Restoring the skull of the basal bat, Onychonycteris

Short one today,
more ‘show’ than ‘tell’ as one picture and a caption pretty much tell the tale.

Figure 1. Onychonycteris is known from an articulated but crushed bottom half of the skull. Uncrushing it and giving it a suitable top half (Myzopoda) provides a restoration with some possibility of resemblance to theo original.

Figure 1. Onychonycteris is known from an articulated but crushed bottom half of the skull. Uncrushing it and giving it a suitable top half (Myzopoda) provides a restoration with some possibility of resemblance to theo original. Images from Simmons et al. 2010. The skull could have been less crushed than imagined here, so may have been proportionately shorter. The hole in the braincase of Myzopoda (above) may be a surgical opening to remove brain tissue. If natural, I do not know what it is.

And a cladogram
for phylogenetic context (Fig. 2).

Figure 1. Subset of the LRT focusing on the resurrected clade Volitantia, including dermopterans, pangolins, bats and their extinct kin.

Figure 2. Subset of the LRT focusing on the resurrected clade Volitantia, including dermopterans, pangolins, bats and their extinct kin.

Onychonycteris finneyi (Simmons, Seymour, Habersetze and Gunnell 2008) Eocene (~52mya), ~27 cm in length, is the most primitive known bat. It retained unguals (claws) on all five digits, a primitive trait not shared with other bats. Derived from a sister to ChriacusOnychonycteris phylogenetically preceded IcaronycterisMyotis and Pteropus in the LRT (subset Fig. 2).

Figure 2. Chriacus and Onychonycteris nest as a sister to the undiscovered bat ancestor and a basal bat. Miniaturization was part of the transition. So was enlargement of the manus. It is still a mystery why the transitional form decided to start flapping.

Figure 3. Chriacus and Onychonycteris nest as a sister to the undiscovered bat ancestor and a basal bat. Miniaturization was part of the transition. So was enlargement of the manus. It is still a mystery why the transitional form decided to start flapping.

Onychonycteris is smaller than Chriacus,
but the preserved portions of the skull and teeth are similar in proportion and morphology (Fig. 3). So… perhaps the proportions of the missing portion of the Chriacus skull are similar (fig. 1). More fossils will tell.

Veselka et al. 2010
concluded that O. finneyi may have been capable of echolocation.

By contrast, Simmons et al. 2010
argued that O. finneyi was probably not an echolocating bat.


References
Simmon NB, Seymour KL, Habersetzer J, Gunnell GF 2008. Primitive Early Eocene bat from Wyoming and the evolution of flight and echolocation. Nature 451 (7180): 818–21. doi:10.1038/nature06549. PMID 18270539.
Simmons NB, Seymour KL, Habersetzer J and Gunnell GF 2010. Inferring echolation in ancient bats. Nature 466: E8.
Veselka et al. (8 co-authors) 2010. A bony connection signals larygenal echolocation in bats.Nature 463: 939–942.

wiki/Onychonycteris

Two primitive extant bats enter the LRT

Yesterday we looked at the smallest of the fruit bats (mega bats). Earlier we looked at several micro bats.

Here, at nearly the same size,
Notopteris (Figs. 1, 2( nests in the large reptile tree (LRT, 1671+ taxa, subset Fig. 5) as the most primitive extant megabat due to its long tail and a few other primitive traits.

Figure 1. Notopteris in vivo. Note the microbat proportions and relatively long tail. The wing membrane begins along a dorsal margin, not laterally as in other bats.

Figure 1. Notopteris in vivo. Note the microbat proportions and relatively long tail. The wing membrane begins along a dorsal margin, not laterally as in other bats.

Notopteris macdonaldi (Gray 1859) is the long-tailed fruit bat or Fijian blossom bat. This is the most primitive megabat in the LRT and the only one that retains a long tail. It roosts in large cave colonies only on South Pacific islands. Note the mid-dorsal attachment of the proximal wing membranes, rather than a more lateral attachment. This is a derived trait not shared with other bats.

Figure 2. Notopteris skull and mandible.

Figure 2. Notopteris skull and mandible. Note the primitive skull and derived simple cusp teeth.

