Hydromys

hydromys
Hydromys chrysogaster. Image credit: Leo, under CC BY-NC-SA 4.0.

Named by: Geoffroy, 1804

Taxonomy: Synapsida, Sphenacomorpha, Sphenacodontia, Sphenacodontoidea, Therapsida, Theriodontia, Cynodontia, Probainognathia, Mammaliamorpha, Mammaliaformes, Mammalia, Theria, Eutheria, Placentalia, Euarchontoglires, Glires, Rodentia, Myomorpha, Muridae

Included species: H. chrysogaster (type), H. hussoni, H. neobritannicus, H. ziegleri

Australia is known for being a land of marsupials, with placentals widely thought of as having only an invasive presence on the island continent. However, this popular impression is far from the truth. In reality, roughly half of the native land mammals in Australia are placentals.

All of these Australian placentals are either bats or rodents. Whether by flying or rafting, these two groups managed to colonize Australia long before humans. Though rarely given as much attention as Australian marsupials, native placentals have evolved strange adaptations of their own on the isolated Australian landmass. This post will focus on just one genus of Australian placentals, the semi-aquatic rodents in the genus Hydromys.

Strictly speaking, not all species of Hydromys live within the country of Australia. All four species can be found on the island of New Guinea (and thus on the Australian continent), but only H. chrysogaster is found on the Australian mainland. H. chrysogaster also happens to be the best-studied species; as such, the information in this article largely pertains to it. The life history of the other species is poorly known; H. ziegleri had not even been scientifically described until 2005.

Hydromys are deeply nested within the Muridae, the clade uniting Old World rats and mice. Weighing up to 1.3 kg (2.9 lb), they are among the larger murids out there. As previously noted, they are semi-aquatic, and have a number of specializations for this lifestyle. Their eyes and nostrils are set high on their head, in the same horizontal plane as their ears. This a common feature of semi-aquatic animals, allowing them to simultaneously expose their eyes, nostrils, and ears above the water surface. The long, flattened skull and relatively small ears of Hydromys improve streamlining, whereas their partially webbed hindfeet are used for propulsion.

Hydromys swim using alternating kicking strokes of the hindfeet. They can see well underwater and regularly hunt by diving to the bottom of rivers and streams. Unusually among rodents, they are primarily carnivorous. In keeping with their diet, they have a wider gape and faster bite than closely related omnivorous rodents (such as the genus Melomys), allowing them to catch fast, mobile prey. Aquatic insects, crayfish (yabbies), spiders, and fish are important prey for Hydromys, and they can kill birds up to the size of musk ducks (Biziura lobata). They occasionally forage outside of water and have been known to inspect tree hollows for roosting bats. Hydromys have been observed performing some interesting behaviors to procure specific types of food. For one, they leave large mussels out in the sun until the bivalves open by exposure. They are also among the few Australian predators that can prey on highly toxic, invasive cane toads (Rhinella marina). They seem to accomplish this feat by attacking the toads’ underbellies, thus avoiding the well-developed poison glands on their back. After a successful foraging trip, Hydromys carry the captured prey item in their mouth and eat it on a preferred log, stone, or island.

The dense fur of Hydromys gives it considerable insulating and waterproofing properties, but these rodents nonetheless have trouble maintaining a constant body temperature in water that is under 20°C (68°F). To partially mitigate this, Hydromys can tolerate a large drop in body temperature, showing no signs of impairment at body temperatures of 32°C (89.6°F, compared to a normal of 36.6°C or 97.9°F). Even so, it is probably to minimize their time spent under such conditions that they typically leave the water when they are ready to feed.

Given the absence of semi-aquatic marsupials in Australia, the otter-like niche that Hydromys have taken is unique among Australian mammals. (The only semi-aquatic marsupial is the South American yapok, Chironectes minimus.) A primarily semi-aquatic lifestyle in Australian mammals is otherwise limited to the platypus (Ornithorhynchus anatinus), which generally feeds on smaller prey.

References

—Albertonykus

Anteosaurus

anteosaurus-lateral-final-small
Restoration of Anteosaurus magnificus. Own work, CC-BY-3.0.

Named by: Watson, 1921

Taxonomy: Synapsida, Eupelycosauria, Sphenacomorpha, Sphenacodontia, Sphenacodontoidea, Therapsida, Dinocephalia, Anteosauria, Anteosauridae, Anteosaurinae

Included Species: †A. magnificus (type), †A. rugosus?

anteosaurus geological time scale
Geological Range of Anteosaurus. Map modified from PBDB.

Anteosaurus is a genus of large carnivorous therapsids, which lived in what is now South Africa roughly 260 to 265 million years ago. With a length of six meters (20 feet) and mass of 600 kilograms, they were the first truly gigantic terrestrial predators and among the largest predatory synapsids to have ever walked on land; their size is comparable to that of polar bears and mid-sized predatory dinosaurs such as Dilophosaurus and Megalosaurus. The largest known skulls of Anteosaurus are over 80 cm (32 in) long, only slightly smaller than the 83-cm skull of Andrewsarchus, the largest carnivorous terrestrial mammal known to have ever lived.

