Tag Archives: Eocene

Carbon emissions rate unprecedented in the past 66 million years

About 55.8 million years ago, the rate of carbon emissions grew abruptly, leading to a period of massive warming. But today’s rate of emissions is ten times higher.

Note the PETM 60 million years ago.

Today’s global warming is often compared to similar geological phases, although the comparison really isn’t fair. Geological shifts happen in millions of years, whereas today’s changes take place on the scale of decades. But even this comparison, as unfair as it is, still doesn’t stand. We’re emitting carbon dioxide at the fastest rate since the Paleozoic (at the least).

Richard Zeebe at the University of Hawaii at Manoa and colleagues compared the timing of climate change with the timing of carbon emissions as recorded by marine sediments, and found that they occurred at essentially the same time. They compared today’s situation to an event called the Palaeocene–Eocene Thermal Maximum (PETM), which took place 55.8 million years ago.

The Paleocene–Eocene Thermal Maximum (PETM) was  a period of massive carbon injection has been estimated to have lasted some 0.2 million years. During this period, global temperatures increased by 5–8 °C. Stratigraphic sections containing the PETM reveal numerous other changes and extinctions. Fossil records for many organisms show major turnovers, especially for marine creatures. But as massive as those changes were, today’s changes are even more striking.

According to Zeebe’s model, the carbon emissions in PETM occurred over a period of at least 4,000 years, at a rate of between 0.6 to 1.1 billion tonnes of carbon per year. Today’s emissions on the other hand are on the order of 10 billion tonnes of carbon per year. The authors suggest that the emissions are so massive that we’ve entered a new age:

“Given that the current rate of carbon release is unprecedented throughout the Cenozoic, we have effectively entered an era of a no-analogue state, which represents a fundamental challenge to constraining future climate projections,” the study writes.

In an accompanying News & Views article, Peter Stassen, one of the researchers who also studies paleoclimate writes:

“If PETM emissions occurred over a slower timescale as proposed by Zeebe et al., pelagic marine ecosystems may have had sufficient time to adapt to environmental changes through migration or evolution. It therefore remains possible that the current rates of change might exceed the adaptive capacity of modern marine ecosystems and their constituents.”

In other words, climate change may be happening too fast for ecosystems to cope with it, and if this is the case then we’re headed for massive extinctions. During the PETM, only the deep-sea biosphere was rapidly disturbed, culminating in the sudden extinction of foraminifera living on the ocean floor. This time, the situation could be much more dire.

Climate change is driven by manking emitting massive quantities of greenhouse gases in the atmosphere, especially carbon dioxide. This is already a scientific fact, with an undeniable level of confidence.

Journal Reference: Anthropogenic carbon release rate unprecedented during the past 66 million years.

The Jesus Lizard running on water

Jesus lizard ancestor skimmed the tropical waters of Wyoming, 48 million years ago

Paleontologists have discovered what looks like the earliest member of the Corytophanidae (also known as casquehead or helmeted lizards) judging from fossils collected in Wyoming. The ancient species is also the earliest ancestor of the modern basilisk, or better known as the Jesus Lizard because of its ability to skim the surface of water over short distances.

The Jesus Lizard running on water

The Jesus Lizard running on water. Image: National Geographic

The early Corytophanidae lived some 48 million years ago in the tropical rainforests of Wyoming. It’s hard to imagine tropics today given the deserts the litter the North American state, but we’re talking about the  Eocene Epoch – a period when greenhouse gas levels were very high in the atmosphere and temperatures were a lot hotter than today. In the Wyoming Bridger Basin where the ancient lizard was found, the temperature was up to 8 degrees Celsius on average higher.

The lizard was named Babibasiliscus alxi, where babi means “older male cousin” in Shoshone Native American – a tribute to the local heritage. Judging from the fossils, the lizard was likely two feet long, was active during the day and likely spent most of its time in trees. Like other casqueheads, the lizard has a ridge over its skull that likely made it look fiercer to its prey. Its teeth had three points suitable for eating snakes, lizards, fish, insects and plants. The larger cheekbones suggest it also hunted large prey.

“The generic name is meant to honor the Shoshone people who originally inhabited the areas in which the specimen was discovered,” Jack Conrad of the American Museum of Natural History explained.

