Evolution of the Eye

“To suppose that the eye […] could have been formed by natural selection seems, I freely confess, absurd in the highest degree.”- Charles Darwin: The Origin of Species (1859)

Eye evolution is a topic of great study and sometimes controversy. The eye is a homologous organ, which is present in a wide variety of taxa. A homologous organ is adapted to different purposes, depending on the animal. Even though there may be changes in eyes from phylum to phylum (such as the ability to see in colour), certain components, such as the visual pigments, appear to have a common ancestry and thus, evolved before animals radiated. (Haszprunar, 1995). Many more complex characteristics of the eye may have evolved 50-100 times, but using the same genes and proteins in their construction (Land et al, 2002). Here, the evolution of the eye will be explored, using both morphological and genetic evidence.

The first, most primitive eye, evolved during the Cambrian Explosion. This happened very quickly in geological terms, within a few million years. There is no fossil evidence for eyes before the Cambrian, but there is fossil evidence in assemblages such as the Burgess Shale and the Emu Bay Shale; Anomalocaris was the very first animal, which we know of, to have eyes, dating back 515 million years ago. Anomalocaris’ eyes were compound and evolved before jointed appendages or a hardened exoskeleton. These eyes were able to sense night and day, and were 30 times stronger than that of trilobites’. In fact, with 16,000 lenses, the resolution of the 3 centimetres wide eyes would have been rivalled only by that of the modern Dragonfly, which has 28,000 lenses in each eye (Salleh, Anna, 2011).

anomalocaris

Here you can see a fossil of an Anomalocaris’ 2–3-cm paired eyes.  Their preserved visual surfaces are composed of at least 16,000 hexagonally packed ommatidial lenses (in a single eye), rivalling the most acute compound eyes in modern arthropods. The specimens show two distinct taphonomic modes, preserved as iron oxide (after pyrite) and calcium phosphate. The inferred acuity of the anomalocaridid eye is consistent with other evidence that these animals were highly mobile visual predators in the water column (Briggs 1994).

But, before the Cambrian Explosion, organisms may have had a use for light sensitivity, but not for fast movement or navigation by vision. The poor fossil record of eyes makes their rate of evolution difficult to estimate however, simple modelling demonstrates that a primitive optical sense organ based upon efficient photopigments could evolve into a complex human-like eye in approximately 400,000 years (Nilsson & Pelger S 1994). One study at Lund University confirmed this; starting with a flat, light-sensitive patch, they gradually made over 1,800 tiny improvements- forming a cup, constricting the opening, adding a lens- until they had a complex, image-forming eye. Every change they made improved the image quality and these steps could have taken place in about 360,000 generations, or just a few hundred thousand years. 550 million years have passed since the formation of the oldest fossil eyes, enough time for complex eyes to have evolved more than 1,500 times.

opsins

A lot of the genetic ‘machinery’ used in the development of the eye is common to all eyed organisms suggesting that ancient ‘toolkit’ genes (opsins, Pax, and Otx) first evolved in a primitive ancestor that gave rise to all animals with eyes. And so, throughout evolution, these genes have been retained and the diversity of eyes we see in different animals are modifications built on top of this basic genetic framework. Opsins, which detect light, only evolved once. All opsins in eyed organisms today, are modified versions of this ancestor 600 million years ago. Different opsins detect a variety of intensities and wavelengths of light and so many species have a variety of opsins, which allows them to see a wide range of wavelengths; this forms the basis of colour vision.

pax6

A variety of proteins interact within a fully-functioning eye. Pax proteins are coordinators and attach directly to the DNA, turning on the necessary genes at the appropriate place and time. Oddly enough, Pax is the same in vertebrates and insects so must have evolved before they separated. Even organisms without eyes, such as sponges, have Pax genes; this finding suggests that Pax proteins originally controlled other processes and were later recruited into the eye. Those individuals born missing eyes had defects in the same gene- Pax6- this is required for normal eye development in all bilaterally symmetrical animals.

It appears that unicellular organisms had very primitive ‘eyespots’. These were made of photoreceptive proteins that sense light and dark, allowing these organisms to have photoperiodism- being able to time day and night. However, this is not sufficient enough for vision, as they cannot detect where the light is coming from, or distinguish shapes (Land and Fernald, 1992).

euglena

The three basic functions an eye needs are: light detection; shading, in the form of dark pigment, for sensing the direction light is coming from and connection to motor structures, for movement in response to light. Sometimes, all three of these functions are carried out by a single cell. The single-celled euglena has a light-sensitive spot, pigment granules for shading, and motor cilia. However, this is not considered as a true eye, but a stigma, a small splotch of red pigment which shades a collection of light sensitive crystals, and is located at its anterior end. With the flagellum, the eyespot allows the single-celled organism to move in response to light, often towards it to assist in photosynthesis (Land and Fernald, 1992). The most-basic structure that is widely accepted as an eye has just two cells: a photoreceptor that detects light, and a pigment cell that provides shading. The photoreceptor connects to ciliated cells, which engage to move the animal in response to light (Nilsson, D.-E., 2009).The marine ragworm embryo (below) has a two-celled eye.

two celled eye

Complex optical systems started out as multicellular eyespots gradually developing a depressed cup, granting the organism the ability to detect the direction of light, and then in iner and finer directions as the pit deepened. Pit eyes were seen in the Cambrian and were seen in ancient snails, and modern representatives such as planaria. This animal can slightly differentiate the intensity and direction of light because of their cup-shaped, heavily pigmented retina cells, which shield the light-sensitive cells from exposure in all directions except for the single opening for the light. But, the proto-eye is still a lot more efficient at detecting the presence of lack of light, than its direction (Autrum, 1979).

Planaria

As animals evolved more-complex bodies and behaviours, the eye too became more complex. Eyes evolved connections to muscle cells rather than cells that moved by waving cilia. Neurons evolved that could process signals and coordinate behaviour (Arendt, Hausen, Purschke, 2009). Based on cells, there appears to be two main designs for eyes- one is seen in the protostomes (molluscs, annelid worms and arthropods) and the other seen in deuterostomes (chordates and echinoderms) (Land and Fernald, 1992). The ‘pinhole camera’ eye is seen in protostomes such as nautiloids. It developed as the pit deepened into a cup, then a chamber. By reducing the size of the opening, the organism achieved true imaging, allowing for fine directional sensing and even some shape-sensing. These animals’ eyes have poor resolution and dim imaging, as they lack a cornea or lens, but are still a massive improvement from eyespots. To prevent infection, a transparent film of cells is grown over the pinhole (Dawkins, 1986). The segregated chamber contents specialised for optimisations such as colour filtering, higher refractive index, blocking of ultraviolet radiation, or the ability to operate in and out of water. It is likely that a key reason eyes specialise in detecting a narrow range of wavelengths on the electromagnetic spectrum- the visible spectrum- is because the earliest species to develop photosensitivity were aquatic, and only two specific wavelength ranges of electromagnetic radiation (blue and green visible light) can travel through water (Fernald, 2001).

nautiloid

So, it seems that different forms of the eye, for example in vertebrates and molluscs, are often cited as a form of parallel evolution. Microvillous receptors of arthropods and molluscs depolarise in response to light, meaning that photon absorptions open Na+ channels. Ciliary receptors of vertebrates, in contrast, hyperpolarise in response to light by closing Na+ channels (Fernald, 2000). The structures of the two major chambered eyes, those of vertebrates and cephalopods, arise from distinctly different parts of the embryo. The cephalopod eye forms from an epidermal placode through successive infoldings, whereas the vertebrate eye emerges from the neural plate and induces the overlying epidermis to form the lens. The cephalopod eye also lacks a cornea, which is present in all vertebrates. The striking diversity in structure, function and development of extant eyes supports their polyphyletic origin (Fernald, 1997).

