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Description
It is dawn, and as the sun finally begins to appear above the horizon, the forest bursts into song. Birds call from all directions, announcing the coming of a new day. A snout emerges from a hollow high in a tall tree. The whole head soon emerges, the large eyes squinting in the bright light of dawn. It is the head of a crocodile, but what is a crocodile doing in a tree, let alone one that is so tall? Another head appears, and then another and another. Soon there are four crocodilians peering out the hollow, staring towards the sun and looking around. One decides to climb out of the hollow, revealing the typical crocodile shape but with longer legs and claws, and a prehensile tail. It heads to and exposed branch to begin basking in the sun. These are Northern Tree Crocs, part of a small genus of mekosuchine crocodiles that have adapted to living in the treetops.

Tree Crocs
Arborsuchus borealis and Arborsuchus australis

Classification: Crocodilia, Crocodylidae, Mekosuchinae

Origins and evolutionary relationships: When Tasmania was attached to Australia the only crocodilians present were the mekosuchines, a subfamily of crocodiles endemic to Oceania. They are now extinct everywhere but Tasmania, with the last few non-Tasmanian populations still surviving on remote islands less than 2,000 years ago, before the arrival of humans to these islands wiped them out. Tasmania is a very cold island, not very suited to cold-blooded crocodilians, but the mekosuchines have begun adapting to this. All crocodilians living on the island today are descended from a single ancestor, originating around 14 million years ago, which had developed a better metabolism. Not warm-blooded, not cold-blooded, but something in between. This helps them cope with colder conditions than other crocodilians can endure. However, they are still mostly restricted to the north, where it is warmer. Only one species, the Southern Tree Croc (Arborsuchus australis), occurs all the way to the island's southernmost areas. It and its close relative the Northern Tree Croc (A. borealis) are unique among modern crocodiles because they spend most of their time in the trees.

Description: These arboreal reptiles still have the time-worn crocodilian bodyplan, but they also have longer legs, large feet with big claws that lack webbing, and a prehensile tail. Their teeth are needle-sharp, and the large eyes are positioned facing forwards, giving them great binocular vision essential for a tree-dweller. They lack the huge scutes other crocodiles possess, rather they have smaller scutes underneath the skin that are more lightweight. They are a browny-green colour. Around the size of a fox, the Southern Tree Croc is a little bit larger.

Habitat and distribution: Together both specie's distributions cover all the forested areas of Tasmania, but, as their names suggest, they occupy different parts of the island to avoid competition. The Northern lives in, well, the north, and the Southern has learnt to dwell in the colder south. They live anywhere where there is sufficient vegetation, including well-vegetated suburbs.

Behaviour: As mentioned earlier, tree crocs are mostly arboreal. Several other crocodilians, like the Australian Freshwater Crocodile, also occasionally climb trees to bask or watch for predators or competitors, but the tree crocs are the only ones to hunt, breed and live out their lives in the canopy. Their adaptions to an arboreal lifestyle are easy to see, and they move about in the branches in an almost monkey-like way, grasping with long fingers and using their tail as a fifth limb.

They live in the trees for two reasons. The first is to avoid predation, as mokoi, thylacines, thylacoleonids and other mekosuchines will readily eat tree crocs. The second reason is so they can access food not available to other crocodilians. Like other crocodiles, they are ambush predators, hunching down in a shady spot in the canopy to wait for prey to pass. They can bring down prey as large as themselves using their strong bite, using their needle-sharp teeth to make sure that the prey does not escape its jaws. They eat birds, small to medium-sized mammals, frogs and other reptiles.

When they need to move from tree to tree, they move across the ground, rather like a koala. While they are more clumsy down on the forest floor, they can move at great speed to scamper back up a tree if they feel threatened. Danger can not only come from below, but from above. Large birds of prey can snatch tree crocs from the branches, and a Striger will try and sneak behind the reptile to kill it with a bite to the back of the neck. When cornered, they lash out, but it often does little to stop a large predator, and the go-to method of escape it to flee.

Unlike many other crocodiles, tree crocs are social animals, constantly yapping from the treetops to one another. However, when hunting, they drive all other crocodiles away from the tree they have decided to hunt in, so any prey that lands in that particular tree will be theirs. However, once they have eaten, they will socialise with other crocs. They are thought to be the most intelligent of all reptiles, and some say that the crocodiles communicate to recommend hunting and resting sites. Because Tasmania gets really cold at night, tree crocs are diurnal, and spend their night inside a tree hollow. Several crocodiles will often share a single hollow, all curled up alongside each other.

Unlike all other crocodilians, tree crocs mate for life. A female will simply choose a male she likes, and they are together from then on. When the female is ready to lay, they drive away all other crocodiles from their hollow. They lay their 2-5 eggs at the base, and then fill the hollow with fermenting vegetation. This keeps the eggs warm, and they can keep the temperature consistent by either removing or adding vegetation. Once the eggs hatch, the hatchlings are looked after by both parents until they are half of adult size.

Conservation status and additional information: The Northern Tree Croc has been hunted for its skin in the past and has had much of its habitat destroyed, and so is classed as Vulnerable. The Southern Tree Croc had also been hunted for skins, but as the southern areas are much harsher the hunters killed less of this species, and so it is still classed as Least Concern. Tree crocs are some of Tasmania's most famous animals and are popular in local literature because of their likeable looks and demeanour. Some people with special licenses keep them as pets, and they are generally unaggressive in captivity.

These crocodiles look bizarre and have a unique lifestyle, but it clearly works as they are the most abundant mekosuchines on Earth.

