Ammonites


 * Did ammonites really start by living in the deep and then progressively start living in shallower water? **


 * Suture patterns and lifestyle **: The diversity of this suture geometry has inspired paleontologists to investigate its function. In one study, paleontologists (Daniel et al. 1997) used modeling to determine if there was a relationship between the pattern of lobes and saddles and buoyancy and the ability to withstand pressure. They found that simple sutures, like those in nautiloids and early ammonoids, can withstand great pressure but have poor buoyancy control. They interpret that these animals lived at depth and were not fast moving. In contrast, complex sutures like those in ammonites of the Cretaceous did not withstand pressure well, but allowed for very effective buoyancy control. They infer that this reflects a lifestyle at shallower depths. Base d on this evidence, it appears that many ammonoid lineages evolved over millions of years, beginning in deep water habitats and evolving to inhabit relatively shallow ones.



 All ammonoids show some type of suture pattern. The term "suture pattern" refers to the featured line that makes contact with the septa and the interior of the aragonitic shell. Ammonoid suture patterns show more complexity in comparison to the nautiloids whose sutures are comparatively simple.



For most living organisms, if the environment changes drastically or even slightly, there is going to be adverse effects in how those organisms interact within their habitat. The ammonoid, for the reasons noted, underwent these trials of change and made remarkable comebacks each time there was near abolishment up until the Cretaceous-Tertiary boundary. At this time the ammonoid finally disappears from the fossil record. However there was the continuance of its predecessor and competitor, the nautiloid. The survival of the nautiloid and disappearance of the ammonite has long puzzled scientists and left many unanswered questions as to why the ammonite could not persevere.

(Or do the fossils show different species living at different depths at the same time and the near extinctions were just boundaries between different depths.)