Flies have compound eyes; compared with simple eyes, compound eyes possess a very large view angle, and can detect fast movement and, in some cases, the polarisation of light (Völkel et al., 2003). Below is a table comparing simple eyes to compound ones. As you can see, compound eyes are ideal for insects as they detect movement and create a 3D image.

compound eye table

Trilobites also had compound eyes (although some were eyeless); their lenses were made of inorganic calcite crystal, a mineral that is also the main component of limestone and chalk. These crystal eyes are unique to trilobites, with the compound eyes of modern invertebrates being made of chitin, an organic substance. Due to their unusual composition, trilobite eyes were completely rigid and could not be adjusted to focus; instead, the trilobite corrected its focus with an internal eye mechanism which not only solved any potential problems caused by the mineral lens, but also gave the trilobite such good vision, that it could keep both close and distant objects in focus at the same time (Clarkson et al., 1975).

trilobite eye

  Even though we are vertebrates and cephalopods are not, our eyes seem very similar. Squid and octopus have arguably the best eyes in the invertebrate world. They have a camera-type eye, consisting of a lens projecting onto a camera. Unlike the vertebrate camera eye, the cephalopods’ form as invaginations of the body surface (rather than outgrowths of the brain), and consequently they lack a cornea. A cephalopod eye is focused through movement, like the lens of a camera or telescope, rather than changing the shape as the lens in a human eye does. The eye is almost spherical, like the lens, which is internal (Yamamoto, 1985). The crystalins, a water-soluble structural protein found in the lens and the cornea of the eye accounting for the transparency of the structure (Jester, 2008), used in the lens appear to have developed independently from vertebrate crystalins, suggesting a homoplasious, or convergent evolution, origin of the lens (Brahma, 1978).

The eyes of many animals show their evolutionary history in their contemporary anatomy. For example, our vertebrate eye is built ‘backwards and upside down’, whereas cephalopods’ eyes are built the ‘right way out’. We require photons of light to travel through the cornea, lens, aqueous fluid, blood vessels and all manner of cells before they reach the light sensitive rods and cones, allowing us to see. While such a construct has some drawbacks, it also allows the outer retina of the vertebrates to sustain higher metabolic activities as compared to the non-inverted design (Reichenbach and Bringmann2010). However, in the cephalopod eye, the nerves are attached to the rear of the retina, meaning they do not have a blind spot. This may because of the origins of eyes; in cephalopods they develop an invagination of the head surface whereas in vertebrates they originate as an extension of the brain.

Autrum, H (1979). “Introduction”. In H. Autrum (editor). Comparative Physiology and Evolution of Vision in Invertebrates- A: Invertebrate Photoreceptors. Handbook of Sensory Physiology. VII/6A. New York: Springer-Verlag. pp. 6–9.

Arendt, D., Hausen, H., Purschke, G. (2009). The ‘division of labour’ model of eye evolution. Philosophical Transactions of the Royal Society of London, Biological Sciences, 364(1531), 2809-2817.

Samir K. Brahma1 (1978). “Ontogeny of lens crystallins in marine cephalopods”

 

Brett Williamson (30 June 2011). “Ancient discovery puts world’s scientific eyes on Kangaroo Island”. ABC News (Australia).

 

Briggs, D. E. G. Giant predators from the Cambrian of China. Science 264, 1283–1284 (1994)

Clarkson, E. N. K.; Levi-Setti, R. L. (1975), “Trilobite eyes and the optics of Descartes and Huygens”, Nature 254 (5502): 663–7

Dawkins, Richard (1986). The Blind Watchmaker.

Fernald RD: The evolution of eyes. Brain Behav Evol

1997, 50:253-259

Fernald, Russell D. (2001). The Evolution of Eyes: Why Do We See What We See? Karger Gazette 64: “The Eye in Focus”.

Haszprunar (1995). “The mollusca: Coelomate turbellarians or mesenchymate annelids?”. In Taylor. Origin and evolutionary radiation of the Mollusca : centenary symposium of the Malacological Society of London. Oxford: Oxford Univ. Press.

“Homology”. Encyclopædia Britannica Online.

Jester JV (2008). “Corneal crystallins and the development of cellular transparency”. Seminars in Cell & Developmental Biology 19 (2): 82–93.

Lamb, T. D., Collin, S. P., Pugh, Jr., E. N. (2007). Evolution of the vertebrate eye: opsins, photoreceptors, retina and eye cup. Nature Reviews Neuroscience, 9(12), 960-976 (subscription required).

Land, M.F. and Nilsson, D.-E., Animal Eyes, Oxford University Press, Oxford (2002).

M F Land; R D Fernald (1992). “The Evolution of Eyes”. Annual Review of Neuroscience 15: 1–29

Nilsson, D.-E. (2009). The evolution of eyes and visually guided behaviour. Philosophical Transactions of the Royal Society of London, Biological Sciences, 364(1531), 2833-2847.

Nilsson, D-E; Pelger S (1994). “A pessimistic estimate of the time required for an eye to evolve”. Proceedings of the Royal Society B 256 (1345): 53–58

Reichenbach A, Bringmann A. (2010). Müller cells in the healthy and diseased retina. New York: Springer. pp 15 – 20.

Salleh, Anna (December 8, 2011). “Cambrian predator had killer eyes”. ABC Science.

Shubin, N., Tabin, C., & Carroll, S. (2009). Deep homology and the origins of evolutionary novelty. Nature, 457, 818-823

Völkel, R; Eisner, M and Weible, K. J (June 2003). “Miniaturized imaging systems” (PDF). Microelectronic Engineering. 67–68 (1): 461–472.

