HOME | DD

Description
Most macropods may be specialised for a cursorial ground-dwelling existence today, but phylogenetically they are actually a group of terrestrial possums and over the course of their evolutionary history they have moved in and out of the trees on numerous occasions. The most notable example of this would be the tree kangaroos of New Guinea and the north-eastern mainland, a more recently evolved group that originated after the collapse of Australia's expansive Miocene rainforests. During the Pleistocene there were even tree kangaroos and other arboreal macropods in drier southern Australia and they have since expanded back down the east coast to reclaim some of their former range, ranging as far south as the Bass Plain during the Recurocene. In addition to this the Recurocene has fostered the evolution of another arboreal macropod, but this one is especially unique. The Honey Potoroo (Orientalipotorous nectarus) is not only the first potoroid to return to the trees but also, in terms of diet, one of the most specialised macropods that have ever lived.

The Honey Potoroo is a descendant of the only species of potoroo to last through the Holocene, the Long-nosed Potoroo, with all others succumbing to predation by invasive predators, habitat destruction and the rapidly changing climate. The Long-nosed Potoroo itself was almost a victim of the final factor, managing to hang on only in north-west Tasmania and in small pockets of coastal hinterland on the south-eastern mainland where suitable tracts of wet forest lasted through the drying of southern Australia during the climatic optimum. As conditions normalised and glaciation returned the normal distribution of wet forest on the continent's east coast was restored and this allowed the potoroos to regain their former range, later extending even further into the jungles of north-east Queensland. Most potoroos are generalists but nonetheless their diets consist mostly of fungi, and it would be the moist conditions of the northern rainforests encouraging the growth of their favoured food in unusual places that would first spur the potoroos into experimenting with arboreality. Many fungi species here grow on trees, and thus the ability to scamper up slanted trunks and branches to reach this previously unavailable food source was a great advantage. Gradually the rainforest potoroos became more and more adept at climbing until they produced a new lineage of specialised macropods whose diets consisted largely of arboreal fungi, also supplementing this with any fruits, flowers or insects they found among the branches. The group would see great success for over the course of a million years and end up colonising most of tropical northern Australia including the southern lowlands of New Guinea.

During an ice age conditions are rarely stable for long however and this would begin to cause significant trouble for the tree potoroos. During particularly severe glacial maximums most rainforest lineages would experience some degree of reduction or decline as their habitat retreated dramatically but the tree potoroos were among the hardest hit. Not only did their habitat shrink but also their primary food source, with arboreal fungi seeing a great decrease in abundance during each extreme glacial maximum and resulting in mass starvation for the potoroos. Some two and a half million years ago came one such cycle that was so severe that it almost completely wiped out the arboreal potoroos, the lineage saved by one particular population at the very southern limit of their distribution that had resorted to adapting to wet eucalypt forest to scrape by during these hard times. A good portion of their diet in these drier forests was insects, but they also began supplementing their diets with nectar from the seasonal blooms of the eucalyptus trees. Australia's vegetation is quite unique in being dominated by an incredibly diverse community of flowering plants, many of which are adapted to be pollinated by larger animals like birds and mammals. During the Holocene Australia even housed the world's only completely nectarivorous mammal, the Honey Possum, whose descendants still thrive in the isolated south-west corner of the continent. In eastern Australia the blooms of many different plants were visited by mammals as varied as pteropodid bats, a variety of possums and even a few of the usually predatory dasyurids. This side of the continent had no specialised mammalian nectarivores however and it would be this absence that encouraged the evolution of the Honey Potoroo.

The Honey Potoroo can now be found right down the east coast of Australia from Cape York in the north to just before Tasmania in the south but throughout this vast distribution they have a patchy occurrence and are only common locally. Unlike birds or bats these marsupials cannot move elsewhere to find more flowers and therefore require a varied community of flowering plants capable of supporting them year round. They are most abundant in coastal hinterland with well-filtered soil, with the bountiful moisture rising from the sea creating the conditions that support a thriving community of flowering bushes and low trees that make great food plants and shelter for the Honey Potoroo. They also occur in taller wet forests with a dense understory as well as certain woodland environments if the right mix of plants can be found. Honey Potoroos are pretty much entirely nectarivorous with their main food plants being members of Proteaceae, Myrtaceae, Ericaceae and the Xanthorrhoea grass trees. In some was the ancestral potoroo snout was already long enough to be suitable for probing flowers, but it has since elongated further to allow them to feed from a wider variety of flowers. Along with this their tongue has become greatly specialised, now being not only long and flexible but also brush-tipped to help them lap up nectar as efficiently as possible. Such a diet is less efficient at supporting a larger mammal and so it is unsurprising that the Honey Potoroo is the smallest of all macropods, for weighing in at only 40 grams or less (just larger than a mouse) they are completely dwarfed by all their relatives. The long claws on their hands, once used for digging up truffles, have become curved and hooked for use in climbing and the hind legs have shortened and adapted to moving independently from one another. Potoroid tails retained some degree of prehensility from their arboreal ancestors which they used to gather nesting material and carry it back to their den, and now that they are back in the trees the tail has lengthened and gained its former flexibility. It is now completely hairless and covered in rough scaly skin for grip, similar to that of the Wyulda or Scaly-tailed Possum. The prehensility of their tails is one of the most notable anatomical differences between the Honey Potoroo and tree kangaroos, for the latter are macropodids and hence lost most of the flexibility in their tails before entering the trees and have not redeveloped it since.

