Archive for October, 2016

6 Scariest Species to have Ever Lived in Georgia

October 30, 2016

6. The Hell Pigs

Vicious entelodonts lived on earth from the late Eocene to the mid Miocene (for over 20 million years).  They were 4 feet tall and reached weights of 930 pounds.

Entelodonts are known as hell pigs because their fossil remains represent a once terrifying animal that resembled a giant pig.  They occurred across most of the Northern Hemisphere, and there were many species over time.  Entelodonts existed between 37.2 million years BP-16.3 million years BP.  Although they resembled pigs, anatomical evidence suggests they were more closely related to the common ancestor of hippos and whales.  Enteledonts were 4 feet tall and weighed up to 930 pounds.  They were fast runners, and paleontologists believe they rammed into their prey, knocking their victims down and biting them until their bones were broken, probably similar to the way hippos kill humans in Africa today.  Fossil evidence of enteledonts has been found in Twiggs and Houston Counties in Georgia.  The tooth found in Houston County compares favorably with Archaeotherium, a once widespread species of enteledont.

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Entelodont tooth found in Bonaire, Georgia.  I am not the author who took a photo of this tooth.

4. (tie) The Giant Short-faced Bear (Arctodus simus) and the Saber-toothed Cat (Smilodon fatalis)

I can’t decide which 1 of these was more frightening.  Giant short-faced bears were on average as large as Kodiak bears–the largest subspecies of brown bear ( Ursus arctos ).  However, they probably made a lot of noise and could be easily detected and avoided.  Saber-tooths were ambush predators and could sneak up on prey in the dark or in thickly vegetated habitat.  Arctodus was much larger, weighing about 1000 pounds compared to ~350 pounds for Smilodon.  But the latter was very powerful and sported fangs.  Fossil evidence of this big cat has been found in all of the states bordering Georgia.  Fossil evidence of Arctodus has turned up in an Alabama county adjacent to Georgia as well as several sites in Florida.  Both undoubtedly once ranged into Georgia.

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Giant short-faced bear and saber-toothed catThe illustration of this saber-tooth is inaccurate.  Smilodon had a bob-tail and their forelimbs were much more powerfully built than depicted here.

3. Appalachiosaurus

 

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Appalachiosaurus terrorized upstate Georgia during the late Cretaceous.

Appalachiosaurus was a species of tyrannosaur that lived on the eastern side of the Western Interior Seaway during the late Cretaceous (~80 million years BP-65 million years BP).  They were the top land predator, probably hunting hadrosaurs or anything else they could catch.  Fossil evidence of this species has been excavated from Hannahatchee Creek near Columbus, Georgia.  The type specimen, a nearly complete skeleton, was found in Alabama.

2. Deinosuchus rugosus

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Evidence suggests Deinosuchus rugosus ate tyrannosaurs.

This extinct crocodylian, a relative of alligator ancestors, grew to an estimated 36 feet long and weighed up to 17,000 pounds.  They were large and powerful enough to seize and drag a tyrannosaur into the water, and there is some fossil evidence they preyed upon them.  They likely ate dinosaurs as a significant part of their diet.  Fossil evidence of this species has also been found in Hannahatchee Creek as well as the Chattahoochee River in Georgia.

1. Man (Homo sapiens)

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Homo sapiens is clearly the scariest species to have ever walked on earth.  Here is a photo of an atomic bomb mushroom cloud.  Humans can wipe out entire cities with nuclear weapons.

Human beings construct weapons of mass destruction capable of turning livable habitat into uninhabitable wasteland.  I can’t think of anything scarier than that.

Shell Bluff, Burke County, Georgia

October 24, 2016

40  million years ago, the entire coastal plain of southeastern North America was below sea level.  In Georgia sea shore occurred along a line that roughly corresponds with the latitudes of Columbus, Macon, and Augusta.  Rich zones of zooplankton nourished near shore oyster beds populated by a species that grew up to 20 inches in length. Fossils of this extinct giant oyster ( Crassostrea gigantissima ) are exposed at many locations along the ancient shoreline wherever rivers or creeks erode into Eocene Age formations.  Perhaps the best exposure can be found at Shell Bluff in Burke County, Georgia.  This site is a 30 minute drive from my house, and I have long wanted to visit it, but alas it is private property not generally open to the public.