The most primitive extant microbat
in the LRT (Figs. 3, 4) is the newly added Rhinopoma, the lesser mouse-tailed bat (Fig. 3). It is similar, to Notopteris (Figs. 1, 2), but with a shorter rostrum and retains primitive multiple cusps on its teeth. Both are cave dwellers.

Figure 3. Rhinopoma is the most primitive extant micro bat in the LRT. Note the long tail, long legs and small feet, all Chriacus-like and Onychonycteris-like primitive traits.

Figure 3. Rhinopoma is the most primitive extant micro bat in the LRT. Note the long tail, long legs and small feet, all Chriacus-like and Onychonycteris-like primitive traits. Note the lateral insertion of the wing membrane on the torso, distinct from Notopteris (Fig. 1).

Rhinopoma hardwickei (Gray 1831) is the extant lesser mouse-tailed bat, an insectivore found from North Africa to India. The tail is 3/4 free and no calcar is present on the heel. The legs are long and the feet are small.

Figure 4. Rhinopoma skull from Digimorph.org and used with permission.

Figure 4. Rhinopoma skull from Digimorph.org and used with permission. Note the prominent ear bones (yellow) in this echolocating microbat.

Simmons et al. 1984 looked at echolocation in Rhinopoma.
They concluded, “Except for duration these signals are relatively inflexible and suggestive of a primitive kind of echolocation in which only one dimension is changed to achieve qualities which most other species of bats obtain by changing a variety of signal dimensions simultaneously.”

Nelson and Hamilton Smith 1982 looked at echolocation in Notopteris.
They concluded, “Some field experiments… showed these flying foxes were unable to avoid obstacles in complete darkness or when blindfolded, but were able to do so in very dim light. No audible or ultrasonic sounds that could be used in echolocation were detected during their flight.”

Holland et al. 2004 looked at echolocation in the megabat Rousettus.
They reported, “Rousettus aegyptiacus Geoffroy 1810 is a member of the only genus of Megachiropteran bats to use vocal echolocation, but the structure of its brief, click-like signal is poorly described.Rousettus aegyptiacus Geoffroy 1810 is a member of the only genus of Megachiropteran bats to use vocal echolocation, but the structure of its brief, click-like signal is poorly described. However, the low energy content of the signals and short duration should make returning echoes difficult to detect. The performance of R. aegyptiacus in obstacle avoidance experiments using echolocation therefore remains something of a conundrum.”

Simmons and Geisler 1998 looked at echolocation in Icaronycteris.
They reported, “We propose that flight evolved before echolocation, and that the first bats used vision for orientation in their arboreal/aerial environment. The evolution of flight was followed by the origin of low-duty-cycle laryngeal echolocation in early members of the microchiropteran lineage. This system was most likely simple at first, permitting orientation and obstacle detection but not detection or tracking of airborne prey.”

Veselka et al. 2010 concluded that Onychonycteris finneyi may have been capable of echolocation. in reply, Simmons et al. 2010 argued that Onychonycteris finneyi was probably not an echolocating bat.

Echolocation seems to have been convergently acquired
in microbats and Rousettus.

Figure 1. Subset of the LRT focusing on the resurrected clade Volitantia, including dermopterans, pangolins, bats and their extinct kin.

Figure 5. Subset of the LRT focusing on the resurrected clade Volitantia, including dermopterans, pangolins, bats and their extinct kin.

Basal bats in the LRT have more plesiomorphic traits overall,
like small ears, simple nose, long legs, long tail and small feet, all Chriacus-like (Fig. 6) traits. This is what we should expect when any cladogram models micro-evolutionary changes.

Figure 2. Chriacus and Onychonycteris nest as a sister to the undiscovered bat ancestor and a basal bat. Miniaturization was part of the transition. So was enlargement of the manus. It is still a mystery why the transitional form decided to start flapping.

Figure 6. Chriacus and Onychonycteris nest as a sister to the undiscovered bat ancestor and a basal bat. Miniaturization was part of the transition. So was enlargement of the manus. It is still a mystery why the transitional form decided to start flapping.

