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HOME | DRAGONS | EVOLUTION
Komodo Dragon - Evolution theory of the Komodo Dragon | | Proterozoic Period 2.5 billion to 545 million years ago.
| Although primordial RNA (the molecules of first life) may have appeared some 4 billion years ago, the Earth was still heavily volcanic, with low quantities of surface water and free oxygen. The oldest microfossils of bacteria date from around 3.5 billion years ago, however the earliest fossils of more complex organisms and animals do not appear until the Proterozoic period.
Protoctista (microorganisms with nuclei) have existed for over 1.2 billion years and include algae, slime molds, amoeba, plankton and other protozoans. During this period, certain protoctists would evolve into the other four kingdoms of Animals, Plants, Fungi and Bacteria.
By around 545 million years ago, the earliest Chordates (animals with a spinal chord) appeared. The Phylum Chordata would eventually include mammals, birds, reptiles, fish and the dinosaurs. 545 million years ago however, our ancestor was a small multicelled organism with a rudimentary group of nerve cells creating a nerve chord.
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| | Cambrian Period 545 million to 490 million years ago.
| Around 500 million years ago, Chordates, the ancestors of Vertebrates (backboned animals) further evolved in the oceans. The spinal chord of the Chordates that appeared in the Proterozoic period was a amazing control system that allowed for the eventual evolution of higher brain function. At the same time, it needed protection and these species developed cartilage based structures around this spinal chord that would eventually evolve into bone and other hard body components that would assist in the move onto land and allow for out-of-water mobility. During the Cambrian, most life and all animal life remained water bound.
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| | Ordovician Period 490 million to 443 million years ago.
| Invertebrate life diversified greatly during the Ordovician period, from around 160 families at the start to some 530 families at its close.
Although there is some arguable evidence of a move by plants on to land, in the form of mosses and liverworts, the evolution of life remained predominantly waterbound. The greatest variety of animal life then, as now, was invertebrate. No true vertebrate animals existed during the Ordovician. The Chordates found in fossils had no bony internal skeletons and structure is therefore assumed to have been cartilaginous. The fish were small jawless forms (Agnatha). It would take the initial move of plant species and the subsequent evolution of Vertebrates with stronger internal body structures to begin the animal migration to land.
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| | Silurian Period 443 million to 417 million years ago.
| The Silurian period saw a relative stabilisation of the Earth's climate. Coral reefs made their debut, as did freshwater fish and the first fish with jaws. Perhaps most importantly, both plant and animal life made significant appearance on land. Some animals of a form similar to spiders and centipedes have been found in land based fossils.
Most important for significant future moves to land, primitive plants such as Cooksonia and more complex lycopods began to find traction in the tough climate of largely lifeless and windblown land. The first Vertebrates with bone instead of cartilage most likely appeared in the late Silurian, although fossil structures only confirm them during the Devonian period to follow.
Numbers of Vertebrate species, in the form of Amphibians would increase rapidly after the Silurian for some hundred million years before declining during the rule of the Reptiles, from around 300 million years ago, until the extinction of the Dinosaurs some 65 million years ago, followed by the era of Mammals which continued through to modern times.
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| | Devonian Period 417 million to 354 million years ago.
| Amphibians were the first Vertebrates to make the transition from water to land. Some 360 million years ago, toward the end of the Devonian period, Amphibians would begin to spend longer on land. Whilst still laying soft eggs in water, mature Amphibians had bone structure and circulatory systems capable of sustaining them out of water. The tetrapods (four-legged animals) were the predecessors of all later Vertebrates (including mammals, birds and reptiles).
Also during the Devonian period, the world's land masses were drifting together to form the super-continent, Pangea. This aggregation of land would accompany the explosion of Vertebrates out of the sea and onto land, ensuring that Reptiles and other Vertebrates would be found in almost all quarters of the modern world.
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| | Carboniferous Period 354 million to 295 million years ago.
| All modern reptiles, with the exception of turtles, descended from the subclass Diapsida. Meaning 'two-arched reptiles', this classification refers to the presence of two openings in the temporal region of the skull (Ciofi, 1999). These holes enabled wide jaw opening as a result of longer and stronger jaw muscles.
