The term Paleocene dinosaurs describes families or genera of non-avian dinosaurs that may have survived the Cretaceous–Paleogene extinction event 66 million years ago. Although almost all evidence indicates that birds are the only dinosaur group that survived past the K–Pg boundary, there is some scattered evidence that some non-avian dinosaurs lived for a short period of time during the Paleocene epoch. The evidence for Paleocene non-avian dinosaurs is rare and remains controversial.
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Implications
Several researchers have stated that some non-avian dinosaurs survived into the Paleocene and therefore the extinction of non-avian dinosaurs was gradual. Their arguments were based on the finding of dinosaur remains in the Hell Creek Formation up to 1.3 m (4.3 ft) above (40,000 years later than) the K–Pg boundary. Similar reports have come from other parts of the world, including China.
There is possible evidence of a dead clade walking: in 2001, evidence was presented that pollen samples recovered near a fossilized hadrosaur femur recovered in the Ojo Alamo Sandstone at the San Juan River indicate that the animal lived during the Paleogene period, approximately 64.5 million years ago. Direct dating of bone has also been used to present an age of 64.8 ± 0.9 million years for one specimen. Many scientists, however, dismiss the "Paleocene non-avian dinosaurs" as reworked, that is, washed out of their original locations and then reburied in much later sediments. A compelling argument against reworking would be a complete or at least associated skeleton (e.g. more than one bone from the same individual) found above the K–Pg boundary. As yet no such finds have been reported.