Fossils, and digital reconstructions based on CT scans of the Babibasiliscus skull. Image: PLOS ONE

Fossils, and digital reconstructions based on CT scans of the Babibasiliscus skull. Image: PLOS ONE

Based on phylogenetic analysis Babibasiliscus is closely related to the modern genus Laemanctus, which includes the famous Jesus Lizard. The Jesus Lizard likes to live near water, that way, when it is frightened by an approaching predator it can get to the water and run across the surface. The lizards can run on water because they have a fringe of scales on their hind toes which makes little webs that can trap bubbles of air and water beneath their feet. This keeps them from sinking into the water if they run quickly enough across. When they do stop running they don’t mind taking a little swim. It’s not clear whether Babibasiliscus also skimmed water.

The Jesus Lizard and its genus relatives however are endemic only to the tropical areas of Central and South America. Babibasiliscus proves that the genus used to have a wider distribution going much farther North, according to the paper published in the journal PLOS ONE. This shows the cooling conditions following the Eocene period forced the lizards to migrate farther South, echoing current ecosystem crises.

“Given our current period of global climate fluctuation, looking to the fossil record offers an important opportunity to observe what is possible,” Conrad said, “and may give us an idea of what to expect from our dynamic Earth.”

Saber-tooth cats grew their fangs faster than human fingernails

Saber-tooth cats, the bane of early humans (and pretty much every creature that co-existed with them), roamed the Earth for 42 million years before going extinct at the end of the ice age. Now, a new study has found that their trademark teeth may have evolved later in their evolutionary stage, but when they grew, they grew fast.

Skeleton of Smilodon (Smilodon fatalis). Exhibit in the National Museum of Nature and Science, Tokyo, Japan.

The saber-tooth cats were found worldwide from the Eocene epoch (42 million years ago) to about 11,000 years ago – the earliest human cultures might have actually seen them in action. Despite the “cat” in their name, these animals are not closely related to modern cats, belonging to a different evolutionary tree. The most well known saber-tooth cat is the Smilodon, who emerged 2.5 million years ago and weighed up to 440 kg.

With their incredibly long teeth, they have fascinated us for centuries, and researchers have been striving to understand how, and why these teeth evolved. Now, they are one step closer, after learning that these teeth grew incredibly fast.

“For predators such as big cats, an important determinant of an individual’s full hunting ability is the time required to grow their weapons—their teeth,” explains Z. Jack Tseng, who is a National Science Foundation and Frick Postdoctoral Fellow in the American Museum of Natural History’s Division of Paleontology. The study co-author goes on to say, “This is especially crucial for understanding sabertoothed predators such as [the species] Smilodon.”

The sabers they developed were a remarkable adaptation, and Tseng wanted to see just how long it took for a specimen to grow its teeth. So he and his team conducted chemical analysis on fossils and meticulously analyzed the chemical composition and structure of the sabers. They came up with a stunning results: the saber teeth grew by 6 mm per month – twice as fast as human fingernails!

“Timing of development is critical for many aspects of vertebrate ecology and evolution,” reports New York State Museum Pleistocene vertebrate paleontology curator Robert Feranec and study co-author. “Changes in the timing of life-history events can have major effects on an organism’s adult features and final appearance. For extinct species, we can usually only determine the relative sequence of development events. This technique will permit the determination of absolute developmental age not only for Smilodon, but other extinct species.”

Reconstruction o saber-tooth cat by Marcus Dublin.

So even though they had huge fangs, much longer than those of today’s lions, they didn’t take so much time to grow them. However, when it comes to biting, tooth size isn’t everything. Using computer models, scientists estimated the bite strength that saber cats use and found that it was actually weaker than their gripping force – so it seems likely that they killed their prey by gripping, not biting. However, the long canines were extremely efficient at biting the neck.

Saber tooth cat mostly hunted large, slow prey. The Smilodon for example was an apex predator and primarily hunted large mammals like bison, camels, horses and even mammoths. They were experts at ambushing and used their large mass to disrupt the balance of their prey, making it vulnerable. They would likely still be alive today, if most of their prey hadn’t gone extinct.

The study is published in the journal Proceedings of the National Academy of Sciences.


