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

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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.

Resurrecting the clade ‘Volitantia’ Illiger 1811.

Volitantia
was defined by Illiger 1811 as Chiroptera (bats) + Dermoptera (colugos). Wikipedia authors consider this clade obsolete and polphyletic. The large reptile tree (LRT, 1233 taxa) nests these two taxa together in a monophyletic clade that also includes the pangolins and their closest ancestors (e.g. Zhangheotherium). We looked at their traditionally overlooked relationships a few days earlier here.

Szalay and Lucas 1996 reported, “We find support for the Volitantia in the nature of the shared derived similarities (and phyletically significant differences as well) in the elbow complex, and in Leche’s (1886) suggestion of the synapomorphus and unique presence (in non aquatic mammals) of an interdigital membrane of the hand in bats and colugos. They studied Chriacus and Mixodectes (not yet tested), not pangolins.

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

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

Like another clade traditionally considered obsolete,
Enaliosauria, that was resurrected by the LRT, Volitantia is likewise resurrected as a monophyletic clade, but it now includes the Pholidota (pangolins) according to LRT results.

Goodbye ‘Ferae’
The putative clade ‘Ferae‘ (pangolins + carnivorans) is not supported by the LRT because pangolins nest within the Volitantia.

As long-time readers know,
many traditional relationships between placental clades are not supported by the LRT, which continues to document a gradual accumulation of derived traits at every node in nearly full resolution for a wide gamut of tetrapod taxa.

Many arboreal mammals were experimenting with gliding
(e.g. Volaticotherium and  Maiopatagaium), but only one clade, bats, experimented with flapping. This was, perhaps not coincidentally, during the Middle to Late Jurassic (Oxordian, 160 mya). Remember, these membranes were all extensions of the infant nursery found in colugos and other volatantians, not far from the basalmost placental, Monodelphis. It is possible that all basalmost mammals had these membrane extensions and most of their ancestors lost them.

References
Illiger C 1811. Prodromus systematis mammalium et nivium additis terminis zoograhicis utriudque classis. Berlin: C. Salfeld.
Szalay F and Lucas SG 1996. The postcranial morphology of Paleocene Chriacus and Mixodectes and the phylogenetic  relationships of archontan mammals. Bulletin of the New Mexico Museum of Natural History and Science 7: 47 pp.

wiki/Volitantia

 

Much more interesting than pterosaurs: BATS!

Evidently,
(Fig. 1) interest in the origin and evolution of bats blog post (September 21, 2011) far exceeds that of any other subject here at PterosaurHeresies.Wordpress.com. Every day of every week this single page has several to ten times the views of any other page. Curious about the numbers, I finally looked up the viewing history of this blogpost:

Figure 1. WordPress stats for the evolution and origin of bats page here at PterosaurHeresies.

Figure 1. WordPress stats for the evolution and origin of bats page here at PterosaurHeresies. 2018 could exceed 2017 at this rate.

Bats origins are fascinating
and in need of more precise data and hypotheses. I hope the present data spurs further discovery in this small corner of the reptile family tree. Parts 2 and 3 of this subject were posted here and here.

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

Figure 2. Hypothetical bat ancestors arising from a sister to Chriacus, which may be a large late survivor of a smaller common ancestor.

Phylogenetic (trait-based) analysis
is a powerful tool that can answer our most baffling traditional enigmas. In many cases this tool is only a blunt instrument, but as more pertinent taxa are added, it becomes a finer and sharper needle and scalpel.

Figure 4. Ptilocercus, Icaronycteris and a hypothetical transitional taxon based on the ontogenetically immature wing of the embryo Myotis. If you're going to evolve wings it looks like you have to stop using them as hands early on. Note in the bat embryo there is little indication of inter-metacarpal muscle. That area looks identical to the web.

Figure 3. Ptilocercus, Icaronycteris and a hypothetical transitional taxon based on the ontogenetically immature wing of the embryo Myotis. If you’re going to evolve wings it looks like you have to stop using them as hands early on. Note in the bat embryo there is little indication of the fleshy inter-metacarpal muscles. That area looks identical to the web, even in the Myotis embryo.

No matter what you like to read about here at PH
thank you for your continued interest.

The origin of flight in bats: what we knew in 1992.

Famous for his whale studies,
JGM (Hans) Thewissen turned his attention to bats as a postdoctoral fellow in 1984. His co-author, SK Babcock, was a graduate student at the time.

