Survival of the Fittest and Dwarfism–A Paradox

September 4, 2015

The concept of natural selection forms the basis for the Theory of Evolution.  Environmental forces select the fittest members of each population to pass on their genes.  Most people think survival of the fittest means selecting the biggest, fastest, and strongest; and that is often true.  However, insular evolution (the evolution of species on islands) shows that survival of the fittest can mean the opposite as well.  During the Pleistocene many species of megafauna became stranded on islands.  Islands are often devoid of large predators.  Megafauna evolved to a greater size in response to predation, so without the presence of predators, there was no longer selective pressure toward a larger size.  Smaller individuals were just as likely to survive.  Moreover, these smaller individuals had an advantage on islands where less food was available.  On continents megafauna could migrate to different regions when forage became scarce, but they didn’t have this luxury on islands.  Smaller individuals were more likely to survive during times of scarcity because they required less food.  This explains the tendency toward dwarfism among Pleistocene megafauna that lived on islands.

During the Pleistocene there were 8 species of dwarf ground sloths living on Cuba, 7 on the island of Hispaniola, and 1 on Puerto Rico.  Megaloncus rodens was 1 of the species that lived on Cuba, and it grew to 200 pounds.  By contrast the smallest species of continental ground sloth grew to 500 pounds.  Dwarf ground sloths survived in the Caribbean until as recently as 4700 BP, about 1200 years after humans colonized the region.  Humans must be responsible for their extinction because there was no major climatic change during this time period.

Skeletal mount of Caribbean dwarf ground sloth (Megalocnus rodens) next to a paleontologist in 1920.  All continental species of ground sloths were larger than men.

Full-sized Columbian mammoths (Mammuthus colombi) swam to the Channel Islands off the coast of California and eventually evolved into a dwarf species known as Mammuthus exilis.  Evidence suggests they arrived as early as 250,000 years BP and survived 2 complete glacial/interglacial cycles but became extinct when men found the island.  The late surviving population of mammoths living on Wrangel Island off the Alaskan coast were not a dwarf species, but those living on St. Paul’s Island off Alaska were.

Each island in the Mediterranean Sea had its own species of dwarf elephant or mammoth.  Dwarf elephants lived on Cyprus, Malta, Sicily, Sardinia, and Stylus (now underwater).  Dwarf mammoths lived on Crete.  Every time sea level fell in response to glacial expansion, new waves of elephants colonized these islands, and all evolved into dwarf species.  Distances were shorter between the mainland and the islands during glacial expansions, and it was easier for these large animals to swim there.  Some of these dwarf species were still large animals, weighing as much as 500 pounds, but others reached heights of just 3 feet tall.

Size comparison between human, full sized elephant, and 2 different species of dwarf elephants.

Some Mediterranean islands also hosted populations of dwarf hippos.  Sicily, Malta, Crete, and Cyprus were home to 4 different species of dwarf hippos respectively.  There were 3 different species of dwarf hippo living on Madagascar until 1000 years ago when humans wiped them out.

Hippo in Middle~Late Pleistocene Mammalian by sinammonite

Artist’s depiction of extinct Mediterranean dwarf hippos.  P. minor lived on Cyprus, H. melitensis lived on Malta, H. creutzburgi lived on Crete, and H. pentlandi lived on Sicily.

Stegodon floresiensis insularis was a dwarf species of elephant that lived on the Indonesian island of Flores.  It shared the island with a dwarf hominid, Homo floresiensis, known famously as the hobbit.  This hominid likely evolved from Homo erectus, but in isolation from the parent population became a dwarf species.  The hobbit grew to 3.5 feet tall and had the brain capacity of a chimpanzee.  Nevertheless, the area of their brain associated with language was well developed, and they may have been as intelligent as modern humans because their ratio of brain capacity to body size was similar.  They hunted dwarf stegodons.  Komodo dragons and even marabou storks were a threat, especially to juvenile hobbits.  Homo floresiensis lived as recently as 14,000 BP.

Artist’s depiction of real life hobbits (Homo floresiensis) battling marabou storks on the Indonesian island of Flores.

Ground sloths, elephants, and hippos were/are excellent long distance swimmers.  That explains how they colonized islands.  The ancestors of the hobbit either built rafts or accidentally rafted to the island on flood debris.  If they built rafts, they may have forgotten the technology after several generations.

There are over 200 medical causes of dwarfism, and some traits that cause it can be inherited.  A human dwarf is defined as an adult less than 4’10” in height.  Some kinds of dwarfism in children can be treated with growth hormones and drugs that stimulate appetite.  Parents fear their children will face societal prejudice, if they don’t reach a “normal” height.  Few realize the trait for dwarfism could potentially be favorable for natural selection, if environmental conditions on earth deteriorate.  The traits that favor future survival of the fittest on this island earth can’t be predicted.

What happened when James Lusted, who stands just 3ft 7in tall, took his fiancee for a romantic meal at a Harvester in Cardiff?

If the world suffered a severe shortage of food for millennia, human evolution would tend toward dwarfism.  Humans with smaller body size have an  advantage in environments with less food.

References:

Muhs, Daniel; et. al.

“Late Quaternary Sea-Level History and the Antiquity of Mammoths (M. exilis and M. colombi) on the Channel Islands National Park, California, USA”

Quaternary Science Review May 2015

Poulakatis, Nikos; et. al.

