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Chapter 13

Chapter 13- From Hominin to Homo.docx

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1Chapter 13 From Hominin to Homoabout 18 ma a new creature called Homo ergaster appearedovery similar to humans in that these developed slowly and infants must have been helpless at birtholarge robust bodies with long legs and short armscommitted to life on groundoprobably learned to master fire and to hunt large gameohave smaller brains that humans do and their subsistence technology seems to have been much less flexible than oursHominins of the Lower Pleistocene Homo ergasterPleistocene epoch began 18 mya and saw a cooling of worlds climateodivided Pleistocene into three parts Lower Middle and Upperlower18 myasharp cooling of worlds climatemiddlesharply increased fluctuations in temperature and first appearance of immense continental glaciers that covered northern Europe 900 kyaupperended about 12 kya when a warm interglacial phase of world climate beganHomo ergaster appears in African fossil record about 18 mya and disappears 06 myaofossils found in Ethiopia Tanzania Kenya and South Africaomost paleontologists assigned these African fossils to the species Homo erectus but a growing number of paleontologists have come to believe that African specimens have become too distinctonew name given was Homo ergaster or work manHomo ergaster appeared in Eurasia about the same time it was first known from AfricaoHomo ergasterwas the first hominin to make its way out of Africaknow this because there was a discovery of a lower jaw and Oldowan tools in sediments dated to 11 or 18 mya in Georgian at archeological site Dmnaisialso uncovered two nearly complete crania at Dmnaisi that are very similar to African specimens of H ergaster and dated around 17 myaH ergaster migrated out of Africa to Eurasia about 17 mya taking their tools with themMorphologydiffer from those of both earlier hominins and modernskulls of H ergasterhumans12oretain many of characteristics of earlier hominins marked narrowing behind eyes receding forehead no chinoalso show many derived traits some of which are shared by modern humanssmallerless prognathic face a higher skull and smaller jaws and teethoalso has some derived traits not shared by humanshorizontal ridge at back of skull occipital toruslarge brow ridgesoderived traits are probably related to dietbetter adapted for tearing and biting with canines and incisorsless suited for heavy chewing with molarsteeth are smaller than australopithecines and paranthropines but molars are reduced relatively more in comparison with incisorsohas substantially larger brain than earlier homininsaverage brain volume was about 800 cc larger than brains of earlier apelike hominins 500700 ccolarger body than earlier homininsPostcranial skeleton of H ergaster is much more similar to skeleton of modern humans that to that of earlier hominins but it still differs from ours in interesting waysofound skeleton where fossils of Australopithecus anamensis Paranthropus aethiopicus and Kenyanthropus platyops were also foundskeleton of the H ergaster was named KNMWT 15000oKNMWT 15000 had same body proportions as people who live in tropical savannas today long legs narrow hips and narrow shouldersalso had short arms compared with earlier homininsquite tall and also robust and heavily muscledinfants probably matured slowly and were dependent on their mothers for a long period of timemothers birth canal was same as it is in modern humanssexual dimorphism was reducedmales were about 20 to 30 larger than females making them less dimorphic than apelike hominins and only slightly more dimorphic than modern humansmay not have had spoken languagevertebral canal in thoracic region of back is larger in modern humans than in apes and it contains proportionally thicker spinal cordstudies show that extra nerves that enlarge spinal cord innervate muscles of rib cage and diaphragmothe KNMWT 15000 probably had less precise control over muscle of his rib cage and diaphragmwas first hominin that could run for long distancesmay be useful in longdistance scavenging and hunting in open country2
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