For the speculative evolution project Van Diemen's Land, see here: s1.zetaboards.com/Conceptual_E…

Description
It is dawn, and as the sun finally begins to appear above the horizon, the forest bursts into song. Birds call from all directions, announcing the coming of a new day. A snout emerges from a hollow high in a tall tree. The whole head soon emerges, the large eyes squinting in the bright light of dawn. It is the head of a crocodile, but what is a crocodile doing in a tree, let alone one that is so tall? Another head appears, and then another and another. Soon there are four crocodilians peering out the hollow, staring towards the sun and looking around. One decides to climb out of the hollow, revealing the typical crocodile shape but with longer legs and claws, and a prehensile tail. It heads to and exposed branch to begin basking in the sun. These are Northern Tree Crocs, part of a small genus of mekosuchine crocodiles that have adapted to living in the treetops.

Tree Crocs
Arborsuchus borealis and Arborsuchus australis

Classification: Crocodilia, Crocodylidae, Mekosuchinae

Origins and evolutionary relationships: When Tasmania was attached to Australia the only crocodilians present were the mekosuchines, a subfamily of crocodiles endemic to Oceania. They are now extinct everywhere but Tasmania, with the last few non-Tasmanian populations still surviving on remote islands less than 2,000 years ago, before the arrival of humans to these islands wiped them out. Tasmania is a very cold island, not very suited to cold-blooded crocodilians, but the mekosuchines have begun adapting to this. All crocodilians living on the island today are descended from a single ancestor, originating around 14 million years ago, which had developed a better metabolism. Not warm-blooded, not cold-blooded, but something in between. This helps them cope with colder conditions than other crocodilians can endure. However, they are still mostly restricted to the north, where it is warmer. Only one species, the Southern Tree Croc (Arborsuchus australis), occurs all the way to the island's southernmost areas. It and its close relative the Northern Tree Croc (A. borealis) are unique among modern crocodiles because they spend most of their time in the trees.

Description: These arboreal reptiles still have the time-worn crocodilian bodyplan, but they also have longer legs, large feet with big claws that lack webbing, and a prehensile tail. Their teeth are needle-sharp, and the large eyes are positioned facing forwards, giving them great binocular vision essential for a tree-dweller. They lack the huge scutes other crocodiles possess, rather they have smaller scutes underneath the skin that are more lightweight. They are a browny-green colour. Around the size of a fox, the Southern Tree Croc is a little bit larger.

Habitat and distribution: Together both specie's distributions cover all the forested areas of Tasmania, but, as their names suggest, they occupy different parts of the island to avoid competition. The Northern lives in, well, the north, and the Southern has learnt to dwell in the colder south. They live anywhere where there is sufficient vegetation, including well-vegetated suburbs.

Behaviour: As mentioned earlier, tree crocs are mostly arboreal. Several other crocodilians, like the Australian Freshwater Crocodile, also occasionally climb trees to bask or watch for predators or competitors, but the tree crocs are the only ones to hunt, breed and live out their lives in the canopy. Their adaptions to an arboreal lifestyle are easy to see, and they move about in the branches in an almost monkey-like way, grasping with long fingers and using their tail as a fifth limb.

They live in the trees for two reasons. The first is to avoid predation, as mokoi, thylacines, thylacoleonids and other mekosuchines will readily eat tree crocs. The second reason is so they can access food not available to other crocodilians. Like other crocodiles, they are ambush predators, hunching down in a shady spot in the canopy to wait for prey to pass. They can bring down prey as large as themselves using their strong bite, using their needle-sharp teeth to make sure that the prey does not escape its jaws. They eat birds, small to medium-sized mammals, frogs and other reptiles.

When they need to move from tree to tree, they move across the ground, rather like a koala. While they are more clumsy down on the forest floor, they can move at great speed to scamper back up a tree if they feel threatened. Danger can not only come from below, but from above. Large birds of prey can snatch tree crocs from the branches, and a Striger will try and sneak behind the reptile to kill it with a bite to the back of the neck. When cornered, they lash out, but it often does little to stop a large predator, and the go-to method of escape it to flee.

Unlike many other crocodiles, tree crocs are social animals, constantly yapping from the treetops to one another. However, when hunting, they drive all other crocodiles away from the tree they have decided to hunt in, so any prey that lands in that particular tree will be theirs. However, once they have eaten, they will socialise with other crocs. They are thought to be the most intelligent of all reptiles, and some say that the crocodiles communicate to recommend hunting and resting sites. Because Tasmania gets really cold at night, tree crocs are diurnal, and spend their night inside a tree hollow. Several crocodiles will often share a single hollow, all curled up alongside each other.

Unlike all other crocodilians, tree crocs mate for life. A female will simply choose a male she likes, and they are together from then on. When the female is ready to lay, they drive away all other crocodiles from their hollow. They lay their 2-5 eggs at the base, and then fill the hollow with fermenting vegetation. This keeps the eggs warm, and they can keep the temperature consistent by either removing or adding vegetation. Once the eggs hatch, the hatchlings are looked after by both parents until they are half of adult size.

Conservation status and additional information: The Northern Tree Croc has been hunted for its skin in the past and has had much of its habitat destroyed, and so is classed as Vulnerable. The Southern Tree Croc had also been hunted for skins, but as the southern areas are much harsher the hunters killed less of this species, and so it is still classed as Least Concern. Tree crocs are some of Tasmania's most famous animals and are popular in local literature because of their likeable looks and demeanour. Some people with special licenses keep them as pets, and they are generally unaggressive in captivity.

These crocodiles look bizarre and have a unique lifestyle, but it clearly works as they are the most abundant mekosuchines on Earth.

For the speculative evolution project Van Diemen's Land, see here: s1.zetaboards.com/Conceptual_E…