Australopithecus sediba and "missing link"

Skull of juvenile male Australopithecus sediba. Photo from National Geographic.

The announcement last week of a new hominin, Australopithecus sediba, garnered a lot of media attention and of course among the academic circle. The remains of an adult female and a juvenile male was found deposited inside a cave in Malapa, South Africa by Lee Berger and his 9 year-old son. These fossils are thought to date about 1.9 million years ago and are probably a descendant of Australopithecus africanus.

Brain scans reveals the possibility that a chunk of brain is still intact inside the brain case, along with some fossilized bugs. Google Earth was also credited for discovering these fossils. Lee Berger have been used Google Earth to map out known fossil deposits and caves. Armed with these knowledge, Berger found 500 previously unidentified fossil deposits and cave sites.

For more about A. sediba, read:

• Kambiz's post on Anthropology.net, Australopithecus sediba (UW88-50) of Malapa, South Africa.
• Jackaroo's post on Lawn Chair Anthropology, Holy Effing Crap II: Australopithecus from Malapa.
• John Hawk's post on John Hawks Weblog, What, if anything, is Australopithecus sediba?
• Scientific America: Discoverer of "Lucy" raises questions about Australopithecus sediba, the new human species from South Africa.
• Science/AAAS: Special Feature: Australopithecus sediba.

The discovery of A. sediba, along with the "Denisova hominin" and Homo floresiensis, sparked a lot of media coverage but unfortunately the lingo "missing link" seems to be almost always paired with such discoveries. One should be cautious when using the term "missing link" as most links among known fossil records are not really "missing". Our evolutionary past is not a long linear chain but more like branches coming out of a tree trunk. Remember the missing link, "Aunt Ida" (Darwinius masillae) who turned out to be just a fossil primate on the dead end of an evolutionary branch? Some of these branches indeed lead to evolutionary dead ends, so claiming that all new discoveries are "missing link" is false. For more on the etymology of the phrase "missing link", read John Hawks's "A missing etymological link" and Carl Zimmer's "Yet Another 'Missing Link'".

Algeripithecus and Azibius: Anthropoids or Strepsirhines?

The mandible of Algeripithecus. Photo from Science Daily.

The debate for the origin of anthropoid points to two locations. One hypothesis supports the notion that anthropoids originated from Africa while the other argues that anthropoids originated from Asia. The model for the African origin hypothesis rests on Algeripithecus minutus, a fossil discovered in Algeria, Africa that lived 45 million years old. Algeripithecus and Azibius are Eocene primates that lived around the same time in Africa some 50 million years ago.

Much more complete craniodental fossils of Algeripithecus and Azibius were recently excavated and reveal that they might not be anthropoids but were strepsirhines instead. New data from the fossils, according to a recently published paper by Tabuce et al. (2009), suggest that Algeripithecus and Azibius were the earliest primates to branch out of the Afro-Arabian strepsirhines clade.

According to Tabuce et al. (2009), there are anatomical evidence suggesting that Azibius were nocturnal. They also found that Algeripithecus has a long, thin and forwardly inclined lower canine alveolus, features that match the long and and flat lower canine in the tooth comb (dental comb) of crown strepsirhines. These physical characteristics suggest that both Algeripithecus and Azibius are closely related to crown strepsirhines. The researchers concluded that both Algeripithecus and Azibius were not members of the anthropoid family but instead an early representative of the crown strepsirhines. Crown strepsirhines gave rise to modern day lemurs, galagos and lorises.

Tooth comb of a ring-tailed lemur (Lemur catta). Notice the two lower canines that are long, thin and forwardly inclined. Together with four lower incisors, it makes up the tooth comb. Photo from Wikipedia.

These recently excavated fossils support the origin of crown strepsirhines from Africa. However, it also challenges the hypothesis that points to Africa as the origin of anthropoids since Algeripithecus should be classified as strepsirhines instead of anthropoids (and no longer provide evidence for the Africa origin hypothesis) according to this published paper by Tabuce et al.


