"Long before it's in the papers"
June 05, 2013

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Oldest nearly complete primate fossil reported

June 5, 2013
Courtesy of Northern Illinois University
and World Science staff

Sci­en­tists say they have found the old­est known nearly com­plete ske­l­e­ton of a pri­mate—an an­i­mal an­ces­tral to peo­ple, apes and mon­keys.

The fos­sil of the ti­ny tree-dweller dates back an es­ti­mat­ed 55 mil­lion years, to the so-called Eo­cene Ep­och, and was found in Hu­bei Prov­ince in cen­tral Chi­na. This adds to grow­ing evi­dence that pri­mates ori­gin­ated in Asia, sci­ent­ists said.

An artist's con­cep­tion of what Arch­i­ce­bus achil­les might have looked like. (Cred­it: Mat Sev­er­son, North­ern Il­li­nois U.)


“This is the old­est pri­mate ske­l­e­ton of this qual­ity and com­pleteness ev­er dis­cov­ered and one of the most prim­i­tive pri­mate fos­sils ev­er doc­u­ment­ed,” said North­ern Il­li­nois Uni­vers­ity an­thro­po­l­o­gist Dan Ge­bo, a mem­ber of the re­search team. “The or­i­gin of pri­mates sets the first mile­stone for all pri­mate lin­eages, in­clud­ing that of hu­man­ity. 

“Although sci­en­tists have found pri­mate teeth, jaws, oc­ca­sion­ally skulls or a few limb bones from this time pe­ri­od, none of this ev­i­dence is as com­plete as this,” Gebo added. “With com­pleteness comes more in­forma­t­ion and bet­ter ev­i­dence for the adap­tive and ev­o­lu­tion­ary themes con­cern­ing pri­mate ev­o­lu­tion. It takes guess­ing out of the game.”

Pri­ma­tes com­prise two sub­groups, or sub­or­ders, called pro­simi­ans (lemurs, lor­ises, and tar­siers) and an­thropoids (mon­keys, apes, and peo­ple).

The re­search team, led by Xi­jun Ni of the In­sti­tute of Ver­te­brate Pa­le­on­tol­ogy and Paleo­an­thro­po­l­ogy at the Chin­ese Acad­e­my of Sci­ences in Bei­jing, de­scribes the fos­sil in the June 6 edi­tion of the jour­nal Na­ture.

Ni said that while do­ing field­work years ago in Hu­bei Prov­ince, he first came across the fos­sil, which had been found by a lo­cal farm­er and was lat­er do­nat­ed to his in­sti­tute. The fos­sil was en­cased with­in a rock and dis­cov­ered af­ter the rock was split open, yield­ing fos­sils and im­pres­sions of the pri­mate on each side of the two halves.

Fossil of Arch­i­ce­bus achil­les. (Pho­to Cre­dit: Xijun Ni, Inst. of Ver­te­brate Pale­on­tology & Paleo­anthro­pology, Chi­nese Aca­demy of Sci­ences)


It was dis­cov­ered in a quar­ry that had once been a lake and is known for pro­duc­ing an­cient fish and bird fos­sils from the Eo­cene. The quar­ry is near Jing­zhou, south of the Yang­tze Riv­er, and about 270 km south­west of Wu­han, the pro­vin­cial cap­i­tal.

“This re­gion would have been a large se­ries of lakes, sur­rounded by lush trop­i­cal forests dur­ing the early Eo­cene,” Ni said. “This new pri­mate was very small and would have weighed less than an ounce. It had slen­der limbs and a long tail, would have been an ex­cel­lent ar­bor­e­al [tree] leap­er, ac­tive dur­ing the day­time, and mainly fed on in­sects.” 

The fos­sil has been named Arc­hi­ce­bus achil­les. Arc­hi­ce­bus roughly means “first long-tailed mon­key,” and achil­les is an al­lu­sion to its in­ter­est­ing heel anat­o­my and to the myth­o­lo­g­i­cal Greek war­ri­or, for whom the Achil­les ten­don is named.

Archice­bus marks the first time that we have a rea­sonably com­plete pic­ture of a pri­mate close to the di­ver­gence be­tween tar­siers and an­thropoids,” which in­clude peo­ple, Ni said. “It rep­re­sents a big step for­ward in our ef­forts to chart the course of the ear­li­est phases of pri­mate and hu­man ev­o­lu­tion.”

Artist's illustration of the ske­le­ton of Arch­i­ce­bus achil­les. Dark­ened parts re­pre­sent the known ele­ments. (Cred­it: Mat Sev­er­son, North­ern Il­li­nois U.)


Arc­hi­ce­bus has an un­usu­al blend of fea­tures nev­er seen in this com­bina­t­ion be­fore, mak­ing it hard for the sci­en­tists to in­ter­pret, they added. Their study of the fos­sil in­cluded a detailed 3D re­con­struc­tion, aided by high-tech scan­ning of the sam­ple.

Archice­bus dif­fers radic­ally from any oth­er pri­mate, liv­ing or fos­sil, known,” said co-author Chris­topher Beard of the Car­negie Mu­seum of Na­tural His­tory in Pitts­burgh. “It looks like an odd hy­brid with the feet of a small mon­key, the arms, legs and teeth of a very prim­i­tive pri­mate, and a prim­i­tive skull bear­ing sur­pris­ingly small eyes. It will force us to re­write how the an­thropoid line­age evolved.”

