The majority of ammonite species feature planispiral shells, tightly coiled in a flat plane. The most fundamental difference in spiral form is how strongly successive whorls expand and overlap their …

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.

Other unique features of the ammonites include the sexual dimorphism between the female shell (macroconch), and the male shell (microconch). The microconch is smaller and wider, while the …

What does the shell reveal about the ammonite? Most ammonite shells are coiled, and all contain a series of linked chambers. The body of the ammonite was contained within the large final, open …

Jul 6, 2023 · After death, ammonite shells sank to the seafloor and were buried by sediments. Over millions of years, chemical processes transformed these shells into stone — a process known as …

Some ammonites had long, straight shells, while others had helix-shaped shells. Most species, however, had coiled shells lined with progressively larger chambers separated by thin walls...

The ammonite shell grows by continually adding layers of calcium carbonate to the leading edge or aperture of the conch, so that their entire life history is recorded in their shells, from embryo to adult …

Jul 22, 2025 · These fascinating marine animals are now extinct, but their fossilized shells can still be found today. Ammonite fossils are spiral-shaped and often resemble the modern nautilus.

The shells of ammonites were divided into chambers by intricately folded walls or septae. These walls left distinct suture lines where they joined with the outer shell, making patterns that are important in …

Nov 11, 2025 · Most ammonoid genera became extinct at the end of that period, but a few survived and evolved into many diverse forms during the Cretaceous Period. These forms are characterized by an …