“Ancient DNA Forces Reconsideration of Evolutionary History of Mediterranean Pygmy Elephants”

Biology Letters 2006

Humans Co-occurred with Real Dragons (Varanus sp.) in Pleistocene Australia

August 28, 2015

Giant monitor lizards roamed Australia during the Pleistocene.  Scientists are aware of 3 species of giant lizards that lived in Australia: the Komodo dragon (Varanus komodensis), a larger undescribed species, and megalania (Varanus priscus).  Komodo dragons still occur as a relic species confined to a remote island owned by Indonesia.  They grow to 6 feet long and have a venomous bite.  The undescribed species is poorly known from just 1 fossil site. Megalania is an extinct species that grew to over 20 feet long and also had a venomous bite.  Megalania remains have been excavated from 5 sites–Wyandotte, Cuddie Springs, Darling Down, Lake Eyre basin, and Colosseum Chamber.  Archaeologists are interested in knowing whether humans overlapped in time with megalania.  Humans arrived in Australia about 50,000 years ago.  The megalania remains from Cuddie Springs and Wyandotte may be less than 50,000 years old, but the dating at these sites is considered unreliable.  Now for the first time, scientists have found remains of giant lizards that unequivocally overlapped in time with humans.

Photo: Capricorn Caves

Photo taken inside the Capricorn Cave System, Australia.  The Colosseum Chamber, where the youngest reliably dated remains of a giant monitor lizard were found, is part of this cave system.

The last 0.5Ma

The Capricorn Cave system is located near Mt. Etna.

Size comparison between human and megalania, the extinct giant lizard that roamed Australia until humans colonized the continent.

Scientists excavated a bony osteoderm of a giant lizard from a cave deposit inside Colosseum Chamber.  This hard skin plate could’ve belonged to any of the 3 species of giant monitor lizards mentioned above, but was 4x larger than the osteoderm of the largest species of monitor lizard found in Australia today.  Komodo dragon remains are not known from Australian sites younger than the mid-Pleistocene, so this specimen likely belonged to 1 of the even larger species of Varanus lizards.  Most of the fossil remains in this cave deposit consist of owl prey–the inside of the cave served as an owl’s roost for thousands of years.  But bones of kangaroos and wallabies are mixed with the ancient owl pellets.  Scientists used carbon dating of charcoal and uranium-thorium dating of straw stalactites to estimate an absolute age for the level of the deposit where the giant lizard specimen was found.  The age of the deposit ranges between 51,000 BP-30,000 BP.  The giant lizard skin plate was found closer to the deeper older level of the deposit.

Although the temporal co-occurrence of humans and giant lizards in Australia doesn’t prove humans were responsible for the extinction of megalania, it shows overhunting by or competition with humans can’t be ruled out.   I have no doubt humans were the cause of megalania’s extinction.  Megalania existed for millions of years, yet didn’t become extinct until man arrived on the continent.  This species survived dozens of dramatic climatic changes, but they didn’t become extinct until man shows up.  That can’t be coincidence.

Environmental changes resulting from Ice Age aridity may have made it more likely that humans came into conflict with giant lizards.  I hypothesize that during mid-Pleistocene arid climate cycles, megalania outcompeted Komodo dragons for dwindling resources, explaining why there are no certain remains of Komodo dragons younger than 283,000 BP in Australia.  However, during the late Pleistocene when environmental conditions deteriorated, this time humans outcompeted megalania for the dwindling resources.  Moreover, megalania feared nothing–a disastrous behavior pattern for a large animal when confronted by men with projectile weapons.

Hominids did co-exist with Komodo dragons for 900,000 years in the region of what today is Indonesia.  These islands are lush and surrounded by abundant seafood.  Humans had no need to hunt big lizards for food here.  But the interior of Australia, especially during dry climate stages, was an harsh environment where humans were forced to hunt giant lizards for food.  Australian aborigines were the real dragon hunters.  A few men with atlatls could’ve easily dispatched the former top predators of Australia.  But I’m sure some people were killed and eaten by giant lizards before the real life dragons were eradicated from the land.

Reference:

Gilbert, Price; et.al.

“Temporal Overlap of Humans and Giant Lizards (Varanidae; Squamata) in Pleistocene Australia”

Quaternary Science Reviews October 2015

Pleistocene Apples (Malus sp.)

August 26, 2015

The ancestor of all domesticated apples (Malus domestica) still grows in montane forests located in Kazkhstan, Kyrgyztan, and western China.  A genetic study shows that all modern cultivated apples descend from Malus sieversii, a species that reaches 60 feet in height and grows among pine and oak trees as a co-dominant.  Traders brought seeds of M. sieversii to Europe where it readily crossed with the European crabapple, M. sylvestris.

Image

The mountains of Kazakhstan are where the ancestors of modern apples grow wild.

Photo of apples hanging from a tree.

Malus sieversii, 1 of the ancestors of the domesticated apple (Malus domestica).

Scientists believe the first apple trees evolved 10 million years ago and originally were a small sour fruit spread by defecating birds.  Elephants and bears favored larger sweeter mutations of this fruit, and they helped shape the evolution of a food that was more palatable to humans by also spreading the seeds in their dung.  Humans began cultivating apples 4000 years ago, and there are 3000 known varieties.  Just .03% of these varieties equals 70% of the world’s production.

