The Clarendonian Land Mammal Age

July 13, 2020

Many science writers often describe the Pleistocene of North America as resembling the modern day African Serengeti.  I debunked that notion 7 years ago in an article I wrote for this blog (See: https://markgelbart.wordpress.com/2013/12/09/the-faunal-diversity-of-pleistocene-north-america-was-less-than-that-of-modern-day-africa/ ) In terms of biomass Pleistocene North American might have been as impressive but not when it comes to biodiversity.  Africa has almost twice as many species of mammals as Pleistocene North America. However, there was a time period during North America’s natural history when it was biologically more diverse than modern day Africa.  The Clarendonian Land Mammal Age during the middle Miocene lasted from ~13 million years ago to ~9 million years ago.  The age is named after the Clarendon local fauna based on fossils found from 24 sites in Donley County, Texas.  Scientists are aware of 34 mammal families that lived in North America during this age.  This includes 8 genera of artiodactyls such as camels and llamas, peccaries, deer, and pronghorns.  There were 15 genera of horses plus tapirs and 2 species of rhinoceros.  1 species of primitive oreodont still clung on, though they were formerly more diverse.  Bear-dogs (Amphycyon sp.) also still survived but were headed for extinction.  4-tusked gompotheres, kin to elephants, entered North America by crossing the Bering Land Bridge and colonized the continent.  Predators included 8 genera of canids, 11 genera of weasels, and 9 genera of rodents.  River dolphins and dugongs swam in the waters.  The bone-eating dogs (Borophagine), ancestors of saber-tooth cats (Nimravides), and false saber-toothed cats (Barbourofelis) were the dominant large predators.  Fanged cats and cat-like animals came in all sizes.

Among the amazing diversity of mammals were some remarkable morphological convergences with modern day species of African fauna.  There were giraffe-like camels that evolved long necks to feed on the tops of trees, aquatic hippo-like rhinos, and fast running gazelle-like horses.

Teleoceras | Animal of the world Wiki | Fandom

The hippo-like rhino Teleoceras.

Aepycamelus | Extinct animals, Ancient animals, Prehistoric animals

The giraffe-like camel Aegypcamelus.

Nannippus sp. by Dinogod.deviantart.com on @DeviantArt

The gazelle-like nannihippus.

Climate over most of North America during the middle Miocene was warm and mostly non-seasonal.  Before the Clarendonian Land Mammal Age tropical and sub-tropical forest covered most of North America, but the uplift of the Sierra Nevada and Cascade Mountain Ranges caused increased aridity.  Warm savanna grassland and open woodland replaced the thick forest, and this resulted in a greater diversity of mammals, taking advantage of this more productive habitat.  Grazing herds of ungulates and burrowing populations of rodents in deep grassland soils thrived in this environment.  Climate change brought an end to the Clarendonian Land Mammal Age.  Conditions became even more arid and seasons became more pronounced.  Warm savannahs and open woodlands were replaced with steppe grasslands where  winters started to trend toward sub-freezing temperatures.  Many species of mammals could not adapt to harsher winters and simply went extinct. By the end of the Miocene and beginning of the Pliocene large mammal diversity was much reduced, but new cold-adapted species from Eurasia (crossing the Bering Land Bridge) and new immigrants from South America (crossing the newly emerged Isthmus of Panama) helped replenish biodiversity in North America. Though large mammal diversity never again approached that of the Clarendonian, it was an healthy cavalcade until the end of the Pleistocene when man wiped most of them out.

Eastern Range Extensions of Western Fauna on Xeric Limestone Prairies

July 6, 2020

I wrote an article a few years ago about roadrunners (Geococcyx californiannus). (See: https://markgelbart.wordpress.com/2016/08/05/pleistocene-roadrunners-geococcyx-californianus/ ) I noticed roadrunners ranged into Arkansas–a curious eastern range extension–and I wondered why.  A few weeks ago, a scientist sent me a box of science books, and I found the answer to my question in 1 of them.  Xeric limestone prairies in Arkansas and Missouri provide excellent habitat for 3 species of western fauna including roadrunners, collared lizards (Crotophytus collaris), and Texas brown tarantulas (Aphonopelm hentzi).  Xeric limestone prairies are openings in woodlands that are created naturally but may be maintained with or without human influence.  Dry shallow soils, not more than 3 feet deep, on a bed of limestone or dolomite, favor the growth of grass over trees. Little bluestem grass dominates xeric limestone prairies, but Indian grass, side oats gramma, and big bluestem also grow on them with the summer annual grass, poverty dropseed, on areas with even shallower soils.  Grazing and fire help maintain these openings, but the dry shallow soils high in calcium can remain open without these influences.  Nevertheless, in the absence of fire or grazing woody encroachment can occur.  Juniper, blackjack oak, and black hickory may invade some xeric limestone prairies.

