List of Transitional Fossils - Human Evolution

Human Evolution

Further information: Timeline of human evolution
The Human Evolutionary Series
Appearance Taxa Relationships Status Description Image
36-32 Ma

Genus

  • Apidium
The oldest primitive monkey known in the fossil record, dating back before the split between Old and New world monkeys. Basal to both Old and New world monkeys. Primitive traits
  • Smaller canines than later monkeys such as Parapithecus
  • Retains some post-cranial characters seen in prosimians

Derived traits

  • Fused mandibular symphysis
  • Scapula similar to modern squirrel monkeys
  • Low rounded molar cusps rather than high cusps as is seen in tarsiers and strepsirrhine
33 Ma

Genus

  • Aegyptopithecus
A Miocene monkey which bridges the gap between the Eocene ancestors of Old world monkeys and Miocene ancestor of Hominoidae. Tentatively positioned transitional form prior to the Old world monkey/ape split. Primitive traits
  • Retained auditory features similar to Old world monkeys
  • Incapable of true brachiation unlike extant apes
  • Reduced capitular tail, but was proportionally smaller than Apidium

Derived traits

  • Ape-like teeth including broad, flat incisors and sexually dimorphic canines
  • A low sagittal keel and strong temporalis muscles
  • Increased size in the visual cortex
27-14 Ma

Genus

  • Proconsul
This primate has very ape-like features like its teeth, but much of its post-cranial remains are more similar to monkeys. Universally accepted to be intermediate between 'ape-like monkeys' such as Aegyptopithecus and later apes including hominids. Primitive traits
  • Monkey-like wrist
  • Narrow, monkey-like illium

Derived traits

  • Completely lacked a fully formed tail
  • 5-Y pattern on lower molar cusps as also seen in hominoids
13 Ma

Genus:

  • Pierolapithecus
A European ape which is considered to be the predecessor of the great apes. Some objections have been raised to this fossils status due to its location in Spain, but Pierolapithecus is likely a transitional taxon between generalized apes and the lineage which led to great apes. Pleisomorphic traits
  • Relatively short fingers and walked in a similar quadrupedal fashion like baboons
  • Lacks adaptations for both gibbon-style brachaition as well as derived knuckle-walking like in chimpanzee's and gorilla's

Derived traits

  • Flat, wider rib cage like great apes for tree-climbing
  • The clavicle is large and similar to modern chimps suggesting a dorsally positioned scapula
4.4 Ma

Genus:

  • Ardipithecus
A woodland hominid adapted to quadruped arboreal locamotion, but also for bipedalism. Intermediate between the last common ancestor of chimps and humans, and the australopithecines. Primitive traits
  • Brains smaller than later hominids ranging from about 300-350 cc
  • Foot thumb is not retracted into the foot as a 'big toe'
  • Phalanges are more heavily curved than in Australopithecus

Derived traits

  • Reduced size in canines, however still retained dimorphic characters
  • Hind leg dominant, bipedal locomotion while walking, however were quadrupedal while climbing trees
4.4-2.0 Ma

Genus:

  • Australopithecus
First known genus of fully bipedal apes which are probably ancestral to robust australopiths and the genus Homo Intermediate between extinct quadrupedal and bipedal apes. While the relationship between some species are being revised, Australopithecus afarensis is considered to be, by most experts, the ancestor to all later hominids. Primitive traits
  • Some species retain a sagittal crest
  • Curved phalanges, indicating semi-arboreal lifestyle
  • Semisectorial premolar is present
  • Prognathic face to varying degrees

Derived traits

  • Fully bipedal as indicated by many features including the knee joint, hips, lumbar curve in the spine, position of the foramen magnum, and feet
  • Increase in brain size ranging from about 375-500 cc
  • Development of a parabolic jaw
2.5-1.5 Ma

Species:

  • Homo habilis
An early human which is the morphological link between australopithecines and later human species. Perfect intermediate between early hominids and later humans, possibly ancestral to modern humans. Primitive traits
  • Pronounced brow ridge
  • Foramen magnum is not positioned as anteriorly like in modern humans, giving a slightly semi-erect appearance
  • Although reduced in size the teeth are still fairly large

Derived traits

  • Increase brain size ranging from 510-800 cc
  • Face is slightly prognathic, but at a much steeper angle
  • Bulge in the Broca area, possibly the first hominid to use rudimentary speech
  • Associated with the first use of stone tools
2.0-1.0 Ma

Species:

  • Homo erectus
Very successful hominid, which was probably ancestral to both modern humans and neanderthals. Probably the first hominid to leave and successfully colonize territories outside of Africa. Ancestral to modern humans and neanderthals. Primitive traits
  • Still retains a heavy brow ridge and nuchal torus
  • Lacked the complexity of modern human language, but does show increase in the Broca area
  • Thicker bones and larger teeth than modern humans

Derived traits

  • Rounder and larger brain (about 900-1100 cc) than H. habilis
  • Face is orthognathic compared to H. habilis
  • Probably lived in bands and was an active group hunter
  • Associated with advanced stone tools and possibly the first hominid to use and produce fire
500 Ka-recent

Species

  • 'Archaic' sapiens
Archaic sapiens were the immediate ancestors of modern humans which evidently displaced the neanderthals in Europe and the island 'hobbits' of southeast Asia. 'Archaic' H. sapiens evolved from Homo erectus about half a million years ago but still retains some primitive characteristics such as relatively thick bones and molars larger than modern humans. Ancestral to modern humans. Primitive traits
  • Large teeth
  • Heavy brow ridge
  • Extremely robust build in most groups

Derived traits

  • Rounder, less broad based cranium
  • Larger brain size, approaching (and sometimes exceeding) modern values

Read more about this topic:  List Of Transitional Fossils

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