A Shocking New Study of Dire Wolf (Canis dirus) DNA Redux

I first published this blog article in January of 2021. I wanted to reblog it but found the last 4 paragraphs and a reader’s comment had vanished from the article. I have no idea why this happened. I almost always write my articles in a notebook before I type them up, and it took some time, but I found the notebook I wrote this article in, and I have now retyped it.

Dire wolves were one of the most common large predators of Late Pleistocene North America, and sub-fossils of this species are common, but scientists have had difficulty finding specimens with enough intact DNA to analyze.  There are thousands of dire wolf fossils excavated from the La Brea Tar Pits in California, but this DNA is contaminated with tar and can’t be used.  There are also many specimens of dire wolf fossils from Florida, but the humidity there causes DNA to deteriorate and become unusable.  However, Angela Perri, a zooarchaeologist from Durham University, made a concerted effort to find dire wolf specimens with enough viable DNA to study, and she found 5 specimens.  Labs from Australia and England analyzed the DNA from these specimens and came to a stunning conclusion–dire wolves were not closely related to gray wolves (Canis lupus) as most paleontologists had assumed, and they were not really even wolves.  Instead, they were the last in a lineage of now extinct ancient canids.

Mauricio Anton’s depiction of an interaction between dire wolves and timber wolves. Genetic evidence suggests dire wolves had short red coats.

The genetic study determined the ancestors of dire wolves diverged from the ancestors of gray wolves at least 5.7 million years ago. The closest living relative of the dire wolf is the African jackal (C. mesomeles), but the ancestor of that species diverged from dire wolf ancestry 5.1 million years ago. Interestingly, jackals can interbreed with wolves, but the study of dire wolf DNA found no evidence of interbreeding between gray wolves and dire wolves. Apparently, the 2 species had been geographically isolated for too long for them to recognize each other as possible sex partners. This study casts doubt on my hypothesis that an extinct ecomorph of Beringian wolf was a gray wolf/dire wolf hybrid.

Paleontologists assumed dire wolves were close relatives of gray wolves because their anatomy was so similar. Dire wolves had broader skulls, bigger teeth, shorter limbs, and were more robust; but otherwise they were much alike. This similarity can be attributed to convergent evolution.

Canids originated in North America, but the ancestors of gray wolves, coyotes, and jackals colonized Eurasia and evolved separately from dire wolves whose ancestors remained in North and South America. Dire wolves ranged from Alberta south to Peru and from California east to the Atlantic Ocean. Dire wolves appear suddenly in the fossil record 200,000 years ago. Most paleontologists believe they evolved from Armbruster’s wolf (C. armbusteri). Dire wolves were adapted to live in climates ranging from temperate to subtropical. Scientists weren’t able to sequence the entire genome of the dire wolf, but they may have had shorter more reddish hair than gray wolves and probably preferred warmer climates. Ancestors of gray wolves and coyotes crossed the Bering Land Bridge about 20,000 years ago and overlapped with dire wolves for 10,000 years. Gray wolves co-evolved with humans and learned to fear man. Dire wolves never learned to fear man, and likely could not compete with humans. I think this explains their extinction, while wolves and particularly coyotes continue to hang on.

The authors of the new study think dire wolves are so different, they should be given a separate genus–Aenocyon. One of the first paleontologists who looked at dire wolf bones assigned this name to dire wolves, but it fell from fashion because of the misinterpretation that dire wolves were close kin to gray wolves. Turns out, he was right; later paleontologists were wrong.

