Small shelly fossils facts for kids

Cloudina, a tiny animal, part of the small shelly fauna

Small shelly fossils (often called SSF) are super tiny fossils. Many are only a few millimeters long, which is about the size of a grain of rice! These amazing little fossils come from a time long, long ago, right at the end of the Ediacaran period and the start of the Cambrian period. This means they are much older than many other well-known fossils, like trilobites.

Most of these small fossils were kept safe over millions of years because they were quickly covered by a mineral called phosphate. This special way of preserving fossils mostly happened during the late Ediacaran and early Cambrian times. So, the animals that made these fossils might have lived even earlier or continued to live after this period.

What Are Small Shelly Fossils?

Some small shelly fossils are complete skeletons of tiny creatures. One famous example is Cloudina, a mysterious animal that looked a bit like stacked cones. There are also some early snail-like molluscs found as complete fossils.

However, most of these fossils are actually just small pieces or parts of bigger animals. Imagine finding a tiny piece of a puzzle! These fragments come from many different types of creatures, including sponges, other molluscs, and slug-like animals called halkieriids. You can also find pieces from brachiopods (which look a bit like clams), echinoderms (like sea stars), and even creatures similar to velvet worms. These velvet worm-like animals might have been very close to the ancestors of arthropods, which include insects and crabs!

Why Did Animals Grow Shells?

Scientists used to think that animals started growing hard shells because there was a sudden increase in a mineral called calcium in the ocean. While calcium is important for many shells, we now know that many small shelly fossils are made of other minerals, like silica (which is like glass).

A more exciting idea is that these hard shells appeared around the same time that animals started burrowing into the seafloor. Why burrow? To hide from predators! So, it's likely that these tiny shells and hard parts were an early step in an "evolutionary arms race". This is where predators get better at hunting, and prey animals get better at defending themselves. Animals probably used the minerals that were easiest for them to find in the ocean to build their defenses.

Why Are They Important?

It can be tricky to identify and classify small shelly fossils because they are so tiny and often broken. But they are incredibly important! They give us clues about how the main groups of marine invertebrates (animals without backbones) first evolved. They also help us understand how fast and in what ways evolution happened during the Cambrian explosion.

The Cambrian explosion was a time when many new types of animals appeared on Earth. Small shelly fossils include the earliest known members of some modern phyla (major groups of animals). They offer a nearly continuous record of early Cambrian organisms that had hard body parts, which is very rare and valuable for scientists studying ancient life.

Images for kids

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  Fossil of Halkieria, showing many small plates (sclerites) on its sides and back, and cap-like shells at both ends.

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  The tiny Helcionellid fossil Yochelcionella is thought to be an early mollusc. This picture shows how water might have flowed in under its shell, over its gills, and out through a special "exhaust pipe."

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See also

In Spanish: Pequeños fósiles con concha para niños Template:KIDDLE XL END