Pleistocene Settlement at Creswell Crags

Creswell Crags in Derbyshire, UK, is a limestone gorge where settlements from the Pleistocene have been discovered. Although the caves were the primary shelters, there would have been man made huts made from animal skin and bones. But why did Creswell Crags prove to be an ideal site for prehistoric settlements? 

Creswell Crags Cave, Derbyshire, UK. Image Credit
hedgeduid.com

It is possible that early humans visited the Crags with the seasons in order to track herds of reindeer and horse. This was due to the herds being a vital source of food for early humans. They would have then returned to the South as the winter arrived. A stream ran nearby to the crags, water is a vital resource for humans and the herds of animals, providing a source of prey. Caves and rock overhangs would have sheltered early humans from the elements. But living in caves would have been dangerous as lions and bears also used caves as shelter. It is possible that the humans would have settled on top of the gorge's cliffs away from predators and the insects near the stream. The crags could have also been a meeting place, where information was shared and products traded. 

The settlements could be improved with simple amenities. Large rocks and post holes are found at the crags, this is evidence of primitive windbreaks being built from skins and wooden posts. Fire would have also been used for warmth and cooking. Fire also scares off animals. 

The caves are south facing, this allows for more sunlight to enter the caves. We find larger archaeological deposits in south facing caves because of this reason.

Mammoth cave painting, Roufignac, France. Image
credit mammoth.psu.edu

Many caves are found with early paintings. The purpose of cave paintings is not known. They are not believed to be decoration as the caves don’t show signs of long term habitation. Paintings are similar around the world they show mostly animals. Humans typically appear as hand stencils that were made by blowing pigment on a hand held on the wall. There are a number of theories behind the paintings; Henri Breuil interpreted the paintings as being hunting magic; meant to increase the number of animals present in the area to make hunting better. David Lewis-Williams developed the theory that suggests that the paintings were made by shamans. The shaman would enter the cave and enter a trance, then paint images of their visions.

Pleistocene Mammal Defences

Tusks:
A Mammoth could have used its tusks to defend itself like the modern day African Elephant. They would have been used to keep predators at bay; this would have made the young and oldest members of a herd particularly vulnerable as they wouldn’t have the strength or tusks to repel attack. Due to their curvature, the tusks were not suitable for stabbing at predators.

Mounted Woolly Mammoth tusk. Image credit
geoclassica.com

The tusks could also be used in the mating season. The adult males would battle each other to earn the right to breed. These animals may have also had to defend their territories from other herds. The size of the tusks may have been used as an intimidation tool, and physical contact being the final resort.


Communication:
Communication between modern day animals can be transferred onto extinct Pleistocene mammals. Mammoths may have communicated in a similar way to modern day elephants. They communicate over long distances using infrasound. This is inaudible to human hearing, which can detect sound between 20 and 20,000 hertz. However, over shorter distances they may have used louder bellows to warn of predators or to seem more threatening. This is a form of defence as the herd can escape or fight off the predator more efficiently than if it was attacked without warning.


Early humans had also developed speech in order to coordinate hunts. Without communication it is unlikely that hunts would have been so successful. It was 7 million years ago that hominids began to show signs of primitive speech, therefore by the time the Ice Age occurred, communication would have been more efficient, but not as evolved as present day speech.


Numbers:
Safety in numbers in the ice age would have been a major survival tactic. Even large animals such as Mammoths travelled in herds as a form of protection, this ensured that the young would reach an age where they are able to produce the next generation, the population would then thrive and either grow or remain constant.


Humans also survived in numbers. Cooperation between the tribe members would have ensured their survival. Food preparation, hunting and construction would have been shared between all members of the tribe, providing defence from the harsh conditions of the Ice Age as well as the predators that they share the land with.


Size:
Giant animals do not always need to be a part of a herd. The solitary Megatherium, could stand at a maximum height of six metres tall, it would have been intimidating to even a pack of Smilodon. At only 1.2 metres tall, Smilodon would have been dwarfed by Megatherium and therefore only the young and the weak would have been vulnerable. This is similar to the Mastodons and Mammoths.


Tools:
Humans developed the use of stone tools at the start of the Pleistocene, 2.5 million years ago. This included knives, spearheads and axes, all would have been used in everyday life to build shelters and hunt for food. This made humans more successful due to their coordination and range of tools.

Early humans harvesting meat, bone and skin from a mammoth. Image credit
humanorigins.si.edu

Humans also used animals as tools. The use of domesticated dogs was a key to the Homo sapiens outdoing their relatives the Neanderthals. The energy burden was now taken by the dog and not the human aiding in the taking down larger prey that essentially helped the humans to survive the harsh winters.

Mammalian and Human Evolutionary Timeline

I did some work for Peterborough Museum and looked at the evolution of mammals and then humans so I am going to do a post on a timeline of this evolution.