Reference:

Perri, A., et al

“Dire Wolves were the Last of an Ancient New World Canid Lineage”

Nature 591 (2021)

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Sabertooths (Xenosmilus hodsonae) ate as Much Bone as African Lions

A few weeks ago, a reader requested a source for something I had written in an article from 2013. I stated in the caption below an image from the article that a study of 4 flat-headed peccaries estimated they ranged in size from 260 pounds to 360 pounds. (See: https://markgelbart.wordpress.com/2013/03/10/when-sand-dunes-buried-herds-of-flat-headed-peccaries/ ) He informed me most sources on the internet claimed this species was less than 100 pounds. I remembered reading the paper with this information about the peccary size estimate, but I couldn’t recall the title of the paper. The information I stated was very specific, so I’m sure I read it somewhere. I make mistakes, but I don’t make shit up. I spent some time trying to hunt my source down. First, I looked through the reference at the bottom of my article–that reference was hard to find, but I did locate the 50-year-old research paper. There was no size estimate in it. I scoured the internet, but I could not find my source. I cursed my laziness for not being more thorough in referencing sources for my information. The paper is probably in some obscure journal that is either hard to find or just isn’t on the internet anymore. Still, I am certain flat-headed peccaries reached weights of greater than 100 pounds contrary to most sources on the internet. Bjorn Kurten, author of the classic Pleistocene Mammals of North America, stated flat-headed peccaries were the size of a wild boar. Male wild boars can reach weights of 440 pounds. I looked over the contrary sources and found the original error in the underestimation of how big flat-headed peccaries could get. Wikipedia cites the paleobiology data base in estimating the size of flat-headed peccaries. According to the paleobiology database, the size estimate of the type specimen was 60 pounds. The type specimen is the first fossil for which a species is named and is just 1 animal and not the average-size of every specimen of a species. The type specimen may have been from a juvenile. Various sites on the internet then copied the misleading fact from Wikipedia that flat-headed peccaries weighed on average less than 100 pounds, and so now there are a bunch of sources making this incorrect claim.

While reviewing the literature about flat-headed peccaries, I discovered an interesting new study about the dietary habits of Xenosmilus hodsonae. Xenosmilus was a species of saber-toothed cat that lived during the early Pleistocene from 1.6 million years ago to 1 million years ago. The species was first named in 2001 and is known from fossil sites in just 7 counties in Florida. It was named the “cookie-cutter cat” because a scientist proposed this species took a cookie cutter sized bite from its prey, then sat back and waited for its victim to bleed to death. How ridiculous. No predator is going to cease attacking prey that is struggling to survive. I’m sure Xenosmilus wrestled its prey down and bit through its throat. Xenosmilus was related to the scimitar-toothed cat (Homotherium) but was built more like Smilodon, a robust ambush predator. Homotherium by contrast had long legs and ran down its prey. Xenosmilus’s similarity to Smilodon is an example of convergent evolution when organisms not closely related to each other evolve the same characteristics to adapt to certain environmental conditions. Xenosmilus and Homotherium are classified in the same family as Smilodon–the Machairodontinae–but recent genetic evidence suggests the scimitar-toothed lineage (Xenosmilus and Homotherium) diverged from the saber-toothed lineage (Smilodon) 18 million years ago.

Xenosmilus hudsonae fossil remains are known from just 7 counties in Florida. It was related to the long-legged scimitar-toothed cat (Homotherium) but was built more like the ambush predator–Smilodon fatalis. Both lines of fanged cats are in the same family (Machairodontinae), but they are separated by 18 million years of evolution. Map from the University of Florida Museum of Natural History.

Image of mounted Xenosmilus skeleton from the University of Florida Museum of Natural History along with bones of flat-headed peccary that Xenosmilus chewed upon. Image from the below referenced paper.

A fossil site in Florida known as Haile 21 A is thought to have been a predator den site and not a natural trap cave because just 1 species of megaherbivore has been found here. The site has yielded the remains of 4 predators–Xenosmilus, Smilodon gracilis (the evolutionary ancestor of the famous Smilodon fatalis), Edward’s wolf, and Armbruster’s wolf. 1 of the latter 2 may be the evolutionary ancestor of the dire wolf. The site has also yielded the remains of over 60 flat-headed peccaries (Platygonnus vetus, the evolutionary ancestor of P. compressus). Scientists looked at the bones of the flat-headed peccaries found at this site to determine how much bone Xenosmilus ate. They compared these chewed on bones to those of African warthogs that were eaten by African lions. According to the authors of this paper, African warthogs are about the same size as flat-headed peccaries and reach weights of between 110-220 pounds (note: larger than the erroneous size estimates given by most sources on the internet). They found 85% of the peccary bones had at least 1 tooth mark, and the bones that were consumed or chewed upon by Xenosmilus were similar to those gnawed upon by lions. There were puncture marks on neck bones. Xenosmilus removed much of the shoulder muscles, and they chewed on the soft bones of the limbs and ribs. They didn’t bite into the middle of large bones. Previous to this study, scientists thought Xenosmilus and other fanged cats avoided bone completely to prevent breaking their long fangs. But this wasn’t true. They ate as much bone as lions and more than cheetahs.