Map of Georgia highlighting Burke County

Location of Burke County, Georgia.  Shellbluff is located on the eastern boundary by the river.  A small local community is named after the site.

http://digitalcommons.gaacademy.org/cgi/viewcontent.cgi?article=1012&context=gjs

I couldn’t find a photo of Shellbluff that I could directly link to my blog, but the above linked Georgia Journal of Science article has a nice picture in the pdf file.

Old photo of the fossil oyster bed at Shell Bluff.

crassostrea gigantissima_griffins_landing_savannah_river_burke_co_ga_alan_cressler_2, I_AMC1300

Look at the size of the extinct Crassostrea gigantissima. A chemical analysis of these giant oyster shells determined a cool shift in climate occurred during the late Eocene.  Average winter sea surface temperatures were the same then as they are today, but summer sea surface temperatures were 3-12 degrees F cooler than those of today.

The bluff is 150 feet high and reportedly the giant oyster shell beds are 80-100 feet from the Savannah River.  The soil near the bluff consists of limestone and sandy marl, and it is rich in calcium.  Because of the unique microclimate and calcium-rich soil, there is a natural community quite different here from the surrounding fire-adapted longleaf pine/turkey oak sand hills.  This natural community is known as a bluff forest with northern affinities or as some other botanists refer to it, a mesic slope forest.  The steep slope and cooling river protect this forest from fire, and the north-northeast exposure helps keep temperatures cooler than in the surrounding terrain.  Many of the plants growing here are disjunct populations of species more commonly found in the Appalachian Mountains or the Midwest.  Species of northern affinities present at Shell Bluff include green violet, tall bellflower, wild ginger, black cohosh, ravine grass, and black walnut.  The overstory consists of white oak, beech, pignut hickory, basswood, and black walnut.  Dogwood, red buckeye, hop hornbeam, 2 species of pawpaw, beautyberry, Carolina buckthorn, and redbud comprise the midstory.  3 of these species–red buckeye, Carolina buckthorn, and red bud–are notable calciphiles (plants that prefer calcium rich soils).  Some rare plants grow here too such as the Ocmulgeee skullcap.

Ocmulgee Skullcap for sale buy Scutellaria ocmulgee

Shellbluff is home to this rare mint–Ocmulgee Skullcap (Scutellaria ocmulgee).

William Bartram found mock orange (Philadelphus inodorous) growing at Shell Bluff in 1775.

John Bartram and his son, William, visited this site in 1765, and William returned 10 years later.  They saw the forest before it was ever logged.  The virgin timber consisted of white oaks, beech, and sweetgum with trunks that were 5 feet in diameter.  Cypress trees were over 6 feet in diameter.  There are probably few, if any, trees this large at the site today.  Bartram included tupelo, tulip, and mulberry in his list of tree species here.  I’m not sure, if these species still exist on the site since it has been logged.  Other rare plants that Bartram cataloged may also be extirpated from the site including mock orange, leather wood, Carolina spice bush, and ginseng.

Bluff forests with northern affinities are relic habitats that represent natural communities formerly more widespread in the surrounding region.  Oak and beech forests with cool climate associates likely formed a more continuous range throughout the mid to deep south during cool moist interstadials.  (Though interstadials were warm phases of climate within Ice Ages, average temperatures were still cooler than those of the present day.)  But these mesic forests also waned during arid cold stadials when grasslands and scrub habitat expanded.  River bluffs have provided refuge for this type of forest during both hot and cold extreme shifts in climate, probably for millions of years.

Reference:

Edwards, Elliott

“Shell Bluff–A Fossiliferous Ridge, The Site of the Extinct Oyster Crassostrea gigantissima and History of its Identification”

Georgia Journal of Science 74 (2) 2016

 

 

Sisters Eating Each Other’s Babies

October 18, 2016

Animals are not people too, contrary to the emotional assertion of some humans who weigh the rights of animals as greater or equal to that of men.  Almost all vertebrates exhibit some behavior patterns that if they were human would get them incarcerated in prison or a mental hospital.  Imagine a mother, usually a vegetarian, who regularly attempted to break into her sister’s house to feed upon her babies.  A case such as this would horrify everybody, and it would attract national attention.  But it is normal behavior for the black-tailed prairie dog ( Cynomys ludovicianus ).

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39% of prairie dog litters are cannibalized by lactating sisters.

