Mammoth Extinction

The extinction of the Pleistocene megafauna is a heavily debated topic, was it over hunting by man or was it climate change? We now have the answer thanks to the University of Adelaide.

By analysing ancient DNA, using radiocarbon dating and other geologic analysis methods, the University of Adelaide has shown that short rapid warming events, known as interstadials, experienced during the past ice age at the end of the Pleistocene coincided with major extinction events even before man became dominant.

Professor Alan Cooper says that "abrupt warming had a profound impact on climate that caused marked shifts in global rainfall and vegetation patterns". It was therefore sudden warming not extreme cold that killed the Woolly Mammoths in Eurasia.

However, Professor Chris Turney believes that "man still played an important role in the disappearance of megafauna".

The culminating factors of rapid warming and the constant pursuit of man pushed the Mammoth's over the edge as they were already under extreme stress with a lack of tundra shrubs and grasses available as the ice retreated further north, this would have lowered reproduction success and limited the sizes of the herds as the food could not support the animals.

Let me know what you think of this, do you think the Mammoth's extinction was a result of the rapid warming of the climate or did early man hunt the Mammoths to the point of extinction?

http://www.sciencedaily.com/releases/2015/07/150723181113.htm?utm_source=feedburner&utm_medium=email&utm_campaign=Feed%3A+sciencedaily%2Ffossils_ruins%2Fpaleontology+%28Paleontology+News+--+ScienceDaily%29

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.

The Fossilisation Process

When a land dwelling vertebrate dies its carcass is commonly disarticulated, this means its limbs are removed, often by predators and scavengers alike. Most of the decomposition of the organic material is done by bacteria that will feast on the rotting flesh that remains on the bones. Some bones are completely stripped clean of flesh and bleached in the sun. Others might be carried off or gnawed by rodents. Sometimes, disarticulated remains are trampled and scattered by herds of animals.


Sooner or later the bones are either destroyed or buried. If they aren’t digested their destruction can come from weathering; this is when the minerals in the bone begin to break down and the bones disintegrate. But the weathering can be stopped by rapid burial, it’s at this point fossils are formed. A body fossil is part of an organism that is buried and a trace fossil is an impression left behind in the ground by the organism.


Bone is made out of calcium-sodium hydroxyl apatite, this mineral weathers easily, this means that the mineral is no longer present once a bone becomes fossilised. This mineralogy can remain intact if the bone doe not come into contact with any fluids during its burial, something that is extremely rare.

It is possible to find tissues of extinct animals. Since bones are porous, the spaces once occupied by blood vessels and nerves fill up with minerals. This is called permineralisation.

Fossil of Archaeopteryx. Image credit Humboldt
Museum Fur Naturkunde Berlin

Pristine fossils can be found in geological lagerstatte, feathers of dinosaurs are known from these lagerstatte. Most famously the early bird Archaeopteryx is known from the Solnhofen lagerstatte in Germany.

Ammonite shells are originally made of aragonite, this is unstable so when fossilisation begins the aragonite becomes the more stable calcite. This calcite creates a cast of the shell and this is what we find today.

Woolly Mammoths and Woolly Rhinos have been discovered mummified in the permafrost in Siberia and Alaska. Soft tissue of a Tyrannosaurus Rex has even been found which allowed palaeontologists to see that the animal was female, within the fossil, red blood cells and connective tissues were found.

Natural mummies have been found in a variety of locations around the world; bog deposits or tar pits, deep inside caves, glacier ice and in the permafrost of Alaska and Siberia. A Woolly Rhinoceros was found mummified after it was covered in salty ground water that essentially pickled the carcass, preventing bacteria and microorganisms digesting the flesh by altering the pH of the environment which means that microorganisms cannot survive in these acidic conditions.

Mummified dinosaurs have been found, good examples of these mummies come from Brachylophosaurus and Edmontosaurus. Leonardo, the Brachylophosaurus that features in the palaeoart post, had skin impressions, muscle impressions that showed an excess of tissue around the neck, even parasites are found on Leonardo.


