Fangs!

This year, I’m devoting my annual Halloween essay to fangs, those scary anatomical structures that have evolved independently among many unrelated groups of ambush predators.  Some of the earliest placental mammals to evolve fangs were the nimravids and barbourofelids.  These 2 families of carnivores were formerly thought to be closely related, and some scientists still classify them as such.  There are 9 known species of nimravids and 7 known species of barbourofelids.  Both families had representative species that lived from the late Eocene (~40 million BP) to the late Miocene (~9 million BP).

Illustration of Barbourofelis fricki, also known as the false saber-tooth.  It was a very large carnivore that may have preyed upon rhinos, the most abundant large prey species of the Miocene.  The background environment of this illustration is likely not accurate.  Forested environments predominated during the Miocene.

Illustration of Hoplophoneus, a nimravid that grew to about 320 pounds.

The nimravids and the barbourofelids were formerly thought to have been ancestral to the cat family–they have similar builds and likely occupied similar ecological niches.  However, fundamental differerences in the auditory bulla (an inner ear bone) distinguish cats from nimravids and strongly sugggest nimravids could not be of ancestral lineage to cats.  NImravids and barbourofelids also walked flat on their feet, like bears, whereas cats walk on their toes.

Click to enlarge the image.  Cats have multi-chambered auditory bulla.  Nimravids had a single chamber in some species, and in others the structure was made out of cartilage.  This is evidence that nimravids were not ancestral to cats, despite the similarity in appearance.  Click to enlarge.  This illustration is from a page in the book The Big Cats and their Fossil Relatives by Alan Turner and illustrated by Mauricio Anton.

Cats ecologically replaced nimravids.  Whether they outcompeted them or took advantage of their extinction due to other causes is unknown.  There were 2 species of fanged cats during the late Pleistocene of North America–the famous saber-tooth (Smilodon fatalis) and the lesser known scimitar-tooth (Dinobastis serus).

Illustration of Smilodon fatalis.

An extinct species of vampire bat (Desmodus stocki) fed upon the blood of megafauna during the Pleistocene.  It ranged all across the continent of North America.  See (https://markgelbart.wordpress.com/2011/10/24/the-pleistocene-vampire-bat-desmodus-stocki/)

Photo of 1 of the 3 species of extant vampire bats which live in South America.

A person doesn’t have to go far to find a creature with fangs.  Most suburban yards host a plethora of wolf spider species.  Venomous fangs help subdue dangerous prey, such as bees and wasps, quickly.  Wolf spider venom is not hazardous to people.  Venom also helps protect rattlesnakes.  Venomous snakes withdraw after injecting their venom with a quick strike, so they avoid injury while the victim struggles in its death throes.  They don’t begin swallowing prey until it has been immobilized by venom.

Illustration showing how snake fangs work.

Wolf spider (Lycosidae) fangs.

There was even a family of saber-toothed salmon swimming in the Western Interior Seaway that separated Eastern and Western North America during the Cretacous age of the dinosaurs.

Illustration of the extinct saber-toothed salmon (Enchodus sp.) that swam in the seas when dinosaurs roamed the earth.

There is a clear evolutionary advantage in the repeated occurrence of fangs in the animal world.  Individuals that carry the mutation for fangs are more likely to be able to subdue their prey without sustaining injury, and therefore are more likely to pass that gene mutation to their offspring.  Although there are no large mammalian predators with fangs today, it’s possible and likely a big cat with fangs could evolve again…if man allows enough of the natural world to exist.

The Red Bat (Lasiurus borealis)–Another Pleistocene Survivor

When I was about 10 years old, I woke up one night and heard something flying around my bedroom.  The creature kept clumsily hitting the walls and from the sound of leathery wings smacking into plaster I knew it was a bat and not a bird.  I walked down the hall to my parents bedroom.

“There’s a bat in my bedroom,” I told my mom.

My mom’s not a girly type of woman who freaks out at the sight of a bug, so her reaction really surprised me.  She later told me she thought I was dreaming, and she did not expect to actually see a bat.  But as soon as she turned on the hall light, a big bat, looking just like a prop from a vampire movie, came flying straight toward us.  My mom slammed her bedroom door in my face, and I ducked under the bat which proceeded to fly down the stairs.  A few minutes later, my mom opened the bedroom door a crack and told me to round up my sisters.  She wanted us to sleep in her room that night because she was afraid the bat might carry rabies.

