Summary and Reflection

Today I will be overviewing the position of Ardi and the entire Ardipithecus species with regards to the larger picture of human evolution. I will also be going over any question I have regarding Ardipitheucs ramidus and how research could answer some of those questions.

            Ardipithecus ramidus is an early hominin, meaning that it lived before the Australopithecines that led to modern humans. The main question that needed answering is whether or not Ardi has a direct link to human evolution, or because it has similarities to modern apes, if it led to their lineage. A study titled “Ardipithecus ramidus and the evolution of the human cranial base” looked at the basicranium of Ardipithicus ramidus and compared it to modern humans, apes, and Australopithecines. The results of the study demonstrated that Adripithecus ramidus is a human ancestor because its bacarotid breadth, 45.6%, is close to the modern human sample of ~49% and Australopithecine sample of 43.6%. The Ardipithecus sample does not overlap with the ape sample of 35-39%. This similarity, along with others makes it clear that Ardi is likely ancestral to Australopithecines.

This chart shows the results of the cranial base study

            I believe that Ardipithecus ramidus is a good species because it is very distinct from any other fossil. The anatomy of Ardi is so unique that it has its own genus, shred only with the slightly different Ardipithecus kadabba. The actual fossil in question, ARA-VP-6/500 is undoubtedly Ardipitheucs ramidus as it is one of the most compete skeletons attributed to the species and displays all of the morphological characteristics that define the ramidus species.

Many of the questions I have concerning Ardi have to do with not having enough individuals to study or the technology needed to study the fossil in ways that would answer important questions. Firstly I would like to know more specifically how Ardipithecus ramidus fits into the human lineage, and what tis direct descendent species was. More fossils would likely have to be found in order to answer this question. I also want to know what Ardipithecus ramidus evolved from. At the moment there is not definite known lineage before Ardi, which I hope will one day be known. If modern science could obtain DNA from older fossils I think we would find some very interesting and more concrete answers. Unfortunately it will likely be a long time before DNA can be extracted from older fossils, and Ardi’s DNA is most likely degraded due to time.

With every discovery in paleoanthropology many more questions are asked that cannot be answered because it is a guessing game. There is no way to know for sure if answers are true which can be frustrating. There are also usually only a handful of fossils with which scientists are asked to infer an entire species behavior from. As this is the last post on this topic I hope I have been able to provide sufficient information on how Ardipithecus ramidus lived despite the uncertainty of those answers.

An artist's representation of Ardipithecus ramidus that I think highlights it's humanity.

Bibliography:

Kimbel WH, Suwa G, Asfaw B, Rak Y, White TD. 2014. Ardipithecus ramidus and the evolution of the human cranial base. Proceedings of the National Academy of Sciences [Internet] 111:948–953. Available from: http://www.pnas.org/content/111/3/948.full 

Second Image source:

http://www.age-of-the-sage.org/evolution/ardi_human_origins.jpg

Behavioral reconstruction

Today I will be talking about the behavior of Ardipithecus ramidus, because this is a fossil and not a living animal, behavior will have to be assumed from physical characterizes of the fossil as well as environmental characterizes which I talked about in a pervious blog post. I will specifically be looking at the article: “Behavioral and phylogenetic implications of a narrow allometric study of Ardipithecus ramidus” and critically analyzing it.

The article compared the dimensions of the fossil bones of Ardi to different primates like chimpanzees, baboons, and humans. The authors of the study were hoping to find some correlation in the length on Ardi’s limbs and teeth dimensions to a living primate, which could give some insight into the behavior and lifestyle of Ardipithecus ramidus. They only compared Ardi to primates with weights close to 44.6-58.3kg, which is the estimated weight that Ardi would be if she were living today. One thing that I think would have made the study better is if the researcher had direct access to Ardi, instead they used the measurements given in the initial articles and analysis of the Ardipithecus ramidus fossil, some of which were estimated based on other lengths so they were not direct lengths.

In the discussion section of the article the authors concluded that “Body segment lengths of Ardipithecus showed greatest overlap with those of hominoids,” and not with the monkeys that they included in the study. This makes sense because Ardi is a hominin. All of the measurements were almost exactly in the middle of the chimpanzee and ape lengths and the human lengths. So far none of the findings surprised me because Ardipithecus ramidus is an intermediate hominin and possibly a stem hominin and could have bridged the gap between human’s last common ancestors with non-human apes. One thing that the study said that I do not agree with is that they concluded that Ardi was mostly a palmigrade walker and only practiced habitual bidealism. Multiple other studies about Ardipithecus ramidus’ pelvis have proven that Ardi was bipedal and but retained arboreal qualities. I think because the study only compared limb length is was limited in its analysis of the pelvis and that could be why they came to this conclusion.

