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.

Overview of Ardi

           This blog is going to be all about the fossil remains of the early hominin Ardipithecus ramidus nicknamed ‘Ardi’. In the coming weeks I am going to be exploring many aspects of this fossil species including in-depth looks at classification, locomotion, and behavior. Today I will be simply going over some basic information about Ardi that will provide an important foundation for later analysis. 

          Ardipithecus ramidus was first discovered in 1994 by paleoanthropologist Tim White at Aramis in the Middle Awash region of Ethiopia. The partial skeleton ARA-VP-6/500 known as Ardi was announced in 2009. Ardi is estimated to by 4.4 million years old, making it one of the earliest human ancestors ever discovered. Over one hundred fossil specimens of Ardipithecus ramidus have been uncovered, but the fossil known as Ardi is the only partial skeleton of its kind (Ardipithecus). Ardi is believed to be female, based on the shape of the pelvic fragments found. While the pelvis of Ardipithecus ramidus is suggestive of bipedalism, Ardi also displays a widely divergent big toe, which is similar to the toes of contemporary great apes. The pelvis and the feet taken together is suggestive of both arboreality and bipedalism which is a topic I will go more into depth about in a few weeks. The fossil was about 120 centimeters tall and 50 kilograms (Gibbons, 2009) Ardi is neither chimp-like nor human-like but instead a unique mix of both that may answer some of the most interesting questions about how modern Homo sapiens evolved.

         This is an artist's rendition of what the complete Ardipithecus ramidus skeleton might have looked like based on fossil evidence. 

Citations:

Ardipithecus ramidus. Smithsonian National Museum of Natural History

<http://humanorigins.si.edu/evidence/human-fossils/species/ardipithecus-ramidus> . Accessed 2016 Jan 31.

Gibbons A. 2009 Oct 2. A New Kind of Ancestor: Ardipithecus Unveiled. Science

326:36-40. JSTOR database <http://www.jstor.org/stable/40328554>. Accessed 2016 Jan 31.

Photo citation: 

"Ardipithecus Gesamt1" by Ori~ - Norberak egina after File:Ardipithecus Gesamt.jpg. Licensed under CC BY-SA 3.0 via Wikimedia Commons - https://commons.wikimedia.org/wiki/File:Ardipithecus_Gesamt1.jpg#/media/File:Ardipithecus_Gesamt1.jpg