The permafrost is also effective as the low temperature prevents the bacteria from respiring by removing any moisture on the carcass through freezing. However, once the mummy is excavated the bacteria become active and decomposition begins.

Buttercup the Mammoth

Natural mummies have been found in a variety of locations around the world; bog deposits or tar pits, deep inside caves, glacier ice and in the permafrost of Alaska and Siberia. A Woolly Rhinoceros was found mummified after it was covered in salty ground water that essentially pickled the carcass, preventing bacteria and microorganisms digesting the flesh by altering the pH of the environment which means that microorganisms cannot survive in these acidic conditions.


The permafrost is also effective as the low temperature prevents the bacteria from respiring by removing any moisture on the carcass through freezing. However, once the mummy is excavated the bacteria become active and decomposition begins.


In May 2013, scientists from the Siberian North-eastern Federal University took an expedition to Maly Lyakhovsky, an island in the far north of Siberia, whilst acting on information that there was a Mammoth in the permafrost. Indeed they did find two tusks exposed and as they excavated the animal they found that it also had three legs intact, most of the body and part of the head and trunk was still attached as well.

Buttercup the Mammoth mummy. Image credit techentice.com

During the excavation, the carcass released a dark red liquid. The carcass still had fresh blood inside it, this was unique as mummies have only yielded dry specks of blood containing no complete DNA.


The researchers took the Mammoth, nicknamed Buttercup, to Yakutsk where a group of experts were to study the specimen for three days before the find was refrozen to prevent rotting. Carbon dating shows that the Mammoth lived around 40,000 years ago, tests on the animal’s teeth reveals that it died between the age of 50 and 60.


Faeces and bacteria in the lower intestines of the animal, reveal a diet of ice age grasses, buttercups and dandelions. Tooth marks on the Mammoth’s bones enabled the scientists to determine how she died, she was eaten alive by predators after becoming trapped in the peat bog that had assisted in her mummification.


More blood was found in the Mammoth’s elbow, analysis of this blood showed that the cells were broken, but some still contained haemoglobin, the protein that carries oxygen within the red blood cell. Unlike humans, the Mammoths had evolved haemoglobin that was more resistant to freezing temperatures.

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.

Coping With the Cold of the Ice Age

In cold climates, plant material is rather scarce. It is usually limited to grasses, low lying shrubs and coniferous forests. Woolly Mammoths would have survived on eating mainly grasses. This is evident from the adaptation of its teeth; the enamel ridges were not suited to grinding twigs and leaves. To access this grass, the Mammoth would have had to clear snow away. Palaeontologists know that Mammoths did this because tusks have been found with a small patch of smoothed ivory on the underside that would have been closest to the ground. The tusk would have been smoothed by the constant abrasion against the ground.

Reconstruction of Woolly Mammoth herd. Image credit news.chicago.edu

In contrast to the Mammoth’s ridged teeth, the Mastodon displays a different adaptation. As the Mastodon lived in more southern regions of North America there were more deciduous trees to feed on, therefore the Mastodon has more conical teeth to deal with the grinding of twigs and leaves.


The fur of animals such as the Woolly Mammoth and Coelodonta were specially adapted to cope with the freezing temperature of the ice age. The coat consisted of two layers; the outer layer was a coarse layer that would protect the second layer. The hair on the outer layer was between 30 centimetres long and 90 centimetres long depending on where about on the body it came from. The denser inner layer was much shorter at only 8 centimetres long; it was this wool that provided the greatest amount of insulation for the animals. It is believed that the Mammoth had sebaceous glands under its skin which would secrete oils onto the hair to make it greasy; this would provide yet more insulation for the Mammoth.


As discussed before, it is necessary for an animal such as the Mammoth to have a small surface are to volume ratio in order to preserve heat. This is the reason behind the size of its ears and tail. By shortening these, the Mammoth is able to reduce its surface area to volume ratio, therefore there is less surface to heat to be lost to the external environment. African elephants have larger ears so they can increase their surface area to volume ratio which allows them to lose more heat during the day. Also by minimising the size of its tail and ears, the Mammoth is able to prevent frostbite.


