Toumaï: shaking our conceptions on the earliest steps of hominid history.
Fossil remains have been discovered in the occidental part of the Djurab
desert, North Chad, in the Toros-Menalla region.
 The
amazing fossil material discovered by the M.P.F.T. (a nearly complete cranium,
two lower jaw fragments and three isolated teeth), and described by Michel
Brunet and his colleagues in the last issue of the journal Nature, is assigned
to a new hominid, new genus new species, nicknamed Toumaï . In the Djurab
desert, babies born before the dry season are named Toumaï. This name has been
suggested as a vernacular name for the new hominid by the highest Chadian
authorities, it means "hope of life" in Goran language.
The Mission Paléoanthropologique Franco Tchadienne (Professor Michel Brunet,
Dr.), a scientific collaboration between the University of Poitiers, the
University of N'Djamena and the Centre National d'Appui à la Recherche (C.N.A.R.,
N'Djamena) includes forty scientists from ten countries. The M.P.F.T. leads an
international and interdisciplinary research program on early hominid origin and
environments.
 In
this vast desert, searching and finding first the fossiliferous level and then
the small-sized fossil remains, never abundant in the hominid case, is a long
and hard task requiring significant geological knowledge, appropriate
methodologies and a lot of perseverance. This scientific adventure started about
twenty years ago when two members of M.P.F.T., Michel Brunet and David Pilbeam,
begun field excavation in Cameroon.
The new hominid displays a unique combination of primitive and derived
characters suggesting a close relationship to the last common ancestor between
Humans and Chimpanzees suggesting him as a likely ancestor of all later
hominids.
 The
new hominid, recovered from the late Miocene of Toros-Menalla (Djurab desert,
northern Chad), is associated with a fauna the evolutionary level of which
indicates a biochronological age close to 7 million years ago. The fauna is
composed of aquatic and amphibious vertebrates, and also species inhabiting
gallery forest, wooded savanna and grassland. Sedimentological data are in
agreement with this mosaic of environments, showing a vegetated perilacustrine
belt between lake and desert.
The geographic location of Toumaï, 2500 km west of the Rift Valley, and his
great antiquity suggest an early pan African distribution of hominids (at least
from 6 million years ago) and an earlier chimpanzee-human divergence (at least
as early as 7 million years ago) than previously indicated by most of the
molecular studies.
The Toros-Menalla fossiliferous area has been discovered by the M.P.F.T. in
1997. More than 300 fossil vertebrates localities are already known from this
area. One of them, TM 266, has yielded the new fossil hominid remains.
 Ahounta
Djimdoumalbaye, undergraduate Life Science student at the University of
N'Djamena, the best M.P.F.T. fossil hunter, found the new hominid cranium on
July the 19th, 2001. Ahounta has found half of the six fossil hominid remains
(one cranium, two lower jaw fragments, three isolated teeth) discovered by the
M.P.F.T. from July 2001 to February 2002.
Ahounta Djimdoumalbaye is also specialized in finding micro-vertebrates. In
N'Djamena he leads the effort to wash, screen and sort sediment to recover small
mammal fossils, notably minute teeth of size less than one millimeter
(especially rodents).
The Hominids are represented by a nearly complete cranium, two lower jaw
fragments, and three isolated teeth (one upper central incisor, one lower canine
and one upper third molar) belonging at least to five individuals of the new
species.
 The
new hominid is associated with more than 700 vertebrate remains assigned to 42
species including 24 primitive mammals: carnivores, elephants, three-toed
horses, giraffes, antelopes, hippopotamus, anthracotheriids (close relative of
the hippopotamids), a very large wild boar (Nyanzachoerus), rodents, monkeys,
etc…
What does Toumaï look like?
Taking into consideration the skull alone, the new hominid is probably close
to the size of a common chimpanzee (Pan troglodytes). Toumaï doesn't look like
a chimpanzee, neither a gorilla nor the more recent fossil hominids currently
described.
Because limb morphology is still
unknown, it is not yet possible
to infer reliably whether or not Toumaï was a habitual biped.
Nevertheless, such adaptation could be acquired by Toumaï given the skull’s
basicranial and facial similarities to later true bipedal fossil
hominids.Toumaï displays several distinctive features which clearly relate him
to the human lineage: small canines with apical wear, non-honing C-P3 complex,
enamel thickness of cheek teeth intermediate between Pan and Australopithecus,
reduced sub-nasal prognathism, no canine diastema, thick and continuous brow
ridge, long and narrow horizontally oriented basicranium.
A new genus, a new species?
Toumaï displays a unique mosaic of primitive and derived characters
distinguishing him from both great apes (chimpanzee, gorilla) and other fossil
hominid genera (Homo, Kenyanthropus, Australopithecus, Paranthropus,
Ardipithecus and Orrorin).
Studies in progress (isotopic analyses of dental enamel, micro and meso tooth
wear analyses) will allow more precise definition of the environment and the
ecological habits of the new hominid.
Background
The first early hominid, Australopithecus africanus Dart, 1925 had
been recovered in South Africa.
Then, discoveries occurred only in South and East Africa where new
Australopithecine species have been described. These species are dated from 4.1
to 2.5 Myrs and were living in wooded savanna environments. Coming after, the
robust Australopithecines (Paranthropus), larger, more robust and adapted
to open environments hominids, are known from 2.6 to 1.3 Myrs.
This particular geographic distribution, and the fact that the oldest early
hominid was East African, led some authors to suggest an Eastern-African-savanna
hominid origin. (East Side Story, Coppens 1982).
Older hominids, associated with wooded environment faunas, have been
successively discovered in Ethiopia: Ardipithecus ramidus (4.4 - 5.8 Myrs),
and in Kenya: Orrorin tugenensis (ca. 6 Myrs).
In the eighties, Michel Brunet (University of Poitiers) and David Pilbeam
(Harvard University) started research west of the Rift Valley, initially in
Cameroon.
Set up and headed by Michel Brunet, the M.P.F.T. (Mission
Paléoanthropologique Franco-Tchadienne) conducted, from January 1994, an
international, interdisciplinary research program in North Tchad (Djurab
Desert). Two major discoveries arose:
Abel, Australopithecus bahrelghazali Brunet et al, 1996 (3-3,5
Myrs), the first Australopithecine west of the Rift Valley (2500 km);
Toumaï, Brunet et al, 2002 , the oldest known hominid (ca. 7 Ma).
These discoveries strongly shake our conceptions on the earliest steps of
hominid history.
Implications of the find
The Hominids (all representatives of the human lineage) share a common
ancestor with the Chimpanzees, their sister group.
Toumaï displays a unique combination of facial, dental (canine) and
basicranial characters that clearly supports closer relationships with the human
lineage than with Chimpanzees or Gorillas.
His great antiquity (around 7 Myrs) and all his anatomic characters
together suggest a close relationship to the last common ancestor between Humans and
Chimpanzees. This implies a probable earlier chimpanzee-human divergence (at
least as early as 7 millions years ago) than previously indicated by most of the
molecular studies.
Toumaï's canines are more primitive than in Ardipithecus (4.4 - 5.8 Myrs) of
whom he could be the ancestor.
Comparisons with Orrorin (6 Myrs) are difficult because of the fragmentary
condition of the available cranio-dental material of the latter. However,
Orrorin and Toumaï are quite distinct, with the upper canine of the former being more
similar to those of a female chimpanzee.
Toumaï, the earliest known hominid, could be considered as the ancestor of
all later hominids, i.e. as the ancestor of the human lineage.
More Information:
Contact Laurence Paoli
E-mail: lpaoli@free.fr
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