11.2 Primate Systematics: Primates, Origins and Evolution Part 2 - Bent Lindow

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Origins - Formation of the Universe, Solar System, Earth and Life

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University of Copenhagen

Origins - Formation of the Universe, Solar System, Earth and Life

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The Origins course tracks the origin of all things – from the Big Bang to the origin of the Solar System and the Earth. The course follows the evolution of life on our planet through deep geological time to present life forms.

From the lesson

Primate Origins and Evolution / Human Origins and Evolution

Finally, we have come to the evolution of the primates – the group to which humans belong. Bent Lindow tells you about the evolution of primates, leading up to the early humans. Bent will also introduce you to a web-based exercise called “The Human Animal” (http://snm.ku.dk/english/school_services/human_animal/). In this exercise you will explore skulls of living as well as extinct hominids. Apart from the exercise itself the “Human animal” includes some background reading material and some interesting videos. Included is footage from the dissection of a dead chimpanzee from a Danish Zoo; do not watch this if you think it will make you uncomfortable. In order to do the exercise you need a computer with a mouse (since you need to measure distances in 3D between different parts of the skulls that you will be studying). It will not run on iPads and iPhones. Finally, Tom Gilbert will tell you about how the early modern humans (Homo sapiens) managed to colonize almost every land mass of our planet. Although many details of our own evolution still remain obscure, recent advances in genomics have given us a much better understanding of how extant humans colonized the entire planet after leaving their original home in Africa.

11.1 Primate Systematics: Primates, Origins and Evolution Part 1 - Bent Lindow9:18

11.2 Primate Systematics: Primates, Origins and Evolution Part 2 - Bent Lindow13:52

11.3 Primate Systematics: Human Evolution Assignment Part 3 - Bent Lindow3:56

11.4 Human Origins and Evolution: The Global Dispersal of Anatomically Modern Humans - Tom Gilbert7:36

11.5 Human Origins and Evolution: Leaving Africa - Tom Gilbert5:59

11.6 Human Origins and Evolution: Multiple dispersals from Africa - Tom Gilbert8:57

Meet the Instructors

Henning Haack
Associate Professor
Natural History Museum
James Connelly
Professor
Natural History Museum of Denmark
Vivi Vajda
Professor
Department of Geology, Lund University
Jon Fjeldså
Professor, Curator
Thomas Gilbert
Professor
Michael Houmark-Nielsen
Associate Professor
Natural History Museum of Denmark
Bent Erik Kramer Lindow
Curator
Natural History Museum of Denmark
Gilles Guy Roger Cuny
Associate Professor
Natural History Museum of Denmark
Ole Seberg
Associate Professor
Natural History Museum of Denmark
Gitte Petersen
Associate Professor
Natural History Museum of Denmark
Tais Wittchen Dahl
Assistant Professor of Geobiology
Arne Thorshøj Nielsen
Associate Professor
Natural History Museum of Copenhagen
Martin Vinther Sørensen
Associate Professor, Curator
Natural History Museum of Denmark
Svend Stouge
Associate Professor
Natural History Museum of Denmark
Danny Eibye Jacobsen
Associate Professor, Curator
Natural History Museum of Denmark
Jan Audun Rasmussen
Associate Professor
Natural History Museum of Denmark
Emily Catherine Pope
Assistant professor
Natural History Museum of Denmark

Welcome to the second lecture in the session on primate evolution.

In this one, we will look at the origin of primates, and review their evolution during

the last 55 million years through the lens of prehistoric global climate change.

However, the most important event paving the way for the origin of primates, took place

65 million years ago. As you may recall from a previous lecture

this was the global mass extinction, which wiped out two thirds of the species on Earth,

including the non-flying dinosaurs. Significantly, the disappearance of the dinosaurs

allowed the mammals to diversify and evolve into new ecologies and forms.

One of these mammal groups was the Plesiadapiformes, who developed an arboreal lifestyle.

The first fossils of the group turn up in deposits just after the Cretaceous/Tertiary-boundary

and the great mass extinction. Fossils indicate that the plesiadapiforms

were a very diverse group and common in North America, Europe and Asia during the geological

epochs of the Paleocene and Eocene. Systematical studies comparing their fossil

anatomy indicate that the plesiadapiforms are the sister group to primates, and thus

inform us about how the earliest primates lived and appeared.

This figure shows the origin and radiation of plesiadapiforms and primates shortly after

the K/T-mass extinction. The time of the extinction event is indicated

by a horizontal red line; various lineages are indicated by vertical lines.

The duration of these lineages in geological time are known from fossil finds of animals

which belong to them. Circled in blue are the plesiadapiforms.