The Woolly Mammoth also had very wide and flat feet. This was to increase the animal’s grip on the snow and ice. Polar bears have the same adaptation; acting like snow shoes they spread the weight of the animal over a larger area, providing more stability than a smaller foot.

Smilodon Hunting

The prehistoric predator, Smilodon, was an apex predator in North and South America. The animal would have hunted large prey such as bison, camels, horses, ground sloths and mammoths. Isotopic studies of dire wolf and American lion bones show that there is an overlap in prey with the Smilodon; this suggests that they were competitors.


It is believed that Smilodon was an ambush predator, concealing itself in the vegetation. Then, using its massive body strength it would wrestle its prey to the ground.


Smilodon’s hunting has been compared to its closest relatives, the big cats that still roam Africa and Asia. Lions and tigers have smaller canines than Smilodon, a mere 3.5 inches compared to a massive 8 inches, but they are still able to bring down prey that is six times larger than itself. The lion would use its claws and teeth to pull itself up until they can get to the throat. They would then clamp down on the throat.


A lion’s bite force is relatively mild and so a lions choke hold rarely punctures the skin. Scientists have assumed that they are simply strangling their victims. However, Dr Frank Mendel believes that they squeeze vital arteries that feed the brain, causing the prey to pass out in 3 to 5 seconds. A lion would then apply a kind of sleeper hold on its prey which must be sustained for five minutes, depriving the brain of oxygen rendering it brain dead; the prey will therefore not fight back. This poses a problem for lions as the scent of a fresh kill will attract other predators, including crocodiles and hyenas.


The Smilodon bite force is even less than that of a lion and due to a greater number of scavengers and larger prey, a five minute choke hold seems unlikely. The fossil record has produced evidence that shows the massive 8 inch canines could have easily broken in a struggle or if they were to hit bone.


In an experiment, Mendel recreates the jaws and bite-force of a Smilodon and mounts it on an articulator. He then uses the carcass of a cow to demonstrate how the Smilodon could have used its canines.


The first theory is that Smilodon would have given a bite to the abdomen; there are no ribs here, only the abdominal wall so the canines wouldn’t be damaged. The gape of a Smilodon is approximately 110º, but this still only leaves 3 inches of clearance between the mandible and the tip of the canine. The mandible is able to gather a mouthful of skin but the canines do not make contact with the carcass. Therefore this is not a plausible hypothesis.


Mendel’s hypothesis is that the Smilodon would puncture the neck rather than the abdomen. The gape easily clears the neck. The canines also puncture the neck with ease, leaving big holes. To gain further evidence that the prey would be killed quickly, Mendel opened up the throat to examine the damage.

Several arteries were damaged, indicating that the animal would have been killed in seconds. This shows that Smilodon was able to kill its prey quicker than modern day big cats.

A pack of saber toothed cats attack a young Columbian Mammoth. Art by Mauricio Anton

This artist’s impression of a pack of Smilodon hunting a juvenile Columbian Mammoth is rather accurate. It shows the Smilodon in the foreground, pinning the calf to the ground and using its canines to puncture the throat. Other impressions show Smilodon biting the hide or limbs of its prey. This would not have occurred during a hunt as damage would have been sustained to the canines.


The belief that Smilodon was a social animal is further supported by the discovery of Smilodon fossils with healed injuries; this would suggest that individuals depended on others to provide food while it was injured. Also juvenile Smilodon had smaller canines which have led palaeontologists to believe that they would have been fed after a kill until they could participate in the hunt itself.

Mammalian Dentition

Diagrams of the three types of
mammalian teeth. Image credit Pearson
Education Inc.

The teeth of a carnivore consist mainly of sharp teeth. What is typical of carnivorous dentition is that there are no flat molars as these are characteristics of herbivores and omnivores. The most prominent feature of carnivorous teeth are large canines.


There are four canines in the oral cavity; two on the upper jaw (maxillary) and two on the lower jaw (mandibular). Canines are also found in omnivores including humans; however in humans the canines are much smaller. These canines act as knives that slice deep into flesh and cut chunks away. It should be noted that unlike human teeth, the teeth of a carnivore are widely spaced to prevent debris getting caught.


