Archive for the ‘Pleistocene Mammals’ Category

The Adaptability of Pleistocene Peccaries

June 30, 2018

Two lineages of peccaries lived all across North America for over 5 million years but both became extinct about the time man appears in the archaeological record.  The long-nosed peccaries in the Mylohyus genus were forest edge species, and the flat-headed peccaries in the Protherohyus-Platygonnus genuses inhabited scrubby thickets.  A new study looked at dental microwear and bone chemistry in these lineages and compared them with the teeth and bone chemistry of the extant white-lipped peccary to determine the dietary similarities and differences of the extinct and extant species of peccary.  Peccaries in the Mylohyus genus co-existed with Protherohyus peccaries during the Miocene over 5 million years ago.  The former ate more woody browse and forest vegetation, while the latter mostly ate grass.  During the Pliocene between 5 million years BP-2million years BP both Mylohyus and Platygonnus ate mostly woody browse in Florida.  Their diets shifted during the early-mid Pleistocene with an increased consumption of grass.  During the late Pleistocene Mylohyus ate more forest vegetation such as twigs, acorns, and nuts, while Platygonnus ate more tough leaves and grass.  This study shows how adaptable these lineages were to environmental change–their diets shifted with changes in climate.  It seems obvious to me that overhunting and/or disruption of the overall ecosystem by humans, not whole scale environmental change, caused the extinctions of both Mylohyus and Platygonnus.  Surviving extant species of peccaries live in deserts and remote jungles where human populations remain sparse.

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Illustration of Platygonnus peccary.

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White-lipped peccaries eat forest vegetation.  They can be dangerous.

The proliferation of feral pigs (Sus scrofa) in North America today demonstrates how favorable the environment still would be for Pleistocene peccaries, if they still existed.  Pigs co-evolved with humans in Eurasia to produce large litters, making them capable of surviving human hunting pressure.  Pigs produce litters of 8-12, but peccaries only birth 2-4 young.

Some archaeologists reject the likelihood that humans hunted peccaries to extinction because there are no known kill sites, other than a peccary shoulder blade with a spear hole in it next to a spear.  See: https://markgelbart.wordpress.com/2014/03/10/the-sheridan-cave-pit-fossil-site-in-wyandot-county-ohio/

This is a ridiculous assumption. There are also no known white-tailed deer kill sites in the archaeological record, but we know Indians hunted deer.  Evidence humans killed Pleistocene peccaries simply faded away over time.

Reference:

Bradham, J. et. al.

“Dietary Variability of Extinct Tayassuids and Modern White-Lipped Peccaries (Tayassu pecari) as Informed from Dental Microwear and Stable Isotope Analysis”

Palaeogeography, Palaeoclimatology, Palaeoecology April 2018

 

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An Anatomical Comparison Between the Extinct North American Cheetahs (Miracynonyx sp.) and the Late Pleistocene/Holocene Cougar (Puma concolor)

May 28, 2018

One of my readers recently asked whether the cougar (Puma concolor) might be the same species as the extinct North American cheetahs (Miracynonyx inexpectatus and M. trumani).  This is not as ridiculous a question as a layman might think because paleontologists often mistakenly identify multiple species from fossil remains that after re-evaluation are eventually determined to be from 1 species.  I love reading articles about vertebrate paleontology, but I usually skip over anatomical descriptions because they are pretty dry.  But to answer his question, I used google to search for a paper comparing the anatomical differences between Puma and Miracynonyx.  I did not find a journal article with a comprehensive anatomical comparison between the 2, but I did recall a paper I’d already read that discussed some of the differences.  I’ve linked the paper below in  my references.

Cougars and North American cheetahs had different-sized teeth.  Cougars have larger canines and lower molars than North American cheetahs, but they have smaller lower premolars (p4) and smaller upper pre-molars (P3).  They also have a “less reduced protocone on upper premolar P4.”  North American cheetahs had longer limbs than cougars as the below photos from the linked paper show.  So the answer is no.  Cougars were definitely not the same species as the North American cheetahs.

Fossil history of the panther (Puma concolor) and the cheetah-like cat (Miracinonyx inexpectatus) in Florida - Page 208

Comparison of limb bones between cougar and North American cheetah shows the latter had longer hind foot bones and were better runners.

Fossil history of the panther (Puma concolor) and the cheetah-like cat (Miracinonyx inexpectatus) in Florida - Page 210

North American cheetahs had longer front foot bones as well.