Anteosaurus lived in an upland environment, where they were among the most abundant predators, and hunted large prey such as dicynodonts and herbivorous dinocephalians. Due to their large size and short limbs, Anteosaurus were unlikely to have been particularly fast by modern standards. However, they didn’t need to be. Specialized cursorial animals had yet to evolve, and Anteosaurus lived in an environment rich in large, slow herbivores. Being able to tackle their prey was more important than being able to chase it, and Anteosaurus were certainly more than capable of outrunning and bringing down the large herbivores of their time. Furthermore, as the largest and most powerfully-built predators in their ecosystem, Anteosaurus could have also easily driven off smaller predators, such as the early gorgonopsian Eriphostoma and the therocephalians Glanosuchus and Pristerognathus, in order to steal their kills.

As was common in early therapsid predators, Anteosaurus had large incisors and canines, but only small teeth behind the canines. The incisors interlocked for a precise, flesh-shearing bite. Unusually, the small postcanine teeth were robust and somewhat turned out to the side, and may have been used for crushing bone.

Like other dinocephalians, Anteosaurus were characterized by cranial pachyostosis, or thickening of the skull bones. Anteosaurus had the greatest cranial pachyostosis of any predatory dinocephalian genus and bore thick forehead domes and bosses over their eyes, on their cheeks, and on their lower jaws. Such robust, knobby skulls are not uncommon among large predators, such as tyrannosaurids, and would have provided reinforcement for powerful, bone-crushing bites. It is possible that these adaptations were also involved in display and intraspecific combat, with rival Anteosaurus participating in shoving matches and trying to bite each other with their powerful canine teeth. Similar behavior has been recorded in modern hogs.

It is possible that a second species, Anteosaurus rugosus, lived in Russia, but the known remains are too incomplete to conclusively prove that they belong to Anteosaurus rather than its slightly smaller Russian relative Titanophoneus. A. rugosus lived alongside Titanophoneus and a much smaller anteosaur, Syodon.

Anteosaurus went extinct, along with the rest of the dinocephalians, approximately 260 million years ago. This extinction event is likely to be the result of volcanic activity in what is now China leading to darkened skies and less plant growth, thus collapsing the food chain Anteosaurus relied upon.

References:

—John

Anomalurus

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Anomalurus derbianus. Image credit: “Jonhall100”, under CC BY-NC 4.0.

Named by: Waterhouse, 1843

Taxonomy: Synapsida, Sphenacomorpha, Sphenacodontia, Sphenacodontoidea, Therapsida, Theriodontia, Cynodontia, Probainognathia, Mammaliamorpha, Mammaliaformes, Mammalia, Theria, Eutheria, Placentalia, Euarchontoglires, Glires, Rodentia, Anomaluromorpha, Anomaluridae

Included species: A. derbianus (type, as A. “fraseri”), A. beecrofti, A. pelii, A. pusillus

Gliding locomotion has evolved several different times in mammaliaforms. Among living mammals, well-developed gliding has arisen independently in the genera Acrobates and Petaurus among marsupials, the colugos among archontans, and the flying squirrels among rodents. (A few primates such as sifakas have been suggested to be capable of some degree of gliding, but they lack the extensive membranes connecting the front and hind limbs that the aforementioned groups have.) What is less frequently appreciated, however, is that there exists a second group of gliding rodents restricted to the forests of central Africa, where there are no flying squirrels to be found. These poorly known gliders are the anomalures.

The “official” common names of anomalures used by mammalogy organizations tend to be some variation of “scaly-tailed squirrel”. I for one don’t understand why this is the case when “anomalure” is a perfectly serviceable name that additionally emphasizes the uniqueness of these animals. Despite superficial similarities, anomalures are not at all closely related to squirrels beyond the fact that both are rodents. The closest living relatives of anomalures are another group of African rodents, the springhares, whose lineage diverged from theirs around 57.1 million years ago. Today, springhares are rodents of open country that get around primarily by hopping, whereas anomalures are forest dwellers that spend most of their time in trees.

Though “squirrel” misses the mark as a common name for anomalures, the “scaly-tailed” descriptor does not. All anomalures have two rows of scales underneath their tail, which provide them with extra grip while sitting or moving in the trees. With the exception of one species (Zenkerella insignis), most extant anomalures are gliders, and it is said that the slap of their tail scales against tree bark can be audible when they come in for a landing. Another unusual feature of the gliding anomalures is the cartilaginous spur that extends from each of their elbows and helps support their gliding membrane. Similar structures are found in flying squirrels, but those instead extend from the wrist. The gliding anomalures are divided into two genera, and here we will focus on the larger species, those in the genus Anomalurus.

The largest species of Anomalurus is A. pelii, which can weigh up to 2 kg (4.4 lb). In both size and gliding capacity Anomalurus are comparable to the largest flying squirrels, with documented gliding distances of up to 100 m (328 ft). Some species (especially A. derbianus) are known to prune branches around their preferred food sources to keep their glide paths clear.

Anomalures are largely herbivorous and Anomalurus are known to eat a variety of plant-based foods, including sap, leaves, bark, fruits, and flowers. A. derbianus often feed on the bark of the tree genera Strombosia, Klainedoxa, and Neoboutonia, and A. beecrofti feed on the pulp of palm fruits. A. beecrofti have a notably narrow snout, which may be an adaptation to this feeding behavior given that ripening palm fruits are protected by short spines.

Young Anomalurus are born with their eyes open and a complete covering of fur, at least in species (mainly A. derbianus) for which relevant observations have been made. In A. derbianus, both parents have been seen provisioning the young with chewed-up food, and the young remains in a hollow tree until it is almost fully grown.

