Debunking the Claim that Burmese Pythons are causing Severe Mammal Declines in the Everglades

The National Academy of Science often publishes some really bad studies.  Two years ago, the journal of this organization published a paper entitled “Severe Mammal Declines Coincide with the Proliferation of Burmese Pythons in Everglades National Park.”  This study was authored by Michael Dorcas, an herpetologist from Davidson College, along with a long list of other scientists.  I’m always leery of studies with a long list of contributing scientists.  I suspect the lead authors of these studies do most of the work, and misleadingly include many co-authors.  With minimal input, the many co-authors lend legitimacy to a study in exchange for getting the publishing credit that is so important for their academic careers.

Michael Dorcas.  This scientist authored a really bad study of Burmese pythons that led him to conclude they were wiping out mammal populations in the Everglades National Park.  His study was debunked by the Florida Fish and Wildlife Conservation Commission.  Nevertheless, the media took his ridiculous conclusions as gospel.  Not a single journalist questioned this terrible amateurish study.

I read Dr. Dorcas’s study and knew the results didn’t fit within ecological reality.  He went back to records of road-killed animals in Everglades National Park during the 1990’s before the population of Burmese pythons had become significant and compared them with the number of road side sightings of these same species 10 years later.  He concluded that the populations of raccoons, possums, bobcats, and marsh rabbits had been decimated and in some cases had been reduced by 100%.  This doesn’t make any sense ecologically.  If the population of prey declines in abundance, than the population of predators declines as well because there is nothing for the predators to eat.  Burmese pythons couldn’t decimate mammal populations without eventually succombing to starvation themselves.  So the results of Dr. Dorcas’s study were unbelievably ridiculous.  Nevertheless, every news media outlet picked up this alarmist nonsense and not a single journalist questioned the credibility of such an absurd conclusion.  This demonstrates the ignorance of basic ecology among the average layperson.  I mentioned my logical objections to this study’s findings on my blog about a year ago but thought I was a lone voice in the wilderness.  However, I discovered someone from The Florida Fish and Wildlife Conservation agrees with me.  They found the following flaws in Dr. Dorcas’s study.

1. The survey for road-killed animals (Dr. Dorcas’s data from the 1990’s) didn’t include critical information–how many observers, the number of miles driven, the number of days the survey was done, and the procedures used to avoid double counting.  In other words this data is anecdotal and useless.

2. The year of the pre-python survey was a high water year when more animals were forced to take refuge on the high ground where the road exists.  This explains why more animals were counted during the survey than during later drought years.  Road-side surveys yield dubious data.  Dr. Dorcas should have used live trapping to get an accurate count of mammal populations.

3. There is no actual data on python densities.

4. The timing of the python population increase and the supposed decline in mammal populations is not documented.  Scientists can’t explain how python populations could increase following prey population declines (my point exactly).

5. There is no mention in Dr. Dorcas’s study of coyotes.  Coyotes recently re-colonized south Florida and may play a role in the decline of mammal populations there.

6. The differences in prey density inside and outside Everglades National Park are likely due to differences in habitat, not the presence of pythons.  Everglades National Park is actually very poor wildlife habitat.  More wildlife lives outside the park than inside.  With very few exceptions most of the best wildlife habitat left in the world is occupied by humans.  We give animals the wastelands that are too expensive to commercially develop and call them national parks.

Burmese python killed by alligator.  Burmese pythons are beneficial additions to Florida’s ecology, despite what alarmist environmentalists claim.  South Florida’s ecology was in desperate need of a large predator.

Contrary to the claims of alarmist environmentalists, Burmese pythons are a beneficial addition to South Florida’s ecosystem.  During the Pleistocene in this region there were 5 species of big cats plus dire wolves, bears, and alligators.  Now, there are just alligators and pythons.  (Very few Florida panthers live in Everglades National Park.  Most occur on cattle ranches located well north of the park.) Without the presence of large predators, the populations of smaller predators such as raccoons and possums increased.  These predators eat reptile eggs and put a big dent in the population of 17 endangered and threatened species of reptiles, including rare sea turtles.  Pythons help control the numbers of raccoons and possums, helping increase the nesting success of endangered reptiles.  Pythons are beneficial for twice as many endangered species than ones they might prey upon.