My mom refused to cook breakfast the next morning.  We went to eat at IHOP instead.  My dad owned a private medical practice at the time, and  one of his patients was in the pest control business, so my dad sent him to our house to look for the bat.  He did examine the living room curtain, but evidentally didn’t see the roosting bat.  That night, we watched a war movie on television, and the explosions from World War II artillery awoke the bat.  The bat crawled down the curtain and started flying around the room.  My dad grabbed his tennis racquet, I opened the front door, and he backhanded the bat out the doorway.

Big brown bat (Eptesicus fuscus).  I believe this is the species that startled my mom into slamming her door in my face.

Based on my memory of its wingspan, I believe the bat that invaded our home on Hogarth Avenue in Niles, Ohio circa 1972 was a big brown bat.  They commonly crawl down chimneys and get inside houses.

There are  9 species of bats that range into Georgia today.  During the Pleistocene there were at least an additional 2 species.  The extinct Pleistocene vampire bat (Desmodus stocki) must have lived in what’s now Georgia then.  And prior to the Last Glacial Maximum, Brazilian free-tailed bats (Tadadira brasiliensis) probably lived here as well, but this species has yet to recolonize its former range, since the climate has warmed following the end of the Ice Age.  Fossils dating to ~40,000 BP of this species have been excavated from Mammoth Cave, Kentucky which is far outside its present day range.  Fossil evidence of bats in Georgia is limited to cave dwelling species–gray myotises (Myotis grisescens), big brown bats, and pipistrelles (Pipistrellus subflavus).  The latter species has a wingspan of only 3 inches–a pipsqueak–and can be confused with a large moth when viewed from a distance.  There are several interesting species of bats that roost in Georgia’s forests, and therefore are not as likely as cave dwelling species to be represented in the fossil record.  Rafinesque’s big-eared bat (Plecotus rafinesquii) roosts in hollow cypress trees, and yellow bats (Lasiurus intermedia) exclusively spend days hidden in Spanish moss.  Perhaps the bat best adapted to the climatic fluctuations of the Pleistocene is the still abundant red bat.

The Red Bat (Lasiurus borealis), still extant, is well adapted to climatic fluctuations and is a real survivor of the Pleistocene when climate fluctuations were drastic compared to those of the most recent 11,000 years. 

Unlike most bats, this species is covered in fur and has short ears.  It’s capable of surviving at lower temperatures than any other species of bat, though it does become inactive below 68 degrees F.  They migrate south during the winter but spread as far north as Canada during the summer. They can also hibernate, if necessary.  They roost in trees, shrubs, and even within leaf litter on the ground.  They become active 90 minutes after sunset when they begin hunting for moths (26% of their diet), flies, mosquitoes, crickets, bugs, beetles, and cicadas.  They use echolocation to catch flying insects on the wing and to pounce on crawling arthropods.  Most species of bats give birth to 1 or 2 young, but red bats have litters as large as 5.  The mother bats leave the baby bats at the roost while foraging.  They will transport them to new roosts, however.  7% of the red bat population carries the rabies virus.  A predator such as a house cat or possum could easily become infected, if they find a red bat in the leaf litter.  Surprisingly though, blue jays are the top predator of red bats, mostly attacking the young.

Red bats have been excavated from fossil sites in Missouri, West Virginia, Virginia, Florida, and even Bermuda.  Apparently, a red bat washed up on a Bermuda beach 400,000 years ago and became fossilized.  Red bats are an ancient species and will probably survive the scourge of white nose syndrome, the disease that is wiping out all cave dwelling bats in eastern North America.  Because red bats are a solitary forest dwelling species, they are less likely to become infected with the communicable disease.  They’ll still be with us when, sadly, most other species of North America’s eastern bats are probably going to become extinct–an ecological disaster.

The Pleistocene Vampire Bat (Desmodus stocki)

A drawing of the type specimen’s skull and fang.  Desmodus stocki was 20% larger than the still extant common vampire bat (Desmodus rotundus), and it was probably adapted to a cooler climate.

