The Font of the Placentals

The large-scale incorporation of molecular data into phylogenetics over the last few decades has caused a revolution in our understanding of life's evolution. Taxa whose interrelationships were previously regarded as intractable have been opened up to study, and many of our previous views on relationships have been forced to shift. Because conflict always makes for a good story, certain cases of the latter have become causes celebres, receiving extensive attention in both the technical and popular literature. One of these subjects of particular interest, not surprisingly, involves the relationships of the living orders of mammals.

Reconstruction of Arctostylops steini by Brian Regal, from Janis et al. (1998). The arctostylopids are a Palaeocene to Eocene group of mammals of uncertain affinities but probably belonging somewhere in the Boreoeutheria.

A lot of this attention has focused around the revelation of the Afrotheria, a grouping of animals (tenrecs, elephant shrews, hyraxes, aardvarks, elephants and manatees) with likely African origins that was completely unsuspected by studies based on morphological data only but which molecular studies have identified with ever-increasing levels of support. Recent molecular studies of placental phylogeny have agreed on three basal divisions within the placental mammals: the Afrotheria, the Xenarthra (armadillos, anteaters and sloths, a grouping that was recognised even before the advent of molecular data), and the remaining placentals in the largest of the three, the Boreoeutheria.

To the best of my knowledge, the Boreoeutheria is a clade that has also so far been supported by molecular data only with no morphological features yet recognised as defining the group. Nevertheless, its support can be considered as well established. The name Boreoeutheria refers to the clade's likely northern origins in contrast to the more southern distribution of the other two. Within the Boreoeutheria, molecular studies indicate a basal divide between the Euarchontaglires on one side and the Laurasiatheria on the other. The Euarchontaglires include the primates and rodents (as well as a handful of smaller orders). The Laurasiatheria include the Eulipotyphla, a group of insectivorous mammals including shrews, moles and hedgehogs, as sister to a clade containing bats, carnivorans, perissodactyls and artiodactyls.

Molecular phylogeny of mammals, from Springer et al. (2004) (note that not all branches shown in this tree are supported by all studies).

This all has interesting ramifications for the early evolution of placentals. There is an extensive fossil record of mammals from the Palaeocene, the epoch of time immediately following the end of the Cretaceous. However, most of these mammals do not belong to the orders alive today and their exact relationships to living mammals remain open to debate. The molecule-induced shake-up of pacental relationships just increased this uncertainty: for instance, the interpretation of a given group of fossil mammals as close to the common ancestry of perissodactyls and elephants rather goes out the window when perissodactyls and elephants are no longer thought to be closely related. And detailed studies that may resolve these issues remain few and far between. One of the most notable analyses in recent years has been that by Halliday et al. (2017) which covered most of the well-preserved placentals and their close relatives from the Cretaceous and Palaeocene periods. However, it is difficult to say just what to make of their results. The unconstrained analysis of their data presents results that remain deeply inconsistent with the molecular tree. Conversely, constraining the analysis to more closely match the molecular data provides results that are intriguing but difficult to accept at face value; I suspect they may be artefacts of the algorithm forcing taxa into the least unacceptable position for inadequate data. Suggesting that pangolins are the last specialised survivors of a broad clade of condylarths, pantodonts, notoungulates and creodonts is... I suppose not a priori impossible, but definitely a big call. A later analysis based on an expanded version of the same data set by Halliday et al. (2019) irons out some of the kinks but still fails to resolve the base of the Boreoeutheria beyond a massive polytomy of 25 branches (an icosipentatomy?). The Euarchontaglires are recovered as a clade but not the Laurasiatheria or any of its molecular subgroups above the ordinal level. And while some of the newer analysis' placements may seem like an improvement (notoungulates are placed as the sister to litopterns instead of hanging out with pangolins), others may still raise an eyebrow (mesonychids are associated with carnivorans but viverravids and miacids are not).

As always, the best answer to this conundrum is likely to involve more research. While researching this post, I did come across comments from people suggesting issues with the Halliday et al. data. Frankly, for a data set of this size (involving 248 taxa and 748 characters in the 2019 paper), it would be incredible were it otherwise. I know from my own experience that as you add more characters and taxa to a phylogenetic analyses, the challenge of keeping everything in line rises exponentially, and the data sets I've dealt with have been nowhere near the size of this one. Nevertheless, it's a start. And we can but hope that even those who find fault with it ultimately take it as inspiration to themselves do better.

REFERENCES

Halliday, T. J. D., M. dos Reis, A. U. Tamuri, H. Ferguson-Gow, Z. Yang & A. Goswami. 2019. Rapid morphological evolution in placental mammals post-dates the origin of the crown group. Proceedings of the Royal Society of London Series B—Biological Sciences 286: 20182418.