During the day, Anomalurus retire to their nests, which are usually situated in tree cavities. Individuals may maintain up to six different nests at once. They are known to reuse the same nests over periods of months or even years. A. derbianus have also been seen resting in abandoned beehives, and A. beecrofti often sleep in dense vegetation at the tops of trees. Anomalurus are known to share their nesting hollows with other small mammals, including other species of anomalures as well as bats. However, the giant A. pelii aggressively deter larger potential nestmates such as hornbills by growling, hissing, and snapping their teeth. This is also their response to being disturbed by predators, and it has been suggested that the contrasting black and white coloration of this species warns potential aggressors of their belligerence.

Some species of Anomalurus do venture out before dark. A. derbianus regularly sunbathe during early mornings and occasionally evenings, whereas A. beecrofti have been seen clinging vertically to tree trunks during the day (sometimes even sleeping in this position). This does not necessarily make them any easier to observe, however. A. beecrofti have been credited with “exceptional powers of concealment”, likely because their mottled fur provides excellent camouflage. Their pelt has even been claimed to be “leaf green” in life, but this coloration allegedly fades at night and after death, and is thus not apparent in preserved specimens. The mechanism of this color fading has never been studied in detail, but it would appear to be a particularly unusual case of mammalian coloration.

References

—Albertonykus

Lophiomys (Maned rat)

lophiomys_imhausi
Lophiomys imhausi. Image credit: Kevin Deacon, under CC BY-SA 3.0.

Named by: Milne-Edwards, 1867

Taxonomy: Synapsida, Sphenacomorpha, Sphenacodontia, Sphenacodontoidea, Therapsida, Theriodontia, Cynodontia, Probainognathia, Mammaliamorpha, Mammaliaformes, Mammalia, Theria, Eutheria, Placentalia, Euarchontoglires, Glires, Rodentia, Myomorpha, Muridae

Included species: L. imhausi

Lophiomys are rarely-seen rodents that live in the forests and woodlands of eastern Africa. They are members of Muridae, the clade uniting Old World rats and mice, but, at up to 920 g (2 lb) in body mass, Lophiomys are quite a bit larger than your average rat.

The large size of Lophiomys compared to most other murids has allowed them to evolve a stomach partitioned into five compartments, not unlike the four-part stomach of cows and other ruminants. This in turn allows them to process their mainly plant-based diet in a similar way: by fermenting it in their foregut. Lophiomys are good climbers and regularly forage in trees, but their movements are slow and sluggish.

A large, slow-moving rodent would make a substantial meal for many predators. However, there are strong indicators that Lophiomys are not easy prey. When threatened, the long, gray-tipped hairs that normally cover their body are flared out, erecting a crest along their back and exposing boldly-patterned black and white tracts of shorter hair along their flanks. Such an eye-catching threat display would appear to be a warning to predators of a potent defense mechanism, but what this defense is has not been clearly understood until recently.

Historically, some have speculated that Lophiomys are harmless in themselves and that their black and white coloration are adaptations for mimicking other mammals with more repugnant defenses, such as zorillas (Ictonyx striatus, small carnivorans capable of spraying a noxious secretion) or porcupines. However, anecdotal accounts have long suggested the possibility of a chemical defense in Lophiomys. Dogs that had attacked these rodents were said to exhibit loss of coordination, froth at the mouth, and sometimes even drop dead. Detailed observations of Lophiomys behavior and anatomy, published in 2012, have given us a more complete understanding of antipredator adaptations in these rodents, and the truth is remarkable.

The observations presented in the 2012 study confirm that Lophiomys do indeed employ a chemical defense against predators, but the rodents do not use chemicals that they produce themselves. Instead, they chew the bark of a highly toxic tree species (Acokanthera schimperi), mix the toxin with their saliva, and then carefully apply this mixture to the shorter hair on their flanks. Examination of these hairs underneath a microscope reveals that they have a distinctive spongy structure, which allows them to absorb and retain the toxin. Considering that Acokanthera toxin is also used by native hunters to hunt and kill elephants, any predator that recklessly tries to make a meal out of Lophiomys is undoubtedly in for a nasty (and potentially fatal) surprise.

Even that is not quite the full extent of defensive adaptations in Lophiomys. Given that Lophiomys lack any means of injecting the toxin into would-be attackers, the only way for the toxin to take effect is if a predator grabs a Lophiomys individual in its mouth. As such, Lophiomys also have features that protect them from harm while being handled by large predators. The skin of Lophiomys is extremely dense and tough, their vertebrae are stout, and their skull is box-like and covered in bony granules. Mammals typically have a large opening on either side of skull, but in Lophiomys these openings are sealed off by bone, forming an inbuilt helmet. (In fact, the skull of Lophiomys has been likened to that of turtles, which also have similarly sealed-up skulls.) Though not the most extreme form of armor among mammals, this suite of adaptations is evidently sufficient to prevent serious injury to Lophiomys while the poison does its job.

Much remains unknown about the biology of Lophiomys, but one particular mystery stands out regarding their unique defense mechanism. Given that their defense requires them to regularly chew on highly toxic material, how do Lophiomys protect themselves from the toxin? Perhaps this is where the true significance of their multi-chambered stomach lies. The diet of Lophiomys consists primarily of soft plant parts that should be easily digestible even without foregut fermentation. Breaking down a deadly toxin, on the other hand, might just call for the involvement of an unusually complex digestive system.