Carnivores have rather undeveloped molars in the sense that they are not flat and remain pointed. These molars act as scissors, slicing the flesh into smaller pieces in an up and down motion.


While herbivores and omnivores have enzymes in their saliva to aid with digestion of plants, carnivores do not possess an enzyme that breaks down proteins as they would damage the interior of the mouth. Therefore carnivores must swallow their food in chunks which requires a strong digestive system.


Carnivores have a large hole behind each eye socket; this is called the temporal fenestrae. This allows the jaw muscles to grow larger, therefore the larger the hole, the more powerful the bite. The bite of a hyena is strong enough to crush bone making it a successful scavenger, when food is scarce the animal can eat bone to survive.


Although impressive, the oversized canines of the Smilodon, or saber toothed tiger, were not strong enough to bite through bone; they were extremely fragile compared to most canines. Depictions of Smilodon hunting are usually inaccurate as the canines would be more commonly used on the throat as opposed to the shoulder or hide of its prey.


In the herbivorous mandible it is clear to see that there are no canines at all. A herbivore only possesses incisors and a large number of molars. This is because the teeth are not designed for slicing through meat but rather plant matter. Plant matter is difficult to digest which requires strong, grinding molars. This is the prototype for a herbivores oral cavity, however there are variations.


The teeth of a Woolly Mammoth for instance. They are not individual molars, the teeth were a large mass with sharp enamel ridges that were not worn down easily over the animal’s lifetime; this allowed it to eat large quantities of vegetation, making the animal successful in the colder climate.


Herbivores, unlike carnivores, can chew their food. The reason that vegetation is chewed is that it releases the digestible insides of the plant. Chewing also exposes the food to enzymes, aiding to speed up digestion.




Omnivores display characteristics of both herbivores and carnivores in the sense that they have canines and flat molars. The human canines are not very large. This is because around 3.6 million years ago, when Australopithecus afarensis first evolved, human dentition began to change. One theory suggests that Australopithecus were not as reliant on raw meat as a food source, either because they ate more vegetation or they had developed the ability to cook their meat using fire, however this theory has not been proven.


In comparison, the skull of a Chimpanzee displays much larger canines but very similar molars to that of a human’s. The reason for the difference in canine size is that Chimpanzees are still reliant on raw meat, which requires sharp teeth to tear through.

Omnivores have the same enzymes that herbivores do in order to aid with the digestion of vegetation. The stomachs of omnivores are similar to carnivores, as omnivores have to digest meat as well, as they are unable to produce the enzymes that break down protein in the mouth as it would damage the interior of the oral cavity. Therefore, omnivores and carnivores have a stomach acid that has a very low pH of 1 or 2.


Omnivores have proven to be rather successful in the wild. This is because if one source of food was to vanish, the animal could still eat the remaining source, for example if an animal that was prey to a Chimpanzee was to become extinct, it could still survive on plants until another source of meat became available.

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.

Evolution - A Brief Explanation

Here I want to go through the basic principles of the Theory, the mechanisms of Evolution and the history of the theory.

In 1859, Charles Darwin published his theory on Evolution. Here he made four key observations. Firstly, organisms produce more offspring than actually survive, for instance for every five offspring born only two will survive to maturity. He also noted that there is variation in the characteristics of members of the same species and that some of these characteristics can be passed on from one generation to the next. Finally, individuals that are best adapted to their environment are more likely to survive. Natural selection is just one process by which evolution occurs. 

Darwin's theory of evolution by natural selection explains his observations. Individuals within a population show variation in their characteristics, this is caused by mutations as a retaliation to predation, disease and competition which creates a struggle for survival. Individuals with better adaptations are more likely to survive, reproduce and pass on their advantageous adaptations to the next generation. Over time, the number of individuals with the advantageous adaptations increases. 