Mammal Evolution:
256 Ma - Wuchiapingian age, Lopingian epoch, late Permian period, Palaeozoic era:

Dimetrodon, an example of a pelycosaur. Image credit
extinctanimals.org

Shortly after the first appearance of reptiles in the Carboniferous period, two evolutionary branches split. The first branch is the Sauropsids, which later become the birds and reptiles of the modern day, the first example of the sauropsid is the Hylonomus. Synapsida is the other branch which gives rise to the mammals.

Both of these branches have temporal fenestrae (openings) behind the orbit which allows for larger jaw muscles. 

The earliest mammal-like reptiles are the pelycosaurs. These animals were the first to have temporal fenestrae. The pelycosaurs gave way to the therapsids, the direct descendants of mammals. The temporal fenestrae of therapsids are larger and more mammal-like than pelycosaurs.  

220 Ma - Norian age, Upper Triassic period, Mesozoic era:
The cynodonts were a subgroup of therapsids and bore the most mammal-like features; it's jaws for example resembled the modern jaws of mammals. It is likely that with in the cynodonts, the direct ancestor to all mammals can be found. 

Artist's impression of Juramaia sinensis alongside
skeleton. Image credit Mark A. Klingler

From Eucynodontia came the first mammals. These were very small, shrew-like animals that fed on a diet of insects. They evolved the neocortex region of the brain and so it is unique to animals.

160 Ma - Oxfordian age, Upper Jurassic period, Mesozoic era:
The earliest known mammal fossil of Juramaia sinensis comes from the Jurassic period, this is the first true mammal that we know of.

100 Ma - Cenomanian age, Upper Cretaceous, Mesozoic era:
The last common ancestor of mice and humans is found here in the Cretaceous period.

Primate Evolution:
85 to 65 Ma - Santonian to Maastrichtian age, Upper Cretaceous, Mesozoic era:
A group of small, insect eating mammals called Euarchonta evolved at the end of the late

Reconstruction of a group of Plesiadapis. Image credit
odec.ca

Cretaceous. This group would give rise to primates, treeshrews and lemurs. Plesiadapis is an animal from the subdivision primatomorpha and lived on the lower branches of trees feeding on fruits and leaves. Plesiadapiformes are very likely to contain the species that are the ancestors of the primates.

63 Ma - Danian age, Palaeocene epoch, Palaeogene period, Cenozoic era:
Primates diverge into strepsirrhini, wet nosed primates, and haplorrhini, dry nosed primates.

Strepsirrhini contains ancestors to lemurs and lorises. The haplorrhines include prosimian tarsiers, simian monkeys and apes. Haplorrhini metabolism lost the ability to make its own Vitamin C, this means that the descendants had to include fruit in their diet. 

30 Ma - Rupelian age, Oligocene epoch, Palaeogene period, Cenozoic era:
Haplorrhini splits into two; platyrrhini and Catarrhini. 

Platyrrhini are new world monkeys that had prehensile tails. It is believed that they migrated to South America, floating on a raft of vegetation is one possible hypothesis for this migration. 

25 Ma - Chattian age, Oligocene epoch, Palaeogene period, Cenozoic era:

Replica skull of Proconsul africanus. Image
credit Don Hitchcock

Catarrhini splits into two groups; old world monkeys, ceropithecoidea, and apes, hominoidea. 

The trichromatic vision had its genetic origins in this period. Proconsul africanus is a possible ancestor of great and lesser apes, including humans.

Hominidae Evolution:
15 Ma - Langhian age, Miocene epoch, Neogene period, Cenozoic era:
Hominidae ancestors speciate from the ancestors of gibbons.

13 Ma - Serravallian age, Miocene epoch, Neogene period, Cenozoic era:
Hominidae ancestors speciate from the ancestor of Orang-Utans. 

The common ancestor of the great apes and humans is believed to be Pierolapithecus catalaunicus. Like humans it had a wide, flat rib cage, a stiff lower spine, flexible wrists and shoulder blades on its back rather than its side. 

10 Ma - Tortonian age, Miocene epoch, Neogene period, Cenozoic era:
The human lineage and the genus of Pan (chimpanzees and bonobos), speciates from the ancestors of gorillas.

7 Ma - Messinian age, Miocene epoch, Neogene period, Cenozoic era:
Hominina speciate from the ancestors of the chimpanzee. 

In the first two years of life, ancestral humans and chimpanzees have a larynx that repositions itself to between the pharynx and lungs; a feature that enabled speech in humans.

3.6 Ma - Piacenzian age, Pliocene epoch, Neogene period, Cenozoic era:
Australopithecus afarensis is evidence for full time bipedalism in early hominids. this ancestor had reduced canines and molars, although still larger than modern humans.

A study of the lower vertebrate of Australopithecus afarensis suggests that in females, changes had been made so that bipedalism could be sustained throughout pregnancy.

3.5 Ma - Piacenzian age, Pliocene epoch, Neogene period, Cenozoic era:
Kenyanthropus platyops is a possible ancestor of Homo, and it emerges from the Australopithecus genus.

3 Ma - Piacenzian age, Pliocene epoch, Neogene period, Cenozoic era:
A loss of body hair takes place in Australopithecines while they evolve on the savannahs of Africa.