As you will notice, they underwent a massive diversification with several lineages appearing

during the first 10 million years after the mass extinction; the Paleocene epoch.

The time of the origin of the primates has so far proven harder to nail down.

Molecular clock studies, which try to discover when a group originated, by comparing and

computing rates of DNA mutation, indicate that the first primates originated as far

back as 85 million years ago. This would have been during the last part

of the Cretaceous era and well before the great mass extinction.

However, no fossils referable to primates have been found which are that old and molecular

clock studies have been found to generally overestimate the age of origin of the lineages

they research. The presence of the plesiadapiforms - the

primates' sister group - indicate that they probably originated sometime within the Paleocene

epoch, but the first certain fossil remains of primates are some 55 million years old.

This is a global proxy temperature curve for the last 65 million years.

It has been constructed on the basis of delta oxygen18-values from the shells of deep sea

bottom-dwelling foraminifera from all over the planet.

The delta oxygen18-values of the shells of these single-celled organisms record the ambient

temperature of their environment, as you may recall from the previous lecture on climate

change. The origin, evolution and diversity of primates

throughout the last 55 million years were influenced by the effects of climate.

We will not go into too many details of this curve, but you will notice that on the left-hand

side of the curve that global temperatures were much higher 65 million years ago.

This was at the end of the Cretaceous period and the beginning of the Tertiary.

Continuing towards the right on the curve and towards recent times, you can observe

that there has been an overall trend towards a steady drop in global temperature.

The first event on the "curve" which we will visit, took place some 55 million years ago

at the boundary between the geological epochs of the Paleocene and Eocene.

Here, the records indicate that deep-sea temperatures may have increased between 3 and 4 degrees

centigrade in as little as 10,000 years. This event is called the Paleocene-Eocene

Thermal Maximum. The reason for the increase is most likely

massive volcanic eruptions in the nascent North Atlantic between Greenland and Norway.

The eruptions emitted large quantity of CO2 into the atmosphere, heating it, and may further

have triggered the release of methane - another effective greenhouse gas - from deepwater

methane hydrates ice on the seafloor. The cumulative effect of this on the Earth's

environment was rampant global warming. Coincident with this global warming event,

we find the first appearance of primates in the fossil record - the first time we find

their fossilized remains. Other mammal groups, such as even-toed and

odd-toed ungulates, also appeared at exactly this moment in time, almost simultaneously

in the northern continents of North America, Europe and Asia.

The mechanism under which global warming may have led to the origin of new lineages among

mammals, is not understood at the moment. A few million years after the Paleocene-Eocene

Thermal Maximum, temperatures remained high and subtropical and tropical evergreen forests

were widespread. Fossil finds indicate that this was crucial

to the primates, as these environments allowed them to diversify rapidly into several lineages,

both living and extinct. It is in the beginning of the Eocene epoch

that we find the roots of the two major divisions within the primates; the Strepsirrhini and

the Haplorrhini. Respectively, the "wet noses" and the "dry

noses" that you may recall from the previous lecture.

The suborder Strepsirrhini consists among others of the living lemurs and the lorises,

as well as the now extinct adapiforms. The other major radiation of primates in the

early Eocene was the Haplorrhini or "dry noses". This very successful group includes recent

Tarsiers, New World monkeys, and our own group, the Old World monkeys.

Fossils referable to several haplorrhine lineages appear at the very beginning of the Eocene

epoch, and the entire suborder was very diverse throughout most of the Eocene.

However, following the Early Eocene Climatic Optimum, global temperatures fell gradually,

and the climate became drier and cooler. This negatively affected the subtropical and

tropical forests, and primate diversity went into a worldwide decline.

This observation is supported by a decrease in the relative number of fossils towards

the end of the Eocene. The plesiadapiforms - their sister-group suffered

worse and became totally extinct. Some 33 million years ago, at the Eocene-Oligocene

boundary, global temperatures plunged due to the formation of the first Antarctic ice

caps. This event radically changed global marine

circulation patterns, as well as resulting in a worldwide drop in sea level.

This led to a minor mass extinction event. It also thrust the planet into the cool and

dry "icehouse" climate, which has lasted until recent times.

The following Oligocene epoch - lasting between approximately 33 and 23 million years ago

- is marked by an all-time low in the fossil record of primates.

Their natural habitats of warm, subtropical broadleaved forest were severely restrained

in the cool and dry Oligocene epoch. However, it is also during the Oligocene epoch

that we find the first evidence for the origin of the catarrhine primates - also called the

Old World monkeys. Their colloquial name stems from the reason

that all recent members live in Africa and Asia - "the Old World".