 Xeric Limestone Prairie in West Virginia.

www.allaboutbirds.org/guide/assets/photo/603886...

Roadrunners primarily are a western species, but they have an eastern range extension into Arkansas because they like limestone prairies.

Texas Brown Tarantula.jpg

Texas brown tarantulas also range into limestone prairies in Arkansas.

Eastern Collared Lizard | MDC Discover Nature

Dry limestone prairies provide habitat for an eastern range extension of the collared lizard.

Reptiles like to sun themselves on the limestone rocks scattered throughout these prairies, and this attracts roadrunners that prefer open areas with lots of the insects, reptiles, and rodents they prey upon.  Collared lizards are 1 of the reptiles that like to sun themselves on rocks, and they may become prey for roadrunners,  but they are also predators that hunt insects and other lizards in this habitat..  Collared lizards are cannibalistic.  Texas brown tarantulas, yet another western species extending their range east on limestone prairies, are large spiders reaching 6 inches in length with a 4 inch leg span.  They can weigh as much as a McDonald’s quarter-pounder.  Their venom is not harmful to humans unless the person is allergic.  But their fangs are large and can cause a painful bite that may get infected.

Other species of animals common on xeric limestone prairies in Arkansas include 6-lined race runners, southern coal skinks, fence lizards, slimy salamanders, leopard frogs, box turtles, Bachman’s sparrows, field sparrows, prairie warblers, cerulean warblers, Kentucky warblers, painted buntings, brown thrashers, hawk wasps, and numerous species of grasshoppers.

Xeric limestone prairies are not confined to Arkansas and Missouri but are also found in parts of West Virginia, Alabama, Tennessee, Georgia, Indiana, Illinois, Ohio, and Pennsylvania.  However, limestone prairies in those states don’t host as many species of western fauna as those in Arkansas and Missouri.  The Mississippi River must be too big an hurdle for them.

Reference:

Cartwright, Jennifer and William Wolfe

“Insular Ecosystems of the Southeastern United States: A Regional Synthesis of Support Biodiversity Conservation in a Changing Climate”

U.S. Geological Survey Professional Paper 1828 2016

New Study of the Seda-DNA in Hall’s Cave, Texas

June 29, 2020

A new study of seda-DNA and bone DNA from Hall’s Cave documents the changes over time in the plant and animal communities on the Edward’s Plateau in Texas.  Previously, scientists had collected and identified thousands of bones in Hall’s Cave from 56 species of mammals, 30 species of birds, 9 species of amphibians, 3 species of reptiles, and 2 species of fish.  The bones date from the Last Glacial Maximum (~20,000 years BP) to the early Holocene (~9,000 years BP).  The new study extracted DNA from the bones but in addition took samples of DNA from the sediment. (Scientists call DNA from sediment samples, “seda-DNA.”)  Sampling DNA from the sediment has the added advantage of detecting the presence of plant remains that were otherwise unidentifiable, and the presence of animals that perchance left no skeletal remains at all in the cave.  For example 2/36 bone samples were from cat but 7/10 sediment samples detected cat.  Jaguars and bobcats urinated, defecated, and shed hair in the cave but left no skeletal remains.  The seda-DNA samples detected 36 of the 56 species of mammals known to have  occurred in the cave from fossil evidence but they found an additional 7 species of mammals as well as additional species of birds not collected as fossils here, including ducks and geese.  They also determined which species of woodrat lived in the cave, an identification not really possible by just looking at the bones.

Deer mouse, cottontail rabbit, and eastern woodrat were the most common species of small mammals found in the cave since the Last Glacial Maximum, and these species occurred throughout all climate phases.  White-tailed deer and bison were the most common large mammals found in the cave and they too were found throughout all climate phases, though they became less abundant over time.  Hackberry and oak were the most common plant species found in the cave, and they were found throughout all climate phases.  Hackberry still grows near the entrance of the cave.  According to local pollen studies, pine was the most common tree growing on the Edward’s Plateau during the Ice Age, but it is absent from the cave.  Pine simply didn’t grow near the cave.