Vopalensky, P. & Kozmik, Z. (2009). Eye evolution: common use and independent recruitment of genetic components. Philosophical Transactions of the Royal Society of London, Biological Sciences, 364(1531)

Yamamoto, M. (Feb 1985). “Ontogeny of the visual system in the cuttlefish, Sepiella japonica. I. Morphological differentiation of the visual cell”. The Journal of Comparative Neurology 232 (3): 347–361

http://learn.genetics.utah.edu/content/variation/eye/

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A Brief History of the Discovery of Dinosaurs

Dinosaur discovery and its history spans back many centuries and over many different continents. Humans since their beginning of their existence have been discovering fossils and questioning their age, meaning and purpose. Here I will give you a brief timeline of discoveries and the people that made dinosaurs what we know they are today.

The Formative Period (750BC-1800AD)

I realise this period spans a long way but it also encompasses many other periods. During this period, terms such as ‘fossil’, ‘extinction’ and ‘deep time’ were worked out. Clark (1997:211) argues that “the creation and deployment of art…promoted governance through covert control of foundational ideologies.”  People were thinking in a different way and coming up with new ideas.

Xenophanes (c.570 – c.475 BC) was a Greek historian who recognised that fossils were the remains of extinct animals. Xenophanes wrote about two extremes predominating the world: wet and dry (water and earth). These two would alternate between each other and would cause extinction and regeneration (a very difficult concept to grasp, especially when you think about how easy it is to explain the word ‘extinction’). The thought of alternating states and human life perishing and coming back suggests he believed in the principle of causation; another distinctive step that Xenophanes takes from Ancient philosophical traditions to ones based more on scientific examination.

xenophanes

James Hutton (3 June 1726– 26 March 1797) was a Scottish naturalist and geologist who is the creator of the term ‘uniformitarianism’. This is a basic principle of geology which states that the same natural laws and processes that operate in the universe now have always operated in the universe in the past and apply everywhere in the universe. Obviously this is now somewhat not always true, especially if we take into consideration the fact that the Earth’s oxygen levels have changed dramatically over deep time, but many still refer to Hutton as ‘The Father of Modern Geology’.

james hutton

Robert Plott (13 December 1640 – 30 April 1696) wrote ‘The Natural History of Oxford-shire’ in 1677 and was the first person to figure out and describe a dinosaur bone. This bone turned out to be a femur of a Megalosaurus. He called it, Scrotum humanum because, well you can guess why. Apart from this Plott believed that most fossils were not remains of living organisms but rather crystallizations of mineral salts with a coincidental zoological form.

robert plotthumanus s

The Pre-Classical Era (1680-1842)

During this period, giant bones were found but their significance was not fully appreciated. For centuries, the Blackfeet Nation had inhabited Montana and Alberta-the same area in which the dinosaur-rich, late Cretaceous Hell Creek and Oldman Formations occur. Dinosaur fossils were known to the Blackfeet who considered them to be the remains of giant, ancestral buffalo. They used these bones in rituals, as they believed it would make them good at hunting. Besides this, they hit on the antiquity, and the organic nature of dinosaur remains, and in comparing them to buffalo showed their sophisticated knowledge of vertebrate anatomy. Referring to dinosaurs as large buffalo was thus good scientific practice in the context of their perception of the natural world.

blackfeet

William Buckland (1784-1856) was a vicar who made a careful analysis of fossil material, including teeth, jaws, and limb bones and in a paper published in 1824, he correctly identified them as deriving from a large, carnivorous fossil reptile, to which he gave the name Megalosaurus. But, he thought this as a lizard rather than a dinosaur. However, this was the first scientifically valid name given to a species of dinosaur.

william buckland

Gideon Mantell (1790-1852) was deeply interested in geology and natural history. He is credited with the discovery of the remains of a large, fossil reptile resembling in some ways the modern iguana, which he named Iguanodon. He also studied the dinosaur’s teeth and surmised that it was herbivorous. It was actually his wife, MaryAnn, who discovered the fossil and provided many of the ink drawings seen in her husband’s paper of the dinosaur. Mantell put a horn on Iguanodon’s nose, which was later discovered to be the creature’s thumb.

mantells

Baron Georges Von Cuvier (1769-1832) was a French Palaeontologist who wrote the ‘Laws of Anatomy’ and worked out that pterosaurs can fly. He also proved that extinction was real by studying mastodons and wooly mammoths. These elephant-like animals are not members of the modern elephant species, and therefore represent earlier elephant relatives that no longer exist. This led people to understand that dinosaurs were an extinct group of animals.

cuvier

The Classical Age (1842-1870)

During this age, dinosaurs were recognised as a unique group of reptiles. This was all because of Sir Richard Owen (1804-1892), who coined the term ‘dinosaur’, meaning ‘terrible lizard’. He was extremely influential in the decades prior to the publication of Darwin’s Origin of Species in 1859. But because he could not accept Darwin’s ideas about evolution, his influence waned considerably after the appearance of Darwin’s great book. Owen was also a major contributor to the study of dinosaurs during the 1830’s, 40’s and 50’s, and published many important papers on these animals during this period. He proposed the idea that dinosaurs may have been warm-blooded (like mammals and birds) rather than cold-blooded like other reptiles.

richard owen

Benjamin Waterhouse Hawkins teamed up with Owen to sculpt the life-size models of dinosaurs then known to exist. Hawkins sculpted life size models following Owen’s directions. It was inside Hawkins’ “Iguanodon” that Owen held his famous dinner meeting. Hawkins’ dinosaurs were also a prime attraction at the Crystal Palace Exhibition of 1853-54.

hawkins

megalnow

The Golden Age (1870-1899)

At this time, dinosaur collecting was the craze and new dinosaurs were discovered in huge numbers. Othniel C. Marsh (1831-1899) was the nephew of the fabulously wealthy banker and philanthropist George Peabody. Whilst in Europe, Marsh convinced Peabody to establish at Yale a new natural history museum – today’s Yale Peabody Museum, and to endow a professorship for Marsh at Yale in palaeontology. Marsh’s great contribution to dinosaur palaeontology is that he found dinosaurs on a grand scale, discovering famous dinosaurs such as: Allosaurus, Apatosaurus, Diplodocus, Ornithomimus, Stegosaurus, and Triceratops.

o marsh

 

Edward Drinker Cope (1840-1897) was another force driving dinosaur discovery. Cope thought that groups of species that shared similar developmental patterns could be grouped into more inclusive groups (i.e. genera, families, and so on). He thought that parts of the body most in use would be most likely to become better developed at the expense of other, less used parts, which would explain why, for example, pterosaurs evolved and lost their tails. Marsh and he were also in a race to see who could discover the most dinosaurs; a race which Cope lost. It also resulted in the mess of some dinosaurs being named twice with two different names!

copesmall

The Baroque Era (1899-1966)

Because this era was filled with wars, cold wars, depression and a European divide, dinosaur collecting and describing was put on hold. And you can understand why; at the time it was far more important to go to war; earn some money or fear the USSR to even think about dinosaurs. Apart from this, there were a few people who continued to write about them such as Sir Arthur Conan Doyle (22 May 1859 – 7 July 1930) who wrote ‘The Lost World’ in 1912. In this story, a exhibition team discover dinosaurs, pterosaurs and other extinct animals in South America. This flung pterosaurs and dinosaurs into the limelight and pushed them into the eye of the general public.

