Fossil studies of the extinct predator Dissacus praenuntius offer clues as to how ancient animals responded to environmental changes. The ancient omnivore was about the size of a jackal or a coyote.
ДиБгд, CC BY 4.0 , via Wikimedia Commons
Long before the supposed "Creation Week" — when creationists claim Earth was magicked into existence just a few thousand years ago — our planet was already teeming with life and undergoing dramatic changes. Around 56 million years ago, a mere tick in geological time, Earth experienced a sharp and rapid rise in global temperatures known as the Paleocene–Eocene Thermal Maximum (PETM). This event had a profound effect on ecosystems and the species that lived through it. Many, of course, did not survive, but those that did, adapted to the new, harsher conditions.
One such survivor was an early mammal, Dissacus praenuntius, a member of the now-extinct Mesonychidae order. D. praenuntius was an omnivore that resembled a hyena, but with small hooves on each toe, and like a hyena, it likely lived as an opportunistic scavenger and predator. Now, a team of palaeontologists has revealed how its behaviour changed during the PETM: it began consuming more bone, presumably because its usual prey had become scarce or disappeared altogether. In this respect, D. praenuntius serves as a record of the environmental pressures of the PETM and how some species responded to survive.
It paints a picture of an Earth that is far removed from the idealised, "perfect" planet imagined in creationist mythology — a planet supposedly fine-tuned for life. Instead, the fossil record tells the story of a world that can quickly become hostile, where survival depends not on divine design but on the ability to adapt — or perish.
The Paleocene-Eocene Thermal Maximum (PETM) - It's Cause and Consequences. The Paleocene–Eocene Thermal Maximum (PETM) was one of the most dramatic and rapid climate change events in Earth's history, occurring about 56 million years ago, at the boundary between the Paleocene and Eocene epochs. It lasted roughly 200,000 years and was marked by a sharp global temperature rise — one that profoundly altered ecosystems, ocean chemistry, and the course of mammalian evolution.The study, led by Andrew Schwartz of Rutgers University, was described in Rutgers Today and published in the journal Palaeogeography, Palaeoclimatology, Palaeoecology.
What was the PETM?
The PETM was a period during which global temperatures rose by 5–8°C (9–14°F) in a geologically short span—possibly as little as a few thousand years. It was a greenhouse climate event characterised by:
- A spike in carbon dioxide (CO₂) and methane (CH₄) in the atmosphere.
- Massive changes in the carbon cycle, as evidenced by a negative carbon isotope excursion (CIE) in sediments worldwide.
- Disruption of ocean chemistry and the deep ocean becoming more acidic and oxygen-depleted.
Likely Causes of the PETM
The precise cause of the PETM is still debated, but most scientists agree it involved a massive and rapid release of greenhouse gases — possibly thousands of gigatonnes of carbon—into the atmosphere and oceans. Several hypotheses have been proposed:
- Methane hydrate release
- Methane trapped in clathrates (methane ice) on continental shelves may have been destabilised by a small initial warming.
- Once released, methane would have rapidly oxidised to CO₂, intensifying the greenhouse effect.
- This scenario is known as the "methane burp" hypothesis.
- Volcanic activity
- Massive volcanic activity in the North Atlantic Igneous Province (NAIP) may have:
- Released CO₂ directly.
- Heated organic-rich sediments, triggering additional methane and CO₂ release.
- Peat and permafrost oxidation
- A warming climate may have triggered widespread oxidation of terrestrial carbon stores, such as peatlands, releasing more greenhouse gases.
- Orbital forcing
- A shift in Earth’s orbit (Milankovitch cycles) might have triggered initial warming, setting off feedback loops involving carbon release.
It's likely the PETM was caused by a combination of factors, with one or more acting as a trigger.
Consequences of the PETM
- Climate & Atmosphere
- Global temperatures rose by 5–8°C.
- High latitudes, including the Arctic, became subtropical.
- Polar regions were ice-free.
- Tropical regions may have become hotter than the thermal tolerance of many species, especially in the oceans.
- Oceans
- The oceans absorbed much of the released carbon, leading to:
- Ocean acidification, damaging organisms with calcium carbonate shells.
- A major extinction of benthic foraminifera (single-celled organisms living on the sea floor), with up to 50% of species disappearing.
- Deoxygenation in deep-sea environments.
- Terrestrial Life
- The PETM spurred major mammalian dispersals and diversification, especially in North America, Europe, and Asia.
- Key modern mammal orders like primates, hoofed mammals (ungulates), and carnivores either originated or spread rapidly during this time.