We looked at the origin of bats from Chriacus-like ancestors
earlier here, here and at earlier links therein. These posts are –by far– the most popular posts at this PterosaurHeresies.

To summarize one of those posts
hanging pre-bats simply listened for the sounds of prey in leaf litter below, then pounced from above. Parachuting with flapping evolved into helicoptering then that evolved into flight to return to the branch the bat fell from. Larger hands and extradermal membranes would have increasingly aided entrapment at the moment of impact. Even larger hands and extradermal membranes would have increasingly helped helicoptering while falling. Smaller size and weight (Fig. 6) was co-opted to aid these behaviors. Echolocation seems to have evolved in bats seeking aerial prey and co-opted to live in caves in complete darkness.


References
Gray JE 1831. Description of some new genera and species of bats. The Zoological Miscellany, 1: 37-38.
Gray GR 1859.
 The annals and magazine of Natural History, Zoology, Botany and Geology 3. Series IV: 4859.
Holland RA, Waters DA and Rayner JMV 2004. Echolocation signal structure in the megachiropteran bat Rousettus aegyptiacus Geoffroy 1810. Journal of Experimental Biology 207:4361–4369.
Nelson JE and Hamilton-Smith E 1982. Some observations on Notopteris macdonaldi (Chiroptera: Pteropodidae) in Australian Mammal Society 5: 247–252.
Simmons JA, Kick SA and Lawrence BD 1984. Echolocation and hearing in the mouse-tailed bat, Rhinopoma hardwickei: acoustic evolution of echolocation in bats. Journal of Comparative Physiology A 154: 347–356.
Simmons NB and Geisler JH 1998. Phylogenetic relationships of Icaronycteris, Archaeonycteris, Hassianycteris, and Palaeochiropteryx to extant bat lineages, with comments on the evolution of echolocation. Bulletin of the American Museum of Natural History 235.
Simmons NB, Seymour KL, Habersetzer J and Gunnell GF 2010. Inferring echolation in ancient bats. Nature 466: E8.
Veselka et al. (8 co-authors) 2010. A bony connection signals larygenal echolocation in bats.Nature 463: 939–942.

wiki/Notopteris

wiki/Rhinopoma

How bat feet turn laterally, then upside-down

Bats are inverted bipeds.
They hang by branches and cave walls by their feet. While inverted, bat forelimbs are folded away until needed for flight. The hind limbs frame membranes linking the laterally oriented legs to the medial tail. We looked at the origin of bats from non-volant ancestors earlier here, here and at several earlier links therein (also see Fig. 3).

Figure 1. Hind limbs and closeup of ankle of Cynopterus, an extant micro bat, from Digimorph.org. Colors and diagram elements added here.

Figure 1. Hind limbs and closeup of ankle of Cynopterus, an extant micro bat, from Digimorph.org. Colors and diagram elements added here. Unlike most mammals, the knees are often above the hips in bats.

Bat experts know this, but it  comes as news to me.
A closer examination of bat hindquarters (Fig. 1) reveals two axial twists that add up to a ~180º rotated hind limb for the micro bat Cynopterus. The ankle is capable of additional rotation.

  1. The acetabulum axially rotates ~90º from ventrolateral to dorsolateral.
  2. The femur axially rotates so the distal end is ~90º rotated from the proximal head (Fig. 2).
  3. The tarsal centralia also rotate upon the tibiale (Fig. 1).
Figure 2. Bat femur animated to show untwisted typical mammal orientation of femoral head.

Figure 2. Two views of a bat femur animated to show typical untwisted orientation of femoral head as found in most mammals.

Axial torsion in proximal bones ultimately produces a pes
that is dorsal side up in flight in derived extant bats. Based on these twists, bat knees appear to bend backwards compared to other mammals.

Figure 3. The basal bat, Onychonycteris.

Figure 3. The basal bat, Onychonycteris. The feet are smaller and the hind limbs are more gracile primitively, like those of the bat precursor, Chriacus in figure 3.

In the transitional basal bat
Onychonycteris, the hind limb appears to be laterally oriented with long gracile hind limbs and the dorsal side of the tiny pes likewise oriented laterally. If you think such tiny feet seem less capable of inverted clinging compared to the relatively big feet of Cynopterus (Fig. 1), you’re being observant. But long legs and small feet are primitive for bats. So is inverted bipedal hanging. What you’re seeing is a transitional phase.

