15. Hominin Evolution - Trends in Fossil Record Flashcards
What is a Hominin?
Group consisting of modern humans, extinct human species and all our immediate ancestors
(including members of the genera Homo, Australopithecus, Paranthropus, and Ardipithecus)
Bipedal
What is a Hominid?
- Group consisting of all modern and extinct Great Apes
- orangutans, gorillas, chimpanzees, bonobos. hominins
- quadrupeds
What is a Great Ape?
- any of several large primates closely related to humans
- orangutans, gorillas, chimpanzees, bonobos
What is a Hominoid?
Encompass an even larger biological group
(includes all hominins, all hominids, and includes lesser apes like siamangs and gibbons)
Relationship between Hominids, Hominoids and Hominins
Essentially, all hominids are hominoids, and all hominins are hominids
The words sound very similar and can be confusing, but it is important to use them correctly so people know which group you are referring to
What are Prosimians?
Prosimians are primitive primates that are smaller in size
- Lemurs, lorises, pottos and Tarsiers
What are Anthropoids?
Anthropoids, (including monkeys and apes) have a fully opposable thumb, in which the tip of all four fingers can touch the thumb
Prosimians and Anthropoids in a Phylogenetic Tree.
What is an Old World monkey?
Old World monkeys (Africa and Asia)
- Probably evolved first
- Lack a prehensile tail
- Nostrils that open downward
What is a New World monkey?
New World monkeys
- Have a prehensile tail able to grasp or hold objects
- Nostrils that are wide open and farther apart
What are Apes?
Apes (hominoids)
– lack a tail
– have relatively long arms and short legs
– have relatively larger brains with respect to body size
– more flexible behaviour
What is Paleoanthropology?
Paleoanthropology is the study of human origins and evolution, the brief history since the divergence of human and chimpanzee lineages
List the four main genera of the hominin lineage (order these genera from oldest to most recent)
- Ardipithecus: This genus includes species like Ardipithecus ramidus, which lived around 4.4 million years ago. Ardipithecus represents some of the earliest hominin-like characteristics.
- Australopithecus: This genus includes famous species like Australopithecus afarensis (such as the famous “Lucy” specimen) and Australopithecus africanus. They lived between around 4 to 2 million years ago and exhibited more advanced bipedal locomotion.
- Paranthropus: Paranthropus species, such as Paranthropus robustus and Paranthropus boisei, existed roughly between 2.7 to 1.2 million years ago. They are known for their robust cranial and dental features, indicating adaptation to a specialized diet.
- Homo: The Homo genus includes modern humans (Homo sapiens) as well as various extinct species such as Homo erectus, Homo habilis, Homo neanderthalensis (Neanderthals), and more. Homo species have increasingly sophisticated tools, more complex cultures, and larger brain sizes. They have been around for roughly 2 million years to the present day.
Differences Between Paranthropus and Australopithecus (SKULL)
Differences Between Paranthropus and Australopithecus (DENTITION)
What are the Trends in hominin development in the Skull? (6)
- Increase in cranial capacity
- Decrease in prominence of brow ridges
- Decrease in sagittal crest
- Prognathism has decreased over time
- Positioning of foramen magnum from posterior towards the base of skull
- Upright posture permitted many kinds of changes
What Trends in “Increase in cranial capacity” occurred?
– Cubic capacity of the braincase
– Cranial capacity increased from 600-800 cm3 to 1200-1400 cm3 over the past two million years
What Trends in
“Decrease in prominence of brow ridges”
occurred?
(4)
- Also known as supraorbital ridge
- Brow ridges did not seem to serve any mechanical function – instead, they were possibly a social signal, a sign of strength and dominance
- for some hominin species, a prominent brow ridge was likely a desirable trait in a mate)
- As time passed, the need to assert dominance became less important and the need to empathize and communicate with others become more important – which may explain why the heavy brow ridges of our ancestors have morphed into the loft foreheads of today
What Trends in
“Decrease in sagittal crest”
occurred?
- AKA the cranial crest
- Ridge of bone running lengthwise along the midline of the top of skull to which jaw and chewing muscles attach
- indication of strong jaw
- Reduced canine size also evolved early in the hominin lineage, although early hominin canines were larger and more pointed than those of later hominins
What Trends in
“Prognathism has decreased over time”
occurred?
- Refers to extension or protrusion of lower jaw beyond the place of the face
- Linked to a reduction in the size of teeth and chewing muscles, as well as changes to masticatory load (reflecting a reduced need for the production of powerful bite forces)
- These changes may reflect dietary shifts in human evolution away from tough-skinned fruits and fibrous plant matter toward more softer or cooked foods and consumption of meat
What Trends in the
“Positioning of foramen magnum”
occurred?
- Foramen magnum refers to hole in base of skull through which spinal cord passes
- Upright posture tied to where foramen magnum is situated
What changes has Upright posture permitted?
(7)
- Hands were free – tools, weapons, food gathering
- Walking/running on two legs – travel great
distances - Visibility of surroundings was greater
- Pelvis changed from a long-form (in apes) to a short robust form (in humans)
- Curvature of spine developed
- Birth canal became more narrow
- Upright posture helps to dissipate excess body heat and reduces the absorption of heat from the sun because less skin has direct exposure to ultraviolet radiation during the hottest times of day
What benefits does Bipedalism give?
(5)
- Walking/running on two legs – travel great distances
- walk greater distances because less energy is expended with their longer strides
- Useful for scavenging for food throughout vast areas
- Over many generations, early hominin legs grew longer and much stronger than their arms
- Their feet became longer and developed arches for more efficient support of their bodies
How has the change in Pelvis Shape Benefited the Skeletal Body? (4)
- Pelvis changed from long form (in apes) to short robust form (inhumans)
- Longer ape pelvis adapted for quadrupedal locomotion
- This adaptation made pelvis more stable for weight support when standing upright
- A shorter, bowl-shaped pelvis helps bring gluteal muscles around to the side of body to help with bipedal locomotion
How has the change in Spinal Shape Benefitted the Skeletal Body? (3)
- The curvature of spine developed
- S-shaped curve to provide support and balance for the upright biped as weight of the chest sits almost directly above the joint between spine and pelvis, rather than further forward
- This improves both balances and it absorbs the shock of walking
Memorize the following important timelines from the phylogenetic trees covered in the lecture:
- Last Common Ancestor that humans had with chimpanzees lived about 6 million to 7 million years ago
- Earliest primates evolved about 50-55 mya