- Vegetation zones shifted poleward.
- Some animals showed dwarfism, likely a response to heat stress and lower food quality.
- Plants and Insects
- Plant distributions changed, reflecting warmer, wetter climates in some regions.
- Evidence suggests increased insect herbivory, possibly due to higher CO₂ levels altering leaf chemistry.
How Do We Know This Happened?
Scientists detect the PETM in the geological record by:
- A sharp negative carbon isotope excursion (CIE) in marine and terrestrial sediments.
- Fossil evidence of faunal turnovers, extinctions, and migrations.
- Sedimentary features like clay-rich layers and carbonate dissolution horizons, showing acidification and loss of marine carbonate.
The PETM as a Climate Warning
The PETM is often studied as a palaeoclimate analogue for modern anthropogenic climate change, albeit imperfectly. Key parallels:
- Rapid carbon release (though modern emissions are ~10× faster than those estimated for the PETM).
- Ecosystem disruption.
- Ocean acidification.
- Species extinction and migration.
Unlike the PETM, today’s climate change is occurring faster and under different baseline conditions, which may make current disruptions even more severe.
Summary Table
- Timing ~56 million years ago
- Duration ~200,000 years
- Temperature rise 5–8°C globally
- Cause Likely methane & CO₂ release from hydrates, volcanism, peat oxidation
- Ocean effects Acidification, deep-sea extinction, oxygen loss
- Land effects Mammal diversification, plant migration, dwarfism
- Modern relevance Insight into carbon cycle, climate sensitivity, and biological response
An Ancient Predator’s Shift in Diet Offers Clues on Surviving Climate Change
Fossil teeth reveal how a 56-million-year-old mammal adapted to global warming and what it means for animals today
About 56 million years ago, when Earth experienced a dramatic rise in global temperatures, one meat-eating mammal responded in a surprising way: It started eating more bones.
That’s the conclusion reached by a Rutgers-led team of researchers, whose recent study of fossil teeth from the extinct predator Dissacus praenuntius reveals how animals adapted to a period of extreme climate change known as the Paleocene–Eocene Thermal Maximum (PETM). The findings, published in the journal Palaeogeography, Palaeoclimatology, Palaeoecology, could help scientists predict how today’s wildlife might respond to modern global warming.
What happened during the PETM very much mirrors what's happening today and what will happen in the future. We’re seeing the same patterns. Carbon dioxide levels are rising, temperatures are higher and ecosystems are being disrupted.
Andrew Schwartz, first author
Department of Anthropology
School of Arts and Sciences
Rutgers University, NJ, USA.
Associate Professor Robert Scott of the Department of Anthropology is a co-author of the study.
Schwartz, Scott and another colleague used a technique called dental microwear texture analysis to study the tiny pits and scratches left on fossilized teeth. These marks reveal what kinds of food the animal was chewing in the weeks before it died.
The ancient omnivore was about the size of a jackal or a coyote and likely consumed a mix of meat and other food sources like fruits and insects.[These] super weird mammals looked superficially like wolves with oversized heads. Their teeth were kind of like hyenas. But they had little tiny hooves on each of their toes.
Andrew Schwartz.
Before this period of rising temperatures, Dissacus had a diet similar to modern cheetahs, eating mostly tough flesh. But during and after this ancient period, its teeth showed signs of crunching harder materials, such as bones.
We found that their dental microwear looked more like that of lions and hyenas. That suggests they were eating more brittle food, which were probably bones, because their usual prey was smaller or less available.
Andrew Schwartz.
This dietary shift happened alongside a modest reduction in body size, likely because of food scarcity. While earlier hypotheses blamed shrinking animals on hotter temperatures alone, this latest research suggests that limited food played a bigger role, Schwartz said.
This period of rapid global warming lasted about 200,000 years, but the changes it triggered were fast and dramatic. Schwartz said studies of the past like his can offer practical lessons for today and what comes next.
One of the best ways to know what's going to happen in the future is to look back at the past. How did animals change? How did ecosystems respond?
Andrew Schwartz.
The findings also highlight the importance of dietary flexibility, he said. Animals that can eat a variety of foods are more likely to survive environmental stress.
In the short term, it’s great to be the best at what you do. But in the long term, it’s risky. Generalists, meaning animals that are good at a lot of things, are more likely to survive when the environment changes.
Andrew Schwartz.
Such an insight may be helpful for modern conservation biologists, allowing them to identify which species today may be most vulnerable, he said. Animals with narrow diets, such as pandas, may struggle as their habitats shrink. But adaptable species, including jackals or raccoons, might fare better.