There are an estimated 30-55 species of apples and crabapples in the Malus genus.  Scientists disagree over species status of some populations, and the propensity of species in this genus to crossbreed adds to the confusion.  Some species of crabapples are native to North America.  Mastodon dung excavated from the Aucilla River in Florida contained some crabapple.  None of America’s native crabapples, however, are comparable in quality to M. sieversii.  American crabapples rarely become a co-dominant tree like M. sieversii does in the mountains of southwest Asia.  Instead, they grow as an occasional tree in early stages of forest succession.

Apple trees descended from orchards planted by Europeans do occur throughout North America.  Circa 1974, I saw an apple tree that produced good quality green apples in an oak-dominated woods in Niles, Ohio.  The quality of most wild apples growing from seed reportedly varies.  Euell Gibbons wrote that most are not worth cultivating for fresh eating, but they do make good cooking apples.  All apples sold in grocery stores are the progeny of rare mutations.  Horticulturalists graft branches of the high quality mutations (known as scions) on rootstocks of uncultivated apple trees.  Trees are available with as many as 5 different varieties grafted on to them, but they are expensive.  Think hard before buying one of these 5 on 1 trees–insect pest can kill the tree thereby wasting money.

Extralimital Species of Pleistocene-aged Turtle Remains Found in the Upper Coastal Plain of Alabama

August 21, 2015

George Phillips wrote his Masters Thesis about Pleistocene-aged, non-mammalian, vertebrate remains found in creeks that flow through the Alabama and Mississippi upper coastal plain, a region also known as the Black Prairie.  Turtle shells are by far the most abundant remains found here because of preservational bias.  Turtle shells are very durable, helping protect the reptile while they are alive.  This durability also makes turtle shells more likely to survive the ravages of time when the bones of most other vertebrates disintegrate.  The results of his study show that several species of turtles have experienced interesting range redistributions since the end of the Ice Age.

Map of Alabama highlighting Dallas County

Dallas County, Alabama.  Bogue Chitto Creek, located in this county, yields many Pleistocene fossil remains.

Blanding’s turtle (Emboidia blandingii) is an endangered species presently restricted to the upper Midwest and parts of New England.  Most of this species’ present day range was under glacial ice during the Ice Age and thus uninhabitable.  Remains of Blanding’s turtle can be found in Pleistocene deposits as far south as the Black Prairie region in Alabama.  The presence of this species in Alabama suggests much cooler summers in the south during the Ice Age (though winters may have been as mild or just a little cooler than those of today). Blanding’s turtles may be unable to endure the long hot summers of the present day south, and this may be the limiting factor on their range today.

Blanding’s Turtle occurred in Alabama during the Ice Age but no longer ranges this far south.

Map of Blanding's Turtle

Present day range of Blanding’s turtle.  During the Ice Age about 70% of this territory was under glacial ice.

The wood turtle (Glyptemys insculpta) is another species of turtle with northern affinities that lived in Alabama (and other parts of the south) during the Ice Age.  This species may also be unable to survive long hot summers.

Plastron of an adult male.

Wood turtle.

Present day range map of the wood turtle.  During the Ice Age >90% of this range was under glacial ice and this species retreated south.  Longer hotter summers chased them back up north.

The only known Pleistocene-aged specimen of a musk turtle (Sternotherus carianitus) was found in Catalpa Creek, Alabama. Today, this species occurs to the west of this site.  Its rarity in the fossil record is unexplained and is probably just due to chance.  During the Pleistocene it apparently ranged further east than it does today.  Any number of unknown reasons could explain its extirpation from the most eastern parts of its range–disease, excessive egg predation, or competition with other species of turtles.

File:Carapace Sternotherus carinatus.JPG

Musk turtle.

Present day range map for musk turtle.  They formerly ranged a little further east during the Pleistocene.

There are 3 species of red-bellied turtles.  The Florida red-bellied turtle (Pseudemys concinna) is presently restricted to peninsular Florida, but Pleistocene-aged remains of this species have been found in Bartow County located in north Georgia.  The Alabama red bellied turtle (Pseudemys alabamensis) is presently restricted to extreme southern Alabama and Mississippi.  The red bellied turtle (P. rubriventris) is presently restricted to the mid-Atlantic states, but Pleistocene -aged remains of this species have been found in the upper coastal plain of Alabama.  It’s likely these 3 species of red-bellied turtles diverged from 1 continuous population that existed before the Pleistocene-Holocene transition when for some unknown reason they became geographically isolated into their present day ranges.  Their curious range distributions beg for a study of their molecular DNA.  The 3 present day species represent a speciation event that may have occurred as recently as 10,000 years ago.  I can’t determine why red-bellied turtles were extirpated from regions in between their present day ranges.  Did overharvesting by humans play a role?

Present day range map for the mid-Atlantic red-bellied turtle (Pseudemys rubriventris)  Remains of this species have been identified from Alabama.

Range map for Alabama red-bellied turtle.  The Pleistocene/Holocene transition was likely a speciation event that caused the 3 species of red-bellied turtles to diverge.

An extinct Pleistocene subspecies of box turtle (Terapene Carolina putnami) was common in Alabama’s coastal plain.  It was larger than present day box turtles but otherwise was similar.  There is no direct evidence of gopher tortoises (Gopherus polyphemus) from the Black Prairie region during the Pleistocene, but a Pleistocene-aged specimen of an indigo snake was found in Bogue Chitto Creek located about 40 miles north of the present day range of this tortoise.  Indigo snakes depend upon gopher tortoise burrows for shelter, so the presence of this snake suggests the presence of gopher tortoises nearby.  Gopher tortoises require sandy soils for burrowing.  They don’t burrow in the heavy upland clay soils so widespread in this region, but they may have burrowed in the alluvial (streamside) sands by the creek.  Gopher tortoises require open environments where they can feed upon short sun-loving plants.  The closure of the forest canopy would have caused their extirpation here.