And this is the group to which we humans belong. The fossil evidence for this is the skull

of Saadanius, a fossil primate from Saudi Arabia which lived around 28 million years

ago. Saadanius displays a number of features, which

indicate it as intermediate between catharrhines and their nearest extinct relatives.

We are now in the exhibitions of the Natural History Museum of Denmark.

On the podium next to me are skeletons of various extinct and living members of the

Hominidae - the great apes. The earliest fossils of this group derive

from middle of the Miocene epoch some 12 million years ago.

Living members of the group include the orang-outans, gorillas, chimpanzees and humans.

This is an overview of the age and duration of the many extinct and extant species within

the hominines for the last 7 million years. The hominines are the subfamily within the

Great Apes to which humans belong. Each line on the figure represents the duration

in time of a separate species. Note how many different species of human relatives

that have been alive in the past - and how often near-similar species existed alongside

each other in time. The pattern of species in time, indicate that

hominine evolution was a bushy, directionless process with no overall end goal.

Notice how our species - Homo sapiens - is just one short-lived branch.

Today we are the only hominine species to survive.

This is a far cry from the situation just 150,000 years ago, where several species of

humans where alive at the same time in different parts of the world: neanderthals, erectuses,

and the diminutive Flores hominid, amongst others.

Going back in time and down at the bottom of the overview, we find the earliest representatives

of the hominines: Sahelanthropus and Orrorin. This is a cast of the skull of Sahelanthropus.

The original fossil was discovered in Chad in Central Africa and is around seven million

years old. It has a brain size of a living chimpanzee.

Interestingly, close investigation of the skull has revealed that Sahelanthropus may

in fact have walked on two legs, not four. This has to do with the position of the foramen

magnum on the skull. The foramen magnum is the hole at the base

of the skull, where the spinal cord enters the cranium.

In hominids walking on two legs, it is situated forward below the base of the skull.

In hominids walking on all fours - such as the chimpanzee - it is situated towards the

back of the skull. However, whether Sahelanthropus walked on

two legs or all fours is still greatly debated amongst palaeontologists.

Another slightly younger fossil, named Orrorin, was most likely bipedal - that is it walked

on two legs. Orrorin was discovered in Kenya and is around

6 million years old. Among the fossil bones is a thighbone, whose

shape indicates a bipedal or two-legged gait. This would indicate that bipedalism - walking

on just the hind limbs - within the hominines, is a feature that is at least 6 million years

old. Now this date is really interesting, because

it could tell us something about the evolution of our closest living relative: the chimpanzee.

Here is the skeleton of a chimpanzee. Humans share a 98.89 % overall similarity

in our DNA with chimpanzees. Molecular clock studies in general indicate

that humans and chimpanzees shared a common ancestor between 6 and 5 million years ago.

This would be the time, when our predecessors were the same species, before branching off

into two divergent evolutionary lineages. If this ancestral species was already walking

bipedally like Orrorin, this in turn would mean that the ancestors of the chimpanzees

returned back down to walking on all fours. So their four-legged gait does not represent

the original primitive condition, but rather an evolutionary redevelopment from a two-legged

stance. Back on the overview of hominine lineages,

we find two extinct species belonging to the genus Ardipithecus, who lived after Orrorin.

Both species derive from Ethiopia in east Africa, and are between 5.6 and 4.4 million

years old. A well-preserved fossil skeleton shows that

Ardipithecus was both able to walk upright, and had arms and hands well suited for grasping

and climbing. Following Ardipithecus in time are the slender

australopithecines. They were a very diverse and widespread group

of hominines, who existed in east and south Africa between 4 and 3 million years ago,

as fossils show us. It is from somewhere amongst the slender australopithecines

that the genus Homo - the human genus - originated. This is a cast of the famous fossil find "Lucy",

which was discovered in the Afar region of Ethiopia in 1974.

This 3.2 million years old skeleton showed for the first time that australopithecines

walked upright, despite having a brain size similar to a modern chimpanzee.

Several later studies of Lucy and many more australopithecines have revealed that although

they were bipedal, they also possessed highly mobile shoulder joints and fingers adapted

for climbing. Additionally, australopithecines may have

used primitive stone tools, but this is currently debated.

Now, Lucy is an adult female; this is the skull of a male Australopithecus.

There was a large degree of size difference between the sexes, with males being as much

as 50% larger than females. As mentioned before, the human lineage originated

from one of the species of Australopithecus. A number of events took place at this point,

such as radical changes in diet; tool use and the taming of fire.

This is something, which you will investigate on your own, in the next video assignment.

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