Cougars and North Americans cheetahs are closely related, however.  Genetic evidence suggests their shared lineage originated 6-8 million years ago, and a puma-like cat, probably Puma pardoides, crossed the Bering Land Bridge from Asia shortly after this.  In North America the puma-like ancestor diverged into 3 lines: cougars, North American cheetahs, and jaguarundis. The Puma genus diverged from Miracynonyx about 3.2 million years ago.

The fossil evidence shows M. inexpectatus  lived all across North America from the late Pliocene to the middle Pleistocene (~3 million years BP-~300,000 years BP).  In the Florida Museum of Natural History there are 47 records in state of M. inexpectatus at sites thought to date from the Pliocene to the mid-Pleistocene, but they are known from just 1 late Pleistocene site in Florida.  This site is named Lecanto 2A. The only other Late Pleistocene site with a possible M. inexpecatus  fossil (1 leg bone) is in Cavetown, Maryland.  These specimens can’t be radio-carbon dated.  The reason the specimen from Lecanto 2A is considered Late Pleistocene is its association with specimens of other species known from this age including dire wolf, Florida spectacled bear, rice rat, and cotton rat.  It’s possible there were relic populations of M. inexpectatus  still living during the Late Pleistocene, but it seems more likely it’s a case of older fossils getting mixed with younger fossils.

M. inexpectatus  expanded its range at a time coinciding with the expansion of grassland habitat.  Its long legs helped it run down prey.  M. trumani was even more adapted for living in open habitat.  This species appeared during the Late Pleistocene and was restricted to western North America as far as we know from the fossil record.  M. trumani is probably a descendent of M. inexpecatus which had intermediate characteristics between cougars and M. trumani. 

The paleobiology database indicates cougar fossils dating to the Early and Mid Pleistocene in California, Idaho, Washington, and Mexico have been reported.  Nevertheless, cougar fossils predating the Late Pleistocene are rare.  In the Florida Museum of Natural History there are 44 records of cougar from the Late Pleistocene but just 2 from the Mid Pleistocene and 2 from the Early Pleistocene.  The early Pleistocene specimens are referred to as Puma lacrustis, but I searched for this scientific name on google and found nothing, so I’m not sure what these specimens actually were.  Genetic evidence suggests cougars were well established in South America between 300,000 years BP-200,000 years BP, and this corresponds with the widespread fossil evidence of this species throughout North America during this time period.  I hypothesize cougars began to expand their range widely during an early Rancholabrean interglacial from a regional ancestral population undetected in the fossil record.  This time period would correspond to when forested conditions expanded.  Cougars are ambush predators that prefer forests and woodlands.

North American cheetahs are not as closely related to Old World cheetahs as previously thought.  Physical similarities between the 2 are just another example of convergent evolution.

References:

Barnett, Ross; et. al.

“Evolution of the Extinct Sabretooth and the American Cheetah-like Cat”

Current Biology 15 (5) August 2005

Culver, M.; W. Johnson, J. Pecon-Slattery, and S. O’Brien

“Genomic Ancestry of the American Puma (Puma concolor)

Journal of Heredity 91 (3) 2009

Morgan, Gary and Kevin Seymour

“Fossil History of the Panther (Puma concolor)  and the Cheetah-like Cat (Miracynonxy inexpectatus) in Florida”

Bulletin of the Florida Museum of Natural History 1997

http://ufdc.ufl.edu/UF00095787/00001/1j

 

 

Recent Items about the Late Pleistocene in the News

May 10, 2018

3 stories relating to the late Pleistocene recently made the mainstream news.  The first story is about the upcoming resurrection of the woolly mammoth (Mammuthus primigenius).  George Church of Harvard University is using CRISPR technology to genetically engineer a woolly mammoth by editing Asian elephant (Elephas maximus) DNA.  (I explained CRISPR technology in a previous blog entry.  See: https://markgelbart.wordpress.com/2016/07/22/possible-resurrection-of-the-mammoth-as-early-as-2018/  ) Scientists at Church’s lab are going to edit in the phenotypical characteristics that make the woolly mammoth able to survive in cold wet climates with extremely short and long days.  These characteristics include a layer of fat, long oily hair, small ears, the ability to withstand cold temperatures, and adjustments to the circadian rhythms animals that live in the Arctic require.  They think they can produce a genetically engineered woolly mammoth by 2019.  Scientists hope to eventually engineer herds of woolly mammoths that can live in Siberia where their activities will convert the tundra landscape into a grassy steppe.  Ecologists believe a grassy steppe environment will better prevent permafrost from melting, thus mitigating anthropogenic global warming.  I’m all in favor of resurrecting herds of woolly mammoths, but I believe their goal of mitigating global warming is a pipe dream, and I doubt woolly mammoths could survive in the present day tundra.  I suspect woolly mammoths were confined to relic steppe habitat during interglacials.  Climate is a much greater influence on sub-Arctic habitat than the activities of megafauna.  Woolly mammoths could probably survive today on the grassy Tibetan steppes but not in the Siberian tundra.  The mammoth steppe of the late Pleistocene was more like the modern Tibetan highlands than the Siberian tundra.

