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Evolution of Giraffes

A presentation previewing the adaptations of the giraffe family lineage.
by

Daniel -

on 14 September 2012

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Transcript of Evolution of Giraffes

Evolution of giraffes Giraffes are some of the most majestic animals in the world. They are also the tallest land animals in the world growing beyond 5 metres tall. This is primarily due to the length of their necks which are seemingly out of proportion to the rest of their body. The majority of giraffes are found in Africa and tend to reside in areas where there is a relatively light amount of bushland and scrubs. Giraffes use their long neck to help them reach into the high branches of trees. With the help of their tongue measuring between 45-50 centimetres, giraffes are able to strip a branch of leafs clean into its mouth. Giraffes move at varying speeds, however the most commonly occurring speed is found to be between 50-60 kilometres an hour. Giraffes are peaceful animals, but will become aggressive in defence when threatened. The most common predators to a giraffe are lions and hyenas. Giraffes have made a number of evolutionary adaptations throughout time. Most notably is the length of their neck. There have been a number of claims made as to the reason why the giraffes neck length has expanded significantly throughout time. One of the theories is that the length of their necks changed to accommodate their need to reach higher up into trees. The vessels and circulatory system within a giraffe have also adapted due to the significant expansion of the giraffes neck. The giraffes heart is bigger, allowing stronger pumps of the heart to allow the blood to reach extremities such as the head and middle-section of the legs. Their circulatory system also allows the giraffe to bend down for water without sustaining brain damage due to the high blood pressure that is placed upon the head when bending over. Giraffes also tend to sleep less, increasing their chances of survival from predators. Hypertragulae are the earliest known species that can be traced to the evolutionary lineage of the modern day Giraffe species. These animals were deer-like animals that thrived approximately 40 million years ago (mya). The Hypertragulae species had a relatively simple low-fibre diet and were commonly found in North America according to fossil remains. Leptomerycidae were the next known piece to the evolutionary puzzle. Leptomerycidae existed 35 mya and were longer limbed and had more protrudent mouths compared to the Hypertragulae. A key change that was beginning to occur in this species is that unlike the Hypertragulae, Leptomerycidae had gained increased control of its neck whilst also inheriting a stronger neck compared to its ancestor. The adaptation in the structure allowed this change to occur and was the foundation for the evolutionary growth of neck through its offspring. Leptomerycidae also had an advanced thermoregulation system in comparison to its ancestor Hypertragulae. Another key feature in the Leptomerycidae was that it was carnivorous. This was to cater for the changing climate as a result of tectonic movements and changes in the environment. Gelocidae was the species that followed the Leptomerycidae and resided in parts of Europe, Asia and around the modern day Middle-East. Fossil findings suggest that the Gelocidae may have existed 20 mya. However, there is evidence to suggest that evolutionary adaptation from the Leptomerycidae to the Gelocidae may have occurred as early as 28 mya. A key feature of the Gelocidae is that it relied heavily on nutrients and its intestinal system adapted to accommodate for a herbivore diet. The Gelocidae can have a comparison of its movement and function drawn to a gazelle of contemporary times. The Gelocidae had superior agility and speed compared to the Leptomerycidae and inherited a head structure not dissimilar to that of a deer. Following Gelocidae was the Palaeomerycidae species. This branch of species paved way for many of the evolutionary offspring that is found after 20 mya. The magnitude of evolutionary change that occurred between the Gelocidae and the Palaeomerycidae suggests that there were many environmental changes taking places in this period. Palaeomerycidae were animals that had a body that could be likened to a horse, had a relatively long neck (35-50 centimetres) and horns on its head. The Palaeomerycidae are traced back to Europe in a time where the climate was warm and the eco-system was thriving. Compared to their ancestor the Palaeomerycidae was considerably heavier and had a greater amount of mass as opposed to the leaner frame of the Gelocidae. Canthumerycidae is the next known evolutionary product leading to the modern day Giraffa Camelopardalis. This animal had slender long legs with a relatively thin and small body. It possessed a head that was wide compared to the Palaeomerycidae and two short horns that protruded from the top of the head. The Canthumerycidae was situated primarily in the Middle-East, with fossil findings suggesting that the Canthumerycidae was migrating into parts of Asia. The Canthumerycidae existed between approximately 18 mya and was went into extinction 10-15 mya. A key feature of the animal was that it was adapting to a giraffe like anatomy, although the length of the neck was still primitive compared to the modern day giraffe. A notable creature that followed the Canthumerycidae was the