Blog( becoming human)

Found:	2001
Where:	Toros-Manalla site 266, Chad
Team leader(s):	Michel Brunet, Alain Beayvilain
Temporal range:	7 to 6 million years ago

Sahelanthropus tchadensis was described in 2002 by French paleontologist Michel Brunet and his team.  It was discovered in Chad from deposits that have been dated by biostratigraphy to between 6 and 7 million years in age.  Central Africa is an unusual place to find hominid fossils, and the conditions under which these paleontological teams work are arduous.  Their efforts are invaluable for documenting the geographic spread of hominids across the African continent.  Many fossils of other animals were recovered at the same site asSahelanthropus, suggesting that the habitat, a dry desert today, was then a lush lakeshore with extensive forests around it. 


http://www.becominghuman.org/node/sahelanthropus-tchadensis

Found:	October 2000
Where:	Tugen Hills, Kenya
Team leader(s):	Martin Pickford, Brigitte Senut
Temporal range:	6.1 to 5.8 million years ago

Orrorin tugenensis is represented by a collection of fossils from the Tugen Hills region of Kenya.  Specifically, O. tugenensis is known from four sites in this region: Cheboit, Kapsomin, Kapcheberek, and Aragai.  “Orrorin” means “original man” in the Tugen dialect, and “tugenensis” pays tribute to the Tugen Hills region.  The sediments in which this specimens have been found are dated to between 6 and 5.8 million years ago using radioisotopic methods, paleomagnetism (dating accomplished using the timing of reversals in Earth’s magnetic poles), and biochronology (dating that utilizes the relative time frames of extinct non-hominin animals).  Orrorin tugenensis is important to hominin evolution because it (along with Sahelanthropus tchadensis, from central Africa) may represent some of the earliest evidence for bipedalism in the human fossil record.
http://www.public.wsu.edu/gened/learn-modules/top_longfor/timeline/05_o_tugenensis.html

Found:	1997
Where:	Middle Awash, Ethiopia
Team leader(s):	Tim White, Gen Suwa, Yohannes Haile Selassie
Temporal range:	5.7 to 5.2 million years ago

Ardipithecus kadabba is an early hominin species recovered from sediments in the Middle Awash Valley of Ethiopia dated to between 5.2 and 5.8 million years ago.  These fossils are of particular importance because fragments from both the skull and body have been found and are argued to demonstrate some of the earliest signs of bipedalism and hominin dental morphology.  As one of the oldest species of human ancestors, Ar. kadabbahelps to push back the origin of hominins into the late Miocene Epoch (roughly 11.6 to 5.3 million years ago). 
http://dhistorika.blogspot.com/2011/11/ardipithecus-kadabba-un-chimpance.html

Found:	December 1992
Where:	Aramis,  Ethiopia
Team leader(s):	Tim White
Temporal range:	4.5 to 4.2 million years ago

Ardipithecus ramidus is a hominin species  dating to between 4.5 and 4.2 million years ago (mya) using paleomagnetic and radioisotopic dating methods. (Paleomagnetic uses periodic reversals in the Earth’s magnetic field; radioisotopic utilizes the known rate of decay of one radioisotope into another)  Importantly, Ar. ramidusrepresents the oldest species that possesses features unequivocally linked to the hominin lineage.  Thus, Ar. ramidus is the best evidence discovered thus far for the root of the hominin family tree.  Fossils of this species, found in the Middle Awash region and the site of Gona in Ethiopia, possess derived features (features different from those found in the ancestor) in the skull and teeth.  The postcranial skeleton of Ar. ramidus, however, suggests  this species had not evolved obligate bipedality ("obligate" means the skeletal anatomy limits locomotion to one means, in this case bipedality. Obligate is the oppodite of functional bibedality, possessed by Chimpamzees - Pan troglodytes - for example, who can walk upright for short distances or climb in trees).  This combination of traits is important because scientists have long considered obligate bipedality to be a defining characteristic of the hominin lineage.  The traits possessed by Ar. ramidus, however, demonstrate that hominin-like skulls and teeth evolved before obligate bipedality and suggest the earliest hominins were not obligate bipeds. 

http://berkeley.edu/news/media/releases/2004/03/04_Akadab.shtml

Found:	September 1994
Where:	Kanapoi and Allia Bay, Kenya
Team leader(s):	Meave Leakey, Alan Walker
Temporal range:	4.1 to 3.9 million years ago

Fossils attributed to Australopithecus anamensis (which means “southern ape of the lake” from “anam,” meaning “lake” in the Turkana language) have been recovered from sediments at Kanapoi and Allia Bay near Lake Turkana in Kenya.  These fossils, which have been dated to between 4.2 and 3.9 million years ago using radioisotopic dating methods applied to volcanic sediments, are significant because they represent the earliest indisputable evidence of obligate bipedality in the human fossil record.  In addition, the morphology of the skull of Au. anamensis provides a glimpse of the evolutionary changes that represent the transition from earlier, more primitive (i.e., ape-like) hominins—such as Ardipithecus ramidus—to later, more derived (i.e., human-like) species—such as Australopithecus afarensis. 
https://www.msu.edu/~heslipst/contents/ANP440/anamensis.htm