Evolution can lead to speciation, this is where a species evolves into a completely new species. A species is defined as a group of similar organisms that can reproduce to create fertile offspring. Species can exist as one or more populations, for instance there are different populations of American Black Bear in the USA and Canada. Speciation happens when populations of the same species evolve to become so different that they can't breed with members of the unevolved species to produce fertile offspring. 

Sketches of Darwin's Finches, the larger beaks are used for feeding on
 hard nuts whilst the small beaks are best adapted for
feeding on fruit. Sketches are by Charles Darwin himself.

Darwin's finches are the best example for the theory of evolution. The finches of the Galapagos Islands are adapted to feeding on different food sources on the islands. All the species of finch had a common ancestor. Different populations became isolated on different islands, and therefore each population has adapted to the varying environment on the islands. The populations evolved to become so different that they could not interbreed to form fertile offspring and thus created different species of finch. 

There is a lot of evidence to support the theory. Most of this evidence comes from the fossil record. By arranging fossils in chronological order, from oldest to youngest, it is possible to identify gradual changes in organisms that lead to the formation of different species. There is also DNA evidence. Evolution suggests that all organisms evolved from common ancestors, the more closely related two species are, the more recently the species diverged. This is a result of the gradual change in the base sequence in DNA. So, species that diverge more recently will have more similar DNA. A good example of this is that humans and chimpanzees share 94% of their DNA base sequences with each other. 

Different Forms of Evolution:
Convergent Evolution - this is where two species evolve similar features because they are living in the same environment. For example, bats and insects both have wings and can fly but they belong to different phyla.

Coevolution - here two species influence each other's evolution. For instance, flowers will emit a scent whilst being brightly coloured in order to attract insects that then act as pollinators. 

Adaptive Radiation - species rapidly evolve in order to take advantage of ecological niches, Darwin's finches in the Galapagos Islands are the best example here, some had large beaks for eating nuts whilst others used smaller beaks to eat fruits. 

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.

Could We? Should We?

I want to discuss the woolly mammoth, Mammuthus primigenius. The mummified remains of calves in the Siberian permafrost have given us a window, from which we can gaze into the world of the Pleistocene.

In 2014, a 28,000 year old mammoth was discovered in Siberia. This mummy was preserved to a high degree with blood, organs, tissues even the animal's last meal was still present. With this discovery and others like it, it has been possible to sequence the genome of a woolly mammoth. But should we clone this extinct beast?

Many people that I talk to simply say 'it would be good to see a live one' and that 'it would be helpful to study'. These are not compelling arguments to bring this animal to life. Yes seeing it would be spectacular, these were magnificent creatures, but they went extinct for a reason, they could not cope in the rapidly changing world. To study them would also be interesting, to look at the way they interact with the world and each other, to give us a true insight into the way they lived, but this would mean having to constantly harrass the mammoth.

A painting of Woolly Mammoths migrating through France near the RIver Somme.
Mammoths would have migrated vast distances with a changing climate in search of food, something
that would be impossible today. Painting by Charles R. Knight.

To even bring this animal to life a surrogate is required. The closest relative is the Indian Elephant. It is unknown what being a surrogate to a prehistoric animal would do to a modern elephant, not to mention the stress. The procedure may not be successful the first time so a number of elephants would have to be put through the procedure to get a result. Ethically we cannot stand for that.

Ecologically the mammoth would not fit in. Since the extinction of the mammoths 10,000 years ago, the world has changed greatly. We no longer have the correct sedges and grasses that the mammoths fed on. The mammoths lived in a habitat called the Mammoth Steppe which stretched right across Europe and into Asia, this has long disappeared, there is not the massive fluctations between glacial and interglacial environments in the present day. Also mammoths migrated great distances during the Pleistocene, from Britain to the South of France, this would be impossible now as the climate is warmer and there is no land bridge between Britain and France anymore.