Overall the forest environment in which Ardi lived in along with its arboreal and terrestrial abilities suggest that Ardipithecus ramidus would have been arboreal to gather food and may have walked upright short distances while carrying food. This also suggests that Ardi lived in groups, which would have helped them gather enough food to survive. As an intermediate hominin Ardi would have been comfortable in the trees or on the ground but unlike what the study suggests, I believe that Ardipithecus ramidus was fully bipedal, even if it was not quite as functional of an upright walker as modern humans. It is difficult to assume factors of behavior from fossils, however I think that most of the evidence points to Ardi living in at least small groups and gathering and carrying food from the trees to the ground in order to survive.

The image on the left shows how Ardipithecus ramidus may have walked, the image on the left shows and artist's reconstruction of how Ardi may have gathered food from the trees in groups.

Bibliography:

Sarmiento E, Meldrum D. 2011. Behavioral and phylogenetic implications of a narrow allometric study of Ardipithecus ramidus. HOMO - Journal of Comparative Human Biology [Internet] 62:75–108. Available from: http://uw8rw3ad9q.search.serialssolutions.com/?genre=article&issn=0018442x&title=homo - journal of comparative human biology&volume=62&issue=2&date=20110101&atitle=behavioral and phylogenetic implications of a narrow allometric study of ardipithecus ramidus&spage=75&pages=75-108&sid=ebsco:sciencedirect&aulast=sarmiento, e.e.

Image from: http://ardipithecusramidus.yolasite.com/resources/Ardipithecus_ramidus.jpg

Locomotion

This week I will be discussing the postcrania fossils and locomotion of Ardipithecus ramidus. I will also be looking at the significance of Ardi’s locomotion and what it means for human evolution. I will only be looking at one article today “The Pelvis and Femur of Ardipithecus ramidus: The Emergence of Upright Walking” by Owen Lovejoy, Gen Suwa, Linda Spurlock, Berhane Asfaw, and Tim White. I will be looking at the anatomical evidence they present as well as how they interpret it.

In order to understand the way an ancient homin moved it is absolutely critical that some part of the postcrania is recovered. Fortunately a portion of the pelvis, femur, and foot of Ardipithecus ramidus were preserved, meaning that scientists have a pretty good idea of how Ardi would have moved. Researchers found an almost complete left os coxa, a part of the right ilium, and a fragment of the distal sacrum. All of the pieces were damaged and were carefully reconstructed before they could be analyzed.

One of the biggest questions that the researchers wanted to answer was if Ardipithecus ramidus was bipedal. In order to determine this they compared the reconstructed pelvis of Ardi to modern chimpanzees and to the Australopithicus afarensis fossil “Lucy”. They found that the ilium were very broad mediolaterally and shaped a lot like the ilium of later Australopithecines and humans, however the pelvis is not as broad as Lucy’s pelvis. Something that confused scientists was that the ischium looks very ape-like. One aspect of the pelvis that is very ape-like is the long superior ischial ramus, which is actually longer than found in any known Australopithecine. Combined together with the fact that lordotic recurvature in the lower spine was also enhanced the researchers concluded that Ardipithecus ramidus was bipedal, but still retained some easy movement arborealy. The pieces of femur and foot bones that were found also indicate bipedalism, however the foot has a divergent big toe just like apes. The foot and ankle are not as flexible as ape’s feet and the wrist and hand bones of Ardi are not suited for the knuckle-walking that apes prefer.

This image shows as comparison of pelvis characteristics of Ardipithecus ramidus to other modern and ancient taxa. 

The findings of Ardipithecus ramidus are extremely significant. Not only do they prove that a hominin can be bipedal with a divergent big toe, they also tell a lot about the last common ancestor between humans and apes. Unlike what was previously thought, many of modern ape characteristics are not in fact primitive, but derived. This was determined for example “it had been thought that the lateral spiral pilaster of apes was primitive,” but the Ardipithecus ramidus’ femur shows characteristcs that looks like human’s femur and not ape’s femur as would be expected if the ape morphotype was more primitive.

While the postcrania fossils of Ardi answer a lot of questions about human evolution, they bring up just as many questions. It is still not clear exactly how much Ardipithecus ramidus used its bipedal ability, or why it evolved. While Ardi could walk upright, its physiology was not suited for walking long distances, carrying heavy loads, or running very fast. The scientists concluded that Ardi spent much of its time in the trees, but moved short distances by foot.

The information in this article is very detailed and at times hard to understand. The evidence they present seems clear and prove that Ardipithecus ramidus was undoubtedly bipedal at leas some of the time. The article was only written about on individual, which could be an outlier to the species as a whole. Until more postcrania from other individuals is compared to these findings a more accurate interpretation of the findings would be difficult. Overall I enjoyed the article and the images they provided were very helpful for understanding the complicated topic.

Join me next post when I attempt to create a behavioral reconstruction of Ardipithecus ramidus!

Picture and article from:

Lovejoy CO, Suwa G, Spurlock L, Asfaw B, White TD. 2009. The Pelvis and Femur of Ardipithecus ramidus: The Emergence of Upright Walking. Science [Internet] 326. Available from: http://science.sciencemag.org/content/326/5949/71.full

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.