| mhorn | Дата: Wednesday, 11.11.2009, 00:50 | Сообщение # 1 |
Admin
Group: Администраторы
Posts: 1060
Reputation: 0
Status: Offline
| Lewy Z. (2009) The possible trophic control on the construction and function of the aulacocerid and belemnoid guard and phragmocone // Revue de Paléobiologie. V.28. no.1. P.131-137.
pdf: http://www.ville-ge.ch/mhng/paleo/paleo-pdf/28-1/pal-28-1-08.pdf
The aulacocerid and belemnoid rocket-like guard and phragmocone persisted more than 300 million years throughout the late Paleozoic and the whole Mesozoic. These coleoids were in neutral buoyancy (horizontal orientation) when the phragmocone chambers were empty. However, the long fossil record of this posterior buoy-ballast combined feature evidences that cameral liquid was exchanged. It is suggested here that liquid introduced into the posterior chambers of the phragmocone balanced a temporary rise in weight in the frontal part of the body when prey on its calcareous skeletal fragments accumulated in the capacious crop just behind the buccal mass [this suggestion contradicts with data on modern coleoids]. The change from the aulacocerid telum to the belemnoid guard of a higher specific gravity may reflect an increase in predation on cochleate prey, whereas the degeneration of the ballast-forming guard in latest Cretaceous times (e.g., Groenlandibelus [these fossils are not connected directly with belemnitids]) probably attest to a diet change to prey with much less calcareous parts. This latter change coincides with the gradual disappearance of ammonoids, which might have provided the main food source of most aulacocerids and belemnoids. These potential prey-predator relationships are suggested by co-occurring belemnoids and ammonites with aptychi (opercula) while in the absence of belemnites no aptychi were found with these ammonite genera (e.g., Baculites) [this idea strictly contradicts with true distribution of belemnites and aptychi during the Jurassic and Cretaceous and cannot be accepted]. The ballast providing rostrum was constructed in various shapes to fulfill several significant defensive and offensive functions.
Middle Jurassic - Lower Cretaceous ammonites & aptychi
|
| |
| |