Figure 1. Hypothetical bat ancestors arising from a sister to Chriacus, which may be a large late survivor of a smaller common ancestor.

Figure 4. Hypothetical bat ancestors arising from a sister to Chriacus, which may be a large late survivor of a smaller common ancestor. Imagine stem bat 3 and Onychonycteris pinching the branch they hang from with long legs acting like pliers, an idea that did not occur to me years ago when this was illustrated.

Rather than clinging to the same side of the twig (or cave wall)
the long legs and small feet of Onychonycteris acted more like tongs or pliers, pinching both sides of a branch medially between them. We also see this in primitive micro bats, like long-tailed Rhinopoma and primitive megabats, like Balionycteris (Fig. 5).

Figure 5. Balionycteris hanging from both sides of a slender branch by laterally-twisted feet.

Figure 5. Balionycteris, the smallest megabat, hanging from both sides of a slender branch by laterally-twisted small feet.

Is there any new process on the bat pelvis that facilitates such adduction?
Yes. The pubis often develops a bump or rod, a prepubic process, analogous to the prepubis in pterosaurs. This process anchors muscles of femoral adduction.

Colugos and pangolins
also hang inverted from branches like that, with feet on both sides of a supporting branch.

The outgroup to bats in the LRT,
Chriacus, (Fig. 4) does not preserve evidence of long bone axial torsion (the mid-portion of the femur is not preserved). The acetabulum does not open dorsally.

Hanging upside-down
is something nearly all small arboreal mammals (e.g. squirrels, tree shrews, monkeys, tree opossums) can do facilitated by a flexible ankle that ensures the claws attach to the bark at any angle. Only bats and their immediate ancestors had such a firm toe grip while inverted they no longer needed their hands to grip. That freed the forelimbs to evolve into infant nurseries and parachute-like wings, not quite like those of birds and pterosaurs (Fig. 5), which were bipedal the conventional way: right side-up.

Figure 6. Click to enlarge. The origin of the pterosaur wing and the migration of the pteroid and preaxial carpal. A. Sphenodon. B. Huehuecuetzpalli. C. Cosesaurus. D. Sharovipteryx. E. Longisquama. F-H. Bergamodactylus.

The axial rotation of long limb bones is rare in tetrapods,
but it also can be seen in metacarpal 4 of Sharovipteryx, Longisquama and basal pterosaurs like Late Triassic Bergamodactylus (Fig. 6). That twist facilitates wing (finger 4) folding in the lateral plane of the wing (Peters 2002) rather than against the palm as in other tetrapods, including bats. Apparently the storage of long wings was just as important as the evolution of the long wings themselves in all volant tetrapods.


References
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. – Historical Biology 15: 277–301.
Simmon NB, Seymour KL, Habersetzer J, Gunnell GF 2008. Primitive Early Eocene bat from Wyoming and the evolution of flight and echolocation. Nature 451 (7180): 818–21. doi:10.1038/nature06549. PMID 18270539.

wiki/Onychonycteris

 

Mystacina: a walking, climbing, scraping micro-bat

The little New Zealand bat, Mystacina
(Figs. 1, 2), provides a living example for the earlier drop and hover hypothesis for the origin of bat flight. Most bats hang by their feet and observe what is below when they are not flying. This one, not so much.

Figure 1. The false vampire bat hovering before attacking a mouse in dry fallen leaves, listening to locate is prey.

Figure 4. The false vampire bat hovering before attacking a mouse in dry fallen leaves, listening to locate is prey. Flapping is key. Pre-bats were not gliders. Prebats flapped their parachute-like forelimbs.

Distinct from other bats,
Mystacina spends about thirty percent of its time on the ground on all fours (see YouTube video link below), wings folded, digit 2, the ventral one, reduced to a bumper.

Figure 1. Skeleton of Mystacina tuberculata from Digimorph.org and used with permission. The large head size is a derived trait.

