You're hiking in the beautiful desert highlands of western Mexico, walking ancient trails winding through hills and high valleys among a scenic mix of cacti and scattered pine trees on a broad Oaxacan plateau. The Sierra Madre Mountains form a distant, majestic background. You make camp under a glorious, velvet canopy of rising stars littering the crystal clear night sky like powdered sugar. It seems a magical paradise ... Until hours later, when your eyes snap open in mid dream and you awaken startled in the darkness. The campfire has burned out, your arm, exposed outside the sleeping bag, is numb with prickly cold. As the cobwebs clear from your mind, you sit up, only to be rewarded by a woozy sensation. You hear something or some things scuttle away softly in the darkness and get a whiff of a foul odor in the air ... The next day you can't seem to get your wind while hiking to the exotic Monte Alban ruins, and you notice a few, small, faint bruises on your hand and arm, each with a tiny scab in the middle. They itch. Absent-mindedly, you scratch your ear and find another bite on the lobe. Locals seeing your marks whisper something about
palo de la sangre among themselves, and keep their distance ...
The order of bats, Chiroptera, meaning hand-wing, is divided into two broad suborders: The Megachiroptera and Microchiroptera. More commonly known as fruit bats and insectivorous bats. Of all the mammals, only these creatures can truly fly. Sugar gliders, flying squirrels, and a few other tree dwellers can glide short distances. But bats take to the air like birds on fully functional powered wings, a membranous skin stretched over four elongated finger bones.
Perhaps no other mammal has been so unfairly maligned, so consistently castigated, and so routinely treated with fear and contempt, as bats. But among the mostly harmless order of Chiroptera, there is one Latin American denizen that fully deserves the unsavory reputation all bats are saddled with. This clade has adapted to a diet of a different kind of, shall we say, nector, and the most common species prefers mammals as its prey: The Vampire Bats.
Desmodus rotundus, the common vampire bat, is about the size of man's thumb with a wingspan of eight or nine inches. This goblin has heat sensors in that nasty nose to help detect prey
True to their mythological name, these guys stealthily crawl up to sleeping cows or people alike during the dead of night, sometimes by the dozen. They ghoulishly feed on livestock, wild animals, or us by first depositing a little topical anesthetic to deaden the skin before chewing a small hole in it. The bat then laps the blood up, consuming their own body weight in sweet claret, while releasing an anticoagulant in the saliva fittingly called Draculin, until they can hold no more. In order to take flight with all that added mass they must urinate generously on the spot. That urine is loaded up with plenty of homemade ketones and nitrogen rich ammonia: It stinks to high heaven. And, because these little bloodsuckers are exposed to all kinds of disease given their diet, they've evolved considerable resistance to most common blood-borne pathogens; which means they make ideal vectors for everything from rabies to malaria. Interestingly, unlike others of their kind, vampire bats can virtually gallop across the land, moving almost as fast as a large rat ... Tricksy, sneaksy, little batsss.
A hypothetical, terrestrial vampire bat of the future. How'd you like to have a pack of these guys on your tail?
Given the evolutionary chance, such an agile sanguinous creature might well discard flying like so many birds have, and become large flightless, terrestrial animals. How'd you like to come across a future population of bloodsuckers descended from vampire bats which have grown to the size of coyotes? Hanging in trees like pendulous black fruit by day, hunting for blood by night... Yikes! Now that's a Halloween nightmare I can relate to!
Because of recent fossil finds shedding light on the cetacean evolutionary tree, creationists have switched from using whales as an exemplar of Darwinian ignoratum, to using bats. If the goal is to confuse adoring fundie audiences while subconsciously playing on a repellent mythological sub-theme, bats are an excellent choice. The evolutionary origin of Chiroptera remains a topic of great interest and greater mystery. Adding to the confusion, there is reasonably good evidence, albeit controversial, that megabats and microbats developed flight independently of one another millions of years apart, but both from a recent common ancestral clade. Muddying that picture even further, it turns out that several species of what were previously called microbats actually descend from fruit bats.
As pets, bats are not for everyone. They require special care and knowledge. And most folks perceive them as a tad revolting, such as this hanging microbat on the left. But not all bats are superficially unappealing. Center: An Australian flying fox warily shields her newly weaned pup from the intrusive camera-man. While "Spencer", the photogenic megabat hamming it up on the right, gets along fine with his human owners; he was permanently injured as a youngster and saved from certain death by a kind researcher
At first glance, bats most resemble pro-simian primates such as lemurs. But genetic analysis places them closer to shrews, hedgehogs, and moles. Another close relative, the colugo from southeast Asia, is the only candidate cousin which has wing surfaces: Colugos in fact have the best developed proto-wings of any mammal outside of bats themselves. But the exact origin of bats is murky. The most likely ancestor being something like a tree-shrew (Both shrews and moles are also thought to use echolocation, although neither clade has developed it to the degree found in some microbats). The fossil record so far has been of little help in clearing up the early phylogeny: The oldest bat pops up in the fossil record about 50 million years ago, in the Eocene Epoch. And is in the words of creationists, "fully formed".