Halliday, T. J. D., P. Upchurch & A. Goswami. 2017. Resolving the relationships of Paleocene placental mammals. Biological Reviews 92 (1): 521–550.

The Mouse Shrews of Africa

Shrews are one of the less appreciated groups of mammals. Small (some are among the smallest mammals on earth), skulking, they are often overlooked but are nevertheless represented by a diversity of species in many parts of the world. Among this diversity are the mouse shrews of the genus Myosorex.

Forest shrew Myosorex varius, from Roberts (1951).

Myosorex is a genus of nearly twenty known species of shrew, some of which have only been identified very recently, with more probably yet to be described. They are known in the modern fauna only from sub-Saharan Africa, though the fossil record indicates they once extended as far north as Spain (Furió et al. 2007). Mouse shrews differ from most other living shrew genera (except the closely related Congosorex) in the presence of a tiny vestigial tooth in the lower jaw behind the first antemolar (the tooth behind the incisors, so called in shrews because it is unclear whether it corresponds to a canine or premolar in relation to the teeth of other mammals). Because their teeth lack the red pigment found in shrews of the subfamily Soricinae, Myosorex have historically been classified with the white-tooth shrews of the Crocidurinae. However, the presence of white teeth is, of course, a primitive feature of questionable significance phylogenetically. Instead, more recent authors have pointed to the retention of the second antemolar and other features to support recognising Myosorex and related African shrew genera as relictual members of a third subfamily, the Myosoricinae, that may also include a number of earlier fossil shrews (this group has also been known as the 'Crocidosoricinae' but 'Myosoricinae' is the name with priority; the argument by Furió et al., 2007, that the latter name cannot be used for the broader subfamily because it was originally used only for the African genera has no standing under current nomenclatorial rules).

Foraging forest shrew, copyright Johnny Wilson.

In the modern fauna, Myosorex species have a very scattered distribution. Species found in central and eastern Africa are restricted to high mountains, among moist, densely vegetated environments. Species found in southern Africa are often found in similar habitats. However, the species M. varius is also found in drier locations at lower altitudes, closer to the South African coast. Nevertheless, it is still restricted to areas with high seasonal rainfall, or (in part of Western Cape Province) zones dominated by succulent vegetation where low levels of actual rainfall may be compensated for by precipitation from mist (Meester 1958). The distribution of the genus as a whole is marked by a broad gap of over 1600 km separating the northern limit of species in South Africa and Zimbabwe from their nearest neighbours to the north in the DRC and Kenya, a gap that they were presumably only able to cross in the past when climate conditions were more amenable.

This sensitivity to environment means that Myosorex species may be very vulnerable to changes in habitat. Several species are restricted to limited ranges and several are recognised as potentially endangered. The prospect of climate change makes this vulnerability even worse: as levels of rainfall decrease, mouse shrews will be forced to retreat to ever higher altitudes, and there's only so high they can go before running out of mountain.

REFERENCES

Furió, M., A. Santos-Cubedo, R. Minwer-Barakat & J. Agustí. 2007. Evolutionary history of the African soricid Myosorex (Insectivora, Mammalia) out of Africa. Journal of Vertebrate Paleontology 27 (4): 1018–1032.

Meester, J. 1958. Variation in the shrew genus Myosorex in southern Africa. Journal of Mammalogy 39 (3): 325–339.

Fishing Mice

In a 1950 discussion of the origins of the fauna of South America, the great American palaeontologist G. G. Simpson dismissed the enormous radiation of muroid rodents in that continent as mere "field mice" exhibiting little regional differentiation. George Gaylord Simpson may have been one of the leading thinkers in mid-20th Century evolutionary theory, but in this respect he was just plain wrong. The South American mice and rats include a wide variety of divergent forms, some of them specialised in surprising ways. Consider, for instance, the fishing mice of the Ichthyomyini.

Illustration of Stolzmann's crab-eating mouse Ichthyomys stolzmanni by Joseph Smit.

The Ichthyomyini are a small assemblage of less than twenty species of mice found between Mexico and the north of South America from Peru to French Guiana (Voss 1988). Though some species are known from lower altitudes, the majority are found in alpine habitats in association with fast-flowing mountain streams (albeit in no location are they known to be common). Ichthyomyins seem to show a particular preference for hanging around waterfalls (Barnett 1997) and are not found in association with standing water such as swamps or ponds. They are moderate in size, ranging from ten to twenty centimetres in length excluding the tail. They show a number of adaptations for foraging underwater: the hind feet are partially webbed and have a more or less elongate fringe of stiff hairs that aid in swimming, the tail is furry rather than scaly, the eyes are small, the external ears are reduced in size (in a couple of species they are completely hidden by the fur and in one, Anotomys leander, the external pinnae are missing entirely), and the whiskers are long, strong, and arranged in such a way that they almost look more like the whiskers of a sea lion than of a mouse. The nerves associated with these whiskers are also enlarged and they evidently provide the main means of finding food.