200px-Lost_world

Arthur Smith Woodward was the head of Palaeontology in 1902 and was better known for his work on fossil fish than dinosaurs. Unfortunately he fell victim to the Piltdown Hoax- bone fragments were presented as the fossilised remains of a previously unknown early human. These fragments consisted of parts of a skull and jawbone, said to have been collected in 1912 from a gravel pit at Piltdown, East Sussex, England. The Latin name Eoanthropus dawsoni (“Dawson’s dawn-man”, after the collector Charles Dawson) was given to the specimen. The significance of the specimen remained the subject of controversy until it was exposed in 1953 as a forgery, consisting of the lower jawbone of an orangutan deliberately combined with the skull of a fully developed modern human.

Piltdown_gang_(dark)

The Dinosaur Renaissance (1966-Present)

I’m not going to go into great depth about this period because it is the one most people know about. Since the Baroque Era, dinosaurs have been in pop culture. We have children’s’ books, TV shows and films staring dinosaurs and themes such as what it would be like if they walked among us. There are constant documentaries that we can watch about dinosaurs, right from the very beginning, to their demise at the Cretaceous Extinction, and how all modern day birds evolved from them. New discoveries are cropping up all the time from countries such as Mongolia and China, wielding new fossils almost every day. We do truly live in the era of dinosaur discovery.

Jurassic-Park

A. J. Turner, ‘Plot, Robert (bap. 1640, d. 1696)’, Oxford Dictionary of National Biography, Oxford University Press

Keith, A. (1914) “The Significance of the Skull at Piltdown”, Bedrock 2 435:453.

McKirahan, Richard D. “Xenophanes of Colophon. Philosophy Before Socrates. Indianapolis: Hackett Publishing Company, 1994. 65. Print.

Robert Plot: A brief biography of this important geologist’s life and work.”. Oxford University Museum of Natural History. Retrieved 4 June 2013.

University of Edinburgh. “Millennial Plaques: James Hutton”. (Hutton’s Millennial Plaque, which reads, “In honour of James Hutton 1726-1797 Geologist, chemist, naturalist, father of modern geology, alumnus of the University,” is located at the main entrance of the Grant Institute).

http://academic.brooklyn.cuny.edu/geology/chamber/dinohist1.html

http://www.ucmp.berkeley.edu/history/cope.html

Images:

academic.brooklyn.cuny.edu

commons.wikimedia.org

fineartamerica.com

friendsofdarwin.com

www.iep.utm.edu

www.nndb.com

screencrush.com

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The Evolution of Snakes

The origin and evolution of snakes have been debated throughout palaeontology for years. There seems to be two main theories, which will be explored in depth in this report. The first main theory is that snakes are a sister group to marine varanoid lizards and snakes thus evolved from them. The second is that snakes were once small burrowing lizards and lost their limbs because it was simply easier to dig without them.

First the ‘marine varanoid theory’ will be looked into. First formally suggested by Victorian fossil hunter and evolutionary biologist Edward Drinker Cope (1849-1897), argues that snakes lost their limbs at sea and are closely related to the extinct marine lizards called mosasaurs.

This idea is mostly pushed by MSY Lee. He looked at the relationships between the major lineages of snakes based on phylogentic analysis. Ecological, osteological and anatomical features were examined. According to Lee:

“The marine, limbed Cretaceous snakes Pachyrhachis and Haasiophis emerge as the most primitive snakes”

However, the link between these and advanced snakes are based on very unlikely interpretations that are debateable; even Lee admits this.  The view that these large marine snakes were the first primitive snakes directly contradicts with the idea that snake ancestors were small, terrestrial, burrowing creatures.

Below is Pachyrhachis and size in comparison to humans. Note the small hind limbs.

pachry

The similarities that snakes and mosasaurs possess are that they both have loose jaws for swallowing large prey. Some snakes have a gular fold that allow stretching in the intramandibular tissues. This is called liberation of the mandibular symphysis and is variable and complex amongst snakes. The only other squamate (scaled reptile) clade which shows this liberation is mosasaurs. They also share with snakes an intramandibular articulation. All these similarities in mandibular mechanics support the theory that snakes and marine reptiles, such as mosasaurs, are very closely related.

Below is Haasiophis swimming in marine waters, supporting Lee’s theory. This primitive snake also appears to have small hind limbs and a dorsal fin-like tail.

Haasiophis

Lee believes that mosasaurs were the “intermediate between lizards and snakes”.  Lee also states that Pachyrhachis is an excellent example of a transitional taxon. It is true that Pachyrhachis is also a sister-taxon of fairly advanced snakes that are able to dislocate and widen their jaws to swallow their prey. However, there is much debate whether this Cretaceous snake was a ‘missing link’, or just a relative of modern snakes that bears no issue to snake origins. Zaher found Pachyrhachis not to be a basal snake, nor a link between mosasauroids and snakes, but the sister-taxon of advanced macrostomatan snakes instead.

Lee put forward a rebuttal to this by putting all snakes, except Pachyrhachis as a single terminal, thus not allowing an empirical test and a potential negative response of Zaher’s results.

Pachyrhachis is found to be a sister group of Macrostomata, and snakes grouped with the dibamid–amphisbaenian clade instead of with mosasauroids, but it is still up to much debate.

Although this theory is seemed the most unlikely out of the two, it is not impossible that the earliest snakes were marine and only the ancestor of the extant forms was burrowing. There are a possible five major groups of marine lizards in the Mesozoic and they are: aigialosaurs, mosasaurs, dolichosaurs adriosaurs and Aphanizocnemus, which might define a lineage of its own. All these show several similarities with terrestrial varanoid lizards that had already settled into their modern form by the late Cretaceous, such as the giant Gila monster. The primitive mosasaur, Dallasaurus retains several aigialosaur-like features. This suggests that the ancestor of the aigialosaurs and mosasaur at least was an amphibious form, much like many extant varanoids. Therefore, the mosasaurs that we know of that were totally marine, seem to be much further down their evolutionary line. The dolichosaurs, Aphanizocnemus and adriosaurs have much longer bodies and elongate necks, with an increase in a number of dorsal vertebrae and reduced forelimbs to different degrees. An example of this is Adriosaurus microbrachis; it had an extreme reduction of forelimbs that was seen as a tendency towards forelimb loss and the emergence of snakes.

Mososaur

What is also believed from this theory is that the fused, transparent eyelids of snakes evolved to combat marine conditions (corneal water loss through osmosis), and the external ears were lost through disuse in an aquatic environment.

To conclude on this theory, genetic studies in recent years have indicated snakes are not as closely related to mosasaurs or monitor lizards as once believed. However, more evidence links mosasaurs to snakes than to varanids.