Hall’s Cave.

Edwards Plateau Savannas map.svg

Location of Edward’s Plateau.

Dendrogram of species found via DNA sampling in Hall’s Cave.  From the below referenced study.

The study sheds light on the changes that occurred on the Edward’s Plateau since the Last Glacial Maximum.  During the height of the last Ice Age weather patterns differed from those of today–more precipitation fell on southwestern North America whereas southeastern North America was more arid.  As a result, the Edward’s Plateau hosted a prairie environment with trees found at scattered locations.  Soils were much thicker because dense grass regularly decayed.  Deeper soils were good environments for prairie dogs, 13-lined ground squirrels, pocket gophers, and marmots.  Common large mammals included camel, pronghorn, and flat-headed peccary that were preyed upon by saber-tooths, dire wolves, and giant short-faced bears.  Birds that preferred treeless plains–prairie chickens, upland sandpipers, horned larks–abounded here then.

The environment changed here about 15,000 years ago during the Boling/Alerod Interstadial when temperatures and precipitation increased.  The prairie converted to open woodland and forest with widely spaced oak, ash, juniper, walnut, mulberry, and hackberry trees.  Plenty of grass still grew between the trees…enough to support a population of horses.  Many of the open plains animals disappeared from the record here including the pronghorn, camel, and flat-headed peccary.  Black-tailed jackrabbits, northern grasshopper mice, and prairie chickens all left the area as well.  However, turkey, bobwhite quail, and barking tree frogs moved onto the Plateau because they liked the newly expanded tree and thicket habitats.

12,900 years ago, during the Younger Dryas cold phase, the climate suddenly became much colder and dryer.  Vegetation decreased and the region became desert-like.  Small and large mammal and plant diversity decreased.  Following the end of this cold phase, temperatures and precipitation increased, though rainfall didn’t increase to the levels of the LGM and Boling/Alerod Interstadial.  Soils of the Edward’s Plateau were still thinner than they were during the LGM and today the region is dominated by a plant community of live oak, juniper, and hackberry.  Plant and small animal diversity rebounded but large mammal diversity did not.  The authors of this paper suggest man is likely responsible.  Plant and small mammal ranges adjusted to climate change, and they disappear and re-appear in the seda-DNA samples over time.  If not for overhunting by man, the same should hold true for large mammals.  14 species of large mammals that lived on the Edward’s Plateau during the late Pleistocene are either extinct or extirpated from the region.

Plant and animal composition does not stay constant, and the study found some non-analogue components living side by side.  Today, white-tailed jack rabbits and barking tree frogs have ranges that do not come close to overlapping, but both species lived on the Edward’s Plateau during the Boling/Alerod Interstadial.    Bog lemmings and least weasels ranged much farther south then and co-occurred with species of more southerly affinities.  Animal and plant communities are dynamic and always changing.

Species Profile: Barking Treefrog (Hyla gratiosa) | SREL Herpetology

Range of barking tree frog.

White-tailed jackrabbit - Wikipedia

Range of white-tailed jack rabbit.  White tailed jack rabbits and barking tree frogs both lived on the Edward’s Plateau during a warm interstadial of the last Ice Age, indicating the existence of non-analogue environments dissimilar to any that occur today.

Reference:

Seersholm, F.; et al

“Rapid Range Shifts and Megafaunal Extinctions Associated with Late Pleistocene Climate Changes”

Nature Communications 2020

https://www.nature.com/articles/s41467-020-16502-3#:~:text=Large%2Dscale%20changes%20in%20global,impacted%20ecosystems%20across%20North%20America.&text=Instead%2C%20five%20extant%20and%20nine,the%20end%20of%20the%20Pleistocene.

Tuna- The Superfish

June 24, 2020

Most people think of tuna as just some fish in a can that is an ingredient in tuna salad.  They don’t appreciate what a spectacular animal it is.  Biology books state that fish are cold-blooded, but tuna are an exception to this rule.  Tuna are actually a warm-blooded fish, and this physiology enables them to swim at ultra high speeds of up to 47 mph.  That is faster than most boats.  However, their warm-blooded physiology has a greater temperature range than those of mammals and birds.  Their blood temperatures do vary, while mammal and bird temperatures generally stay constant, unless they are sick.  The video below shows off the impressive speed of this animal.  They swim with dolphins for protection against sharks, explaining why dolphins can get caught in nets intended for tuna.