For those of us who like to compare reptiles such as the Komodo Dragon to dinosaurs, we have to go back to this period, some 300 million years ago to make the ancestral connection. The subclass Diapsida was superseded after the Carboniferous period by the subclasses Archosauria (which included dinosaurs, birds and crocodilians) and Lepidosauria (from which most other modern reptiles, including snakes and lizards descended).
As much as many modern day reptiles remind us of the extinct dinosaurs of the Jurassic and Cretaceous periods, most reptiles evolved separately from the Carboniferous period onward.
It is also during the Carboniferous period that the mega-continents Laurentia and Gondwana were first brought together by the movement of tectonic plates to form the massive landmass Pangea. Eventually this landmass would separate back into Laurentia (now northern Europe and eastern North America) and Gondwana (now South America, Africa and Australia) eventually resulting in the significant divergence of flora and fauna from these regions (Dixon et. al., 2001).
The climate of this period seems similar to today, with arctic conditions at the poles, including central Gondwana, and rain forests close to the equator.
The Carboniferous period is also notable for the amazing proliferation of insect species and the arrival of winged insects, all forming an important part of the food chain for the evolution of many Reptile species.
The oldest reptile fossils are around 340 million years old and were found in the early Carboniferous formations of Scotland and Nova Scotia (Cogger and Zweifel, 1998).
The Tuatara (Sphenodontia) found today only in New Zealand is perhaps the closest remaining example of the Diapsids of the Cretaceous period. Fossils some 225 million years old are virtually identical to the Tuatara. All species of the order Sphenodontia became extinct some 60 million years ago, at the end of the Cretaceous period, leaving the Tuatara as the sole representative of the Order.
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| | Permian Period 295 million to 248 million years ago.
| It was during the Permian period that the Diapsid line split into the two main subclasses Archosaurs and Lepidosaurs. Two other groups, Ichthyosaurs and Euryapsids also evolved from the Diapsid line, to eventually become extinct some 60 million years ago (unless you subscribe to the Lockness Monster being a surviving Plesiosaur).
Archosaurs, sometimes referred to as 'ruling reptiles' evolved upright stances and would eventually become Dinosaurs, Crocodilians and Birds.
Lepidosaurs retained a sprawling posture and would evolve into the Order Squamata which includes all modern day Snakes and Lizards and the Order Spendodonts of which only the New Zealand Tuatara remains.
Turtles and Tortoises come from an earlier genetic breakaway group during the Devonian or Early Carboniferous periods.
The other modern day Reptile group of Crocodiles and Aligators would break away from the Archosaurs (Dinosaurs) in the early Triassic period.
The Permian period marked the end of the Palaeozoic Era and a dramatic and unprecedented mass extinction. Fossils from after the Permian period are markedly different from those of earlier periods and unlike the later mass extinction at the end of the Cretaceous period, this extinction seems to have taken place over an extended period of time, perhaps as long as 10 million years (Dixon et. al., 2001). The reason for this extinction is not clear, however there is strong evidence of atmospheric change, increased volcanic activity, and other climate change that in combination created the largest mass extinction in the Earth's history.
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| | Triassic Period 248 million to 205 million years ago.
| The Triassic period is arguably one of the most interesting and amazing periods in evolution. The mass extinction at the end of the Permian period brought a number of evolutionary branches to their close. Those that remained adapted and divided. The Triassic period saw the ancestors of the Diapsids form the Orders of Squamata (Lizards and eventually snakes), Crocodylia (Crocodiles and Aligators), Dinosaurs (including the only surviving variety, Birds), as well as other genetic experiments that didn't make it out of the Triassic period.
The Triassic also saw the Synapsids evolve into mammal-like reptiles and toward the end of the Triassic period into the first true mammals and our distant ancestors.
These divisions of life effected almost every corner of the globe and provide a largely common ancestry because of the aggregation of land during the Triassic into the single super-continent, Pangea. The Triassic has been called the 'dawn of the Age of Reptiles'.
