Genetic studies have determined that sponges appeared on Earth at least 600 million years ago, yet the oldest sponge fossils discovered are about 100 million years younger. This discrepancy is explained by the fact that the earliest sponges were soft-bodied and lacked skeletons, so their remains did not preserve well in the fossil record.

Origin and Characteristics of Sponges

Sponges are multicellular invertebrates that inhabit seas and oceans. They lead a sedentary lifestyle, remaining attached to rocky sea floors or other surfaces. Sponges are considered among the oldest animals on the planet, but the exact timing of their emergence has long been a topic of scientific debate.

Genetic and Paleontological Evidence

Analysis of DNA from modern sponges and chemical traces in ancient rocks suggests that sponges existed as early as 650 million years ago, at the beginning of the Ediacaran period. All modern sponges have skeletons made of microscopic glass-like structures called spicules, which are well-preserved as fossils and found in rocks dating to the late Ediacaran (around 543 million years ago). However, spicules have not been found in older rocks, creating uncertainty about the timeline of sponge evolution.

New Research

An international team of researchers analyzed 133 protein-coding genes in the genomes of both modern and ancient sponges. Their findings place the origin of sponges between 600 and 615 million years ago, narrowing the gap between genetic estimates and fossil evidence.

Computer modeling of sponge skeleton evolution was also conducted. The study showed that the first sponges were soft-bodied and did not have mineralized skeletons, which explains the absence of spicules in rocks about 600 million years old—these structures had not yet evolved during that period.

Independent Evolution of Skeletons

The research revealed that mineralized spicules evolved independently several times in different sponge lineages throughout evolution. Structural and genetic differences among modern species confirm that sponge skeletons have evolved repeatedly. Modern sponge skeletons may look similar but are composed of different materials, such as calcite or silica, and are formed with the involvement of different genes.

Reevaluating Views on Sponge Evolution

It was previously believed that the presence of skeletons in all modern sponges indicated the crucial role of mineralized spicules in the early stages of their evolution. However, new data challenge this assumption, pointing to a more complex and ambiguous history of skeleton formation in sponges.