Fossil evidence suggests that snakes may have evolved from burrowing lizards during the Cretaceous period. Podophis descouensi gen. et sp. nov.  is a new fossil that has been described. It is similar to Pachyrhachis as it is a bipedal snake from the Cenomanian. It confirms that bipedal snakes are basal Ophidia. It is not possible to tell whether these two bipedal snakes make up a sister-taxon to the Serpentes, or a stem group of the Serpentes. Below is Podophis descouensi’s immaculately preserved hind limbs.

Podophis descouensi’s

Features such as the transparent, fused eyelids and loss of external ears evolved to cope with burrowing difficulties, such as scratched corneas and dirt in the ears, according to this theory.

However, there are many anatomical differences between snakes and lizards, such as their eyes and optic nerves to the brain. This could just suggest different mutations or further evolution and is not such a great hindrance to this argument, especially when lizard and serpent DNA is examined. Scientists compared the DNA of numerous species of lizards and snakes. Their results have shown that snake DNA is significantly different from the DNA of varanid lizards, but is more like the DNA of other land-based lizards. They concluded that this is strong evidence for land-lizard ideas of snake origins.

To add to this credible evidence, a ‘transitional snake’ fossil was described. Coniophis, from the Cretaceous, lived in a floodplain environment and “lacks adaptations for aquatic locomotion”. Nicholas Longrich also describes it as having a lizard-like head with a snake body. It was small, and reduced neural spines suggest a burrowing nature, supporting this theory greatly.

Coniophis precedens

The skull is intermediate between that of lizards and snakes. Hooked teeth and an intramandibular joint indicate that Coniophis fed on relatively large, soft-bodied prey. However, the maxilla is firmly united with the skull, indicating an akinetic rostrum. Coniophis therefore represents a transitional snake, combining a snake-like body and a lizard-like head. Subsequent to the evolution of a serpentine body and carnivory, snakes evolved a highly specialized, kinetic skull, which was followed by a major adaptive radiation in the Early Cretaceous period. This pattern suggests that the kinetic skull was a key innovation that permitted the diversification of snakes.

To conclude, both the varanoid and the burrowing-lizard theory pose compelling evidence. However, due to recent fossil discoveries, such as Coniophis, it would seem that snakes were more likely to have lived on land, not the sea. Their ancient vertebrae suggest a burrowing lifestyle; they were not adapted for aquatic life. To add to this the varanoid argument has many holes in it, as it does not take into account DNA, only phylogenetic similarities. The fossil record has also supported the burrowing theory more than the marine theory. It is true that there are some aquatic snake fossils, but these examples may have just been a sister taxon and may not infringe on the evolution of snakes at all.

head comp

From left to right: Coniophis skull adaptation; Erhard’s wall lizard’s head; Ralph the Florida Corn snake’s head. You can see that there are similarities and differences between all and that Coniophis was a ‘mid way’ point between a lizard head and a snake head, such as the shape, teeth and most importantly the jaw structure, which was more like a lizards than modern day snakes’. This leads scientists to believe that the rest of the body would be a ‘transition’ also.

References
 
ADRIOSAURS AND THE ORIGIN OF SNAKES AND THE SNAKE-LIKE FORM- Unknown Author
SNAKE PHYLOGENY BASED ON OSTEOLOGY, SOFT
ANATOMY AND ECOLOGY- Lee
http://www.umlauf.websnadno.cz/Morsky-svet.html?framebreaker
http://www.uua.cn/Reptilia/show-4991-1.html
http://news.nationalgeographic.co.uk/news/2004/02/0211_040211_snakeevolution.html
RE-BUILDING THE BRIDGE BETWEEN MOSASAURS AND SNAKES- Reippel and Zaher
ON THE PHYLOGENETIC RELATIONSHIPS OF THE CRETACEOUS SNAKES WITH LEGS,
WITH SPECIAL REFERENCE TO PACHYRHACHIS PROBLEMATICUS (SQUAMATA, SERPENTES)- Zaher and Reippel
http://www.google.co.uk/imgres?um=1&hl=en&sa=N&biw=1366&bih=639&tbm=isch&tbnid=iNunkOYRX6KX-M:&imgrefurl=http://rahuu.wordpress.com/2010/11/18/daily-dino-fact-mighty-mosasaur/&docid=JJVDn93rFQKu4M&imgurl=http://rahuu.files.wordpress.com/2010/11/mosasaur1.jpg&w=574&h=400&ei=qSapUPHwFsyY1AXl0IGIDQ&zoom=1&iact=hc&vpx=257&vpy=189&dur=5019&hovh=187&hovw=269&tx=142&ty=97&sig=109176819055989437236&page=1&tbnh=134&tbnw=180&start=0&ndsp=18&ved=1t:429,r:1,s:0,i:99
http://en.wikipedia.org/wiki/Snake#Evolution
Un nouveau serpent bipède du Cenomanien
(Crétacé). Implications phylétiques- Ragea, Escuillieb
http://nl.wikipedia.org/wiki/Bestand:Eupodophis_descouensi.jpg
Vidal, N. and Hedges, S.B., Molecular evidence for a terrestrial origin of snakes
http://www.google.co.uk/imgres?hl=en&sa=X&tbo=d&biw=1366&bih=639&tbm=isch&tbnid=_s4sfDGUPYHfpM:&imgrefurl=http://www.treknature.com/gallery/Europe/Greece/photo237380.htm&docid=a1MHbqSNzMEFcM&imgurl=http://i1.treknature.com/photos/17006/179__podarcis__erhardii__f.jpg&w=800&h=469&ei=VW_gUMvJL6aI0AWBhoCAAg&zoom=1&iact=hc&vpx=12&vpy=377&dur=421&hovh=169&hovw=288&tx=147&ty=117&sig=109176819055989437236&page=2&tbnh=136&tbnw=225&start=21&ndsp=28&ved=1t:429,r:42,s:0,i:234
http://www.bbc.co.uk/news/science-environment-18998634
A transitional snake from the Late Cretaceous period of North America- Nicholas R. Longrich, Bhart-Anjan S. Bhullar &Jacques A. Gauthier
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3D Printing

3D printing, also known as ‘additive manufacturing’, is a process of making three-dimensional objects from a digital model. This 3D object is made by laying down multiple layers of material. It is useful in almost any field, including Geology and Palaeontology.  (Excell, Nathan, 2010)
3d plane

Creating a 3D object using additive manufacturing involves three stages. First, the 3D printer will take a virtual blueprint of the object it wants to reproduce. This is done either using computer aided design (CAD) or animation modelling software. Digital cross sections are then made to use as a guideline for printing. Then, a binding material is placed on the build bed or platform until the ‘binder layering is complete’.

The next stage is the printing stage. The machine reads the design and yet again successive layers are put down. This can either be of powder, liquid or sheet material. These layers are the same as the virtual cross sections and are fused together to create the final shape. Typical layer thickness is around 100 micrometres and printing can take from several hours to several days, depending on size and complexity of the model.