The most un­usu­al as­pect of Arc­hi­ce­bus is its feet, Gebo added.

“We see typ­i­cal ro­bust grasp­ing big toes, long toes and nailed dig­its of prim­i­tive ar­bor­e­al pri­mates, but we al­so have rath­er mon­key-looking heel bones and mon­key-like long metatarsals, of­ten viewed as ad­vanced fea­tures that you would not nor­mally find in a prim­i­tive early Eo­cene fos­sil pri­mate.

“We have in­ter­preted this new com­bina­t­ion of fea­tures as ev­i­dence that this fos­sil is quite prim­i­tive and its un­ique ana­tom­i­cal com­bina­t­ion is a link be­tween the tar­si­er and mon­key-ape branches of dry-nosed pri­mates,” he said. “This new view sug­gests that the ad­vanced foot fea­tures of an­thropoids... are in fact prim­i­tive for the en­tire line­age of dry-nosed pri­mates.”

Gebo said prim­i­tive pri­mate fos­sils have been dis­cov­ered on sev­eral con­ti­nents, in­clud­ing North Amer­i­ca, but he be­lieves Arc­hi­ce­bus and oth­er an­cient fos­sils point to Asia as the con­ti­nent where pri­mates or­i­ginated.

“In the past, many sci­en­tists be­lieved that Af­ri­ca was the con­ti­nent of or­i­gin for all pri­mates, but it ap­pears over the last dec­ade that Asia is the more likely con­ti­nent of or­i­gin, and this new ske­l­e­ton sup­ports that view,” Gebo said.


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Scientists are reporting the discovery of the oldest known nearly complete skeleton of a primate—an animal ancestral to people, apes and monkeys. The fossil of the tiny, tree-dwelling primate dates back an estimated 55 million years, to the so-called Eocene Epoch, and was found in Hubei Province in central China. “This is the oldest primate skeleton of this quality and completeness ever discovered and one of the most primitive primate fossils ever documented,” said Northern Illinois University anthropologist Dan Gebo, a member of the research team. “The origin of primates sets the first milestone for all primate lineages, including that of humanity. “Although scientists have found primate teeth, jaws, occasionally skulls or a few limb bones from this time period, none of this evidence is as complete as this,” Gebo added. “With completeness comes more information and better evidence for the adaptive and evolutionary themes concerning primate evolution. It takes guessing out of the game.” Primates comprise two subgroups, or suborders, called prosimians (lemurs, lorises, and tarsiers) and anthropoids (monkeys, apes, and people). The research team, led by Xijun Ni of the Institute of Vertebrate Paleontology and Paleoanthropology at the Chinese Academy of Sciences in Beijing, describes the fossil in the June 6 edition of the journal Nature. Ni said that while doing fieldwork years ago in Hubei Province, he first came across the fossil, which had been found by a local farmer and was later donated to his institute. The fossil was encased within a rock and discovered after the rock was split open, yielding fossils and impressions of the primate on each side of the two halves. It was discovered in a quarry that had once been a lake and is known for producing ancient fish and bird fossils from the Eocene. The quarry is near Jingzhou City, south of the Yangtze River, and about 270 km southwest of Wuhan City, the provincial capital. “This region would have been a large series of lakes, surrounded by lush tropical forests during the early Eocene,” Ni said. “This new primate was very small and would have weighed less than an ounce. It had slender limbs and a long tail, would have been an excellent arboreal [tree] leaper, active during the daytime, and mainly fed on insects.” The fossil has been named Archicebus achilles. Archicebus roughly means “first long-tailed monkey,” and achilles is an allusion to its interesting heel anatomy and to the mythological Greek warrior, for whom the Achilles tendon is named. “Archicebus marks the first time that we have a reasonably complete picture of a primate close to the divergence between tarsiers and anthropoids,” which include people, Ni said. “It represents a big step forward in our efforts to chart the course of the earliest phases of primate and human evolution.” Archicebus has an unusual blend of anatomical features that has never been viewed in this combination before, making it challenging for the scientists to interpret, they added. Their study of the fossil included a three-dimensional, high-resolution reconstruction, aided by high-tech scanning of the sample at the European Synchrotron Radiation Facility. “Archicebus differs radically from any other primate, living or fossil, known to science,” Beard said. “It looks like an odd hybrid with the feet of a small monkey, the arms, legs and teeth of a very primitive primate, and a primitive skull bearing surprisingly small eyes. It will force us to rewrite how the anthropoid lineage evolved.” The most unusual aspect of Archicebus is its foot anatomy, Gebo added. “There’s an odd combination of foot features,” he said. “We see typical robust grasping big toes, long toes and nailed digits of primitive arboreal primates, but we also have rather monkey-looking heel bones and monkey-like long metatarsals, often viewed as advanced features that you would not normally find in a primitive early Eocene fossil primate. “We have interpreted this new combination of features as evidence that this fossil is quite primitive and its unique anatomical combination is a link between the tarsier and monkey-ape branches of dry-nosed primates,” he said. “This new view suggests that the advanced foot features of anthropoids (monkeys and apes) are in fact primitive for the entire lineage of dry-nosed primates.” Gebo said primitive primate fossils have been discovered on several continents, including North America, but he believes Archicebus and other ancient fossils point to Asia as the continent where primates originated. “In the past, many scientists believed that Africa was the continent of origin for all primates, but it appears over the last decade that Asia is the more likely continent of origin, and this new skeleton supports that view,” Gebo said.