Scientists’ estimates of Burmese pythons populations in Florida are not based on scientific data.  They are wild guesses bordering on fantasy.  The oft-cited number of 30,000-150,000 is a wild overstimate.  Over the past 12 years, 2000 pythons have been removed from Everglades National Park.  That’s less than 200 per year–nowhere near what one would expect, if there were 30,000 large snakes slithering inside the park.  Last year, there was a python round up.  For a month 1500 snake hunters looked for Burmese pythons to kill.  They netted just 50.  This is strong evidence Burmese pythons are not even close to being as abundant as researchers claim.

Reference:

Dorcas, Michael; et. al.

“Severe Mammal Declines Coincide with Proliferation of Invasive Burmese Pythons in Everglades National Park”

PNAS December 2011

Unnamed author

“Commentary on Mammal Declines in Everglades National Park”

Florida Fish and Wildlife Conservation Commission report 2012

 

The Great American Biotic Interchange

South America broke from Antartica and Australia about 60 million years ago and became an island continent where its fauna evolved in isolation.  The most common mammals were marsupials, edentates, and primitive hooved animals unfamiliar to most non-paleontologists.  Circa 30 million years ago, caviomorph rodents and monkeys arrived from Africa via clumps of floating vegetation originating from that continent.  During this time Africa and South America were closer together than they presently are.  Floods in African rivers must have carried these little islands of vegetation with their clinging inhabitants  far into the sea where favorable currents brought the lucky animals to South America.  These new colonizers diversified into many species.  South America remained an isolated continent until 9 million years ago when volcanic islands began emerging  below North America.  Although there was not yet a landbridge between the 2 continents, the fossil record shows there was an early exchange of species.  Ground sloths went north, while tapirs, peccaries, and primitive mastodons known as gompotheres went south.  All of these animals are excellent swimmers.  Apparently, they island-hopped, swimming to reach new islands and eventually coming to a continent where they became successful newcomers.

 

 

 

 

Map showing the islands that  collided with South America eventually forming the Isthmus of Panama. This joined North America with South America.  Some species of mammals island-hopped and colonized the other continent before the landbridge completely emerged above sea level.

Elephants can swim for miles without getting tired.  They can breath through their trunks while swimming.  This explains how gompotheres (an elephant-like beast) colonized South America 9 million years ago, long before a land connection existed between the 2 continents.

Tapir swimming.  They can breath through their snouts while swimming submerged.  All of the early colonizers in the Great American Biotic Interchange were excellent swimmers.  They island-hopped before the existence of a complete land connection.

A now extinct relative of the raccoon (Cyonasaura) was next to colonize South America 7.3 million years ago.  An extinct species of raccoon (Chapmalania) that was as large as a bear lived in South America during the Pliocene.  Sygmodontine rodents (rats, mice, gophers) from North America arrived in South America 6 million years ago.  Pampatheres (a giant armadillo) and the terror bird spread to North America 5 million years ago.  They were followed by glyptodonts and capybaras 4 million years ago.  The Central American landbridge emerged above sea level ~3 million years ago bringing a cavalcade of animals south–llamas, horses, canids, and weasels; while porcupines headed north.  A new climatic phase ~2 million years ago allowed even more mammals to head south–deer, rabbits, skunks, cats, and bears.

Other vertebrates took advantage of newly available habitat.  South American forms that moved north included cichlid fish, bufo toads, tree frogs, parrots, tanagers, hummingbirds, and flycatchers.  North American vertebrates that went south included lungless salamanders, ranid frogs, snapping turtles, wood turtles, trachemys turtles, rattlesnakes and other pit vipers, coral snakes, sparrows, and condors.

These faunal invasions occurred in pulses influenced by changes in climate.  During Ice Ages sea level fell and this greatly expanded the land area of Central America.  Average temperatures fell by as much as 14 degrees F here, though because the region is so close to the equator they were not subfreezing.  Nevertheless, pollen records indicate tropical forests were replaced with grassy savannahs and temperate species of trees such as oak, sweetgum, myrtle, elm, walnut, and even spruce and fir at higher elevations.  The change to a more open environment allowed horses and llamas to traverse Central America to colonize land further south.  Warm interglacial conditions favored the expanded ranges of tropical species such as very large ground sloths and glyptodonts.  These species eventually made it to southeastern North America.  Some lineages of mammals colonized 1 continent, evolved to a new species, then returned to the original continent of their ancestor.  Examples of these are the collared peccary and jaguarundi.