Prairie dogs are primarily vegetarian; feeding upon wheat grass, buffalo grass, scarlet globemallow, rabbit brush, thistle, prickly pear cactus, and roots.  They occasionally eat insects and bison manure as well.  However, lactating females regularly seek out and cannibalize their sister’s pups.  Prairie dog cannibalism is the leading cause of mortality among pups–39% of baby prairie dogs are killed by their aunts.  Cannibalism occurs among other species of squirrels but at a much lower rate, and the act is executed by unrelated squirrels.

John Hoogland, the scientist who first studied prairie dog cannibalism, believes this cannibalistic behavior evolved for 5 reasons.

  1. Removal of future competition.
  2. Extra nutrition for lactating females.
  3. Less competition for foraging.  After a prairie dog loses her pups she will stop defending her territory and range farther for food.
  4. Females without pups spend more time scanning the landscape for predators, thus helping the security of the entire prairie dog town.
  5. Lactating females who lose their pups are less likely to prey on other prairie dog pups

Prairie dogs are a keystone species that co-existed with bison in the North American short grass prairie region for millions of years.  Studies show prairie dog activity greatly benefits the environment.  Their burrows help drain the soil preventing erosion.  They churn up soil, increasing fertility, and prairie dog towns host a variety of plants that are more nutritious for grazers than areas without prairie dogs.  Yet, most local governments consider prairie dogs a pest and have mandatory eradication programs.  Prairie dogs wrongly get blamed for denuded ranges that have been overgrazed by livestock.  There is also a myth that cows and horses can break their legs in prairie dog holes, though an example of this has never been documented.

The late Larry Haverfield protected prairie dogs on his 7000 acre ranch because he recognized the benefits they provided.  In 2006 the Kansas authorities ordered him to poison the prairie dogs on his land and when he refused, they threw him in jail.  A court injunction stopped the local county in Kansas from eradicating the prairie dogs on his property, and now his land serves as an environmentally friendly refuge where once common but now rare prairie wildlife still thrives.  The endangered black-footed ferret, a predator of prairie dogs, was re-introduced here.  Hopefully, science will some day overcome the myths and misinformation so many ranchers have about this important beneficial species.

Reference:

Hoogland, John

The Black-tailed Prairie Dog: Social Life of a Burrowing Mammal

University of Chicago Press 1995

 

Stuff I Find While Looking up Other Stuff

October 14, 2016

Many of my blog topics originate from information I gathered while researching other blog topics.  My most recent essay is a good example of this process.  I recently reread Rise and Fall of the Third Reich by William Shirer, and this author mentioned another book that interested me.  The Wall  about the Jewish uprising in Warsaw during 1943 is a collection of journal excerpts edited by John Hersey.  I looked for this book on amazon.com and discovered another book by the same author, but this 1 was about bluefish.  I ordered that book too, and it inspired me to write my recent essay about bluefish.  While researching for more information about bluefish, I recalled John Lawson’s brief description of this species in his book– A New Voyage to Carolina. I have this book on my bookshelf, but it was quicker to look for this passage online.  When looking for this passage, I discovered a paper that analyzed the content of Lawson’s book.  I’ve always been fascinated with A New Voyage to Carolina  because it is the very first natural history book ever written in North America.  So I read this paper and learned the “grampus” described by Lawson is an alternative archaic name for Risso’s dolphin.  I became curious about this little known species and decided to write a blog entry about it.  This species is poorly studied and I couldn’t find much about it.  However, I did come across a study that determined Heinrich events caused annual mass whale strandings, and this led to my previous essay, an entry that is far more interesting than any I could have written using the meager scientific literature focused on Risso’s dolphin. The internet is a nearly infinite encyclopedia, and it’s easy to get distracted, but I think these distractions lead to my most interesting blog entries.

Risso’s Dolphin

Illustration of Risso’s dolphin.  Note the scars from its battles with squid–its favorite food.

Risso’s dolphin ( Grampus griseus ) diverged from an ancestor that also gave rise to false killer whales ( Pseudorca crassidens ) about 6 million years ago.  Risso’s dolphins usually live well offshore in pods of 10-50 individuals, and their diet almost exclusively consists of squid.  Adults have many scars, resulting from battles with the tentacular cephalopods, whose suckers tear away flesh.  According to Wikipedia, Risso’s dolphins hybridize with bottlenosed dolphins ( Tursiops truncatus ) in captivity.  This seems odd because they are not that closely related. Risso’s dolphin is little studied, and as I mentioned above, I couldn’t find enough about them to write a more compelling essay, but at least they led me to the paper that inspired Monday’s blog entry.