The 2nd story reported the results of a statistical study that determined the average size of mammal species has declined over the past 130,000 years, and the authors of this study squarely blame man.  Humans have been overhunting large mammals that reproduce slowly to extinction, leaving smaller species that can better replenish their populations with faster breeding.  Rabbits breed faster than mammoths and elephants.  The average size of a North American mammal species during the late Pleistocene was 216 pounds compared with the average North American mammal species of today which weighs 16 pounds. This decline in body size is unprecedented over the past 65 million years and hasn’t occurred since the extinction of the dinosaurs.  The fossil record is pronounced…this statistical study just confirms the obvious.

Evidence humans may or may not have tracked a ground sloth in New Mexico is perhaps the most interesting story.  There are thousands of late Pleistocene-aged animal tracks in the White Sands National Monument.  During the Ice Age weather patterns were different due to altered climate cycles, and southwestern North America was much wetter than it is today.  The site of these tracks, presently a desert, was a lake shore then.  The animals walked on the edge of the lake in the mud and the tracks have been preserved for thousands of years.  Scientists found human tracks adjacent and actually within ground sloth tracks.  Ground sloths usually walked in a straight line, but these tracks appear to show the ground sloth zig-zag, as if it was avoiding a predator.  There are 2 sets of human tracks.  One human was directly following the ground sloth–his steps are inside the ground sloth steps; the other human was walking very gently beside the other person, as if on tiptoe.  The ground sloth circled around and appeared to rise up on its legs and bare its claws.  There are claw marks in the ground too.  Scientists suggest 1 human was distracting the ground sloth, while the other was sneaking up on it to deliver a fatal spear thrust or blow to the head with a club.  The end result is not recorded in the tracks.  Other scientists are skeptical of this interpretation.  Some think it unlikely humans would hunt the sloth in such an open landscape.  However, this site was not as open then as it is today, and humans could easily outpace a ground sloth.

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Human footprint inside sloth print.  The sloth print is 22 inches long.  The human footprint is 5 inches.  The sloth had a wider stride, so the human must have been hopping to get his foot inside the sloth’s print.

I wish there were more mainstream news stories about the late Pleistocene.  It’s much more interesting than waiting for Donald Trump to get impeached.

References:

Daley, J.

“Fossil Tracks May Record Ancient Human Hunting Sloth”

Smithsonian April 20, 2018

Smith, F.; et. al.

“Body Size Downgrading of Mammals over the Late Quaternary”

Science  April 2018

Speculative Distributions of Megafauna in Georgia 36,000 years BP

April 15, 2018

A recent statistical study estimated the abundance and natural ranges of megafauna species (mammals over 40 pounds), if man didn’t exist today.  They analyzed 5,742 megafauna species that have existed over the past 130,000 years, a time span including a full glacial/interglacial cycle.  Not surprisingly, they concluded the natural ranges and abundance of megafauna would be much greater today, if not for man.

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Maps showing natural ranges and abundance of megafauna.  The top shows today’s abundance.  The bottom shows abundance today, if man didn’t exist.  Map is from the below reference.

This study inspired me to draw speculative range maps for selected megafauna species that lived in Georgia 36,000 years ago–long before people ruined the wilderness.  I chose this time period because it was an interstadial, a warmer wetter climate phase within the last Ice Age, and I think wildlife populations were higher then than during the Full Glacial Maximum when at least some of Georgia consisted of desert-like habitat.  My maps are educated guesses because the Pleistocene fossil record of Georgia is extremely incomplete.  Megafauna populations were not evenly distributed throughout the state.  I assumed the northern part of the state held more forest and woodland, while the southern half hosted more grassland.  But both environments existed in most of the state, often side-by-side.  Therefore, forest and forest edge species such as tapirs and long-nosed peccaries were more abundant in the northern part of the state.  Bison and horse were more numerous on the coastal plain.  Some animals migrated in and out of the state.  Isotopic evidence suggest mastodons moved back and forth between Florida and Georgia.  Like leaders of today’s elephant herds, experienced matriarchs knew where rich sources of food and mineral licks were located.  Some herds of mammoths probably moved great distances as well.  Flat-headed peccaries likely favored the sand hill scrub habitat along the fall line.

