Pleistocene Fossil Canid Ratios Recorded in the University of Florida Database

The abundance of Pleistocene fossil sites in Florida has allowed the university in Gainesville to become a center of information for other scientists.  Scientists excavating new fossil sites use existing fossils at the University of Florida Museum of Natural History to help identify the new specimens they pull from the earth.  It’s not always easy to differentiate closely related species–the subject of this blog entry, the canids, are notoriously difficult to distinguish.  Vertebrate zoologists and paleontologists measure and describe every part of every bone and tooth when examining new specimens.  They publish this information in scientific journals and accumulate knowledge of the size limits and shape variations of a particular species’ anatomy.  If a newly discovered fossil tooth for example doesn’t fit any known pattern of shape or size, than scientists suspect they may have discovered a new species.  The more data scientists have, the better able they are to identify new species and spot evolutionary trends over time within a species.

Fossil collecting is popular in Florida, thanks to all the sinkhole lakes and caves with basal chemistry in the soil that preserves bones.  Amateur fossil collectors have many more fossils in their collections than the University of Florida’s Natural History Museum..  Many are for sale as well.  It would be a great benefit to science, if collectors made arrangements to donate their collections to the museum upon their deaths.  Many valuable specimens have been lost when their owners die and family members, not interested in the subject, lose track of where they put the old bones.

My little study is limited to canid fossils listed on the University of Florida database and leaves out the great many more in the hands of amateur fossil collectors.  I also limited this survey to the Rancholabrean Land Mammal Age (300,000 BP-11,000 BP), leaving out Armbruster’s wolf which dominated the middle Pleistocene before being replaced by dire wolves.  Nevertheless, I think there’s enough information to suggest relative canid species abundance during the late Pleistocene.  Keep in mind, I was counting on a computer screen while scrolling down, so my numbers may be off slightly.

Listed on the Florida Museum of Natural History’s database, I counted 64 dire wolf (Canis dirus) specimens, 34 coyote (Canis latrans) specimens, 1 red wolf (Canis niger) specimen, 9 domestic dog (Canis familiaris) specimens, 0 dhole (Cuon alpinus) specimens, and 55 gray fox (Urocyon cineorgenteus) specimens.

The fossil record strongly suggests that from 300,000 BP to about 11,000 BP dire wolves were by far the most common large canid being about twice as abundant as coyotes.  Red wolves were rare but present.  Gray foxes were just as common during the Pleistocene as they are today.  These neat little foxes have the ability to climb trees, a skill that saves them from their larger relatives.  There is no evidence of dholes but as I wrote in a previous blog entry http://markgelbart.wordpress.com/2011/06/01/did-the-dhole-cuon-alpinus-range-into-southeastern-north-america-during-the-pleistocene/ , I suspect they may have periodically colonized parts of the southeast but in numbers too low to leave fossil evidence.

Dire wolves were the dominant large canid in the southeast (and all across North America south of the Ice Sheets) during the late Pleistocene.

Coyotes probably occupied a niche similar to African jackals.

Gray foxes thrived in areas where they had access to trees and could escape larger predators.

The presence of domesticated dogs in the Pleistocene fossil record puzzled and surprised me.  I almost didn’t even do a database search for Canis familiaris and only did so as an afterthought.  Most anthropologists don’t think humans domesticated dogs until after the Pleistocene about 10,000 years ago, but the fossil evidence contradicts this.  In fact scientists recently discovered the skull of a domesticated dog in a Siberian cave that dates to 33,000 BP.  They determined  this particular domesticated dog was not the ancestor of the lineage that led to today’s dogs but instead its descendents died out.  It’s probable that there were many early lineages of domesticated dogs that ceased to exist for various reasons.  Perhaps that group of people died out or stopped keeping dogs.  The popular idea that people domesticated dogs by kidnapping and raising wolf pups is a misconception.  Scientists think it’s the other way around–dogs adopted us.  Dogs are descended from the wolves which had the least flight response.  Wolves that hung closely around human campsites for access to leftovers gave birth to pups with floppy ears, multi-colored coats, and other dog traits that differentiate them from other wolves.  The gene for tameness shares a pathway with the gene for these physical characteristics.  So it’s likely that dogs adopted people in many different geographic locations wherever wolves (Canis lupus) began occupying areas adjacent to human campsites.  Obviously, dogs either followed or were brought to Florida by the Paleo-Indians.

The authors of a chapter in the book The First Floridians and the Last Mastodons suggest that all the coyote fossils found in Florida are actually domesticated dog fossils, but they only knew of a handful of coyote fossils.  Apparently, they didn’t know 34 specimens had been found.  I doubt scientists made that many misidentifications.

Dire wolves succeeded in becoming one of the dominant predators in the environments of southeastern North America where they found a wealth of prey roaming the open woodlands and savannahs.  Everything from bison and horses to deer and rabbits sustained them, and a mammoth or mastodon that died of natural causes provided a feast.  Coyotes successfully co-existed with dire wolves by scavenging large predator kills and by hunting rodents.  Red wolves must have been restricted to islands and perhaps deeply wooded swamps where they could survive on deer and small game.  Their niche must have been areas with lower densities of prey as opposed to grasslands that hosted large herds of ungulates.  Following the extinction of the megafauna and dire wolves, forests replaced grasslands and red wolves increased in number and drove coyotes completely out of the south.  But after European settlers wiped out the red wolves, coyotes returned.