Two scutes of the extinct giant tortoise (Hesperotestudo crassicutata) were found in this region.  Scientists puzzle over the co-existence here of the cold adapted wood turtle and Blanding’s turtle with the giant tortoise, a species they assume required a frost free environment.  I disagree with their assumption.  I hypothesize giant tortoises were capable of surviving freezing temperatures by either burrowing underground, like their closest living relative (the gopher tortoise), or by utilizing burrows dug by giant ground sloths. If giant tortoises could survive mild frosts as I believe, this species could have co-existed in the same region as cold-adapted species of turtles.  However, it’s just as likely their remains represent a warm climate phase, temporally distinct from when wood turtles and Blanding’s turtles roamed the creek bottoms.  As far as I know, none of these specimens has been radio-carbon dated.

Species of turtle remains found in Pleistocene deposits here that still occur in the region include snapping turtle, alligator snapping turtle, spiny softshell, stinkpot, painted, slider, and Alabama map turtles.

Reference:

Phillips, George

“Paleofaunistics of Non-mammalian Vertebrates from the Late Pleistocene of the Mississippi Black Prairie”

North Carolina State Masters Thesis 2006

Pleistocene Fossils Found in Southwestern Georgia and Southeastern Alabama

August 17, 2015

Geologists refer to the upper coastal plain of Alabama and southwestern Georgia as the “southern hilly Gulf Coastal Plain.”  The terrain alternates between irregular flat plains and gently rolling hills.  Many creeks and rivers erode through sediments of differing ages, exposing fossiliferous deposits that date from the Cretaceous to the Pleistocene.  During the Pleistocene a mosaic of deep forest, open woodlands, savannah, prairie, and wetlands covered this region.  Pollen from composite species (sunflowers, daisies, etc.) and pine increased during arid stadials while warmer wetter interstadials saw an increase in broad-leafed tree abundance.  Most of the plant species that occurred here then are still extant but the extinct Critchfield’s spruce; a temperate species that grew alongside oaks, walnut, and elm; was a component of this primeval wilderness.

Fossil hunters have collected mastodon fossils from Hannahatchee Creek in Stewart County, Georgia; Bogue Chitto Creek in Dallas County, Alabama; and the Warrior River in Alabama. (See:http://www.archeologyink.com/Ice%20Age.htm) Hannahatchee Creek is better known for Cretaceous fossils.  Most of the Cretaceous fossils found here are of marine species but teeth of nodosaurs, hadrosaurs, and tyrannosaurs have been collected from the stream bed.  A mastodon tooth was recovered about 1/2 mile west of Union, Georgia along Hannahatchee Creek, and a leg fragment of a mastodon was picked up upstream near Omaha.  I looked at a satellite image of this creek.  The owners of the land here allow a narrow strip of natural creek bottomland to grow, but most of the area appears to be pine plantation.  This is unfortunate because pine tree farms support very little wildlife.  During the Pleistocene the land bisected by Hannahatchee Creek could have consisted of cypress swamp, bottomland hardwoods, beaver meadows, grassy marshes, and/or canebreaks.  All of these environments would’ve made excellent habitat for semi-aquatic mastodons.

Hannahatchee Creek erodes through strata of different ages from the Cretaceous to the Pleistocene.

Mastodon Tooth

A mastodon tooth was found in Hannahatchee Creek.

Other Pleistocene remains have been recovered from at least a dozen small creeks that flow through the upper coastal plain of Alabama and Mississippi.  They include mammoth, horse, tapir, bison, white-tailed deer, long-nosed peccary, flat-headed peccary, giant beaver (Casteroides sp.), pampathere (a 300 lb armadillo), Jefferson’s ground sloth, Harlan’s ground sloth, gray fox, coyote, Florida spectacled bear (Tremarctos floridanus), giant short-faced bear (Arctodus simus), black bear, margay cat (Leopardus wiedii), and indigo snake.  The margay cat currently ranges throughout tropical forests in Central and South America, but it formerly lived in southeastern North America.  Fossil remains of the margay have been found at 2 sites in Georgia, 12 in Florida, and 3 in Mississippi and Alabama.  The latter 3 are not listed in the Paleobiology database, and I was unaware of these specimens when I wrote a blog post about this species (See: https://markgelbart.wordpress.com/2013/05/09/the-mystery-cat-of-pleistocene-georgia/).

Margay hanging from tree.

Margay fossil remains found in Alabama and Mississippi have not been posted on the paleobiology data base or faunmap.

Horse teeth dating to the Pleistocene are particularly abundant in these small creeks.  This suggests the presence of extensive grasslands in the Black Belt Prairie region that stretches across Mississippi and Alabama.  Disjunct areas of Black Belt Prairie are also found in south central Georgia.  Herds of horses attracted large predators such as dire wolf, saber-tooth, scimitar-tooth, giant lion (Panthera atrox), and jaguar.  There is some scant evidence of dire wolf in this region, but it is undocumented.  Fossil remains of the other 4 large carnivores have been found in adjacent regions, so it’s very likely they occurred on the upper coastal plain.  The first Panthera atrox fossil was found in northern Mississippi, and giant lions are part of Florida’s and South Carolina’s fossil record.  Jaguars fossil remains have been found in Georgia, Florida, and South Carolina. Saber-tooth remains have been excavated from northern Alabama, Florida, Tennessee, and South Carolina.  Scimitar-tooth bones were discovered in Tennessee and Florida.