Fossil of Earliest Bird Pollinator Found

Researchers have discovered the earliest evidence of a bird pollinator visiting flowers, presumably to feed on the nectar – if true, this means that bird pollinator/plants interactions were already taking place 47 million years ago.

pollinator bird

When you think about pollinators, you mostly think about bees or butterflies – but birds are significant pollinators too. Birds, particularly hummingbirds, honeyeaters and sunbirds accomplish much pollination, especially of deep-throated flowers. Even some monkeys, lemurs, possums, rodents and lizards act as polllinators, though at a much smaller scale.

However, researchers don’t know that much about the evolutionary history of pollinating birds. Now, Gerald Mayr and Volker Wilde from Senckenberg Research Institute and Natural History Museum Frankfurt report the earliest evidence of flower visiting by birds.

As you might guess, finding such evidence is really hard – you basically have to catch them fossilized in the act, or have a fossil so well preserved, that you can make some indirect deductions; in their new study, they describe such a well perserved fossil.

The complete skeleton of a small, ancient bird (Pumiliornis tessellatus) from the middle Eocene of Messel, Germany, was found in oil shale pits in 2012. The fossil is so immaculately preserved that you can actually observe the contents of its stomach: pollen grains from eudicotyledonous angiosperrms. Researchers believe the grains were ingested when the bird was hunting for nectar in the flowers. Here’s a picture of the fossil, with the pollen grains highlighted. The stomach contents also feature an iridiscent insect.

pollinator bird2

The nectar guzzling bird in case was pretty small, measuring about 8 centimeters long and weighing probably between 5 and 10 grams – comparable to the hummingbirds we see today. Furthermore, its general physiology suggests that it was a nectar collector: it had long, slender nasal openings and a fourth toe that could be turned backward meant the bird could clasp or climb branches, and was also very useful for visiting flowers.

P. tessellatus was not that well understood, as it was only known through two other specimens, and none of them was as well preserved as this one. According to Mayr, pollinating birds probably existed before 47 million years ago, and this began shortly after birds started to take flight.

Using a million suns to shed light on a fossilized plant

Scientists have used one of the brightest light sources in the Universe that we know of to expose the biochemical structure of a 50 million-year-old fossil plant to stunning visual effect. The mixed team of paleontologists, geochemists and physicists bombarded the fossils with extremely bright X-rays and showed that the chemical makeup of the plant hasn’t changed much since the Eocene.

Exceptional fossils, exceptional methods

Optical plus X-ray false color composite image (Cu = red, Zn = green, and Ni =blue). Credit: P. wyomingensis, specimen BHI-3113

The exceptional fossils come from the Eocene (approximately 55-34 million years ago), from a formation called the Green River Formation in the Western United States. The formation is famous due to its exceptional nature and has been used for many studies. Sediments there were deposited in very fine layers, a dark layer during the growing season and a light-hue inorganic layer in the dry season – each pair of layers (called varve) represents a year, holding valuable information about that year (how much it rained for example). The area is very rich in fossils, featuring not only very detailed plant fossils, but also fish, birds and even crocodiles.

Researchers from Britain’s University of Manchester and Diamond Light Source and the Stanford Synchrotron Radiation Lightsource in the US used a particular type of cyclic particle accelerator (called a synchotron) to create a light stronger than that of a million suns, and used it to study the plant fossils.

Diplomystus (left) and Knightia (right), two fossil fish from one of the lake beds in the Green River Formation. Via Wikipedia.

Lead author Dr Nicholas Edwards, a postdoctoral researcher at The University of Manchester, said:

“The synchrotron has already shown its potential in teasing new information from fossils, in particular our group’s previous work on pigmentation in fossil animals. With this study, we wanted to use the same techniques to see whether we could extract a similar level of biochemical information from a completely different part of the tree of life. To do this we needed to test the chemistry of the fossil plants to see if the fossil material was derived directly from the living organisms or degraded and replaced by the fossilisation process.

It may seem surprising that the fossil chemistry can be conserved over such long periods of time, but that shouldn’t really come as a shock.

