A list of enigmas: bamboo bats, frogs-head flyers, Rohu's bat and the false serotines (vesper bats part XVI)

By now (if, that is, you've been following this thrilling, roller-coaster ride of a series) we've gotten through the better part of vesper bat phylogeny: we've climbed 'up' the vesper bat cladogram and are now within the youngest major section of the group. Recent phylogenetic studies have recognised a serotine clade (Eptesicini or Nycticeiini), a hypsugine clade (including Savi's bat and a load of relatives), and a clade that includes pipistrelles and noctules (Vespertilionini).

Seemingly fitting somewhere within these three clades - or, perhaps, close to them - are a list of oddballs that have either proved difficult to place, or haven't yet been incorporated into modern studies on account of being so poorly known and little studied. It's these species that we'll look at here: they include some of the weirdest vesper bats of them all. Species with adhesive pads on their thumbs and feet, and others with weird, flattened, frog-like heads and uniquely short wings.

Club-footed bats or bamboo bats

Arguably among the most interesting of vesper bats are the three club-footed bats, flat-headed bats or bamboo bats (Tylonycteris), known from India and southern China all the way south to Java, Borneo and the Philippines. The newest of the three, T. pygmaeus, was only named in 2008. These bats are tiny: T. pachypus weighs about 2 g and hence competes with Craseonycteris thonglongyai (the Bumblebee bat or Kitti's hog-nosed bat: NOT a vespertilionid) for the title of world's smallest bat (and smallest mammal). A strongly flattened, broad skull and strange flattened pads on the thumbs, wrists and feet allow these bats to squeeze inside, and cling to, the internodes of bamboo stems, and their small size is perhaps a specialisation for this habit as well [image below, showing bamboo bat emerging from slit in bamboo internode, from Wildlife Singapore]. The thumb pads are smooth while the wrist pads are covered in wrinkled skin and have sebaceous glands opening on their surfaces (Thewissen & Etnier 1995). It has been proposed that the thumb pads allow the bats to grip by way of dry adhesion (Thewissen & Etnier 1995).

The idea that there are bats possessing morphological specialisations for roosting inside bamboo stems is remarkable enough: what makes the story perhaps more incredible is that the bats require the bamboo to be damaged by the chrysomelid beetle Lasiochila goryi before they can get inside. Having said all that, club-footed bats will also roost between rocks, so it looks more likely to me that, while those adaptations might allow a bamboo-roosting habit, they didn't obviously evolve under selection pressure associated with this specific choice of roost site.

Incidentally, the use of bamboo stems as roost sites is hardly advantageous in modern times. It seems that the bats are suffering from habitat loss due both to the replacement of bamboo forest with sugarcane plantation, and to the use of bamboo tissue in binding sugarcane bundles. Interviews show that local people preferentially destroy those bamboo stems with bat entry holes since they regard these plants as damaged and unable to grow more. For more on the conservation of these bats, see this article at Bat Conservation International.

Club-footed bats have recently been recovered as part of the hypsugine group discussed in the previous article: Roehrs et al. (2010) recovered them as the sister-group to Hypsugo. Volleth & Heller (1984) had previously found them to be the sister-taxon to Philetor (discussed below).

Mimetillus: the frog's head flyers

Even stranger (in my opinion) than the club-footed bats are the flat-headed bats (Mimetillus), also known as narrow-winged bats or mimic bats [adjacent illustration from Kingdon (1997)]. I have no idea how they got the last name. Most authors have only recognised a single species in this group (Moloney's flat-headed bat M. moloneyi), but here I follow Aulagnier et al. (2010) in also recognising M. thomasi. There's actually some suggestion that Mimetillus might represent a complex of species. I can't see that they've been included in any phylogenetic studies, so have placed them here by default.

These have to be among the strangest bats of all: their wings are proportionally short - so short that, when folded, the wing tips only extend about half-way along the length of the body [the adjacent sketch is copied from a photo (in Nowak (1999)) of a specimen held at the Natural History Museum, London]. This unique configuration gives them extremely high wing-loading and extremely low aspect ratio - as a result, they plot well away on their own in bat morphospace. Here's the wing shape graph we looked at in part II of this series (from Norberg & Rayner (1987)), now with Mimetillus marked with an arrow for emphasis.

The legs are short (for a bat) and the skull is broad and shallow: Kingdon (1997) even described its muzzle as frog-like (thanks to this, I'm forever destined to think of these bats as the 'frog's head flyers'*). Large glands are present on the snout and the short, dark fur is said to be greasy. Unsurprisingly in view of their wings, their flight style is distinctive: direct, without sharp turns, and with unusually fast wing beats. Apparently they need to stop flying and rest every 10-15 minutes (Nowak 1999).

* Baron Greenback's vehicle of choice in the 1980s cartoon series Dangermouse.