We have to take humans into consideration here. We are a species that kill for sport and for trophies, unnecessary killings for no gain. Could we trust the minority that hunt animals like elephants, rhinos and lions to leave the mammoths in peace? At the start of 2016 we pushed the Northern White Rhino to extinction, a whole species has disappeared because of us. The Rhino isn't alone on the list, we've been responsible for numerous extinctions due to hunting, destruction of habitats and pollution. Even if the mammoth survived the human race it wouldn't be long until they are locked away in zoos for our entertainment rather than being allowed to roam the wild. The atmosphere is polluted a great deal more than in the Pleistocene, small environmental changes are partly responsible for the extinction of the mammoth so I don't believe a resurrected one will survive for very long with the environment in the state that it is in today.

Dr Victoria Herridge, who performed an autopsy on the young mammoth in 2014, wrote in The Guardian saying that it 'would be ethically flawed' and that she is yet to hear a convincing argument that supports the cloning of the mammoth.

Personally, we should stop here, we know we have the capacity to do it, we don't need to prove we can do it.

What are your opinions on this matter? Would a mammoth herd fit into our world? Let me know in the comments.

Nurture or Nature?

So far I've only been looking at the prehistoric animals once they are mature, but what about their offspring? Was it best to lay a clutch of eggs and hope that some survive to create the next generation or is nurturing a small number of young to ensure they survive the ideal way to maintain populations.

Amphibians in general are a good example of nature taking hold, for the survival of

Modern day frog spawn, these eggs are incredibly vulnerable
to both predators and environmental changed.
Image credit vernalpool.org

offspring. We've all seen frog spawn in a pond, in prehistory amphibian eggs would be rather similar to this. They need to be laid in water to prevent drying out but have no protective layer like a shell in order to allow for the movement of water across the membrane. This makes the eggs vulnerable, these unprotected eggs would have been preyed on by early arthropods, fish and even other amphibians, possibly to eliminate competition. To counteract the loss of eggs, an individual would have to lay hundreds of these jelly like eggs. It is believed that the shelled amniote egg was the reason behind amphibian decline at the end of the Carboniferous Period. As thee climate began to dry out and become more arid, the amniote egg could tolerate it as the moisture is locked in the egg by the shell, whereas ideal environments for amphibian eggs became scarcer and created more and more competition.

Clutch of ammonite eggs from the Kimmeridge
clay of Dorset, UK. Image credit Terry Keenan

Discoveries in the Kimmeridge clay of Dorset show us something spectacular; ammonite eggs. Initially these clutches have been interpreted as egg sacks attached to the adult ammonite, there is no evidence as of yet that supports this as soft body parts are not preserved. Therefore logically these eggs are laid in well oxygenated sediments. There are two possibilities as to why these eggs failed out of the thousands laid. Firstly, the eggs could have been deposited in an anoxic environment before they could hatch. The other hypothesis is that the environment they were laid in had varying oxygen levels due to seasonal changes. Again the environment is a big threat to the eggs as with the amphibians. Predation probably wasn't as much of an issue, Plesiosaurs are one of few predators that actively searched the sea bed for food, invertebrates and microorganisms being other examples of predators.

Even though some animals leave their offspring to the mercy of nature, we do see some adaptations that help to increase the odds of survival. A good example of this is the famous dinosaur Diplodocus from the late Jurassic period. These eggs are large and round, the size of the eggs is the first adaptation. A large egg means a large hatchling. Size increases survival as it means only predators larger than the hatchlings are a threat. After hatching young Diplodocus will grow at an exponential rate, the larger they are the fewer threats there are, before long the nest raiders are no longer a problem. Diplodocus nests are created underground, this helps to incubate the eggs, not only this it also prevents the eggs being scavenged by nest raiders. These adaptations all come together to improve chances of survival for the young sauropods.

Crushed eggshell of a titanosaur from Auca Maheuvo nesting
site. Image credit dougu.me

Dinosaurs later became more parental, we start to find evidence of a move towards nurturing the young. There is no evidence for direct nurturing of young after they've left the nest, however footprints do show young members of herds so perhaps there is a collective nurture from all mature members of the herd. But when we look at a vast nesting site at Auca Mahuevo in Argentina, there is evidence all around that young Argentinosaurs were kept in the nest and cared for. This evidence is crushed eggshells. This indicates that the young were spending the first stages of life in the nest watched over and fed by the adult. Titanosaurs aren't the only dinosaurs to make this step, a lot of Cretaceous dinosaurs were tending to nests, its believed even Tyrannosaurus rex had a parental instinct until the young were mature enough to fend for themselves. Birds and crocodiles today have this kind of care for their young.

