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Snail Species Composition and Ice Age Summer Temperatures

May 13, 2026

Advancing and retreating glaciers during Ice Ages crushed rock into dust. Meltwater pulses that occurred when climate cycles shifted to warm stages washed this dust into rivers. Then, when climate cycles shifted to arid stages and rivers shrank in size, exposing the sediment, wind blew this dust into huge hills alongside the rivers. This wind-blown dust is known as loess. Hills made from loess are located up and down the Mississippi River Valley, but today they are covered by vegetation that originally took root when climate became more moist and warmer. Land snail shells are often found in the loess. Scientists can use the snail species composition to estimate past average summer temperatures. (Land snails are mostly active during the warmer months.) Every species of snail occurs in ranges within certain temperature parameters. Scientists can also radio-carbon date snail shells. By dating the subfossil snail shells and identifying the species present, scientists can estimate past average summer temperatures.

Map showing where hills made of Ice Age loess sediment are found.

Road cuts reveal loess sediment.

This species of land snail requires warm summers and is evidence of warmer climates.

This is another species of land snail that indicates warmer summers.

The presence of this species indicates cooler summers, like those that occurred during Ice Ages. They still occur in Canada.

Another species of snail that requires cooler summers.

Scientists determined average annual summer temperatures in the upper Midwest near the glacier edge fell drastically about 27,000 years ago–the beginning of the Last Glacial Maximum. Before summer temperatures fell, species of snails favoring warm climate including Anguispira kochi, Hawaii minisculs, and Vallonia perspectiva are found in sediment dating between 30,000 years BP-27,000 years BP. After this for the next 12,000 years snail species that require cool summers are found in the sediment. These species include Columella alticola, Vertigo modesta, and Vallonia gracilicosta. In all scientists found 68 species of terrestrial snails from 4 genera at the study sites. The sites were from 14 midwestern states. Each site had from 5-30 species.

During the Last Glacial Maximum summer temperatures near the glacier margin averaged 6-18 degrees F cooler than those of today. Summer averages were 59-61 degrees F. Near the Gulf Coast summer average temperatures were 77 degrees F compared to 92 degrees F today. The results of this study are consistent with climate data from ice cores, ocean sediment, and pollen composition.

References:

Grimley, D.; and J. Conroy

“Last Glacial Maximum Summer Temperature Gradient from Terrestrial Gastropods in Peoria Silt (loess), Midwestern USA”

Quaternary Science Reviews June 2026

Grimley, D.; et al

“Last Glacial Maximum Ecology and Climate from Terrestrial Gastropod Assemblages in Peoria Loess, Western Kentucky”

Quaternary Science Reviews 35 (5) May 2025

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Megafauna Walking the Beaches of Southern Spain 125,000 Years BP

February 11, 2026

Ichnologists examined animal tracks found near the coast of Spain at 4 sites, and they date to the last Interglacial ranging in age from 90,000 years BP-140,000 years BP. Ichnology is the study of animal tracks. They found tracks that compare favorably to the enormous, extinct straight-tusked elephant (Palaeoloxodon antiquus), horse, red deer (known as elk in North America), wolf, stone marten, and beetle. The sites include Torro de Copa, Calblanque, Monte de la Ceniza, and Pena del Aquela Regional Nature Park. The tracks are important evidence that these species occurred here because their remains are not found in the local fossil record, though they are found in other parts of the Iberian Peninsula.

Location and geological setting of sites where fossil tracks of animals dating to the last Interglacial were found in Spain. From the below referenced paper.

The tracks were found in fossilized sand dunes created by Ice Age winds. Note the impressions of raindrops. This indicates the sand was wet when the tracks were made. From the below referenced paper.

Fossilized elephant tracks. From the below referenced paper.

Map of sites where evidence of extinct elephants have been found. The yellow represent tracks; the red circles represent bones. From the below referenced paper.

Straight-tusked elephants were 1 of the largest land mammals of all time. There were 4 species and they ranged across Africa, Europe, and Asia. I believe they would still exist today, if not for man. During Ice Ages mammoths replaced them in colder regions, but they could still occur in warmer regions of Europe and Asia.