 

Tuna are large predatory fish that can swim up to 47 mph.

There are 15 species of tuna within 5 genera including the Allothonnus (thunder tunas), the Auxil (frigate tunas), Euthynnus (little tunas), Katsunnus (skipjacks), and Thunnus (true tunas).  Bonitos are considered a sister species to the tunas, and both are part of the mackerel sub-group.  4 species of tuna overwhelmingly make up the tuna found in supermarket cans and at fish markets and sushi restaurants.  These include bluefin, yellowfin, skipjack, and albacore.

Tuna did not become a popular food fish until well into the 20th century, but now every grocery store in the U.S. stocks tuna.  It doesn’t seem likely to me that this can go on forever.  Eventually, wild tuna populations will become too depleted to support this fishery.  The future of tuna remaining a staple in our diet is aquaculture, but tuna fish farming is in its infancy.  Some Japanese have had experimental tuna fish farms for decades, but the 1st tuna farm in America just opened business last year in San Diego.  Tuna fish farming, unlike tilapia, catfish, and salmon aquaculture, has a long way to go.

There is evidence from Indonesia that humans caught tuna as early as 42,000 years ago. (See: https://markgelbart.wordpress.com/2011/12/07/deep-sea-fishing-42000-bp/ ) It’s surprising some primitive people had deep sea fishing technology that early, though tuna swam closer to shore during the Pleistocene because land extended over the continental shelf and deep waters were located closer to the coast then.

Albacore - Wikipedia

The most common species of tuna found in a can–albacore.

Giant Bluefin Tuna Sells for $3.1 Million in Tokyo | Fortune

500 pound tuna are worth over 3 million dollars to sushi chefs.

1 of my favorite summer dishes is tuna noodle salad and it is very easy to make. Mix a 12 oz package of tuna with the juice of a lemon.  Add a 16 oz box of cooked macaroni, mayo to taste, a can of peas, chopped celery, chopped Vidalia onion, and couple of chopped hard boiled eggs. Stir it up and serve it warm or cold from the refrigerator.

This is my tuna noodle salad.  It’s great warm or straight out of the refrigerator on a hot summer’s day.

North American Army Ants

June 17, 2020

Most people are familiar with the army ants of South America and the driver ants of Africa featured in many nature documentaries, but few are aware army ants also occur in North America.  There are 30 species of army ants from the Neivamyrmex genus and 1 species from the Novamyrmex genus living on this continent.  North American army ants differ from those of South America and Africa.  North American army ants cross the landscape in more narrow spear-headed swarms than those of their tropical cousins.  Nevertheless, they are just as predatory.

Neivamyrmex nigrescens, Arizona

A species of North American army ant.  Notice how thick their antenna are. Years ago, I witnessed army ants tearing apart an earthworm in Columbia County, Georgia. This photo is by Alex Wild from the below link.

Army ants don’t live in permanent nests.  Instead, they alternate between foraging and stationary phases.  During foraging phases they roam across the land searching for food to feed their larva.  They mostly eat other ants and are built to subdue other species.  They have muscular bodies and thick antennas that other ants can’t bite through.  When the larva go into the pupa stage, army ants enter the stationary phase and live within a swarm of their own bodies.  Colonies produce new queens every 3 years, and the colony will split into 2 after the new queen is born.  Most army ant colonies perish when the queen dies, but some manage to track down a closely related queen and will merge with that colony.

There are over 200 species of army ants worldwide including 5 genera in the Americas and 2 genera in Africa and Asia.  A study of army ant genetics determined some genera of American army ants are closely related to African army ants.  They diverged 100 million years ago before Africa and South America drifted apart.  Other genera of army ants are not closely related to other army ants and are examples of convergent evolution.

neivmap1

Range map of army ants in North America.  Map is also from the below reference.

Cold climate apparently is a limiting factor for army ant distribution, but it might not be the temperatures.  I noticed in the map of their distribution that the northern limits of their range approximately corresponds to the southern limit of Ice Age glaciers.  Like many species of trees, they simply have been unable to colonize deglaciated territory even though they can survive the cold temperatures of Iowa and Nebraska.