More species of South American-originating fauna survive in North America than vice-versa, but most are restricted to the Central American tropics.  There are many species of edentates, marsupials, monkeys, and caviomorph rodents here.  But, excepting Central America’s faunal composition, North America’s invasion to South America could be considered more successful.  There are just 4 successful South American species living today in North America (not counting Central America)–opossum, armadillo, porcupine, and nutria whereas South America is home to tapirs, peccaries, llamas, foxes, cats, sygmodontine rodents, squirrels, rabbits, and shrews.  However, a modern review of this disparity is misleading.  Ground sloths, glyptodonts, and pampatheres were quite successful during the Pleistocene in North America, but humans caused their extinction.  Toxodons and litopterns (primitive South American hooved animals that made it as far north as Mexico) were also vulnerable to human hunting and would likely still live today if not for man.  North America also has a more temperate climate. It is difficult for species that evolved in tropical climates to adapt to freezing temperatures.  The only real losers resulting from this faunal interchange were South America’s marsupial carnivores and the terror birds.  North America’s carnivores eventually outcompeted South America’s meat-eaters.

Reference:

Woodburne, M.O.

“The GABI: Dispersals, Tectonics, Climate, Sea Level, and Holding Pens”

Journal of Mammalian Evolution 17 2010

Glyptodonts Clubbed Their Foes (and each other)

Glyptodonts were unlike any living species of mammal.  A carapace, attached to their hips, covered all of their body except for the head.  This protected them from most predators, though evidence from 1 specimen suggests a frontal attack by a big cat could prove fatal (See:https://markgelbart.wordpress.com/2011/11/02/specimen-f-am-95737/).  Their shell provided a wonderful defense, but glyptodonts were capable of taking the offensive.  When confronted by a predator, a glyptodont turned its back and swung its tail with devastating force.  Paleontologists have determined these tail blows were powerful enough to damage the carapace of other glyptodonts.  They also hypothesize of the existence of a fatty pad behind the shoulder that helped withstand these intraspecific blows.  Male glyptodonts fighting over mates turned their backs to each other and swung their tails, battering each other’s carapace.  Occasionally, these blows caused carapaces to fracture.  There is 1 specimen in a South American museum that shows evidence of such an injury, though the wound healed and this individual glyptodont survived.  Some species of glyptodonts had clubs or spikes on their tails.  They were located where the center of percussion would be.  The center of percussion is the equivalent of the “sweet spot” on a baseball bat or tennis racquet.

Glyptodonts used their tails as defensive weapons and in intraspecific conflicts over mates.  Scientists determined the club on this species was at the center of percussion or sweet spot, just like a baseball batter’s sweet spot.

A glyptodont shell mounted in a South American museum.  A glyptodont mounted in another musuem shows a fracture from being hit by another glyptodont’s tail club.  That carapace healed.

Here’s an artist’s rendition of glyptodonts battling over a mate.

Glyptodonts belonged to the edentate order (some scientists prefer to call it the xenartha order), a classification that includes armadilloes, anteaters, and sloths.  The edentates originally evolved in South America, but some species spread to North America when a landbridge between the continents emerged millions of years ago.  There were 5 genera of glyptodonts living in South America during the Pleistocene, but only 1 species occurred in southeastern North America during the late Pleistocene.  The North American species lived in Florida and the southeastern coastal plain during warm climate phases.  The largest species of glyptodont lived in South America.  This member of the Doedicurus genus reached 4000 pounds.  Glyptodonts were a successful lineage of mammals that lived for tens of millions of years but became extinct about the same time man appears in the archaeological record.  I have no doubt their otherwise well adapted defenses were useless against hunting humans.  A man could simply run forward and hit a glyptodont over the head while avoiding the tail blows.  The fatty deposit behind a glyptodont’s shoulder would have been a delicacy.