Reference:

Hair, R.

“John Lawson’s Observations on the Animals of Carolina”

The North Carolina Historical Review 2011

Heinrich Events Caused Annual Mass Whale Strandings during the Pleistocene and early Holocene

October 10, 2016

Despite the universal chorus of politicized alarmists, earth is currently experiencing a period of relative climatic stability compared to the dramatic climatic fluctuations that occurred during the Pleistocene.  The presence of vast ice sheets in the northern hemisphere contributed to this ancient climatic instability.  Glaciers blocked rivers, creating huge glacial lakes.  Warm spikes in average annual temperatures weakened the ice dams and caused breaches.  Massive outflows of frigid fresh water and icebergs periodically flooded into the North Atlantic, shutting down thermohaline circulation.  The gulf stream normally carries tropically heated water into the North Atlantic, and this keeps overall climate temperate, but after torrents of cold fresh water stopped this process, average annual temperatures dropped as much as 15 degrees F in less than a decade, precipitating severe stadial conditions that lasted for hundreds or even thousands of years. These meltwater pulses are known as Heinrich events, named after the scientist who first recognized this cycle.

During Ice Ages warm stages of climate cyclically caused glacier dams to burst, releasing massive amounts of cold fresh water plus icebergs.  This shut down the North Atlantic Gulf Stream which brings tropically heated water north, resulting in a sudden decline in average annual temperatures.

A graph showing average annual temperature fluctuations over the last 100,000 years from data gleaned inside Greenland ice cores.  Cyclical Heinrich Events caused the sudden declines in temperatures.

I assumed Heinrich Events severely disrupted marine ecosystems, causing decisive population declines in most fish and other ocean fauna, though a few species may have benefitted from reduced competition or other factors.  But I thought there would be no paleontological evidence because preservation and detection of animal remains during brief time intervals in marine environments seemed unlikely.  However, a recent paper highlights evidence that Heinrich Events were detrimental to marine life.  Scientists found this evidence in a seaside Sicilian cave named la Grotta Dell’Uzzo.  This cave had previously revealed the Pleistocene remains of mammoth, rhino, lion, red deer, and wild boar.  Humans have also periodically occupied this cave from the late Pleistocene through the Holocene, and scientists have excavated human skeletons, artifacts, and food remains.  Chemical analysis of human bones found in the cave helped scientists determine the diet of the hunter-gatherers who occupied the cave during the early Holocene.  They ate red deer, wild boar, shellfish, fish caught near shore (such as grouper), acorns, grapes, and wild beans and peas.  However, 1 human specimen and 1 red fox bone, dating to 8200 BP, revealed an interesting difference. Both the human and the fox ate unusual quantities of whale meat during their lifetimes.  Red foxes don’t normally include whale meat in their diet, and humans from other generations of cave dwellers here hardly ever exploited this resource. Moreover, whale bones with butcher marks on them were found associated with the human and fox specimens in the same strata.  The scientists who examined this evidence determined humans exploited climate-driven whale strandings at this locality.

Mass stranding of pilot whales in Australia.  Heinrich Events disrupted marine ecology and caused high annual mortality among many species of whales.

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Evidence of early Holocene mass whale strandings was discovered in this seaside cave in Sicily, known as la grotto dell’Uzzo.

The last major Heinrich Event occurred 8200 years ago, following the final dissolution of glacial Lake Agassiz in Canada.  This massive meltwater pulse disrupted fish migrations and reduced fish populations, making it harder for many species of whales to find prey.  Stressed and malnourished whales are more likely to strand on beaches.  The Gulf of Castallammare, adjacent to la Grotto Dell’Uzzo, is an acoustic dead zone difficult for whales to navigate.  This is where frequent, probably annual, whale strandings occurred for centuries, and the evidence suggests humans and foxes exploited this resource.  Based on the zooarchaeological record, the most common species of whales stranded here were pilot whales (Globicephala melus), Risso’s dolphin ( Grampus griseus ), and short-beaked common dolphin ( Delphinus dolphio ). Frequent whale strandings likely occurred worldwide following Heinrich Events.  Off the coast of North America dire wolves, bears, and other large carnivores scavenged this wealth of protein during the Pleistocene.  There were certain spots, such as the 1 in Sicily, where carnivores learned to regularly search for this bounty.  Carnivore populations may have been higher near the coast due to this additional resource.  Unfortunately, evidence of these sites were long ago inundated by rising sea level.

