Posts Tagged ‘K-T Impact’

Alligator and Heron

July 28, 2013

I once proposed that alligators saved all terrestrial life on earth.  An adult alligator establishes a territory and digs a deep hole in a marsh or swamp where water pools deeper than in the surrounding environment.  These gator holes help them survive droughts and cold fronts, and they also attract other aquatic animals such as fish, frogs, turtles, waterfowl, wading birds, raccoons and other mammals.  Following the fiery K-T impact 65 million years ago, all the dinosaurs died, but crocodiles and alligators along with the animals that sought refuge in their holes, survived.  Everything above ground literally cooked in the superheated atmosphere caused by the friction of asteroid fragments igniting oxygen.  I shared my hypothesis with a paleontologist, but she was skeptical.  She acknowledged that freshwater organisms suffered a lower extinction rate than dry land and marine species.  However, she didn’t think my hypothesis was testable.  Maybe, it’s an exaggeration to claim that alligators saved all  terrestrial life, but ecologists agree they play a crucial role in fostering wildlife populations in the modern day world.

Gator hole in the Big Cypress Preserve in Florida.

The presence of alligators is beneficial for heron and egret rookeries.  Herons and egrets nest in trees located in wetlands, particularly on islands surounded by alligator-patrolled waters.  Alligators do feed upon the occasional nestling that falls from the nest, but they also take a heavy toll on raccoons, opposums, and even bobcats that would otherwise swim to the island, climb into the rookery, and feast on the eggs or nestlings.  The herons in turn benefit the alligators because their manure fertilizes the water and this increases the abundance of fish.

Heron rookery in Venice, Florida.

alligator eating an opossum

Alligator tearing up a possum.  Possums are notorius egg-eaters.

The great blue heron (Ardea herodias) is one of the most spectacular birds of America, and they are common–I see them quite often everywhere.  Green herons (Butoroides stroutal) are supposed to be the most common heron, but I’ve only seen them a handful of times.   Great egrets (Cameroides albus) are about as common as great blue herons, though they seem more tied to larger bodies of water.  By contrast, I’ve seen great blue herons flying over busy highways and hunting in small creeks.  Little blue herons (Egretta caerulea) are supposed to be uncommon, but I’ve seen them more often than I’ve seen green herons.  I saw a yellow crowned night heron (Nyctocorax urolicea) for the first time this summer at Wakulla Springs, Florida.  It was shy and ducked into the weeds.

Great gray heron catching a European rabbit in the Netherlands.  Great blue herons also prey upon rabbits and rodents.  Audubon kept a great blue heron as a pet.  His children were upset when it swallowed their sleeping pet cat.

Yellow crowned night heron with a crayfish.

Scientists studying the Clarks Quarry fossil site near Brunswick, Georgia expressed surprise over the relative lack of abundance of alligator fossils, though the site yielded plenty of remains of aquatic birds.  Alligator fossils were found here, just not as many as one would expect.  Random chance may explain why there were fewer alligator fossils than expected, but I recently realized a possible alternative explanation.  Fossils from Clarks Quarry date to ~14,000 calender years BP.  This was before sea levels and the water table rose to  those of the present day.  Between ~30,000 BP-~7,000 BP, swamps and other wetlands where alligators thrive were rare relic habitats.  Moreover, winters were harsher and summers cooler, even in south Georgia during much of this era.  Alligator populations were at a low ebb in Georgia during the Ice Age.  Yet, they continued to live in low numbers wherever suitable habitat remained.  Alligators withstood the fire of the K-T impact and the icy dry conditions of the Pleistocene.  They are amazing survivers.

There is a Rare Paleocene Fossil Site at Ft. Gaines, Georgia

April 2, 2012

An outcropping of Paleocene fossils can be found at Ft. Gaines Georgia.  The Paleocene lasted from 65 million BP-55 million BP.

Science fiction stories featuring time-traveling heroes from the future often show them solving their own financial problems with knowledge of which stocks to pick.  This is a convenient, if overdone, subplot solution that gives the hero unlimited money without having to muddy up the plot by having the character engage in a mundane occupation.  If I could time travel to just 2 weeks ago, I could have invested in Ohio Arts, the makers of the Etch-A-Sketch.  Its price has tripled from $4 a share to $12 a share after the Etch-A-Sketch became the symbol of a flip-flopping presidential candidate.  The Etch-A-Sketch is a neat toy for kids who can draw a scene, shake it up to erase it, and start over.  This reminds me of a geological era–the Paleocene.

