Ammonites typically lived for two years, although some species survived beyond this and grew very large as pictured above. Evidence of their short lives is estimated by looking at their living relatives - the nautilus. These creatures exist within modern day seas and possess many characteristics similar to ammonites
Like the nautilus, ammonites retained their original shell throughout their life. However, it’s worth noting that in comparison to modern day nautili which live in cold, deep water, ammonites preferred warm shallow waters and may have had a higher metabolism. Consequently, it’s possible that ammonites could reach larger sizes far quicker than modern day nautili. They are frequently found as fossils, witnesses of pre-historic time.