Here and there I had heard rumors of dinosaur fossils found above the K/T boundary, and I even remember one children’s book hypothesizing about dinosaurs that could survive in the cold, “nuclear winter” conditions that would have followed the asteroid impact which devastated life on earth. The thought that most dinosaurs made it into the Paleocene is a romantic notion, especially because dinosaurs were the “ruling reptiles” for so long, but there doesn’t seem to be much of anything to back up the idea. Still, some paleontologists, especially James Fassett, would beg to differ, and he has a new paper out entitled (*deep breath*) “The documentation of in-place dinosaur fossils in the Paleocene Ojo Alamo Sandstone and Animas Formation in the San Juan Basin of New Mexico and Colorado mandates a paradigm shift: dinosaurs can no longer be thought of as absolute index fossils for end-Cretaceous strata in the Western Interior of North America” in the journal New Mexico Geology (the link is only for the sake of completeness; the paper isn’t there). John Wilkins of Evolving Thoughts was kind enough to reproduce the abstract for us;
Extensive geochronologic studies of the rocks adjacent to the Cretaceous-Tertiary (K-T) interface in the San Juan Basin have now provided compelling data attesting to the Paleocene age of the dinosaur-bearing Ojo Alamo Sandstone in New Mexico and the Animas Formation in Colorado. These data consist of radiometric age determinations for Cretaceous strata underlying the K-T interface and palynologic, paleomagnetic, and geochemical evidence attesting to the Paleocene age of the strata above the K-T interface. The identification of the paleomagnetic normal interval – C29n – in the dinosaur-bearing lower part of the Ojo Alamo Sandstone in the southern San Juan Basin at multiple localities allows for the precise dating of the last occurrence of Paleocene dinosaurs at the top of chron C29n at 64.432 Ma.
The conventional wisdom (entrenched dogma) among most geologists, and especially among vertebrate paleontologists has been, for more than 100 years, that all dinosaurs became extinct at the end of the Cretaceous. Thus, dinosaur bone found in place in a formation provided indisputable evidence that the formation was Cretaceous in age. Now, with the discovery of Paleocene dinosaurs, the paradigm of Cretaceous-only dinosaurs must shift. Let us hope that this paradigm-shift will be a smooth and placid lateral-slip along planar fault blocks rather than a grumbling, rumbling, herky-jerky sliding of jagged-edged, opposing sides past each other. Science must always be conservative and accept such paradigm shifts only on the basis of the most solid evidence, however, when the data do finally speak, the shift must be accepted by all of us who follow the data in the noble pursuit of finding out how the world was made.
The first part wasn’t so bad, but the 2nd half is awfully cranky; maybe because Fassett has been trying to prove the existence of Paleocene dinosaurs for some time. He claims that scientists must be conservative and work from evidence, but apparently is very upset that other scientists have not yet accepted his evidence, playing the “they’re all dogmatic fundamentalists” card that is reminiscent of arguments by ID advocates and those who deny birds evolved from dinosaurs. Indeed, creationists have latched on to Fassett’s papers as proof that paleontologists don’t know what they’re doing, and while I am in no way suggesting that Fassett is a creationist or sympathetic to them, creationists clearly enjoy any findings that would seem to discredit the evolutionary biologists. Likewise, it is unlikely that all dinosaurs made it into the Paleocene, so forcing this issue is unproductive; we can only work from what we’ve got, not what we wish to be true.
In any case, Fassett’s hypothesis deserves at least a look; it certainly would be dogmatic of me to say that no dinosaurs survived 1 million years into the Paleocene “because I said so”. First, though, we need to take a look at some of the other supposed “Paleocene dinosaurs,” as this is not the first time the issue has come up. In 1987, Rigby Jr., et al. published the paper “”Dinosaurs from the Paleocene Part of the Hell Creek Formation, McCone County, Montana,” and the abstract (I don’t have access to the paper itself) states;
Dinosaur remains have been recovered from six localities in the uppermost part of the Hell Creek Formation, McCone County, Montana, which on the basis of stratigraphic placement and contained fossil pollen can be shown to be of Paleocene age. This modifies the argument that an extraterrestrial impact event at the Cretaceous / Tertiary (K/T) boundary caused dinosaur extinction (L. W. Alvarez et al., 1984; Alvarez et al., 1980). The occurrence of dinosaurs in sediments younger than the Cretaceous/Tertiary boundary (Rigby, 1985; Rigby and Sloan, 1985; Sloan et al., 1986; and others) supports the argument that dinosaurs survived the impact event.