This creepy creature seems an appropriate enough subject for Halloween week.  It’s perhaps the most surprising and strangest animal included in the list of species that occurred in southeastern North America during the Pleistocene.  Fossil evidence is scant but sufficient to suggest it lived throughout the entire region.

Photo of a caver inside New Trout Cave, West Virginia.  Pleistocene vampire bat fossils were found here.

Fossil bones of the Pleistocene vampire bat have been found in Cuba, Mexico, Florida, Texas, Arizona, northern California, and West Virginia.  The latter two sites are about the same latitude.   The fossils from New Trout Cave, West Virginia date to 29,000 BP, a time of a weak interstadial preceding the Last Glacial Maximum.  Modern vampire bat species can’t survive temperatures that fall below 50 degrees Fahrenheit.  Some scientists think winter climates during the Ice Ages were milder south of the ice sheet than those of today, explaining why vampire bats were able to live this far north, but I don’t agree.  The species of plants inhabiting the south then were temperate and in some areas even boreal.  29,000 years ago, the Laurentide Glacier was very close to New Trout Cave, so winter temperatures must have consistently been below freezing here during winter.  Pleistocene vampire bats were probably able to survive cooler temperatures than their modern cousins.

Pleistocene vampire bats enjoyed an abundant supply of food, likely gorging on the blood of giant ground sloths, mammoths, mastodons, bison, horses, llamas, peccaries, bears, big cats, wolves, and maybe even paleo-Indians.  There’s no direct evidence proving they fed upon the blood of these victims, but I think it’s a safe assumption they did.  Their bones have been found associated with giant sloth remains, though this doesn’t really count as proof.  They did occur on islands where the only large mammals were dwarf ground sloths, making it certain they must have plagued the latter.  Vampire bats require lots of blood (their sole source of nourishment) and will die, if denied food for more than two days.  To survive a shortage of food, they share blood by regurgitating it to each other.

I think the reason Desmodus stocki is not more commonly found in the fossil record is because they usually roosted in hollow trees where their remains would decay into nothingness along with the wood and leaf litter of the forest.  The extinction of Desmodus stocki paralleled the extinction of the megafauna.  They were a commensal species that couldn’t survive the loss of such an abundant source of blood.  A population of Pleistocene vampire bats persisted on San Miguel Island off the coast of California until  3000 BP, indicating pygmy mammoths inhabited the island til then.

Best photo of a common vampire bat found on google images.

Today, there are at least three kinds of vampire bats and all inhabit the tropics of South and Central America.  The white winged (Dianus youngi) and the hairy legged (Dyphylla ecaudata) both feed upon the blood of birds.  The common (Desmodus rotundus) feeds upon the blood of mammals, and its numbers have skyrocketed since the introduction of livestock to South America.  Diseases carried by vampire bats cause the deaths of hundreds of thousands of cattle and horses every year.  The same must have been true of the megafauna during the Pleistocene.  The rate of rabies must have been high in that primeval world.  However, it’s unlikely this contributed to any extinctions because vampire bats and megafauna co-existed for millions of years.

A fourth species, the giant vampire bat (Desmodus draculae), may still be extant.  Scientists dated a fang of this species found in Argentina to be just 300 years old.  It’s the only bat fossil of any kind found in Argentina.  Other fossils of this species have been found in Brazil and Venezuala and date to the Pleistocene.  Cattlemen occasionally report seeing exceptionally large vampire bats feeding on their stock.  Cryptozoologists are on the lookout for it.  In this case they may be chasing a real species, not an imaginary one.

Vampire bats evolved during the Miocene, at least 8 million years ago, probably from bats that specialized in eating either ticks or maggots living on open wounds on large mammals, much like African oxpecker birds do today.  Evolving from eating maggots and/or ticks to consuming blood required only a few inherited mutations.

The legend of the vampire predates the European discovery of the vampire bat by at least 500 years.  The English word, vampire, was derived from the German vampir in 1734, but the German word can be traced back to the Russian word, uper which dates to 1047.  Ancient Babylonian legends include tales of blood-sucking ghosts, predating the origin of the Russian word.  Europeans didn’t discover the existence of vampire bats until 1526 when an early Spanish explorer awoke and found one sucking blood from his toes.