Ammonoidea - Wikipedia
Their fossil shells usually take the form of planispirals, although some helically spiraled and nonspiraled forms (known as heteromorphs) have been found, primarily during the Cretaceous period.
What is an ammonite? - Natural History Museum
Ammonites' growing shells typically formed into a flat spiral, known as a planispiral, although a variety of shapes did evolve over time. Shells could be a loose spiral or tightly curled with whorls touching.
DISCOVERING FOSSILS | What is an ammonite?
Ammonites are perhaps the most widely known fossil, possessing the typically ribbed spiral-form shell as pictured above. These creatures lived in the seas between 240 - 65 million years ago, when they became extinct along with the dinosaurs.
The Intriguing World of Ammonite Fossils! - Rock Seeker
2023年4月17日 · Ammonite fossils are the preserved remains of ammonoids, which were marine creatures with a spiral shell that resembled a ram’s horn. These fossils are often found in sedimentary rocks, such as limestone and shale, and can provide valuable insights into the evolution and ecology of ancient marine life.
The Ammonites Ancient Cephalopods - Fossils Facts and …
Most ammonites have flat spiral shells, (planispiral). Some species had partial spirals, and then uncurled to a straight cone. Still others had a spiral section, then a straight section and then a curved hook so that the animal faced its spiral section.
Ammonite Fossils Unravel the Geological History of Ancient ...
2023年7月8日 · The name “ammonite” originates from the spiral shape of their shells, which resembled the horns of the Egyptian god Amun, often depicted as a ram with twisted horns. The name “ammonite” has since been used to describe this group of extinct cephalopods.
150 Million-Year-Old Fossil Of An Ammonite That Lost Its ...
2021年2月3日 · A study published recently in the Swiss Journal of Paleontology describes an extraordinary fossil - an ammonite from the Late Jurassic preserved outside its shell and showing traces of its ...