Figure 2. Skeleton of Mystacina tuberculata from Digimorph.org and used with permission. The large head size is a derived trait. Note the two large incisors, used for scraping away burrows in soft hollow trees, co-copted by vampire bats to scrape away cattle skin.

The sharp incisor teeth
are used to scrape away soft tree interiors to create arboreal burrows. This trait is co-opted by related and sometimes terrestrial vampire bats to scrape away cattle skin to start  bleeding.

Figure 2. Mystacina skull from Digimorph.org and colorized here.

Figure 3 Mystacina skull from Digimorph.org and colorized here.

The propatagium is small
to aid in terrestrial locomotion. Mystacina has a large brain. A YouTube video (click to view) shows Mystacina in action.

Based on its performance,
and location, I wondered if Mystacina would be one of the most primitive of bats. It is not. So it may have reverted to a more primitive way of getting along (walking on all fours) after earlier achieving inverted bipedality and flight. Perhaps isolation on New Zealand as the only endemic mammal permitted this to happen.

Can you think of another set of animals
that reverted to quadrupedal locomotion after achieving flight? (Answer below).

FIgure 3. Subset of the LRT focusing on bats and kin including Mystacina.

FIgure 4. Subset of the LRT focusing on bats and kin including Mystacina. No, Mystacina does not nest at the base of all bats. Manis is the extant pangolin. Cynocephalus is the extant colugo or flying lemur.

Mystacina tuberculata (Gray 1843; 6-7cm snout-vent length) is the extant New Zealand lesser short-tailed bat. The tail extends beyong the uropatagia. It sometimes feeds on nectar with a long hairy tongue, but is considered omnivorous because it eats beetles and larvae. Today’s post was inspired by the discovery of a fossil relative from the Miocene of New Zealand, Vulcanops jennyworthyae.

Be wary of NatGeo.com stories
with headlines about burrowing bats. Mystacina bats burrow their way into the cores of rotting trees using their scraping incisors, a point missed by the author of the story from 2018, but cited by her in another online story here. Bats did not create small caves in the ground. At best they disturbed or ran into dense leaf litter to locate their prey.

Earlier we looked at the origin of large wings/hands
as holders of fruit hanging from trees (Fig. 5), either for the fruit itself or for the insects boring through it. This allows fruit bats and micro bats to have a phylogenetic common ancestor (Fig. 4 in clawed bats like Icaronycteris and Onychonycteris.

Figure 1. Pteropus and Caluromys compared in vivo and three views of their skulls. Caluromys is in the ancestry of bats and shows where they inherited their inverted posture.

Figure 5. Pteropus and Caluromys compared in vivo and three views of their skulls. Caluromys is in the ancestry of bats and shows where they inherited their inverted posture.

Hanging upside down is something
many, if not all basal placentals did and do (Fig. 5). Those who don’t, like humans, horses and elephants, are derived. In contrast, bats rely only on their feet to hang upside down. The tail is no longer involved and disappears in some taxa.

Figure 1. GIF animation thought experiment on the origin and evolution of bats from a Ptilocercus-like omnivore.

Figure 6. GIF animation thought experiment on the origin and evolution of bats from a Ptilocercus-like omnivore. A change is warranted in this illustration. Abdominal membranes were probably present in pre-bats, extending from the torso to the fingers. These created a flapping steerable  parachute for bat decent to the leaf litter forest floor.

If you’re still wondering about
the other animals that reverted to a quadrupedal configuration after learning how to fly, think of the pterodactyloid-grade pterosaurs, which did so four times by convergence (Figs. 7, 8) according to the large pterosaur tree (LPT). Based on the extreme small size of hatchlings due to phylogenetic miniaturization at the genesis of these clades, these baby pterosaurs were probably relegated to clambering through dense, moist leaf litter until reaching a size that enabled flight without rapid desiccation due to a high surface-to-volume ratio.

Figure 8. Click to enlarge. The descendants of Sordes in the Dorygnathus clade and their two clades of pterodactyloid-grade descendants.

Figure 7. Click to enlarge. The descendants of Sordes in the Dorygnathus clade and their two clades of pterodactyloid-grade descendants.

