Post by Infinity Blade on Jan 18, 2020 3:21:38 GMT 5
It's generally accepted that all non-neornithine dinosaurs perished 66 Ma at the end of the Cretaceous period. But over the years, it looks like some people claimed to have found evidence for non-neornithine dinosaurs surviving into the Paleocene epoch of the Cenozoic. The purpose of this thread is to review and discuss the evidence put forward for these claims.
1.) In 2001, James Fassett et al. have suggested potential evidence for Paleocene non-avian dinosaurs in the form of a hadrosaurid femur found in Paleocene-aged Ojo Alamo Sandstone (Fassett et al., 2001). There have been other papers authored by him regarding this, but of course, it has been disputed (e.g. Lucas et al., 2009). Interestingly, there is also a 2011 paper where Fassett reports directly dating a femur fragment of Alamosaurus sanjuanensis to 64.8 Ma (Fassett et al., 2011). Are there any published responses to this particular paper? EDIT: yes, there have been two replies (Renne & Goodwin, 2012; Ludwig, 2012). As you might imagine, Fassett et al. replied back to these comments (link). Make of that what you will.
2.) The Wikipedia page for Paleocene dinosaurs also claims that there are purported Paleocene non-avian theropod remains from Takatika Grit, Chatham Islands. From looking at the source cited for these, I am not entirely sure where this is claimed in the source. I think it may be this portion? And if it is claiming evidence for Paleocene non-avian theropods, how have other scientists responded to this?
"Vertebrate remains in the marine sediments include a theropod centrum (Fig. 3 A–B), the proximal pedal phalanx II-1 or III-1 of a theropod (Fig. 3 F–G), as well as the probable theropod proximal head of a tibia (Fig. 3 D–E) (all three elements from NPB). In slightly younger sediments, Greensand Package II, a theropod manual phalanx (Fig. 3 K–O) and manual ungual (Fig. 3 H–J) have been recovered. These latter two bones were collected stratigraphically above the major Cretaceous faunal assemblage in greensands together with rich dinoflagellate assemblages clearly of early-to mid-Teurian (Danian) age. Interestingly, these bones exhibit no signs of reworking. The latest Cretaceous theropod fragments were evidently transported into the shallow marine environment from adjacent terrestrial habitats and display differential preservation and wear. The bones are associated with authigenic phosphorite nodules of pebble to boulder size and some of the nodules actually contain bone."
sci-hub.tw/10.1016/j.palaeo.2005.07.017
3.) Perchance the most convincing evidence of non-neornithine dinosaurs surviving past the K-Pg boundary (granted, this is not saying much) is the assignment of Qinornis paleocenica, a Paleocene-aged bird (61 Ma), as a non-neornithine bird (Mayr, 2007). This was justified by the presence of incompletely fused metatarsals, which are either found in adult ornithurines more basal than neornithines or in immature neornithines. This same paper also considers it unlikely that the specimen is merely a juvenile neornithine "...because the distal tarsalia are completely fused with the metatarsalia and the articular ends of the tarsometatarsus do not exhibit the blurred surfaces characteristic for the growing bones of juvenile neornithine birds.". Apparently, this has not been a sufficiently convincing argument (apparently Longrich et al., 2011 dispute this, but I can find no mention of Qinornis in their paper).
As I have alluded to above, refutations (or defenses, if you think you have legitimate defenses for any of these) of any of the supposed evidence Paleocene dinosaurs outlined here are welcome here. Members are free to discuss.
1.) In 2001, James Fassett et al. have suggested potential evidence for Paleocene non-avian dinosaurs in the form of a hadrosaurid femur found in Paleocene-aged Ojo Alamo Sandstone (Fassett et al., 2001). There have been other papers authored by him regarding this, but of course, it has been disputed (e.g. Lucas et al., 2009). Interestingly, there is also a 2011 paper where Fassett reports directly dating a femur fragment of Alamosaurus sanjuanensis to 64.8 Ma (Fassett et al., 2011). Are there any published responses to this particular paper? EDIT: yes, there have been two replies (Renne & Goodwin, 2012; Ludwig, 2012). As you might imagine, Fassett et al. replied back to these comments (link). Make of that what you will.
2.) The Wikipedia page for Paleocene dinosaurs also claims that there are purported Paleocene non-avian theropod remains from Takatika Grit, Chatham Islands. From looking at the source cited for these, I am not entirely sure where this is claimed in the source. I think it may be this portion? And if it is claiming evidence for Paleocene non-avian theropods, how have other scientists responded to this?
"Vertebrate remains in the marine sediments include a theropod centrum (Fig. 3 A–B), the proximal pedal phalanx II-1 or III-1 of a theropod (Fig. 3 F–G), as well as the probable theropod proximal head of a tibia (Fig. 3 D–E) (all three elements from NPB). In slightly younger sediments, Greensand Package II, a theropod manual phalanx (Fig. 3 K–O) and manual ungual (Fig. 3 H–J) have been recovered. These latter two bones were collected stratigraphically above the major Cretaceous faunal assemblage in greensands together with rich dinoflagellate assemblages clearly of early-to mid-Teurian (Danian) age. Interestingly, these bones exhibit no signs of reworking. The latest Cretaceous theropod fragments were evidently transported into the shallow marine environment from adjacent terrestrial habitats and display differential preservation and wear. The bones are associated with authigenic phosphorite nodules of pebble to boulder size and some of the nodules actually contain bone."
sci-hub.tw/10.1016/j.palaeo.2005.07.017
3.) Perchance the most convincing evidence of non-neornithine dinosaurs surviving past the K-Pg boundary (granted, this is not saying much) is the assignment of Qinornis paleocenica, a Paleocene-aged bird (61 Ma), as a non-neornithine bird (Mayr, 2007). This was justified by the presence of incompletely fused metatarsals, which are either found in adult ornithurines more basal than neornithines or in immature neornithines. This same paper also considers it unlikely that the specimen is merely a juvenile neornithine "...because the distal tarsalia are completely fused with the metatarsalia and the articular ends of the tarsometatarsus do not exhibit the blurred surfaces characteristic for the growing bones of juvenile neornithine birds.". Apparently, this has not been a sufficiently convincing argument (apparently Longrich et al., 2011 dispute this, but I can find no mention of Qinornis in their paper).
As I have alluded to above, refutations (or defenses, if you think you have legitimate defenses for any of these) of any of the supposed evidence Paleocene dinosaurs outlined here are welcome here. Members are free to discuss.