Their introduction
includes their intention of reviewing then current controversies despite “extremely sparse” fossil evidence. They mentioned the hundreds of Eocene bat skeletons known from the Messel quarry near Darmstadt, Germany, but note that even late Paleocene bats were “nearly as specialized as their modern relatives.”  Their report preceded by several years the publication of Onychonycteris (Simmons, Seymour, Habersetze and Gunnell 2008), the most primitive bat known at present.

Two kinds of bats were noted, Megachiroptera and Microchiroptera.
“Megabats have a simple shoulder joint and a clawlike nail on thumb and index finger, whereas mi-crobats have a complicated shoulder joint and a claw only on the thumb.” Microbats use echolocation to eat insects with their sharp crested teeth. Megabats generally do not, but a few do. They are herbivores with blunt molars.

Earlier we looked at
the dual origins of turtles,  whales, seals and the four origins of the “pterodactyloid”-grade pterosaurs. Workers have wondered if mega bats and micro bats also had dual origins.  This was the main theme of the Thewissen and Babcock paper, penned before the widespread advent and adoption of computer-based phylogenetic analysis. Instead, everyone looked at a few to many traits and pulled a Larry Martin. Sometimes they were right. Othertimes, they were wrong to slightly wrong. Smith and Madkour 1980 first proposed a dual origin for bats by looking at the penis.

Thewissen and Bacock renege on their headline promise when they report,
“If the problem of bat origins is ever solved, it will be after a careful anal-ysis of all characterso f interesti n the bats and their potential relatives.” Of course this was shortly  before PAUP and MacClade came on the scene the same year.

Thewissen and Babcock report:
“Both microbats and megabats have a propatagial muscle complex, but it is surprisingly different in the two groups.” In mega bats this complex has four proximal origins,

  1. the back of the skull
  2. the side of the face
  3. the ventral side of the neck and
  4. the midline of the chest

compared to only two origins in micro bats (1 and 4). There is also variation within micro bats and within mega bats. As readers know, there is no way to understand this unless outgroups have one or the other pattern and they don’t (at present). Thewissen and Babcock report, “gliding flight has evolved six times in mammals.” But gliders don’t make good flyers. To fly one needs thrust provided by flapping. How and why bats started flapping has really been the key underlying, unanswered question, which we looked at earlier here and here.

Back in 1910
WK Gregory concluded after careful study that bats, flying lemurs, tree shrews, elephant shrews and primates were closely related and called that group (clade) Archonta. According to the large reptile tree (LRT, 1043 taxa) many of these taxa are indeed related. Elephant shrews are not, which Thewissen and Babcock later note. Elephant shrews are also the only ones from that list that are not arboreal climbers. Thewissen and Babcock add the clade Plesiadapiformes, which were thought to be rodent-like primates, but turn out to be primate-like rodents nesting close to multituberculates in the LRT.

Figure 1. Bat cladogram. Here pangolins are the nearest living relatives of bats.

Figure 1. Bat cladogram. Here pangolins are the nearest living relatives of bats.

Flying lemurs,
like Cynocephalus, also have a propatagium that originates from the side of the face and midline of the neck, but the nerves within them terminate in different places in bats. The LRT recovers flying lemurs close relatives to bats, but pangolins, like Manis, are closer.

Thewissen and Babcock conclude: 
“We believe that the evidence from the propatagial muscle complex of bats supports the idea that all bats share a single ancestor with wings. This idea is consistent with bats going through a flying lemur-like stage before acquiring active flight.”

Unfortunately
the LRT recovers a topology in which the last common ancestor of flying lemurs and bats was likely arboreal, but not a leaping glider. That means membranes developed in parallel (close convergence). Remember, gliders don’t become flappers. And flappers usually develop flapping for reasons other than flight, then co-opt flapping traits for flight.

The ancestors of bats and pangolins
have had a long time to diverge. Likely that was in the Late Jurassic because we have the pangolin ancestor, Zhangheotherium, appearing in the Early Cretaceous. That puts the last common ancestor of flying lemurs, pangolins and bats, Ptilocercus, back in the Middle Jurassic, several tens of millions of years after the likely first appearances of therian mammals, like the living and very late surviving Didelphis and Monodelphis sometime in the Early Jurassic. Earlier we looked at the origin of bats here, here and here.

Figure 2. Select basal cynodonts and mammals set chronologically. The divergence times for placentals (Eutheria), marsupials (Metatheria) and monotremes (Mammalia) are estimated here.

