Ard i Overviewn

8/10/2019 Ard i Overviewn

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ARDIPITHECUS RAMIDUS

Ardihttp://dsc.discovery.com/tv/ardipithecus/handbook2/handbook2.html

Discovery

The Middle Awash region of northeastern Ethiopia is located in the Horn of Africa. Named for the AwashRiver that runs through it, the Middle Awash is part of a unique geological feature, the Afar Depression, avast desert with active volcanoes and maor fissures and fractures of the earth!s crust. "t is one of thehottest places on Earth. The area is unique #ecause of its geolog$%%tectonic activit$ here has createdspecial conditions in which la&e and river sediments repeatedl$ trap and #ur$ remains or plants andanimals. Millions of $ears later, the ancient sediments are uplifted to the surface #$ faulting and e'posed#$ erosion. As the$ erode, the now%petrified remains the$ hold spill out. These petrified remains var$ inage, and the oldest in the stud$ area are more than ( million $ears old. Ancient stone artifacts are alsofound here, #ut so far, never in roc&s older than ).* million $ears old.

+aleoanthropologists have #een wor&ing in this region of Ethiopia for nearl$ - $ears. The first earl$hominid s&eleton found here was the famous fossil nic&named !uc$! #$ its discoverers in /01. !uc$!was found in 2.) million%$ear%old sediments in the Hadar stud$ area. The new Ardipithecus s&eleton is

much older, . million $ears old, from the Middle Awash stud$ area, a#out 1* &ilometers south of the!uc$! find.

The Middle Awash proect team wor&ed for 2 $ears to e'cavate the !Ardi! s&eleton at a place calledAramis in the Afar Rift of Ethiopia. The recover$ effort involved man$ do3ens of scientists from aroundthe world.

4hen the s&eleton recover$ effort finall$ ended in /001, the team had recovered more than /)* pieces ofone individual % a . million%$ear%old female, the oldest hominid s&eleton $et found.

"t #elonged to a new creature that the scientists classified as Ardipithecus ramidus. The name comes fromthe Afar language, in honor of the local people who toda$ live in the Middle Awash. Ardipithecus means

567ground ape568 and ramidus means 567root568.

"n addition to the discover$ of Ardipithecus, the team recovered more than (,--- additional identifia#leanimal fossils from the Aramis area, along with /2*,--- other fragments of #one and tooth. +lant remainsand other paleoenvironmental clues li&e land snails allow the team to loo& #ac& into !Ardi569s! .million%$ear%old world.

Ardi Revealed

A fossil has much more value if it can #e accuratel$ dated. To understand the sequence of humanevolution, it is crucial to &now when each species appeared, how fast it evolved, and when it disappeared.At Aramis, scientists &new the$ were wal&ing on sediments older than the :uc$; fossils. dated at 2.) million $ears ago?, andmatched animals from other sites that were dated to more than four million $ears ago.

Argon%argon dating. o far, no one has figured out how to directl$ date the fossili3ed #ones and teeth asold as those at Aramis. o the proect geologists and geochronologists much rel$ on la$ers of volcanic ash


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to :#rac&et; the age of fossil%#earing sediments. $ounger? and #elow >older?. Argon%Argon dating is the technique the$ use to measure elapsed time sincethe eruption that produced the volcanic ash or lava.

4hen volcanoes erupt ash or lava flows that cover the landscape, the argon gas contained in the moltenmaterial is #oiled off #ecause of the intense heat of the eruption. After the ash or lava cools, the

radioactive component of the element potassium deca$s at a &nown rate >called a half life? to form argongas. The gas remains trapped in the roc& or minerals. Beologists sample the volcanic roc&s, ta&e them tothe la# where the$ are melted with a laser to e'tract the argon gas, and then use a mass spectrometer tomeasure the amount of argon gas trapped inside. "f the argon gas is not a contaminant, the more gas thereis, the older the roc&.

At Aramis, geologists sampled the two volcanic la$ers that sandwiched the sediments with the :Ardi;fossils and esta#lished precise dates for the volcanic la$ersC ./0 >#elow? and ./( >a#ove million$ears.