Evidence of caribou in north Georgia dates to the Last Glacial Maximum, but I believe they were so abundant even during interstadials that some herds wandered as far south as Georgia.  There is no fossil evidence of helmeted musk-ox, stag-moose, giant lion, or saber-tooth in Georgia.  I’m certain giant lion and saber-tooth did range into Georgia, and it seems probable helmeted musk-ox and stag-moose did as well.  Fossil evidence of giant lions has been found in Florida and Mississippi.  Saber-tooth bones have been recovered from all the states surrounding Georgia.  Fossil remains of stag-moose and helmeted musk-ox have been excavated from sites on the same latitude as Georgia.

The dots on my maps don’t represent any specific numerical value, but the bigger ones indicate larger populations. The maps include the 10,000 square miles of continental shelf that was above sea level between ~83,000 years BP-~7800 years BP.

Range maps of selected megafauna species in Georgia 36,000 years ago.  Click to enlarge.  I know the labels on the maps are hard to see so from left to right on the top row they are mastodon, mammoth, Jefferson’s ground sloth, stag-moose, stout-legged llama, large-headed llama.  Middle row from left to right: long-horned bison, horse, long-nosed peccary, helmeted musk-ox, giant beaver, saber-tooth.  Bottom row from left to right: tapir, caribou, flat-headed peccary, giant lion, jaguar, dire wolf.

Reference:

Faurby, S; and J.C. Svenning

“Historic and Pre-Historic Human-Driven Extinctions have Reshaped Global Mammal Diversity Patterns”

Diversity and Distribution 21 (10) Augusts 2015

The Late Pleistocene Extinction of Leopards (Panthera pardus) from Sumatra

March 8, 2018

During temperate climate cycles of the Pleistocene leopards enjoyed an even wider geographic range than they do today, living in Europe as well as Africa and Asia.  Leopards colonized the island of Sumatra during the middle Pleistocene but became extinct there at the end of the Pleistocene, despite continuing to thrive elsewhere in Asia.  Scientists used a statistical model to determine why leopards disappeared from Sumatra.  They considered all potential competing carnivores and total prey biomass in their calculations.   Leopards shared Sumatra with orangutans, monkeys, humans, elephants, deer, tapir, pigs, sun bears, tigers, clouded leopard, Asian golden cats, and dholes.  Tigers are known to depress leopard populations in regions where the 2 species overlap; and dholes, a pack-hunting dog, compete for the same large prey species.  Scientists expected the model to show competition with tigers and dholes caused the extinction of leopards on Sumatra.  However, when they removed the influence of these 2 species from their model, leopards still became extinct.  Leopards also became extinct when humans were removed from the simulation.  Surprisingly, the statistical simulation suggests competition with clouded leopards (Neofelis diardi) and Asian golden cats (Pardofelis temminckii) caused the extinction of leopards on Sumatra.

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Location of Sumatra.

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Asian golden cats.  This species along with clouded leopards outcompeted leopards on Sumatra following the end of the Pleistocene.

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Clouded leopard.

The authors of this study propose ecological changes following the end of the Pleistocene greatly favored smaller forest cats over leopards.  During Ice Ages Sumatra was a mix of savannah, woodland, and forest; but wetter climate fostered the spread of thick forest.  Larger prey species became less common, so leopards were forced to compete with the smaller cats for smaller prey items.  Both of the smaller species of cats reproduce faster than leopards and produce larger litter sizes.  The extremely adaptable leopard was actually squeezed out of its ecological niche on Sumatra by 2 smaller felines.

Adult leopards weight between 80-200 pounds compared to a maximum of 57 pounds for clouded leopards and 35 pounds for Asian golden cats.  The latter 2 species are efficient predators of small animals and need less food than leopards, giving them an advantage when available protein biomass declines.

Clouded leopards are 1 of the most primitive species of living cats and may be related to the evolutionary link between big and small cats.  The Sunda clouded leopard is the species that lives on Sumatra.  It diverged from the other species of clouded leopard ((Neofelis nebulosa) about 70,000 years ago.  Clouded leopards from Borneo crossed a now submerged land bridge and colonized Sumatra following the Tuba volcanic eruption that wiped out much of Sumatra’s wildlife ~70,000 years BP. The Sunda clouded leopard was not recognized as a separate species until 2006.

