So you typed 'is it paleogene or paleocene' into a search bar and honestly? Same. These two terms get tangled up constantly, especially in real-food and ancestral-health circles where we throw around words like 'paleo' like everyone already knows the full geological backstory. They don't. Most people don't. I didn't for a long time either. So let's fix that, because I actually think understanding deep time makes the whole 'eat like your ancestors' argument click in a way that no Instagram infographic ever quite manages.

First, the Short Answer

Paleogene is a geological period. Paleocene is an epoch inside that period. That's the whole relationship in one sentence. The Paleogene period contains three epochs: the Paleocene, the Eocene, and the Oligocene, in that order from oldest to most recent. So every Paleocene moment in history is automatically part of the Paleogene, but the Paleogene is a much bigger slice of time that extends well beyond just the Paleocene. Think of it like this: the Paleogene is the chapter, and the Paleocene is the first section of that chapter.

The Geological Timeline, Made Human

The Paleogene period runs from roughly 66 million years ago to about 23 million years ago, according to the International Commission on Stratigraphy, the body that maintains the official geologic time scale. That's 43 million years of Earth history packed into one period.

Breaking it down by epoch:

  • Paleocene epoch: approximately 66 to 56 million years ago. This is the chapter that opens right after the mass extinction event that wiped out the non-avian dinosaurs. Mammals were small, mostly insectivorous, and just starting to radiate into the ecological niches the dinosaurs left behind.
  • Eocene epoch: approximately 56 to 34 million years ago. Things warm up dramatically (the Early Eocene Climatic Optimum is one of the warmest periods in the last 65 million years). Mammals diversify rapidly. The ancestors of modern hoofed animals, primates, and early whales all emerge during this stretch.
  • Oligocene epoch: approximately 34 to 23 million years ago. The climate cools and dries. Grasslands begin to spread. Early relatives of horses, rhinos, and many other familiar mammal lineages take shape.

The Smithsonian National Museum of Natural History lays this out clearly in their geologic time resources, and it's worth bookmarking if you're a deep-time nerd like I've become.

Why People Get These Two Mixed Up

The confusion is completely understandable. Both words start with 'Pale-,' both end in '-ene' or '-ocene,' and they sound nearly identical when spoken fast. The suffix '-cene' (from the Greek 'kainos,' meaning recent or new) appears in all three Paleogene epochs: Paleocene, Eocene, and Oligocene. The word 'Paleogene' itself means 'ancient origin' and refers to the older half of the Cenozoic Era.

The Cenozoic Era, by the way, is the overarching umbrella. It contains the Paleogene period, then the Neogene period (Miocene and Pliocene epochs), and finally the Quaternary period (Pleistocene and Holocene, which is where modern humans show up). If you've heard the word 'Pleistocene' in ancestral-health conversations, that's Quaternary, not Paleogene at all. Different chapter entirely.

So the mental map looks like this:

Cenozoic Era

  • Paleogene Period
  • Paleocene Epoch
  • Eocene Epoch
  • Oligocene Epoch
  • Neogene Period
  • Miocene Epoch
  • Pliocene Epoch
  • Quaternary Period
  • Pleistocene Epoch
  • Holocene Epoch

What Was Actually Happening to Food and Mammals During the Paleogene

This is where it gets interesting for people in the real-food world. The Paleogene is when modern mammalian diversity essentially launched. After the end-Cretaceous extinction cleared the board, the mammals that survived had room to grow, adapt, and specialize in ways that had never been possible when massive dinosaurs dominated every ecosystem.

During the Paleocene specifically, early mammals were small and generalist. They ate insects, fruit, seeds, and whatever they could find. There were no grasses to speak of, no grain fields, no wheat. The plant life was dense tropical and subtropical forest across much of what is now North America and Europe. Early primates were beginning to emerge, small tree-dwellers with grasping hands and forward-facing eyes, eating fruit and insects in the forest canopy.

By the Eocene, the diet of early mammals was getting more complex. Herbivory was diversifying. Some lineages were starting to specialize in leaves, others in fruit, others in roots and tubers. Research published in the journal Palaeogeography, Palaeoclimatology, Palaeoecology has documented how plant communities of the Eocene supported dense tropical canopies, rich in the kinds of whole-food plant diversity that ancestral mammals depended on.

The Oligocene is when the shift toward open, drier environments begins in earnest, setting the stage for the grasslands that would eventually define the Miocene and push grazing mammals, including our much-later ancestors, toward different dietary strategies.

The 'Paleo' in Paleo Diet: A Quick Reality Check

Here's something worth knowing if you've been eating paleo for any length of time. The popular 'Paleo diet' is named for the Paleolithic period, which is a cultural and archaeological term, not a geological one. The Paleolithic ('Old Stone Age') refers to the period of human prehistory characterized by the use of stone tools, running roughly from about 2.5 million years ago to about 10,000 years ago. That places it almost entirely within the Pleistocene epoch of the Quaternary period.

So the Paleo diet is named for the Paleolithic, which is in the Quaternary, which comes after the Neogene, which comes after the Paleogene. The Paleogene itself predates anatomically modern humans by tens of millions of years. No human walked the earth during the Paleocene epoch. Not even close.

