Why did the Giant Great White Shark (Carchocles megalodon) Become Extinct?

April 29, 2016

The giant great white shark (Carchocles megalodon) existed as a species from ~23 million years BP until ~2.6 million years BP, and the evidence suggests this 60 foot monster preyed on whales.  It was 1 of the many marine species to become extinct during the late Pliocene.  Scientists believed megalodon was a warm water species and couldn’t survive cooling ocean waters that resulted from the emergence of the landbridge between North and South America.  However, a brand new study determined climate change could not have been the cause of megalodon’s extinction.

The authors of this study mapped out all of the sites where megalodon fossil teeth have been collected along with all fossil shark collection sites where megalodon remains were absent.  They estimated the range of the species over geologic time. Megalodon, though it originated in tropical waters, later expanded its range to waters that are thought to have been quite cold.  During glacial maximums megalodon’s potential habitat range shrank by a mere 2%, while it expanded by 8% during warmer interglacials.  Most of the area where megalodon lived was not “negatively impacted by climate change.”

Populations of C. megalodon over time. From Pimiento et al., 2016.

Map of megalodon fossil collection sites, dated over geological time periods.  From the below referenced paper.

If climate change didn’t snuff out megalodon, what was the cause of its extinction?  The researchers who published this study suggest 2 possible causes: a reduction in whale species diversity, and competition with other predators.  They note a decline in whale species diversity during the end of the Miocene is correlated with an apparent decrease in megalodon’s range distribution.  This seems a plausible explanation.  Many of megalodon’s favorite prey species went extinct, depriving the giant shark of food that it could efficiently feast upon.  I’m not convinced competition with other predators was a factor in megalodon’s extinction.  An extinct predatory species of sperm whale (Leviathon melvillei) likely fed upon the same prey species as megalodon.  The ancestors of the modern day great white sharks (Carcharodon hubbeli) and killer whales (Orca sp.), also may have shared the same prey items.  However, megalodon co-existed with these species for millions of years, so I have a hard time accepting this explanation.

Size comparison between megalodon, a killer whale, and a human. A pod of killer whales could’ve rubbed out a single megalodon.  Perhaps this was a factor in their extinction.

An extinct species of predatory sperm whale–Leviathan melvillei–probably competed with megalodon for the same prey.  Miocene-age species of baleen whales were smaller than modern baleen whales.

The extinction of megalodon may have  shaped the evolution of baleen whales.  Whales no longer had to be agile fast swimmers to escape megalodon, but instead could grow to a great size that enabled them to store food as blubber.  The stored fat helped baleen whales swim long distances to warmer waters for breeding and calving.  Killer whales, their lone remaining non-human predator, are less common in warmer waters, and whale calves have a greater chance of survival there.

Reference:

Pimiento, Catalina; et. al.

“Geographical Distribution Patterns of Carchocles megalodon over time Reveal Clues about Extinction Mechanisms”

Journal of Biogeography March 2016

Pleistocene Cricket Frogs (Acris sp.)

April 25, 2016

Every year, trillions of horny cricket frogs call to each other along the shores of ponds and slow moving streams wherever emergent vegetation grows. ( https://www.youtube.com/watch?v=QQirydJRs7Q )This is an ancient sound of nature.  Many mighty mastodons heard these mating calls, and the small frogs occasionally were forced to jump, barely avoiding the heavy steps of the lumbering giants.  The 2 far different species shared a preference for the same kinds of wetland environments.  Old beaver ponds in the process of succeeding to wet meadows hosted the highest density of mastodons and cricket frogs.  The beavers and mastodons opened the forest canopy allowing sunlight to reach plant growth along the pond margins–ideal hiding spots for cricket frogs.  The seemingly insignificant cricket frogs outlasted the more spectacular mastodons because they are capable of reproducing at a much faster rate.

Despite their annual abundance throughout North America for well over 5 million years, cricket frogs are recorded from just 10 fossil sites.  According to the paleobiology database, the bones of cricket frogs have been identified from 4 sites in Texas, 2 in Nebraska, 2 in Kansas, 1 in Colorado, and 1 in Florida.  Their remains are associated with Miocene fauna (25 million years BP- 5 million years BP) at 3 of the sites, suggesting cricket frogs have been around for quite some time.  The amount of known fossil material for this genus compared with how many individuals lived during each generation is astonishingly low and is yet another example of how incomplete the fossil record can be.

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Southern cricket frog (A. gryllus).  They also come in a green phase with a stripe down their back.

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Pine pollen washed into the pond just in time for the season’s first hatching of tadpoles.  I wonder if the tadpoles feed on the protein rich plant food.  I have seen ducks eating pine pollen.

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During late March pond margins in Georgia are filled with cricket frog tadpoles.  Click to enlarge.

There are 3 species of cricket frogs in the Acris genus: the southern cricket frog (Acris gryllus), the northern cricket frog (A. crepitans), and Blanchard’s cricket frog (A. blanchardi).  Until recently, some taxonomists regarded these as 3 subspecies of the same species, but a study of cricket frog genetics determined there are species level differences between them.  The southern cricket frog ranges on the coastal plain of southeastern North America; the northern cricket frog occurs from the piedmont region north to southern Canada.  Blanchard’s cricket frog lives west of the Mississippi River, excepting 2 counties in Mississippi.  This grand river serves as a barrier to the flow of genes, resulting in speciation among cricket frogs, spiny lizards, rat snakes, shrews, and some species of fish.