Reference:

Most of the information for this blog entry comes from Alex Wild, a Texas entomologist.  This links to his website.

http://www.myrmecos.net/2008/12/14/army-ants-of-the-north/

Another Pleistocene Survivor–The Bird-Voiced Tree Frog (Hyla avivoca)

June 11, 2020

I discovered a new creature in my yard.  Green tree frogs (Hyla cinerea) are abundant here and often sneak into our house, but I was unaware that my yard is also home to the bird-voiced tree frog until I saw the below specimen in my cat’s water dish.  I saw another one a few weeks later.  Most of the time they stay in the tree tops and that is probably why I’d never seen one before, though maybe they had a good few years of reproduction and are on the increase at my locality.  Bird-voiced tree frogs can be green or gray, depending upon the temperature.

Bird-voiced tree frog.

Video of a bird-voiced tree frog call.

Bird-voiced tree frogs have an interesting range distribution.  They likely diverged from their closest living relatives in the Mississippi River Valley and dispersed across Alabama and Georgia.  Their preferred habitat is swampy bottomland forest, and during warm climate cycles this type of habitat is common in the southeast.  The habitat in my yard is a sandhill loblolly pine/sand laurel oak woodland, but McBean Creek bottomland is just about a mile away.  Bird-voiced tree frogs are absent from peninsular Florida.  They may have occurred in peninsular Florida in the past but were extirpated when most of the state was under ocean during marine high stands.

Species Profile: Bird-voiced Treefrog (Hyla avivoca) | SREL ...

Bird-voiced tree frog range map.

I searched the paleobiology database and learned no fossils of this species have ever been found.  A small animal that lives in a forest has a lesser chance of becoming preserved as a fossil.  Leaves turn the soil acid, dissolving bones.  As far as I can determine, no genetic studies of bird-voiced tree frogs have ever been conducted.  It is an understudied species.

Permafrost as far South as Georgia during the Last Glacial Maximum

June 4, 2020

This is at least the 7th article I’ve written about Carolina Bays, but I keep coming across new and fascinating studies of these curious geological features. (See: https://markgelbart.wordpress.com/?s=Carolina+Bays ) These oval shaped depressions occur across the Carolinas and Georgia.  Their origins baffle scientists, but the commonly accepted explanation is they are topographical formations resulting from Ice Age wind and water erosion.  (Extraterrestrial explanations can be ruled out because Carolina Bays are of different ages, and there are 500,000 of them compared to just 250 known impact craters on the entire earth’s surface.)  I’ve long understood how wind and water erosion shaped the depressions, but I’ve never been satisfied with explanations for how the land initially subsided.  Some think wind simply blew unconsolidated sediment out of the pits, while I’ve suggested the land subsidence occurred due to peat fires (as occasionally occurs today).  In a new book Chris Swezey of the U.S. Geological Service proposed the initial subsidence of Carolina Bays was caused by discontinuous patches of permafrost that thawed during summers and collapsed.

Formerly, scientists thought permafrost (ground that stays frozen year round) extended as far south as northern Virginia during the Last Glacial Maximum, but Swezey believes there were patchy discontinuous areas of permafrost as far south as Georgia.  Carolina Bays resemble geological features found in southern Alaska today where permafrost is scattered and temporary.  The land swells and collapses and fills with water in oval depressions.  Northern Alaska hosts continuous permanent permafrost.

Millions of Arctic Methane Hotspots Detected by NASA – Global ...

Discontinuous patches of permafrost create lakes in southern Alaska that resemble Carolina Bays located in the upper coastal plain of Georgia and the Carolinas.

Average temperature and sea surface level through 35,000 years related to 1990 level

Temperature graph showing average temperatures and sea level fall during the Last Glacial Maximum. Note the dips at about 27,000 and 24,500 years BP.  This is when discontinuous permafrost could have developed on some Georgia and Carolina soils.

I believe this map is misleading.  It shows the southern extent of the boreal forest zone, but zonal forest types as we know them today didn’t exist then.  From the below referenced paper.

Georgia must have been much colder during Ice Ages than I thought.  Most Carolina Bays formed between 35,000 years BP-15,000 years BP when glaciers expanded to cover Canada and New England.  Some date to earlier stadials of the Wisconsinian Ice Age.  Patchy permafrost in the Carolinas and Georgia likely occurred during especially cold phases of the Ice Age that probably lasted for decades rather than centuries.