Peruvian fish-eating rat Neusticomys peruviensis, copyright Carlos Boada.

Or, as I should say, finding prey. As far as we know, these mice seem to be entirely carnivorous. Only a couple of examples are known of specimens with plant matter in their stomachs and the significance of those finds remains uncertain. The primary source of food for most species is small invertebrates such as aquatic insects. Where freshwater crabs are available, a number of species show preferences for those. In larger species, the diet may be supplemented to a greater or lesser degree by small vertebrates such as fish or tadpoles. In line with their carnivorous diet, ichthyomyins are also characterised by a shorter, less complicated gut than other mice. Little is known about breeding and nesting habits in ichthyomyins. A specimen of Chibchanomys kept in captivity made tunnels in mossy vegetation (Barnett 1997). The few known specimens of gravid females indicate that litters are small with no more than two foetuses being carried at a time.

Voss (1988) recognised five genera of Ichthyomyini. The largest of these, Neusticomys, includes about half a dozen species that may more closely resemble the ancestral morphology for the group. Their hind feet are narrower than those of other ichthyomyins and the fringe of swimming hairs is shorter (Packer & Lee 2007). Where one species found in Colombia and Ecuador, Neusticomys monticolus, overlaps in range with Anotomys leander, it shows a preference for more sheltered sections of stream banks whereas A. leander is found in more exposed rapids.

Undescribed species of Chibchanomys, copyright Alexander Pari.

In most ichthyomyins, the coat consists of a layer of dense, woolly underfur covered by an overcoat of long guard hairs mixed with glossy, often distally flattened awn hairs. In Anotomys leander, Chibchanomys trichotis, and Neusticomys monticolus, the awn hairs are missing so these species have a dull grayish black appearance overall rather than than the glossy coat of other species. Chibchanomys trichotis retains minute external ear flaps albeit not ones that are visible past the coat; Anotomys leander, as noted above, lacks external ear flaps but does have the positions of the ear openings marked by a prominent white spot. Both these last two species were placed in monotypic genera by Voss (1988), but Barnett (1997) refers to an at-that-point undescribed species of Chibchanomys.

The remaining two genera were recognised by Voss (1988) as including four species apiece. Species of Rheomys, found in the mountains of Central America, have the most extensively webbed hind feet among the ichthyomyins. This is the only genus of fishing mice found in Central America; the other genera are all restricted to South America. The genus Ichthyomys includes the largest species of the group and also the species that feed on the highest proportion of vertebrates. This difference in diet is reflected in their dentition: Ichthyomys species have proportionately larger incisors and smaller molars than other ichthyomyins, with greater emphasis on using the incisors to grasp and slice struggling prey.

Rheomys raptor, from Villalobos-Chaves et al. (2016).

All told, the ichthyomyins are a remarkable radiation. Ecologically, they are close parallels to forms found elsewhere such as water shrews or desmans, but most other semi-aquatic mammals are distinctly larger in size. Even with less than twenty species, the ichthyomyins represent more species than there are of similarly sized semi-aquatic mammals anywhere else in the world. However, as noted above, ichthyomyins are not common anywhere they occur, and factors such as deforestation and climate change could represent a significant threat to their survival. It would be unfortunate if this remarkable radiation was to fade away.

REFERENCES

Barnett, A. A. 1997. The ecology and natural history of a fishing mouse Chibchanomys spec. nov. (Ichthyomyini: Muridae) from the Andes of southern Ecuador. Zeitschrift für Säugetierkunde 62: 43–52.

Packer, J. B., & T. E. Lee Jr. 2007. Neusticomys monticolus. Mammalian Species 805: 1–3.

Voss, R. S. 1988. Systematics and ecology of ichthyomyine rodents (Muroidea): patterns of morphological evolution in a small adaptive radiation. Bulletin of the American Museum of Natural History 188 (2): 259–493.

Guenons

The common perception of monkeys tends to be dominated by a relatively small number of species, generally those most commonly seen in zoos, such as capuchins, macaques, baboons or tamarins. But as is usual when it comes to biodiversity, there are a lot of varieties of monkey out there that may be less familiar to the general public. This post will look at one of those less familiar groups: the guenons of the genus Cercopithecus.

Moustached monkey Cercopithecus cephus, copyright Rufus46.