Honey Potoroos are largely nocturnal, but their behaviour varies throughout the year and during the winter months they may be active during the cooler parts of the day. Although they forage and sleep solitarily they are social animals and any one home range will overlap with that of many others allowing increased interaction between individuals. Rather than competing the with many other arboreal species that utilise tree hollows as shelter, Honey Potoroos create their own nests in dense understory out of plant material, fur and feathers, forming a kind of drey like that of a squirrel or ringtail possum. Honey Potoroos are still fairly agile on the ground, although given the shortening of their hind legs they now use both their fore and hind limbs in bounding, but nonetheless they rarely need to leave the safety of the trees anyway. Often they will simply leap between different stands of vegetation using their powerful hind legs or, if distances are too great, utilise the understory to pass between trees. During years of food shortage, usually due to drought, the potoroos will usually enter torpor for days on end to conserve energy or, if it goes on for a particularly long while, become forced to search for food elsewhere. Their usual diet of nectar has resulted in notable degradation to their jaw strength, dentition and stomach power which are all generally of little use to a specialised nectarivore, but because of this their options for other food sources have become extremely limited. One of the few things they can consume are worms - they're soft bodied, small, and able to slurped up without chewing - and during hard times Honey Potoroos will descend to the ground and sniff out a morsel from within the ground using their acute sense of smell.

For the speculative evolution project Australia: The Next 54 Million Years. See more here: specevo.jcink.net/index.php?sh…

Description
Most macropods may be specialised for a cursorial ground-dwelling existence today, but phylogenetically they are actually a group of terrestrial possums and over the course of their evolutionary history they have moved in and out of the trees on numerous occasions. The most notable example of this would be the tree kangaroos of New Guinea and the north-eastern mainland, a more recently evolved group that originated after the collapse of Australia's expansive Miocene rainforests. During the Pleistocene there were even tree kangaroos and other arboreal macropods in drier southern Australia and they have since expanded back down the east coast to reclaim some of their former range, ranging as far south as the Bass Plain during the Recurocene. In addition to this the Recurocene has fostered the evolution of another arboreal macropod, but this one is especially unique. The Honey Potoroo (Orientalipotorous nectarus) is not only the first potoroid to return to the trees but also, in terms of diet, one of the most specialised macropods that have ever lived.

The Honey Potoroo is a descendant of the only species of potoroo to last through the Holocene, the Long-nosed Potoroo, with all others succumbing to predation by invasive predators, habitat destruction and the rapidly changing climate. The Long-nosed Potoroo itself was almost a victim of the final factor, managing to hang on only in north-west Tasmania and in small pockets of coastal hinterland on the south-eastern mainland where suitable tracts of wet forest lasted through the drying of southern Australia during the climatic optimum. As conditions normalised and glaciation returned the normal distribution of wet forest on the continent's east coast was restored and this allowed the potoroos to regain their former range, later extending even further into the jungles of north-east Queensland. Most potoroos are generalists but nonetheless their diets consist mostly of fungi, and it would be the moist conditions of the northern rainforests encouraging the growth of their favoured food in unusual places that would first spur the potoroos into experimenting with arboreality. Many fungi species here grow on trees, and thus the ability to scamper up slanted trunks and branches to reach this previously unavailable food source was a great advantage. Gradually the rainforest potoroos became more and more adept at climbing until they produced a new lineage of specialised macropods whose diets consisted largely of arboreal fungi, also supplementing this with any fruits, flowers or insects they found among the branches. The group would see great success for over the course of a million years and end up colonising most of tropical northern Australia including the southern lowlands of New Guinea.