Mammals are a good example of nurture rather than nature. Mammals are known to have few offspring and care for them for much longer in order to ensure survival to sexual maturity. Focusing all this effort and energy on a single offspring is potentially less efficient, given that only one individual reaches maturity. So could it be that the more vulnerable genera require nurture for survival? Look at our own ancestors for an example, the Australopithecines were not as fast as other predators of the time, such as Dinofelis, therefore our ancestors relied on intelligence to trap prey as well as falling back on an omnivorous diet. But we were prey as well, we were and still are a delicate species. Larger mammals and predators had the ability to kill an Australopithecine with ease. Meaning we must have had to protect our young to create the next generation.

So what do you think, is it quantity or quality that you think is more successful? Let me know in the comments.

Palaeoart: A Blast From The Past

I thought it would be interesting to look at the older palaeoart, to see how much our interpretation of the fossils has changed. I've chosen two famous dinosaurs and how they were reconstructed early on in Palaeontology's infancy.

Early reconstruction of Diplodocus. Art by Heinrich Harder.

First up is this early painting of Diplodocus by Heinrich Harder. At the time of this reconstruction, it was believed that dinosaurs were more like lizards, this included having sprawling legs like a lizard. Although it did not take too long for palaeontologists to realise that a sprawling stance could not be supported, not least because the animals abdomen would drag along the ground. Another glaring misinterpretation here is the position the neck and tail are being held in. We know now that sauropods used their tails to balance their long necks. This would require the tail and neck being along the same plane, i.e. neck outstretched in front with the tail raised level. The neck vertebrae of Diplodocus could not create such sharp angles as they differ from those of sauropods such as Brachiosaurus that allowed a more upright neck.

Early reconstruction of Iguanodon by Samuel Griswold Goodrich
c. 1859

Next we have Iguanodon one of the first dinosaurs to be officially described. Statues of these dinosaurs can be found in Crystal Palace Park in London. They are considered a monument to the advancements in Palaeontology that allow for more accurate reconstructions. In the drawing we see a reptilian monster with a bear like posture. The dinosaur is also shown with a horn on the end of it's nose, we know that this was in fact a thumb spike used in defense. The animal also has a more bird like posture, being both a quadruped and biped. Looking at the evolution of the dinosaurs in the present day through our reconstructions, we have gone from drawings of great lumbering lizards to more agile and more advanced animals, and in some cases feathered theropods that are shown to be incredibly bird like, this would have been unprecedented in the early stages of the science.

The Difference Between...Regular and Irregular Echinoids

Toxaster peroni an example of an irregular echinoid exhibiting
bilateral symmetry.

An echinoid is a sea urchin, we find the fossils of the echinoids from the Ordovician to the present day. The two types, irregular and regular, have few similarities and it is relatively easy to identify which is which.

Both echinoids live in marine environments, their anatomy have some similarities as well, they have five ambulacrum and have a mouth and anus. They also use their tube feet for respiration. But this is where the similarities end.

Regular echinoid from the family Toxopneustidae. Note the five
fold symmetry. Image credit nhm.ac.uk

The lifestyles differ completely, irregular echinoids, like the Toxaster peroni pictured right, are infaunal echinoids, meaning they burrow into the sediment. They also favour low energy environments. Regular echinoids are found in the opposite conditions, being epifaunal they lie on the sea bed and prefer high energy conditions.

The feeding habits of the echinoids are different, the regular echinoids, being epifaunal, graze on the sea bed using the Aristotle's Lantern. This is the chewing organ of the sea urchin that is composed of five calcium carbonate teeth and an internal tongue. On the other hand the irregular echinoid particle feeds by filtering the water.

The tube feet have different functions for each echinoid, both use them for respiration but there are more uses. The regular echinoids use them to attach themselves to the sea bed and also to move. This shows that the regular echinoids are more active than the irregular echinoids. The irregular urchins use their tube feet for digging their burrows and maintaining them.