I have to say,
putting together these cladograms of vertebrates, pterosaurs and therapsids has taught me more about the theory of evolution and the way things work than dissecting a frog ever did in high school, or picking matrix off a fossil later on. Comparative anatomy gives one an appreciation and understanding of micro-evolution, not only what happened, but often why it happened over a wide range of taxa, some of which have never been compared to one another before.

The base of the Scaphognathia

Figure 8. Click to enlarge. The base of the Scaphognathia illustrating the size reduction that preceded the size increase in the transition from Scaphognathus to several later, larger “pterodactyloid”-grade clades.

By contrast,
the focus of paleontology textbooks seems to be showing chapter after chapter of skeletons, too often without making such distant comparisons with a freedom not often enough permitted in academia.


References
Gray JE 1843. List of the Specimens of Mammalia in the Collection of the British Museum, George Woodfall and Son, London.

wiki/Mystacina
wiki/Vulcanops

New PBS Eons video on “When Bats Took Flight”

Well, they got the ‘when” kind of right.
Unfortunately, the PBS team had no idea how, who, or why bats took flight.

The following is my summary comment
buried deeper on the PBS YouTube page with each passing hour and day:

“With phylogenetic analysis based on traits we know the ancestors of bats back to jawless fish. Currently Zhangheotherium, a basal pangolin, and Chriacus are proximal outgroups to bats. (see link below). DNA fails too often in deep time experiments (e.g. Laurasiatheria: camels, whales, etc.)

“The best way to understand the genesis of bat flght is to compare it to the colugo, which leaps from its perch and glides for distance using membranes stretched between long limbs. These membranes were coopted from an extended marsupium, a place to keep newborns safe in these very basal placentals not far from their marsupial ancestors. Colugos, like many primitive placentals, also hang upside down, but with four very long limbs and small fingers.

“By contrast bats are inverted bipeds with membranes stretched between elongate fingers and short hind limbs. They don’t fly like birds and pterosaurs do. Instead they push pulses of air down with their huge parachute-like wings and huge pectoral muscles. When pre-bats hung inverted from low branches, they were able to survey the leaf litter below, ready to pounce on insects and worms rustling in the leaves on the ground. The distance could have started at 10cm, then extended to a meter, then 10 meters. So that is where hyper-acute hearing first developed.

“Instead of leaping from tree to tree, pre-bats dropped straight down onto their prey. To slow their fall, they flapped their large parachute-type hands. These became larger over time. Embryo bats with big hands recapitulate the evolution of bats. Leaf litter provided a soft landing for the tiny parachuting pre-bats, but over time flapping before crashing slowly turned into hovering for accuracy inches above the leaf litter before pouncing. Some bats still do this today. Over still more time, improved hovering became flight.

“After flight, returning to their inverted roost was so much safer, due to no more tree trunk climbing.”

More details, images and links here: https://pterosaurheresies.wordpress.com/2018/06/18/the-origin-and-evolution-of-bats-part-4-distance-vs-accuracy/

The origin of bats is by far the most popular topic
here at PterosaurHeresies. Use keyword [bats] in the box above to find out more.

The Mexican free-tailed bat (genus: Tadarida) enters the LRT

Figure 1. Tadarida, the Mexican free-tailed bat, from Digimorph.org and used with permission. Colors added.

Figure 1. Tadarida, the Mexican free-tailed bat, from Digimorph.org and used with permission. Colors added.

I became interested in this genus
because basal bats and their outgroups have a free tail (distal end not attached to uropatagia). But nothing special came of it. Tadarida nests with Myotis in the large reptile tree (LRT, 1413 taxa)

As you can see
(Fig. 1) Tadarida has giant ears (but not the largest among bats) and the soft rostrum extends far beyond the hard rostrum of this micro-bat.

Tadarida brasiliensis (genus: Rafinesque 1814) is the extant Mexican free-tailed bat. Members of this polyphyletic genus extend to all continents except Antarctica. Tadarida hawks for insects on the fly using its enormous ears to hear sonar reflections bouncing off prey and environment.


I should have mentioned the origin of bats
was featured here, here, here and here.