While I am no expert on the subject and could very well have missed some finds, most of the alleged fossils are bone fragments and teeth (teeth being especially durable), fossils that easily could be exhumed and reburied (=”reworked.” “Transport” means travelling some distance away from the original site and only sometimes is such material reworked) in Paleocene deposits (thus being buried with Paleocene-age pollen). To the best of my understanding, there are no Paleocene dinosaur tracks, no articulated Paleocene dinosaur skeletons (which means there was little disturbance/no reworking), no Paleocene dinosaur skulls, no Paleocene dinosaur nests, or anything that would absolutely rule out reworking in some form or another. One of the prominent locales at which this reworking occurs is the Hell Creek Formation of Montana, and the subject has already been dealt with at length in the literature. From the 1990 Lofgren, et al. paper “Reworking of Cretaceous dinosaurs into Paleocene channel, deposits, upper Hell Creek Formation, Montana“;
Dinosaur teeth from Paleocene channel fills have been interpreted as indicating dinosaur survival into the Paleocene. However, enormous potential for reworking exists because these records are restricted to large channel fills that are deeply incised into Cretaceous strata. Identification of reworked fossils is usually equivocal. This problem is illustrated by the Black Spring Coulee channel fill, a dinosaur-bearing Paleocene deposit in the upper Hell Creek Formation of eastern Montana. In this example, the reworked nature of well-preserved dinosaur bones is apparent only after detailed sedimentological and palynological analysis.
Because of the potential for reworking, dinosaur remains derived from Paleocene fluvial deposits should not be assigned a Paleocene age unless they (1) are found in floodplain deposits, (2) are articulated, (3) are in channels that do not incise Cretaceous strata, or (4) are demonstrably reworked from Paleocene deposits. To date, reports of “Paleocene” dinosaurs do not fulfill any of these criteria. Thus, the proposal that dinosaurs persisted into the Paleocene remains unsubstantiated.
[Although it is truncated, more details on Lofgren's analysis can be found here]
Likewise, Buck et al. reports similar findings regarding dinosaur bone and egg shell fragments in the paper “‘Tertiary Dinosaurs’ in the Nanxiong Basin, Southern China, Are Reworked from the Cretaceous.” The report concludes;
Reworking of Cretaceous fossils carried in debris and mudflows deposited during the Tertiary can account for the mixed Cretaceous and Tertiary fossils. On the basis of previous paleontological data and our sedimentological data, we conclude that controversy regarding the presence of dinosaur fossils in Tertiary rocks is the result of sedimentological processes not previously recognized.
Fassett’s dinosaurs, however, are from a different place. In a two page paper from the “Catastrophic Events Conference” called “COMPELLING NEW EVIDENCE FOR PALEOCENE DINOSAURS IN THE OJO ALAMO SANDSTONE, SAN JUAN BASIN, NEW MEXICO AND COLORADO, USA,” Fassett et al. arrive at the following conclusion about a hardosaur femur found in the Ojo Alamo Sandstone;
We suggest that this animal lived in Tertiary time and died near the place where this silicified femur was found. As the corpse decayed, river currents disarticulated the skeleton, dispersing the lighter elements, and leaving this large massive bone behind to be quickly buried and silicified.
According to the researchers, the bone was far too heavy to be transported any distance and hence it’s unlikely it was reworked, so by the very virtue of its location it must have belonged to the Paleocene age. On top of that, pollen associated with the fossil only existed in the Paleocene and rare earth element (REE) analysis is cited as upholding the Paleocene distinction of the fossil. These claims have not gone without criticism, however. In a 2003 GSA presentation titled “NO PALEOCENE DINOSAURS IN THE SAN JUAN BASIN, NEW MEXICO,” Robert Sullivan determined that the pollen associated with some lignite found near the same level as the dinosaur fossils contained pollen that came from the latest Cretaceous (and a few from the K/T boundary), with no Paleocene pollen in sight. With this finding, the status of the hadrosaur fossil being genuine became even more dubious. Furthermore, David Fatovsky and Peter Sheehan responded directly to Fassett two years ago in an issue of GSA Today;
Fassett is wrong: Fassett cites two instances of pollen-dated dinosaur material, as well as magnetostratigraphic evidence. The first instance, an isolated femur, is likely reworked. In the second, re-analysis of pollen from the same locality indicates a Maastrichtian age (Sullivan et al., 2003). This is concordant with the recovery, in the same deposits, of Maastrichtian mammalian index taxa (Weil and Williamson, 2000).