The final stage is not always needed in 3D printing. It involves either enlarging some areas of the object to make them easier to observe, or using other materials to construct certain parts. Supports are also sometimes used if there are overhanging features, and need to be removed at this stage.

Not only can 3D printing be used in industries such as jewellery, footwear, architecture and civil engineering, it can be used in palaeontology. For example, Sergio Azevedo, a Brazilian palaeontologist, discovered the fossilised bones of an unknown animal in São Paulo. He was unsure as to how much of the animal he had so, instead of taking a hammer and possibly damaging the rest of the fossil, he used a portable CT scanner to determine the orientation of the fossil in the ground. A large chunk of rock containing the specimen was then taken back to a lab, probed with a more power scanner and a 3D model was printed out in resin. This gave him and his team safe access to the internal structure of the specimen, not usually accessible in conventional palaeontological techniques. The fossil turned out to be a new species of crocodile that went extinct 75 million years ago. Below is an image of the scan of the fossil that Sergio Azevedo excavated. (Hooper, 2013)

hooper

With a CT scanner, which uses X-rays, you don’t even need to see the object with your own eyes. Fossils can be scanned while still encased in rock. The image is subjected to “virtual preparation” – software processing that digitally removes the surrounding rock. This could cut a palaeontologist’s work in the field down greatly, as they wouldn’t even have to fully excavate the fossil.

Also, laser scanners can capture the surface details of delicate fossils in the field in 3D before they are excavated to provide an in situ record of a fossil or a site before it is disturbed.

Furthermore, 3D printing would be an invaluable tool for those studying Palaeontology and similar courses. If there was a 3D printer in university labs, accurate digital replicas can be made of the rare and inaccessible specimens that make up the fossil collections in museums.

“We are developing several research lines in palaeontology using CT and surface 3D scanning,” says Azevedo. “These include the nervous system and biomechanics of crocodiles, dinosaurs and other vertebrate fossils.”

oviraptor

As well as being able to virtually extract fossils using 3D scanning and printing, behavioural patterns of extinct animals can be explored. Palaeontologist Professor Kenneth Lacovara from Drexel University in Philadelphia and mechanical engineer James Tangorra have been replicating dinosaur bones to see how they moved and behaved. Lacovara works on large sauropods, so manipulating their vast fossils is almost impossible. Instead, he uses scaled down model replicas to test theories of their movement. Even though fossil bones are compressed and distorted over millions of years, the 3D scanner restores them to their original shapes and proportions. Robotic models can then be 3D printed, complete with artificial tendons and muscles to show how these beasts would have moved.

Even though 3D printing seems the way forward and can be very useful indeed, there are some disadvantages. As mentioned, 3D printers use powdered resin, plaster or liquid polymers. These materials are not very strong, so there are a lot of size limitations when creating 3D replicas. Larger objects are often impractical to make due to the amount of time it would take the printer to create.

The surface finish of a 3D printed object is rough and ribbed; this is because of the plastic beads or powder particles that are stacked on top of each other during printing. This gives the end product an unfinished look.

On top of these inconveniences, 3D printers themselves are rather expensive. On average, a 3D printer can approximately cost £3250 and can go as high as £32500 for higher end models. That price does not include the cost of accessories and resins or other operational materials. (Gibson, Rosen, Stucker, 2009)

bunny

Even though 3D printing has been around for decades, it is still very far away from being distributed to the mass market. It seems, however, that the cost of 3D printers is dropping, so maybe 3D printers will become a household item in the future. 3D printing can be useful for all fields of work, especially in palaeontology. Staples are planning on opening large city locations in the Netherlands and Belgium, offering 3D printing to the masses. (Lepitak, 2013) This will be the first time a retailer sells this service to the public. If it is a successful venture, it is very possible that it will be adopted by competitors around the world. However, this may bring up further problems, such as infringement on copyright (if people print off replicas of branded products). This doesn’t seem like too much of an issue for those wanting to make replicas of fossils though.

Additive Manufacturing is incredibly useful from a geological perspective; it can allow someone to know the orientation, nature and size of a fossil without even having to dig it out of the ground. It can allow scientists to have a closer look at some of the more intricate details of specimens. If the specimen is small, the 3D replica can be blown up to make observations easier to make and if the specimen is large, it can be shrunk down to a more manageable size. Misinterpretations of bones might be a thing of the past as a 3D printer can return the fossils to their original dimensions. Furthermore, 3D printers would be an excellent tool in labs in universities all over the world. It would let students be able to study replicas of fossils and specimens that they wouldn’t previously be able to get a hold of. Finally, it may give us an insight as to how extinct animals moved and behaved, by creating robotic replicas with muscles and working moving parts.

hominoid skull

References

3D print a fossil with virtual palaeontology; January 2013 by Rowan Hooper for New Scientist issue 2899

3D printing: A gimmick or a game changer?; January 2013 by Stephen Lepitak

Additive Manufacturing Technologies: Rapid Prototyping to Direct Digital Manufacturing; Ian Gibson, David W. Rosen, Brent Stucker; 2009

The rise of additive manufacturing; 24 May 2010 Jon Excell, Stuart Nathan

http://www.newscientist.com/article/mg21728996.500-3d-print-a-fossil-with-virtual-palaeontology.html

http://www.printware.co.uk/Blog/111/Palaeontologists-Print-3D-Dinosaur-Bones.html

http://en.wikipedia.org/wiki/3D_printing#General_principles

Image 1: http://blogs.telegraph.co.uk/technology/willardfoxton2/100008357/stop-talking-rubbish-about-3d-printing/

Image 2: courtesy of Sergio Azevedo

Image 3: http://www.google.co.uk/imgres?hl=en&tbo=d&biw=1525&bih=714&tbm=isch&tbnid=q_wyBxu5vi89bM:&imgrefurl=http://shapeways.tumblr.com/post/26979753383/madeinthefuture-3d-printing-dinosaurs-digital&docid=iWyB6aZViU8mnM&imgurl=http://24.media.tumblr.com/tumblr_m7054z9O581qgoa30o1_500.jpg&w=500&h=500&ei=v1cBUcLBGcqf0QWr94DQDA&zoom=1&iact=hc&vpx=207&vpy=4&dur=397&hovh=225&hovw=225&tx=156&ty=119&sig=109176819055989437236&page=1&tbnh=141&tbnw=143&start=0&ndsp=27&ved=1t:429,r:8,s:0,i:103

Image 4: http://www.shapeways.com/blog/archives/1354-what-does-a-3d-printed-bunny-cost.html

Image 5: courtesy of Dave Stock

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Two Weeks in the Life of a Palaeontologist

The reason I have not written any articles in a while is because I have just returned from Morocco collecting samples for my dissertation. My project will be titled ‘The Taphonomy of Trilobites in Different Beds in the Alnif Area”. Taphonomy is the study of the decay of different organisms and how they become fossils. Trilobites are great to study because they would shed their exoskeletons, giving them a high preservation rate.