Cercopithecus is a genus of monkeys found in sub-Saharan Africa. The exact number of species has shifted around a bit (though it currently sits around twenty). Some authors have included almost all species of the monkey tribe Cercopithecini, characterised by self-sharpening lower incisors and four cusps on the lower third molars (Lo Bianco et al. 2017), in the single genus Cercopithecus. However, more recent authors have tended to favour dividing this tribe between a number of phylogenetically and ecologically distinct genera. Under this latter system, Cercopithecus would be restricted to a group of more arboreal species. A number of these species have been divided between multiple subspecies and there may be some back and forthing about what is recognised as which. One entirely new species, previously not even known as a subspecies, was described as recently as 2012 by Hart et al.: the lesula C. lomamiensis.

Young female lesula Cercopithecus lomamiensis, from Hart et al. (2012).

A large part of this uncertainty relates to the fact that Cercopithecus species are most diverse in dense forests of western and central Africa, in regions that may be both physically and politically difficult to access and which have received less attention from researchers than others. The aforementioned lesula was described from the Lomami River basin near the middle of the Democratic Republic of the Congo (the one that used to be called Zaire, though I think they prefer not to talk about it). Another Congolese species, the dryas monkey C. dryas, was long thought to be known from only a single juvenile specimen until it was realised that the adult form had been described as a separate species C. salongo. It's still only known from a handful of records and is thought to be critically endangered.

Diana monkey Cercopithecus diana, copyright Ikmo-ned.

Some species of guenon are notable for their striking colour patterns. Perhaps the species I've most commonly seen in zoos is the diana monkey C. diana, native to the region between Sierra Leone* and the Côte d'Ivoire (though it is possible that at least some of these 'diana monkeys' were actually roloway monkeys C. roloway, until recently treated as a subspecies of the diana monkey). This species has a bright white throat, chest and front of the fore arms that contrasts with the black face and dark grey back. It also has a white band across its brow which is where its name comes from, the band having been thought to resemble the crescent moon. De Brazza's monkey C. neglectus of central Africa has a crescent-shaped orange mark on its forehead and a white muzzle and beard, making it look reminiscent of a grumpy old man (Wikipedia claims that it has also been dubbed the 'Ayatollah monkey'). Male De Brazza's monkeys also have a bright blue scrotum. Large bright blue patches are also present around the scrotum and backside of males in the lesula and the owl-faced monkey C. hamlyni.

*Having grown up in New Zealand in the 1980s, I'm going to have that stuck in my head all day now. Nothing to do with the subject of this post, I just thought I'd mention it.

Male De Brazza's monkey Cercopithecus neglectus, copyright Heather Paul.

Guenons tend to be found living in small troops consisting of one adult male and a harem of females with their offspring; unmated adult males will be found living solitary lives. Males are usually larger than females, up to about 1.5 times the size of their mates. Multiple guenon species may be found in a single location though closely related species tend not to overlap. Famously, hybrids have been described from the Kibale forest in Uganda between the blue monkey C. mitis and the red-tailed monkey C. ascanius, two species that are quite distinct in external appearance. Larger species such as the spot-nosed monkey C. nictitans and the blue monkey tend to eat a higher proportion of leaves in their diet. Smaller species such as the mona monkey C. mona may be more insectivorous (Macdonald 1984).

Blue monkeys Cercopithecus mitis stuhlmanni, copyright Charles J. Sharp.

The origins of the Cercopithecus radiation are relatively recent with the tribe Cercopithecini as a whole probably originating in the late Miocene (Lo Bianco et al. 2017). Karyological studies of the group show a wide variation in chromosome number from 58 in the diana monkey to 72 in the blue monkey. In contrast, the sister group of the Cercopithecini, the Papionini (which includes baboons and macaques) always has 42 chromosomes. Polymorphism in chromosome arrangements has also been described within Cercopithecus species. The possibility that this gene variability is related to their rate of speciation remains a worthwhile line of study.

REFERENCES

Hart, J. A., K. M. Detwiler, C. C. Gilbert, A. S. Burrell, J. L. Fuller, M. Emetshu, T. B. Hart, A. Vosper, E. J. Sargis & A. J. Tosi. 2012. Lesula: a new species of Cercopithecus monkey endemic to the Democratic Republic of Congo and implications for conservation of Congo's central basin. PLoS One 7 (9): e44271.

Lo Bianco, S., J. C. Masters & L. Sineo. 2017. The evolution of the Cercopithecini: a (post)modern synthesis. Evolutionary Anthropology 26: 336–349.

Macdonald, D. (ed.) 1984. All the World's Animals: Primates. Torstar Books: New York.