As might be predicted for bats with a broad, shallow skull, Mimetillus roosts under tree bark. Whether their short wings, short legs and short, greasy pelage are linked to this crawling, arboreal roosting habit or to some other aspect of their ecology or behaviour is unknown so far as I can tell [adjacent photo of a live on, taken in Liberia, by K. D. Dijkstra]. Their affinities don't seem to have been thoroughly investigated - authors who have listed Mimetillus in classification schemes have often put it next to the African long-eared bats (Laephotis): if this is right, these bats could be hypsugines. These bats aren't rare or localised in distribution - they occur across much of sub-Saharan Africa and are often easy to find. They definitely warrant further study - what sort of pressures led to a bat ending up being so very, very weird?

Enigmatic Rohu's bat

Philetor brachypterus (sometimes called Rohu's bat*) is a pipistrelle-like species that apparently occurs from Nepal all the way to New Guinea and the Bismarck Archipelago. Prior to 1966 it was thought to be unique to New Guinea, but subsequent discoveries (mostly made in museum collections) have shown that it occurred widely in Indonesia, the Philippines and continental Asia. It's said to have relatively short wings, a large, rounded braincase and a short, deep, wide muzzle [see the skull diagrams below; from Ingle & Heaney (1992)]. Photos reveal a sleek, noctule-like pelage and short, rounded ears.

* After P. rohui Thomas, 1902, regarded by Hill (1971) as a subspecies of P. brachypterus (Temminck, 1840).

It's been suggested that variations in the shape of the narial emargination (that U- or V-shaped gap present, in the skull, along the midline of the rostrum) indicate the existence of three subspecies, but Koopman (1983) regarded this feature as too variable to be reliable. A few species currently included in Hypsugo (and, before that, placed in Pipistrellus) have been suggested to be additional species of Philetor, including H. anthonyi from Myanmar (Koopman 1983). In Philetor, the premolars are strongly reduced in size: in his revision of Philetor, Hill (1971) noted that the Hypsugo species H. stenopterus, H. anthonyi and H. joffrei seemed to form a series in which the dentition became increasingly Philetor-like in its degree of reducion.

This hypothesis hasn't necessarily been supported in recent phylogenies, but those studies that have included Philetor have indeed recovered a relationship with hypsugines. Volleth & Heller (1984) found Philetor to form a clade with the club-footed bats or bamboo bats (Tylonycteris) within a clade that also included Vespertilio, Hypsugo, Vespadelus and Falsistrellus, and Chalinolobus. The inclusion of Vespertilio meant that the name Vespertilionini had to go with this clade, but because most of the other taxa mentioned here belong to the hypsugine clade recovered by Roehrs et al. (2010), I think it's likely that Philetor is indeed an additional hypsugine.

Eudiscopus: another vesper bat with adhesive pads

I don't know how widely known it is that bats have (on a few separate occasions) evolved adhesive disks on their thumbs and/or feet. The best known of such bats are the Madagascan myzopodids and Neotropical thyropterids. These bats are not vesper bats (nor close relatives of them), so won't be discussed here. But rather little known is that adhesive disks evolved at least once in vesper bats: Laos, Thailand, Vietnam and Myanmar are home to Eudiscopus denticulus, an extremely poorly known, superficially pipipstrelle-like bat that possesses large adhesive disks on its feet. So far as I can tell from the literature, an adhesive function is only inferred, since no-one has reported sightings of the bat engaging in normal behaviour (Thewissen & Etnier 1995). These disk-like structures perhaps evolved from thickened pads of the sort discussed above in the bamboo bats.

As of 1999, only eight Eudiscopus specimens were known: Nowak (1999) stated that the species hadn't been reported for years. Since then, additional specimens were reported from Myanmar and Thailand in 2000, and from Vietnam in 2003. The skull in Eudiscopus is relatively broad and flat, leading to suggestions that it might secrete itself in narrow crevices in rocks (Koopman 1972) [skull drawing here from Koopman (1972)]. A fossil bat from the Miocene of Slovakia, Paleptesicus priscus Zapfe, 1950, reportedly has similarities with Eudiscopus (Rossina et al. 2006).

A precise phylogenetic position for Eudiscopus has yet to be reported (so far as I can tell), though it's sometimes been listed close to serotines or to bufferfly bats. I put it here as I don't know where else to discuss it.

The false serotines

The Hesperoptenus species, sometimes called the false serotines, are mid-sized Asian bats with a distribution mostly centred around south-east Asia and Borneo. They superficially recall serotines proper (hence the name); of the five species, H. tickelli is notable in possessing white wing markings and so-called friction pads on its thumbs. Hill (1976) thought that the species within this genus should be split into two clusters, with the subgeneric name Milithronycteris being used for those species with 'fleshier' ears, a less globular braincase and a broader rostrum [Blanford's bat or Least false serotine H. blanfordi is shown here; photo by Pipat Soisook].

Not much is known about these bats. Hill (1976) proposed that false serotines were phylogenetically intermediate between pipistrelle-like bats and the Harlequin bat Scotomanes ornatus and house bats (Scotophilus) (he regarded Scotomanes and Scotophilus as part of the nycticein group). New phylogenetic studies don't yet seem to have incorporated them, so I'm discussing them here, close to other problem taxa.