“We know that plant chemistry can be preserved over hundreds of millions of years — this preserved chemistry powers our society today in the form of fossil fuels. However, this is just the ‘combustible’ part; until now no one has completed this type of study of the other biochemical components of fossil plants, such as metals.”

Identical to today’s plants

Among the things which they wanted to understand was how did the plants’ chemistry change in the tens of millions of years which passed since the Eocene. But interestingly enough, their work showed that the chemical make-up was virtually identical. The distribution of copper, zinc and nickel in the fossil leaves was almost identical to that in modern leaves. Different biological structures concentrated different chemical elements, nd the way these trace elements and sulphur were attached to other elements was very similar to that seen in modern leaves and plant matter in soils.

Co-author Professor Roy Wogelius, from Manchester’s School of Earth, Atmospheric and Environmental Sciences, said:

“This type of chemical mapping and the ability to determine the atomic arrangement of biologically important elements, such as copper and sulphur, can only be accomplished by using a synchrotron particle accelerator.
“In one beautiful specimen, the leaf has been partially eaten by prehistoric caterpillars — just as modern caterpillars feed — and their feeding tubes are preserved on the leaf. The chemistry of these fossil tubes remarkably still matches that of the leaf on which the caterpillars fed.”

This suggests not only that the chemical structure of plants hasn’t changed significantly, but also that fossil plants don’t get their chemical makeup from the environment, as was previously believed by some geologists, but in fact represents that of the living leaves.

The research team also mentioned that the big amounts of copper helped preserve the leaves in such a magnificent way:

“We think that copper may have aided preservation by acting as a ‘natural’ biocide, slowing down the usual microbial breakdown that would destroy delicate leaf tissues. This property of copper is used today in the same wood preservatives that you paint on your garden fence before winter approaches.”, mentioned Manchester palaeontologist and co-author Dr Phil Manning.

New fossil sheds light on the ancestor of dogs, bears and tigers

Cats, dogs, as well as many well known and loved wild animals such as seals, lions, tigers and bears trace their ancestry to primitive carnivorous mammals dating back to 55 million years ago, at the beginning of a time period called the Eocene. A study, published in the most recent issue of the Journal of Vertebrate Paleontology, discusses the origins of this group (called the ‘carnivoraformes’), and describes one of the earliest specimens to belong to it – in other words, one of the earliest primitive animals to belong to the group.

The species in case is called Dormaalocyon latouri, and new fossils of it have been found in Belgium. The new specimens were found by lead author Floréal Solé and his colleagues and they make for a better identification and interpretation of the features and the role that this animal plays.

“Its description allows better understanding of the origination, variability and ecology of the earliest carnivoraforms,” says Solé.

All in all, they found over 250 teeth and ankle bones. The teeth clearly show that Dormaalocyon is close to the origin of carnivoraforms and that it is one of the most primitive members of the group, while the ankles suggest that it was arboreal, living and moving through the trees. There has been some discussion whether or not the species did live or not in the trees (based on previously found fossils), but with new evidence in sight, it seems clear that we are in fact dealing with an arboreal mammal. Dr. Solé also believes that they originated in Europe, and it was at about this time (55 million years ago) that they started to make their way towards North America.

Personally, I find this intriguing. Mind you, the face of the Earth looked much different than it does today, and Europe was much closer to North America, but the distance is still pretty much for an animal. Europe and North America started splitting up in the Jurassic, some 140 million years ago. I may be missing some information, but at least from this point of view, it seems likelier that the emergence of Dormaalocyon in North America took place somewhat earlier than the Eocene, when Europe and North America were closer.

A reconstruction of the continents, as they looked in the Eocene.

Either way, the fossils suggest there were even more primitive species in the group in an earlier time period, the Paleocene.

“The understanding of the origination of the carnivoraforms is important for reconstructing the adaptation of placental mammals to carnivorous diet. Therefore, Dormaalocyon provides information concerning the evolution of placental mammals after the disappearance of the largest dinosaurs (at the Cretaceous-Paleogene extinction event). Our study shows that the carnivoraforms were very diversified at the earliest Eocene, which allows hypothesizing that they were probably already diversified during the latest Paleocene.”

This means that there are even more fossils out there just waiting to be found and provide more information on the ancestry of this magnificent group.