Ichnologists find impressions of rain drops in the sand next to the tracks, indicating the sand was wet from rain when the tracks were made. The tracks were made on coastal sand dunes that formed during a previous Ice Age when climate was dry, and wind blew sand into big dunes. However, by the time these tracks were made, wetter climate fostered the spread of beach shrubs that stabilized the dunes. They were walking through a scrubby habitat with many bare spots. The dunes were adjacent to a mixed forest of ash, birch, fir, and hornbeam. Straight-tusked elephants likely fed on the twigs and leaves of these plants. Some tracks appear as if the animals were just passing through, perhaps as part of a seasonal migration. Other trackways suggest the animals were congregating on the spot and trampling the ground. Neanderthals likely hunted these animals here.

The sites were dated using uranium-series dating of coral and seashells. They must have been rapidly covered by sediment that today is being eroded away, making them visible. It’s a nice snapshot of the local fauna during the interglacial. If not for man, all of these species would still enjoy living next to the Mediterranean Sea today.

Reference:

Carvalho, C.; et al

“New Vertebrate Track Sites from the Last Interglacial Dune Deposits of Coastal Murcia (Southeastern Spain): Ecological Corridors for Elephants in Iberia”

Quaternary Science Review 369 December 2025

https://www.sciencedirect.com/science/article/pii/S0277379125004512

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Marine High Stands During the Sangamonian Interglacial at Myrtle Beach, South Carolina

January 28, 2026

I’ve always been fascinated with the Sangamonian Interglacial, known as the Eemian Interglacial in Europe. It’s the most recent climate phase when average annual global temperatures were the same or even higher than those of today. No major extinction of megafauna occurred during this phase–the best evidence against climate models of Pleistocene megafauna extinction. The Sangamonian Interglacial lasted from 132,000 years BP-118,000 years BP, although the below referenced study frames it between 128,000 years BP-117,000 years BP. Climate was likely not noticeably different during the discrepancy between these 2 parameters. The north polar ice cap completely melted during the Sangamonian Interglacial, resulting in higher sea levels than today. The north polar ice cap also completely melted during the early Holocene about 10,000 years ago. (Note: and polar bears did not become extinct as alarmists claim will happen.) Scientists are also interested in the Sangamonian because it provides an analogue for today’s climate but without the influence of manmade greenhouse gases. Recently, scientists studied ancient shorelines that existed during the Sangamonian Interglacial at Myrtle Beach, South Carolina. They appear today as ridges or terraces, referred to as outcrops as well, and they consist of crushed consolidated seashells including coral, clams, and oysters. 1 of these outcrops has a layer of peat inside the shelly sediment, suggesting the existence of a marsh, and another 1 has an eolian or windswept sand dune embedded in the layer from dunes that formed during an arid climate cycle.

Location of the area studied in the below referenced paper. Yellow lines represent high stands. Peninsular Florida was mostly submerged with the exception of a few islands. During the Pliocene shoreline was even higher and extended into the middle of South Carolina where the shoreline consisted of sea cliffs. Today, it is the eroded Orangeburg Escarpment.

Another map from the below referenced study showing terraces from former shorelines when sea level was higher than today.

Cold water coral (Desmophyllum pertusum) occurs on the Blake Plateau off the coast of South Carolina. It forms an important ecosystem. Scientists date ancient shorelines using radiometric dating, specifically Uranium series dating of coral found in the terraces.

Ribbon corals, also known as sea whips occur in shallow water off the coast of South Carolina. They are not a true coral.

The scientists dated these old shoreline ridges using uranium series dating from coral fossils and by using optically stimulated luminescence. (See: https://en.wikipedia.org/wiki/Optically_stimulated_luminescence ) They determined sea level rose no more than 15 feet during the early Sangamonian. Throughout the Sangamonian sea level fluctuated between 9-21 feet higher than that of today. Sea level rose rapidly during the early Sangamonian, stabilized, then rose again. Fluctuations were rapid and corresponded with unstable ice sheets. This new study agrees with earlier studies of these marine high stand terraces at other locations. During Ice Ages sea levels retreated as more of earth’s moisture became locked in glaciers, and dry land habitat occurred as much as 50 miles off the modern-day coast.