Ankylosaurs and glyptodonts are a good example of convergent evolution.  Ankylosaurs, a dinosaur that became extinct 65 million years ago, also had carapaces and swung their tails in self defense in battles over mates.

Ankylosaurs had a similar adaptation as glyptodonts–an example of convergent evolution.

References:

Alexander, R.

“Tail Blow Energy and Carapace Fractures in Large Glyptodont (Mammalia: Xenartha)”

Zoological Journal of the Linnean Society  126 1999

Blanco, Ernesto; Washington jones, and Andres Ringle Knecht

“The Sweet Spot of a Biological Hammer: The Centre of Percussion of a Glyptodont (Mammalia: Xenartha)”

Proceedings of the Royal Society of Biological Science 276 (1675) 2009

 

The Pleistocene Penis

Organisms with separate male and female sexes evolved from hermaphroditic ancestors.  Hermaphroditic species are still common.  Many species of plants and some species of animals are able to self-fertilize because they are both male and female.  One would think the evolution of an hermaphroditic organism to a species with separate male and female sexes happened so long ago that it would be impossible for biologists to study.  But, surprisingly, this is not true.  There are over 100 species of plants in the evolutionary process of transitioning between hermaphroditism to a state of separate sexes.  The most familiar species in this transitional state is the wild strawberry, Fragaria virginiana.

Biologists believe the evolution of separate sexes was the result of a beneficial mutation.  Organisms that have separate sexes have increased genetic variation, thus improving the chances the species will survive.  Hermaphrodites suffer higher rates of inbred defects and eventually are eliminated from transitioning populations by the hybrid vigor of male x female combinations.  In stressful environments organisms with separate male and female sexes can allocate resources to seed or pollen, not both–another advantage over the hermaphrodite.

Plants rely on wind and insect pollination.  Males and females of many primitive aquatic animals release sperm and egg in each other’s vicinity, relying on water flow to aid fertilization.  But the evolution of a structure to directly deliver a male’s sperm inside a female’s body was a great advance.  This structure is known as a penis.  The oldest known penis in the fossil record belonged to an extinct species of shrimp (Colymbosathon ecplecticas) that lived 425 million years ago. 

Mammoths and mastodons had the largest penises of any land mammal during the Pleistocene and theirs was comparable in size to those of modern day elephants.

This bull elephant is in the mood to mate.  Note the large penis.  Mammoths and mastodons had the largest penises of any Pleistocene land mammal.

Homo sapiens has the largest penis of any primate.  There’s no evidence Pleistocene humans ever practiced the bizarre and barbaric practice of genital mutilation known as circumcision.  Circumcisions originated in Egypt about 4400 years ago. Religious fanatics in the ancient Egyptian culture rejected the concept of sexual pleasure.  Circumcision spread throughout the Middle East and Africa and was always popular among religious nuts who thought sexual pleasure was bad.  According to the bible (an unreliable source), the early Jews practiced circumcision, but Moses outlawed the practice.  Joshua brought circumcision back because he wanted his men to focus on smiting gentiles rather than sexual pleasure.  Jews have continued this idiotic tradition ever since.  Circumcision became popular in the United States after the Civil War when once again religious nuts were trying to stop boys from masturbating.   It didn’t work–98% of circumcized males admit to masturbating.  Greedy physicians made up falsehoods, supporting the pro-circumcision crusade, so they could make money on a common but unnecessary procedure.  Even today, most American males suffer genital mutilation shortly after birth, though, thankfully, rates are declining.

About a decade ago, the American Academy of Pediatricians admitted there was no medical reason for male circumcisions.  However, in 2012 religious nuts pressured the AAP to restate their position.  The AAP now states, “the health benefits of circumcision outweigh the risks but the existing scientific evidence is not sufficient to warrant universal circumcision…the final decision should be left to parents to make in context of their religious, ethical, or cultural beliefs.”  So in other words, the AAP is saying it’s ok to torture a baby, if their parent’s religion tells them they are supposed to.  The words cowardly and callous come to mind.

The CDC recently released a report supporting the practice of circumcision because in Africa circumcized men are less likely to spread HIV than uncircumcized men.  Well, first of all, the CDC represents America not Africa.  Second, this reasoning is incredibly illogical.  The spread of HIV could be be completely eliminated if every man had their entire penis cut off, just like broken legs could be prevented with universal leg amputations.  Or less dramatic measures could be taken.  Men could use condoms or engage in sex with less dodgy partners.