References:

Ovodov, Nikolai, et. al.

“A 33,000 Year Old Incipient Dog from the Altai Mountains of Siberia: Evidence of the Earliest Domestication Disrupted by the Last Glacial Maximum”

Plos One 6 (7) 2011

http://www.flmnh.ufl.edu/databases/vp/intro.htm

The Dunwoody Nature Center

I attended my nephew’s bar mitzvah in Dunwoody, Georgia last weekend.  Dunwoody consists of dozens of subdivisions and plenty of shopping centers and absolutely no rural farmland.  I didn’t hold out much hope for a nice nature walk here–the traffic is terrible.  But at least the developers left a lot of trees standing.  I decided to walk from my sister’s house to a little park known as the Dunwoody Nature Center and I discovered a surprising gem.

This white oak was about 4 feet in diameter.  White oak is a common tree in Dunwoody.

From the composition of the trees left standing most of Dunwoody must have once hosted a pretty nice dry upland forest.  Too bad developers converted it into a crowded suburb.  Today, white oaks, black oaks, southern red oaks, shortleaf pines, and loblolly pines are the dominant trees.  The Dunwoody Nature Center slopes sharply down toward Wildcat Creek, the name of which is a relic to its former status as a wilderness.  The woods here are dominated by beech, white oak, sweetgum, river birch, and loblolly pine.  I was stunned to see a woodlot of mostly beech trees in central Georgia.

A mature beech tree growing on the edge of a rocky creek.  It’s surrounded by many immature beech saplings.

Fossil pollen studies show beech was a common tree in the south during the end of the Ice Age when the Laurentide glacier began melting and releasing more moisture in the atmosphere creating a climate that was still cool but more rainy than it was during the height of the Ice Age.  The presence of abundant beech in the fossil record is indirect evidence of massive flocks of passenger pigeons.  Passenger pigeons fed on acorns–in some places completely eliminating the oak seed crop…and the beech’s competition.  Although beech trees produce an edible nut, they can also spread from roots and could survive their seed being consumed by passenger pigeon flocks.  Since the passenger pigeon’s demise, oak forests have been replacing beech forests in many areas.  So I was delighted to see this remnant beech forest in central Georgia.

Wildcat Creek flows through a granite outcropping.  Here is a miniature waterfall.

Two little league baseball fields take up about half the space of the park.  The park is heavily used by dog and toddler walkers.  It’s popularity shows that the planning commission in charge of developing Dunwoody should have arranged for the purchase of more land for more parks.

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Pleistocene Passenger Pigeon Populations

(Please forgive the excessive alliteration in the title.)

It’s hard to imagine the massive number of passenger pigeons (Ectopistes migratorius) that used to live in North America as recently as the mid to late 19th century.  For a description of their numbers, I’ve dug up an account J.J. Audubon gave in his Ornithological Biography.  Before I reprint this passage I want to comment on his writing style.  I enjoy his prose, but he does have a bad habit of writing in the passive voice, a style Stephen King in his book, On Writing, referred to as farting in an elevator.  Also, English was his second language because he was born in France.  Nevertheless, I think this makes for a fascinating description of a nature scene that no longer exists.

“The multitudes of wild pigeons in our woods are astonishing.  Indeed, after having viewed them so often, and under so many circumstances, I even now feel inclined to pause, and assure myself that what I am going to relate is fact.  Yet I have seen it all, and that too in the company of persons, who, like myself, were struck with amazement.

In the autumn of 1813, I left my house at Henderson, on the banks of the Ohio, on my way to Louisville.  In passing over the barrens a few miles beyond Hardensburgh, I observed the pigeons flying from north-east to south-west, in greater numbers than I thought I had ever seen them before, and feeling an inclination to count the flocks that might pass within the reach of my eye in one hour, I dismounted, seated myself on an eminence, and began to mark with my pencil, making a dot for every flock that passed.  In a short time finding the task which I had undertaken impractical, as the birds poured in countless multitudes, I rose, and counting the dots put down, found that 163 had been made in 21 minutes.  I traveled on, and still met more the farther I proceeded.  The air was literally filled with pigeons; the light of the noon-day was obscured as by an eclipse; the dung fell in spots, not unlike melting flakes of snow; and the continuing buzz of wings had a tendency to lull my senses to repose…

“It may not, perhaps, be out of place to attempt an estimate of the number of pigeons contained in one of those mighty flocks, and of the quantity of food consumed by its members.  The inquiry will tend to shew the astonishing bounty of the great Author of Nature in providing for the wants of his creatures.  Let us take a column of one mile in breadth, which is far below average size, and suppose it passing over us without interruption for three hours, at the rate mentioned above as one mile in a minute.  This will give us a parallelogram of 180 miles by 1,  covering 180 square miles.  Allowing two pigeons to the square yard, we have one billion, one hundred and fifteen million, one-hundred and thirty-six thousand pigeons in one flock.  As every pigeon daily consumed fully half a pint of food, the quantity necessary for supplying this vast multitude must be eight million seven hundred twelve thousand bushels per day.”