The cricket frogs belong to the tree frog family (Hylidae), but their ancestors left the trees and inhabited pond margins instead.  The adults eat insects, but during the tadpole stage, they primarily subsist on algae.  I hypothesize cricket frog tadpoles feed on protein rich pine pollen.  The tadpoles seem most abundant when pollen washes into ponds in early spring.  A diet that includes pollen may increase the rate of tadpole growth and development, improving the odds of surviving to adulthood.  It would be interesting to test this hypothesis.  Southern cricket frogs do breed year round, but there is a peak during spring and a slow down during winter.

Herons take a heavy toll of tadpoles and adults when they swarm near shore, and the frogs often fall prey to bass and catfish when the jump in the water to avoid the long-legged birds.  Cricket frogs survive by constantly breeding, producing more frog than predators can catch and eat.

Reference:

Gamble, Tony; et. al.

“Species Limits and the Phylogeography of North American Cricket Frogs (Acris: Hylidae)”

Molecular Phylogenetics and Evolution 2008

A New Study about the Devil’s Den Site in Florida was Published

April 20, 2016

An unpublished study of radiocarbon dates of extinct Pleistocene megafauna excavated from the Devil’s Den site in Florida produced unusually recent dates.  Specimens from this site were dated to between 7,000 BP-8,000 BP; about 4,000 years after the time most believe these species became extinct. I often wondered why this data seemed to be ignored in the scientific literature and why no one had attempted a follow up study of the specimens from this site.  The specimens were described in 1974, then seemingly forgotten.  (See: https://markgelbart.wordpress.com/2012/07/08/the-devils-den-fossil-site-may-have-been-located-in-one-of-the-last-refuges-of-the-megafauna/ )Finally, several scientists began analyzing the Devil’s Den specimens again, and they just recently published their data in  brand new journal named PaleoAmerica.

Devils Den - Williston, FL

Photo of the Devil’s Den site from inside the sinkhole.

I had wrongly assumed the specimens were radiocarbon dated in 1974, but I learned from reading this study that they were dated in 1961 when radiocarbon dating was primitive and not particularly reliable.  Moreover, the authors of this new study determined radiocarbon dating of these specimens could not be accurate because they didn’t have enough bone collagen left.  They also suggest radiocarbon dating for most Pleistocene-aged specimens found in Florida is not possible because the regional environmental conditions eat away at bone collagen so rapidly.  This poses a problem for scientists who want to know if humans overlapped in time with Pleistocene megafauna in North America.  Surprisingly, there is little direct evidence of this, despite the universal assumption that they did.  Human remains of confirmed Pleistocene age in North America are extremely rare.  However, human bones associated with those of extinct Pleistocene mammals have been found in several sites in Florida including Vero Beach, Warm Mineral Springs, Melbourne, and Devil’s Den.  Though this is suggestive, it’s possible humans buried their dead in the Pleistocene-aged strata, mixing the bones from different time periods.  Scientists need something more definitive than association.  Because radiocarbon dating can’t be used at these sites, the authors of this study decided to try rare earth element analysis on the specimens from Devil’s Den.

Here is an explanation of rare earth element analysis. Rare earth elements (a bit of a misnomer because they’re not particularly rare) include elements on the periodic table numbered 57-71.  They occur in groundwater in certain fixed ratios.  Animals absorb ground water by ingestion and then for thousands of years after they die their bones continue to become saturated with it.  Eventually, the bone reaches a saturation point and won’t take in any more.  The ratio of rare earth elements in that particular fossil becomes fixed.  However, over thousands of years the ratios of rare earth elements in ground water changes.  So an animal that lived 13,000 years ago will have a different ratio of rare earth elements than an animal that lived  200 years ago.

The authors of this study compared the ratios and concentrations of rare earth elements from specimens they categorized into 4 groups.  They analyzed 26 specimens from 5 different individual human skeletons found in the Devil’s Den sinkhole and compared them with the associated bones of extinct Pleistocene fauna, extant fauna thought to be of Pleistocene age, and extant fauna from the modern local environment.  They used specimens of the Florida spectacled bear (Tremarctos floridanus), flat-headed peccary, Jefferson’s ground sloth, mastodon, and muskrat that were found in the sinkhole.  The first 4 of these species are extinct, and this species of muskrat hasn’t occurred in Florida for about 3,000 years.  The extant fauna thought to be of Pleistocene age found in the sinkhole included white-tailed deer, woodrat, striped skunk, gray fox, and gopher.  Local fauna of modern age used in the study were deer, fox squirrel, gray fox, and gopher.  Specimens from 4 of the 5 human skeletons shared similar ratios of rare earth elements with Pleistocene fauna, showing they lived during the same time period.  One of the human skeletons is probably of Holocene age, but this study demonstrates without a doubt that humans overlapped in time with Pleistocene megafauna.

The authors of this study assume 4 of the human remains are older than 13,000 years old, but they have no way of knowing for sure.  The rare earth element analysis shows these individuals lived at the same time as Pleistocene megafauna, and the bones are of great antiquity, but the date of deposition is not known.  As I’ve written previously on this blog, I hypothesize some species of Pleistocene megafauna survived in small relict populations well past their accepted terminal extinction date of ~12,500 BP.  The exact extinction dates of Pleistocene megafauna in Florida will remain a mystery, especially if radiocarbon dating can’t be used.