References

  • Happold, D.C.D. (ed.). 2013. Mammals of Africa Volume III: Rodents, Hares and Rabbits. A&C Black Publishers Ltd., London. 784 pp.
  • Kingdon J., B. Agwanda, M. Kinnaird, T. O’Brien, C. Holland, T. Gheysens, M. Boulet-Audet, and F. Vollrath. 2012. A poisonous surprise under the coat of the African crested rat. Proceedings of the Royal Society B 279: 675-680. doi: 10.1098/rspb.2011.1169

—Albertonykus

Eomaia

eomaia
Restoration of Eomaia scansoria preying on the orthopteran insect Parahagla sibirica. Image credit: S. Fernandez, under CC BY 2.5.

Named by: Ji et al., 2002

Taxonomy: Synapsida, Sphenacomorpha, Sphenacodontia, Sphenacodontoidea, Therapsida, Theriodontia, Cynodontia, Probainognathia, Mammaliamorpha, Mammaliaformes, Mammalia, Theria?, Eutheria?

Included species: †E. scansoria

The Yixian Formation in northeastern China is most famous for its treasure trove of feathered dinosaur fossils. The bodies of the dinosaurs came to rest in fine-grained sediments at the bottom of calm lakes, often allowing their soft tissues such as feathers and scales to be preserved along with their skeletons. However, the world of the Mesozoic was not one populated solely by dinosaurs, and indeed the Yixian has far more to offer than just its attention-grabbing theropods. A great diversity of fossil organisms has been recovered there, including plants, insects, fish, amphibians, lizards, and, yes, mammals.

Mesozoic mammals were small-bodied animals, so they are not often preserved as complete fossil specimens. In fact, they are frequently known only from their teeth and jaws. However, like the famous feathered dinosaur fossils, many mammals of the Yixian Formation are preserved as complete (albeit flattened) skeletons, surrounded by soft tissues (in these cases, mostly hair). As such, they have much potential to shed light on the Mesozoic evolution of mammals. One Yixian mammal taxon that has been hailed as a particularly important discovery is Eomaia.

Eomaia was discovered in fossil beds that have been dated to the Early Cretaceous, 124.4 million years ago. It is known from a fantastic fossil specimen, but what really made the headlines was the fact that it was considered to be the oldest known eutherian mammal. Many features of its teeth were similar to those of previously known eutherians from later in the Cretaceous, as were the shape of its wrist and ankle bones. The vast majority (~94%) of mammal species alive today are eutherians. If the describers of Eomaia are correct, then everything from sloths to elephants to humans to whales can trace their ancestry back to a creature similar to Eomaia.

Eomaia
The holotype specimen of Eomaia scansoria. Image credit: Zofia Kielan-Jaworowska and Jørn H. Hurum, under CC BY 2.0.

Considering its exceptional preservation and scientific value, one might expect that dozens of papers have been written describing Eomaia in detail… but not really. Relatively little has been said about its anatomy since it was originally named. However, some doubt has been cast on its status as a eutherian. In 2013, an extremely large-scale analysis of the phylogenetic relationships between eutherian mammals was published, and this study instead recovered Eomaia as a stem-therian. Theria is the clade that unites both eutherians and metatherians (the latter includes marsupial mammals), and Eomaia was found to be closely related but not belonging to this group. Some subsequent analyses (such as Luo et al., 2017) have continued to support eutherian affinities for Eomaia, but other studies (such as Averianov and Archibald, 2016) have identified additional anatomical evidence to consider it a stem-therian.

Even if Eomaia was a eutherian, its claim to fame as the earliest known example of one may no longer hold true. In 2011, Juramaia from the Late Jurassic, 160.7 million years ago, was described as another putative eutherian, though its eutherian status has also since been questioned. Additionally, a couple of eutherian teeth from 145 million years ago were reported in 2017. These were given the names Durlstodon and Durlstotherium.

All of this does not necessarily diminish the importance of Eomaia. After all, if Eomaia was closely related to the last common ancestor of all therian mammals, then it serves as a potential model not only for the ancestral morphology of eutherians, but for that of both eutherians and metatherians (which together comprise 99.9% of extant mammal diversity). Of course, none of this would have been of any concern to the Eomaia going about their lives in the Early Cretaceous. What do we know about Eomaia as living animals?

Like typical Mesozoic mammals, Eomaia were small, estimated as having weighed 20-25 g (0.71-0.88 oz). They possessed many anatomical features indicative of a climbing lifestyle, including elongate bones in the tips of their fingers, arched claws that were compressed from side to side, and a long tail. All in all, Eomaia were likely agile climbers, able to clamber quickly through vegetation and run along the tops of tree branches. However, the describers of Eomaia concluded that insufficient information was available to determine whether Eomaia were scansorial (habitual climbers but also spending much time on the ground) or arboreal (spending most of their time in trees). A later study published in 2015 favored the interpretation that Eomaia were arboreal.

At present, that is the extent of what has been inferred about the lifestyle of Eomaia. Regardless of its exact phylogenetic affinities, the well-preserved nature of the Eomaia holotype means that it has the potential to reveal much about how it lived and functioned. We know it probably climbed, but did it move in a similar manner to any living mammal? What was it most suited to eating? What was the color of its fur? As the debate continues on what Eomaia means for the origins of modern mammals, the story of Eomaia as living organisms in their own time remains largely untold.

References

—Albertonykus

Cynocephalus (Philippine colugo)

Colugo - 1
Cynocephalus volans. Image credit: Pinay06 under CC BY-SA 3.0.