Reference:

Volmer, R.; et. al.

“Did Panthera pardus (Linneaus 1758) become Extinct in Sumatra because of Competition for Prey?  Modeling Interspecific Competition within the Late Pleistocene Carnivore Guild of the Paday Highlands, Sumatra”

Paleogeography, Paleoclimatology, and Paleoecology 2018

More Evidence against the Climate Change Model of Late Pleistocene Extinctions

March 4, 2018

Many extinct species of Pleistocene megafauna had a wide ranging geographic distribution.  Jefferson’s ground sloth, long-nosed peccary, Columbian mammoth, and mastodon occurred from coast to coast and from Florida to the glacial boundary.  These species and their similar evolutionary ancestors existed across the continent for millions of years, surviving dozens of major and minor climatic fluctuations.  They lived in a variety of environments and were capable of subsisting on many different foods.  Multiple lines of evidence show these pre-historic beasts ate a varied diet.  Mastodon coprolites (subfossil feces) contain bald cypress, buttonbush, spruce twigs, fruit, acorns, aquatic plants, and numerous other items.  Now, a new study of mastodon teeth using dental microwear texture analysis confirms that mastodons ate a wide variety of foods.

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Mastodon tooth.  Scientists looked at mastodon teeth using microscope technology and determined mastodons from different regions ate different foods.

Scientists microscopically examined 65 mastodon teeth that were found in 4 different geographic locations including Florida, Missouri, Indiana, and New York.  The microwear found on mastodon teeth from Florida differed from wear on teeth from northern mastodons.  Florida mastodons primarily ate bald cypress twigs, while northern mastodons ate spruce, hemlock, pine, larch, and juniper.  The differences in tooth wear indicate mastodons could eat a variety of plant foods and were not dependent upon a single species.  The authors of this study also looked at mastodon teeth from different climatic stages in Missouri.  Mastodon teeth from a climate stage when open jack pine and prairie predominated showed little difference from teeth dated to a climate stage when spruce dominated the landscape.  The microwear on mastodon teeth resembles the microwear found on 2 living species–moose and black rhino.  Like mastodon, these 2 species subsist on woody browse.

I think this study is just more evidence against the climate change model of extinction that proposes changes in climate caused corresponding changes in plant composition, leading to megafaunal extinctions through nutritional deficit starvation.  None of the plants mastodons ate ever disappeared or even became rare in the environment. The authors of this study take a more neutral stance toward the debate.  They acknowledge the “plasticity” of mastodon diet but seem reluctant to admit their study is strong evidence against the climate change model of extinction.  Instead, they suggest future studies using dental microwear texture analysis could uncover the reason why megafauna became extinct.  In my opinion it already has.  Their data rules out the climate change model of extinction by revealing the dietary adaptability of mastodons.  Through the process of elimination, human overkill is the only plausible cause left standing.

Reference:

Green, J.; Larisa DeSantis and G. Smith

“Regional Variation in the Browsing Diet of Pleistocene Mammut americanum (Mammalia, Proboscidea) as Recorded by Dental Microwear Texture Analysis”

Paleogeography, Paleoclimatology, and Paleoecology August 2017

The Galerian Migration hypothesis

February 25, 2018

During the middle Pleistocene the faunal diversity of Europe increased.  Scientists attribute this to glacial/interglacial transitions that changed the environment, transforming it from forest to grassland and savannah.  Forests were restricted to narrow corridors along rivers and upper elevations.  Cooling temperatures and aridity caused these changes.  Animals from Africa and Asia colonized the open savannahs that became established along the Danube and Po River valleys.  Red deer, atlas deer, wild boar, bison, aurochs, an extinct species of Indian water buffalo (Hemibos galerianus), and horses invaded from Asia.  An extinct species of temperate-adapted elephant (Elephas antiquus), mammoth (Mammuthus trogontherii), rhino, lion,  leopard, spotted hyena, and Homo erectus came from Africa.  The Galerian Migration Hypothesis posits archaic humans first colonized Europe during this time period because they were a part of this savannah ecosystem, and they used the same route as their contemporaries in the animal world.

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Map of the Danube River.  The Po River goes through northern Italy.  The Galerian Migration Hypothesis proposes archaic humans first entered Europe through savannahs in these 2 river valleys.