Reference:

Dean, S.; et al

“Last Interglacial Relative Sea Level Changes at Myrtle Beach, S.C.”

Quaternary Science Review 375 2026 (in progress)

Click to access 125489.pdf

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The Jurassic Age Dinosaur Extinctions in Western North America

November 19, 2025

The extinction of all dinosaurs (except birds) at the end of the Cretaceous Age was made famous 45 years ago when a crater was found in the Gulf of Mexico–confirming a comet impact as the cause of the extinctions 66 million years ago. A lesser-known local extinction of dinosaurs occurred 145 million years ago at the end of the Jurassic Age. From geological and paleontological evidence scientists determined dinosaurs were diverse and abundant in western North America from 152 million years ago to 145 million years BP, but these species became extinct after a sudden cataclysmic event. Scientists suspect a mega volcano eruption rubbed out all the dinosaurs in this region then. During the late Jurassic sauropods such as diplodocus (the largest known land animal in earth’s history), allosaurs, stegosaurs, and small ornithomimids (bird-like dinosaurs but not ancestral to birds) dominated the faunal composition. After the extinctions Cretaceous Age species gradually colonized the region and ecologically replaced the Jurassic Age species, although sauropods continued to live in other regions of the earth. Iguanodons, ankylosaurs, and smaller species of ornithomimids were the new inhabitants of the region. The early Cretaceous dinosaur composition was less diverse in this region than the late Jurassic.

The Morrison formation consists of sedimentary rocks that have the best evidence of Jurassic Age dinosaurs in North America.

Scientists found an interesting faunal turnover between the late Jurassic and the early Cretaceous in the Morrison Formation located mostly in Utah. Poster from James Kirk’s twitter feed.

Plant fossils from the Morris Formation include conifers, cycads, and ancestors of ginko.

The northern part of the Morris Formation yielded fossil remains of a different species of allosaur than the southern part. Scientists don’t know why 2 different species evolved. They don’t know of any physical barrier between the 2 areas.

Sauropods like this diplodocus and stegosaurs were the main species of large plant-eaters in western North America before the Jurassic Morrison extinctions.

Stegosaurs didn’t make it to the Cretaceous.

Evidence of this faunal turnover comes from the Morrison Formation–mountains of sedimentary rock found in western North America, mostly Utah. During the late Jurassic this area was a floodplain bordered by a newly forming mountain range. Cycads and conifers grew on the plain, and rivers flowed from the mountains into a vast marshy lake. Some of these trees have been preserved in petrified forests located in Dinosaur National Monument. The northern and southern part of this region hosted 2 different species allosaurs and 2 different species of carnosaurs. Scientists haven’t figured out why the northern and southern parts of this region had different species of carnivorous dinosaurs. They know of no physical barrier that would have contributed to this speciation. The region shifted frequently between wet and dry climate cycles, but scientists don’t think this was a factor in the sudden extinctions of Jurassic Age dinosaurs here. Dinosaurs were thriving and diverse up until their sudden end here.

Reference:

Kirkland, J.; E. Sampson, M. Wizecurch, and D. Deblieux

“Paleosols in the Lower Yellow Cat Member of the Cedar Mountain Formation in Eastern Utah Indicate the Earliest Cretaceous (Borrasian) in the Colorado Plateau was Exceptionally Wet”

75th Annual Meeting of the Rocky Mountain Geological Survey 2025

Maidmont, S.

“Diversity Through Time and Space in the Upper Jurassic Morrison Formation, western USA”

Journal of Vertebrate Zoology 43 (5) 2023

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More Species of Mammals Discovered Living in Costa Rica

October 15, 2025

If the U.S. government ever expelled me from this country, I would choose to live in Costa Rica. It’s a beautiful tropical paradise. The cost of living is very cheap and reportedly delicious fresh produce is available year-round. 28% of Costa Rica is protected wilderness, and I can imagine living in a home next to a nature reserve. Costa Rica is situated between North and South America, and accordingly it’s 1 of the most ecologically diverse regions in the world with more species of mammals than most other countries, despite its small size. I’ve written about Costa Rican mammal diversity before, but I came across an article updating the list of mammal species that occur there. Over the past 10 years, 22 new species of mammals have been discovered living in Costa Rica bringing the total number of mammal species known to occur in the country to an astonishing 271. By contrast the U.S. is 74 times bigger than Costa Rica but has less than twice as many species.