Reference:

Purdy, Barbara; Kathryn Rohlwing and Bruce Macfadden

“Devil’s Den, Florida Rare Earth Element Analysis Indicates Contemporaneity of Humans and Late Pleistocene Megafauna”

PaleoAmerica 1 (3) 2015

Gavialosuchus americanus

April 14, 2016

The false gharials, a type of crocodylian, were widespread throughout the world during the Miocene between 25 million years BP- 5 million years BP.  They inhabited the coastal regions of Eurasia, and North and Central America when worldwide climate was warmer than it is today.  With their long snouts and rows of sharp teeth, they were well adapted for catching the fish that abounded in salt marshes and saltwater lagoons.  Fossil evidence of false gharials has been found along the eastern seaboard of North America from Florida to as far north as New Jersey.  Gaviolosuchus americanus is the species that lived in eastern North America during the late Miocene, while G. carolinensis occurred here during the Oligocene (33 million years BP- 25 million years BP).  The false gharials likely arose as early as the Eocene.

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Skeleton of Gavialosuchus carolinensis on display at the Charleston Museum.  This species lived during the Oligocene.

Gavialosuchus americanus Skull

Skull of Gavialosuchus americanus.  Note the long snout.

Some scientists use the scientific name of Thecachampus americanus instead of Gavialosuchus americanus.  Scientific nomenclature is a tedious topic, so I won’t delve too deeply into it on my blog.  The first scientific name ever given to a species holds precedence.  Paleontologists often find fossil material they mistakenly think is from a new species, and they will give it a name.  Later studies then determine the “new” species is actually the same as a species that had already been named.  The older species name is accepted as the correct one.  The dispute between the usage of Gavialosuchus americanus and Thecachampus americanus has yet to be unanimously resolved.

Gavialosuchus americanus was a little larger than the sole surviving species of false gharial–Tomistoma schlegeli.  The extinct species grew to 18 feet, surpassing T. schlegeli by a couple of feet.  T. schlegeli survives today in parts of Malaysia and Indonesia, but they’ve been extirpated from Thailand.  They mostly eat fish but will opportunistically take monkeys, deer, birds, other reptiles, and humans.

Tomistoma schlegelii false gharial LA zoo 03.jpg

The only species of false gharial still extant–Tomistoma shlegeli.  Various species  of false gharials occurred along the coasts  of Eurasia and North America  from the late Eocene to the early Pliocene.

Anatomical studies suggested the false gharials are distantly related to the true gharial (Gaviatis gangetives) of India.   The long narrow snout of the false gharial was considered an example of convergent evolution when unrelated or distantly related organisms evolve the same adaptation to similar environments.  However, a genetic study determined the false gharial and the true gharial are closely related sister species.  The vertebrate zoologists were wrong.

Gavialosuchus americanus co-existed with a species of alligator in North America.  An analysis of chemical isotopes in the bones of both crocodylians suggests they occupied different habitats.  The false gharial of America inhabited saltwater environments and alligators ruled the freshwater lakes and streams.

References:

Harshman, J. ; et. al.

“True and False Gharials: A Nuclear Genophylogeny of Crocodylians”

Systematic Biology 2003

Whiting, Evan; David Steadman, and John Krigbow

“Paleoecology of Miocene Crocodylians in Florida: Insights from Stable Isotope Analysis”

Paleogeography, Paleoclimatology, Paleoecology March 2016

The Largest Saber-toothed Cat, Smilodon populator

April 9, 2016

Smilodon populator may have been the largest cat ever to have hunted in the wild.  Richard Farina, a South American paleontologist, estimated this species reached a weight of over 800 pounds.  This is more than twice as big as the more famous Smilodon fatalis, a species that lived all across North America during the late Pleistocene.  Smilodon fatalis also ranged into South America west of the Andes Mountains, while S. populator occurred east of this mountain chain.  Apparently, the Andes Mountain chain served as a geographical barrier, resulting in the evolutionary divergence of the 2 species of Smilodon.

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Smilodon populator reached an astonishing 800 pounds in weight.

S. populator was an ambush predator that wrestled its prey to the ground and bit its throat, slicing through windpipe and jugular with its long fangs.  Scientists assumed it lived in forested environments where it could more easily surprise its prey from behind cover.  However, a recent study, using isotopic analysis of bone collagen from sub-fossil specimens, determined S. populator and its favorite prey lived in an open dry environment.  According to this study of specimens from 6 different sites in Argentina, S. populator’s favorite prey was macrauchenia, a now extinct primitive ungulate.  Macrauchenia occupied an ecological niche similar to that of a modern day giraffe’s.  With its long neck it could reach tree leaves unavailable to horses and deer, but it also grazed on grass.  S. populator also often preyed upon 2 species of ground sloths–the enormous megatherium and lestodon.  Prey species other than macrauchenia, megatherium, and lestodon made up less than 5% of S. populator’s diet, if this isotopic analysis accurately reflects the big cat’s diet.  Giant ground sloths moved so slowly that S. populator would likely have had no problem seizing an individual.  I suspect they mostly attacked weaned sub-adults, no longer protected by their mothers.  Full grown sloths would have been difficult to subdue because they were large, powerful,  armored under thick skin, and armed with big claws.  Some scientists believe ground sloths dug burrows as a kind of strategy to defend themselves from S. populator.  These burrows still exist.  (See: https://markgelbart.wordpress.com/2012/10/10/some-giant-ground-sloths-dug-long-burrows/ )  A ground sloth in a burrow with its back protected would have been impossible for a Smilodon to kill.