Reference:

Dominguez-Rodrigo, M., C. Egelund, L Cobo-Sanchez, Baquedano, E., R. Hulbert

“Saber-tooth Carcass Consumption Behavior and the Dynamics of Pleistocene Large Carnivore Guilds”

Scientific Reports 12 6045 (2022)

https://www.nature.com/articles/s41598-022-09480-7

Pleistocene Gray Foxes (Urocyon cinereoargenteus)

Almost every major Pleistocene-aged fossil site in southeastern North America yields specimens of the gray fox. Bones of this species have been found at 58 sites across North America and 22 sites in Florida alone. The gray fox is an extremely successful species and has existed for at least 10 million years, though paleontologists assign the scientific name Urocyon cinereoargenteus just to those individuals that have lived over the past 300,000 years. Its evolutionary ancestors are barely distinguishable from modern day gray foxes. (Scientists are quick to make up new scientific names, so they can claim they discovered a new species.) The Miocene gray fox (U. webbi) grew a little larger than modern day gray foxes. The Pliocene gray fox (U. progressus and U. galushia) are known from just a few specimens and were apparently also slightly larger. The early Pleistocene gray fox (U. citrinus) in Florida anatomically resembled modern western subspecies of gray foxes, while the mid Pleistocene gray fox (U. minicephalus) in Florida resembled modern eastern gray foxes. This is consistent with a genetic study that determined eastern and western gray foxes became isolated from each other for a while 800,000 years ago. Gray foxes prefer wooded habitat, and the eastern and western halves of North America must have been separated by unsuitable arid habitat then. Eastern gray foxes evolved some minor differences during this separation that occurred during the mid-Pleistocene. This same study found northern populations of gray foxes are less diverse, reflecting their recolonization of the region following the retreat of Ice Age ice sheets. Gray foxes are considered the most primitive canid species, and they are not closely related to any other living canids.

Gray fox range map. Western and eastern populations of gray foxes diverged 800,000 years ago, but they are still the same species. The Urocyon genus is at least 10 million years old.

This gray fox entered my yard in October of 2019. They are relatively common in my neighborhood.

Gray foxes are 1 of only 2 species of Canids that can climb trees. This helps them escape larger predators.

Part of the reason for the success of the gray fox is their ability to climb trees, making them capable of escaping larger predators. Of the 35 species of canids, they are 1 of 2 species that can climb trees. (Raccoon dogs, native to east Asia, are the other species that can climb trees.) They are omnivorous–another reason for their success. They can eat a wide variety of foods, including rabbits, rodents, birds, lizards, carrion, fruit, and acorns. At the present time their main predators and competitors are bobcats and coyotes. Studies show gray foxes will live and roam closer to suburban and urban habitats than bobcats or coyotes often will. This also helps them avoid predators. Bobcats and coyotes that kill gray foxes usually will not eat them, showing they are viewed more as competition than food. Gray foxes live in my neighborhood, and I see them on occasion. Once, my wife and I saw a gray fox carrying a squirrel in its mouth in front of our house. Red foxes (Vulpes vulpes) are less common near my vicinity, but I have seen them as well. They prefer more open country in contrast to the gray fox’s favored wooded habitat. Unlike gray foxes, red foxes are a recent immigrant to North America, having crossed the Bering land bridge about 15,000 years ago.