11 species of possum are known to live in Costa Rica.

Whales are now classified with the even-toed ungulates due to genetic evidence.

The Tacaruna bat was recently rediscovered to be living in Costa Rica after not being seen for 31 years.

6 species of cats, including the oncilla or northern tiger cat are known to occur in Costa Rica. All populations of these species are decreasing in abundance.

Dozens of species of rodents live in Costa Rica.

6 species of raccoons and their relatives live in Costa Rica.

The authors of the below referenced paper reviewed all of the scientific literature published over the past 10 years to update the list of species living in Costa Rica. They added 22 species to the list. 10 are bats and 8 are rodents. Some species were known formerly to have lived in Costa Rica but hadn’t been seen in decades. A colony of thumbless bats (Feripterus horrens) was rediscovered living in a tourist cabin after not beeing seen for 44 years. I couldn’t even find a photo of this species on the internet. The Tacaruna bat (Lasiurius castaneus) was rediscovered after a 31 yar absence. Costa Rica is home to 12 species of possums, 3 species of anteaters, 2 species of sloths, 2 species of armadillos, 4 species of monkeys, 6 species of cats, 6 species in the raccoon family and dozens of species of rodents and bats. Populations of all 6 species of cats are decreasing. Populations of 103 species of mammals here are stable, while 18 species are decreasing. 84 species are of unknown status. 3 species are increasing, including coyotes, sea lions, and spinner dolphins.

I learned about an interesting taxonomic controversy when reading the paper referenced below. Genetic evidence suggests whales should be classified with artiodactyls (hooved animals). Whales were formerly classified as cetaceans but apparently the genetic differences between whales, hippos, pigs, deer, etc. is not as great as assumed based on anatomical characteristics. (Of course, not all scientists agree with this reclassification.) Now, scientists can’t decide what name should be given to the combined whale and hooved animal classification. They’ve come up with all sorts of ridiculous names, but they’ve decided to call this order cetartiodactyl.

Reference:

Mora, J.; and L. Ruedas

“Updated List of the Mammals of Costa Rica, with notes on Recent Taxonomic Changes

Zootaxa 5357 (4) October 2023

https://www.researchgate.net/publication/374869193_Updated_list_of_the_mammals_of_Costa_Rica_with_notes_on_recent_taxonomic_changes

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Glyptodonts were Armadillos, not Just Close Relatives

October 8, 2025

I find some of the most interesting and surprising topics for my blog from reading obscure scientific journals. I recently discovered Zootaxa, a journal I never encountered in my 18 years of doing research for this blog. I searched through their archives looking for additional topics and found the subject of last week’s blog entry, but in the bibliography of that article, I found reference to yet another surprising paper. Scientists long classified the extinct glyptodonts as relatives of armadillos but not actually armadillos. Glyptodonts were much larger and most likely subsisted on grass, while armadillos mostly eat invertebrates. Glyptodonts had stiff turtle-like shells; armadillos had flexible carapaces. Some scientists noticed anatomical similarities in the skulls and jaws of glyptodonts and small pink fairy armadillos in the Chlamyphoridae Family, and they did suspect a close relationship between the 2. Scientists succeeded in extracting DNA from a 12,000-year-old glyptodont carapace. They were able to map the whole genome. Amazingly, they determined glyptodonts were not just close relatives of armadillos but should actually be classified in the same family as the diminutive pink fairy armadillos.

Surprisingly, the extant pink fairy armadillo, the smallest species of armadillo, is the closest living relative of the huge extinct glyptodonts. Evolution can occur rapidly because scientists believe glyptodonts evolved to their enormous size shortly after divergence from fairy armadillos.