Reference:

http://www.nature.com/articles/srep16288

Marcello, Mannino; at. al.

“Climate-driven Environmental Changes around 8200 Years Ago Favored Incidences of Cetacean Strandings and Mediterranean Hunter-Gatherers Exploited Them” 

Scientific Reports 2015

 

Pleistocene Bluefish (Pomatomus saltatrix)

October 4, 2016

The bluefish, a powerful fast-swimming predator, is popular with many saltwater anglers because it fights hard when hooked.  They inhabit tropical and semi-tropical waters year round, but a segment of the American population migrates as far north as Nova Scotia when water temperatures exceed 64 degrees F during summer.  They prey on small fish, such as silversides, menhaden, sand eels, and their own young; as well as squid and sea worms.  The blues prefer shallow coastal waters and especially like to congregate the down current side of shoals between narrow gaps of land. Here, they wait in underwater holes for  small fish swept over submerged sandbars by strong currents. Populations of bluefish have historically and mysteriously fluctuated, and like most other marine species of fish are in danger of being overfished.

There is little fossil evidence of bluefish dating to the Pleistocene.  In the ocean fish remains usually won’t survive the ravages of time.  But a few middens do hold evidence of bluefish.  The Old Oak midden in Florida–a mound consisting of shellfish and vertebrate bones made by generations of the Weeden Island Culture–contained bluefish bones.  This culture existed from 1200-200 years ago. However, bluefish didn’t suddenly pop into existence then.  Without paleontological evidence it’s still possible to learn something interesting about a species’ past by studying their DNA. One genetic study determined western Atlantic bluefish populations off the coast of America have been reproductively isolated from eastern Atlantic and Mediterranean populations for 480,000 years.  And there are 2 populations of bluefish living in the Mediterranean Sea that have been reproductively isolated from each other for over 100,000 years.  The isolation of these 2 Mediterranean populations is associated with barriers that formed during Ice Ages.  These underwater geographic barriers still remain.

The divergence of the western and eastern bluefish populations occurred during Marine Isotope Stage 13a–a warm peak with a cold split.  Deep waters of the mid-Atlantic are the present day barrier that keeps these 2 populations reproductively isolated from each other.  Blues prefer shallow water and are unlikely to traverse deeper waters where baitfish may be scarce over large areas.  The last time a population of bluefish traversed the mid-Atlantic could have been a summer migration that may have gone off course chasing a massive school of menhaden.  It seems likely this occurred during a stadial when the distance between the continents was smaller.  Perhaps a normal summer migration swam into unseasonably cool water that occurred because the Gulf Stream suddenly shut down, and they headed east because they became disoriented.  Bluefish probably originated long before the Pleistocene, before continents were as widely spaced as they are today.

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Map of the Georgia bight.  The shaded area was above sea level from ~80,000BP-~7,000 BP.  Bluefish prefer shallow coastal water, so their range must have been shifted off the continental shelf during Ice Ages.

Bluefish range map.  DNA studies suggest American and eastern bluefish populations have been isolated from each other for 480,000 years.

Bluefish

John Lawson said bluefish taste like salmon.  I’ve never caught one, nor have I ever seen one in the grocery store.

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School of bluefish.

During glacial periods when much of the continental shelf was above sea level, bluefish must have inhabited bays and river mouths.  There were steep drop-offs adjacent to the continental shelf with deeper water than bluefish prefer.  The Gulf Stream shut down during stadials (the coldest periods of Ice Ages), and there would have been no bluefish migration north because the water temperatures were too cold.  Bluefish range was restricted to tropical/semi-tropical waters during stadials.  The northern bluefish migrations resumed during interstadials when the Gulf Stream periodically restarted and began carrying tropically heated water farther north again.

References:

Hersey, John

Blues

Vintage Books 1987

Miralles, Laura; et. al.

“Paleoclimate Shaped Bluefish Structure in the Northern Hemisphere”

Fisheries 2014