References:

Geffen, E.; A. Mercure, P. Gorman, D. Macdonald, A. Wayne

“Phylogenetic Relationship of the Fox-like Canids: Mitochondrial DNA Restructure Fragment, Site, and Cytochrome B Sequence Analysis”

Journal of Zoology September 1992

Reding, D. et. al.

“Mitochondrial Genomes of the U.S. Distribution of Gray Fox (Urocyon cinereoargenteus) Reveal a Major Phylogeographic Break at the Great Plains Suture Zone”

Frontiers of Ecological Evolution and Population Genetics June 2020

Tedford, R.; X. Wang, and B. Taylor

“Phylogenetic Systematics of the North American Fossil Caninae (Carnivora: Canidae)”

Bulletin of the American Museum of Natural History 325 2009

The Megafauna Release Hypothesis

The Megafauna Release Hypothesis postulates the extinction of the megafauna at the end of the Pleistocene caused an increase in the populations of species of plants that were preferred food for the megaherbivores, an increase in fire frequency due to the greater fuel load of uneaten vegetation, and the spread of non-analogue forests with no modern floral composition equivalent. Oak trees and maples did increase in abundance after megafauna extinctions because herds of animals were no longer eating acorns and saplings. And the hardwood trees were growing next to spruce trees in strange kinds of forests that no longer exist. A new study (Perotti 2022) attempted to test this hypothesis with new data from 5 sediment cores taken from lake bottoms at 5 sites, and they compared this with existing data from 14 other sites. Scientists took samples of mud from lake bottoms and carbon dated the layers. They analyzed the pollen composition to determine the abundance of various genera of plants, and they looked at the abundance of dung fungus spores used as a proxy for megafauna populations. They also looked at the amount of charcoal to determine fire frequency. With all this data they can get a general idea of the environment during past time periods. The authors of this study found the Megafauna Release Hypothesis held up well in Northeastern and Midwestern North America but did not for Southeastern North America.

Megafauna declined in abundance in the Northeast and Midwest about 14,600 years ago, and by 14,400 years ago there was a marked increase in hardwood tree abundance. However, fire frequency increased slightly before this–a clue humans were on the scene setting fires and overhunting the megafauna. In Southeastern North America the timeline doesn’t support the Megafauna Release Hypothesis. Hardwood trees began increasing about 16,300 years ago, preceding megafauna population decline by 2000 years. I have no doubt the extinction of megafauna had a major impact on floral composition, but I believe climate was a much bigger factor. I think the non-analogue forests in all regions can be explained by rapid climate fluctuations that led to temperate species growing with boreal species.

Graph showing pollen and foraminifera abundance from a core of sediment located off the coast of Georgia. The layers of sediment date from ~130,000 years ago-50,000 years ago. Oak increased during wet warm climate stages. Spruce increased during cold dry climate stages. Pine stayed relatively constant. Graph from the below reference by Huesser and Oppo.

A study of sediment taken from Ocean Drilling Project 1059A covers the period from 130,000 years BP to 50,000 years ago, long before megafauna became extinct. The location of the core is the South Atlantic off the Georgia coast. The time period includes the Sangamonian Interglacial and the first half of the Wisconsinian Ice Age. I wrote about this study in a long blog article about 12 years ago. (See: https://markgelbart.wordpress.com/2011/05/09/ocean-drilling-project-1059a-found-a-treasure-for-paleoecologists/ ) During warm wet climate phases hardwood trees such as oak increased in abundance, while spruce decreased. During cold dry climate cycles spruce increased in abundance, while hardwood trees decreased. Pine abundance stayed relatively stable during all climate phases. Broadleaf trees thrive in atmospheres high in carbon dioxide concentrations with higher precipitation rates, and they outcompete spruce trees under these conditions. Spruce trees are more resistant to the windy and icy conditions that occur during Ice Ages, and they can tolerate lower carbon dioxide levels as exist during a stadial. Transitions between stadial and interstadial likely always fostered transition (non-analogue) forests.