Based on genetic evidence, glyptodonts should be classified with fairy armadillos. From the below referenced study by Delgur et al.

DNA from doedicurus, a type of glyptodont was used in the 2 below referenced studies.

Glyptodonts were about the size and shape of an old-fashioned Volkswagon.

The species of glyptodont used in the below referenced studies belonged to the Doedicurus genus. They were huge animals 12 feet long and weighing 3000 pounds–about the size and shape of an old-fashioned Volkswagon. Some species had spiked clubs on their tails they used for defense and probably battles over mates. Scientists believe the first species weighed just 15 pounds, but they rapidly evolved into a much larger size and a diet dominated by plant matter instead of invertebrates. They diverged from smaller armadillos about 35 million years ago, according to genetic evidence. This evidence is consistent with the fossil record. Glyptodonts first appear in the fossil record about the same time. This rapid evolution is a good example of punctuated equilibrium, a process of evolution marked by isolated episodes of rapid speciation between long periods of little change. I hypothesize the rapid evolution of glyptodonts occurred after some unknown extinction event that left an ecological niche open for a large grass-eating animal.

There are 2 species of extant fairy armadillos–Chlamyphorus truncatus and Calyptophraetus retusus. The former lives underground in a desert area of Argentina where they feed upon insects, worms, snails, and some plant matter. The latter lives in scrubland habitat along the borders of Argentina, Bolivia, and Paraguay. Chlamyphorus is considered endangered; the status of Calyptophraetus is unknown. These types of armadillos can bury themselves in desert sand with surprising speed, but they still fall prey to domestic dogs and cats.

References:

Delgur, F.’ et. al.

“The Phylogenetic Affiliation of the Extinct Glyptodonts”

Current Biology 26 (4) Feb 2016

Mitchell, K. et. al.

“Ancient DNA From the Extinct South America Giant Glyptodont Doedicurus sp. (Xenartha Glyptodontidae) Reveals that Glyptodonts Evolved from Eocene Armadillos”

Molecular Ecology 14 2016

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New Species of Extinct Pampathere (Holmesina criptae) Found in Brazil

October 1, 2025

Until about 11,000 years ago, armadillos the size of bears roamed parts of South America and southeastern North America. The species that lived in Florida and coastal Georgia was Holmesina septentrionalsis and is known by the common name of northern pampathere. There were 3 genera of giant armadillos including the tonnicinctus, pampatherium, and holmesina. They should not be confused with glyptodonts, though they were related. Glyptodonts were much larger and had stiff turtle-like shells whereas pampathere carapaces were flexible, allowing them to roll up in the shape of a ball to protect themselves from predators. There were 6 species in the holmesina genus. Most species lived in South America–their continent of origin.

The largest pampatheres grew to 9 feet long. The species that lived in Florida grew to about 7 feet long.

Location of the site where 2 complete specimens of a newly discovered species of pampathere was discovered. From the below referenced paper.

Skulls of the newly discovered species. From the below referenced paper.

Image from the below referenced paper.

Cave explorers discovered the complete skeletons of 2 pampatheres in Lapinha Cave located in Bahia, Brazil. Scientists examined the specimens and determined they belonged to a previously unknown species, and they gave it the scientific name Holmesina cryptae. It had a more triangular-shaped head than any other species of pampathere. Its osteoderms, the boney plates that make up its carapace, were similar in some ways to those in the pampatherium genus and similar in other ways to species in the holmesina genus. Based on skull morphology, they placed it in the holmesina genus.

Reference:

Mauro, J.; F. Gais, F. Galleri, M. Fernandes

“A New and Most Complete Pampathere (Mammalia, Xenartha, Cingulata) From the Quaternary of Bahia, Brazil”

Zootaxa 4661 (3) 2019

https://www.researchgate.net/publication/335474229_A_new_and_most_complete_pampathere_Mammalia_Xenarthra_Cingulata_from_the_Quaternary_of_Bahia_Brazil

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Scientists Now Recognize Three Species of Alligator Snapping Turtles

September 10, 2025

I learned about this from a Facebook post that algorithms randomly chose for my feed. Chris Gillette manages the Bellamy Acres Animal Sanctuary where injured wild animals are nursed back to health and released back into the wild, if possible, and he shares results on Facebook. This post was about an alligator snapping turtle they restored to good health but couldn’t release to the wild because it was not from the correct river drainage. Apparently, someone had captured the turtle and didn’t return it to its river of origin. At first the decision not to release it back into the wild didn’t make sense to me. Why not improve the genetic vigor of the population? I didn’t know that in 2014 scientists determined there were 3 different species of alligator snapping turtles. The study was published in a really obscure scientific journal and didn’t get much publicity, so no wonder I was ignorant of it.