Named by: Boddaert, 1768

Taxonomy: Synapsida, Sphenacomorpha, Sphenacodontia, Sphenacodontoidea, Therapsida, Theriodonta, Cynodontia, Probainognatha, Mammaliamorpha, Mammaliaformes, Mammalia, Theria, Eutheria, Placentalia, Euarchontoglires, Archonta, Dermoptera, Cynocephalidae

Included Species: C. volans

Colugos were originally known as ‘flying lemurs’, a name that has serious problems considering that these animals are not true flyers and are not lemurs nor closely related to them. Colugos belong to the clade Dermoptera and are seem to be the closest living relations to primates, as understood by several morphological and molecular studies. Whether treeshrews (Scandentia) are allied with colugos in a singular clade called Sundatheria (itself allied with Primates) is a current controversy of phylogenetics.

Though they are lemur-like in their face, their postcranial anatomy is very unique and specially adapted to gliding. A thin membrane connects the limbs, digits, and tail and this allows them to soar at lengths of up to 100 meters or more while simultaneously remaining within 10-12 meters of elevation. Indeed, they are fully arboreal: living in the thick-foliage of rainforest canopies and understories. Colugos nest in tree-hollows and holes and move slowly among the branches, sometimes resting or feeding upside-down. Incidentally, the tail does not appear to be prehensile, so staying secure in the trees requires work solely from the limbs and digits. If a colugo finds itself stuck on the ground, it is totally vulnerable and will desperately try to climb upon any surfaces.

There are two extant species of colugos: one (Galeopterus) is found throughout Southeast Asia, while the other, discussed in this article, lives solely on the southern Philippine islands. Nocturnal in habit, Philippine colugos will take small journeys around specific routes: they have fixed homes and will only glide about roughly 1 to 1.7 kilometers in small durations of under 14 minutes or so before returning to the same nest before sunrise. In fact, there is a peak in foraging activity in the hours after the sun sets and before it rises. These static feeding routes were (and are) well understood by Filipino-hunters who will follow the animals and trap or shoot them with arrows. Though they are not social animals, colugo home ranges (ranging from 6.4 to 13.4 hectares in size) will overlap a considerable amount.

On the menu for Philippine colugos is almost always young leaves, though occasionally soft fruits and flowers are consumed – typically all food is eaten at the same spots every night. Also shared among colugos is their tree-hole shelters. Multiple individuals will share the same home, though males may fight amongst each other.  Allogrooming (grooming among members of the same species) has been observed for colugos among males and females, young and old.

Breeding occurs throughout the year and females will give birth to one (rarely two) young: usually newborns are very small and almost fetal – in the vein of marsupial joeys. As such they are closely cared for by the mother, clinging to one of her single-paired teats for the first six months of its life. As she glides, feeds, and rests, the infant is there nursing, until old enough to fend for itself. Philippine colugos are full-grown at two/three years of age.

The colugos of the southern Philippines are not considered seriously threatened species – they are classified as a “Least Concern” on the IUCN Red List. Though hunting and deforestation are serious concerns – as they are for all rainforest organisms – their population is currently stable.

References:

  • eol.org. (2018) Encyclopedia of Life. [online] Available at: http://eol.org/pages/289811/details
  • Grzimek, B. and Fiedler, W. (1972). Grzimek’s Animal Life Encyclopedia: Mammals II. New York [etc.]: Van Nostrand Reinhold.
  • iucn.org. (2018). The IUCN Red List of Threatened Species. [online] Available at: http://www.iucnredlist.org
  • Jackson, S. and Schouten, Peter. (2012). Gliding Mammals of the World. Collingwood, Australia: CSIRO Publishing.
  • Nowak, Ronald. (1999). Walker’s Mammals of the World Vol. 1: Sixth Edition. Baltimore, Maryland: John Hopkins University Press.

—Joan

Nandinia (African palm civet)

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Nandinia binotata. Image credit: Mathias D’haen, under CC BY-NC 4.0.

Named by: Gray, 1843

Taxonomy: Synapsida, Sphenacomorpha, Sphenacodontia, Sphenacodontoidea, Therapsida, Theriodontia, Cynodontia, Probainognathia, Mammaliamorpha, Mammaliaformes, Mammalia, Theria, Eutheria, Placentalia, Laurasiatheria, Ferae, Carnivoramorpha, Carnivora, Feliformia, Nandiniidae

Included species: N. binotata

Viverrids (civets) are one of those groups of organisms that have experienced dramatic taxonomic revision in recent times. Particularly with the advent of molecular phylogenetics, many groups formerly considered viverrids have been booted out. These ex-civets include mongooses (more closely related to hyenas than to civets), Malagasy carnivorans such as the fossa (Cryptoprocta ferox) (also more closely related to hyenas), and linsangs (more closely related to cats).

One former viverrid, however, sits alone in the family tree of feliforms, the large clade of carnivorans that comprises all species more closely related to cats than to dogs, encompassing all of the groups mentioned in the previous paragraph. The single living species in the genus Nandinia is descended from a lineage that may have split from all other feliforms 40-50 million years ago and has no close living relatives. Despite this, it is still known by the vernacular names “African palm civet” and “two-spotted palm civet”.

feliforms
Phylogenetic tree of feliform relationships.

