Fossil dating and context

In this blog post I will be addressing the time period when Ardi lived as well as its habitat. Knowing the age of the fossil is extremely useful in figuring out how Ardi relates to the rest of the hominins and to modern humans. Knowing the environment in which it lived is very important in discovering its locomotion and how it lived in its society.

Most scientists today agree that Ardipithecus ramidus is dated to have lived around 4.4 million years ago, however that was not always the case. Dr. John Kappelman and Dr. John G. Fleagle had an issue with the initial date published, 4.387± 0.031mya. Their argument said that because this date was only taken from stratigraphic markers and was assumed to be the maximum age of the Ardi fossil, there is not enough data to make this assumption. They said that Ardipithecus ramidus should be dated at between 3.89 and 4.39 million years ago. However, further research with argon dating and paleomagnetic data prove that the fossil is dated 4.388±0.053mya, which is very similar to the initial date of 4.387±0.031mya. In my opinion it is better to be challenged and do more research to clarify the date of a fossil than to assume to date based on one piece of evidence (Kappelman).

Past and present.

Ardipithecus's woodland was more like Kenya's Kibwezi Forest (left) than Aramis today (Gibbons).

Ardipithecus ramidus was found in Aramis, Ethiopia, which today is a dry grassland with a few sparse trees. However, the landscape was very different in when Ardi lived there. Research based on fossil bones of other animals found near the Ardipithecus ramidus site showed an abundance of birds as small mammals living around Ardi. The 29 species of birds include parrots and peafowl (Louchart). The presence of peafowl is important because modern peafowl live in open forests and indicates that Ardipithecus ramidus “was close to or in [a] forest, with watercourses” (Pickford). Another study used carbon-isotope techniques of the teeth of five individuals, which showed that “Ar. ramidus ate mostly woodland, rather than grassland, plants” (Gibbons). All of this evidence combines into a picture of Ardi living in a forest instead of a savannah or grassland.

An artist reconstruction of what Ardipithecus ramidus may have looked like in its natural habitat (Matternes).

Before scientists looked at the area around Ardipithecus ramidus and actually studied the fossils, they assumed that bipedalism evolved in a grassland. I think that it was very presumptuous of scientists to think that without any evidence. I am glad that with the discovery of Ardi has come a new, better, understanding of the environment in which humans evolved.

Gibbons A. 2009. Habitat for Humanity. Science [Internet] 326:40. Available from: http://science.sciencemag.org/content/326/5949/40.full

Kappelman J, Fleagle JG. 1995. Age of early hominids. Nature [Internet] 376:558–559. Available from: http://search.proquest.com/docview/204469195?accountid=11667

Louchart A, Wesselman H, Blumenschine RJ, Hlusko LJ, Njau JK, Black MT, Asnake M, White TD. 2009. Taphonomic, Avian, and Small-Vertebrate Indicators of Ardipithecus ramidus Habitat. Science [Internet] 326:66. Available from: http://www.jstor.org/stable/40328574

Matternes J. 2009. Standing Tall. Society for Science & the Public. Available from: https://www.sciencenews.org/article/evolutions-bad-girl

Pickford M, Senut B, Mourer-Chauviré C. 2004. Early Pliocene Tragulidae and peafowls in the Rift Valley, Kenya: evidence for rainforest in East Africa. Comptes Rendus Palevol 3:179–189.

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