Tephrachemistr$An$ volcano!s magma cham#er contains a unique mi' of chemicals. Each time it erupts, the ash that

settles on the surrounding landscape >sometimes thousands of miles awa$, depending on the si3e of theash cloud and the wind direction? contains the same diagnostic geochemical fingerprint. Thesegeochemical fingerprints allow scientists to match outcrops of volcanic ash at each fossil localit$scattered across the modern eroding landscape. nce a volcanic ash is characteri3ed, it is dated >ifpossi#le? #$ the Argon%Argon method >see a#ove?. 4ith a date esta#lished for an$ one outcrop of thevolcanic hori3on, all the scientists have to do to determine the age of the volcanic roc&s the$ find is matchthe fingerprint to ma&e the correlation. thepartial hominid s&eleton is fossil num#er ARA%F+%(G*--, the five%hundredth catalogued fossil from thatpatch called Aramis ocalit$ (?. ther plant and animal fossils were found in the same hori3on as the

s&eleton.


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Ardis skeleton

The s&eleton includes man$ important #ones of the hands, feet, lim#s, and pelvis. Most of the s&ull withits teeth was preserved, #ut it had #een #ro&en and scattered #efore #urial. These fossil #ones offer &e$insights into how !Ardi! was #uilt, and how she moved. !Ardis! s&eleton demonstrates that she was acreature capa#le of #oth wal&ing upright and clam#ering through trees with a grasping #ig toe, in a wa$unli&e an$ other creature &nown to science.

The s&ull and teeth. ArdiJs little%worn third molar suggests that she was a $oung adult when she died. Her#rain was small, a#out the si3e of a chimpan3eeJs. Her canine was the smallest of her species, so itJsli&el$ that she was a female. The male and female canines were much smaller and differentl$ shaped thanthose in an$ living or fossil ape. And the construction and chemical composition of the teeth show thatthe$ ate foods availa#le in a woodland ha#itat rather than those found in savannas.

The pelvis. Even though #adl$ damaged, the pelvis offers much insight into how :Ardi; moved. Most ofits more important characters are reasona#l$ well%preserved. ome of its muscle attachments and shape inthe upper pelvis are more li&e those of an upright wal&ing human than of a &nuc&leKwal&ing chimpan3ee,#ut the lower pelvis is more primitive than &nown from an$ &nown true hominids >li&e :uc$;?. Amongthe most interesting contrasts are the differences #etween the upper pelvis >the ilium? and the lower pelvis

>particularl$ the ischium?. The upper pelvis indicates a su#stantial adaptation to upright wal&ing. Thelower pelvis shows retention of attachment sites for large muscles used in clim#ing. These would havemade the lower lim# quite massive and would have limited ArdiJs speed and agilit$ when on the ground @#ut this is one the evolutionar$ trade%offs that the species made to #e a #iped who retained significantclim#ing a#ilit$.

The hand. The Ardi s&eleton preserves almost all of the hand #ones. The #ones in the palm of her handare short, #ut her finger #ones are long. This is neither an ape hand nor a human hand, #ut somethingunique. Her wrist #ones show that she did NT wal& on her &nuc&les li&e chimps and gorillas. The$ alsoshow that her hand could #e placed in a variet$ of positions that would have made clim#ing relativel$eas$ for her.

The foot. The foot #ones reveal that Ardi had a foot with a D"FERBENT Australopithecus afarensis?, and has man$ surprising anatomical elements %% grasping feet adaptedto tree clam#ering, small canine teeth in #oth males and females, and a pelvis adapted to an earl$ mode


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upright wal&ing.O Her hands lac& an$ of the adaptations that distinguish living apes, and show that !Ardi!was NT a &nuc&le%wal&er, and was an animal not specificall$ li&e living chimpan3ees. himpan3ees areour closest "F"NB relatives, #ut the$ have also #een EFF"NB%%ust in a different direction%%for thesame si'%to ten million $ears since the A we shared with them.

Human +h$logen$. Ardi! is onl$ one individual from the genus and species Ardipithecus ramidus. At .million $ears old, Ardipithecus ramidus is one of the earliest hominid species.


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ver time some hominid species lineages went e'tinct. #viousl$, ours persisted until toda$. Iossils fromEthiopia, had, and Pen$a, show that there were #ipedal hominids living in eastern Africa as earl$ as (million $ears ago. These have each #een given a different genus name, #ut the$ ma$ all #elong toArdipithecus. nl$ more complete fossils will allow scientists to understand how man$ species linesthese fossils represent.

The evolution of #ipedal wal&ing is now #etter understood #ecause of the evidence from Ardipithecus.These fossils suggest that this #ipedal hominid was also well%adapted for slow and careful clam#ering andclim#ing in the trees. ver time, however, hominids lost their tree clim#ing a#ilities.

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