References
Rafinesque-Schmaltz CS 1814. Précis des décuvertes et travaux somiologiques de m.r CS Rafinesque-Schmaltz entre 1800 et 1814 ou Choix raisonné des ses principales décourvertes en zoologie et en botanique, pour servir d’introduction á ses ouvrages futures. Royale Typographie Militaire, Palermo, Italy.

Image from Digimorph.org and used with permission.

New ground effect study supports origin of bat flight hypothesis proposed here

A new paper by Johansson, Jakobsen and Hendenstram 2018
introduces the benefit of ground effect (the surface acts as an aerodynamic mirror, interrupting the downwash, resulting in increased pressure underneath the wing and suppression of wingtip vortex development) in the origin of bat flight.

This is something every student pilot learns.
Ground effect is basic aerodynamics whether applied to bats, airplanes or flying fish.

Figure 1. The false vampire bat hovering before attacking a mouse in dry fallen leaves, listening to locate is prey.

Figure 1. The false vampire bat hovering before attacking a mouse in dry fallen leaves, listening to locate is prey.

Even so, it is measured here for bats for the first time.
You might remember, an earlier hypothesis first published here proposed an origin of bat flight associated with dropping out of trees while frantically flapping to break the fall in order to attack insects heard in the leaf litter (Fig. 1). The benefit of such unprofessional flapping increases as the ground gets closer and closer. In bats this frantic flapping while parachuting evolved to hovering before ground contact (with the help of ground effect). And this evolved to powered flight in bat-fashion, distinct from bird and pterosaur flight origins.

Highlights of the Johansson, Jakobsen and Hendenstram 2018 paper:

  1. Aerodynamic power is 29% lower when bats fly close to rather than far from ground
  2. Measured savings are twice the savings expected from models
  3. Wing motion is varied with distance to ground, which may modulate ground effect
  4. The results challenge our understanding of how animals use ground effect

References:
Johansson LC, Jakobsen L and Hendenstram A 2018. Flight in ground effect dramatically reduces aerodynamic costs in bats. Current Biology. DOI: https://doi.org/10.1016/j.cub.2018.09.011
https://www.cell.com/current-biology/fulltext/S0960-9822(18)31206-5

Not that closely related to bats…

…even so, the resemblance
clearly shows what pre-bats were like (Fig. 1), and not by convergence. Caluromys (right) is the last of the marsupials, transitional to basal placentals. Bats, like Pteropus (left), are not too far from basal placentals.

Figure 1. Pteropus and Caluromys compared in vivo and three views of their skulls. Caluromys is in the ancestry of bats and shows where they inherited their inverted posture.

Figure 1. Pteropus and Caluromys compared in vivo and three views of their skulls. Note the hourglass-shaped nasals, similar frontals, similar overall silhouettes and similar palates. Juvenile Caluromys has only two molars, the same number found in all members of the Carnivora and by convergence Pteropus. Other basal placentals retain 4 or 4 molars.

Caluromys is in the ancestry of bats
in the large reptile tree (LRT, 1272 taxa). Caluromys shows where bats inherited their signature inverted posture, even though that genus is several nodes away from Pteropus.

Since Caluromys is basal to all other placentals,
maybe bats aren’t the odd ones after all, for hanging inverted. It’s the primitive way to go.  All the other placentals that stopped hanging inverted are the derived ones.

We looked at the origin of bats
here and in earlier posts linked therein.

YouTube video supports newest bat origin hypothesis

Figure 1. The false vampire bat hovering before attacking a mouse in dry fallen leaves, listening to locate is prey.

Figure 1. The false vampire bat hovering before attacking a mouse in dry fallen leaves, listening to locate is prey in accord with a hypothesis of bat origins first presented here. The first pre-bats were not as adept at falling on prey, but refinements followed.

Earlier we looked at a new hypothesis for bat origins
that separated the distance gliding origins of small-hand colugos from the accurate falling, flapping origin of big-hand bats. Today readers get to see a video (below, Figs. 1, 2) showing that ancient and original behavior – still retained by the carnivorous wooly false vampire bat (genus: Chrotopterus). This may not be the most primitive extant bat, but this video demonstrates the predatory behavior that led to the origin of bats:

  1. inverted hanging >
  2. falling on prey while flapping to brake its descent >
  3. covering the prey item with ankle-to-hand membranes >
  4. capturing the prey item with its mouth >
  5. leaving the scene of the attack with prey in tow to feed later.
Figure 2. Scenes from the video showing the stages in the bat attack on the mouse in the leaf litter.

