally they placed LH 4 and the other fossils from the site in the genus Homo but later work by Tim White, Don Johanson, and others linked the Laetoli fossils to the ones being uncovered 1,500 KM north in Hadar, where the famous Lucy skeleton was found.
(if you want to learn more about how this debate went down, and the idea that the fossils represent a single, dimorphic species, check out the book “Lucy: The Beginnings of Humankind” by Johanson & Edey. There is also a fascinating & frankly intense story behind why it is the type specimen rather than Lucy, which you can read about in the book “Bones of Contention” by Roger Lewin.)
Australopithecus afarensis is one of the best-studied hominin species. However, the level of variation among the fossils that make up the sample leads some to suggest the presence of more than one species, though this also may be explained by sexual polymorphism
One interesting question is how similar the Au. afarensis sample from Laetoli is to the Hadar sample. Mary Leakey wasn’t convinced that LH 4 represented the same species as Lucy and in the last few decades a lot of research has gone into discerning how similar and different the two samples are. Bill Kimble and Lucas K. Delezene note that LH 4 closely resembles the Hadar mandibles in some features but has important differences (especially in the cross-sectional shape at the center of the mandible). That, plus some evidence of difference between juvenile mandibles at both sites leads them to suggest that there may be biological distinctions between the two populations, though they don’t seem to favor naming 2 species from these materials.
Laetoli is also the site of the famous hominin footprints, a trail of ~70 prints left by australopiths 3.6 mya as they walked through wet volcanic ash which was then covered by another eruption which sealed their prints (and others, such as insects and bird prints). They show the locomotion pattern of 2 (or maybe 3) individuals who were fully bipedal. Unlike the fossil evidence, which is often difficult to interpret conclusively, this is direct data that by 3.6 mya human ancestors were walking bipedally on the ground!
Recent work at Laeotli have uncovered new sets of prints left by the same species (though these individuals seem to have been taller). While difficult to prove, there is some indication that these newly uncovered footprints were left around the same time as the original ones (they were walking the same direction and at a similar moderate speed as the original set) which opens up a lot of possibilities about the behavioral characteristics of this species.
Personally, I think LH 4 is a great fossil. Also, Laetoli would be a great name for a cat.1
the new footprints from Site S at Laetoli from Masao et al. 2015
Further reading
It is also my daughter’s middle name, but only because my wife wouldn’t let it be her first name…:) ↩︎