There is no medical reason for male circumcision.  There is no significant statistical difference in rates of penile cancer or urinary tract infections between circumcized and uncircumcized men as some have falsely claimed.  There is no moral justication for torturing babies, and I think it is sickening how so many parents are willing to approve of such a stupid, barbaric, religious tradition.  The practice of circumcision, both male and female, should be outlawed.

Comparison between a normal penis and the more common (in the U.S.) mutilated penis.

I’m glad I can’t remember my circumcision.  Most American males are strapped down when they are babies and have 12 inches of skin cut off from the most sensitive area of their body…all in the name of religion and tradition.  WHAT AN OUTRAGE!  Are people this insensistive, gullible, and stupid that they would subject their children to torture, just because some stupid rabbi or greedy doctor says they should?

The removal of the foreskin slices off the 5 most sensitive areas of the penis.  Circumcized men are 4.5 times more likely to use erectile dysfunction drugs than uncircumcized men.  These men probably wouldn’t need such medication, if their penises had not been mutilated with the approval of their brainwashed parents.

Reference:

Ashman, T.

“The Evolution of Separate Sexes: A Focus on the Ecological Context”

In chapter 11 of The Ecology and Evolution of Flowers edited by Lawrence Hader and Spencer Barrett

Oxford University Press 2007

Giant Ground Sloths Probably Scavenged Meat

Caves located in arid climates preserve ground sloth dung that is tens of thousands of years old.  The shasta ground sloth (Nothrotheriops shastensis) ranged throughout the American southwest during the late Pleistocene and left telltale evidence of its diet in several of these caverns including Rampart Cave, Arizona; Shelter Cave, New Mexico; and Gympsum Cave, Nevada.  From the macrofossils and DNA evidence in this dung we know this species ate a wide variety of plants–pine, mulberry, mustards, agave, yucca, grass, mint, globe mallow, saltbush, Mormon tea, grape, water leaf, creosote bush, hop sage, sagebrush, and willow.  There is no evidence from these coprolites that ground sloths ate meat.  Nevertheless, some scientists hypothesize ground sloths did scavenge meat .   Although ground sloths were too slow to actively hunt most prey, they could have taken advantage of available carrion, and perhaps even usurped the kills of predators.  Ground sloths were powerful beasts with long claws capable of severely injuring a carnivore contesting ownership of a carcass.  Some scientists have even suggested ground sloths could have actively turned over glyptodonts to attack their vulnerable underbelly.

The lack of meat in known sloth coprolites doesn’t preclude the possibility they did on occasion eat animal protein.  Over 99% of white-tail deer feces will show no evidence of flesh-eating.  Yet, we know they do sometimes scavenge meat and even prey on nestling birds and eggs (See: https://markgelbart.wordpress.com/2012/05/11/unexpected-items-in-the-diet-of-the-white-tail-deer/)  Without evidence the hypothesis that ground sloths ate meat is mere speculation.  However, evidence from 1 specimen supports this hypothesis.

 

 

 

 

 

 

 

Artist’s rendition of a Megatherium, a large ground sloth that formerly lived in South America.  The deer in the foreground is a pampas deer (Ozotoceros bezoarticus)), still extant but very rare.

Photo of a rib interpeted to have been gnawed on by a Megatherium.  From the below referenced book.

A fragmentary rib in the collection of a museum in Uruguay has gnaw marks on it that match the teeth of Megatherium americana, a large ground sloth.  The rib is from either another ground sloth or a mastodon.  (Scientists can’t differentiate among these 2 species from just this part of the anatomy.)  It has 7 shallow marks.  Weathering marks exist over the tooth marks, eliminating the possibility that natural abrasions caused the scratches.  The marks are too dull to have been the result of human cutting.  The marks don’t match those of rodents or carnivores.  However, they exactly match the “transversely bilophodont” teeth of a megatherium.  The spacing of the tooth marks also match the distance between the bottom teeth of a megatherium.  The scientist who examined the marks believes the sloth held the bone upside down and gnawed on it with its bottom teeth.

