Lucas et al. argue that Paleocene palynomorphs have only been recorded
physically beneath dinosaur bone at two localities in the San Juan Basin.
This is correct; however, dinosaur bone has only been observed in
the Ojo Alamo in the three areas shown on
Figure 1, thus Paleocene pollen has been found beneath dinosaur bone in the
Ojo Alamo at two of the three areas where this formation is known to contain
dinosaur fossils. (The arguments of these authors criticizing the value of palynomorphs in determining the age of the Ojo Alamo and its contained dinosaur fossils at these two localities are addressed in detail in
Fassett (2009) and are briefly summarized below.)
San Juan River Locality
A large (length 1310 mm, maximum proximal width 370 mm, maximum distal width 330 mm) pristine hadrosaur femur was found embedded in conglomeratic sandstone of the Ojo Alamo Sandstone, 15 m above its base, at the San Juan River locality (Fassett and Lucas, 2000). Subsequent to the collection of this bone, samples collected from a coaly layer 3.5 m below it yielded Paleocene index palynomorphs. Lucas et al. concede that these palynomorphs confirm the Paleocene age of the Ojo Alamo at this locality, but argue that this bone is reworked. It is particularly ironic that Lucas now makes that claim because in a paper coauthored with me (Fassett and Lucas, 2000) he described this femur in detail and stated that (p. 228): "The bone (Figs. 4B, 5) has a pristine outer surface with no abrasions or scratches, and all of its delicate features are intact; there is thus no evidence of transport of this bone." At the time we coauthored this paper, Lucas (pers.
commun., 2000) assured me that no vertebrate paleontologist examining this specimen would conclude that it had been reworked. In a second paper published that same year (Fassett, et al., 2000) titled: "Compelling new evidence for Paleocene dinosaurs in the Ojo Alamo Sandstone, San Juan Basin, New Mexico and Colorado, USA" Lucas's name again appeared as a coauthor. Rather than reiterate the detailed discussion of this bone found in
Fassett (2009), or
Fassett and Lucas (2000) readers can make their own observations and draw their own conclusions from the photographs of this bone in those publications or by examining the specimen itself (on display at the University of New Mexico Geology Department in Albuquerque). Lucas has obviously now changed his mind about this bone, however he and his coauthors offered no evidence to support a revised opinion that this bone was reworked.
Lucas et al. (2009) further stated that "the well preserved nature" of the San Juan River bone "does not preclude reworking" and they go on to compare this fossil with Paleozoic brachiopod shells with preserved shell morphology that have been found embedded in limestone pebbles in the Ojo Alamo Sandstone. Indeed, such fossiliferous limestone pebbles and cobbles are commonly found today in recent river-terrace deposits along the San Juan and Animas rivers in the northern part of the San Juan Basin, but to date, no meter-long dinosaur fossils have been found therein. To compare the reworking of fossils weighing a few tens of grams embedded in limestone pebbles with a pristine hadrosaur femur weighing upwards of 100 kg seems hardly apt, to say the least.
Barrel Spring Locality
The Barrel Spring locality is in the eastern part of the Ojo Alamo Sandstone type area of
Figure 1. At that locality
Fassett (2009) reported that a sample collected from a carbonaceous mudstone less than1 m below the base of the Ojo Alamo Sandstone had yielded a Paleocene palynomorph assemblage. Dinosaur bone is abundant in the Ojo Alamo Sandstone in this area.
Lucas et al. (2009) and
Sullivan et al. (2005) discount the value of this Paleocene palynomorph assemblage because they stated that they were unable to find identifiable palynomorphs in their samples that they claim were collected from this same stratigraphic level. However, these authors do not document their sample collection sites in their publications, thus it is impossible to fully evaluate those claims. Moreover, as stated in detail in
Fassett (2009), samples containing identifiable palynomorphs in K-T strata in the San Juan Basin have been notoriously difficult to find, and the 244 palynomorph species identified from Cretaceous and Paleocene (K-T) strata in the San Juan Basin and listed in Appendix 1 of
Fassett (2009) are the product of decades of sample collection. Thus, the Paleocene palynomorph assemblage from the Barrel Spring locality remains unchallenged. A true challenge to the palynologic data presented in
Fassett (2009) showing that the Ojo Alamo Sandstone is Paleocene in age would consist of the finding of Cretaceous palynomorph assemblages anywhere in the Ojo Alamo Sandstone. To reiterate, all the palynomorph assemblages from rock samples from the Ojo Alamo Sandstone were found to be Paleocene in age.
In Fassett (2009) the palynology of the Ojo Alamo Sandstone is discussed in detail based on sample collections from three other localities in the basin where palynomorph-productive samples were found; at all of those localities, palynomorph assemblages throughout the Ojo Alamo were found to be Paleocene in age.
Lucas et al. (2009) fail to address the importance of these data nor do they attempt to challenge them. As these authors correctly point out, palynology is the keystone to the
Fassett (2009) paper as evidenced by a 67-page appendix containing 25 tables listing palynomorph species from K-T boundary strata throughout the San Juan Basin. It is suggested that the challenge to the Paleocene palynologic age of the Ojo Alamo Sandstone in the San Juan Basin by
Lucas et al. (2009) is trivial when compared to the massive palynologic data set presented in