Why do soft-bodied cephalochordates leave few fossils?

Cephalochordates, such as lancelets, leave a poor fossil record primarily because they are soft-bodied animals.12

The process of fossilization generally requires two key conditions: the possession of hard, resistant parts—such as bones, teeth, or shells—and rapid burial to prevent decomposition and scavenging. Because cephalochordates lack these solid skeletal structures, their bodies tend to decompose rapidly after death, leaving little to no trace in the geological record.341

While soft-bodied organisms can occasionally be preserved under exceptional circumstances—such as in the Burgess Shale, where rapid burial by sediment slumping occurred—such instances are rare. Consequently, most of our understanding of ancient life is heavily biased toward organisms with hard parts, making the discovery of well-founded cephalochordate fossils an uncommon event in paleontology.5341