George Phillips wrote an excellent Masters Thesis about Pleistocene fossils from this region, focusing on the non-mammalian species.  He did mention in his thesis that he would write in the future about ocelot (Leopardus pardalis) and dire wolf (Canis dirus) remains found here.  His thesis was written in 2006, yet I can find nothing on the internet about ocelot and dire wolf remains found from Alabama.  I assume this data is still unpublished.  However, an amateur fossil collector informed me that he collected a dire wolf tooth (along with mammoth, bison, and horse bones) from the Flint River in Georgia.  Dire wolves undoubtedly were a major predator of the upper coastal plain during the late Pleistocene.  As far as I know, no scientist has ever prospected the Flint River for fossils.

George Phillips thoroughly studied fish and turtle remains eroded from streamside fossil deposits.  The fish remains belonged to the same species that swim in Alabama creeks today–gar, bowfin, suckerfish, catfish, freshwater drum, and sunfish.  But some of the turtle remains belonged to species that are extinct or no longer live in the region.  That will be the subject of my next blog entry.

References:

Kurten, Bjorn and John Kaye

“Late Quaternary Carnivora from Black Belt, Mississippi”
Boreas 1982

Phillips, Georgia

“Paleofaunistics of Non-mammalian Vertebrats from the Late Pleistocene of the Mississippi-Alabama Black Belt Prairie”

North Carolina State Masters Thesis 2006

Shwimmer, David

“First Mastodont Remains from the Chattahoochee River Valley in Western Georgia, with implications for the Age of Adjacent Stream Terraces”

Georgia Journal of Science 1991

Snake Island, Brazil

August 12, 2015

Rising sea levels can cause speciation (the evolution of new species) by geographically isolating populations.  A small rocky island off the coast of Brazil is home to a perfect example of this.  Genetic evidence suggests the golden lancehead viper (Bothrops insularis) diverged from the jaracara (B. jaracara) approximately 2 million years ago when sea level rise isolated Snake Island from the rest of South America.  The ancestral population of snakes that became stranded on this island evolved different characteristics than the jaracara, a species that is widespread throughout the mainland of eastern South America.  Jaracaras primarily feed upon rodents, birds, and lizards; but there are no rodents on Snake Island.   Resident birds co-exist with the high density of snakes on this island.  The birds that live on this small island quickly learn to be wary and avoid snake predation.  So golden lanceheads depend heavily upon naïve transient birds that are just visiting the island.  Golden lanceheads evolved more potent venom, shorter fangs, and longer heads.  The more potent venom kills the birds faster, and the shorter fangs are less likely to break when the golden lanceheads hang on to a struggling bird.  By contrast jaracaras strike, release, and wait for their prey to die; thus avoiding injury.  The longer head on the golden lancehead allows them to switch to larger prey at an earlier age than a jaracara.  Golden lanceheads grow to almost 4 feet long, over a foot less than jaracaras.  The smaller size means they require less food.  They do also take lizards and other lanceheads.

Location of the island just off the coast of Brazil

Location of Snake Island.

Snake Island.

 

 

 

 

 

 

 

 

 

The golden lancehead snake (Bothrops insularis.)  Beautiful snake.

Jaracara (B. jaracara).  Genetic studies suggest golden lance heads evolved from this species about 2 million years ago when sea level rise isolated them from the parent population on Snake Island.  The fer-de-lance also belongs to this genus.

There are 37 species of snakes in the Bothrops genus, and all live in South America.  Every species has potent venom, but the golden lancehead’s venom is 5x more potent than that of the jaracara.  The venom causes extensive tissue damage.  People bitten by these vipers sometimes require amputation, but antivenin has reduced the rate of death.  Marlin Perkins of Wild Kingdom fame was bitten by venomous snakes several times during his career.  He wrote the only good thing about getting bitten by a venomous snake was that after the effects dissipated, he recovered completely.  There is no evidence a human has ever been bitten by a golden lancehead.  A legend that a lighthouse keeper and his family were killed by golden lanceheads in 1920 has never been confirmed.  There are 200 golden lanceheads on Snake Island.  They exist in the wild nowhere else in the world.

Reference:

Wuster, Wolfgang; et. al.

“Morphological Correlates of Incipient Arboreality and Ornithophagy in Island Pit Vipers and the Phylogenetic Position of Bothrops insularis”

Journal of Zoology 2005

The Hoyo Negro Fossil Site in Yucatan, Mexico

August 8, 2015

The Hoyo Negro (black hole) fossil site is a cave located near the coast of the Yucatan Peninsula in Mexico.  The cave entrance is still above water, but most of the cave has been submerged by a rising water table.  During the late Pleistocene this cave was well above sea level.  Rising sea levels following the end of the Ice Age flooded the cave, probably about 7,000 years ago.  Inside the pitch black cave, a steep cliff, nearly the length of a football field, doomed many large vertebrates.  The cave environment preserved these remains, and scuba divers discovered them in 2007.

hoyo negro

Location of Hoyo Negro Cave.

