Archive for December, 2018

Late Pleistocene Megameanders

December 30, 2018

Glacial recession during the end of the last Ice Age caused dramatic changes in the climate and river drainages of southeastern North America.  All that melting Canadian ice released moisture into the atmosphere and average annual precipitation in the region tripled to an estimated 47 inches.  But average temperatures were still cooler than they are today and as a result evapotranspiration rates were lower. This increased precipitation and reduced evaporation caused rivers to meander more than they do today.  These supermeanders eroded scars that are still visible in satellite photographs.  Recently, scientists studied 6 paleomeander scars adjacent to the Oconee, Ogeechee, Black, Neuse, Pee Dee, and Congaree Rivers.  These rivers are located in Georgia, North Carolina, and South Carolina.

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Satellite photo of a paleomeander scar located along the Oconee River.  From the below referenced paper.

The scientists found these paleomeanders dated to between ~17,000 years BP-~11,000 years BP.  The scar next to the Oconee River was radio-carbon dated using a 17,000 year old pine log.  The supermeanders cut through the former braided channels that existed during the Last Glacial Maximum when rivers shrank and became clogged with sandbars due to aridity.  Eventually, when present day climatic conditions began to predominate, the supermeanders became cut-off from the main flow of the river.  For awhile they existed as oxbow lakes but then filled with clay and sand.  Scientists estimate the supermeanders were 2-5 times larger than modern meanders and the discharge was up to 4 times larger.  The typical flow was equal to a modern day 5 year flood event.  Scientists aren’t sure of the exact mechanism that caused supermeanders.  It was likely a combination of increased precipitation, low evapotranspiration rates, and seasonal monsoons.  The distance between the frigid air over the Laurentide Ice Sheet and tropical air was much smaller during the Ice Age, and this could have caused an increase in major storm events.

I hypothesize canebrakes and river bottomland forests really expanded during the supermeandering phase.  Canebrakes are a now nearly extinct environment consisting of pure stands of bamboo cane.  Canebrakes formerly occupied hundreds of square miles of river bottomland in the southeast, but European settlers cleared them for agricultural purposes.  They were the most fertile pieces of land in the region.  Canebrakes depend upon a complex regime of flood and fire.  Suppression of either results in the growth of river bottomland forests that shade bamboo out.  During the late Pleistocene canebrakes attracted herds of bison and horses which fed on the nutritious bamboo.  Newly arrived humans facilitated the spread of canebrakes by setting fire to the landscape.  However, canebrakes must have also existed along the braided rivers of the Glacial Maximum, perhaps growing on the sandbars in the middle of partially  dried up rivers. The supermeander oxbow lakes likely hosted the last North American capybaras and giant beavers (Casteroides sp.) before they were hunted into extinction by people.

Reference:

Suther, Bradley; David Leigh, George Brook, and L. Yann

“Megameander Paleochannels of the Southeastern Atlantic Coastal Plain, USA”

Paleogeography, Paleoclimatology, and Paleoecology July 2018

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2 Additional Extralimital Bird Species found in Florida’s Fossil Record

December 22, 2018

Some species of birds that lived in Florida during the Pleistocene no longer occur in state or even the region.  A few of the more notable species include the California condor, magpie, and trumpeter swan.  The extinction of the Pleistocene megafauna caused the extirpation of condors and magpies because they depended upon scavenging these animals as their most important food source.  Other species of birds periodically disappeared from the state due to sea level rise when their nesting habitat became inundated.  During some climate phases most of Florida became submerged, and a number of bird species simply never recolonized the state.  I was reading through an article on the University of Florida Museum website the other day and learned of 2 additional species that lived in Florida during the Pleistocene but no longer occur in state–the Manx shearwater (Puffinus puffinus) and the northern jacana (Jacana spinosa).

See the source image

The Manx shearwater is an oceanic bird that nests in burrows on islands.

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Manx shearwater range map.

The Manx shearwater is an oceanic bird that nests in burrows on rocky islands off the coasts of Canada and Europe.  They migrate to the South Atlantic during winter, flying over open ocean where they prey on small fish schooling near the surface.  They rest by floating on top of the water.  Scientists don’t know how they navigate to the same island colonies year after year.  During Ice Ages when sea level fell and the land area around Florida expanded there must have been some offshore islands that emerged and provided nesting sites for colonies of Manx shearwaters.  Islands emerged above sea level off the coasts of Georgia and South Carolina as well, and Ice Age oceans probably hosted higher populations of Manx shearwaters than exist today.  I couldn’t determine from the available information where fossil remains of this species were found in Florida.  It’s not listed in the Florida Museum of Natural History database and neither is the northern jacana, though I did find a paper that notes the presence of this species at 2 fossil sites.