The extinction of megafauna has a big impact on various species of plant and animal abundance. A new study posits the impact was greater in the Midwest and Northeast than in the Southeast. Illustration from the below reference by Gallett et. al.

Landscapes were much richer when megaherbivores roamed the land. Their foraging and trampling created a variety of different habitats. They fertilized the soil and spread seeds with their dung. They provided food for predators, scavengers, and parasites. Their extinction had a major impact on the environment, but it was less than the influence of climate.

References:

Gallett, M.; M. Moleon, P. Jordeno, and J. Suenim

“Ecological and Evolutionary Legacy of Megafauna Extinction”

Biological Reviews October 2007

Huesser, L. and D. Oppo

“Millennial and Orbital Scale Climatic Variability in Southeastern United States during MIS 5: Evidence from Pollen and Isotope in ODP site 1059A”

Earth and Planetary Science Letters 214 (2003)

Perrott, A. et. al.

“Diverse Response of Vegetation and Fire after Pleistocene Megaherbivore Extinction across the Eastern United States”

Quaternary Science Review 294 October 2022

Snowy Winters and Dry Summers Prevailed in Southwestern North America during the Late Pleistocene

Ice Age climates spawned dramatically altered weather patterns compared to those of the present day. The result of those different weather patterns is evident in how changed Southwestern North America has become since then. During Ice Ages Southwestern North America was a land of vast lakes, abundant springs, and widespread wetlands. There even was a lake in Death Valley, California where it almost never rains today. There were especially large lakes in Utah, Nevada, and central Oregon–areas that today are quite arid. Scientists debate the source of the greater precipitation that occurred then. Some think the source was summer rains coming from fronts originating in the tropics, while most believe the polar jet stream carried moisture from the North Pacific that fell as heavy snows during winter. A new study of carbon and oxygen isotope ratios in tooth enamel from Pleistocene mammals supports the latter scenario.

Scientists analyzed 39 teeth from mammoth, bison, horse, and camel excavated from the Tule Spring Fossil Bed National Monument in Nevada. They can determine how precipitation was delivered based on the ratios of carbon and oxygen isotopes in the teeth because the animals ate the plants that absorbed the water, and the animals directly drank it. Most of the precipitation in the region came from heavy snows, and the lakes refilled every spring and early summer from snow melt. They believe summers were relatively dry, and lakes began to evaporate until seasonal snowfall. Mammoths, bison, and horses ate a lot of the fresh grass that grew tall on water from snowmelt. Horses may have eaten more grass here during Ice Ages than they do today. But camels browsed on saltbush (Atriplex sp.). The presence of this species indicates dry summers and arid localities within the lush landscape. Scientists think glaciers to the north of the region split the polar jet stream, and the lower stream carried moisture from the North Pacific, causing winter precipitation. Lake levels were highest during the Last Glacial Maximum following Heinrich Events that occurred when ice dams melted, and massive pulses of freshwater studded with ice bergs flooded into the oceans. Moisture in earth’s atmosphere increased following Heinrich events.

Map of Southwestern North America during the Late Pleistocene. Meltwater from much snowier winters caused the formation of giant lakes in the region then. From the below reference by Munroe and Laabs.

Beth Zaiken’s depiction of wildlife in Nevada during the last Ice Age. Vegetation was much lusher than it is today due to higher annual precipitation.

When glaciers retreated at the end of the Ice Age, the polar jet stream recombined and began to flow to the north. Winter snowfall was greatly reduced, and the lakes gradually evaporated. The Great Salt Lake of Utah is a remnant of a much larger freshwater lake that existed during Ice Ages.

The abundant wetlands and lakes of the region hosted many species of birds that today breed in the Arctic during summer. These species could not live in the Arctic during the Ice Ages because their present-day ranges were under miles of glacial ice. Their breeding ranges shifted to the Southwest. See also:

https://markgelbart.wordpress.com/2017/04/09/ice-age-western-lakes-and-altered-bird-migrations/

References:

Kohn, M. et. al.