Journal Reference:

  1. Solé, F., R. Smith, T. Coillot, E. De Bast, T. Smith. Dental and Tarsal Anatomy of ‘miacis’ Latouri and a Phylogenetic Analysis of the Earliest Carnivoraforms (mammalia, Carnivoramorpha). Journal of Vertebrate Paleontology, 34(1): 1-21; 2014 [link]
Pre-glacial topographical reconstruction for Antarctica during Eocene–Oligocene times.

Antarctica was home to a rainforest some 50 million years ago

Scientists who studied sediment cores drilled from the ocean floor off the Antarctic coast, have found on subsequent analysis fossil pollens that came from a tropical forest. Most likely, the continent was covered by rainforest some 52 million years ago. The researchers involved warn however that by the end of the century, ice from the Antarctic might retreat at the current rate of global warming, leaving the continent once again ice-free.

Pre-glacial topographical reconstruction for Antarctica during Eocene–Oligocene times.

Pre-glacial topographical reconstruction for Antarctica during Eocene–Oligocene times.

Kevin Welsh, an Australian scientist who traveled on the 2010 expedition,  said that the international team of researchers he was a part of had discovered temperature-sensitive molecules in the cores showing that Antarctica was as warm as 68°F (20 Celsius) some 52 million years ago.

“There were forests existing on the land, there wouldn’t have been any ice, it would have been very warm,” Welsh told AFP of the study, published in the journal Nature.

“It’s quite surprising, because obviously our image of Antarctica is that it’s very cold and full of ice.”

The warmest global climates of the past 65 million years occurred during the early Eocene epoch (about 55 to 48 million years ago). Back then CO2 estimates of anywhere between 990 to “a couple of thousand” parts per million were presented in the atmosphere, compared to today’s CO2 levels estimated at 395ppm. The high level of CO2 is considered the major driver for atmospheric warming and Welsh said the most extreme predictions by the Intergovernmental Panel on Climate Change would see ice again receding on Antarctica “by the end of the century.”

“It’s difficult to say, because that’s really controlled by people’s and governments’ actions,” said Welsh, a paleoclimatologist from the University of Queensland. “It really depends on how emissions go in the future.”

During this mentioned period, the scientists believe the climate in lowland settings along the Wilkes Land coast (at a palaeolatitude of about 70° south) supported the growth of highly diverse, near-tropical forests characterized by mesothermal to megathermal floral elements including palms and Bombacoideae.

Currently, The ice on east Antarctica is 1.9-25 miles thick, and is thought to have formed about 34 million years ago.

ancient mammoth

Diversity is what helped mammals survive through deep time

ancient mammoth

After the great dinosaur extinction some 65 million years ago, mammals finally had their big shot as numerous niches became free for the taking. Thus, from mouse size, some mammal species surfaced which were as large as a bus, the so called mammal megafauna, like mammoths, giant sloths or saber-tooth tigers. However, a dire trial of their own was to come. Through out millions of years, mammals were challenged by a series of alternating climate cycles. According to a recent study by scientists at Vanderbilt University, diversity was the key to their survival.

The study focused on the various ups and downs in range and diversity of families of mammals that inhabited the continental U.S. during  the period that began with the Eocene and ended 12,000 years ago with the terminal Pleistocene extinction. The scientists involved in the study looked at a myriad of fossil records, however its almost impossible to distinguish highly related species between one another, so instead they concentrated on performing a family-level analysis. They analyzed 35 different families, such as Bovidae (bison, sheep, antelopes); Cricetidae (rats, mice, hamsters, voles); Equidae (horses, donkeys); Ursidae (bears); Mammutidae (mammoths); and Leporidae(rabbits and hares).

What their analysis showed was that the range and distribution of mammalian families stayed surprisingly consistent, despite major climate changes through out the 56 million year period, which saw temperature differences of several degrees, in alternating warm/cold cycles, and finally ended with the Ice Ages that alternated between relatively cold glacial and warm interglacial periods.

“These data clearly show that most families were extremely resilient to climate and environmental change over deep time,” said Larisa R. G. DeSantis, assistant professor of earth and environmental studies at Vanderbilt University who directed the study.