With the biostratigraphy unresolved, the assignment of normal and reversed magnetic polarity zones in the SJB to global magnetochrons remains tenuous. The issue is further complicated by the likelihood of post-Paleocene remagnetization (Butler, 1985). We thus cannot rule out the possibility that the stratigraphy proposed by Fassett is flawed.
Fassett is right: Consider an analogy by paleontologist Peter Dodson (1993, personal commun.): we might see a Model T on the road, but we would never conclude that the car was part of a modern automotive (metaphorical) ecosystem. Even if a few dinosaurs survived a million years past the K-T boundary, dinosaurs were casualties of an extinction that, the best evidence suggests, was geologically instantaneous.
As Sheehan and Fatovsky rightly point out, even if Fassett’s bone was not reworked and belonged to a genuine Paleocene dinosaur, it does not prove that all dinosaurs jumped the boundary or that the K/T impact didn’t kill the dinosaurs. If Fassett’s analysis is accurate, then the last dinosaurs seem to have been remnants that died in the instant after their relatives; in the perspective of deep time, such dinosaurs would have died a split second after those killed because of the K/T impact. How likely is it that any dinosaurs survived the impact, though? If dinosaurs were to persist into the Paleocene, then there has to be a reason they survived and others did not. Fassett has some rather odd thoughts on this subject. Quote a 2001 GSA paper by Fassett;
It is suggested that these “Lazarus” dinosaurs may have survived the short period of maximum devastation, immediately following the impact, as eggs laid shortly before the impact occurred. Even though all mature dinosaurs were probably killed by the impact and the ensuing period of global darkness, their recently laid eggs would have provided a survival sanctuary for some of the developing dinosaur embryos for from one to two years. The San Juan Basin’s Paleocene dinosaur fauna is named the Alamoan fauna for the Ojo Alamo Sandstone, the formation in which these dinosaur fossils have been found.
Fasset even extends his hypothesis to state that frequent volcanic activity in North America prior to the end-Creataceous impact even selected dinosaurs who could survive ash-falls and other events associated withe eruptions. In a GSA presentation, Fassett argued;
Assuming even a modest compaction ratio of 10:1 for fresh-volcanic-ash/devitrified clay it is clear that these ash falls were meters thick – as much as 5.5 m for the thickest ash observed in these rocks! If we assume that the 7 dated ashes represent one-tenth of the eruptions that occurred during the 2.72 m.y., seventy such eruptions could have occurred during that time interval resulting in a frequency of one of these devastating events every forty-thousand years or so! These events, and their inevitable evolutionary consequences, must clearly have prepared the dinosaurs for the much more devastating end-Cretaceous event allowing some of them to live on into the Paleocene.
Granted, I have not read the actual papers, but this doesn’t make much sense to me. Dinosaur eggs that somehow were preserved hatched out into a world devastated (essentially deep-fried, if you will) by a meteor impact and persisted for another million years before vanishing for some undisclosed reason. Given what we have been learning about dinosaurs and the way they cared for their young, it is highly unlikely this scenario would have panned out; the eggs would need care and the young would likely need some amount of assistance as well, and there would be no adults (as per Fassett’s hypothesis) to do it. I find it equally unlikely that volcanic eruptions every 40,000 years ago created “eruption-resistant dinosaurs” through natural selection, so the mechanism by which Paleocene dinosaurs would have persisted is still unknown.
As I stated before, however, I have not yet seen the new paper and I am indeed very interested in it. I am skeptical (and there’s no reason why I should not be), but if Fassett’s find is as significant as he suggests then it is certainly something of note and requires more attention. Still, I am a little put-off by the title and abstract of the new paper; the author comes off as self-righteous and as looking for a smooth acceptance of his own ideas rather than argument. Right or wrong, the paper will not pull the rug out from underneath paleontology, but rather add to our understanding of how whole groups of animals go extinct, be it with a bang or a whimper.