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Some archaeologists believe the massive population of passenger pigeons that colonists in North America reported from 1700-1870 was a temporary phenomenon.  Thomas Neuman has written at least two journal articles suggesting passenger pigeon populations exploded following the decimation of Indians after their first contact with European diseases such as smallpox, influenza, and measles.  Before this, Dr. Neuman believes this species was not particularly common.  Supposedly, when Indian populations were reduced, there was more forest mast available for birds because humans weren’t gathering the nuts and acorns they fed upon.  In his book 1491 Charles Mann discusses this theory and notes that archaeologists find few passenger pigeon bones at sites of large Indian settlements.

I disagree with this theory because it makes little sense for several reasons which I shall enumerate.

1. Passenger pigeons could not survive as a species unless they existed in extremely large populations.  The survival strategy of this species was to reproduce rapidly and roost and nest in enormous colonies so that they overwhelmed predation.  Predators ate many individuals, but there was a limit to how much their stomachs could hold.  If, as these archaeologists suggest, the passenger pigeon was just an occasional bird, the species would’ve become extinct long before the white man arrived on the continent because their defense mechanisms revolved around living in large colonies.

2. Even if human populations were at the high end of what archaeologists believe, they would’ve made little impact on the amount of forest mast available.  Pre-Columbian forests were extensive, and there was always plenty of forest mast for both humans and huge pigeon colonies.

3. Archaeologists don’t find many passenger pigeon bones in sites of large Indian settlements because Indians probably went to their roosting grounds and feasted on them there and simply didn’t bring the bones back to their villages.

4. Jacques Cartier, an early explorer, reported large pigeon colonies on Prince Edward Island in 1534…before Indian populations were reduced by disease.

5. Pigeon fossils are abundant in an early Holocene fossil site in Western Canada (Charlie Lake, British Columbia).  They are also a common fossil in late Pleistocene avifaunas including Bell Cave, Alabama, Cheek Bend Cave, Tennessee, and Ladds and Kingston Saltpeter Cave in Georgia.

At Ladds fossils of only 4 bird species were discovered.  Passenger pigeons were 1 of the 4.  This may be coincidence, but it’s believed that passenger pigeon biomass made up 25% of all bird populations in North America during the early part of the 19th century.  Many more species of birds were found in the deposit at Kingston Saltpeter Cave.  I compared the minimum number of individual passenger pigeon fossils from KSC to the total bird remains of all other species found there.  Ruffed grouse were the most common species, making up 30% of bird remains, but passenger pigeons made up 6%, despite being a highly migratory bird.  Assuming they spent 6 months of the year around KSC, that means at times, they may have made up to 12% of the bird population in the area.  If they stayed in the area around the cave for only 2 months of the year, they quite possibly made up 36% of the bird population at certain times of the year there.

I must mention, however, that estimating ancient bird populations based on the number of bird fossils found in cave deposits is a rather dubious method.  Nevertheless, habitat for passenger pigeons in southeastern North America during the Pleistocene must have been ideal for this species.

During colonial times this bird nested throughout the midwest, but spent September-February in southeastern states.  For much of the duration of the Wisconsin Ice Age, most of the area where they later nested was under glacial ice, so it’s likely their nesting areas shifted south.  They probably were year round residents everywhere south of the Laurentide ice sheet, except during nesting season when they nested in southern river bottomlands where beech and oak trees remained plentiful, even during cold arid climatic phases.

Today, beech trees are a rare relic in much of the southeast, but during certain climatic phases of the Wisconsin Ice Age, they were even a dominant tree on some lands, according to records of fossil pollen in Alabama, and South Carolina.  From 14,000-11,000 years BP beech was a common tree, while pine, which dominated southern forests during the LGM, temporarily declined drastically.  Beech is well adapted to pigeon and squirrel foraging because this tree spreads through sucker roots, and if animals eat the tree nuts, this species can still propagate.  Beech tree pollen is also present in the Nodoroc fossil site in central Georgia near Winder and at the Gray’s Reef site off Sapelo Island, which was above sea level 30,000 years ago.  The latter site yielded evidence of a forest consisting of a strange mixture of cool temperate and warm weather species of plants.  The south’s Ice Age ecosystem was a mixture of woodlands and grasslands, and it provided excellent habitat for passenger pigeons.  I think the expansion of southern beech tree forests, as the Ice Age waned, is evidence the population of pigeons may have spiked about 14,000 years BP, creating the nucleus that later colonized the midwest after the glacier melted and broadleaf trees re-established themselves there.

References.

Driver, J.C.; and K.A. Hobson

“A 10,500 year sequence of bird remains from the southern boreal forest region of western Canada”

Arctic 45 (2) 1992

Ellsworth, Joshua; and Brenda McComb

“Potential effects of Passenger Pigeon flocks on the structure and composition of pre-settlement forests of eastern North America”

Conservation Biology 17 (6) pp. 1548-1558 2003

Mann, Charles

1491

Knopf 2005

www.paleodb.org