trilo

We began the journey by flying to Marrakech, and after staying there for a night, we took an 8 hour bus journey to Tinghir. As you can imagine, an 8 hour journey was not fun, and even after that we still had an hour car journey to Alnif. Alnif is a very small town in the desert by the Sahara and Anti-Atlas mountains. Life there is very different to that in the UK, as there are barely any shops apart from fossil shops!SAM_0433

However, the geology in this area is wonderful, with exposures starting from the Pre-Cambrian, ranging all the way through the Palaeozoic (apart from the Permian, as there was no sea here at that time) and then through to the Mesozoic. The Kem Kem is a great area for finding dinosaur fossils. Unfortunately, we did not visit here, as it would take a very long jeep ride and we just didn’t have enough time.SAM_0465

The journeys out into the desert every day were long and required a car. Walking to localities is not advised and especially at midday. The first day of field work we made the mistake of trying to walk at midday and in the desert heat I thought we were going to die- no matter how much water we drank, our heads were still spinning and we were so dehydrated. So, we made a decision that we would either go very early in the morning, or late in the afternoon. And it was a good decision; specimens were collected almost every single day. And a lot of them! We almost went over our baggage allowance!

We visited every time period in the Palaeozoic here (bar Permian of course), as trilobites ruled the seas during this time. Trilobite morphology also changes drastically throughout these time periods, which may reflect the palaeoenvironment. For example, Phacops had eyes during the Ordovician, but had lost them by the Carboniferous. Could this be because the water was getting deeper? Or could it be because they changed their lifestyle and preferred living in underwater caves and holes? It appears that, in Morocco certainly, the latter would be the case, as the seas in the Carboniferous were very shallow and then non-existent in the Permian.

Most trilobites here are found in Ordovician and Devonian rock, and are preserved in limestone and sandstone. These rocks mean the fossils are fairly easy to extract, except when the rock contains coral. Coral is a rock-building organism; when it dies it forms sedimentary structures and created a very hard baffle or bound stone. Trilobites fossils that are found settled in coral is best leaving, as a hammer will just bounce off. Photographs of these are usually adequate anyway. I found that most of the trilobite fossils were fragmented; mostly thoraxes and pygidiums were found- very few cephalons. Why, you ask? This has all to do with the fact that trilobites shed. This is called ecdysis and we see it in modern crabs, lobsters and insects today. The trilobite, when it was too big for its exoskeleton, would detach its libragena (its ‘free cheek’) from its fixigena (you guessed it- ‘fixed cheek’) and the rest of its cephalon, and wriggle out. This is why the rest of the head, apart from the glabella, is not normally found.

ecdysis

We also visited areas that didn’t have trilobites. This was just so we could understand the overall palaeoenvironment more. In the Silurian, there were no trilobites, but many many orthocones. Here, the locals polish this black limestone, filled with orthocones, and use it for kitchen countertops (fashionable and scientific!). A lot of them were all facing the same direction; this suggests that the current was constant. The limestone was black, indicating anoxic deep water- possibly an alluvial fan. This is supported by lack of trilobites, coral or crinoids.

Another area without trilobites was an outcrop of the Carboniferous. This was an area of alternating limestone, sandstone and shale. There were very few fossils here except for the occasional brachiopod. This was because at this time the sea was regressing so much that any dead animals would have floated down to deeper areas.

The Cambrian was definitely the deepest part of the succession, except for possibly the Silurian, and we saw a general marine regression, until there was no sea whatsoever in the Permian. And, of course, then there was a mass extinction (want to know more? Read my Top 5 Extinctions!) At which this point trilobites went extinct.

So what next for my project? Well, the samples I collected will take a lot of preparation, trying to uncover as much of the specimens as I can. I also made several logs over the trip, which will have to be put on a computer and some conclusions drawn up. Stay tuned as I will be posting pictures of my prepared fossils!

SAM_0472

palaeos.com

www.trilobites.info

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The World of Fossil Smuggling

There have been many recent palaeontological findings, such as new dinosaurs and perfectly preserved specimens, from places such as China and Mongolia. These countries do not allow fossils to be exported and taken from them, and this has led to a lot of fossil smuggling and theft.

This could lead to a slow decline in new understanding in palaeontology; museums will obviously not display or even have in their archives illegal fossils. In order for a fossil to make it on display in any museum, it must be backtracked to origin. Any dodgy dealings along the way will not be tolerated and the institution will reject the specimen if it is found to be illegitimate. Museums are filled with equipment and researchers, so illegal fossils aren’t investigated as well as they should be if at all. Many collectors that buy stolen fossils will not care about the science behind it- simply its exotic origin and appearance.

Also, in the countries where fossil laws are strict, skilled government palaeontologists are appointed to carefully excavate newly discovered fossils, where they can then be removed properly and studied in depth. Fossil smugglers will very often hurry to remove the fossil from the ground, as to not get caught, and damage the specimen. This means that important features of the animal can be greatly damaged.

Furthermore, selling fossils (if you get the good ones) can get you millions of pounds, whereas giving them to science will get you credit and possibly your name on the scientific paper. To a lot of people, the latter is not that important and a couple of million is hard to say no to. Recently, a commercial fossil dealer had been taken to court for importing several fossils into the USA; namely a Tarbosaurus. This creature comes only from Mongolia, which forbids fossil export. When the dinosaur came up in an auction catalogue, the Mongolian government pressed charges. This dealer is now in a lot of trouble for customs violations relating to the value and stated identity of the objects being imported.

Vital information about the fossils can also be lost along the way with smugglers. The smugglers want keep quiet the place of origin of the specimens, for obvious reasons, and that means that all geological history is taken from that animal. It’s like taking a phrase out of context; all you are left with are the bare bones with no understanding as to where they come from. Boring as geology can be, it is incredibly important, almost the foundations of palaeontology, as it allows us to understand what the Earth was like when these creatures were alive.

Finally, a small tale that sums up why fossil smuggling can be so detrimental to science: In 1999, National Geographic published an article on the missing link between dinosaurs and birds. The article was titled: “Feathers for T. rex?”. It showed the ‘new discovery’ of Archaeoraptor liaoningensis, which had actually been smuggled out of China and brought by the Dinosaur Museum in Blanding, Utah for $80000. The funny part is that it doesn’t exist- the fossil was a fake- a mish-mash of several species of Microraptor and Yarornis. No one knows if this fake was meant to be a scientific fraud but it was more likely to have been created to take the fancy of an unsuspecting fossil collector.