Dirk Settlement Americas 5

Diagram of the Hoyo Negro (Black Hole) Cave.

The remains were found in a giant underwater cave called Hoyo Negro.

View from inside the cave.

At least 26 large mammals, including 12 different species, fell off the cliff and died here.  (I wonder why they were wandering deep inside the cave.)  It didn’t happen very often.  The cave existed for tens of thousands of years–the total number of individual specimens amounts to an animal falling off the cliff once every thousand years or so.  Nevertheless, the composition of species provides enough information to assume the environment surrounding the cave during the late Pleistocene consisted of tropical forest, thorny scrub, and wetlands.  The extent of each of these types of environments varied over time depending upon climatic cycles.  The remains of 5 generalist species, 5 forest species, 2 scrub species, and 1 wetland species were found in the cave.  The generalist species include saber-tooth, cougar, bobcat, coyote, and human.  Fruit bats, tapir, spectacled bear, coati-mundi, and a new species of unidentified unnamed ground sloth were species that prefer (or preferred in the case of the extinct sloth) deep forest.  Collared peccaries and the extinct Shasta ground sloth inhabit (or inhabited) thorny scrub habitat.  The gompothere, an elephant-like species, lived in marshes.  The new species of ground sloth, yet to be described in the scientific literature, was related to Jefferson’s ground sloth, a species formerly found across most of North America.

Scuba divers also excavated fruit bat guano and plant macrofossils from the cave.  The guano contained seeds from species of fruit trees that still grow wild in the region.  Fruit bats deposited the seeds of nancete fruit (Byrsonima crassifolia), sapodilla (Manicara sp.), sea grape (Coccoloba sp.), and Thevetia peruviana, (a species that produced a pod edible for fruit bats but poisonous for humans).

Panama Bats Gallery Photo

The Great Fruit Bat (Artibeus lituras).  Fossils of fruit bats rest inside of Hoyo Negro.  Fruit bat guano also found in the cave contains seeds of the plants that grew in the surrounding Pleistocene environment.

Nancite fruit (Byrsonima crassifolia).  Seeds from this fruit were found in bat guano deposited in the cave.  South Americans use this fruit for flavoring ice cream and carbonated beverages.

HoyoNegro

A mostly intact human skeleton was found inside the cave.  It dated to ~12, 800 Calendar years BP.

Most people are more interested in the human skeleton found inside the cave than in the paleoecological evidence that fascinates me. The girl was about 15 years old when she fell (or was tossed off) the ledge.  She was barely more than 4 feet tall, and the morphology of her skull resembles that of other American skulls that date to 9000 BP or older.  Ancient American skulls are longer and their faces are shorter than those of modern native Americans.  Dental characteristics differ as well.  This led some anthropologists to believe the original human colonizers of the Americas were later displaced by the ancestors of native Americans.   However, mitochondrial DNA extracted from this specimen’s tooth suggests she is closely related to the ancestors of native Americans.  The difference in skull morphology between paleo-Americans and modern native Americans can be explained by evolution within the population over the past 10,000 years.

The human skeleton found in Hoyo Negro Cave dates to between 12,900-12,700 calendar years BP.  The gompothere specimen found next to it dates to between 36,000-33,000 calendar years BP.  But humans did overlap in time with gompotheres in Mexico.  There is evidence of humans killing a gompothere in western Mexico over 13,000 years ago.  See: https://markgelbart.wordpress.com/2014/07/23/humans-killed-gompotheres-cuvieronius-sp-in-mexico-13390-years-ago/

So…why was a teenaged girl wandering around a pitch black cave?  I suppose the most likely explanation is this: she was with a group of other reckless teenagers, some carrying torches, and she happened to step a little way away from the group and fell off the ledge.  Other explanations are almost as likely.  A jealous romantic rival, a jealous sibling, or mentally ill tribe member could’ve deliberately pushed her off the ledge. Did she kill herself because her lover rejected her?  Or did a rapist throw her off, so she couldn’t tell on him?  Maybe her pagan tribe thought returning her to mother earth would improve their luck.  Maybe she died from a parasitic infection and her pagan tribe thought she would be reborn, if they returned her to mother earth.  We will never be able to solve this mystery.

Reference:

Chatters, James. C; et. al.

“Late Pleistocene Human Skeleton and mtDNA from Mexico Links Paleoamerican and Modern Native Americans”

Science May 2015

Pleistocene Spiders

August 5, 2015

My fascination with the ecology of southeastern North America prior to man’s colonization of the region is frustrating.  Most of the data dating to this time period has been lost to the ravages of time.  I can make educated guesses about the appearance of pristine landscapes untrammeled by man, but this is little better than conjecture based on the pollen and fossil records from a handful of sites.  Many species of plants produce so little pollen they don’t even register in samples collected by palynologists.  And the pollen that is recovered usually can’t be identified below the genera level.  So we know that pine may have produced up to 50% of the pollen at 1 site during a certain time span, but we don’t know whether it was from jack pine, a cool climate species, or longleaf pine, a denizen of warm climates.  But at least we have some data about Pleistocene plant composition.  There are thousands of species of spiders living in the south today, yet I’m unaware of a single Pleistocene-aged site in southeastern North America where the remains of spiders have been recovered.  Spiders have been a vital part of land ecosystems ever since life crept out of the sea.  Nevertheless, there is no evidence of spider species composition dating to the Pleistocene.  Spiders are soft bodied creatures, and their remains get crushed into dust over time.  The remains of hard-shelled beetles, millipedes, and snails have been found in cave deposits located in the southern Appalachians because their hard exoskeletons can remain intact for millennia.  Spiders were also certainly abundant in caves during the Pleistocene, but evidence of their presence is gone.

