Species and Classification of Ardipithecus ramidus

          This week we are going to explore how Ardipithecus ramidus was named and classified in its species. We will also look at how it fits into the hominin “family bush” and how it related to the evolution of modern humans.

          Before the most complete specimen of Ardipithecus ramidus, fossil ARA-VP-6/500 or “Ardi”, was discovered, scientists initially classified the remains as Australopithecus ramidus (White, 2009). The first article that called it Australopithecus ramidus was about the fossil ARA-VP-6/1, which is only a set of associated teeth that were compared with both Australopithecus afarensis and Australopithecus africanus  (White, 1994). It was determined that Australopithecus ramidus was the most primitive of the Australopithecines. When the more complete fossil skeleton of Ardi was found, researchers realized that that “relative to body size, its dentition was small,” unlike what was found in the Australopithecines, and it was renamed Ardipithecus ramidus (White, 2009). The species name ramidus is derived from the local language of Afar from the word “ramid” which means root, emphasizing the idea that Ardipithecus ramidus is a possible origin species of humans (Dorey, 2015).

ARA-VP-6/500 or “Ardi” provided more evidence that lead to its change in classification from Australopithecus to Ardipithicus ramidus.
Image: (White, 2009)

          The discovery of Ardipithecus ramidus completely changed how scientists thought about the origin of modern humans and the hominin “family bush.” Previously the human origin story relied on the idea that apes were primitive and the Australopithecines were the evolutionary transition between ape-like and human-like. However, the discovery of Ardipithecus ramidus proves this assumption to be false (Lovejoy, 2009). The anatomy of Ardi has a mixture of more ape-like features like a divergent toe and more derived features like bipedalism, we will explore those adaptations more in later posts. The mixed anatomy of Ardipithecus ramidus demonstrates that apes are not as primitive as previously thought but instead have “evolved specifically within extant ape lineages,” (Lovejoy, 2009). There are many hypotheses about where Ardi belongs in the hominin family bush; some researchers believe that Ardipithicus ramidus is a direct ancestor to the Australopithecines and modern humans. However, the more well-recognized theory is that Ardi is a sister taxa to Australopithicus and Homo because although it shares many features with other early hominids, it has some derived features of more recent hominids and does not fit as an ancestor to Australopithicus africanus. There is some evidence that Ardipithicus ramdus may be the direct dicendent of Australopithicus anamensis and could be an indirect ancestor to Australopithicus afarensis (White, 2009). Unfortunately due to the limited number of Ardipithicus ramidus fossils and how limited the range of known dates for the species there are, it is almost impossible to know how Ardi is related to the other hominins and to modern humans.

Ardipithecus ramidus may provide a link between earlier and later hominins, but there is limited evidence.

Image: Gibbons, 2009

Citations:

Dorey F. 2015 Oct 26. Ardipithecus ramidus. Australian Museum. http://australianmuseum.net.au/ardipithecus-ramidus. Accessed 2016 Feb 19.

Gibbons A. 2009 Oct 2. A New Kind of Ancestor: Ardipithecus Unveiled. Science 326:38. JSTOR database http://www.jstor.org/stable/40328554. Accessed 2016 Jan 31.

Lovejoy CO. 2009 Oct 2. Reexamining Human Origins in Light of Ardipithecus ramidus. Science 326:74. JSTOR database http://www.jstor.org/stable/40328582. Accessed 2016 Feb 19.

White TD, Asfaw B, Beyene Y, Haile-Selassie Y, Lovejoy CO, Suwa G, Woldegabriel G. 2009 Oct 2. Ardipithecus ramidus and the Paleobiology of Early Hominids. Science 326:75–86. JSTOR database http://www.jstor.org/stable/40328583. Accessed 2016 Feb 19.

White TD, Suwa G, Asfaw B. 1994 Sept 22. Australopithecus ramidus, a new species of early hominid from Aramis, Ethiopia. Nature [Internet] 371:306–312. http://www.nature.com/nature/journal/v371/n6495/pdf/371306a0.pdf. Accessed 2016 Feb 19.