Figure 2. Scenes from the video showing the stages in the bat attack on the mouse in the leaf litter. Note how the former nursery membrane, now a flight membrane, covers the prey, preventing its escape.

Click the video to view it.

Before bats had sonar
bats relied on rustling sounds in the leaf litter to find their rodent and insect prey. Gradually refining this ability is what led to sonar in micro bats.

Before bats could fly
inverted pre-bats fell from tree limbs, flapping their small hands to slow their inevitable descent. Gradually refining this ability, while gradually enlarging those big membraned bat hands is what led to slowing the decent, hovering prior to the attack and ultimately flying and chasing flying insect prey.

This bat origin hypothesis
solves the problem of bat flapping without display (as in theropods and fenestrasaurs) and without WAIR (wing-assisted inclined running, as in theropods and fenestrasaurs). Remember bats have very weak and rotated backwards hind feet. Bipeds they were, but inverted and non-cursorial, distinct from pterosaurs and birds.

Remember
colugos, bats and basal pangolins, like Zhangheotherium, were members of the clade Volitantia. This placental clade is close to metatherian stem placentals, like Monodelphis, that have ventrally open pouches. These pouches were originally to protect nursing underdeveloped newborns, then expanded to form nursery membranes, then further expanded and co-opted for gliding in colugos and flying in bats.

How wonderful
that some bats retain their original and ancient method of hunting, as shown in the video. So many times in paleo, the answer has been staring at us, out in the open, waiting for recognition. On that note, I have sent emails to several leading bat experts, referring them to the earlier blogpost on bat origins, asking for their feedback. None, so far, have responded.

References
photographer: Anand Varma

wiki/Chrotopterus

What would bats be, if Chriacus was not known?

This is a lesson in taxon exclusion…
to see where select clades would nest in the absence of their proximal taxa. This might find highly convergent clades or taxa.

Bat origins
have befuddled traditional paleontology. In the large reptile tree (LRT, 1241 taxa) bats arise from a sister to Chriacus, an arboreal mammal, nesting with dermopterans and pangolins. We looked at bat origins most recently here and at earlier posts in that series.

Figure 1. Subset of the LRT focusing on basal placentals, including bats.

Figure 1. Subset of the LRT focusing on basal placentals, including bats.

With a large gamut cladogram
we can cherry-delete taxa to see where bats would nest, if not with Chriacus.

  1. Chriacus deleted: no change, bats still nest with pangolins and colugos.
  2. Dermopterans and pangolins deleted: bats nest with with lemurs, with loss of resolution leading to 5 MPTs. This follows the ‘flying primate‘ hypothesis (Pettigrew 1986, Pettigrew  et al. 1989) for bat origins — but that only works with taxon exclusion, so it is invalid.
Figure 3. Subset of the LRT focusing on basal placentals, including bats.

Figure 3. Subset of the LRT focusing on basal placentals, including bats.

Let’s delete mega-bats and then delete micro-bats.

  1. Pteropus deleted: no change, microbats still nest with pangolins and colugos.
  2. Microbats deleted, Pteropus/Rousettus restored: Pteropus/Rousettus nests between colugos and Chriacus + pangolins.

Taxon exclusion
has been the number one problem in traditional paleontology. That’s why the LRT includes such a wide gamut of taxa. The result is a minimizing of taxon exclusion and the problems that attend it.

We’ll look at other former enigmas in future blog posts
and run deletion tests on their proximal outgroups as well.

References
Pettigrew JD 1986. Flying primates? Megabats have the advanced pathway from eye to midbrain. Science. 231(4743): 1304–1346.
Pettigrew JD, Jamieson BG, Robson SK, Hall LS, McAnally KI, Cooper HM 1989. Phylogenetic relations between microbats, megabats and primates (Mammalia: Chiroptera and Primates). Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences. 325 (1229): 489–559.