Homo Evolution:
2.5 Ma - Gelasian age, Pleistocene epoch, Quaternary Period, Cenozoic era:
Appearance of the genus Homo. Homo habilis and Homo ergaster lived side by side in the lower Pleistocene. The first stone tools were used here.

1.8 Ma - Calabrian age, Pleistocene epoch, Quaternary period, Cenozoic era:
Homo erectus evolves in Africa. Homo erectus resembles more modern day humans, the forehead is less sloping and the teeth are smaller.

Homo georgicus is the oldest hominid fossil outside of Africa, showing that they had the ability to travel long distances, probably following herds of animals.

The evolution of dark skin came with the loss of hair. The brain evolved to be larger and therefore tool crafting was more successful. They could then hunt bigger prey such as wild horses.

1.2 Ma - Calabrian age, Pleistocene epoch, Quaternary period, Cenozoic era:
Homo antecessor may be a common ancestor of humans and Neanderthals. Humans share 99% of their DNA with the now extinct Neanderthals.

600,000 years ago - Middle Pleistocene epoch, Quaternary period, Cenozoic era:
Homo heidelbergensis was found in Italy, it had a larger brain case and was therefore more intelligent than its ancestors, but more muscular than modern humans.

200,000 years ago - Middle Pleistocene epoch, Quaternary period, Cenozoic era:
Earliest fossils of anatomically modern humans found in Ethiopia dating back 0.2 Ma.

60,000 years ago - Upper Pleistocene epoch, Quaternary period, Cenozoic era:
Homo sapiens migrate out of Africa. Homo sapiens interbreed with the Neanderthals that they encounter.

50,000 years ago - Upper Pleistocene epoch, Quaternary period, Cenozoic era: 
Homo sapiens migrate to Southern Asia.

40,000 years ago - Upper Pleistocene epoch, Quaternary period, Cenozoic era:
Homo sapiens migrate to Australia and Europe. The European Homo sapiens known as Cro-Magnon.

25,000 years ago - Upper Pleistocene epoch, Quaternary period, Cenozoic era:
Neanderthal lineage becomes extinct.

20,000 to 10,000 years ago - Upper Pleistocene epoch, Quaternary period, Cenozoic era:
Homo floresiensis dies out, leaving Homo sapiens as the only species of Homo still surviving. Evolution of light coloured skin in Europeans took place around this time.

The Pleistocene Extinction

This extinction is not as catastrophic as the Big Five that I discussed in a separate post, but here we see a massive 73% of large mammal genera disappear from Earth's ecosystems. There are two theories that have been put forward to explain this extinction; climate change and the Prehistoric Overkill Theory. It is possible that both of these worked in tandem to push the mammals to extinction. Due to the disappearance of the megafauna there is a shift in the planet's flora, grasslands becomes woodland, this increases the number of forest fires.

Theory 1 - Climate Change: This is the more popular theory. The warming of the the climate would have melted the vast ice sheets that covered a lot of the Northern Hemisphere, the sea levels would have risen preventing the migration of mammals to southern latitudes.

A warming climate would also alter the plant life; we see a transition from grasslands and confier forests that withstood the cold of the Ice Age to deciduous woodland. The herbivorous megafauna depended on the grasslands as their primary source of food, thus when the grasses disappear the mammals have to move further North following the receeding grasslands. This explains why the last populations of mammoths are found in the Arctic Circle in Siberia.

In part this change was natural, part of the fluctuation between glacial interglacial periods that characterise Ice Ages. The change to interglacial was exacerbated by the increase in forest fires, they contribute to an increase in greenhouse gases and therefore allow for the warming of the climate.

Humans managed to survive the extinction as we had the ability to quickly adapt our lifestyles to the changing climate.

Early humans hunting a woolly mammoth. The bones and skin would be used to
make shelters and the meat would be eaten. But did early man hunt to often?
Image credit sciencemag.org

Theory 2 - Prehistoric Overkill Theory: This theory was put forward by Paul Martin of the University of Arizona. Martin noticed a chronological and casual link between the appearance of humans and the disappearance of the megafauna mammals. The theory suggests that when humans first entered areas such as North America, the megafauna did not recognise humans as a threat as they had not come into contact with humans before. This meant that hunting the large mammals was much easier initially and therefore the humans exploited this through overhunting. The loss of the megafauna is also believed to have been the reason behind the extinction of smaller species as there would have been a major ecological disruption.

This extinction event lasted for 1,000 years. In comparison to the K/T Extinction it was a very rapid event, it is believed that the extinction of the dinosaurs took close to 55,000 years from the impact of the meteorite in the Gulf of Mexico.

There is evidence to support this theory. For instance, some Mastodon bones are found with the scarring of tuberculosis. This is not seen in fossils before the appearance of humans in the area, indicating that these animals were susceptible to new diseases that humans were carrying. Also in Africa where large mammals and humans had coevolved and coexisted for millions of years, there were very few extinctions, only two out of twenty three large mammal genera went extinct.

Which theory do you think is correct? Climate change, Prehistoric Overkill or both? Let me know in the comments.