Dinosaurs that did not die: Evidence for Paleocene dinosaurs in the Ojo Alamo Sandstone, San Juan Basin, New Mexico

Abstract

Palynologic and paleomagnetic data confirm a Paleocene age for the Ojo Alamo Sandstone (and its contained dinosaurs) throughout the San Juan Basin of New Mexico. The recently reported discovery of 34 skeletal elements from a single hadrosaur in the Ojo Alamo provides unequivocal evidence that these bones were not reworked from underlying Cretaceous strata. Geochemical studies of samples from several single-dinosaur-bone specimens from the Paleocene Ojo Alamo Sandstone and the underlying Late Cretaceous (Campanian) Kirtland Formation show that mineralized bones from these two rock units contain distinctly different abundances of uranium and rare-earth elements and demonstrate that Cretaceous and Paleocene bones were mineralized at different times when mineralizing fluids had distinctly different chemical compositions. These findings indicate that the dinosaur bone from the Paleocene Ojo Alamo is indigenous and not reworked.These data show that a relatively diverse assemblage of dinosaurs survived the end-Cretaceous asteroid-impact extinction event of 65.5 Ma. The San Juan Basin's Paleocene dinosaur fauna is herein named the Alamoan fauna. Magnetic-polarity chronology shows that these survivors lived for about one million years into the Paleocene and then became extinct around 64.5 Ma. We suggest that a plausible survival mechanism for this Lazarus fauna may have been the large numbers of buried dinosaur eggs, laid just before the asteroid impact occurred. These buried eggs would have provided a safe haven for developing dinosaur embryos for the first one to two years after the impact, thereby making it possible for them to survive the worst of the impact's early devastation.

Timescales and mechanisms of REE and Hf uptake in fossil bones

“…As a consequence, results proposing that fossils were not reworked may be ambiguous. For example, in part based on their REE patterns, dinosaur bones excavated from Early Tertiary sediments have been interpreted to have mineralised in place and thus to represent Tertiary dinosaurs (Fassett et al, 2002;Fassett, 2009). This interpretation is not conclusive if these bones behaved as open systems with respect to REE.…”

“…First, trace elements, and REE in particular, are widely used as proxies for palaeoenvironment (Metzger et al, 2004;Patrick et al, 2004;Martin et al, 2005;Anderson et al, 2007), taphonomy and provenance (e.g. Trueman and Benton, 1997;Trueman, 1999;Staron et al, 2001;Fassett et al, 2002;Patrick et al, 2002Patrick et al, , 2007Trueman and Tuross, 2002;Trueman et al, 2004Trueman et al, , 2005Trueman et al, , 2006Trueman et al, , 2008aMacFadden et al, 2007;Suarez et al, 2007Suarez et al, , 2010Fassett, 2009;Grandstaff and Terry, 2009), and palaeoceanography (Staudigel et al, 1985;Elderfield and Pagett, 1986;Wright et al, 1987;Martin and Haley, 2000;Martin and Scher, 2004). Secondly, approaches to date fossil bones include U-Pb chronometry (e.g.…”

Roveacrinids (Crinoidea, Echinodermata) survived the Cretaceous-Paleogene (K-Pg) extinction event

“…The qualifi cation "dead clade walking" is given to taxa that survive one of the big fi ve mass extinctions but immediately thereafter become extinct without descendants (though this point might be challenged in the future). Recent spectacular, though not uncontroversial, examples of taxa surviving the Cretaceous-Paleogene (K/Pg) extinction without recovery include: Early Paleocene dinosaurs from the San Juan Basin in New Mexico and Colorado, United States (Fassett et al, 2002;Fassett, 2009), and an earliest Paleocene ammonite from Denmark and adjacent areas (Machalski, 2005;Machalski and Heinberg, 2005). The present fi nd allows us to add roveacrinids to the list.…”

Early Paleocene Magnetostratigraphy and Revised Biostratigraphy of the Ojo Alamo Sandstone and Lower Nacimiento Formation, San Juan Basin, New Mexico, USA

“…The lack of detailed geochronology for the Ojo Alamo Sandstone has led to uncertainty about the age and duration of the Ojo Alamo Sandstone and Naashoibito Member with some authors arguing that both units are Paleocene (Fassett, 2009), that the Naashoibito Member is early Maastrichtian and the Ojo Alamo Sandstone is early Paleocene (Sullivan and Lucas, 2003;Sullivan et al, 2005), or that the Naashoibito is late Maastrichtian and the Ojo Alamo Sandstone is earliest Paleocene (Williamson and Weil, 2008a;Williamson et al, 2008;Peppe et al, 2013;. The lack of an age model for the Ojo Alamo Sandstone and confusion about stratigraphic terminology has also lead some researchers to argue for the occurrence of early Paleocene dinosaurs from the San Juan Basin (e.g., Fassett et al, 2002Fassett et al, , 2011Fassett, 2009).…”