The Triassic came to a close with another Gee-Gee event (a Global Geographic Event) that created further extinctions. One-third of sea animals, one-third of land based vertebrates, and the majority of plant species died out in what appears to have been a short period of time accompanied by a relatively sudden increase in average temperatures (Dixon et. al., 2001).
The Triassic saw Lepidosaurs divide into Squamata and Spendodonts. The modern day Tuatara from New Zealand is the only surviving Spendodont, unchanged for almost 200 million years. The Order Squamata were more successful and would eventually divide into the thousands of species of modern day snakes and lizards. Click here to see our breakdown of surviving Squamata species >>
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| | Jurassic Period 205 million to 144 million years ago.
| The Order Squamata, which includes modern lizards and snakes probably divided from the Lepidosaurs during the Triassic period, however the oldest squamate fossil comes to us from the Jurassic Period. Lizard like squamates dominated during the Jurassic and snakes would not evolve from this group until the Cretaceous period. Squamate groups included iguanids and chameleons, skinks and lacertids, geckos and the varanids (monitor lizards). The monitor lizards also included the largest marine reptiles, the mososaurs.
The Jurassic is also notable for the emergence of the first Bird species that separated from the Theropod group of dinosaurs of the Triassic period, that themselves split from the Diapsids of the Permian period, which were also the ancestors of modern day snakes and lizards.
The Jurassic period would also see the break-up of the super-continent, Pangea, that formed during the Devonian period. Some 200 million years ago, tectonic forces split Pangea into two smaller super-continents. The northern continent, Laurasia, contained most of present day Europe, Asia and North America. The southern continent, Gondwana, contained most of South America, Antarctica, New Zealand, India, Africa and Australia. Hence this important period of evolution for Squamates saw their progress divided into two key groups, those of either laurasian or gondwanan origin. The Komodo Dragon and most Monitor Lizards (Varanids) are gondwanan, with the largest group and number of species found in Australia. Some Varanids, such as the extinct Necrosaurids may have been laurasian in origin, with fossils found in North America, however the lineages follow two quiet distinct paths.
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| | Cretaceous Period 144 million to 65 million years ago.
| About 100 million years ago, fossil records in central Asia show the arrival of a species related to contemporary Varanids (Monitor Lizards) known as mosasaurs. This marine species became extinct, along with the dinosaurs about 65 million years ago.
Mosasaurs are important not only because they are the direct ancestors of Monitor Lizards (Varanids) such as the Komodo Dragon, but also because they have played a role in the argument as to whether snakes evolved in the water or on land. Snakes evolutionary path split from the other Squamates, Lizards, some 150 million years ago and debate over their origin has centred around the Mosasaurs.
Recent analysis of both snake and lizard gene sequences shows that snakes evolved on land and are not closely related to either the Mosasaurs or the Varanidae family of Lizards (Monitors). The genetic evolution of snakes supports the terrestrial arguments that adapting to burrowing and other confined spaces helped drive the snake families toward the loss of limbs (Vidal and Hedges, 2004).
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| | Paleogene Period 65 million to 24 million years ago.
| Around 50 million years ago, land monitors spread throughout Europe and South Asia. The Varanus genus (today's Monitor Lizards) appeared in Asia about 40 million years ago and evolved during the remainder of the Paleogene period. Squamate fossils in Australia date back as far as 30 million years, the oldest of which are representatives of the Varanid group (Monitor Lizards, including Goanna's and the modern-day Komodo Dragon). Evidence supports a much larger range of species including significantly larger specimens than those surviving today.
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| | Neogene Period 24 million to 1.8 million years ago.
| The Varanid species of Australia and Asia had another opportunity to migrate about 15 million years ago when Australia collided with southeast Asia and about 13 million years ago, a second lineage differentiated and moved throughout Australia and the Indonesian archipelago.
Varanus komodoensis differentiated from its earlier Australian ancestors around 4 million years ago and may have extended widely throughout Australia and South-East Asia at some point during the late Neogene period (Ciofi, 1999).