The Shrinking World of Bandicoots

A bandicoot is a very disagreeable animal to clean, therefore it should be done as soon after killing as possible, and then the flesh can be left in strong vinegar and water for a few hours before dressing. Sweet potatoes and onion make a good stuffing for bandicoot, which is good either boiled or baked.--Mrs Lance Rawson, Australian Enquiry Book of Household and General Information.

Golden bandicoots Isoodon auratus barrowensis, copyright Kathie Atkinson.

Back when I used to work on Barrow Island in the north-west of Australia, one of the more noticeable animals to be seen around the place was the golden bandicoot Isoodon auratus. In the evenings, the place seemed to absolutely swarm with them. About the size of a guinea pig, with no tails to speak of (bandicoots are actually born with fairly long tails but tend to lose them in the course of their quite vicious fights with one another; few if any individuals reach maturity with their tails intact), there was no question about their qualifications when it came to cuteness.

Bandicoots are a group of twenty-odd species of marsupial found in Australia and New Guinea (one species, the Seram bandicoot Rhynchomeles prattorum, was described from montane forest on the Indonesian island of Seram to the west of New Guinea). Most are primarily insectivorous, but they also eat varying amounts of small vertebrates and plant matter such as bulbs and fruit. The largest bandicoot, the giant bandicoot Peroryctes broadbenti, has been recorded to reach close to five kilograms in weight. The smallest, the Papuan bandicoot Microperoryctes papuensis, weighs less than 200 grams. I suspect many people in Australia assume that the name 'bandicoot' comes from one of the the Aboriginal languages, but it is in fact Indian (specifically Telugu) in origin. The original bandicoot Bandicota indica is a large rat that is widespread in southern Asia and Australian bandicoots were named for their resemblance to this species. Personally, I have maintained in the past that Australian bandicoots look more like rats than rats do: with their relatively long snouts, bandicoots bear a distinct resemblance to the sort of cartoon figure that comes to most people's minds when they hear the word 'rat'.

New Guinea spiny bandicoot Echymipera kalubu, copyright Michael Pennay.

Bandicoots are highly distinctive from all other marsupials in appearance. Their hind legs are noticeably longer than their forelegs and more or less specialised for cursorial locomotion (especially so in one example that I'll get to shortly). The fourth and fifth toes of the hind foot are much larger than the other three; the first toe in particular is reduced to a non-functional stub. The second and third toes of the hind foot, as in diprotodontian marsupials such as kangaroos and possums, are externally joined together with the two claws at the end forming a comb that is used in grooming more than in locomotion. The fore feet, in contrast, are mostly functionally three-fingered (with the first and fifth fingers reduced) and adapted for digging with the claws large and flat.

Many bandicoots are rapid reproducers with their gestation periods among the shortest of any mammal, less than two weeks between fertilisation and birth. Bandicoots also have the most developed placentas of any marsupial group (yes, most marsupials do have a placenta, albeit a much simpler one than found in placental mammals); it is presumably because of this that, despite their short gestation, bandicoot young are born at a more advanced stage of development than those of some other marsupials. When the young are born, they initially remain attached to their mother via the umbilical cord; this latter does not become detached and the placenta ejected until after the joey is firmly attached to a teat in the rearward-opening pouch. The young remain in the pouch for about two months and grow rapidly; they may reach full sexual maturity at the age of only three months. As a result, bandicoot populations may increase rapidly if conditions permit.

Greater bilby Macrotis lagotis, copyright Bernard Dupont.

In terms of classification, there is a general consensus that Recent bandicoots can be divided between four groups though there has been some disagreement about exactly these groups are interrelated (and hence exactly how they should be ranked). The most diverse, but probably also the least studied, group of modern bandicoots are the rainforest bandicoots of the Peroryctidae or Peroryctinae. These are about a dozen species found mostly in New Guinea with the aforementioned Rhynchomeles prattorum on Seram and the the long-nosed spiny bandicoot Echymipera rufescens extending its range to the northern tip of Queensland. Most of continental Australia is home to the dry-country bandicoots of the Peramelidae sensu stricto or Peramelinae, of which there are six Recent species (one of these, the northern brown bandicoot Isoodon macrourus, is also found in southern New Guinea). Peramelids tend to have shorter snouts and flatter skulls than peroryctids. The other two groups are both very small and also native to arid regions of Australia. Two Recent species are known of the genus Macrotis, the bilbies, though one of these is extinct and the other is endangered. Bilbies are larger than most other bandicoots, with long ears (hence their alternative vernacular name of 'rabbit-bandicoots') and a long, silky-haired tail.

Gerard Krefft's 1857 illustration of the pig-footed bandicoot Chaeropus ecaudatus, from here.

