| Titre | Nautilus and Allonautilus in the Nanaimo Group, and in the modern oceans |
| |
| Auteur | Ward, P; Haggart, J; Ross, R; Trask, P; Beard, G |
| Source | 12th British Columbia Paleontological Symposium, 2018, Courtenay, abstracts; 2018 p. 10-11 |
| Image |  |
| Année | 2018 |
| Séries alt. | Ressources naturelles Canada, Contribution externe 20180183 |
| Éditeur | British Columbia Paleontological Alliance |
| Document | livre |
| Lang. | anglais |
| Media | papier; numérique |
| Formats | pdf |
| Sujets | Holocène; Néogène; Miocène; Paléogène; Eocene; organismes marins; fossiles; paléontologie systématique; taxonomie; paléotempératures; milieux marins; etudes isotopiques; isotopes; azote; morphologie des
fossiles; Groupe de Nanaimo ; Biologie; Animal; paléontologie; stratigraphie; géochimie; Nature et environnement; Phanérozoïque; Cénozoïque; Quaternaire; Tertiaire; Mésozoïque; Crétacé |
| Illustrations | dessins paléontologiques |
| Programme | Division CGC Pacifique |
| Diffusé | 2018 08 01 |
| Résumé | (disponible en anglais seulement)
There is a long held fallacy that the nautiloid cephalopods passed through the K/Pg transition without major effect. This is far from true. The vast majority of
taxa and individuals of the Late Cretaceous are ornamented. Not a single ornamented nautilid survived the transition, nor was there a new ornamented species of any genus until Allonautilus perforatus.
What we now know is that there are seven
living nautiloid species in two genera: Nautilus pompilius, N. macromphalus, N. stenomphalus, N. belauensis, and the three new species (still in definition), from Samoa, Fiji, and Vanuatu (Ward et al., in prep.) A second fallacy about Nautilus (for
most of the 20th Century) was that it had no fossil record. The definition of N. praepompilius Shimansky changed that: the taxon ranges back at least to the Turonian of California, and possibly the Cenomanian of Australia. Here we show three new
species of Nautilus, all from the Nanaimo Group but oddly absent from California. All are ribbed.
There has also been a discovery of what might be the only known fossil of Allonautilus Ward and Saunders 1997, also from the Nanaimo Group.
The
exquisite shell preservation of many Nanaimo nautilids has allowed paleotemperature analyses, and, for the first time, accurate Nitrogen isotope analyses. These data demonstrate that Nautilus and all other known Cretaceous through Paleogene nautilids
were shallow water carnivores. Only Aturia lived in cooler water in the Cenozoic. Aturia, common from the Eocene until its late Miocene extinction, also had jaws with piranha-like teeth, and attained a maximum shell size at least twice that of the
largest known Nautilus individual (~250mm).
Presumably, Nautilus and Allonautilus took the dive to a new, deep-water habitat to escape shell-breaking predators in the Miocene, and still live today on cool fore-reef slopes in environments that
rarely fossilize. Nautiluses now show Nitrogen isotope values of 7-8 in captivity, where they are fed frequently. In nature, however, their values are typically less than 10 to 12, which are comparable to giant squids and grizzly bears - and from
animals that are starving.
Our new video evidence indicates a major extinction of the remaining and very rare nautiluses across the Pacific is taking place due to the removal of deep-water fish by humans, an event that has produced an explosion of
deep-water octopus, the major current predator of Nautilus as evidenced by shell borings, elliptical in shape. Can such borings be found in the hundreds of specimens of Nanaimo nautilids in current collections? |
| Sommaire | (Résumé en langage clair et simple, non publié)
Ceci est un résumé d'une conférence qui sera présentée lors d'une réunion scientifique consacrée à la paléontologie de la Colombie-Britannique.
Dans leur exposé, les auteurs décriront de nouvelles espèces de mollusques de céphalopodes marins, Nautilus et Allonautilus, provenant des roches sédimentaires du Crétacé du sud-est de l'île de Vancouver, âgées d'environ 75 à 80 millions d'années.
Les espèces ont des liens avec les descendants modernes qui vivent encore dans le sud-ouest de l'océan Pacifique. Les auteurs présenteront également des données utiles pour interpréter l'écologie de ces anciens mollusques de céphalopodes. |
| GEOSCAN ID | 311140 |
|
|