Former range map of alligator snapping turtles. The soup industry extirpated them from the northern parts of their range.

Map showing where specimens of alligator snapping turtles were sampled in the below referenced study. The different colors represent different species.

The 3 species differ anatomically. They have different sized caudal notch areas in the rear of their shell. Photo from the below referenced study.

The 3 species also differ in the angle of the squamosal region of their skulls. Photo also from the below referenced study.

The wormlike tongue of the alligator snapping turtle lures fish to their doom.

The scientists who published this article looked at the anatomy and genetics of 93 alligator snapping turtles from the Mississippi River and Mobile Bay Drainage systems, 17 from the Apalachicola River Drainage, and 18 from the Suwannee River Drainage. They determined from genetic evidence that Western alligator snapping turtles (Macrochelys temminckii) diverged from Apalachicola alligator snapping turtles (M. apalachicola) 5.3-13.4 million years ago. The latter diverged from the Suwanee alligator snapping turtle (M. suwanniensis) 3.2-8.9 million years ago. This is quite a difference in their genetic ancestry. Unlike common snapping turtles (Chelydra serpentina), alligator snapping turtles don’t disperse great distances over land. (I’ve seen common snapping turtles a considerable distance from any body of water.) Therefore, these populations of alligator snapping turtles became genetically isolated from each other a very long time ago. Sometime during the middle of the Miocene, the Mississippi River and the Apalachicola Rivers must have been connected but became geographically separated, and the same must be true for the Apalachicola and Suwannee River systems. The study suggests ancestors of alligator snapping turtles diverged from common snapping turtle ancestors at least 17.5 million years ago.

The study also found that purported fossils of alligator snapping turtles from the peninsula of Florida dating to the early Pleistocene were probably an extinct species of giant common snapping turtle. Sea level rise during an Interglacial caused the extinction of this yet to be named species.

These 3 species of alligator snapping turtles differ anatomically as well. They have different sized notches on the back of their shells, and the angle of the squamosal region of their skulls differs.

All 3 species of alligator snapping turtles are endangered, and the western alligator snapping turtle was extirpated from the northern part of its range because Campbell’s soups used them for their turtle soup during the 1970s and 1980s. This is a shame. They are fascinating long-lived creatures that unfortunately breed slowly. Some live alligator snapping turtles have been found with musket balls and Indian arrowheads embedded in their shells, demonstrating just how long they live. They grow up to 200 pounds, growing fat by luring fish to their doom with their worm-like tongue.

Reference:

Thomas, T. ; M. Granatosky, J. Bourque, and K. Krysko

“Taxonomic Assessment of Alligator Snapping Turtles (Chelydridae: Macrochelys) with the Description of Two New Species from the Southeastern U.S.”

Zoo Taxa 3786 (2) 2014

https://www.researchgate.net/publication/261556927_Taxonomic_assessment_of_Alligator_Snapping_Turtles_Chelydridae_Macrochelys_with_the_description_of_two_new_species_from_the_southeastern_United_States

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Great White Sharks (Carcharadon carcharias) Almost Went Extinct During the Last Ice Age

August 13, 2025

Scientists attempting to solve a genetic mystery about great white sharks instead discovered a surprising detail about the history of this species. 20 years ago, scientists learned there were big genetic inconsistencies between great white shark mitochondrial DNA, mostly inherited from the female side, and nuclear DNA material inherited from both parents. This could be caused by genetic variation before speciation, hybridization before speciation, different dispersal patterns between sexes, or different environmental selection processes between sexes. Scientists collected genetic data from great white sharks for 13 years and put this data into different models to try and understand why. They assumed this dissonance was most likely caused by females staying in the same geographic area, while males migrated long distances and interbred with other populations. The models they used couldn’t solve the mystery. Even extreme models that assumed females didn’t migrate at all couldn’t explain why mitochondrial DNA was so different. However, the scientists who studied this did learn great white sharks almost became extinct during the last Ice Age.

