Skull shocker: a 7-million-year-old skull has scientists asking "who is it?" (Earth/life science: fossils/hominids).When it lived, the creature was probably just another small flat-faced animal dwelling on the wooded shore of a giant lake. But now--7 million years after death--its remains are shaking the human family tree clear to the roots. A skull, discovered last year in the Djurab Desert of Chad, Africa, is arguably the most momentous fossil (remains preserved as rock) find of the past 75 years. Michel Brunet Michel Brunet stands for:
Any member of the zoological family Hominidae (order Primates), which consists of the great apes (orangutans, gorillas, chimpanzees, and bonobos) as well as human beings. ," he says. A hominid is a member of the family that includes modern humans (Homo sapiens Homo sapiens (Latin; “wise man”) Species to which all modern human beings belong. The oldest known fossil remains date to c. 120,000 years ago—or much earlier (c. ) and their extinct ancestors and cousins, but not apes. Scientists classify humans in the primate order, along with 200 species of monkeys and apes (see chart, p. 17). Modern humans' unique features include their upright walk, spoken language, advanced use of tools and fire, small canine teeth, and level of intelligence. "Human ancestors are recognizable because they have a few of these features, in particular upright posture and small canines," says Harvard University Harvard University, mainly at Cambridge, Mass., including Harvard College, the oldest American college. Harvard College Harvard College, originally for men, was founded in 1636 with a grant from the General Court of the Massachusetts Bay Colony. paleontologist David Pilbeam David Pilbeam is the Henry Ford II Professor of the Social Sciences at Harvard University and curator of paleoanthropology at the Peabody Museum of Archaeology and Ethnology. He is a member of the National Academy of Sciences. He received his Ph.D. from Yale University. . To determine if the skull belonged to a hominid, Brunet's team obsessed ob·sess v. ob·sessed, ob·sess·ing, ob·sess·es v.tr. To preoccupy the mind of excessively. v.intr. over its every detail (see diagram, p. 16). Because the skull resembled no known species, the discoverers classified it in a new genus and species, naming it Sahelanthropus tchadensis Sahelanthropus tchadensis is a fossil ape. Originally classified as the oldest possible member of the human family tree, the species has been more recently identified as a Miocene ape related to humans and other living African apes. S. . But the fossil is nicknamed Toumai, meaning "hope of life" in a Chadian language. A few scientists say Toumai might be an ancient ape. But Brunet holds his ground: "I'm completely confident this is a hominid." And many who have examined the skull support Brunet's hypothesis (testable scientific explanation). "Most scientists agree that Toumai is a hominid," says Pilbeam. But one factor could silence skeptics: Proof of bipedalism--the ability to walk upright, a key hominid trait. A pelvis or thigh bone (Anat.) the femur. See also: Thigh would be the best proof. But for now the skull offers a tantalizing tan·ta·lize tr.v. tan·ta·lized, tan·ta·liz·ing, tan·ta·liz·es To excite (another) by exposing something desirable while keeping it out of reach. piece of evidence: The position of the spinal-cord opening (foramen magnum foramen mag·num n. See great foramen. Foramen magnum The opening at the base of the skull, through which the spinal cord and the brainstem pass. ) in the skull's base resembles that of skulls belonging to known bipedal bipedal adjective Capable of locomotion on 2 feet species. At 7 million years old, Toumai is 3.5 million years older than Australopithecus afarensis Noun 1. Australopithecus afarensis - fossils found in Ethiopia; from 3.5 to 4 million years ago Australopithecus, genus Australopithecus - extinct genus of African hominid , a family of small, long-armed upright walkers discovered in 1972 in the eastern African nation of Tanzania. A. afarensis was the earliest known human ancestor until 1992. Since then, a series of early hominid fossil discoveries have thrust back the fossil record beyond 4 million years ago. A handful of 6-million-year-old fossils vied for the title of oldest hominid--until Toumai was found. WAKE-UP CALL Fossil hunters discovered Toumai thousands of miles from the Rift Valley in eastern Africa, where previous hominid fossil troves led scientists to assume they might ultimately discover the oldest human ancestor (see map, above left). "In hindsight, we should have expected this," Harvard paleontologist Daniel Lieberman told The New York New York, state, United States New York, Middle Atlantic state of the United States. It is bordered by Vermont, Massachusetts, Connecticut, and the Atlantic Ocean (E), New Jersey and Pennsylvania (S), Lakes Erie and Ontario and the Canadian province of Times. "We weren't looking at all of Africa. This fossil is a wake-up call." In the Djurab Desert, ceaseless wind moves the dunes and exposes new fossils, says Brunet. After sifting sand there for a decade, his team amassed a hoard of 10,000 fossils, dating from 3 to 7 million years ago and representing 42 animal species. They would have preferred to find the bones sandwiched between layers of volcanic ash, which naturally contain the elements potassium and argon argon (är`gŏn) [Gr.,=inert], gaseous chemical element; symbol Ar; at. no. 18; at. wt. 39.948; m.p. −189.2°C;; b.p. −185.7°C;; density 1.784 grams per liter at STP; valence 0. . These minerals can be radiometrically dated because they decompose de·com·pose v. de·com·posed, de·com·pos·ing, de·com·pos·es v.tr. 1. To separate into components or basic elements. 