“Seasonality of Precipitation in the Southwestern U.S. during the Late Pleistocene Inferred from Stable Isotopes in Herbivore Tooth Enamel”

Quaternary Science Review 290 November 2022

Munroe, J.; and B. Laabs

“Temporal Correspondence Between Pluvial Lake High Stands in Southwestern U.S. and Heinrich Event 1”

Journal of Quaternary Science 28 (11) 2013

The Early-Mid Pleistocene European Jaguar (Panthera gombaszoegensis) was not Actually a Jaguar

During 1938 M. Kretzoi, a paleontologist, studied some unidentified lower fossil teeth and concluded they belonged to an extinct species of jaguar that roamed Europe during the early to mid-Pleistocene. He gave the species the scientific name Panthera gombaszoegensis. Paleontologists long thought this species was ancestral to the American jaguar (P. onca) and some thought it was the same species. A mostly complete skull was finally found in a Belgian sinkhole (the La Belle-Roche fossil site) during 1980, but paleontologists didn’t really study it until recently. They compared this fossil skull with those from extant species of cats in the Panthera genus including lion, leopard, tiger, jaguar, and snow leopard. They concluded P. gombaszoegensis was not a jaguar after all, though the lower teeth were similar. Instead, this species was most closely related to the tiger (P. tigris) and based on the characteristics of the skull they believe it was a sister species to the tiger, having diverged directly from the same common ancestor. This makes sense geographically because its range was much closer to the tiger than the jaguar. P. gombaszoegensis lived from 2 million years BP to 350,000 years BP, and it is thought to have been a generalist predator, taking whatever prey species they could bring down. Lions and leopards expanded their ranges into Europe from Africa about 350,000 years ago and likely ecologically replaced P. gombaszoegensis.

Map showing range of modern tigers, modern jaguars, and the extinct Panthera gombaszoegensis. An anatomical comparison concludes European jaguars were more closely related to modern tigers than jaguars. This makes more sense geographically. The lower image is a map showing fossil localities where this species has been found in Belgium. Image from the below reference.

Skull of Panthera gombaszoegensis. A comparison of this skull with extant species of cats in the Panthera genus suggest it is a sister species of modern tigers, not jaguars. Image also from the below reference.

Paleontologists think the Panthera genus originated in central Asia about 6 million years ago during the late Miocene. The direct ancestor of the jaguar is unknown. The oldest jaguar fossil known was found in a cave in West Virginia and dates to 850,000 years ago. It descended from a species that crossed the Bering land bridge sometime during the early Pleistocene.

Reference:

Chator, N.; M, Michaud, and V. Fischer

“Not a Jaguar After All: Phylogenetic Affinities and Morphology of the Pleistocene Felid Panthera gombaszoegensis“

Papers in Paleontology 2022

link https://www.researchgate.net/publication/363739515_Not_a_jaguar_after_all_Phylogenetic_affinities_and_morphology_of_the_Pleistocene_felid_Panthera_gombaszoegensis

Pleistocene Howls

Hyoid bones are rarely found in most fossil sites. Canid hyoid bones are a collection of 9 small bones held together with ligaments. The hyoid bone supports the pharynx, larynx, and tongue. During the process of decomposition after an animal dies, the larger bones are more likely to be preserved, but the small bones such as the ones that make up the hyoid get separated and oftentimes crushed. They then dissolve or are broken into unrecognizable fragments. However, the La Brea tar pits are an exceptional fossil site with excellent preservation, and many complete hyoid bones have been found there. Scientists recently studied the canid hyoid bones found there and compared them to the hyoid bones found in extant species of coyotes and wolves.

Diagram of a dire wolf hyoid bone from the below reference.

Illustration by Mauricio Anton. During the Pleistocene big cats mostly hunted in forested areas while dire wolves mostly hunted in open areas.