Nandinia may be phylogenetically lonely, but in many parts of their range they are considered the most abundant small carnivorans in the forests of central Africa. They are generally solitary, though this doesn’t mean that their lives are devoid of social interaction. The home range of a dominant male overlaps with those of several females and smaller males, and he communicates with the females in his range using a loud cry that can be heard up to almost 1 km (3280 ft) away. The smaller males, on the other hand, generally keep to their individual sectors within the larger range of the dominant male, a sensible choice given that conflicts between males are known to be fatal. Several individual Nandinia may gather in close proximity where food is abundant, such as groves of fruiting trees.

Fruit constitutes roughly 80% of the diet in Nandinia, and they assist in the seed dispersal of at least 12 different plant species. After feeding on fruit for 5-10 minutes at a time, Nandinia typically rest for about 2 hours on a tree branch a short distance away before returning to partake in another meal. Perhaps not coincidentally, the digestive system of Nandinia works quickly; it takes only 2-3 hours for consumed fruit to pass through the digestive tract. When more than one individual is feeding in the same tree, females have priority access to food.

Their largely frugivorous habits should not be taken as a indicator of Nandinia lacking predatory prowess, however, considering that they are known to go after small primates such as pottos (Perodicticus potto) and juvenile monkeys. Nandinia dispatch their prey by holding it down with their forefeet while biting them all over the body. Their climbing skills serve them well when hunting; they have been observed catching fruit bats and raiding the nests of weaver birds at the tips of very thin branches.

The arboreal agility of Nandinia is facilitated by their large, ridged foot pads and a long, balancing tail. They are able to climb smooth posts, hang upside down by their feet, and descend trees headfirst. They can also jump across gaps 1 m (3.3 ft) wide and leap 1.8 m (5.9 ft) vertically into the air. One anecdotal account described an individual Nandinia repeatedly climbing to a height before apparently parachuting to the ground by extending its legs and tail. As one might expect, regular performance of such stunts can be risky. A wild specimen was once caught with healed fractures across its femur and kneecap.

Despite their acrobatics, it appears that Nandinia rarely venture higher than 40 m (131.2 ft) above the ground, preferring heights of 5-35 m (16.4-114.8 ft). During the day they rest on thick horizontal branches or in tree hollows 12-15 m (39.4-49.2 ft) above ground. Unlike many other specialized arboreal mammals though, Nandinia display no aversion to traveling and foraging on the ground, and are regularly caught in traps set at ground level.

References

—Albertonykus

Thylacinus (Thylacines)

Thylacinus
Thylacinus cynocephalus individuals, photographed at the National Zoo, Washington, DC, ca. 1904. Image credit: Baker & Keller, public domain under US law.

Named by: Temminck, 1824

Taxonomy: Synapsida, Sphenacomorpha, Sphenacodontia, Sphenacodontoidea, Therapsida, Theriodontia, Cynodontia, Probainognathia, Mammaliamorpha, Mammaliaformes, Mammalia, Theria, Metatheria, Marsupialia, Australidelphia, Dasyuromorphia, Thylacinidae

Included species: †T. cynocephalus (type), †T. macknessi, †T. megiriani, †T. potens, †T. rostralis, †T. yorkellus

Few mammals are more emblematic of extinction than the thylacine. The largest marsupial predator of modern times, this shy, nocturnal animal (also known as the Tasmanian wolf or Tasmanian tiger) was never numerous anywhere in its range, but it wasn’t always constrained to the island of Tasmania. At one point, thylacines could be found across Australia and New Guinea (which were joined in a landmass called Sahul before the end of the last ice age), but by around 2,000 years before the present, they had been completely extirpated from New Guinea and mainland Australia, and became constrained to the island whose name the species later bore. After almost 2,000 years of persecution by humankind and other stressors, the thylacine became even scarcer in its remaining Tasmanian range in the first four decades of the 20th century. The last known thylacine died in captivity in 1936, marking the end of this remarkable marsupial’s time on earth.

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A thylacine pictured in rock art at Ubirr, Northern Territory, Australia, >2,000 years old. Image credit: Original author unknown, photographed by Dave Pape, under CC BY 2.0.

Of course, this whole sorry saga is only a small part of the history of the thylacine and its relatives. Thylacinus cynocephalus was only the last of its family, which arose late in the Oligocene epoch and lasted for almost 30 million years before its extinction. Some of these extinct thylacine genera are worth discussing later, but there also existed extinct members of Thylacinus itself, which varied in some respects from the modern variety. Most noteworthy of these is the so-called “powerful thylacine”, T. potens, which is known from the Late Miocene Alcoota fauna of Northern Territory, Australia. A large, robust thylacine, it approximated a grey wolf in size and had a shorter snout. T. cynocephalus itself arose during the Pliocene and outlasted its relatives to become widespread, for a time, across the continent.

The modern thylacine was a medium-sized predator, a little bigger than a red fox. Males usually measured in at a direct length of around 1.63 meters (5.34 feet), and females at around 1.54 meters (5.05 feet). Males and females also possessed a degree of sexual dimorphism unusually high for marsupials in possessing different facial structures, with females tending to have shorter, more slender snouts. Notably, the thylacine was one of only two marsupial species known to have retained a pouch in males, which was repurposed as a sheath for the scrotal sac. In its more typical use, the female pouch, which (in another unusual twist) faced rearward, could bear up to four joeys (or “pups”), but typical litters were fewer than that, at two or three. Their fur was a sandy brown, with anywhere from 13 to 22 dark bands striping their haunches. There was a great deal of individual variation in these stripes, and no two thylacines would have had the same pattern. Museum specimens have even been matched to previously captive individuals on the basis of these stripes. In gross bauplan, they strongly resembled canids, despite having no close relation to them. They could be easily distinguished by, among other things, their significantly taller hindlimbs in proportion to their bodies, which gave them a strange, loping gait. The thylacine possessed the greatest mouth gape of any known modern mammal, and was capable of achieving as much as 80 degrees of jaw flexion during its “threat yawn” warning display.