I hypothesize S. populator had a black or dark gray coat that made it difficult to see in the dark.  This allowed them to ambush sleeping macrauchenia in the open.  It explains how a large relatively slow predator could catch a better runner, like macrauchenia. I believe S. populator hunted ground sloths during the day when they left their burrows to feed and sleeping macrauchenia at night when the latter were less alert.

An isotopic study suggests macrauchenia was Smilodon populator’s favorite prey.

An extinct canid, Protocyon trogl0dytes, may have competed with S. populator.  The isotopic values of 1 specimen of this species closely matches those of the many specimens of S. populator analyzed in the study referenced below.  This suggests Protocyon ate the same prey species as S. populator, however, the sample size is too small to reach a definite conclusion about this species diet.  It’s not known whether this species was an active hunter, a scavenger, or both.  Isotopic evidence from a single specimen of a jaguar from the late Pleistocene of South America indicates it preyed on different species–horse, deer, and rodent.

S. populator lived in South America for at least 750,000 years.  It ecologically replaced a saber-toothed relative of the marsupials known as Thylacosmilus atrox.  Smilodon may have outcompeted Thylacosmilus and driven it to extinction.  However, there is a 1 million year gap in the fossil record between the most recent specimen of T. atrox and the earliest specimen of S. populator.  It’s not known for certain whether the 2 species ever overlapped in time.

In the conclusion of the below referenced paper the authors suggest a change from dry open environments to more humid forested conditions may have contributed to the extinction of S. populator.  I strongly disagree with this notion because a) S. populator survived as a species for over 750,000 years of climatic changes and b) dry open environments are still widespread in South America, most notably in the Gran Chaco region.

Smilodon populator hunted in a dry open environment, not dissimilar from this palm savannah in the Gran Chaco region of Argentina.

I’m convinced man is entirely responsible for the extinction of S. populator.  Humans overhunted Smilodon’s favorite prey, depriving the big cat of food, and probably directly hunted the big cats.  Its great size became a disadvantage after man colonized the region because it was an easy target to hit with spears thrown from a great distance.

Reference:

Bocherens, Herve; et. al.

“Paleobiology of Sabretooth Cat Smilodon populator in the Pampean Region (Buenos Aires Province, Argentina) around the Last Glacial Maximum: Insights from Carbon and Nitrogen Stable Isotopes in Bone Collagen”

Paleogeography, Paleoclimatology, and Paleoecology March 2016

Sign my White House Petition to Create a Pleistocene Park

April 4, 2016

https://petitions.whitehouse.gov/petition/transformation-great-smoky-mountains-national-park-pleistocene-park

I visited the Great Smoky Mountains National Park a few years ago and left greatly disappointed.  I had hoped to see an abundance of wildlife.  Instead, I saw a grand total of 1 squirrel, 4 Canadian geese, and 6 crows.  My daily constitutional in my neighborhood yields a greater variety of wildlife than that.  It was depressing to discover suburban Augusta, Georgia offers better wildlife viewing opportunities than a famous national park.  There are 2 areas of the Great Smoky Mountain National Park where wildlife watching is recommended–Cades Cove and the Cataloochee.  However, when I visited, the road to Cades Cove was closed.  The access road to the Cataloochee is a single-lane unpaved path winding up a steep mountain without guard rails.  I judged it far too dangerous to continue up this life-threatening hazard.  The National Park service should be ashamed of the sorry infrastructure here.  It’s like something one would expect in a Third World country.

In a National Park, good wildlife viewing shouldn’t be confined to just a couple small areas.  Wildlife should be abundant throughout the park.  The problem with the Great Smoky Mountains National Park is the hands-off management policy of the park service.  A dense old growth forest covers most of the park.  This is poor habitat for most large mammal species, and it supports very low wildlife populations.  An attempt to re-establish red wolves in the park some years ago failed because there was nothing in the park for them to eat, showing just how low wildlife populations are here.  Red wolves can live off rabbits-the park doesn’t even have many of those.  Moreover, this park, wrongly thought to be natural, is like nothing that ever existed in nature prior to ~1900.  Native Americans, beginning about 14,000 years ago, set fire to the woods every year.  This created a mosaic of habitats including open woodlands and grassy prairies.  Large centuries-old oaks and chestnut trees were widely spaced with luxurious grasses and flowers growing in between.  Before man colonized the region, large herds of megafauna maintained a similar landscape.

I propose that the National Park service transform Great Smoky Mountains National Park into a Pleistocene park by actively managing it to improve habitat for wildlife.  After a detailed study they could install a management plan that would recreate an environment more similar to that of the Pleistocene than that of today’s aberrant abomination.  Some old growth forest would remain standing, especially along creeks and rivers that serve as natural fire breaks.  But most upland areas would need to be clear cut in some places and thinned out in others.  Pasture grasses and native flowers could be planted and large mammal species such as bison, horses, and llamas could be introduced, so that the open environment could be maintained by their foraging and trampling.  A fire management plan would also maintain this environment.  Eventually, Siberian tigers could be introduced to control the population of large ungulates.  Tigers would also cull wild boar and bears.  A functioning Pleistocene-like ecosystem would be far more interesting and worthwhile than the park as it currently exists.