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The earliest confirmed bat in the fossil record. The Microchiropteran Icaronycteris at 50 MYA already shows specialization of the auditory region of the skull, suggesting this bat could echolocate
Why the lack of transitional forms? Well, if we looked at bat evo the same way we look at dino-to-bird evo we could legitimately say we have loads of transitional forms just in small placental mammals such as shrews, rodents, or primitive insectivores. Early Chiropterans and their inferred ancestors would be fragile creatures, lightly built, which likely lived in forests and jungles where lots of predators and scavengers picked the remains clean. And the acidic soil discouraged fossilization. Moreover, given that birds were widespread and one of the most successful vertebrates on earth during the period in question, bat ancestors probably only took to flight in a geographically limited area further restricting the potential fossil record. Lastly, it's almost impossible to distinguish a mere gliding critter like a flying squirrel from a run of the mill non-glider using only fossil scraps: Soft tissue such as skin folds rarely preserves.
A couple of key morphological features which separate bats from mere gliders, and from birds for that matter, is the extension of the wing past the wrist and the ability to control those flying surfaces with great precision. Bats are incredibly maneuverable, rivaling the agility of a humming bird with the swiftness of a small hawk. Both the fine control and the extra extension is a product of the bat hand, four long fingers, which frames that portion of the lifting surface. These fingers were plausibly already quite powerful and dexterous if bats descend from climbers. Now greatly elongated and serving as framework for the wing, they activate the equivalent of ailerons, flaps, and elevator.
And a recent genetic discovery indicates that bats may have evolved that specific wing anatomy relatively rapidly from a gliding/climbing mammal; relatively meaning over a few hundred thousand years or so as opposed to millions. A single gene which turns growth plates off and on in the finger bones is unusually plastic in bats. This would give the owners a huge degree of variability in the length of their finger bones. When applied to a creature with gliding membranes supported by outstretched limbs, that would be just the evolutionary engine needed to further refine their aerodynamic repertoire. (For a photo essay featuring this digit to wing development in fascinating detail inside mommy's batcave, see this post of bat fetal development; very much worth a quick look.)
So here's a plausible thumbnail sketch of a hypothetical evolutionary lineage for bats, stipulating the two suborders did indeed acquire flight separately from the same ancestral family: Left, a tree-dwelling shrew-like critter develops keen hearing and rudimentary echolocation during the reign of the dinosaurs around 70 MYA and grows larger between 65 MYA and 60 MYA; after the K-T Boundary. Center: A descendent of the echolocating shrew develops folds of skin to aid in gliding, similar to the Colugo around 60 - 55 MYA. Right, the glider acquires the gene for finger bone plasticity and further extends and refines the wing giving rise to powered flight, and we have a microbat at 55 - 50 MYA, consistent with the fossil evidence. Then, 50 - 40 MYA a descendant of that same glider gives rise to a second clade which also develops flight producing the first mega or fruit bat. Both suborders of Chiroptera radiate into various eco-niches assuming a wide range of sizes confusing the phylogeny of micro Vs mega bats. Viola!
Is that how it happened? No one knows for sure, it's overly simplistic, and it raises a lot of other questions. But it's a reasonable starting point. It's consistent with what we do know or can reasonably infer.
(In the interests of balance I'm honor bound--and likely soon to be legally required in several backassward states-- to present the competing creationist hypothesis)
Left: The Bat Kind, or Baramin, is created ex nihilo by a lightning bolt from an 'unknown' Intelligent Designer, as companions for another 'unknown' being, let's call that one Satan, roughly 6,000 years ago along with the earth, sun, and universe. Center: Some Bats get loose from Hell when Satan is preoccupied, date uncertain. Right: Bats are invited on a big boat to escape a magic flood about four or five thousand years ago. After landfall they subsequently micro evolve at a hitherto unheard of breakneck pace for three or four thousand years into one-thousand species: But only within the Bat Baramin of course. This hyper-evolution suddenly comes to a complete stop between one-thousand and five-hundred years ago, because humans start paying attention. Note: The bats are not pictured in the last illustration because it's daytime and they're sleeping. We can however confidently infer at least one breeding pair is onboard using inerrant Old Testament data.