Dire wolves had larger hyoid bones than modern species of wolves including gray and red wolves and coyotes. They howled with a lower frequency and deeper pitch than any species of extant American wolf. Scientists couldn’t find any difference between the hyoid bones of coyotes and red wolves. Pleistocene coyotes were larger than modern coyotes and so were their hyoid bones. They howled with a lower frequency and deeper pitch than modern coyotes. If we could hear a dire wolf howl, we would definitely notice a much deeper howl than normally heard today by people lucky enough to live where wolves and coyotes’ howl.

Reference:

Flores, D., E. Eldridge, E. Eliminowski, E. Dickinson, A. Hartstone-Rose

“The Howl of Rancho La Brea: Comparative anatomy of Modern and Fossil Canid Hyoid Bones”

Journal of Morphology April 2020

https://www.researchgate.net/publication/340726915_The_howl_of_Rancho_La_Brea_Comparative_anatomy_of_modern_and_fossil_canid_hyoid_bones

All Modern Wolves (Canis lupus) Descend from a Population that Originated in Beringia

All wolves in the northern hemisphere descend from a population originating in Beringia, according to a recent study of wolf DNA. Beringia is the geographic region including western Alaska, eastern Siberia, and formerly the Bering land bridge when it was above sea level during Ice Ages. Scientists examined the DNA from 90 “modern” wolf specimens (those dating to less than 500 years old and 40 “ancient” wolf specimens (those dating to more than 500 years old). They concluded the population of wolves living in Beringia 50,000 years ago eventually expanded across Eurasia and North America and displaced the populations of wolves that were already living there. Ice sheets blocked expansion into North America until about 15,000 years ago. There is not enough data to know for sure how similar Beringian wolves were to North America wolves living below the Ice Sheet before the expansion.

Graph showing expansion of the Beringian wolf population across the Northern Hemisphere during the Late Pleistocene. From the below referenced paper.

Late Pleistocene wolves were larger and had teeth, skulls, and jaws that were more robust than modern gray wolves, though they were not as robust as those of the extinct dire wolves (C. dirus) formerly found throughout most of North America. Dire wolves were not at all closely related to gray wolves and were separated by at least 1 million years of evolutionary divergence. Late Pleistocene wolves were well adapted to scavenging and/or hunting mammoths, horses, and bison. The population of wolves from Beringia may have specialized in hunting caribou and perhaps followed caribou herds over long distances. Maybe this explains how they became so widespread. The other wolves, so well adapted to hunting megafauna, didn’t survive megafauna extinctions, but Beringian wolves following caribou herds did.

The results of this recent study contradict an older study that concluded modern gray wolves didn’t descend from the more robust Beringian wolves. The authors of the newer paper explain their study had a greater sample size and looked at more of the wolf DNA than the older study did. It certainly eliminates the mystery of where modern Alaskan wolves originated. They’ve had a continuous presence in the region for a very long time.

Reference:

Loog, Lisa, et. al.

“Ancient DNA Suggests Modern Wolves Track their Origin to a Late Pleistocene Expansion from Beringia”

Molecular Ecology Jan 2020

https://onlinelibrary.wiley.com/doi/full/10.1111/mec.15329

Mammoth Populations Decreased While Horse Populations Increased in Europe during the Late Pleistocene

Anatomically modern humans hunted mammoths in Europe over 34,000 years ago. There is plenty of archaeological evidence for this, but the evidence gets scarcer after this date. A recent study places the blame for this decline in mammoth populations on humans. Scientists analyzed the chemical isotope ratios in the bones of mammoths, horse, red deer, caribou, and wolf from a time period dating between 34,000 years BP-23,000 years BP. They determined the environment favorable to mammoths remained intact during the time period, yet mammoth populations declined significantly. Climatic changes were minimal. Therefore, the only explanation for this decline in mammoth populations was overhunting by humans. People likely decimated populations by focusing on the juvenile individuals. This might also explain the scarcity of the scimitar-toothed cat in the fossil record after this date in Europe. The scimitar-toothed cat specialized in hunting juvenile mammoths, and their decline coincided with the decline of their prey.

