Although it didn't boast as wide an array of prehistoric mammals as the epochs that succeeded it, the Paleocene epoch was notable for immediately following the demise of the dinosaurs--which opened up vast ecological niches for the mammals, birds, reptiles and marine animals that survived the K/T Extinction. The Paleocene was the first epoch of the Paleogene period (65-23 million years ago), the other two being the Eocene (56-34 million years ago) and Oligocene (34-23 million years ago); all these periods and epochs were themselves part of the Cenozoic Era (65 million years ago to the present).
Climate and geography. The first few hundred years of the Paleocene epoch witnessed the dark, frigid aftermath of the K/T Extinction, when an asteroid collision in the Yucatan peninsula raised enormous, worldwide clouds of dust that obscured the sun. By the end of the Paleocene, however, the global climate was nearly as warm and muggy as it had been during the preceding Cretaceous period. The northern supercontinent of Laurasia had yet to completely break apart into North America and Eurasia, but Gondwana in the south was already well on its way to separating into Africa, South America, Antarctica and Australia.
Terrestrial Life During the Paleocene Epoch
Mammals. Contrary to popular belief, mammals didn't suddenly appear on the planet after the dinosaurs had gone extinct; small, mouselike examples existed as far back as the Triassic period (at least one genus, Cimexomys, actually straddled the Cretaceous/Paleocene boundary). The mammals of the Paleocene epoch weren't much larger than their predecessors, and only barely hinted at their later forms: for example, the elephant ancestor Phosphatherium only weighed about 100 pounds, and Plesidadapis was an extremely early, extremely small primate. Frustratingly, most mammals of the Paleocene epoch are known only by their teeth.
Birds. If you were somehow transported back in time to the Paleocene epoch, you might be forgiven for thinking that birds, rather than mammals, were destined to inherit the earth. During the late Paleocene, the fearsome predator Gastornis (once known as Diatryma) terrorized the small mammals of Eurasia, while the very first "terror birds" began to evolve in South America.
Reptiles. Paleontologists still aren't sure why crocodiles managed to survive the K/T extinction, while their closely related dinosaur brethren bit the dust. In any case, prehistoric crocodiles continued to flourish during the Paleocene epoch, as did snakes--as evidenced by the truly enormous Titanoboa, which measured about 50 feet from head to tail and may have weighed more than a ton.
Marine Life During the Paleocene Epoch
Dinosaurs weren't the only reptiles that went extinct at the end of the Cretaceous period. Mosasaurs, the fierce, sleek marine predators, also disappeared from the world's oceans, along with the last remnants of the plesiosaurs and pliosaurs. Filling the niches vacated by these voracious predators were prehistoric sharks, which had existed for hundreds of millions of years but now had the room to evolve to truly impressive sizes. The teeth of Otodus, for example, are a common find in Paleocene and Eocene sediments.
Plant Life During the Paleocene Epoch
A huge number of plants, both terrestrial and aquatic, were destroyed in the K/T Extinction, victims of the enduring lack of sunlight (not only did these plants die, but so did the herbivorous animals that fed on the plants and the carnivorous animals that fed on the herbivorous animals). The Paleocene epoch witnessed the very first cacti and palm trees, as well as a resurgence of ferns, which were now unharassed by plant-munching dinosaurs. As before, much of the world was covered by thick, green jungles and forests, which thrived in the heat and humidity of the late Paleocene climate.
Next: the Eocene Epoch