All bats are either nocturnal or crepuscular--meaning they hunt and forage at night or in the twilight of dusk and dawn. Their vision ranges widely from good to poor depending on species, they're not blind contrary to what many believe. Echolocating bats have refined their acoustical 'sight' to an amazing degree. The common microbat can pluck a struggling gnat from a spider web without becoming entangled, or detect a hair floating on the surface of a rippling pond, using sound alone! We cannot be certain how a bat 'sees' the world. But the auditory data is probably processed by the visual cortex, providing in all likelihood an acoustically enhanced overlay of traditional vision: Bats can peer through objects using the biological equivalent of ultrasound! Fruit bats, which lack the highly developed sense of echolocation, depend on their keen hearing, smell, and eyesight.
Because of their nocturnal predilections, even completely harmless bats are understandably associated with all manner of dark foreboding mythical creatures and folk legends. Some Native Americans cultures considered the bat a trickster spirit, a sort of anti-eagle. Medieval societies associated them with plague, decay, witchcraft, and death; which incidentally may stem from the bats descending on just such afflicted communities to gobble up the hordes of flies and other insects arising from piles of corpses. Literary works include The Legend of Dracula in which the vampiric immortal could shape shift into a giant bat-like creature. In our modern times we have batman, batwoman, and Kenneth Oppel's Silverwing Series, just to name a few. The familiar bat silhouette adorns Halloween products, sports team icons, and various genres of rock and roll. Bats are sometimes good, but usually portrayed as a dark evil portent.
Bats are often said to carry rabies in some unusual concentration. But aside from the aforementioned vampire bats, even in areas where rabies is common only perhaps half of one percent are infected. They have the good sense to be wary of people, hey they're not stupid. Indeed; many bat owners claim their unconventional pets are as smart as a cat or a dog. You are thousands of times more likely to contract a dangerous disease from a mosquito or other insect pest, the preferred prey of many bats, as you are from bats themselves.
Usually, only bats suffering from debilitating illness or brain trauma will make an appearance in a well lit area amid the hustle and bustle of human society. There the poor creature will often flail around wildly and clumsily in the grip of fatal delirium, giving rise to our erroneous perception that all these animals are demented; at best confused, at worst wickedly insane. Thus we talk of someone gone batty, who has bats in the belfry, and is therefore batshit crazy.
But Chiroptera are not crazy, or even particularly dangerous: They simply do not deserve their reputation as evil or threatening; quite the opposite in fact. They're mostly small, the majority of common species weigh only a few ounces, and they consume prodigious quantities of insects, especially relishing flies and mosquitos, thus protecting our crops, our livestock, and ourselves. They are shy, perfectly happy to avoid the limelight, and stay clear of people, choosing to silently go about their business when we are asleep. We rarely even notice them, unless we're specifically looking. Bats are a splendid living laboratory of evolutionary biology: They remain the only naturalized mammalian ambassador to the sky.
[Enlarge Photo] Every evening from March to early November, 1.5 million Mexican free-tailed bats emerge from their roosts under the Congress Avenue Bridge in Austin, Texas. The exodus lasts for a full hour. Learn more about this amazing phenomena and the creatures behind it by clicking here.
There really are few vertebrate creatures more useful to our basic interests and less visible in our everyday lives, than these winged creatures of the night. Even the revolting vampire species have given us hints for amazing new drugs.
Back to Jocko, the damned soul cursed to wander the night for all eternity surrounded by flying demons. This ghost story scared the shit out of me, in a delicious way, when I was young. I'd duck under the blanket from time to time, you know, to stay 'safe', during the telling of the more frightening parts. It probably didn't help that older kids would cloak themselves in a blanket pretending to be giant bats and come after us youngsters hissing and moaning ... "Jockoooo, wheeere'sss Jockooo ..." I'll probably be working that one out in therapy at some point.
Anyway, my childhood tormentors may have been adding the part about bats to elicit screams of terror from me as a sadistic counterpoint harmony for their peals of laughter. Most forms of the actual Irish folk story do not include the bat portion. But in every version Jocko, sometimes called Jack or Jacko, has to find his way back out of the dark realm of the netherworld, his nocturnal haunts forever lit only by Satan's gift of the burning coal. Unwilling to carry the fiery ember in his hand, he places it in an old, hollowed out turnip he happened to have with him forming a sort of ad hoc lantern. The turnip was eventually replaced with a winter gourd, or a pumpkin, with holes carved in the sides to allow the light out. And that of course is how the modern Jack-o'-lantern, along with the colors of fiery orange and black night, became a symbol of lost souls and the one time they can roam freely every year; All Hallows Eve.
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