Paleocene dinosaurs

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The term Paleocene dinosaurs describes families or genera of non-avian dinosaurs that may have survived the Cretaceous–Paleogene extinction event, which occurred 66 million years ago. Although almost all evidence indicated 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, although at least one non-neornithine ornithuran is known from the Paleocene, and it's known as Qinornis.

Implications

Several researchers have stated that some non-avian dinosaurs survived into the Paleocene and therefore the extinction of non-avian dinosaurs was gradual.[1] 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.[2] 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.[3] Direct dating of bone has also been used to present an age of 64.8 ± 0.9 million years for one specimen.[4] 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.[5] 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.

The non-neornithine ornithuran Qinornis, is a peculiar fossil from China, that is dated as having 61 million years old, five million years after the K-Pg extinction event. This seems to be the very first indication that non-neornithine dinosaurs have survived for some millions of years after the extinction.

List of purported Paleogene dinosaur fossils

Footnotes

  1. ^ National Geographic
  2. ^ Sloan, R. E., Rigby, K,. Van Valen, L. M., Gabriel, Diane (1986). "Gradual dinosaur extinction and simultaneous ungulate radiation in the Hell Creek formation". Science. 232 (4750): 629–633. Bibcode:1986Sci...232..629S. doi:10.1126/science.232.4750.629. PMID 17781415. Retrieved 2007-05-18.
  3. ^ a b Fassett, JE, Lucas, SG, Zielinski, RA, and Budahn, JR (2001). "Compelling new evidence for Paleocene dinosaurs in the Ojo Alamo Sandstone, San Juan Basin, New Mexico and Colorado, USA" (PDF). Catastrophic events and mass extinctions, Lunar and Planetary Contribution. 1053: 45–46. Retrieved 2007-05-18.
  4. ^ Fassett, JE, Heaman, LM, and Simonetti, A (2010). "Direct U-Pb dating of Cretaceous and Paleocene dinosaur bones, San Juan Basin, New Mexico". Geology. 39 (2): 159–162. Bibcode:2011Geo....39..159F. doi:10.1130/G31466.1.
  5. ^ Sullivan, RM (2003). "No Paleocene dinosaurs in the San Juan Basin, New Mexico". Geological Society of America Abstracts with Programs. 35 (5): 15. Retrieved 2007-07-02.
  6. ^ Stilwell, J.D.; Consoli, C.P.; Sutherland, R.; Salisbury, S.; Rich, T.H.; Vickers-Rich, P.A.; Currie, P.J.; Wilson, G.J. (2006). "Dinosaur sanctuary on the Chatham Islands, Southwest Pacific: First record of theropods from the K–T boundary Takatika Grit". Palaeogeography, Palaeoclimatology, Palaeoecology. 230 (4): 243–250. doi:10.1016/j.palaeo.2005.07.017.
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