Hope you enjoyed look at 'the weird ones' - more to come!

For previous Tet Zoo articles in the vesper bats series, see...

• Introducing the second largest mammalian 'family': vesper bats, or vespertilionids
• The vesper bat family tree: of myotines, plecotins, antrozoins, and all those cryptic species (vesper bats part II)
• Bent-winged bats: wide ranges, very weird wings (vesper bats part III)
• Of southern African wing-gland bats, woolly bats, and the ones with tubular nostrils (vesper bats part IV)
• The many, many mouse-eared bats, aka little brown bats, aka Myotis bats (vesper bats part V)
• Long-eared bats proper: Plecotus and other plecotins (vesper bats part VI)
• Desert long-eared bats - snarling winged gremlins that take scorpion stings to the face and just don't care (vesper bats part VII)
• Hairy-tailed bats: a tale of furry tails, red coats, cold tolerance, migration and sleeping out in the open (vesper bats part VIII)
• Robust jaws and a (sometimes) 'greenish' pelt: house bats (vesper bats part IX)
• Australasian big-eared bats, and how to (perhaps) single-handedly wipe out an entire species, 1890s-style (vesper bats part X)
• Antrozoins: pallid bats, Van Gelder's bat, Rhogeessa... Baeodon!! (vesper bats part XI)
• Putting the 'perimyotines' well away from pips proper (vesper bats part XII)
• Nycticein bats: apparently, a nice example of how assorted distant relatives can be mistakenly considered close allies on the basis of one or two characters (vesper bats part XIII)
• Eptesicini: the serotines and their relatives (vesper bats part XIV)
• Hypsugines: an assemblage of 'pipistrelle-like non-pipistrelles' (vesper bats part XV)

And for previous Tet Zoo articles on bats, see...

• Desmodontines: the amazing vampire bats
• Giant extinct vampire bats: bane of the Pleistocene megafauna
• Camazotz and the age of vampires
• Dark origins: the mysterious evolution of blood-feeding in bats
• A new hypothesis on the evolution of blood-feeding: food source duality involving nectarivory. Catchy, no?
• Oh no, not another giant predatory flightless bat from the future
• The most terrestrial of bats
• I stroked a pipistrelle
• Red bats
• We flightless primates
• Big animalivorous microbats
• Hidden in plain sight: discovering cryptic vesper bats in the European biota
• PROTOBATS: visualising the earliest stages of bat evolution

Refs - -

Aulagnier, S., Avenant, N., Benda, P., Haslauer, R., Hazevoet, C. J., Kearney, T., Kemp, A., Markotter, W., Seamark, E. C. J., Turni, H., Van Cakenberghe, V., Volleth, M. & Wendelen, W. 2010. African Chiroptera Report. African Chiroptera Project, Pretoria.

Hill, J. E. 1971. The status of Vespertilio brachypterus Temminck, 1840 (Chiroptera: Vespertilionidae). Zoologische Mededelingen 45, 139-146.

- . 1976. Bats referred to Hesperoptenus Peters, 1869 (Chiroptera: Vespertilionidae) with the description of a new subgenus. Bulletin of the British Museum (Natural History), Zoology, London 30, 1-28.

Ingle, N. R. & Heaney, L. R. 1992. A key to the bats of the Philippine Islands. Fieldiana Zoology, New Series 69, 1-44.

Kingdon, J. 1997. The Kingdon Field Guide to African Mammals. Academic Press, San Diego.

Koopman, K. F. 1983. A significant range extension for Philetor (Chiroptera, Vespertilionidae) with remarks on geographical variation. Journal of Mammalogy 64, 525-526.

Norberg, U., & Rayner, J. (1987). Ecological Morphology and Flight in Bats (Mammalia; Chiroptera): Wing Adaptations, Flight Performance, Foraging Strategy and Echolocation Philosophical Transactions of the Royal Society B: Biological Sciences, 316 (1179), 335-427 DOI: 10.1098/rstb.1987.0030

Nowak, R. M. 1999. Walker's Mammals of the World, Sixth Edition. The Johns Hopkins University Press, Baltimore and London.

Roehrs, Z. P., Lack, J. B. & Van Den Bussche, R. A. 2010. Tribal phylogenetic relationships within Vespertilioninae (Chiroptera: Vespertilionidae) based on mitochondrial and nuclear sequence data. Journal of Mammalogy 91, 1073-1092.

Rossina, V. V., Kruskop, S. V., Tesakov, A. S. & Titov, V. V. 2006. The first record of Late Miocene bat from European Russia. Acta Zoologica Cracoviensia 49A (1-2), 125-133.

Thewissen, J. G. M. & Etnier, S. A. 1995. Adhesive devices on the thumb of vespertilionid bats (Chiroptera). Journal of Mammalogy 76, 925-936.

Volleth, M. & Heller, K.-G. 1984. Phylogenetic relationships of vespertilionid genera (Mammalia: Chiroptera). Journal of Zoological Systematics and Evolutionary Research 32, 11-34.