If sloths ate carrion, I’m sure they would have also eaten ground-nesting bird nestlings and eggs as well.  They likely snacked on insects.  Ground sloths are related to armadilloes and anteaters.  Armadilloes eat carrion, small mammals, eggs, and insects.  Ground sloths probably retained the ability to digest animal protein from their shared ancestry with armadilloes. The evolutionary ancestor of both lines was likely omnivorous.  There’s no reason to assume ground sloths could not have taken advantage of an easy source of protein, though their diet was primarily vegetarian.  This feeding strategy would not be unlike those of bears, hogs, and apes.

Reference:

Farina, Richard; Sergio Vizcaino, and Gerry Del Iuliis

Megafauna: Giant Beasts of Pleistocene South America

Indiana University Press 2013

Poinar, Henrick; et. al.

“Molecular Coproscopy: Dung and Diet of the Extinct Ground Sloth, Nothrotheriops shastensis”

Science 281 (5375) 1998

 

The Antelope Jack Rabbit (Lepus alleni) Lived in Southeastern North America During the Pleistocene

Today, the antelope jack rabbit is restricted to desert grassland habitat in western Mexico and southern Arizona, but during the Pleistocene it occurred as far east as Florida.  Fossils of this species have been found at 2 sites in Florida, dating to the middle Pleistocene.  Over 50 fossils of unidentified hare species (Lepus sp.) that probably also were antelope jack rabbits have been found at many sites in Florida, dating to the early Pleistocene and the Pliocene.  The early Pleistocene/late Pliocene climate was much drier than it is today, and desert grassland habitat was more prevalent.  Several species of pronghorns lived in the southeast as well.  Antelope jack rabbits gradually declined in abundance and may have disappeared from the southeast completely by the late Pleistocene, but the fossil record is so incomplete that there is no way of knowing exactly when they became extirpated from the region.

The antelope jack rabbit prefers arid habitat and does not need water.  It gets enough moisture from the plants it eats.

 

Modern day range of the antelope jack rabbit.  During the Pliocene and early to mid Pleistocene, it lived as far east as Florida.  It now is relegated to relic status.

 

The antelope jack rabbit’s favorite present day habitat looks like this.  They are most abundant in mesa type vegetation.

 

There are probably several factors explaining the decline of this once more widespread species.  About 300,000 years ago, a prolonged interglacial climate phase occurred.  During interglacials, precipitation increases, causing forests, woodlands, and wet meadows to predominate over arid grasslands.  Antelope jack rabbits are absent from fossil sites in Florida that date to after this prolonged interglacial.  However, this doesn’t mean they became completely extirpated in the region. Antelope jack rabbits may have persisted in relic populations in sandhill areas where the conditions allowed the continued existence of dry scrub habitat.  But these isolated populations would have been more susceptible to diseases.  Tularemia, also known as rabbit fever, is caused by the bacterium, Francisella tularensis.  It is spread through ticks, deer flies and other insects.  This plague causes a high fatality rate among all species of lagomorphs, and there are some regions of the antelope jack rabbit’s present day range where the disease has completely eliminated local populations.  Incidentally, hunters should wear gloves and surgical masks when cleaning rabbits.  If untreated, tularemia has a 7% fatality rate among humans.

 

Climate change combined with disease may have wiped out antelope jack rabbits in the southeast, but if there were still any surviving populations here during the late Pleistocene, the extinction of the megafauna would have been the final blow.  Jack rabbits favor overgrazed habitat. The trampling, feeding, and defecating of large mammals increases the types of forbs and other plants that jack rabbits like to eat.  Herds of mammoth, bison, and horses certainly overgrazed the landscape.  Without the presence of these species, jack rabbit habit was further degraded.

 

Though there were similarities between the modern day arid grasslands of the southwest and the early Pleistocene environment of the southeast, they were not exactly the same.  In the southeast the range of the cottontail rabbit and the antelope jack rabbit overlapped.  Today, the ranges of these 2 species do not overlap at all.  Antelope jack rabbits can live without ever drinking water.  They can get all the moisture they need from their diet which includes green grass, mesquite, and cactus.  (Insects are ingested accidentally.)  Therefore, they can live in areas where water was scarce.  But water holes did exist in Florida during the early Pleistocene, though they were less abundant than they are today.  Alligators, raccoons, and river otters all occur in the early Pleistocene fossil record of Florida.  So antelope jack rabbits did formerly occur in areas where water sources were more available.  This is evidence that some Pleistocene environments just have no modern analogue.