Accordingly, I ask that you sign my White House petition, requesting the Obama administration to order the Park Service to create a Pleistocene Park.  You can do so in the following link:

https://petitions.whitehouse.gov/petition/transformation-great-smoky-mountains-national-park-pleistocene-park

If the petition gets 100,000 signatures by May 2, 2016, the White House will write a response.  President Obama has shown little interest in the environment, since he’s been in office.  He has not called for the establishment of more protected wilderness lands, and he’s thrown wolves under the bus by taking them off the endangered species list.  I am curious how he would respond to this.  I’m sure he will defer to the Park Service party line.

The National Park Service won’t like my proposal.  I believe their policy, though they would never admit it, is to keep wildlife populations as low as possible, so they don’t have to bother with problematic human-animal interactions.  U.S. Fish and Wildlife recently chose to delist grizzly bears as a threatened species.  This will allow redneck states, such as Wyoming, to reduce the overall population of grizzly bears.  (See: http://www.grizzlypeople.com/topten.php ) These jerks want to maintain a population of 500 grizzly bears by killing 50 per year.  If there were only 500 humans left on earth, and 50 were killed every year, humans would rapidly become extinct.

A non-profit organization in Russia has already established a Pleistocene Park located in Yakutia, Siberia.  Surgey Zimov hypothesized the extinction of the Pleistocene megafauna caused the transformation of a steppe grass environment in northern Asia to willow shrub tundra.  Twenty years ago, he spear-headed an experiment to reverse this transformation.  His organization bought tundra land and introduced horses to an enclosed area.  They helped the horses along by converting this land into pasture.  At first many horses were killed by wolves or died because they ingested poisonous plants.  But the horses have learned not to eat the harmful plants, and they have proved capable of surviving the deep snows that some thought would doom the whole herd.  The experiment supports Zimov’s hypothesis because the horses (with a little initial help) have transformed willow shrub tundra to grassland in their enclosed living space.  The grassland is similar to what existed during the Pleistocene.

Pleistocene Park, Russia

Pleistocene Park in Siberia.  The introduction of horses led to the transformation of tundra shrub to grassland habitat in areas where the horses are enclosed.

Caribou, bison, moose, elk, and musk-oxen have also been introduced.  (A small population of the former already occurred here.)  Caribou are now the most abundant ungulate in the park. Researchers hope the moose browse down the willow shrub, so that more grazers can be introduced on a larger scale.  Introduced elk escaped from an enclosure, but some found there way to the park without human help.  The list of potential future introductions includes Bactrian camels, saiga antelopes, yaks, asses, Siberian tigers, and cloned woolly mammoths.

A secondary discovery of this experiment determined the conversion of willow-shrub habitat to grassland mitigates the effects of climate change.  The hard compacted surface resulting from horse trampling keeps the permafrost intact.

Siberia is too far to travel.  I want to see a Pleistocene Park established within driving distance of my house.  Please sign my petition.

https://petitions.whitehouse.gov/petition/transformation-great-smoky-mountains-national-park-pleistocene-park

 

 

Pleistocene Dung Beetles

March 31, 2016

An odd thought occurred to me the other day involving Hindu reincarnation myths and dung beetles.  I happened to jog past a female rainbow scarab beetle (Phanaeus vintex), rolling a dog turd on the asphalt-topped road.  (Female scarab beetles lack the male’s horn, making the sexes easy to distinguish.)  Scarab beetles bury feces and lay their eggs in it.  Both the adults and larva eat shit.  Apparently, this particular scarab beetle was looking for soft earth where it could bury its offspring’s food supply, but it couldn’t find the end of the hard road–it kept rolling the turd in circles.  I felt sorry for the creature because it would roll the turd within inches of the side of the road, almost to the dirt, then it would turn around and roll it toward the other side.  A car ran over the turd, busting it into 3 pieces.  Undeterred, the dung beetle picked the largest piece left and began rolling it in circles again, never quite reaching the dirt for as long as I observed it.  I’m not familiar with the Hindu religion, but I think they believe human spirits can be reincarnated as animals.  Suppose the Hindu Gods punished a human, whose sin during life was laziness, by reincarnating his soul as a dung beetle stuck rolling a heavy turd on a hard surface where it could never find a soft place to rest.  The soul could spend an eternity of hard labor to make up for his earthly slothfulness.  In reality a dung beetle never gets discouraged because insects are automatons with no emotions.  Before man built hard roads the only environment where dung beetles could become indefinitely trapped rolling turds were large granite outcroppings.  Dung beetles are yet another organism suffering a high death toll because of man’s extensive road network.

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I saw this female rainbow scarab beetle rolling a dog turd on the street in front of my house.  It was aimlessly rolling it around in circles.  It just missed getting run over by cars.  Click to enlarge.