References:

CNRS (Délégation Paris Michel-Ange) (2009, September 15). African Origin Of Anthropoid Primates Called Into Question With New Fossil Discovery. ScienceDaily. Retrieved September 15, 2009, from http://www.sciencedaily.com­ /releases/2009/09/090915101355.htm

Rodolphe Tabuce, Laurent Marivaux, Renaud Lebrun, Mohammed Adaci, Mustapha Bensalah, Pierre-Henri Fabre, Emmanuel Fara, Helder Gomes Rodrigues, Lionel Hautier, Jean-Jacques Jaeger, Vincent Lazzari, Fateh Mebrouk, Stéphane Peigné, Jean Sudre, Paul Tafforeau, Xavier Valentin, and Mahammed Mahboubi. Anthropoid versus strepsirhine status of the African Eocene primates Algeripithecus and Azibius: craniodental evidence. Proc R Soc B 2009 : rspb.2009.1339v1-rspb20091339.

Homo floresiensis Walked Out of Africa

Skull of LB1 (Homo floresiensis, or the hobbit). Photo from Science Museum

New analysis by a team led by Australian National University doctoral student Debbie Argue showed that Homo floresiensis, nicknamed hobbits, were early hominin and walked out of Africa to Flores. Their findings supports the argument that Homo floresiensis had a unique wrist anatomy that originated from a lineage that lived long before the common ancestor of Homo sapiens and Neanderthals.

With Mike Moorwood from University of Wollongong and Thomas Sutikna from Indonesian Center for Archaeology, Debbie Argue compared 60 skulls and skeletal features from two individual hobbits to those of hominins, chimpanzees and gorillas using cladistic analysis. The result shows that Homo floresiensis "probably took one of two evolutionary paths from Africa to Flores. One began 1.66 million years ago, the other 1.9 million years ago".

Read more here: Hobbits Walked Out of Africa

New Branch of Archaeology: Paleoanthropology Meets Primatology

A chimpanzee mother using rocks (hammer and anvil) to break open nuts, an example of tool use in primates.
Photo from Duke University.

A new branch of archaeology is being introduced by international scientists. Led by University of Calgary archaeologist Julio Mercader and 17 other co-authors of the paper "Primate archaeology", advocate a new "Paleoanthropology meets Primatology" inter-disciplinary field that seek to examine primate tool use in a long term, evolutionary context.

Read more about the article from redOrbit: International Scientists Establish New Branch Of Archaeology.

Homo Floresiensis: Hobbits of Southeast Asia

What is Homo floresiensis? This question has plagued scientists since the 2003 discovery of these hominids in the remote island of Flores, Indonesia. A few specimens, found only inside the cave of Liang Bua in Flores, were given the names LB1, LB2 and so on. Their small stature, thought to be no taller than a three-year-old human child, led to them being nicknamed “Hobbits” by scientists after J.R.R. Tolkien's tiny “Lord of The Rings” characters. Homo floresiensis is thought to have co-existed with modern humans starting from about 18,000 years ago to about 13,000 years ago -- pretty recent in geological time. What Is The Hobbit?

Height comparison between Homo sapiens sapiens and Homo floresiensis. Illustration from www.amnh.org

Cranial comparison between LB1 (Homo floresiensis) and modern human. Photo from www.bbc.co.uk

A recent article suggests that Homo floresiensis existed alongside modern humans (Homo sapiens sapiens). If Homo floresiensis were indeed contemporaneous to modern humans, then they could have been the sourceof local myths such as the “Ebu Gogo” and “Orang Pendek”. Cryptozoology and mythology aside, scientists are still debating whether Homo floresiensis is a species of its own or just a small population of Homo sapiens sapiens that suffered from cretinism.

Putting a face to the hobbit (Facial reconstruction from LB1 cranial). Photo from www.blogs.discovermagazine.com

So who really were Homo floresiensis? A species of their own or just individuals that suffered from cretinism? We still do not know.

If Homo floresiensis were indeed a species of their own, did they evolve out of Austrolopithecine, Homo erectus or even archaic Homo sapiens?

If Homo floresiensis were actually archaic Homo sapiens suffering from cretinism, how did they survive well pass adulthood and use stone tools to hunt?

Currently there is no consensus whether Homo floresiensis were a separate species or just individuals who suffered from cretinism. What do you think?