2. To cause to rot. v.intr. 1. at a measurable rate and serve as an accurate historical clock. Luckily, scientists could tell a lot about Toumai's age by studying nearby fossils: The specimens included extinct relatives of elephants and pigs. French paleontologist Patrick Vignaud at the University of Poitiers The University of Poitiers (French: Université de Poitiers) is a university located in Poitiers, France. History Founded in 1431 by Pope Eugene IV and chartered by King Charles VII, the University of Poitiers was originally composed of five faculties: theology, compared them with nearly identical specimens found and radiometrically dated in eastern Africa, where volcanic ash is plentiful. This comparison helped him estimate Toumai's age at nearly 7 million years old. FAMILY TREE Toumai now reigns as the oldest known hominid, but that doesn't mean it was the first. "It will never be possible to know precisely where or when the first hominid species originated," Brunet says. The hominid fossil record now includes thousands of specimens, representing as many as 18 species over 7 million years of history, says Pilbeam. "If you pack all the fossils nearly in boxes and stack them, they'd fill quite a large building." How do those species relate to each other? Scientists are busy connecting the dots. Anthropologists think modern humans first appeared around 100,000 years ago in Africa and spread throughout the world. Today, Homo sapiens is the only living hominid species. "In some parts of Europe and Asia, they lived alongside the humanlike species Homo neanderthalensis, or Neanderthal," Pilbeam says. Neanderthals went extinct 30,000 years ago. "But they were a population that appears to have no genetic link to living humans." Could the same be true of Toumai? It's too soon to tell. Says Pilbeam: "Prior to 4 million years ago, the hominid fossil record is thin. Toumai is exciting because it offers a glimpse at one of the earliest chapters." IT'S YOUR CHOICE Choose the correct answer to these questions: 1 What is the genus and species of the new skull? A Sahelanthropus tchadensis C Homo sapiens B Homo neanderthalensis D Australapithecus afarensis 2 Which is a defining feature of bipedal animals? A use of fire C use of tools B use of language D two-legged upright walking 3 Which statement best explains how scientists classified Toumai? A They compared the skull with other fossilized mammals they found near it. B They compared Toumai's anatomical features with the skulls of other primate species. C They compared the skull's teeth to other primates' teeth. D They examined the fossil with a radiometric-dating machine. 4 Which of the following would help scientists accurately identify Toumai as bipedal? A a pelvis C a nearly complete skeleton B a thigh bone D all of the above ANSWERS IN TEACHER'S EDITION APE OR HOMINID: SIX POINTS OF COMPARISON How scientists classified the new fossil 1 SKULL The skull's size suggests Sahelanthropus was no larger than a chimpanzee chimpanzee, an ape, genus Pan, of the equatorial forests of central and W Africa. The common chimpanzee, Pan troglodytes, lives N of the Congo River. Full-grown animals of this species are up to 5 ft (1. . 2 BRAIN The creature's brain was about the size of a modern chimp's. 3 BROW RIDGE This 18-millimeter-thick brow ridge is thicker than any modern male ape's brow ridge. Modern humans don't have a prominent brow ridge, but early members of the genus Homo did. 4 FACE The face is short and flat. By comparison, the lower part of a chimp's face juts forward to hold its large canines, The lower part of a modern human's face is even smaller and flatter. 5 TEETH Canines are smaller and shorter than a chimp's. Tooth enamel is thicker than a chimp's, which suggests a diet with less fruit. 6 FORAMEN MAGNUM The opening at the base of the skull The base of the skull (lat. basis cranii) is the most inferior area of the skull. Structures Structures found at the base of the skull are for example:
[ILLUSTRATIONS OMITTED]
HOW SCIENTISTS CLASSIFY PRIMATES
Scientists place humans, gorillas, and chimpanzees (along
with 200 other ape and monkey species) in the primate order.
TOUMAI MODERN MODERN MODERN
HUMAN CHIMPANZEE GORILLA
KINGDOM ANIMALIA ANIMALIA ANIMALIA ANIMALIA
PHYLUM CHORDATA CHORDATA CHORDATA CHORDATA
CLASS MAMMALIA MAMMALIA MAMMALIA MAMMALIA
ORDER PRIMATES PRIMATES PRIMATES PRIMATES
FAMILY HOMINIDAE HOMINIDAE PONGIDAE PONGIDAE
GENUS SAHELANTHROPUS HOMO PAN GORILLA
SPECIES TCHADENSIS SAPIENS TROGLODYTES GORILLA
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