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Northern jacana.

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Northern jacana range map.  Inundation by rising sea levels probably caused the extirpation of this species from Florida.

The northern jacana inhabits marshes.  This species of bird often walks on floating mats of vegetation while it hunts the small fish and insects it preys upon. Because it appears to walk on water, it is sometimes referred to as the Jesus bird. Fossils of this species have been found at 2 sites in Florida–Lecanto 2A and Leisey Shell Pit.  It likely became extirpated from Florida when rising sea levels eliminated its favored habitat.

 

 

There was No Such Species as the Fugitive Deer (Sangamona fugitiva)

December 16, 2018

During 1920 Oliver Hay, a noted paleontologist of that era, named a new species based on a tooth discovered in a Tennessee Cave 35 years earlier.  He believed it was from an extinct species of deer, and he gave it the scientific name of Sangamona fugitive because he thought it may have been common during the Sangamonian Interglacial, though most specimens of this proposed species came from deposits dating to the Wisconsinian Ice Age.  For the next 60 years scientists assigned additional specimens found at fossil sites located in Tennessee, Illinois, Maryland, and Iowa to this species.  The fugitive deer was thought to be a species intermediate in size between a white-tail deer and an elk.  However, during the early 1980s a paleontologist by the name of George Churcher looked at all the specimens assigned to this species and determined they were actually the bones of white-tail deer, elk, or caribou.  Some were from large white-tails and others were from small elk, explaining why they seemed to fall between the range of the 2 species.  Churcher declared Sangamona fugitive an invalid species.  No such animal ever existed.  Taxonomists refer to this as a nomen nudem or naked name because it was assigned to a non-existent animal.

I was unaware of Churcher’s study when I wrote about the fugitive deer in my book and in a few of my earliest blog entries.  His paper is buried in the middle of an obscure special bulletin of the Carnegie Museum.  I did come across this paper a few years ago, but I never felt motivated to write about it until now.  I’m in the middle of researching future topics for my blog and ran into a delay with a couple I had planned, so I finally decided to note this old mistake that originated from a long dead paleontologist.

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Most bones mistakenly assigned to the fugitive deer actually belonged to white-tail deer or elk.

The fossil record suggests there were just 4 species of deer living in southeastern North America during the late Pleistocene.  White-tail deer lived throughout the entire region.  Caribou and the extinct stag-moose (Cervalces scotti) periodically colonized the upper south during cooler climatic stages of the Ice Age.  Elk probably didn’t enter the upper south until 15,000 years ago.  Mule deer may or may not have occurred in western Arkansas.  A single specimen of the South American marsh deer found in Florida was probably a misidentified white-tail deer bone.  (See: https://markgelbart.wordpress.com/2013/02/28/sabertooth-cave-in-citrus-county-florida/ )

Reference:

Churcher, George

“Sangamona: the Furtive Deer”

Bulletin of the Carnegie Museum: Contributions in Memorial to John Guilday 1984

Homo sapiens is a Meat-Eater

December 9, 2018

An Hindu vegetarian didn’t like my blog post, “Native American Cannibalism and Dog-Eating,” (See: https://markgelbart.wordpress.com/2012/10/24/native-american-cannibalism-and-dog-eating/ ).  In the comments section he went on a long rant, explaining how humans are frugivores (fruit-eaters) and how humans aren’t anatomically built to eat meat.  He also has a pro-vegetarian website, promoting the same pseudo-science and misinterpretations of scientific facts that he wrote about in my comments section.  He claims meat-eating has been rare throughout human history, and our evolutionary ancestors ate a plant-based diet.  While it may be true that our very ancient ancestors lived on a diet of leaves and fruit with the occasional bird’s egg or insect, humans have evolved significant differences in dietary requirements and capabilities since then.  Meat is actually much easier for humans to digest than plant foods.  For example humans digest 97% of beef but just 89% of flour and 65% of most vegetables.