A scientific study determined mammoth populations in Western Europe declined beginning about 34,000 years ago. Scientists believe overhunting by humans “decimated mammoth populations.” Horse populations increased during this time period because more food became available for them when there were fewer mammoths. The environment remained stable during this time period.

This study found a great overlap in the diets of mammoths and horses. More food was available for horses following the decline of mammoth populations, and horse populations increased during this time period. Eventually though, humans overhunted horses too. The bones used from this study were from Germany and France, and it was an extensive study with a large sample size. It shows how humans impacted landscapes even before we were common.

Reference:

Drucker, D.; et. al.

“Tracking Possible Decline of Woolly Mammoth during the Gravettian in Dordogne (France) and the Ach Valley (Germany) Using Multi-Isotope Tracking (13 C, 14 C, 15 N, 34 S, 18 O)”

Quaternary International Mar 2016

Missing Pieces of the Ecosystem

The extinctions of Pleistocene megafauna had a profound impact on ecosystems. Large herds of megafauna with the exception of bison were no longer foraging, trampling, and defecating on the landscape in North America. Plant communities were altered, and many predators and scavengers disappeared when all that meat was no longer available. A new study of fossil bones from sites located in the Edward’s Plateau, Texas examined some of the changes in the surviving fauna following the extinction of late Pleistocene megafauna. The authors of this study looked at bone chemistry to determine diet of species before and after extinctions, and they also estimated average size based on fossil remains (in some cases just the teeth). (I should note studies based on stable isotope analysis should be viewed with caution. See: https://markgelbart.wordpress.com/2016/06/24/trust-the-coprolites-not-the-stable-isotope-analysis/ )

Edward’s Plateau, Texas. Study area of the below reference.

The Edward’s Plateau is located in the middle of the North American continent and hosted species from the West, East, and those that had a continental distribution. During the Pleistocene there were grazers, browsers, and mixed feeders. Grazers included mammoths, bison, and horses. Browsers included mastodon, deer, pronghorn, tapir, llama, rabbits, and hare (jackrabbit). Gompotheres, camels, and peccaries were mixed feeders. The authors of this study could not obtain data from ground sloths, glyptodonts, and helmeted musk-ox to determine what they ate. Scientists found saber-toothed cats (Smilodon fatalis) and scimitar-toothed cats (Homotherium latidens) both had a specialized diet of juvenile grazers that were still nursing. These predators fed mostly upon young mammoths and bison that were still dependent upon their mother’s milk. Elephants lactate for up to 3 years after giving birth. Still nursing mammoths faced danger when they wandered away from the safety of the herd. Giant lions (Panthera atrox) and dire wolves (Canis dirus) had more generalist diets, eating grazers and mixed feeders. Black bears mostly ate plants. The lone specimen of giant short-faced bear (Arctodus simus) in this study had a diet similar to the striped skunk. Strange as it might seem, this giant bear was eating insects, mice, and fruit. Jaguars replaced other large Pleistocene predators as the main predator of juvenile bison and horses, following the extinctions of proboscideans, saber-tooths, giant lions, and dire wolves, but only for a short period of time. Horses are absent in the fossil record during the early Holocene, but this study and others suggest they lingered for a while after other Pleistocene megafauna went extinct. Eventually, jaguars become absent in the fossil record of this region, though historical accounts indicated they occurred as far east as Louisiana into historical times. They probably occurred in low numbers in this region. Cougars, formerly absent in the fossil record from this region, became more common.

In the Edwards Plateau, Texas jaguars temporarily replaced saber-toothed cats as a predator of juvenile bison and horses during the early Holocene about 10,000 years ago. Jaguars eventually became rare in this region too. Chart from the below referenced paper.

After the extinction of Pleistocene megafauna surviving herbivores responded differently. Deer and hare became larger, while cottontail rabbits and bison grew smaller. Hares and rabbits shifted to a diet of plants preferred by grazers.

Reference:

Smith, F., E. Elliot Smith, A. Villegenor

“Late Pleistocene Megafauna Extinction Leads to Missing Pieces of Ecological Space in North American Mammal Community”

PNAS 119 (39) September 2022