There are 3 types of dung utilization behaviors among the many species of dung beetles.  Some take a piece of shit and roll it some distance away from the manure pile before digging a hole and depositing an egg in it.  These dung beetles are known as “rollers” and include members of the Phanaeus genus.  The “tunnelers,” including members of the Onthophagus genus, dig holes adjacent and under the dung pile where they deposit their eggs.  The “dwellers” live and lay their eggs inside the dung pile.  These include members of the Aphodius genus, and they release chemicals that keep the dung patty moist.

It is likely the widespread extinction of megafauna at the end of the Pleistocene caused a drastic reduction in the abundance and diversity of dung beetles.  One study found that the diversity and size of dung beetle species in Africa was higher in regions with abundant populations of megafauna.  Researchers counted 50 species of dung beetles in savannahs where elephants still occurred, 41 species where just cattle ranged, and 30 species in regions with no large mammals.  Dung beetles that switched to donkey shit in regions where elephants became extirpated were reduced in size.

Most species of extinct Pleistocene dung beetles will likely remain unknown to science because the odds of preservation for insects are even lower than those for large vertebrates.  However, 3 extinct species have been recovered from the La Brea Tar Pits in California–Onthophagus everestae, Copris pristinus, and an unnamed species in the Phanaeus genus.  (It’s possible some of these may be extant but undiscovered, but so far no entomologist has found a living specimen.)  The only species of dung beetle found in a preserved mammoth turd is the still extant Aphodius fossor, a large insect found in cow and horse pastures of Eurasia and North America.  Aphodius fossor probably followed herds of megafauna across the Bering land bridge almost 2 million years ago.  The specimen of mammoth dung containing the sub-fossil dung beetle was recovered from Bechan Cave, Utah.  An excavation at Snowmass, Colorado has yielded the remains of 9 species of dung beetles associated with the bones of megafauna dating to 120,000 years BP-77,000 years BP.  Scientists have identified 3 of the species, and they still occur in the region.  The remains of the other 6 species are too fragmentary to positively identify to the species level, but they may or may not represent extinct beetles.  Dung beetles have yet to be discovered from giant ground sloth dung, but fly larva from the Diptera genus, and a fly pupa from the Scairidae family have been found in sloth shit occasionally preserved in caves.  Flies compete with dung beetles.  Some species of dung beetles have evolved to prey on fly larva they capture inside feces.

Aphodius fossor - David Gould - The Spearwort Fields - 06 July 2014

Aphodius fossor, the only species of dung beetle ever found inside mammoth feces, though without a doubt many species were attracted to piles of megafauna shit during the Pleistocene.  The rarity of manure preservation in the fossil record explains the absence of evidence for other species.

Dung Beetle Life Cycle

Life cycle of a dung beetle roller.  Some other species tunnel into dung and lay their eggs inside the patty.

Dung beetles are beneficial organisms that expedite the recycling of nutrients.  The adults and larva also serve as food for birds and mammalian insectivores.  Birds, moles, shrews, skunks, possums, and armadillos apparently don’t mind the taste of the manure-flavored beetle grubs.

References:

Hanski, Ilkka; and Yues Cambefust

Dung Beetle Ecology

Princeton University Press 2014

Krell, Frank-Thorsten

“Pleistocene Dung Beetles from MIS 5 at Ziegler Reservoir, Snowmass Village, Colorado (Coleoptera: Scarabaedae: Aphodine)”

Denver Museum of Nature and Science Annals 2014

Pierce, W. D.

“Fossil Arthropods of California: Descriptions of Dung Beetles (Scarabidae of the Tar Pits”

Bulletin of Southern California Academy of Science 1946

 

Pleistocene Chickadees

March 27, 2016

It is difficult to discern the difference between a black-capped chickadee (Poecile atricapillus) and a Carolina chickadee (P. carolinensis).  The former has a longer tail and is a little heavier on average, but as the below photos show, they are hard to distinguish, even if examined side-by-side.  Moreover, the 2 species hybridize in regions where their ranges overlap.  The hybrid zone extends from New Jersey to Kansas with an outlying zone in the Appalachian Mountains.  In captivity male Carolina chickadees outcompete black-capped chickadees for mates, and scientists know female black-capped chickadees will choose male Carolina chickadees in the wild, often as “extra pair sires.”  Supposedly Carolina chickadees have a 4 note song, while black-capped chickadees have a 2 note song.  (See: https://www.allaboutbirds.org/search/?q=chickadee ) In the hybrid zone chickadees use both songs.  However, I live in Augusta, Georgia; far from the hybrid zone, and I discovered Carolina chickadees here use both the 2 note and the 4 note song.  I conclude the 2 species can’t be distinguished by which song they use.

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Partial range map for Carolina and Black-capped Chickadees.  

Black-capped chickadee

Black-capped chickadee.

Carolina Chickadee

Carolina chickadee.

 

The chickadees are tough Pleistocene survivors.  They are a year round resident of forest and woodland, capable of enduring harsh winters because they stash caches of seeds utilized during lean times.  Chickadees belong to the Paridae family that also includes tits and titmice.  Genetic evidence suggests the ancestors of all American Paridae originated in Asia and then colonized North America about 3.5 million years ago.  Cyclical climate change caused corresponding changes in the environment over time.  The founding population of these forest-dwelling birds became isolated into different populations by expanding desert grassland or in some cases by glaciers, resulting in the evolution of different species.

