Ammonites Vs Trilobites

During the Palaeozoic, a group of arthropods called the Trilobites ruled the ocean ecosystems. However, the majority died off by the end of the Devonian and the last few stragglers were eliminated by the Permian extinction. During the Mesozoic, a group of cephalopod molluscs with spiral shells called Ammonites populated the ocean until they met their demise alongside the (non-avian) dinosaurs in the K-Pg extinction. Both are common and popular fossil finds. Today we’ll be looking at these two types of prehistoric critters to see which is the best.

ammonite and trilobite
Ammonites Versus Trilobites – Credit and Onikaizer. Tyrannosaur University edited images


  • The name ‘Ammonite’ comes from the Egyptian God Ammon, who had ram’s horns around his head.
  • Ammonites lived from the Permian to the Cretaceous, amazingly surviving through the Permian mass extinction. They may have overlapped with the last Trilobites. Ammonites came in many sizes.
  • The biggest, Parapuzosia seppenradensis, grew almost three metres in diameter and the smallest is, well, very small. You see, ammonites are so common and many are very small so we don’t actually know the smallest. Ammonites had shells that looked very similar to a snail’s, although they didn’t twist one side like a snail’s. The first few sections of the shell were for the body to retract into, and the last ones were filled with liquids for buoyancy.
  • They are very often compared to the Nautilus, a modern shellfish with a very similar body plan. Despite the comparison to the Nautilus, they are often drawn with very un-nautilus like bodies – more like a squid or octopus. Like an octopus, some species may have been able to change colour, but as no soft tissues have been found Ammonite’s shape is left to the unknown. To imagine an Ammonite alive you could simply stick a squid’s head on to your fossil and add colour, and hey presto, you’re done. Or think of a Nautilus with a different type of shell. Depends if you’re the Ammonite-squid or Ammonite-Nautilus type.

See link for Nautilus Video: (

  • Ammonites are very common and are often found on beaches and cliffs. Due to their frequent occurrence, they are sometimes used to date other fossils.


  • “Trilobite” means three-lobed because they have three lobes. Genius. Okay, I’ll explain. Trilobites most simply can be broken down into three sections cutting vertically through their body; two pleural lobes on the outside and the axial lobe on the inside. You can also separate them by head, body and tail, except they have fancy names. The head is called the cephalon, the body is called the thorax and the tail is called the pygidium.
  • Trilobites come in many weird and spiky forms and have much more on the weirdness scale than Ammonites. One type of trilobite, Walliserops, has a trident sticking out of its face. Don’t beleive me? Watch.

See Link for Trident Trilobite (

  • Triobite fossils are often amazingly preserved and show off these aniamls in awesome glory. Despite being small, these animals came in intricate and awesome forms. Some crawled along the bottom, some swam in shoals. Soem were plankton feeders, whilst others were deadly predators. There are so many species they were like the beetles of the Mesozoic*.
  • Trilobites’ eyes were made of calcite crystal so their eyes were literally gems.
  • Impressions of their legs show that their legs actually ahd two legs steming from one leg – one for walking, the other was a gill. How awesome is that?

Ammonites Vs Trilobites

So, which is the best? Like a lot of things, it is a matter of opinion. My personal favourites are the trilobites. The reason I like trilobites is because of their amazing diversity and ingenuity. Whilst Ammonites tend to (there are some exceptions) stick to the same body plan, Trilobites go all out in their amazing arrays and forms.

What’s your favourite, Ammonites or Trilobites? Comment your opinion below!


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