And that’s why you should never smuggle fossils, kids!GE DIGITAL CAMERA

References:

http://www.walkingwithdinosaurs.com/news/editorial/fossil-smuggling-threat-to-understanding-dinosaurs/1/

‘The Week’ magazine, March 2013 issue

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Strange Ice Age Mammals

Technically there have been many ‘Ice Ages’ in our geological past, but the most recent glacial period happened during the Pleistocene, from approximately 110,000 to 10,000 years ago. Interestingly enough, an ice age is where there is a long-term reduction in the Earth’s temperature, resulting in the polar ice caps to be present or expand. So, in this way, we are still in an ice age that began 2.6 million years ago, simply because of the presence of the Arctic, Antarctic and Greenland ice sheets.

During this time, mammals were significantly bigger than their modern relatives but the harsh, cold climate led to the decline and extinction of these mega-fauna. The extinct animals will be described in this article:

Mammoths: the extinct genus Mammuthus had long, curved tusks. The northern species commonly had long hair, also. They lived from the Pleistocene, about 5 million years ago, to the Holocene, 4500 years ago. These creatures lived in Europe, Asia, Africa and North America and were members of the family Elephantidae. The word ‘mammoth’ was first used to describe anything that was huge, which is what mammoths indeed were; the largest known species were 4m tall and weighed up to 8 tonnes, even though some sizable males weighed up to 12 tonnes! Both sexes had tusks, which is quite unusual. They were pregnant for the long period of 22 months and gave birth to only one calf.

Mammuthus primigenius, woolly mammoth

The woolly mammoth (M. primigenius) was the last species to die out. It seemed that they all died out 10000 years ago in a mass extinction of the mega-fauna. It is still unsure as to why they went extinct. It may have been because of the warming during the Holocene, leading to the decline in the glaciers and sea level rise. This caused there to be more grassland environments, and not forests that the mammoths lived in. But, these kinds of warming periods had already happened during the ice age and it hadn’t led to the extinction of mega-fauna. Other causes might have been from infectious diseases or overhunting from humans.

Mastodons: these are related to elephants and lived in North and Central America and went extinct also in the Pleistocene about 10000 to 11000 years ago. These were also forest dwellers and lived in herds, which may too have gone extinct because of climate change and hunting, particularly by the Clovis hunters. The word ‘mastodon’ means nipple tooth because of their cone-shaped cusps of their teeth, which looked like nipples. They were similar in appearance to mammoths and elephants, although they are not closely related. In comparison to mammoths, they had shorter legs, a longer body and more heavily muscled, similar to Asian elephants. The males could reach up to 2.8m high and could weigh up to 4.5 tonnes. Their tusks were curved, supported by a low and long skull.

220px-Knight_Mastodon

Saber-toothed cats: Machairodontinae are a subfamily of true cats that went extinct in the Pleistocene. Included in this subfamily was the famed genus Smilodon, which I will describe here. Several fossils have been found with one of the largest collections taken from the La Brea Tar Pits. Three species of the genus are known and they vary in size and build. They were a lot more robust than any other modern big cat and their defining feature being the long upper canines, reaching up to 28cm in length. Its jaw had a much bigger gape and its large teeth were made for precision killing. They fed on bison and camels. They probably lived in forest where they could hide and then ambush prey. It might have gone extinct because it fed only on large animals. Smilodon were about the same size as modern lions or tigers, but were built more like bears, and their brains were a lot smaller than other cats. It is suggested that although their gape is much bigger than other cats, and their teeth substantially great, their bite was only a third that of a lion’s. This is because instead they could grasp and latch onto their prey, and kill them that way.

saber

Glyptodon: these large, armoured relatives of armadillos were roughly the same weight as a Volkswagen Beetle. They almost looked like turtles, with squat limbs and a round shell, reaching up to 3.3m in length. Their hard, protective shells were made up of more than 1,000 2.5 cm-thick scutes, with each species having its own unique plate pattern. Even the tail was armoured, and they had bony caps on top of their skulls. This animal was most probably hunted to extinction also.

Glyptodon_old_drawing

Irish elk: these were one of the largest deer that ever existed and went extinct about 7700 years ago. Despite the name, it was not exclusive to Ireland and wasn’t closely related to elks and this is why the term ‘Giant Deer’ is often used. It was up to 2.1m tall and had the largest antlers of any cervid, weighing up to 40kg. Large specimens weighed 700kg in total. There have been many discussions as to why this large beast went extinct; some have put it down to over hunting, where others have even suggested that the animal’s large antlers disabled them from moving through forests. High amounts of calcium and phosphate were needed to sustain antler growth and maybe the lack of these minerals in their diets led to their downfall.

irish elk

These animals, along with giant ground sloths, short-faced bears and cave bears went extinct in this time, which paved the way for much smaller mammals that we see today. Neanderthals also became extinct during this period. At the end of the last ice age, cold-blooded animals, smaller mammals like wood mice, migratory birds, and swifter animals like whitetail deer had replaced the mega-fauna and migrated north. It was most severe in North America, where camels and horses were completely wiped out in that region.

ice age

Agusti, Jordi and Mauricio Anton (2002). Mammoths, Sabretooths, and Hominids. New York: Columbia University Press. p. 106

Antón, M.; García-Perea, R.; Turner, A. (1998). “Reconstructed facial appearance of the sabretoothed felid Smilodon”. Zoological Journal of the Linnean Society 124 (4): 369–86.

Clayton, Lee; Attig, John W.; Mickelson, David M.; Johnson, Mark D.; Syverson, Kent M. “Glaciation of Wisconsin”. Dept. Geology, University of Wisconsin

David Lambert and the Diagram Group. The Field Guide to Prehistoric Life. New York: Facts on File Publications, 1985. pp. 196

Gribbin, J.R. (1982). Future Weather: Carbon Dioxide, Climate and the Greenhouse Effect. Penguin

Hsieh, T. H.; Chen, J. J. J.; Chen, L. H.; Chiang, P. T.; Lee, H. Y. (2011). “Time-course gait analysis of hemiparkinsonian rats following 6-hydroxydopamine lesion”. Behavioural Brain Research 222 (1): 1–9.

MOEN, R.A.; PASTOR, J. & COHEN, Y. (1999): Antler growth and extinction of Irish Elk. Evolutionary Ecology Research 1: 235–249

Simpson, J. (2009). “Word Stories: Mammoth.” Oxford English Dictionary Online, Oxford University Press. Accessed 05-JUN-2009

Turner, A.; Antón, M. (1997). The Big Cats and Their Fossil Relatives: An Illustrated Guide to Their Evolution and Natural History. Columbia University Press. pp. 57–58, 67–68.

Woodman, N. (2008). “The Overmyer Mastodon (Mammut americanum) from Fulton County, Indiana”. The American Midland Naturalist 159 (1): 125–146.

“Woolly Mammoth (Mammuthus primigenius)”. The Academy of Natural Sciences of Drexel University. Retrieved 2012-03-07.

Images from:

http://www.bbc.co.uk

commons.wikimedia.org

epiccreature.blogspot.com

igs.indiana.edu

paleospot.com

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