It’s unfortunate that we know nothing about spider species composition and distribution in the south during the Pleistocene. Even modern spiders are poorly known. There are over 120,000 species of spiders in the world, but only a tiny fraction of these have been studied in detail.  The vast majority of spider species have yet to be described and named in the scientific literature.  Spiders vastly outnumber the scientists willing to study them. Spiders have high rates of reproduction, and therefore evolve rapidly, making them an ideal candidate for an evolutionary biologist to study.  During the Pleistocene many present day species already existed, but there may have been some now extinct species.  Some were evolutionary ancestors of present day species, while others may have left no descendants.  The abundance of certain species varies annually for unknown reasons, perhaps chance.  Below are some interesting species of spiders.

drawing

Artist’s depiction of a trapdoor spider (Ummidia sp.).  I can usually find 1 of these when I dig in my garden.

Common garden spider aka black and yellow argiope (Argiope aurantia).  They build big beautiful webs capable of catching small birds and bats.  Some natives use orb-weaver webs as fishing nets.  Spider webbing is incredibly strong.

Green lynx spiders  (Peucetian viridans) are beneficial for gardeners.  This individual caught a moth.  The larva of some species of moth eat through garden vegetables.

Spined Micrathena, Micrathena gracilis

A spined micrathena (Micrathena gracilis).

Diet of elusive red widow spider revealed by MU biologist

The red widow spider (Latrodectus bishop) lives in the Florida sandhills and feeds upon beetles.

The red widow spider inhabits the pine sandhills of Florida which were islands surrounded by ocean during the marine highstands of Pliocene and Pleistocene warm climate phases.  They construct funnel webs in rolled up palmetto leaves.  This ancient species specializes in capturing flying scarab beetles. The beetles fly low to avoid bat and common nighthawk (Chordeiles minor) predation, but this strategy makes them more likely to fly into red widow spider webs.  Red widows are related to the more common black widow spiders.  They exist as a relic population today but were likely more common when sand scrub habitat prevailed in the south during the late Pliocene/early Pleistocene.

The ancestor of spiders was closely related to the horseshoe crab.  It colonized land about 400 million years ago.  Fossil remains of spiders and spider webs dating to the Cretaceous (~100 million years BP) have been found.  Some were preserved in amber, and others were fossilized in layers of ash that turned to rock.  Though the Cretaceous species are extinct, scientists classify them as belonging to extant genera.

Earth will undoubtedly host spiders long after Homo sapiens becomes extinct.  The drastic changes man has wrought to the environment have barely phased spiders.  Compared to the changes spiders have seen over the 400 million years of their existence, anthropogenic effects are but a minor blip.  Look around, there are spiders inside your house now.

Reference:

Carrell, James; and Mark Deyrup

“Red Widow Spiders (Araneae: Theridiidae) Prey Extensively on Scarab Beetles Endemic in Florida Scrub”

Florida Entomologist 97 (1) March 2014

Hey Hollywood, Dinosaurs had Feathers

August 1, 2015

I enjoyed the first Jurassic Park movie when it premiered in 1993.  But even then, scientists were aware that some dinosaurs had feathers, and I always thought it was a bad oversight to depict every dinosaur in the movie as featherless.  Over the past 2 decades, paleontologists have discovered 43 species of dinosaurs that definitely had feathers.  These species ranged in size from the small tyrannosauroid, Dilong paradoxis, to the huge yutyrannus.  There’s no evidence Tyrannosaurus rex had feathers, but scientists believe it’s highly likely they were at least partially feathered because the 2 species mentioned above were related to T. rex.  The failure to depict dinosaurs with feathers in this year’s version of Jurassic Park is inexcusable, and I refuse to watch a movie produced by Hollywood shmucks who don’t bother to acknowledge scientific fact.  The movie is an insult to paleontology.

Artist's impression and fossil specimen of Sinosauropteryx

Note the visible quill feathers on the fossilized impression of a Sinusopteryx.

 

Yutyrannus, a relative of T. rex, is the largest known dinosaur that had feathers.

Feathers evolved from membrane-like structures that can still be found on the dorsal spines of reptiles and fish.  Originally, feathers served 2 purposes–thermal regulation and reproductive display.  Birds arose from a dinosaur order known as Dromaeosauridae, and these dinosaurs probably behaved like birds.  The males displayed their colorful feathers to attract the females for mating.  Most people, when they think of dinosaurs, imagine terrible monsters tearing each other apart.  They don’t realize these beasts had mating rituals that included males spreading their feathers and dancing and probably vocalizing while a discriminating female watched.  I suppose this interesting behavior is too mundane for a big budget action movie.  Hollywood shmucks would rather show dinosaurs running amok and terrorizing humans.  In truth (if dinosaurs somehow co-existed with people in a fictionalized scenario) a few humans with high powered rifles could destroy a whole herd of dinosaurs in a disgusting slaughter that would not be entertaining at all.