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| | Pleistocene Period 1.8 million years ago to 10,000 years ago.
| Komodo Dragons appear to have extended throughout the Indonesian archipelago to as far east as Timor. In Australia, the even larger Varanid, Megalania prisca (meaning 'ancient giant butcher') ranged in broad distribution from Queensland, down through central Australia and New South Wales and into South Australia, with the discovery of remains in Naracoorte, South Australia in 2000. This enormous Monitor Lizard, the ancestor of today's Goanna's and possibly the Komodo Dragon, grew to as large as 7 meters (23 feet) in length and may have weighed well over 500kg (up to half a ton).
These lizards could have fed on stegodonts (pygmy elephants) and other large prey of the era with similar distributions. The disappearance of these giant lizards coincides with the extinction of many large mammals toward the end of the Pleistocene, some 100,000 to 10,000 years ago. The exact cause of this extinction is unclear, however it would leave the world with very few remaining 'mega-reptiles'. Salt water crocodiles, pythons, some large sea turtles and the largest monitor lizards are the last vestiges of an era, hundreds of millions of years long, in which reptiles 'ruled the planet'.
The recent extinction of Megalania prisca (probably around 25,000 years ago) would have meant that humans would have crossed paths with this incredible 'monster'. This creates all sorts of interesting considerations in relation to the multiplicity of mythologies that refer to 'Dragons', of particular interest are Chinese and other asian Dragon representations (illustrations, sculpture and mythology).
Around 20,000 years ago, the islands of the Komodo national park were joined with surrounding areas of the Indonesian archipelago during the last Ice Age. With the passing of the Ice Age, the Varanus komodoensis (Komodo Dragon) was isolated to an area comparable with its modern day distribution.
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| | Holocene Period 10,000 years ago to the present.
| The Komodo Dragon is an example of evolutionary adaptation and the results of specific environmental conditions.
After the dramatic sea level changes of the late Pleistocene period, Komodo Island and its neighbours found themselves in their current geographic situation. The large Komodo Dragon stranded from further migration on this section of the Indonesian archipelago. On these islands, the Komodo Dragon does not seem to have had to compete with other large predators for prey.
To the west, further along the archipelago, there are large cats such as the Fishing Cat and Golden Cat. To the east, human progression has reduced the distribution of the Komodo Dragon, limiting their reach on the island of Flores and likely leading to their disappearance from Padar in the late 1970s. By comparison, Australia, also devoid of many larger carnivores has seen large Varanids, such as the Parentie, survive and prosper. However these large Goannas still had to compete with large carnivores such as the extinct Marsupial Lion (Thylacoleo carnifex), as well as the introduced Dingo. In Australia, the arid environment and the ecologically sustainable lifestyle of indigenous Aboriginal tribes, seems to have allowed Varanid species to flourish. Goannas have a strong connection with the 'Dreamtime', the oral and cultural tradition of the Aboriginal people. One wonders whether the mythology of other Asian cultures and the spirituality of the Dragon comes from a time when Varanid species co-existed with other humans throughout Asia.
On Komodo Island and nearby islands, the Komodo Dragon assumed the absolute pinnacle of the food chain, able to grow to a size that the environment could sustain, and forced perhaps to a size that could prey on the larger herbivores such as Deer and Goats.
The fact that Islands generally have fewer food resources than large landmasses, favors reptiles in the race for the top of the predatory chain. Reptiles can subsist on much lower total calorific requirements than warm-blooded animals, and have a larger size to consumption ratio than other classes of predators.
The Komodo Dragon is still under threat. The Holocene has seen the most rapid rate of extinction in the history of animal life on our planet, primarily as a result of humans and our accompanying habitat destruction. Even with the protection of the Komodo National Park, Komodo Dragon numbers are in decline. Aggressive fishing practices, human expansion and the destruction of the underlying food chain all threaten the Komodo Dragon. Only some 2,500 individuals survive today.
Nature may also have its say. The Komodo National Park is in a geographically active region and is itself a rather recent geographic formation. A single volcanic event could remove the Komodo Dragon from our list of surviving reptiles.
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