The ability of humans to digest large quantities of meat helped them survive the harsh climatic conditions of the Pleistocene when edible plant foods often became an unreliable or scarce resource.  If it wasn’t for man’s ability to eat meat, Homo sapiens would likely have become extinct. The added protein also contributed to brain development, making humans more intelligent.  The human brain is a large fatty organ that requires lots of protein.  The larger brain gave humans a crucial advantage over competing species.

The vegetarian’s response to my blog article made me curious about man’s diet during the Ice Age, so I searched for scientific studies of stable isotopic analysis of ancient human remains.  Scientists can determine the past diet of organisms by analyzing their bone chemistry.  I found 2 studies and was surprised to learn just how dependent upon meat at least some populations of humans were.

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Neanderthals relied heavily upon rhino and mammoth meat.

One study determined Neanderthals (H. neanderthalis) enjoyed a diet that was 80% animal and 20% plant.  The authors of this study looked at Neanderthal specimens from Troisiemo Cave in Belgium.  Apparently, Neanderthals relied heavily upon mammoth and rhino for their diet.  Other carnivores in the region fed more on horse, bison, and caribou.  Some scientists believed H. sapiens displaced Neanderthals because they had more flexibility in their diet.  But a 2nd study debunks this notion.  Scientists analyzed the bones of 3 anatomically modern human skeletons from Buran-Kay III, a rock shelter located in Crimea.  The specimens dated to between 37,000 years BP-33,000 years BP–shortly after the most recent date of Neanderthals.  They found these early humans also had a meat heavy diet, though they “possibly” ate more plant foods than Neanderthals.  This population of humans ate Saiga antelope, red deer, horse, and hare; but mammoth was their most important source of food. This study suggests H. sapiens competed with H. neanderthalis for the same food resources.

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The vegetarian claimed meat is not appetizing and kept comparing it to “roadkill.”  Meat looks appetizing to me.

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I’ll eat this roadkill every time.

Humans have continued to evolve since the Pleistocene.  The agricultural revolution has made plant foods more available, and the human body has evolved to eat more of them.  So, I don’t agree with the paleo-diet fad either.  I believe in eating a balanced diet that includes all 4 food groups.

References:

Drucker, D; et. al.

“Isotopic Analysis Suggests Mammoth and Plants in the Diet of the Oldest Anatomically Modern Humans from far Southeastern Europe”

Scientific Reports 2017

Wilburg, C.; et. al.

“Isotopic Evidence for Dietary Ecology of Late Neanderthals in Northwestern Europe”

Quaternary International 2015

Pleistocene Anhingas

December 3, 2018

I saw an anhinga (Anhinga anhinga) on my trip to Florida last week.  It was on the edge of a pond on the golf course behind my sister’s house.  I always see more wildlife there than I do in Florida’s much vaunted preserves and parks.  Anhingas belong to the Anhingidae family which includes just 1 genus and 4 species, but they have a wide distribution in the tropical to warm temperate regions of North America, South America, Africa, India, and Australia.  The Anhingidae family diverged from the cormorant family (Phalacrocoridae) early during the Miocene about 25 million years ago, and there is fossil evidence of anhingas in Florida during the late Miocene.  This early Florida anhinga goes by the scientific name of Anhinga grandis.  Anhingas probably originated in South America and later spread throughout the world.  There were 2 species of anhinga that co-existed in Florida during the Pleistocene–the extant A. anhinga and the extinct A. beckeri.  Anhinga remains have been recovered from 15 sites in Florida but A. beckeri fossils are known from just 4 sites.  Little is known about this extinct species, but it probably became extinct following the end of the last Ice Age when rising sea levels inundated important rookeries.  Anhingas often nest in colonies with herons and egrets, and the extinct species likely just never moved its breeding range to higher land as other species did.

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Anhinga range map.

Video of an anhinga swimming.

Anhingas are often seen drying their wings after swimming in the water while hunting for fish.  

Anhingas are also known as darters or snakebirds.  Note the snake-like head.

Anhingas hunt fish, amphibians, reptiles, and large invertebrates.  They swim underwater and impale their prey with their long bills.  When they return to shore they toss their prey up in the air and swallow it whole.  Crocodilians prey upon anhingas, but the birds are a dangerous adversary.  They aggressively fight predators with their bills, aiming for the eye.  A scout who guided the first academic ornithological expedition to the Okefenokee Swamp was blind in 1 eye because his pet anhinga had gouged it.  The anhinga is another amazing adaptable animal that has survived for millions of years.