Landscapes in Georgia during the LGM must have been varied and interesting.  Wetlands on Carolina Bays likely attracted summer populations of ducks, geese, and swans.  Sand dunes from dried out riverbeds rolled over the land, smothering mixed woodlands of pine, spruce, and oak.  Arid conditions favored grasslands that fed horse, bison, and llama; in turn pursued by giant lions and dire wolves.  Strange as it may seem, caribou and stag-moose ranged into this latitude.  Zonal vegetation as we know it didn’t exist then.  Instead, habitats were patchy and species compositions were dissimilar to those of any existing types of forest.  Local microclimates might favor oak thickets, open spruce woodlands, mature pine forests, grassy meadows, small marshy wetlands, or bare soil.  Less than 100 miles east of the inner coastal plain the climate was markedly warmer.  Land extending into what today is the Atlantic Ocean  hosted more warm weather species of plants and animals because it was closer to warmer ocean currents that moderated coastal climates.  Inland, the boundary between cold and warm climates frequently fluctuated, contributing to the patchy unstable environments unlike those of today.

Reference:

Swezey, Chris

“Quaternary Eolian Sand Dunes and Carolina Bays of the Atlantic Coastal Plain Province, USA”

in

Inland Dunes of North America

edited by Lancaster, Nicholas and Patrick Hesp

Springer Books 2020

 

 

My 4th Visit to Phinizy Swamp

May 28, 2020

Phinizy Swamp is a protected wetland located in Augusta, Georgia about a 20 minute drive from my house, and if I could, I would visit it more often than I do.  We strolled through the swamp 2 weeks ago for the first time since my daughter almost stepped on an alligator’s head here.  I wasn’t expecting to see as much bird life during late spring because wintering ducks have already migrated north.  However, I did see big flocks of spotted sandpipers (Actitis macularious) and chimney swifts flying over the water, and I also saw a couple of lesser yellowlegs (Tringa flavipes).  The spotted sandpipers and lesser yellowlegs winter south of Augusta and spend their summers farther north.  Both are migratory transient species for this area.  The lesser yellowlegs breeds in Alaska, so these particular individuals were lagging far behind.  Spotted sandpipers breed through much of the Midwest.

2 spotted sandpipers and a lesser yellowlegs.

8 spotted sandpipers, 1 lesser yellowlegs, and a yellow-bellied cooter.

This was the biggest yellow-bellied cooter I’d ever seen.

We encountered a classroom with a professor and students who were studying the macroinvertebrates and water quality of the swamp.  Some of the macroinvertebrates they may have collected were backswimmers, a bug in the Notonectidae family.  These true bugs (Hemiptera) should not be confused with water boatmen of the Corixidae family.  Backswimmers swim on their backs, while water boatmen swim right side up.  Backswimmers are predators that feed upon insects, tadpoles, and minnows; water boatmen feed upon algae.  Surprisingly, both can fly and find isolated puddles where they won’t be eaten by fish. There is a dragonfly in the below photo as well.  Dragonflies are beneficial predators that eat mosquito larva.

Blue dragonfly perched over backswimmers.

The forest around the swamp consists mainly of water oak, loblolly pine, red maple, sweet gum, and cypress.  My favorite trees here, though, are the beech–otherwise rare in Augusta.

A week after I visited the swamp a man posted a photo on facebook of a bald eagle in Phinizy Swamp.  I hope I get to see a bald eagle here on my next visit.

 

The Lujanian Land Mammal Age, the South American Equivalent of the Rancho La Brean Land Mammal Age

May 19, 2020

(Note: I accidentally published this article earlier today before I added the text.  I deleted that mistake. Here is the text.)

The Rancho La Brea Fossil site in California produced so many spectacular fossils that it gives the name to the Rancho La Brean Land Mammal Age, a period of time including the last 300,000 years of the Pleistocene.  All the fauna from this age in North America is referred to as Rancho La Brean.   In South America this age is known as the Lujanian Land Mammal Age and is named after a former site in Lujan, Argentina where fossil hunters found in quality and quantity specimens that are at the very least the equal of those found at Rancho La Brea.   People began collecting fossils here as early as the late 18th century and continued to do so well into the 20th century until the site was swallowed up by urban development.  The Lujanian Land Mammal Age was originally considered to have begun when horses of the equus genus first entered South America, however, paleontologists have since determined equus horses colonized South America much earlier, perhaps over 1 million years ago.  (Horses from the hippidion genus lived in North America even earlier.)  In any case land mammal ages are an artificial construct invented by men to define the composition of fauna that lived during certain periods of time.