The scientists’ research shows that families retained more or less similar niches through out millions of years and is consistent with the idea that family members may inherit their ranges from ancestral species. However, the biggest takeaway is the fact that the researchers observed a highly important link  between a family’s diversity and its range – the greater diversity a family has, the better the stability and range.

“Diversity is good. The more species a family has that fill different niches, the greater its ability to maintain larger ranges regardless of climate change,” says DeSantis.

Mammals have demonstrated a remarkable ability to adapt to their environmental conditions, re-sizing and migrating easily. Understanding how mammalians have adapted through out deep geological time is highly important to understanding how they will adapt in the future, especially considering that one in four species of land mammals in the world faces extinction.

“Before we can predict how mammals will respond to climate change in the future, we need to understand how they responded to climate change in the past,” says DeSantis.

“It is particularly important to establish a baseline that shows how they adapted before humans came on the scene to complicate the picture.”

The findings were published in the journal PLoS One

source: Futurity  / image credit : Wikimedia Commons.

A computer forecast of how the ocean pH will look in 2100 under emission scenarios. Purple dots show cold-water coral reefs. Red dots show warm-water coral reefs. The pH scale is shown on the right. (Credit: NOAA)

Ocean life threatened by mass extinction as acidification rate nears 300 million year max

A computer forecast of how the ocean pH will look in 2100 under emission scenarios. Purple dots show cold-water coral reefs. Red dots show warm-water coral reefs. The pH scale is shown on the right. (Credit: NOAA)

A computer forecast of how the ocean pH will look in 2100 under emission scenarios. Purple dots show cold-water coral reefs. Red dots show warm-water coral reefs. The pH scale is shown on the right. (Credit: NOAA)

A newly published paper in the journal Science provides a worrisome report – the world’s oceans are acidifying at a rate, which if set to continue, will be unprecedented in the last 300 million years. The scientists report that this comes as a direct consequence of the alarming ever increasing carbon dioxide concentration in the atmosphere, which also gets absorbed by the oceans, with dramatic effects on the marine ecosystem.

To trace back the other periods of accelerated ocean acidification in Earth’s history, the scientists from the U.S. National Oceanic and Atmospheric Administration (NOAA) studied the isotopic composition of carbon changes found in marine rock samples. Rock records dating back as far as 300 million years were studied, which allowed tracking the ocean’s water pH over an impressive time frame. Thus, the researchers identified a number of key periods in Earth’s history when atmospheric CO2 concentration, and thus ocean water pH too, reached milestone levels. These spurred evolutionary changes, as well as  marine and animal extinction, like 65 million years ago when the dinosaurs died off.

An interesting period was the Paleocene-Eocene Thermal Maximum (or PETM), dating back 56 million years ago, when an abrupt carbon dioxide release caused a global temperature increase of 6°C over 20,000 years. During PETM, the oceans became 0.4 units more acidic on the 14-point pH scale. This period marked the largest deep-sea extinction of foraminifera of the last 75 million years, and was one of the four biggest coral reef disasters of the last 300 million years. The study authors warn that what happened 56 million years ago was a fast warm-up and quick acidification, however when compared with the current rate of CO2 levels increase and water acidification since the start of the industrial age 150 years ago, we’re currently on a trend that will far out shadow it.

Climate change comes in cycles, warming and cooling, and  the Earth has gone through a number of such periods during its history. It’s enough to compare some charts and time frames for relevancy to understand that there’s nothing really natural to what’s going on today on our planet, however. For instance, the first period the NOAA scientists decided to study was the end of the last ice, which started 18,000 years ago. Over a period of about 6,000 years, atmospheric CO2 levels increased by 30 percent, translating in a change of roughly 75 ppm – the same amount of increase was recorded in the past 50 years alone!

“Ocean acidification may have severe consequences for marine ecosystems,” reads the study. “However, assessing its future impact is difficult because laboratory experiments and field observations are limited by their reduced ecologic complexity and sample period.”

A similar report such as the from NOAA, was presented last summer at an U.N. conference. Then, the panel found that oceanic conditions are similar to those of “previous major extinctions of species in Earth’s history,” and that we face losing marine species and entire marine ecosystems, such as coral reefs, within a single generation.