Southeastern Giant Beavers of the Pleistocene have been Declared a Distinct Species from Northern Giant Beavers

The giant beaver of the Pleistocene was semi-aquatic like its modern living cousin (Castor canadensis), but it ate different plant foods, and therefore occupied a different ecological niche.  Giant beaver fossils are fairly common throughout the midwest but have also been found at numerous localities in the southeast, particularly Florida.  Scientists formerly thought southern giant beavers were the same species (Casteroides ohioensis) that ranged throughout the midwest and northeast.  The reason for this misconception was the lack of complete skulls in the collections of southern museums.  Skulls of giant beavers were excavated from the Leisey Shell Pits in Florida, but this site dates to the early Pleistocene, and paleontologists thought they represented a species that was ancestral to the late Pleistocene giant beaver, thus explaining the differences in skull characteristics.  However, a complete skull resembling those early Pleistocene giant beavers was discovered in the Cooper River in South Carolina, and this was from a late Pleistocene deposit.  Recently, paleontologists got their hands on 2 more giant beaver skulls dating to the late Pleistocene of Florida.  Scuba divers found 1 in Lake Rousseau, and the other was found in the Aucilla River.  After a careful anatomical analysis, scientists determined the late Pleistocene giant beaver of Florida, coastal Georgia, and coastal South Carolina was a different species than the giant beaver of the midwest and northeast.  They gave it the scientific name Casteroides dilophidus.

Size comparison between the Pleistocene giant beaver and the extant beaver.  The 2 species co-existed for 2 million years.  Scientists recently realized there were 2 different species of giant beaver–a northern and a southern.

Casteroides dilophidus had a shorter ridge on the top of its skull than C. ohioensis.  This ridge is known as the saggital crest.  One of its skull sutures bears in a different direction than that same suture on C. Casteroides, and C. dilophidus’s cheek row teeth are located differently in relation to the zygomatic arch.  The projection of the frontal bone of the eye socket is “better developed” in C. dilophidus than in C. casteroides, according to the study.  Some C. dilophidus specimens have grooves in their teeth that are never found in C. casteroides, but this can’t always be used as a distinguishing characteristic.  The authors of the study don’t have enough data to determine whether giant beaver fossils found in the mid-south (Alabama, Arkansas, Mississippi, and Tennessee) belong to C. dilophidus or C. ohioensis, so they suggest classifying those specimens as Casteroides sp.  Many fossil specimens (mostly teeth) of Casteroides have been found in the mid-south but no complete skulls.

Casteroides preferred treeless freshwater marshes where they could feed on the aquatic plants that flourished in full sunlight.  Wooded swamps and bottomlands are too shady for the plants they liked to eat.  Much erroneous speculation surmises modern extant beavers outcompeted Casteroides.  Instead, the smaller species of beaver created habitat favorable to Casteroides.  Extant beavers fell trees and open up the forest canopy, allowing succulent shade-intolerant vegetation to thrive.  Old beaver ponds eventually become filled with sediment and are converted to the wet treeless marshes Casteroides required.  Moreover, Casteroides co-existed with Castor canadensis for 2 million years.

An ecological cycle of alternating beaver species during the Pleistocene is apparent.  Castor canadensis converted wooded swamps and bottomlands to treeless marshes.  When trees became scarce, Castor canadensis would abandon the locality while Casteroides would move in. But Casteroides didn’t eat trees, allowing the forest to grow back. Castor canadensis would then recolonize the location as Casteroides moved away in search of a more open habitat.  The presence of both species in the fossil record reflects a varied environment and a much more diverse ecosystem than exists today.

Reference:

Hulbert, R. C.; A. Kirne, and G.S. Morgan

“Taxonomy of the Pleistocene Giant Beaver Casteroides (Rodentia: Casteroidae) from Southeastern U.S.”