Luján | Argentina | Britannica

Location of Lujan, Argentina highlighted in white.

At least 31 species of mammals weighing over 40 pounds lived in and around what is now known as Lujan during the late Pleistocene.  This list includes an astonishing 14 species of xenarthans: 2 large species of armadillos, 7 species of glyptodont, and 5 species of giant ground sloth.  By comparison Rancho La Brea was home to just 3 species of xenarthans.  Ecologists puzzle over how the environment could support such a wide variety of closely related species.  The different species of animals likely ate different species of plants.  The ground sloths Glossotherium and Lestodon were bulk feeders of grass, Mylodon and Scelidotherium were mixed selective feeders, and the huge Megatherium was the most selective feeder of all the sloths.  Similar niche partitioning likely occurred among the large armadillos and glyptodonts.

Doedicurus clavicaudatus

The glyptodont, Doedicurus clavicaudatus.

3 species of primitive ungulates occurred during the Lujanian Age–2 species of toxodon and the bizarre ancient litoptern.  Toxodons were hippo-like in build and may have been semi-aquatic.  Litopterns (Macruachenia patachonica) diverged from the ancestors of horse, tapir, and rhino before the dinosaurs became extinct, yet those odd-toed ungulates are their closest living relatives.

The Toxodon was so weird - Business Insider

Toxodon platensis.

Darwin's dilemma: Bizarre ancient animal identified through DNA

The extinct litoptern, Macrauchenia patachonica.

More modern ungulates ranging near Lujan during the late Pleistocene were 4 species of llamas (3 now extinct), collared peccaries, an extinct species of horse, and a large extinct species of deer (Morenelephus lujanensis.  A mastodon-like gompothere (Stegomastodon platensis) roamed the land with them.

5 large species of carnivores preyed upon the plant-eating beasts.  Smilodon populator, a 750 pound saber-toothed cat, took on and took down some of the megaherbivores.  Jaguars and cougars attacked smaller prey than Smilodon’s victims.  The little known small wolf (Dusicyon avus) may or may not have hunted in packs but was probably more a scavenger, like a coyote.  An extinct bear (Arctotherium tarijensis) opportunistically ate meat whenever it had a chance.

Reference:

Farina, Richard; Sergio Vizcaino and Gerry De Juliis

Megafauna: Giant Beasts of Pleistocene South America

Indiana University Press 2013

 

Squirrel Monkeys (Saimiri oerstedii) and their Co-Horts

May 13, 2020

Several species of birds follow foraging squirrel monkeys through the jungle tree tops of Central and South America.  Troops of squirrel monkeys look for insects and fruit to eat, often overturning leaves and thrashing branches.  Their actions dislodge hiding insects and lizards, and this exposes them to predators.  Double-toothed kites (Harpagus bidentatus) perch on nearby branches, looking for insects or lizards forced to leave their hidden refuges.  Normally, their prey blends in with their surroundings, but the kites are attracted to the exposed prey forced to move.  Gray-headed tanagers (Eucometis pencillata) and tawny-winged woodcreepers (Dendrocineeb anabatina) also find insects this way.  These birds also follow white-throated capuchin monkeys, and they are among the many species that follow army ants. This behavior has occurred for tens of millions of years, ever since monkeys accidentally rafted over from Africa.

Guianan squirrel monkey information from Marwell The Zoo

Squirrel Monkey

Gray-headed Tanager - eBird

Gray-Headed Tanager

Tawny-winged Woodcreeper - eBird

Tawny winged woodcreeper

Double-toothed Kite - eBird

Double-toothed kite

Army ant columns attract even more birds than troops of monkeys do.   Fleeing insects and small vertebrates become prey to a family of 18 species of antbirds known as the Thamnophilidae, as well as cuckoos, thrushes, and chats.  The bird-ant relationship is parasitic.  Studies determined army ants obtain 30% less food when they are followed by antbirds.  It’s not always a beneficial relationship for the birds either.  4 ant stings is all it takes to kill the small birds.

Reference:

Boinski, S.; Peter Scott

“Association of Birds with Monkeys in Costa Rica”

Biotropics 20 (2) 1988