The final representative of the Recent bandicoots is unquestionably the weirdest of them all. Unfortunately, it is also now extinct, last recorded some time about the middle of the 20th Century, a fact that cannot be called anything less than a fucking tragedy. The pig-footed bandicoot Chaeropus ecaudatus was the most cursorial of all bandicoots. Its forelegs, rather than being adapted for digging as in other bandicoots, had only two functional toes on which the claws were modified into hooves. The hind legs went a step further and had only a single functional toe (raising the question of how this animal groomed itself without the aforementioned claw-comb of other bandicoots Edit: That was a bit of a blonde moment; a second look at the Krefft illustration above shows that the comb is definitely there). The most extensive observations of its habits seem to have been made by Gerard Krefft (1866) who kept a pair alive for about six weeks in 1857 on a trip to the Murray-Darling region before killing them to provide specimens because, you know, 19th-Century naturalist. Krefft recorded that his bandicoots subsisted primarily on plant foods such as lettuce, grass and roots, refusing all meat offered to them (Krefft also refers to providing grasshoppers for them but his account is unclear about whether they were ever eaten). A herbivorous diet was also indicated by the animals' droppings, which where dry and similar to a sheep's. The bandicoots constructed a covered nest from grass and leaves in the tin enclosure in which Krefft kept them in which they sheltered during the day, only becoming active after nightfall. Krefft notes that he acquired "about eight" specimens of pig-footed bandicoot during his six-month camp, admitting that some met a stickier end than others: "They are very good eating, and I am sorry to confess that my appetite more than once over-ruled my love for science; but 24 hours upon "pig-face" (mesembryanthemum) will dampen the ardour of any naturalist". Krefft also noted that several of the specimens found were female, and that despite being provided with eight teats the females never carried more than two joeys. A particularly interesting detail was that the fourth toe of the joeys' fore foot, rather than being reduced as in the adults, remained large so that the feet resembled those of other bandicoots. Presumably this was so that the fore-claws could still be used to allow the newborn joeys to climb from the birth canal to the pouch.

Krefft also noted that the pig-footed bandicoot was already declining in abundance, blaming its increased rarity on competition with introduced grazing livestock. Sadly, changing habitats and introduced predators have caused other bandicoot species to also become endangered since Krefft's time. Please, don't let them go the way of the pig-footed bandicoot.

REFERENCES

Gordon, G., & a. J. Hulbert. 1989. Peramelidae. In: Fauna of Australia vol. 1B. Mammalia. Australian Biological Resources Study: Canberra.

Krefft, G. 1866. On the vertebrated animals of the lower Murray and Darling, their habits, economy, and geographical distribution. Transactions of the Philosophical Society of New South Wales 1862–1865: 1–33.

The Diprotodontids: Marsupials Go Large

Reconstruction of Diprotodon optatum by Anne Musser, from Long et al. (2002). Offhand, running a search for Diprotodon through Google Image brings up some true horrors of digital imagery.

Prior to the arrival of humans, the Australian fauna included many strange, and often dramatic, animals that are sadly no longer with us. Enormous python-like snakes, monitors that would have made a Komodo dragon look underwhelming, drop bears, and of course the notorious demon duck of doom. But among the most iconic of Australia's extinct fauna were the Diprotodontidae, heavyset herbivores that included the largest of all marsupials. Diprotodontids are sometimes referred to in the popular press as giant wombats, but this is a bit misleading: though more closely related to wombats than any other living marsupials, they were a quite distinct group of animals (besides, they shared their world with actual giant wombats that reached the size of a cow). A potentially more appropriate descriptor that has been suggested is 'marsupial rhinos', though at least some diprotodontids were decidedly not like rhinos either.

Skull of Zygomaturus trilobus in Museum Victoria, photographed by Nigel Waring.

The most famous of the diprotodontids was also the first to be described, and indeed the first fossil mammal of any kind described from Australia. Diprotodon optatum, named by Richard Owen in 1838, was the largest of the diprotodontids, sometimes standing more than six feet tall at the shoulder, and reaching estimated weights of around two and a half tonnes. At the time of human arrival, Diprotodon would have been one of the dominant herbivores in the arid central region of Australia. A number of species of Diprotodon have been named over the years, but a review of the genus by Price (2008) recognised only a single species, with the two different size classes present probably representing the different sexes. In the less arid coastal regions, Diprotodon was replaced by various species of the slightly smaller (but still formidably sized) genus Zygomaturus (Long et al. 2002). The best known species in this genus, Z. trilobus, bore a distinctive large bony boss on the snout, giving its skull a profile reminiscent of a cartoon bear. Two other diprotodontid species that would have come into contact with humans are known from the Pleistocene of montane New Guinea, Hulitherium tomasettii and Maokopia ronaldi. Both these species were smaller than the mainland Australians, being about the 100 kg mark. Maokopia has been interpreted as a grazer, while Hulitherium has been seen as a browser, and suggested as a direct analogue of the Asian giant panda (Long et al. 2002).