Most Media Outlets Misreport A New Study Linking Interstadials with Pleistocene Megafauna Extinctions

July 28, 2015

A new study of Pleistocene megafauna extinctions published in the latest issue of Science received considerable publicity.  Most of the media outlets misrepresented the study’s conclusions.  Perhaps journalists were confused by the title of the article: “Abrupt Warming Events Drove Late Pleistocene Holarctic Turnover.”  The overwhelming majority of media outlets reported that the study suggests climate, not overhunting by man caused the late Pleistocene megafauna extinctions.   None of these journalists must have read the abstract because the last sentence of it concedes that man played an important role in megafauna extinctions.  The following passage is the last sentence of the abstract (capital letters mine).

The presence of many cryptic biotic transitions prior to the Pleistocene/Holocene boundary revealed by ancient DNA confirm the importance of climate change in megafaunal population extinctions and suggests that METAPOPULATION STRUCTURES NECESSARY TO SURVIVE SUCH REPEATED AND RAPID CLIMATE SHIFTS WERE SUSCEPTIBLE TO HUMAN IMPACTS.”

This means the authors of this study believe rapid climate change reduced and scattered megafaunal populations, making them more vulnerable to human hunting.  They make it clear that humans were ultimately responsible for the megafauna extinctions in the last 2 sentences of the main body of this study.

Human presence could have had a major and negative impact on metapopulations by interrupting subpopulation connectivity, especially by concentrating on regular pathways between resource-rich zones, potentially leaving minimal sign of direct hunting.  By interrupting metapopulation processes (i.g. dispersal, recolonization), humans could have both exacerbated regional extinctions brought on by climate change and allowed them to coalesce, potentially leading to the eventual regime shifts and collapses observed in megafaunal ecosystems.  The lack of evidence for longer such ecological shifts during earlier periods of the glacial (i.g. >45 kyr) when interstadial events were known, but humans were not, suggests a synergistic role for humans in exacerbating the impacts of climate change and extinction in terminal events.”

The authors of this study collected no original data.  Instead, they analyzed data already available from previous studies.  They plotted climate data from Greenland Ice Cores with studies of megafauna DNA that determined changes over time in population structures.  (Scientists can determine past average annual temperatures by analyzing oxygen isotope ratios in Greenland ice cores that go back 100,000 years.  These ice cores have annual rings from summer glacial melt.)  The scientists used genetic data from 31 species, including 2 from North America (mastodon and elk), 3 from Beringia, and 26 from Eurasia.  They found a close correlation between sudden warming pulses, known as Dansgaard-Oeschger Events, and reduced populations and local extinctions of megafauna.   Dansgaard-Oeschger Events precipitated interstadials (warm climatic phases) within the Ice Age that lasted for 1-3 thousand years.  In some regions some species of megafauna became locally extinct.  Later, when the climate returned to a cooler more arid stage, different clades of the same species recolonized these regions from relic refugia where they found suitable habitat during the interstadial.

DO and Heinrich events

Chart showing Greenland Ice Core data.  This data shows past average annual temperature fluctuations.  The arrows point to Dansgaard-Oeschger Events–abrupt warming events that caused brief interstadials during the Ice Age.  Prior to the appearance of Homo sapiens in Europe, these interstadials were not associated with local extirpations of megafauna species.  But after modern man colonized Eurasia, various species of megafauna did suffer local extinctions following Dansgaard-Oeschger events.  Sudden climate change made these species more vulnerable to human overhunting, according to the study linked below.

Populations of megafauna remained stable during stadials, the cold phases of the Ice Ages, because the environments they lived in were static.  Stadials were longer lasting than interstadials, and open grassy plains prevailed for millennia.  The megafauna became adapted to living in these environments.  But rapid warming with increased precipitation caused dramatic changes to the environment.  Unproductive spruce forests started expanding, and this fragmented and reduced grassland habitat, forcing megafauna to migrate longer distances for suitable pasturage.  They followed the same routes between pastures, making them easier for humans to ambush.

I have a couple quibbles with this study.  First, I think this study is not applicable to North America.  The overwhelming majority of genetic data is from Eurasian populations of megafauna.  Just 2 North American species were used–a database that is far too small upon which to base any conclusions.  Moreover, I hypothesize mastodon populations likely increased during interstadials because they were a semi-aquatic species that favored wetland habitat.  Warm wet interstadials caused wetlands to expand. The scientists involved in this study used genetic data from just a single population of mastodons.  I’m extremely skeptical that mastodons declined in abundance when wetland habitat expanded.

Second, the authors note woolly mammoths survived later in Eurasia than in North America, despite having a longer exposure to human hunting there.  I assume they were making the point that climate played a greater role than human hunting in regulating megafauna populations.  Indeed, a radio-carbon date of 9760 BP from a woolly mammoth rib found in northern Russia is more recent than a 10,800 BP date from the latest mammoth specimen from continental North America.  However, the latter very likely does not represent the last mammoth that ever lived in North America, and sedaDNA from Alaska permafrost suggests mammoths still lived in Alaska 9000 calendar years ago.  Mammoths may have lasted longer in North America–there just isn’t enough data to know for sure.  It’s unlikely that the absolute last mammoth was preserved.  Moreover, northern Russia was probably uninhabited or more sparsely inhabited than most of North America during the late Pleistocene, rendering the author’s point moot.

Reference:

Cooper, Alan; et. al.

“Abrupt Warming Events Drove Late Pleistocene Holarctic Megafaunal Turnover”

Science 2015

http://www.researchgate.net/publication/280302381_Abrupt_warming_events_drove_Late_Pleistocene_Holarctic_megafaunal_turnover


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