Over the past 150 years, the Earth’s oceans have become more acidic by 0.1 unit of pH, and the study’s scientists predict that by 2100 there will be an increase to 0.2 or 0.3 pH.

“Given that the rate of change was an order of magnitude smaller compared to what we’re doing today, and still there were these big ecosystem changes, that gives us concern for what is going to happen in the future,” said Baerbel Hoenisch, one of the study’s lead authors.


A suggestive illustration portraying a modern day Morgan horse nose-to-nose to an artist's impression of the Sifrhippus sandrae, the first horse, which was just about the size of a house cat. (c) anielle Byerley, Florida Museum of Natural History

The first horse was the size of house cat and got even smaller as climate warmed 56 million years ago

Bergmann’s rule states that mammals of a given genus or species are smaller in hotter climates, and bigger in colder climates. Adapted, when faced with climate change cycles, mammals shirk as temperature rises and scale back up in size, once the cycle ends and makes room for cooling. Simple correlation, based on fossils and temperature readings from their given periods, seems to offer evidence supporting this principle – mammals shrink as the Earth warms. A latest study performed by scientists at Florida Museum of Natural History at the University of Florida, which looked at a brief, yet dramatic climate change,comes to the same conclusion.

A suggestive illustration portraying a modern day Morgan horse nose-to-nose to an artist's impression of the Sifrhippus sandrae, the first horse, which was just about the size of a house cat. (c) anielle Byerley, Florida Museum of Natural History

A suggestive illustration portraying a modern day Morgan horse nose-to-nose to an artist's impression of the Sifrhippus sandrae, the first horse, which was just about the size of a house cat. (c) Danielle Byerley, Florida Museum of Natural History

Called the Paleocene-Eocene Thermal Maximum or PETM for short, this period in Earth’s history took place 56 million years ago and was marked by significant global warming, which lead to a temperature increase between 9 to 18 degrees Fahrenheit at the start, only to drop to almost initial values at the end – the age lasted for 175,000 years. It may seem like a long time, but in geological terms, well it’s nothing more than a blink of an eye – still a lot had happen.

“We had known it was a really unique event for a while in the sense that it was a very rapid, large scale global warming event. And it marks one of the most important moments in mammalian evolution in the sense that we see the first occurrence of several modern orders of mammals, including the primates that are clearly traceable as the direct ancestors of the group that we’re a part of, as well as the ancestors of horses, the ancestors of cows and hippos and camels,” said Jonathan Bloch, associate curator of vertebrate paleontology at the Florida Museum of Natural History at the University of Florida.

The tiniest horse to roam the Earth

One such mammal was Sifrhippus, one of the first horse species, which  shrank from about 12 pounds average weight to about eight and a half pounds as the climate warmed over thousands of years. The first horses were a lot different from those of today; back then, they weren’t larger than a small dog or house cat. Interesting enough, the only Sifrhippus fossils found have been in Bighorn Basin of Wyomin, which today is the largest wild mustang reservation.

By studying various fossils like teeth or fragmentary jaws, the researchers were surprised to see the Sifrhippus become 30 percent smaller through the climate event , only to get 75 percent larger as it passed. They were able to tell this by studying the oxygen isotopes found in the horses’ teeth.

“What he showed was that exactly coincident with this body size change that we had documented there were shifts in the oxygen isotope that showed it was getting warmer as the horses were getting smaller. And then as the horses became larger again it became cooler,” Bloch said.

Indeed, the researcher’s findings conclude the change in size was, as suspected, driven primarily by the warming trend. A warmer climate seems to induce a shrinkage effect in mammals, which might be  able to shed excess heat easier.

Mammals and climate change today?

Right now, the Earth is warming at a constant rate, however the temperature increase ins’t taking place through thousands of years, but hundreds – induced by humans, if not accelerated. Will today’s mammals get smaller in the future as well? Well, late last year I wrote a piece on how climate change has lead to a lose in size of  3-17% for most plants, while fish shrank by 6-22% – polar bears, among others, have been reportedly getting smaller as well. So, this is already happening. As for humans, we’ve been getting bigger and bigger, mostly because of better nutrition – the same goes for the ego, only its food is gluttony.

The team of researchers’ findings were reported in the journal Science.

Story and illustration via NYT.