Figure 2. Select basal cynodonts and mammals set chronologically. The divergence times for placentals (Eutheria), marsupials (Metatheria) and monotremes (Mammalia) are estimated here.

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.
Smith, J. D., and G. Madkour. 1980. Penial morphology and the question of chiropteran phylogeny. Pages 347-365 in D. E. Wilson and A. L. Gardner, eds. Proceedings of the 5th International Bat ResearchC onference. Texas Tech Press, Lubbock.
Thewissen JGM and Babcock SK 1992. The origin of flight in bats. BioScience 42(5):340–345.

wiki/Onychonycteris

 

Better data on Protictis shifts it from bats to carnivores

Updated January 06, 2016 based on additional taxa.

This is what happens
when you get data more directly. In this case data that used to come from a freehand drawing (Fig. 1) now comes from a photo of Protictis (Cope 1883, Mac Intyre 1966; middle Paleocene; Fig. 1). As everyone knows, in Science, you have to be willing to let go of any pet hypotheses of relationships whenever better data recover different results. And this is how you do it: You just do it!

Figure 1. Protictis skull based not on a free hand drawing, but on this published photo.

Figure 1. Protictis skull based not on a free hand drawing, but on this published photo from Mac Intyre 1966. Note all difference with the original freehand drawing, also from Mac Intyre 1966. Preserved elements about 5 cm in length.

More than five years ago,
before ReptileEvolution.com was first created with about 260 taxa in the large reptile tree (now 915 taxa), Protictis was not included in that data matrix. Rather it nested in a separate ‘bat’ cladogram between Chriacus and bats based on data gleaned from the line art reconstruction in Mac Intyre 1966  Now Protictis joins the LRT with data based on a published photo (Fig. 1) in Mac Intyre 1966. Now it nests with Vulpavus, Deltatherium and the carnivore specimen of Ectocion. all within the Carnivora. That makes sense based on several traits, including the very large canine teeth.

That early Palaeocene date
along with the rather derived node occupied by Protictis anticipate (currently without much evidence) a wider radiation of the Carnivora during the Jurassic and Cretaceous than prior workers surmised. An early member of this clade, Vincelestes, is found in Early Cretaceous strata, yet even at that early date, already shows distinctly derived traits. Phylogenetic and chronological bracketing predict that mongoose- and civet-like carnivore taxa will be found in Jurassic and Cretaceous strata.

I’ll have to go back and update
any figures that have not yet been updated. Here (Fig. 2) is the latest on bat origins (now sans Protictis). And there’s more here. It’s the same topology, only without Protictis now.

Palaechthon has been added today
but it nests, as it did before, with the dermopteran, Cynocephalus.

Figure 2. Known bat ancestors to scale. Click to enlarge.

Figure 2. Known bat ancestors to scale. Click to enlarge. Protictis is no longer among them. It is likely that bat ancestors never got as large as Chriacus, but it is the only representative of that morphology, between Ptilocercus and bats.

And we can still use Ptilocercus as a pretty good model
for bat origins. It nests close to their ancestry without showing signs of great deviation.

Figure 4. Ptilocercus, Icaronycteris and a hypothetical transitional taxon based on the ontogenetically immature wing of the embryo Myotis. If you're going to evolve wings it looks like you have to stop using them as hands early on. Note in the bat embryo there is little indication of inter-metacarpal muscle. That area looks identical to the web.

Figure 3. Ptilocercus, Icaronycteris and a hypothetical transitional taxon based on the ontogenetically immature wing of the embryo Myotis. If you’re going to evolve wings it looks like you have to stop using them as hands early on. Note in the bat embryo there is little indication of inter-metacarpal muscle. That area looks identical to the web.

 

References
Cope ED 1882. Synopsis of the Vertebrata of the Puerco epoch. Proceedings of the American Philosophical Society 20:461-471.
Mac Intyre GT 1966. The Miacidae (Mammalia, Carnivora) Part 1. The systematics of Ictidopappus and Protictis. Bulletin of the American Museum of Natural History 131(2):115-210.

The origin and evolution of bats, part 4, an inverted thought experiment

There are no fossils
that currently document the origin of bats from non-volant carnivores or omnivores. Birds have a long fossil history. So do pterosaurs. For bats we have to conduct thought experiments in order to get from points we know: 1) a skilled arboreal omnivore like Ptilocercus, to 2) an Eocene fossil bat, like Icaronycteris (Fig. 1). It won’t help to have a Paleocene tooth, or skull. Those don’t change much in bat origins. We need to see, or visualize, the post-cranial body. Earlier forays into bat origins can be seen here, here and here.