Data from magnetstratigraphy supports the Galerian Migration Hypothesis.  Scientists can date objects based on which direction the magnetic minerals within associated rocks are oriented.  The earth’s polarity has shifted periodically throughout history, causing magnetic minerals in rocks to point in certain directions.  Scientists calibrate changes in polarity with radiometric dating, so magnetstratigraphy provides useful parameters.  Scientists know from magnetstratigraphy that Homo erectus probably first colonized Europe between 780,000 years BP-990,000 years BP. The oldest  Homo erectus fossil known from Europe falls within these dates. These dates correspond well with environmental changes, and changes in faunal composition.  Homo erectus originated in Africa and colonized Asia and the Middle East as early as 1.9 million years ago, but there was a delay before they reached Europe.

The invasion of humans and spotted hyenas likely drove the extinction of hyena species already in Europe–Pachycrocuta breverosti and Pliocrocuta perra.  The newcomers outcompeted the native hyenas for the narrow hunter/scavenger niche.

During full glacial maximums southern Italy and Spain served as refuges for species such as Elephas antiquus and a temperate-adapted species of rhino.  However, during the Last Glacial Maximum, the superior hunting humans (Homo sapiens) probably overhunted these species to extinction in their glacial refugia.

Reference:

Muttoni G.; Giancarlo Scardio, and Dennis Kane

“Early Hominins in Europe: The Galerian Migration Hypothesis”

Quaternary Science Review 180 Jan 2018

Scientists Recognize New Species of Late Pleistocene Horse (Haringtonhippus francisi)

January 29, 2018

Scientists recently recognized a new species and genera of extinct Pleistocene horse from fossil specimens already in museums.  Some of these specimens were collected over 100 years ago and were wrongly assumed to represent previously known species or genera.  During the Pleistocene there were 3 lineages of horses in the Americas–the caballine horses, the New World stilt-legged horses, and the hippidion horses.  The caballine horses belong to the Equus genus which includes all living species of horses, donkeys, and zebras.  The species of caballine horses that lived in North and South America likely included the predecessor of the modern day domesticated horse.  It was probably the same species.  The New World stilt-legged horses so anatomically resembled Asiatic wild asses and donkeys that paleontologists mistakenly thought they were closely related.  In recent years paleontologists began to reject this assumed affinity, and the genetic study cited in this blog entry supports their re-assessment.  The hippidion horses were robust species restricted to South America.  A new genetic study determined the New World stilt-legged horses, previously classified as belonging to the equus genus, were different enough to deserve their own genus.  Scientists gave this species the scientific name Haringtonhippus francisi. The species was named after the renowned Canadian paleontologist, Richard Harington.  The type specimen anatomically described in the paper was originally discovered in Wharton County, Texas.

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Artists’s representation of Haringtonhippus francisi.  The coat color is the artist’s fanciful guess.

The genetic evidence suggests haringtonhippus  horses diverged from equus horses between 4-5 million years ago.  The hippidion horses diverged from the equus/haringtonhippus genera between 5-7 million years ago.  Convergent evolution explains why haringtonhippus horses anatomically resembled Old World asses.  Both evolved long slender limbs as an adaptation to arid environments.

Fossil remains of Haringtonhippus francisi  have been found in east Texas, eastern Mexico, Kansas, Nevada, California, the Yukon, and Alaska.  Stilt-legged horse fossils are known from sites thought to be 3 million years old, and they occurred until as recently as 12,000 years ago about the time man became prevalent on the continent.

If scientists are able to extract DNA from even more ancient extinct genera of horses, they may be able to straighten out horse evolution.  Many biology textbooks use the fossil record of horses and their ancestors as an example of evolution, but these family trees are based on anatomical analyses that can be misleading.  DNA evidence would produce more reliable family trees.

Reference:

Heinztman, P; et. al.

“A New Genus of Horse from Pleistocene North America”

Genomics and Evolutionary Biology Nov. 2017

Raccoon (Procyon lotor) and Swamp Rabbit (Sylvilagus aquaticus) Latrines

January 23, 2018

Many animals defecate to mark their territory, but raccoons share communal latrines where all the individuals in an area deposit their feces. Communal raccoon latrines impact the ecosystem. The raccoon roundworm (Baylisascaris procyonis) is a parasite that spends part of its lifecycle in a raccoon’s intestine. Raccoons can live with this parasite, but it can kill mice, birds, and humans. Therefore, mice and birds avoid raccoon latrines, despite the nutritional value found in undigested seeds embedded in raccoon feces. Somehow, they evolved the ability to sense the danger of a parasite playground. However, raccoon roundworm is not dangerous to rats, so raccoon latrines actually attract rats seeking edible seeds. Seeds that survive transport through a raccoon’s digestive system and are overlooked by rats may then germinate. Raccoon’s play a role in the dispersal of some plant species.