Reconstruction of Hulitherium tomassettii as a panda analogue, by Peter Schouten.

The broader record of diprotodontids goes back to the Oligocene, with two main lineages being recognised, the Diprotodontinae and Zygomaturinae. Of the species referred to above, all but Diprotodon optatum are zygomaturines. The two groups are primarily distinguished by their dentition, with the premolars being generally more complex in zygomaturines than diprotodontines. In both lineages, the earlier members were smaller: Long et al. (2002) describe a number of genera as 'sheep-sized'. The smallest known diprotodontid, the late Oligocene Raemeotherium yatkolai, they describe as 'lamb-sized'. Black et al. (2012) estimated the weight of the middle Miocene Nimbadon lavarackorum as abut 70 kg. They also suggested that it was an adept climber, in a similar manner to the modern koala, making it the largest known arboreal mammal from Australia. It might seem odd to picture an animal of this size up in a tree, even allowing for the higher density of the canopy in Australia's Miocene rainforests. However, there are larger arboreal mammals alive even today: male orangutans, for instance, may weigh over 100 kg.

Reconstruction of a climbing pair of Nimbadon lavarackorum (adult and juvenile) by Peter Schouten, from Black et al. (2012).

Interestingly, Nimbadon is not placed as a particular basal diprotodontid in the phylogeny of zygomaturines presented by Mackness (2010). As other related marsupial families, such as koalas or thylacoleonids (marsupial lions), also include climbers, it would not be unreasonable to consider such habits plesiomorphic for diprotodontids as a whole. The 'rhino-like' appearance of the later giants would then be something of a novelty, an adaptation to the drier conditions and more open woodlands that arose at the end of the Miocene. If we are to regard the diprotodontids as marsupial rhinos, then we must consider the possibility of rhinos in trees.

REFERENCES

Black, K. H., A. B. Camens, M. Archer & S. J. Hand. 2012. Herds overhead: Nimbadon lavarackorum (Diprotodontidae), heavyweight marsupial herbivores in the Miocene forests of Australia. PLoS ONE 7 (11): e48213. doi:10.1371/journal.pone.0048213.

Long, J., M. Archer, T. Flannery & S. Hand. 2002. Prehistoric Mammals of Australia and New Guinea: One hundred million years of evolution. University of New South Wales Press: Sydney.

Mackness, B. S. 2010. On the identity of Euowenia robusta De Vis, 1891 with a description of a new zygomaturine genus. Alcheringa 34 (4): 455–469.

Price, G. J. 2008. Taxonomy and palaeobiology of the largest-ever marsupial, Diprotodon Owen, 1838 (Diprotodontidae, Marsupialia). Zoological Journal of the Linnean Society 153: 389–417.

Barrallier's Monkey

"Gogy told me that they had brought portions of a monkey (in the native language "colo"), but they had cut it in pieces, and the head, which I should have liked to secure, had disappeared. I could only get two feet through an exchange which Gogy made for two spears and one tomahawk. I sent these two feet to the Governor in a bottle of spirits."

In November 1802, Governor Philip King sent an exploratory expedition west of Sydney under the command of Ensign Francis Barrallier, a French ex-pat who had taken service with the British after fleeing France with his parents following the French revolution. As well as finding a passage across the mountains that barred Sydney from the interior, Barrallier was trying to find the seat of a figure that Governor King later referred to in letters as the 'King of the Mountains'. Who exactly this King of the Mountains was supposed to be is unclear. Many have thought he was supposed to be some sort of overlord of the local Aboriginals. David Levell, in his 2008 book Tour to Hell, argues the King of the Mountains to have been the head of a secret inland settlement that many of the convicts imprisoned in Sydney believed would offer sanctuary to any who escaped there. Barrallier returned to Sydney in late December, having failed to locate either passage or king (the one would be discovered later, the other would prove to be mythical under any interpretation). Barralier's journal of his expedition languished in relative obscurity until an English translation was published in 1897.

The main interest for later readers of Barrallier's account has been in his dealings with the indigenous people he encountered and worked with. Barrallier had an interest in developing a rapport with the local people he met that was not shared by most of his British associates and his notes, sparse as they may be, provide one of the few direct records available of pre-colonial life in the Sydney region. I've brought Barrallier into this post, however, because of an incident he describes briefly in his journal where the game procured by some of Barrallier's aboriginal associates included an animal that Barrallier refers to as a 'monkey'. Barrallier did not see the animal's remains before it had already been butchered, but he is still the first European known to have acquired a specimen of one of Australia's most iconic animals: the koala.