The reason I think this is worth knowing is not to split hairs. The philosophical foundation of real-food eating, the idea that our bodies are designed for a particular way of eating shaped by millions of years of evolutionary history, is sound and well-supported. But the more precisely we understand that evolutionary timeline, the better we can actually apply it. The dietary patterns that matter for human health were shaped most acutely during the Pleistocene, when Homo sapiens and our immediate predecessors were actually living, hunting, foraging, and eating. That's the context that directly informs what our digestive systems, our metabolisms, and our immune systems expect.

The Paleogene is the deep backstory. It's the era when our mammalian ancestors were laying the groundwork. It matters, but in a foundational, deep-roots kind of way, not a 'eat like you're in the Paleocene' way.

Why Deep Time Is Worth Understanding in a Real-Food Context

I'll be honest with you. I didn't care about geology until I started going deep on functional medicine and ancestral health, and someone finally connected the dots for me in a way that made sense. Understanding deep time changes how you see modern food.

When you realize that the human body has been shaped by millions of years of eating whole, recognizable foods, before industrial seed oils, before ultra-processed flour products, before high-fructose corn syrup, you stop seeing real food as a trend or a diet. You start seeing it as what we were actually built for. That's not just philosophy. The National Institutes of Health has published research on evolutionary discordance, the mismatch between our ancestral dietary environment and the modern Western diet, as a framework for understanding chronic disease.

The Paleogene gave us our mammalian inheritance. The Neogene refined it. The Pleistocene shaped it into the human dietary template we carry today. And then in roughly the last 200 years, the food system blew past all of that in a blink. Our genes have not caught up. That's the core argument for real food, and deep time is what makes it stick.

I believe with everything in me that these bodies we've been given are designed with intention, and that eating close to the way humans have always eaten is part of stewarding that gift. Understanding the geological and evolutionary timeline doesn't undercut that. It deepens it.

Quick Reference: Key Terms Defined

Because I know some of you are going to need this in a tidy format:

Era: The broadest division we're working with here. The Cenozoic Era covers the last 66 million years.

Period: A subdivision of an era. The Paleogene is a period (66 to 23 million years ago). The Neogene and Quaternary are also periods within the Cenozoic.

Epoch: A subdivision of a period. The Paleocene, Eocene, and Oligocene are all epochs within the Paleogene period.

Paleogene: The geological period from approximately 66 to 23 million years ago, containing the Paleocene, Eocene, and Oligocene epochs. Characterized by the radiation and diversification of modern mammals after the dinosaur extinction.

Paleocene: The first and oldest epoch of the Paleogene period, from approximately 66 to 56 million years ago. The immediate aftermath of the mass extinction, when early generalist mammals began to diversify.

Paleolithic: Not a geological term. A cultural/archaeological term for the period of human prehistory marked by stone tool use, roughly 2.5 million to 10,000 years ago. This is what the popular 'Paleo diet' references.

Pleistocene: The epoch within the Quaternary period (approximately 2.6 million to 11,700 years ago) during which Homo sapiens evolved and lived. The most directly relevant geological epoch for human dietary evolution.

So: Paleogene is the period. Paleocene is one epoch inside it. And neither one is the same as Paleolithic, which is where the 'Paleo diet' name actually comes from.

This article is for general informational purposes only and is not medical advice. Always consult a qualified healthcare professional before making changes to your diet or health routine.

Key Takeaways

  • Paleogene is a geological period (66 to 23 million years ago); Paleocene is the oldest epoch within that period (66 to 56 million years ago).
  • The Paleogene contains three epochs in order: Paleocene, Eocene, and Oligocene.
  • The popular Paleo diet is named for the Paleolithic, a cultural term for a much later period of human prehistory, not for the Paleogene or Paleocene.
  • Human dietary evolution was shaped most directly during the Pleistocene epoch of the Quaternary period, not the Paleogene.
  • Understanding deep evolutionary time gives the real-food argument its full weight: our bodies were shaped for whole foods over millions of years, not the last 200 of industrial processing.

Frequently Asked Questions

Is the Paleogene the same as the Paleocene?

No. The Paleogene is a geological period spanning roughly 66 to 23 million years ago. The Paleocene is the oldest of three epochs within the Paleogene period, covering approximately 66 to 56 million years ago. Every Paleocene moment is part of the Paleogene, but the Paleogene also includes the Eocene and Oligocene epochs.

What is the difference between the Paleogene, Neogene, and Quaternary?

All three are periods within the Cenozoic Era. The Paleogene (66 to 23 million years ago) is the oldest, marked by the radiation of mammals after the dinosaur extinction. The Neogene (23 to 2.6 million years ago) follows, characterized by grassland expansion and further mammal diversification. The Quaternary (2.6 million years ago to present) is the most recent, encompassing the Pleistocene and Holocene, and is when modern humans evolved.

Is the Paleo diet based on the Paleogene or Paleocene era?

Neither. The Paleo diet is named for the Paleolithic, which is an archaeological term for a period of human prehistory marked by stone tool use, running roughly from 2.5 million to 10,000 years ago. The Paleolithic falls within the Pleistocene epoch of the Quaternary period, tens of millions of years after the Paleogene and Paleocene.

What came after the Paleocene epoch?

The Eocene epoch followed the Paleocene, beginning approximately 56 million years ago. The Eocene was characterized by a warming climate, dense tropical forests, and rapid diversification of mammals, including early primates and ancestors of modern hoofed animals. After the Eocene came the Oligocene, the final epoch of the Paleogene period.

Sources

This article is for general informational purposes only and is not medical advice. Always consult a qualified healthcare professional before making changes to your diet or health routine.