Stunning trilobite fossils include never-before-seen soft tissues (2024)

FAQs

Why do petrified fossils not usually include soft tissue? ›

The hard parts of organisms, such as bones, shells, and teeth have a better chance of becoming fossils than do softer parts. One reason for this is that scavengers generally do not eat these parts. Hard parts also decay more slowly than soft parts, giving more time for them to be buried.

From these, geologists know that trilobites had a pair of jointed antennae protruding forwards from beneath the cephalon and rows of jointed limbs on each side of the body. There were three pairs of limbs beneath the cephalon and a single pair of limbs beneath each segment of the thorax and pygidium.

And ever since the discoveries made within the famed Burgess Shale over a century ago we've been aware that trilobites possessed an impressive array of soft body parts -- including antennae, multiple walking legs and even basic respiratory systems.

Their fossilized remains are found in the rugged mountains of western Canada, the rolling plains of eastern Europe, the scorching deserts of northern Africa and the verdant hills of southern China. Indeed, trilobites can be discovered on every continent on earth where Paleozoic outcroppings exist.

Soft tissues are rarely preserved in fossils because they are not as durable as bones and other hard tissues. Over time, soft tissues decompose and are not as likely to be preserved in the fossil record.

Preservation of cells and soft tissues in fossil bone was unexpected at first, but it now appears to be relatively common in Cenozoic and Mesozoic fossil bone (Schweitzer et al., 2007; Huang et al., 2022).

Trilobites were the first group of animals in the animal kingdom to develop complex eyes. Cambrian Period (about 500 million years ago). Trilobites lived in marine waters. Some trilobites could swim, others burrowed or crawled around on muddy sea floors.

Fossil burrows and tracks have been found that match trilobite bodies very precisely; these show that trilobites could burrow into sediment to feed or to avoid predators. Many trilobites living after the Cambrian developed the ability to roll up, also probably as a defense against predators.

Because trilobites had wide diversity and an easily fossilized mineralised exoskeleton, they left an extensive fossil record. The study of their fossils has facilitated important contributions to biostratigraphy, paleontology, evolutionary biology, and plate tectonics.

The first body fossils of trilobites appeared in the Early Cambrian Period, about 540 million years ago.

What are the morphological features of trilobites? ›

Such characteristics as occipital lobes, anterior margins and facial sutures (which allowed early trilobites to shed their molting shell), were shared by the majority of trilobite species, as were such exotic-sounding features as axial rings, articulating facets and pleural spines.

In rare cases the soft (i.e., non-biomineralized) parts of animals survive and are fossilized alongside the hard skeleton, and even wholly soft-bodied organisms (those without biomineralized tissues) can be preserved.

While complete fossil specimens stand as relatively rare discoveries, the fact is that trilobite remains are nothing short of pervasive; throughout the globe, entire strata and biozones have been named for their prolific remains.

The name 'trilobite' comes from the distinctive three-fold longitudinal division of the dorsal exoskeleton into a central axis, flanked on either side by lateral (pleural) areas. The anterior region of trilobite body is the head shield, or cephalon, which is made up of a series of fused segments.

Organisms with soft parts are rarely preserved because the soft tissue rapidly decomposes. Hard parts such as bones and shells are more readily fossilized.

Fossilization more commonly occurs in organisms with hard, bony body parts, such as skeletons, teeth, or shells. Soft-bodied organisms, such as worms, are rarely fossilized, because soft parts quickly decompose or are eaten. Sometimes, however, the sticky resin of a tree can become fossilized.

Soft body parts decay soon after death, but the hard parts, such as bones, shells and teeth can be replaced by minerals that harden into rock.

Petrified wood typifies this process, but all organisms, from bacteria to vertebrates, can become petrified (although harder, more durable matter such as bone, beaks, and shells survive the process better than softer remains such as muscle tissue, feathers, or skin).