Injanatherium, however there is not enough evidence to make distinguishing differences between the two animals. Giraffokeryx followed the Canthumerycidae. Giraffokeryx could be likened to a half deer, half horse, given the proportion of its body and limbs in comparison to the size of its head and neck. Whilst the Giraffokeryx was not similar in height to the modern day giraffe, they had similar anatomical traits, albeit less advanced. The head of the Giraffokeryx appeared somewhat similar to that of a deer, however the spout of the Giraffokeryx was longer compared to the modern day deer. Giraffokeryx resided mainly in the Middle-East and favoured a forest environment for survival. The Giraffokeryx species lived 12 to 15 mya. The Palaeotraginae originated from Northern-Africa and the Middle-East and existed 12-15 mya. There is evidence that the Palaeotraginae even resided in areas as far east as Mongolia. The Palaeotraginae were larger forms of the Giraffokeryx and had larger, wider heads with a single pair of horns. The growth of the Palaeotraginae from the Giraffokeryx is mainly attributable to the adaptation of their limbs and neck to become increasingly elongated. Characteristics key to this animal was its powerful leaping ability and relative pace on the run. The Palaeotraginae died out approximately 9-10 mya. Samotheres are a larger form of Palaeotraginae with advances such as a larger nasal cavity, having larger skulls with an increase in the level of protrusion of the mouth as opposed to the Palaeotraginae. A key feature of the Samotheres is the increased size of the skull due to the expanded nasal cavity. This will allow for the growth of the neck. Samotheres and Palaeotraginae share similar features, however are different enough to be classified as different animals. S. Africanum are the species that follow the Samotheres. However, it is unclear whether the link between these species is strong enough to justify the connection that is made. There is evidence of fossils in Greece and surrounding areas. The evolutionary finds in the fossil place the S. Africanum after the Samotheres as the most logical species to follow in the evolutionary line of Giraffes. S.Africanum is characterised by it’s increased neck length, stronger limbs and increased mobility. Giraffinae is the link that follows S. Africanum, however there is not enough evidence to solidify this view. Bohlinia is the evolutionary form of Giraffe that follows S. Africanum. It is evident that the skull has once again enlarged in response to elongation of the neck. The Bohlinia was primarily situated in Eastern Europe and Western parts of the Middle-East with fossil finds being traced back to North Africa. One key feature of the Bohlinia was that it was actively prepositioned to favour particular sources of food. Bohlinia was also a fairly good mover, although lateral movement wasn’t a strength. This is as opposed to the S. Africanum of whom was less selective. Bohlinia is gradually developing key characteristics of the modern day giraffe with features such as the neck and skull structure quickly advancing towards it. G. Gracilis is identified as the first true giraffe species and the earliest African species of giraffe. The G. Gracilis species fossils were most commonly found in the dry East-Africa environment. A few key features of the G. Gracilis included: a light frame with a thin, long neck, small feet and it is estimated to be half the size of the modern day giraffe. However, G. Gracilis is larger than its ancestor G. Stillei. G. Stillei was a giraffe species that existed between 2.7 and 3.3 mya. It mainly resided in central and northern parts of Africa. It is theorised that the G. Stillei evolved from the Bohlinia and then moved into East-Africa which then allowed it to grow bigger and stronger due to the good environmental and climatic conditions that was existent in this part of Africa. G. Camelopardalis is the species that is otherwise known as the modern day giraffe. These species of giraffe appeared 1-1.5 mya. This giraffe was mainly found in African and parts of Asia. However, climate and environmental changes have squeezed giraffes mostly into Africa. Many different variations of the modern giraffe are existent today, which can be distinguished by the shape and patterns of the stripes that are on their bodies. Giraffes in Africa roam freely and are scattered in various areas including North, North-East, North West and in the centre of the continent. Initially, I believed that a giraffe would have evolved from a deer-like creature that resembled a horse. My hypothesis wasn’t too far off, with the beginnings of the giraffe culminating from the evolution of a small rabbit/horse animal which eventually developed characteristics of a deer. It is particularly interesting to see how the ancestors of the giraffe have changed variously throughout time from beginning short and stout in stature, to being quick and relatively skinny like a gazelle. However, the development of the length of the giraffes neck hadn’t been as streamlined as I thought, with periods of time where the neck ceased to develop. There are still many gaps to fill in the evolutionary puzzle of giraffes and hopefully with the advances in modern technology, that these gaps may be completed to gain a greater perspective on the life and behaviors of giraffes. The evolutionary path leading to the modern day giraffe "giraffa camelopardalis" is being explored.
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