Thylacines apparently bred year-round, with the peak breeding seasons in the spring and winter. They formed and hunted in family groups rather than packs, and seem to have opportunistically taken birds, lizards, small marsupials, and wallabies, but occasionally were adventurous enough to hunt eastern grey kangaroos. When in pursuit, they would move at a leisurely jog or canter rather than sprinting, and seem to have relied on superior stamina to outpace their prey. They also very occasionally preyed on domestic sheep and poultry, something which earned them the enmity of European settlers. Although indigenous Australians had occasionally poached thylacines for tens of thousands of years, the high-impact persecution of these settlers, whether government-led or private, led to the deaths of thousands of thylacines through the 19th and early 20th centuries. Hefty bounties for the animal would have driven the motivation for the killings just as much as any alleged predation upon livestock; at least one famous photo of a thylacine clutching a chicken in its mouth in fact comes from a sequence which, in context, shows it clearly being fed the bird in captivity. Habitat degradation caused by humankind and possible outbreaks of disease noted by trappers may have also contributed to the decline of this species. By the turn of the century, they were very rare, and the last thylacine shot in the country was in 1930; the last capture was of an individual posthumously named “Benjamin” in 1933, whereupon the male thylacine was transported to the Beaumaris Zoo, Hobart, where it lived for three years until dying, apparently of neglect. The death of “Benjamin” on 7 September 1936 also marks the last known human contact with this species, for from this point on, no confirmed sightings of this remarkable marsupial have been made. In 1982, it was declared extinct by the IUCN, and in 1986 by the government of Tasmania.

Thylacine-chicken
Staged photograph of a thylacine feeding upon a chicken, 1921. Image credit: Henry Burrell, public domain under Australian law.

Despite more than eighty years having passed since the death of the last known living individual, the thylacine has remained a darling of career and amateur cryptozoologists alike, and the possibility of its continued existence remains an article of serious public fascination. Surveys in 1938 turned up potentially credible scat and markings in the west of Tasmania, and alleged physical evidence has continued to surface in the decades since, not always convincingly. Some sightings and would-be photographic evidence have come from mainland Australia, but since the animal was not even known to exist there in the historical record, these must be regarded as improbable. If it really has persisted to the present, it would be in an incredibly small population deep in western Tasmania, since determined searches have turned up nothing conclusive and the projected population in the 1930s was that of only a few hundred individuals at most. Sadly, the fact that this marsupial predator is gone for good must be held as almost a certainty, and an object lesson in the effects of misinformed persecution against animal populations.

References

  • Australian Museum. The Thylacine. Accessed 16 December 2017.
  • Naturalworlds.org. The Thylacine Museum. Accessed 15 December 2017.
  • Paddle, R. 2000. The Last Tasmanian Tiger: The History and Extinction of the Thylacine. Cambridge University Press; Cambridge, UK. 273 pp.
  • Yates, A.M. 2014. New craniodental remains of Thylacinus potens (Dasyuromorphia: Thylacinidae), a carnivorous marsupial from the late Miocene Alcoota Local Fauna of central Australia. PeerJ 2: e547. 10.7717/peerj.547

—Valerie

Rhynchocyon (Giant sengis)

1200px-rhynchocyon_petersi_from_side
Rhynchocyon petersi. Image credit: Joey Makalintal, under CC BY 2.0.

Named by: Peters, 1847

Taxonomy: Synapsida, Sphenacomorpha, Sphenacodontia, Sphenacodontoidea, Therapsida, Theriodontia, Cynodontia, Probainognathia, Mammaliamorpha, Mammaliaformes, Mammalia, Theria, Eutheria, Placentalia, Afrotheria, Afroinsectiphilia, Macroscelidea, Macroscelididae

Included species: R. cirnei (type), R. chrysopygus, R. petersi, R. udzungwensis

Sengis are great. They are commonly known as “elephant shrews”, and it’s not hard to see why. Like shrews, they are small, mostly insectivorous mammals, and, like elephants, they have an elongated, mobile snout. However, prior to the rise of phylogenetic analysis incorporating molecular data, perhaps no one would have guessed that they are, in fact, more closely related to elephants than to shrews!

In terms of their size, the most elephantine sengis are members of the genus Rhynchocyon, hence their vernacular name of “giant sengis”. By “giant”, we mean up to 750 g (1.7 lb), slightly larger than a gray squirrel. These gargantuan sizes are attained by the most recently discovered species, R. udzungwensis, which was only scientifically described in 2008. Other species range between 300-700 g (0.7-1.5 lb).

Rhynchocyon live in the forests of Africa. They uncover invertebrates hiding under leaf litter by using their snout and long claws, and, like other sengis, capture prey with their tongue. Unusually among sengis, they don’t clear trails to use as runways within their home range. At night, they sleep in nests made from leaves on the forest floor. These nests lack a proper entrance; instead, the sengis enter simply by digging into them from one side. Unlike other sengis, which have highly precocial young that can run shortly after birth, juvenile Rhynchocyon stay in a nest for several weeks before they are old enough to forage.