During an ice age conditions are rarely stable for long however and this would begin to cause significant trouble for the tree potoroos. During particularly severe glacial maximums most rainforest lineages would experience some degree of reduction or decline as their habitat retreated dramatically but the tree potoroos were among the hardest hit. Not only did their habitat shrink but also their primary food source, with arboreal fungi seeing a great decrease in abundance during each extreme glacial maximum and resulting in mass starvation for the potoroos. Some two and a half million years ago came one such cycle that was so severe that it almost completely wiped out the arboreal potoroos, the lineage saved by one particular population at the very southern limit of their distribution that had resorted to adapting to wet eucalypt forest to scrape by during these hard times. A good portion of their diet in these drier forests was insects, but they also began supplementing their diets with nectar from the seasonal blooms of the eucalyptus trees. Australia's vegetation is quite unique in being dominated by an incredibly diverse community of flowering plants, many of which are adapted to be pollinated by larger animals like birds and mammals. During the Holocene Australia even housed the world's only completely nectarivorous mammal, the Honey Possum, whose descendants still thrive in the isolated south-west corner of the continent. In eastern Australia the blooms of many different plants were visited by mammals as varied as pteropodid bats, a variety of possums and even a few of the usually predatory dasyurids. This side of the continent had no specialised mammalian nectarivores however and it would be this absence that encouraged the evolution of the Honey Potoroo.

The Honey Potoroo can now be found right down the east coast of Australia from Cape York in the north to just before Tasmania in the south but throughout this vast distribution they have a patchy occurrence and are only common locally. Unlike birds or bats these marsupials cannot move elsewhere to find more flowers and therefore require a varied community of flowering plants capable of supporting them year round. They are most abundant in coastal hinterland with well-filtered soil, with the bountiful moisture rising from the sea creating the conditions that support a thriving community of flowering bushes and low trees that make great food plants and shelter for the Honey Potoroo. They also occur in taller wet forests with a dense understory as well as certain woodland environments if the right mix of plants can be found. Honey Potoroos are pretty much entirely nectarivorous with their main food plants being members of Proteaceae, Myrtaceae, Ericaceae and the Xanthorrhoea grass trees. In some was the ancestral potoroo snout was already long enough to be suitable for probing flowers, but it has since elongated further to allow them to feed from a wider variety of flowers. Along with this their tongue has become greatly specialised, now being not only long and flexible but also brush-tipped to help them lap up nectar as efficiently as possible. Such a diet is less efficient at supporting a larger mammal and so it is unsurprising that the Honey Potoroo is the smallest of all macropods, for weighing in at only 40 grams or less (just larger than a mouse) they are completely dwarfed by all their relatives. The long claws on their hands, once used for digging up truffles, have become curved and hooked for use in climbing and the hind legs have shortened and adapted to moving independently from one another. Potoroid tails retained some degree of prehensility from their arboreal ancestors which they used to gather nesting material and carry it back to their den, and now that they are back in the trees the tail has lengthened and gained its former flexibility. It is now completely hairless and covered in rough scaly skin for grip, similar to that of the Wyulda or Scaly-tailed Possum. The prehensility of their tails is one of the most notable anatomical differences between the Honey Potoroo and tree kangaroos, for the latter are macropodids and hence lost most of the flexibility in their tails before entering the trees and have not redeveloped it since.

Honey Potoroos are largely nocturnal, but their behaviour varies throughout the year and during the winter months they may be active during the cooler parts of the day. Although they forage and sleep solitarily they are social animals and any one home range will overlap with that of many others allowing increased interaction between individuals. Rather than competing the with many other arboreal species that utilise tree hollows as shelter, Honey Potoroos create their own nests in dense understory out of plant material, fur and feathers, forming a kind of drey like that of a squirrel or ringtail possum. Honey Potoroos are still fairly agile on the ground, although given the shortening of their hind legs they now use both their fore and hind limbs in bounding, but nonetheless they rarely need to leave the safety of the trees anyway. Often they will simply leap between different stands of vegetation using their powerful hind legs or, if distances are too great, utilise the understory to pass between trees. During years of food shortage, usually due to drought, the potoroos will usually enter torpor for days on end to conserve energy or, if it goes on for a particularly long while, become forced to search for food elsewhere. Their usual diet of nectar has resulted in notable degradation to their jaw strength, dentition and stomach power which are all generally of little use to a specialised nectarivore, but because of this their options for other food sources have become extremely limited. One of the few things they can consume are worms - they're soft bodied, small, and able to slurped up without chewing - and during hard times Honey Potoroos will descend to the ground and sniff out a morsel from within the ground using their acute sense of smell.

For the speculative evolution project Australia: The Next 54 Million Years. See more here: specevo.jcink.net/index.php?sh…