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Raccoon latrine.  This batch is full of blackberry seeds.

Unlike raccoons, swamp rabbits don’t defecate in communal latrines, but oddly enough they often crap on moss-covered stumps or fallen logs. Perhaps the moss disguises the odor, preventing predators from triangulating their scent. It is also elevated, so a predator following its nose might miss it.  Researchers surveying swamp rabbit populations use these latrines to record their presence because this nocturnal species is difficult to find in the thick swamps and wetlands where they range.

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Swamp rabbit latrine. Note the moss.

Swamp rabbits are a species of cottontail that inhabits aquatic habitats from the Mississippi River Valley east to western Georgia and northwestern South Carolina. Another species of semi-aquatic cottontail–the marsh rabbit (S. palustris)–inhabits wetlands from western Georgia to the Atlantic Ocean and throughout all of Florida. There is little overlap between the 2 species, though they occupy the same ecological niche. How curious?

Swamp rabbit genetics has rarely been studied. A 20 year old genetic study determined swamp rabbits and marsh rabbits are closely related sister species, but this doesn’t explain why their ranges don’t overlap. So far, no geneticist has employed a molecular clock to estimate when swamp rabbits and marsh rabbits diverged or when they diverged from eastern cottontails (S. floridanus). The latter is an habitat generalist with an extensive Pleistocene fossil record. Specimens of Pleistocene eastern cottontails have been found all over North America. By contrast marsh rabbit remains dating to the Pleistocene are restricted to 8 sites in Florida and 1 site near the Georgia coast. Pleistocene swamp rabbit remains are even less common, having been discovered at 1 site in Missouri, and 1 site in Tennessee where Pleistocene remains were mixed with Holocene material, so this specimen might not even be from the Pleistocene. Some marsh rabbit remains date to the Sangamonian Interglacial (132,000 years BP-118,000 years BP). Swamp rabbits, as a species, are probably at least that old too. Both species thrived during wetter stages of climate when wetland habitat expanded. I hypothesize the common ancestor of both was a semi-aquatic species that was isolated into 2 separate founder populations during arid Ice Ages when unsuitable desert grassland habitat expanded between refuges along the Mississippi River Valley and Florida. But I still can’t figure out why they haven’t invaded each other’s ranges since then.

Genetic studies may be the best way to resolve this mystery because the fossil evidence is scant. I hope a geneticist takes an interest in this unresolved secret of nature.

References:

Fantz, Debbie; et. al.

“Swamp Rabbit Distribution on the Northern Edge of their Range in Missouri”

Southeastern Naturalist  16 (4) 2017

Halanych, K.; T. Robingon

“Phylogenetic Relationships of Cottontail (Sylvilagus, Lagamorpha) Congruence of 125r DNA and Cytogenetic Data”

Molecular Phylogenetics and Evolution 7 (3) June 1997

Weinstein, Sara; et. al.

“Fear of Feces? Trade-offs between Disease Risk and Foraging Drive Animal Activity around Raccoon Latrines”

Oikos  Jan 2018

The Presence of Caribou in Southeastern North America during the Pleistocene and it Paleoecological Implications

December 19, 2017

 

The reindeer, legendary conveyor of Santa’s sleigh, is an Holarctic animal, meaning it lives south of the Arctic Circle in both North America and Eurasia.  In North America the reindeer is more commonly known as caribou.  When Europeans colonized the New World caribou lived as far south as upstate New York, but today their range in North America is restricted to Canada and Alaska.  During Ice Ages, however, almost all of their present day range was under glaciers–unsuitable habitat even for such a cold hardy animal.  Caribou range shifted south then, and caribou fossil material has been found at numerous southeastern sites including Bell Cave in Alabama, Yarbrough Cave in Georgia, 3 caves in Tennessee, off the North Carolina coast, off Myrtle Beach, and in Charleston, South Carolina (the most southeastern known occurrence).  Apparently, caribou occurred at least as far south as the piedmont region.