Koalas Phascolarctos cinereus, photographed by Dinkum.

Koalas are widespread in the east of Australia, though loss of habitat has rendered their distribution localised in some areas. To most people outside Australia, the koala seems like a plush toy come to life, the essence of cuteness manifest in a single animal. The Australians themselves often have a more ambivalent attitude: while the koala is certainly a high-ranking member of the pantheon of the Australian fauna, together with such luminaries as the kangaroo, the platypus, the kookaburra and the gumnut baby, Australians also tend to look upon it as indolent, bad-tempered, and steeped in the kind of aroma that only an exclusive diet of eucalyptus leaves can give an animal (many Australians look more affectionately on the koala's closest living cousin, the wombat). To zoologists, Phascolarctos cinereus is the only surviving species of a lineage that goes back at least to the late Oligocene. Three subspecies of koala have been recognised, but these probably represent clinal variations rather than geographically discrete units (Houlden et al. 1999).

At just what point koalas became eucalyptus specialists is something we don't know for sure. The late Oligocene Perikoala palankarinnica possesses an ankylosed lower jaw (i.e. one that has the two sides fused together at the front) that may indicate a diet of tough leaves (Long et al 2002). Eucalyptus would be at least one candidate for such a diet. However, Perikoala's rough contemporary, Madakoala, lacked such a fused jaw and may have taken softer browse. Nor is a fused lower jaw present in the Miocene genera Litokoala or Nimiokoala (Louys et al. 2009). It seems likely that specialisation on Euclayptus may only have developed with the modern genus Phascolarctos, corresponding with the rise of eucalypt dominance in the Australian flora in the late Miocene. As well as being potentially less specialised, the fossil genera of koalas were also distinctly smaller than the living species. Koala evolution reached an apogee of sorts in the Pliocene and Pleistocene with the fossil species Phascolarctos yorkensis, which tipped the scales at nearly twice the size of P. cinereus (Long et al. 2002) (somewhat disappointingly, no-one seems to seen fit to present a fossil koala with the name of Katastaxarctos).


Koalas can be very vocal animals, using bellows and grunts as their main method of communicating. This video of a vocalising bull comes from here.

The specialisation of the modern koala is truly a remarkable thing. True exclusivity of diet seems to be a rarity among large terrestrial vertebrates (and as it can reach sizes of 20 kg, there is no denying that the koala is a large vertebrate). Many have their preferred delicacies but remain far from averse to the occasional variation (something that I really wish the ABC had been more aware of with that lorikeet article). Thus we have cattle gnawing on bones, cats eating grass, or deer killing and eating birds. Even the giant panda, perhaps the other specialist mammal most familiar to the general public, has been known to supplement its bamboo diet with roots and small animals. But the koala turns up its nose at almost anything other than Eucalyptus leaves—and usually only a small number of Eucalyptus species at that. The toughness of Eucalyptus leaves mean they require a great deal of digestive processing, and the small nutritive return is responsible for the extended periods of inactivity that koalas are known for. Early British naturalists often compared the koala to the South American sloth, which functions under similar constraints. The low nutrition of their diet is also reflected in the notoriously small brains of koalas, which have one of the smallest brains relative to body size of any mammal. So noxious is the eucalypt diet that koala joeys have to be weaned onto it through stages. When a joey is about six months old, its mother starts producing a faecal pap of half-digested leaves that the joey eats direct from her cloaca before moving to a more direct leaf diet about a month later.

Nevertheless, by specialising on Eucalyptus leaves, koalas have access to an abundant food source that few other mammals can handle. Even after the arrival of Europeans, koalas have handled the incursion of foreign predators better than many other Australian natives. The main threat to their continued existence is clearing of the forests on which they depend for food. The koala deserves its position as an icon, and an icon is worthy of respect.

Video of a koala joey feeding on pap, from Arkive.

REFERENCES

Houlden, B. A., B. H. Costello, D. Sharkey, E. V. Fowler, A. Melzer, W. Ellis, F. Carrick, P. R. Baverstock & M. S. Elphinstone. 1999. Phylogeographic differentiation in the mitochondrial control region in the koala, Phascolarctos cinereus (Goldfuss 1817). Molecular Ecology 8 (6): 999–1011.

Long, J., M. Archer, T. Flannery & S. Hand. 2002. Prehistoric Mammals of Australia and New Guinea: One Hundred Million Years of Evolution. University of New South Wales Press: Sydney.

Louys, J., K. Aplin, R. M. D. Beck & M. Archer. 2009. Cranial anatomy of Oligo-Miocene koalas (Diprotodontia: Phascolarctidae): stages in the evolution of an extreme leaf-eating specialization. Journal of Vertebrate Paleontology 29 (4): 981–992.