Bulletin of the Florida Museum of Natural History 53 (2) 2014

 

The Cat Food Scavenger

I prepared baked chicken for supper 2 weeks ago.  American chickens are nice and fat but for some dishes they are too fat.  I removed the skin from the chicken pieces before rolling them in cracker crumbs and black pepper.  This reduces the unwanted grease that nutritionists claim clog our arteries.  However, I hate wasting food, so I boiled the chicken skins and put some of them with the broth in a bowl for the cat.  I placed the bowl on the back step.  A few minutes later, I looked out the window to see if the cat was enjoying his warm treat on such a frosty night.  Instead, an unidentifiable gray object was over the bowl.  I turned on the light and saw an opossum.  I ran to fetch my camera, but when I opened the door, the creature scurried away quickly, a piece of chicken skin dangling from its mouth.    Later, the possum returned and I took a decent photograph of it.

I discovered this opossum eating food I put on the back step for my cat.

The feral cat that I tamed (see:https://markgelbart.wordpress.com/2014/06/24/mr-claw/) used to eat every speck of food I placed outside.  But now that he realizes I’m going to feed him everyday, he doesn’t devour every bit at once.  There’s no telling how often that opossum has been scavenging cat food.  Possums are quite common in my neighborhood.  Several weeks ago, I saw a road-killed possum down the street that a flock of vultures made disappear in less time than it took me to jog 3 miles.

The Virginia opossum (Didelphis virginiana) is an amazing survivor.  Opossum remains are found in just about every Pleistocene-aged fossil site in Georgia, and they are still abundant today.  Their rapid rate of reproduction is their most important survival attribute.  They become sexually mature at 6 months, and their gestation period is less than 2 weeks.  They produce up to 18 young but the females only have 13 nipples.  An average of 7 young survive to adulthood.  Nevertheless, in about a year’s time 2 opossums can result in roughly a 20 fold increase.  When attacked by a large predator, opossums can escape by climbing a tree.  Their prehensile tails allow them to hang upside down from branches, giving them a good view of potential threats.  If they are unable to make it to a tree when attacked, their nervous system becomes overwhelmed, and they literally shit and faint.  The noxious fluid that leaks from their anus makes them unappetizing to predators.  Unless a predator is especially hungry, the lack of movement and bad smell will cause them to lose interest.  The opossum then recovers and goes on with its business.

Opossums are also omnivorous–another contributing factor to their success as a species.  They eat fruit, carrion, insects, worms and grubs, birds and eggs, small mammals, reptiles, and even venomous snakes.  They are immune to rattlesnake venom.  A recent study found there is an evolutionary arms race between opossums and pit vipers.  Scientists discovered opossums have rapidly evolving gene codes for Von Willibrandt’s Factor, an important blood-clotting protein targeted by snake venom.  Natural selection has strongly favored those individuals of the opossum population immune to snake venom.  Creationists often use “living fossils” such as the opossum as evidence that evolution doesn’t occur.  They are wrong.  Although the modern Virginia opossum is anatomically identical to the opossum of 3 million years ago, its physiology has evolved considerably.  If we could bring an opossum from 2 million years ago to the present, it would likely not be able to survive the bite of a modern day rattlesnake like its modern day descendents can.

The opossum is 1 of the oldest species of North American mammals.  Ancestral opossums first evolved about 65 million years ago when the dinosaurs became extinct.  This is also the time when the shared ancestry of American opossums and Australian marsupials diverged.  These ancestral species of opossums became extinct in North America about 25 million years ago, but they continued to live in South America which at that time had become an island continent.  A landbridge emerged 3 million years ago, connecting North and South America, and this is when Virginia opossums moved north.  At least 103 species of opossums live in South America, but only 1 evolved the ability to survive in the temperate climates that occur in North America.  All the other species are restricted to tropical climates.  There are 5 other species of opossums in the Didelphis genus that are closely related to the North American opossum.  There are also 4-eyed opossums (they don’t actually have 4 eyes), 14 species of woolly opossums, 20 species of short-tailed oppossums, 56 species of diminutive mouse opossums, and a water opossum well adapted to a semi-aquatic existence.

Reference:

Jansa, Sharon A.; and Robert Voss

“Adaptive Evolution of the Venom-Targeted vWF Protein in Opossums that eat Pit Vipers”

Plos One 6 (6) 2011