I was surprised to learn Carolina chickadees and black-capped chickadees are not sister species, even though they appear so similar and hybridize.  (Sister species are organisms that most recently evolved from the same common ancestor.  The official definition is “taxa derived from a common ancestral node.”)  Instead, the genetic evidence suggests the black-capped chickadee is a sister species of the mountain chickadee (P. gambeli), a bird that ranges throughout the Rocky Mountains, and the Carolina chickadee is a sister species of the Mexican chickadee (P. sclateri).  The chestnut-backed chickadee (P. rufescens) of the Pacific northwest, the boreal chickadee (P. hudsonicus) of Canada, and the gray-backed chickadee (P. cinctus) of Alaska and Scandinavia are sister species with each other.  Genetic evidence also shows black-capped chickadees and boreal chickadees have greatly expanded their ranges from single source populations, since the end of the last Ice Ages after the massive glaciers that covered their present day ranges melted.

Chickadees have likely been a common bird in southeastern North America for over 2 million years.  Yet, I’m aware of just a single specimen found in this region dating to the Pleistocene.  This specimen belongs to the University of Florida Museum of Natural History and was found at the Inglis fossil site in Florida.  It is early Pleistocene/late Pliocene in age (~1.9 million years old).  It was identified as a boreal chickadee, a species restricted to Canada today.  I can’t find the scientific journal within which this specimen was described.  Considering how hard it is to distinguish between species of chickadees, I’m uncertain how accurate this species diagnosis is.  However, boreal chickadees may have once been more widespread in North America before other chickadees, such as the Carolina, evolved and outcompeted them in various regions. The rarity in the fossil record of a species that was probably abundant for millions of years shows how fleeting evidence of an organism’s existence is.

References:

Gill, FB; B. Slikas and F.H. Shulde

“Phylogeny of titmice (Paridae): 11 Species Relationships Based on Sequences of the Mitochondrial Cytochrome Gene”

The Auk 122 Jan 2005

Reudink, Matthew; et. al.

“Structure and Dynamics of the Hybrid Zone between Black-Capped Chickadee (Poecile atricapullus) and Carolina Chickadee (P. carolinensis) in Southeastern Pennsylvania”

The Auk 124 (2) 2007

Australian Aborigines Probably Ate Some Species of Birds into Extinction

March 21, 2016

Genyornis newtoni, a 500 pound flightless bird related to geese and ducks, roamed Australia during the Pleistocene.  Most scientists believe genyornis primarily ate plants, like its cousins; but a minority think it was carnivorous.  Supposed egg shells of this extinct bird occur frequently in the fossil record along with eggshells of the still extant emu (Dromaus novachellandiae) until between 50,000-45,000 years ago.  This is the time period when people first colonized the Australian continent.  A group of scientists examined 700 eggshells from 500 sites and determined that human exploitation of genyornis eggs led to its extinction between 53,000 BP-44,000 BP.  Many of the eggs were apparently cooked in embers–direct evidence humans were eating the eggs.  After this time period humans continued to eat emu eggs, but genyornis eggshells no longer occur in the archaeological record.  Emus were more resilient to human exploitation than the slower breeding, larger species.

However, a recent study casts doubt on the identification of the genyornis eggs.  The scientists who authored this paper suggest the alleged genyornis eggs are far too small to have been laid by a bird the size of genyornis.  These eggs are slightly smaller than emu eggs, and emus are much smaller than genyornis was.  They suggest the eggs thought to be from genyornis belonged to another extinct species, a bird in the progura genus that is related to the Australian brush turkey and the mallee bird.  This extinct species likely reached just 12 pounds.  They believe the data from the first study mentioned above strongly suggests man is responsible for the extinction of the progura species but does not explain how genyornis became extinct.  If this second study correctly identified the bird genus in question, than there are no known specimens of genyornis eggs.  The emu and progura eggshell fragments were found in arid sand dunes.  Genyornis probably lived in wetter more wooded environments where their egg shells didn’t survive the ravages of time.

Ancient%2Bextinction%2Bof%2Bgiant-Geolog

Illustration of megalania hunting a large (also extinct) bird known as Genyornis newtoni.  Humans probably overexploited them into extinction, but the evidence that aborigines cooked and ate their eggs may be a case of misidentified eggshells.

A red ochre painting, which depicts two emu-like birds with their necks outstretched

Archaeologists believe this Australian cave painting is of a Genyornis newtoni.  Paintings of other extinct Australian megafauna have been found in the same region.  It is estimated to be at least 40,000 years old.

The purported genyornis egg on the left has probably been misidentified.  Note how small it is compared to the genyornis leg.  Instead, eggs identified as being laid by Genyornis newtoni were probably laid by a species in the Progura genus.

Leipoa ocellata -Ongerup, Western Australia, Australia-8.jpg

A new study suggest the eggs belonged to an extinct genus related to this species–Leipoa ocellata, the mallee bird.

A recent statistical study does implicate overhunting by man as the reason for the extinction of Australia’s megafauna.  The authors of this study determined climate change could not have caused the extinctions.  Proponents for climate change models of extinction in Australia claim increasing aridity eliminated habitat for many species of megafauna including megalania, a land crocodile, a giant kangaroo, a giant echidna, a marsupial lion, and genyornis.  However, these extinctions took place during Marine Isotope Stage 3 (60,000 years BP-30,000 years BP), a climate stage that was less arid than the previous MIS 4.  All of these species survived the greater aridity of MIS 4 and its harsher condition but became extinct after man arrived on the continent.  The megafauna extinctions took place within less than 13,500 years after man’s arrival on the continent, supporting a protracted overkill scenario.  The authors concede that overhunting by man for some species in some regions may have resulted in a more rapid extinction in some cases, but overall it took millennia for aborigines to wipe out most of Australia’s megafauna.