When looking at the fossils it is easiest to identify which is which by looking at the symmetry. Regular echinoids have five fold symmetry due to being a lot more round, whereas irregular echinoids have bilateral symmetry. It is easy to see this in the images.

The Carboniferous Period

The Carboniferous period is divided in two; the Mississippian and Pennsylvanian Carboniferous. Lasting between 358.9 to 298.9 Ma, the Carboniferous is a period of intense coal formation, the name Carboniferous comes from this fact. The Mississippian carboniferous' sedimentology is mostly composed of Carboniferous Limestone, whereas the Pennsylvanian is where we find most of the coal deposits. 

Artist's impression of a Carboniferous landscape. Image credit: Plant Evolution
and Palaeobotany

The sea level here remained low from the Devonian. The levels dropped again in the middle of the period, this caused major marine extinctions, mainly crinoids and ammonoids. Gondwana was still glaciated at this time, but it had little effect on the overall climate, this is evident from the swamplands that were present in the tropics. The formation of Pangaea caused more mountain building in the Appalachians region, this is known as the Alleghenian Orogeny. The Hercynian Orogeny was taking place in Europe at this time. The Eurasian continent came together to push up the Ural Mountains as the supercontinent formed. The Average temperature was twenty degrees Celsius but cooling in the Middle Carboniferous reduced this average to twelve degrees Celsius. The continued glaciations on Gondwana carried on into the Early Permian period. 

The Carboniferous is characterised by a peak in global oxygen content in the atmosphere. This made the atmosphere flammable, forest fires were therefore common. The expanse of forests and abundance of dead plant matter are responsible for the coal deposits. 

Lepidodendron trunk fossils. Image credit: tentree.com

The plant life was similar to that in the late Devonian, including horsetails, mosses and ferns. But there is the emergence of Lepidodendrales, or scale trees that grew to unseen proportions before this time. Cycads and Conifers also evolved in the Pennsylvanian Carboniferous. 

In the oceans there is the appearance of Foraminifers, a group of marine protists. Brachiopods and the Echinodermata had continued success in the oceans. Trilobites are becoming increasingly rare as time progresses. 

Terrestrial animals were evolving rapidly with the new climate. Giant insects are famous from this time period. The 2.6 metre long millipede like Arthropleura foraged on the forest floor whilst the giant dragonfly Meganeura, with it's 75 centimetre wingspan, took to the sky above. Arthropleura is the largest terrestrial invertebrate, and

Artist's impression of Arthropleura and Meganeura. Image
credit: Richard Bizley

Meganeura is the largest flying insect. The size of these animals is due to the moist and oxygen rich atmosphere. 

Amphibians were more diverse in the Carboniferous than they are today, but they could not cope with the change of environment after the Carboniferous Rainforest Collapse. 

Sharks were exploiting the ecological gap left by the extinction of the Placoderms. The radiation of sharks created some weird animals, Stethacanthus had a large flat topped dorsal fin. 

Reptiles make their earliest appearance in the Carboniferous, exploiting the gradual decline of the amphibians. This was alongside the emergence of the synapsids and diapsids. These animals were more advanced through the amniote egg which allowed for further exploitation of the land as these eggs are more protected than the soft amphibian eggs. The earliest reptile to evolve is Hylonomus from the Pennsylvanian.

There are two major events from the Carboniferous. Firstly, there is Romer's Gap. This is a gap in the fossil record from the first 15 million years of the period, it is unknown whether this was a lack of ideal fossilisation environments or an extinction event. Studies by Ward et al. (2006) shows that there was a drop in oxygen levels which indicates an ecological collapse. We do see that the Ichthyostegalian Labyrinthodont amphibians begin to decline early in the Carboniferous and give rise to the reptiliomorph amphibians. The Carboniferous Rainforest Collapse was due to climate change to arid conditions. Reptiles cope better with this environment than the water dependent amphibians as their scales lock in more moisture and the amniote egg does not need to be laid in water to keep moist.