There are three higher classifications of suture lines: goniatite, ceratite and ammonite. As ammonites evolved through the ages, suture patterns tend to become more and more complex. As previously mentioned, suture lines are found on the inner shell of ammonites and demarcate where the septa divides the ammonite’s shell into individual chambers. They are called suture lines and are an important characteristic that allow paleontologists to differentiate between the different ammonite species. The markings on an ammonite’s shell are there for a reason. These lines are only on the inner shell and are observed when the protective outer layer of the shell is removed or broken during the extraction process. All ammonites have these markings on their shells, though they aren't always visible. The squiggly lines you see on ammonite fossils are sutures. Why Do Some Ammonites Have Squiggles On Their Shells? Red flash ammonites of the genus Cleoniceras are only a couple of inches across, but were swimming in the same seas as the colossal Kranosphinctites ammonites that were almost 2 feet in diameter and had large, knobby bumps around the outer whorls of their shells. For example, many of the ammonites from Madagascar are found in a huge variety of sizes. As with most animals, availability of resources is a limiting factor in growth, which is why certain species at specific locations are smaller or larger than their compatriots. The most popular ammonites that circulate through the general public and the scientific community are in the range of 1 inch to a foot in diameter. Had it's living chamber been complete it is estimated it would have been 8.4 feet wide. The world's largest ammonite fossil, a 5.9 foot wide specimen of the species Parapuzosia seppenradensis at the Museum of Natural History in Münster. These ginormous species have been found in Europe and Mexico, painting an interesting picture of the resource availability of both locations to allow for such incredible growth.

Some of the smallest ammonites measure less than an inch long, opposed to the largest which could reach diameters of almost 3 meters (9 feet). These specimens are amazing when bisected and polished.Īmmonites had a wide range of sizes that varied depending on location and prey preference.

Depending on the mineral composition of the sand in which the ammonite fossilizes, gnarly pockets of calcite crystals and agate have been known to appear. The composition of the seafloor was such that sediments and bacteria quickly enveloped a dead organism where oxygen was then leached from the sand, concreting the shell and preserving it. A major facet of why ammonites are so prevalent in the fossil record is that they lived in shallow seas and spent their lives near the ocean floor, where they inevitably settled as they died. Because of their prevalence throughout the Paleozoic and Mesozoic age, rapid evolutionary radiation and their calciferous shell composition, they make excellent candidates for fossilization and are a useful tool to properly age geologic formations. Ammonites just happened to have the “right stuff” to maintain their lineage throughout a wide range of habitats and over a span of nearly 200 million years.

Ammonite crystal