References:

Miller, Gifford; et. al.

“Human Predation Contributed to the Extinction of the Australian Megafaunal Bird Genyornis newtoni”

Nature Communications 2016

Grellel-Tinner, Gerald; Nigel Spooner, and Trevor Worthy

“Is the “Genyornis” Egg of a Nihirung or Another Extinct Bird from the Australian Dreamtime?”

Quaternary Science Reviews 2016

Saltre, Frederick; et. al.

“Climate Change not to Blame for Late Quaternary Megafauna Extinctions in Australia”

Nature Communications 2016

 

The Little Salt Spring Fossil Site in Southwestern Florida

March 14, 2016

About 50 years ago, scuba divers discovered Little Salt Springs was not the shallow brackish pond everybody thought it was.  They were surprised to find it was 200 feet deep.  From an aerial view the lake is perfectly round, but underneath the surface it is hourglass-shaped with ledges that were above the water table until ~7,000 years ago.  Below 20 feet the water here has no dissolved oxygen, making it inhospitable to fish and microorganisms that would normally decompose organic material.  The conditions are exceptionally favorable for the preservation of animal bones and human artifacts.  The real estate company that owned the sinkhole and the land around it donated this scientifically significant site to the University of Miami.  That institution employed scientists who administered and studied the sinkhole for over 30 years.   Then, a few years ago, some budget-cutting troglodyte sold the site to Sarasota County, probably so the university can spend more money hiring football coaches, like Mark Richt.

Click to View Larger Map

Little Salt Spring is located on the outskirts of North Port, Florida, not far from Sarasota.

Picture

Illustration of Little Salt Spring.  There is no dissolved oxygen below about 20 feet, and therefore no bacteria, resulting in excellent preservation of ancient fossil remains and organic artifacts.

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Deer antler with 28 notches carved into it marking the 28 days of the lunar month.  It’s a kind of archaic Indian calendar. It was found in the sinkhole along with many other artifacts.

The most famous specimen discovered in Little Salt Spring is a giant tortoise (Hesperotestudo crassicutata) shell with a wooden stake stuck through it.  Archaeologists believe it fell on to a ledge that was above the water table at the time.  A Paleo-Indian killed the tortoise with a wooden stake, turned it on its back, and cooked the unlucky chelonian in its shell.  Despite the likelihood that overhunting by humans caused the extinction of this species, this is the only direct evidence that people exploited them.  Some researchers initially rejected this interpretation because the carbon date for the wooden stake didn’t match the radiocarbon date of the tortoise shell.  But improved radiocarbon dating techniques since then have confirmed the wooden stake and the tortoise shell are the same age.

A series of wooden stakes, now submerged, were planted above the ledge where the cooked tortoise shell was found.  Archaeologists think the stakes may have supported some kind of camouflage that hid the steep ledge.  Prey animals blundered or were chased off the precipice and became trapped on the ledge.  The stakes may have also supported rope ladders, so the Indians could climb down and kill the animal trapped on the ledge.

A National Geographic News article from 2009 mentions the butchered remains of a Jefferson’s ground sloth were found on a submerged ledge at this site.  This would be just the 2nd known case of human exploitation of a ground sloth in North America.  However, I can find nothing in the scientific literature about this specimen.  Although professors from the University of Miami studied this site for decades, they published just an handful of papers about it.  The volume of research they produced surprises and disappoints me.

Most of the human artifacts found at this site are early archaic.  Some of the most interesting include 4 non-returning boomerangs made of oak wood that date to ~9,000 years ago, a carved atlatl handle, a green stone pendant, and a notched deer antler used as a lunar calendar.  There are hundreds of archaic Indian graves where human remains have rested for over 5000 years.  The water table rose shortly after people were buried by the lake’s edge, resulting in excellent preservation–some skulls still have brain matter inside.

Scientists have identified the bones of mastodon, Jefferson’s ground sloth, saber-tooth, rabbit, wood stork, giant tortoise, gopher tortoise, Florida cooter, red-bellied turtle, an extinct species of box turtle, diamondback rattlesnake, and largemouth bass from Little Salt Spring.  Less than 5% of the site has been surveyed for subfossil remains and artifacts.  I’m sure the list would grow, if there was a concerted effort made by scuba-diving paleontologists.

During the late Pleistocene, Little Salt Spring was much farther inland from sea level than it is today.  Dry land extended for many miles into the Gulf of Mexico.  The composition of species suggests that when Indians first discovered this sinkhole it was a wetland oasis surrounded by arid sand hill savannahs dotted with a sparse tree canopy.

References:

Holman, J.; and Carl Clausen

“Fossil Vertebrates Associated with Paleo-Indian Artifacts at Little Salt Spring”

Journal of Vertebrate Paleontology 4 (1) September 1984

Wisner, G.

“Diving into Paleo-Florida”

Mammoth Trumpet 23 (1) 2008

 

 

 


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