Great white sharks almost went extinct during the last Ice Age because their shallow water habitat was replaced by dry land. There were no great white sharks in the Atlantic Ocean until about 7000 years ago, though they may have repopulated it during previous interglacials. Loss of shallow coastal habitat is probably the same reason megalodon went extinct 2 million years ago when Ice Ages became more severe.

Seals make up a good part of great white shark diet in some regions.

Frontal view of a great white shark.

10,000 years ago, great white sharks were on the decline and limited to 1 population between South Africa and Australia. Their favored habitat–shallow coastal waters–was nearly eliminated when sea levels fell, as so much of earth’s atmospheric moisture became locked into massive glaciers. Dry land extended into what was formerly and would become shallow coastal waters. This is also likely the reason megalodon became extinct at the beginning of the Pleistocene. 7,000 years ago, great white sharks began to increase in numbers and today there are 3 populations–the coasts of South Africa and Australia, North Atlantic coasts, and North Pacific coasts. Scientists estimate the great white shark population worldwide is only 20,000. They are still vulnerable to extinction.

Reference:

Lasa-Judart, R.; S. Corrigan, C. Yang

“A Genomic Test of Sex-Biased Dispersal in White Sharks”

PNAS 122 (32) July 2025

https://www.pnas.org/doi/10.1073/pnas.2507931122

See this article for an explanation about how scientists use the molecular clock to study the history of a species.

https://www.nature.com/scitable/topicpage/the-molecular-clock-and-estimating-species-divergence-41971/

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Mexican Mammoths (Mammuthus columbi) Ate a Varied Diet

June 18, 2025

The skeletal remains of 14 mammoths were found at the Tultepec Fossil Site, Mexico between 2016-2019. Scientists recently used bone collagen and tooth enamel from these specimens to determine what they fed upon. They analyzed the isotopic composition of the teeth and bones, and they looked at their teeth under a microscope. Most trees, bushes, and forbs are known as C3 plants, and most species of grass are known as C4 plants. They have recognizably different ratios of carbon isotopes, and the animals that eat these plants reflect those isotopic ratios in their bones. Animals that eat leaves and twigs tend to have microscopic pits in their teeth; grass-eating animals tend to have microscopic scratches in their teeth. A previous study found a discrepancy between the isotopic evidence and the dental evidence. The latter suggested mammoths mostly ate grass, but the isotopic evidence suggested they were mixed feeders.

Location of fossil sites in Tultepec where mammoth remains used in the below referenced study were found.

Isotopic and dental evidence suggests Mexican mammoths were mixed feeders and ate grass, leaves, and twigs. From the below referenced study.

Scientists looked at mammoth teeth under a microscope and found scratches caused by eating grass and pits caused by eating twigs and leaves. From the below referenced study.

The new study found no discrepancy. Both the dental and isotopic evidence suggests mammoths were mixed feeders. They came to another interesting conclusion. Some of the mammoths from this region were year-round residents and ate the same kinds of plants their whole lives. Other mammoths, however, migrated long distances and apparently ate a different variety of plants than the year-round residents. Mammoths had a curious population dynamic with some migrating from far away and others staying in the same region for most of their lives. Perhaps, the migrating mammoths were males seeking new territories. Evidence from another study showed that some mammoths migrated back and forth from central Georgia to central Florida. In any case mammoths were adaptable animals, and if not for man would surely still exist.

Reference:

Rodrigues,-Franco, S., et al

“Dietary Reconstruction of Mammuthus columbi from Tultepec, Estrada de Mexico: A Multi-Proxy Approach”

Paleogeography, Palaeoclimatology, Paleoecology 666 May 15, 2025

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