Image result for reindeer
Reindeer and Caribou are the same species.
Caribou fossils have been found associated with an interesting mix of species at the above-mentioned fossil sites, though it’s unclear if they all lived at those localities during the same climatic phases.  Cave and offshore sites can collect the bones of animals from many different time periods.  Nevertheless, caribou bones have been found with the remains of giant beavers, flat-headed peccary, long-nosed peccary, woodland muskox, white tail deer, stag-moose, horse, tapir, mastodon, ground sloth, jaguar, and dire wolf.  Pleistocene caribou in eastern North America likely preferred open spruce woodlands interspersed with prairies.  This habitat would have also been favorable for horse, flat-headed peccary, bison, and mammoth.  By chance caribou remains haven’t been found with the latter 2, but they probably co-occurred at some locations.  Dire wolves, habitat generalists, likely co-occurred with caribou as well and probably preyed on them.
Baker Bluff Cave in northeastern Tennessee has well stratified deposits that contain many vertebrate bones from 2 different climate phases.  Information from this site can help determine the faunal composition that co-occurred with caribou.  The oldest deposits at Baker Bluff Cave are interpreted as representing a temperate forest consisting of oak, northern pine, birch, beech, etc.  Gradually, this environment gave way to the open spruce woodland/prairie as the climate became colder and drier during the Last Glacial Maximum.  White-tailed deer remains are abundant throughout all layers of the deposit, and they co-occur with caribou in Canada today, so undoubtedly they were a contemporary of Pleistocene caribou.  Long-nosed peccary, a forest edge species, like white-tail deer, likely co-occurred with caribou as well.  Mastodon, giant beaver, and stag-moose inhabited wetland environments adjacent to caribou habitat, and I’m certain they were contemporaries with caribou.  Woodland musk-ox, another likely contemporary, foraged in shrub habitat near caribou range.
A jaguar tooth found at Baker’s Bluff Cave was excavated from the lowest oldest level.  This is evidence Pleistocene jaguars inhabited cool temperate forests, but it seems unlikely they survived in the region when the forest gave way to boreal environments.  However, caribou may have also occurred in the southeast during interstadials.  (Good carbon-dating of regional caribou fossils has yet to be conducted.)  It’s impossible to determine from available data whether jaguars inhabited the same range as caribou.  The same can be said for the tapir, a species that preferred thick forest.
Cave deposits contain an even greater abundance of small vertebrate fossils.  Most smaller animals are more restricted to certain environments than larger species, and their composition better reveals what natural communities of this locality were like.  The Baker Bluff Cave deposits are particularly interesting.  Fossil material of species still found in the region today (gray squirrels, eastern chipmunks, southern flying squirrels) were present throughout the deposit but were less common during the open spruce woodland/prairie phase.  By contrast some species that today live to the north and west of the region (13-lined ground squirrels, least chipmunks, northern flying squirrels, badgers, pine martens, fishers, magpies) were also found throughout the deposit but were less common during the cool temperate forest stage.  Red squirrels were also less common during this phase but more common after the landscape changed.  Fossil remains of 13-lined ground squirrels have been excavated from sites throughout the southeast but no longer occur east of the Mississippi.  Fossil material of birds that prefer open spaces such as upland sandpiper and prairie chicken were excavated from Bell Cave and Yarbrough Cave.  The presence of these species is evidence prairie habitat was common in the region during Ice Ages.  Pine marten specimens, dating to the Pleistocene, were discovered as far south as northern Alabama, and Pleistocene fisher specimens turned up in northern Alabama and north Georgia.  This is evidence of boreal environments in the upper south.
I hypothesize Ice Age ecosystems in southeastern North America were more diverse than they are today due to rapid climate fluctuations.  Climate phases of warm wet interstadials (but cooler on average than today) and cold arid stadials alternated but the response of the floral and faunal composition to these rapid climate changes lagged behind.  Some climate phases lasted for a few thousand years or perhaps just centuries or even decades.  They weren’t long enough to completely eliminate habitat for species with warm temperate affinities, nor did they last long enough to extirpate habitat favorable for species with boreal affinities.  This explains why eastern chipmunks co-occurred with least chipmunks, and why caribou may have shared the range with jaguars and tapirs.  During cold phases though prairie and boreal forest expanded, oak woodlands persisted on some tracts of land, especially south-facing slopes.  During warm phases oak woodlands expanded, but spruce forests persisted on north facing slopes.
Herds of caribou formerly wandered through Georgia followed by packs of dire wolves and prides of lions.  The herds traveled through fingers of prairie between open woods consisting of pine and spruce and oak where turkeys foraged on the ground and fishers chased gray squirrels through the tree tops.  Landscapes of present day Georgia are unrecognizable by comparison.
Reference:
Guilday, John; H. Hamilton, E. Anderson, and P. Parmalee
“The Baker Bluff Cave Deposit, and the Late Pleistocene Faunal Gradient”
Bulletin of the Carnegie Museum 1978