Ammonites - British Geological Survey
Ammonites were marine animals belonging to the phylum Mollusca and the class Cephalopoda. They had a coiled external shell similar to that of the modern nautilus. In other living cephalopods, e.g. octopus, squid and cuttlefish, the shells are small and internal, or absent.
Ammonoidea - Wikipedia
Ammonites are excellent index fossils, and linking the rock layer in which a particular species or genus is found to specific geologic time periods is often possible. Their fossil shells usually take the form of planispirals, although some helically spiraled and nonspiraled forms (known as heteromorphs) have been found.
List of ammonite genera - Wikipedia
The list includes genera that are commonly accepted as valid, as well as those that may be invalid or doubtful (nomina dubia), or were not formally published (nomina nuda), as well as junior synonyms of more established names, and genera that are no longer considered ammonites.
Ammonite Fossils Unravel the Geological History of Ancient …
2023年7月8日 · Ammonites belong to the subclass Ammonoidea within the class Cephalopoda, which also includes living cephalopods like squid, octopuses, and nautiluses. Let’s explore the key aspects of their evolution and classification.
Ammonites: Anatomy, Classification & Time Period - Fossilicious
Ammonites are classified by the shape, structure, and ornamentation of their shells. The suture patterns along with the positioning of the siphuncle are also considered in classification. The suture patterns mark where the septa joins the outer shell or phragmocone.
The Intriguing World of Ammonite Fossils! - Rock Seeker
2023年4月17日 · Within each order, there are many different types of ammonite fossils. Some of the most well-known types include: Goniatites – These are the oldest type of ammonite fossils, dating back to the Devonian period. They are typically small and have a simple, coiled shell.
Ammonites, facts and photos - National Geographic
Based on the fossil record, ammonites came in a wide range of sizes and shapes, from smaller than an inch to as large as nine feet wide. Some ammonites had long, straight shells, while others...
An Introduction to Ammonites – UK Fossil Collecting
2013年6月13日 · Ammonites (Ammonitida) were shelled cephalopod molluscs that lived throughout the world’s oceans during the Mesozoic (Triassic, Jurassic and Cretaceous periods) and they were an extremely successful order, as evidenced by the frequency with which their remains are found.
2.3 Ammonoidea - Digital Atlas of Ancient Life
Ammonoidea, or ammonoids, constitute one of the most important clades of extinct invertebrate animals. Their lovely shells have long made them favorites of collectors and their fossils have been known since ancient times.
Fossil Focus: Ammonoids - PALAEONTOLOGY[online]
Ammonoids (Ammonoidea) are an extinct group of marine invertebrates with an external shell. They were cephalopods, and hence closely related to modern cuttlefish, squid, octopuses and the pearly nautilus.