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

Figure 1. GIF animation thought experiment on the origin and evolution of bats from an inverted Ptilocercus-like omnivore. Click to enlarge. Perhaps long fingers originally pulled maggots out of fruit and excellent hearing helped probate find where to dig.

We start with what we know

  1. All or most bats hang inverted
  2. The basal phylogenetic split is between Megachiroptera (fruit eaters) and Microchiroptera (insect eaters)
  3. Bat embryos probably recapitulate the development of those unknown phylogenetic predecessors, And they have big webbed hands early on.
  4. Bats don’t fly until their wings are nearly full size.
  5. What separates Ptilocercus from Icaronycteris is chiefly the size of the hands.
  6. There is no evidence that bats find their wings or wing size sexually attractive
  7. Caves are derived roosting spots. You have to fly in those to get a spot.
  8. Likewise, catching insects on the wing and echolocation follows the advent of flying, but listening to maggots munching fruit might have been a precursor skill.

The big question has always been
how do you get a flight stroke out of quadruped? Pterosaur and bird ancestors were both bipeds with strong hind limbs and they evolved wings as 1) gaudy secondary sexual traits; and 2) to aid in locomotion, especially up steep inclines (Heers et al. 2016 and references therein). The only way that bats were bipeds was inverted with weak hind limbs, which is a whole different story, or, in this case, a whole different thought experiment.

Figure 2. Pteropus, a fruit bat.

Figure 2. Pteropus, a fruit bat, has relatively shored clavicles and larger scapulae extending over most of the rib cage. The extremely long toes are derived. Parallel interphalangeal joints present on bat wings show the phalanges flex in sets.

Hypothetical stages in bat development

  1. Start with an agile arboreal omnivore like Ptilocercus, derived from long-legged arboreal carnivores in the Cretaceous/Paleocene, like Chriacus.
  2. Hanging fruit and the maggots therein can be attacked by likewise hanging on the supporting branch.
  3. The tiny hands of Ptilocercus could hold the fruit more steadily if the f fingers were longer. Maybe digging out maggots was aided by longer, thinner fingers.
  4. Webbing on even longer fingers would help trap juices, pieces, maggots from dropping out, and (see #6).
  5. At this stage the inverted biped no longer uses those hyper-elongate fingers for climging, so they are capable of being folded, not from the metatarsophalangeal joint, but at the wrist.
  6. In tropical forests bats use their wings as fans to cool themselves off (see video here), often after salivating on themselves for evaporative cooling. This is one of two pre-flight-stroke actions I have found.
  7. To rise from an inverted position on a branch, bats will flap vigorously (Fig. 3), which is the other pre-flight-stroke action.
  8. Mother bats wrap developing infants in their folded wings, but that doesn’t get them into the air.
  9. At a certain point, the pro-bat has wings that are capable of fanning the air, but incapable of flying. This is when the first branch-to-branch and tree-to-tree flapping leaps took place. If the pro-bat falls to the ground, it dies. Only successful arboreal flapping ‘acro-bats’ survive and improvements increase those odds.
Figure 1. Is this the origin of bat flapping. From an inverted position, this bat rises to horizontal by flapping, still clinging to its perch until release and flight. Click to open video.

Figure 3. Is this the origin of bat flapping. From an inverted position, this bat rises to horizontal by flapping, still clinging to its perch until release and flight. Click to open video.

In summary,
hanging pro-bats first developed long fingers to hold hanging fruit and perhaps remove maggots. Fanning for cooling could only develop with large webbed hands. Vigorous flapping from an inverted configuration is one solution to elevating the head and body. Letting go with the feet during this activity is the first awkward and potentially lethal stage to ultimately perfecting the flight stroke over many generations. The origin of flapping in bats is only a thought experiment at present with no other evidence currently available.

References
Heers AM, Baier DB, Jackson BE & Dial  KP 2016. Flapping before Flight: High Resolution, Three-Dimensional Skeletal Kinematics of Wings and Legs during Avian Development. PLoS ONE 11(4): e0153446. doi:10.1371/journal.pone.0153446
http: // journals.plos.org/plosone/article?id=10.1371/journal.pone.0153446