We already see this happening. In my earlier research, jackals in Africa started eating more bones and insects over time, probably because of habitat loss and climate stress.
Andrew Schwartz.
The study also showed that rapid climate warming as seen during the ancient past can lead to major changes in ecosystems, including shifts in available prey and changes in predator behavior. This may suggest that modern climate change could similarly disrupt food webs and force animals to adapt, or risk extinction, he said.
Even though Dissacus was a successful and adaptable animal that lived for about 15 million years, it eventually went extinct. Scientists think this happened because of changes in the environment and competition from other animals, Schwartz said.
Schwartz conducted his research using a combination of fieldwork and lab analysis, focusing on fossil specimens from the Bighorn Basin in Wyoming, a site with a rich and continuous fossil record spanning millions of years. Schwartz chose the location because it preserves a detailed sequence of environmental and ecological changes during the ancient period of climate warming.
Schwartz has been interested in paleontology, specifically dinosaurs, since he was a boy, journeying with his father, an amateur fossil hunter, on treks through New Jersey’s rivers and streams. Now, as a late-stage doctoral student, he hopes to use ancient fossils to answer urgent questions about the future.
He also wants to inspire the next generation of researchers.
I love sharing this work. If I see a kid in a museum looking at a dinosaur, I say, ‘Hey, I’m a paleontologist. You can do this, too.’.
Andrew Schwartz.
In addition to Schwartz and Scott, Larisa DeSantis of Vanderbilt University is an author of the study.
Publication:
AbstractThe Paleocene–Eocene Thermal Maximum (PETM) challenges creationist views of a recently created perfectly stable Earth by highlighting ancient periods of severe environmental change. Earth's history is marked by intense climate shifts and extinctions, illustrating that survival depends on evolutionary adaptation rather than intelligent design.
The effect of climate change and ecological disruption on species diets is critical for understanding the evolution of mammalian adaptations and potential risks from the current climate crisis. Here, we use dental microwear texture analysis (DMTA), a likely correlate of the mechanical properties of masticated food, to infer changes in diet within the mesonychid Dissacus praenuntius across the Paleocene-Eocene Thermal Maximum (PETM), a period of geological rapid warming and aridification ∼56 million years ago. Our results clarify previous reconstructions of this species as a small vertebrate mesocarnivore by emphasizing a durophagous dietary component. By comparing dental microwear across the PETM, we conclude that Dissacus praenuntius consumed less flesh and more bone during and after the PETM in comparison to before the event. Coupled with body mass reduction, dietary change during the PETM supports reduced primary and secondary productivity, rather than increased temperatures directly as a major probable cause of body mass reduction. We show that climate and ecological changes during the PETM caused dietary shifts in a species of flesh-eating mesonychid. These results reveal the ecology of the first large mammal predators as well as how mammalian diet may respond to modern climatic and habitat disruption.
Schwartz, Andrew; DeSantis, Larisa R.G.; Scott, Rob S. (2025)
Dietary change across the Paleocene-Eocene Thermal Maximum in the mesonychid Dissacus praenuntius
Palaeogeography, Palaeoclimatology, Palaeoecology 675 113089; DOI: 10.1016/j.palaeo.2025.113089
© 2025 Elsevier Inc.
Reprinted under the terms of s60 of the Copyright, Designs and Patents Act 1988.
If Earth were perfectly suited for life, we wouldn't see abrupt climate events like the PETM that caused mass extinctions, migrations, and ocean acidification. The fossil record reveals that no species was ever completely safe; even well-adapted organisms perished when conditions changed dramatically. This suggests our planet is shaped by unpredictable physical processes, not careful design.
The PETM serves as a cautionary example for current climate change: while its warming occurred over thousands of years due to a massive carbon release, human-driven carbon emissions today are happening about ten times faster. This rapid rate suggests grave consequences could lie ahead, as we undertake an unprecedented experiment with Earth's climate.
In this light, the PETM serves both as a refutation of creationist mythology and a dire warning. It reminds us that Earth has changed before, but always at a cost. Those changes were survivable only for species that could adapt quickly enough — or simply by chance. Unlike the creatures of the PETM, we understand what's happening. But whether we choose to act on that knowledge remains to be seen. Allowing creationist ideology — rooted in wilful ignorance and denial of deep time, evolution, and climate science — to influence education or government policy poses a serious threat. It fosters ignorance at precisely the moment when informed, science-based decisions are most urgently needed.
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