Being active during the day, Rhynchocyon must remain on the lookout for a variety of predators, including birds of prey and chimpanzees. Sengis are highly specialized for rapid, almost antelope-like quadrupedal bounding, allowing them to escape from danger (at least much of the time). Rhynchocyon have been recorded reaching speeds of 27 km/h (17 mph). If a predator is detected before it gets close enough to be an immediate threat, R. chrysopygus are known to slap their tail against the ground while walking away, perhaps signalling to the predator that it has been spotted. R. chrysopygus are additionally notable for the golden patch of hair on their rump, which may divert predator attacks towards the thickened skin in this region and increase the sengis’ chances of escape. The rump shield also protects R. chrysopygus against bites from rivals.

Typical of most sengis, Rhynchocyon are socially monogamous, probably mating for life. Within their shared territory, each member of a mated pair drives off rivals of the same sex. However, mates don’t spend much time with each other and don’t even share the same nest at night. The adaptive function of monogamy in sengis is debated, because male sengis contribute little, if any, parental care of the young. In Rhynchocyon, it appears that the primary selective pressure for monogamy may be the high energetic cost that would be required for a male to defend multiple females from his competitors. Indeed, male Rhynchocyon will enter temporary polygynous relationships if the opportunity arises, usually when a female in a neighboring territory loses her mate.

References

—Albertonykus

Phataginus

manis_tricuspis_san_diego_zoo_03-2012
Phataginus tricuspis. Image credit: Николай Усик, under CC BY-SA 3.0.

Named by: Rafinesque, 1821

Taxonomy: Synapsida, Sphenacomorpha, Sphenacodontia, Sphenacodontoidea, Therapsida, Theriodontia, Cynodontia, Probainognathia, Mammaliamorpha, Mammaliaformes, Mammalia, Theria, Eutheria, Placentalia, Laurasiatheria, Ferae, Pholidotamorpha, Pholidota, Manidae

Included species: P. tricuspis (type), P. tetradactyla

Pangolins are some of the most peculiar mammals. They are toothless, relying on their long, sticky tongue to capture insect prey. They are also covered in a coat of hard scales that serve as protection from predators. These unusual features may recall similarities with the anteaters and armadillos of South America. However, genetic studies have shown that the closest living relatives of pangolins are the carnivorans, the great radiation of predatory placental mammals including cats, dogs, bears, seals, and more.

Living pangolins are currently split into three different genera, of which the smallest are members of the genus Phataginus. Weighing around 2 kg (4.4 lb) as adults, Phataginus live in the forests of central Africa. Like other pangolins, they can roll into an armored ball to protect themselves from attack, but their scales are generally thinner and flimsier than those of larger pangolins. This, combined with their small size, likely makes them more vulnerable to predation, and they may rely more on their repulsive anal secretions to deter large carnivores.

P. tricuspis is the better-studied of the two species of Phataginus. Members of this species can retract their eyes into their sockets (an ability apparently shared by at least some other pangolin species). They regularly forage in trees and are able to climb quickly using a “caterpillar-like” motion. To get down from trees, they spiral around the tree trunk while supporting themselves using their tail. They have also been observed performing more expeditious descents by rolling into a ball before dropping directly to the ground.

Despite being at home in the trees, however, P. tricuspis spend much of their time on the ground, perhaps due to the greater availability of their preferred prey on the forest floor. While feeding, they flick their scales continuously to shake off attacking soldier ants and termites, and sweep their tail from side to side to herd their prey within reach. After feeding, they groom themselves meticulously using their hind feet to uncover any insects that may have ventured underneath their scales. During the day, P. tricuspis rest in tree cavities or in shallow burrows. They breed throughout the year; one field study rarely found females that were not pregnant.

Pangolins are typically solitary, but P. tricuspis exhibit behaviors suggestive of greater sociality in this species. Pairs have been found using the same tree hollows, and in captivity groups of up to six individuals have been observed sharing sleeping quarters and following one another around in single file. Juveniles in particular appear eager to seek contact with other pangolins and even their human handlers. One individual regularly returned to visit its handlers over a period of six months after being released into the wild. In general, P. tricuspis seem like a friendly bunch. However, males are known to fight to the death by slashing each other with their front claws. P. tricuspis have poor eyesight, so their social contacts are established using scent. They are also quite sensitive to vibrations, including sound.

Though most pangolins are competent climbers, members of the other species of Phataginus, P. tetradactyla, are particularly specialized for arboreal life. Their incredibly long, prehensile tail contains up to 47 vertebrae, more than that of any other mammal. The tail is strong enough to support their entire body weight for long periods, allowing them to hang by their tail. P. tetradactyla almost never descend to the ground. They rest in tree hollows or hollowed-out insect nests. Cavity-nesting birds are reportedly known to mob them, perhaps seeing them as competition for tree hollows.

P. tetradactyla are said to be more diurnal than P. tricuspis, which may reduce competition between the two species. It is likely that the highly arboreal habits of P. tetradactyla, along with their preference for forests that experience regular flooding, correspond to a specialization in feeding on ants and termites that avoid floods by nesting high in the forest canopy. Such insects tend to have well-developed chemical weaponry, so it is plausible that P. tetradactyla possesses adaptive countermeasures to these defenses. However, due to the lack of detailed study, such specializations, if present, remain unknown.

Reference

  • Kingdon, J. and M. Hoffmann (eds.). 2013. Mammals of Africa Volume V: Carnivores, Pangolins, Equids and Rhinoceroses. A&C Black Publishers Ltd., London. 560 pp.

—Albertonykus