The famous asteroid collision that wiped out the dinosaurs occurred about 65 million years ago and is known as the K-T impact.  Scientists believe the impact cooked the atmosphere, and the only organisms able to survive were those burrowed underground or living in water.  100% of the dinosaurs and 57% of the megaflora became extinct.  Like an Etch-A-Sketch drawing, most life on earth simply vanished.  Crocodiles, turtles, birds nesting in burrows, fossorial mammals, insects, and plant seeds survived and provided the basis for a redrawing of the ecological picture.

Ferns thrive in ashy soils, and there was a lot of ash after the fires of the K-T impact.  They were the first plants to dominate the landscape when they grew their new shoots into an environment with no shady competition.  Seeds of surviving plants germinated, and plant species eventually evolved to fill new ecological niches left vacant by the mass extinctions.  The same was true for animals.  All animals alive today evolved from detritus feeders because for decades dead plant material formed the base of the food chain.

The rapid evolutionary response to the K-T impact makes the Paleocene a fascinating period of time for paleoecologists to study.  Unfortunately, most paleocene fossils in southeastern North America are almost a mile underground and inaccessible.  However, there are 4 small localities where the face of the land has eroded into Paleocene outcroppings.  A couple are in Mississippi, 1 is in Alabama, and the 4th is located in Ft. Gaines, Georgia.  For the layman there’s not much to get excited about here–the fossils consist of foraminifera (single-celled protozoa with shells) and pollen.  But for the paleoecologist these microfossils are thrilling.

Pollen and foraminifera reveal quite a lot about the environment of the Paleocene.  The Paleocene flora consisted of a strange mix of temperate and tropical species, though the former were probably adapted to much warmer temperatures than those of today.  Plants from the walnut, birch, and elm families grew side-by-side with those from the mango-cashew, balsa, sweetsop, palm, frankinscense, and tea families.  The Paleocene lasted for 10 million years, and the pollen record shows that plant diversity steadily increased by 15% until the PETM.  The PETM is an acronym for the Paleocene-Eocene Thermal Maximum.  For some undetermined reason average global temperatures suddenly increased by 10-20 degrees Fahrenheit, and CO2 levels in the atmosphere spiked too.  This either directly or indirectly caused the extinction of 38% of plant species and is known as the terminal Paleocene extinction event.  Scientists think there are several possible ecological causes for the floral extinctions:  The climate became drier to the detriment of water-loving species of plants, the increase in CO2 levels in the atmosphere may have favored some species of plants over others, and new species of animals evolved that the plants had no defenses against.  Scientists don’t think the climate changed faster than the plants could adjust their geographical range to, but this may have been a an indirect contributing factor.

Only 1 Paleocene vertebrate fossil has ever been discovered in southeastern North America.  In 1932 at Caddo Parrish, Louisiana while drilling a core for an oil well, workers accidentally hooked the skull of Ansinochus fortunatus–a kind of archaic ungulate.  Half of the southeast was under ocean water during the Paleocene, but uplands hosted an interesting cavalcade of primitive mammals, if we assume they were similar to those found at Paleocene fossil sites in other parts of the world.  Marsupials, monotremes, and multituberculates were common.  Multituberculates were a family of rodent-like mammals that lived in the tree tops of the Cretaceous but became extinct during the early Eocene.  Though they resembled rodents, they were not placental mammals and therefore not at all closely related to any extant family of mammals.  Insectivores were the evolutionary base for many placental mammals including the nyctertheridae (pre-bat) and tree shrews (pre-primate).  Condylarths were archaic hooved animals.  Extinct creodonts were the dominant meat-eaters along with primitive carnivores and carnivorous ungulates.  Pantedonts, uinitheres, and xenoungulates were the first large herbivores to evolve following the extinction of the dinosaurs.  The below link is an excellent source of information on Paleocene vertebrate life.

http://www.paleocene-mammals.de/pal_intro.htm

Reference:

Harrington, Guy; and Carlos Jaramill

“Paratropical Floral Extinction in the Late Paleocene-Early Eocene”

Journal of the Geological Society V. 164 2007 pp. 323-332