The discovery of fish fossils provides a unique window into the deep past of life on Earth. These ancient remains offer tangible evidence of some of the earliest vertebrates, revealing how life diversified and evolved over hundreds of millions of years. Understanding these fossils is important for tracing the lineage of all backboned animals, including humans. Each new find pushes back the known timeline for the emergence of complex life forms.
The Earliest Fossil Evidence
Among the oldest fish-like vertebrates discovered are Myllokunmingia fengjiaoa and Haikouichthys ercaicunensis. These fossils were unearthed in 1999 near Kunming, Yunnan Province, China, within the Chengjiang biota. The geological strata where they were found date back to the Lower Cambrian Age, approximately 530 to 540 million years ago.
Separate teams of paleontologists made these discoveries, which were published in Nature in November 1999. The Chengjiang site, a UNESCO World Heritage Site, is known for preserving soft-bodied organisms, allowing for the exceptional detail seen in these ancient fish fossils.
Unlocking Vertebrate Evolution
The discovery of Myllokunmingia and Haikouichthys altered our understanding of early vertebrate evolution. Before these finds, it was thought that fish evolved much later. Their presence in the Lower Cambrian period pushed back the known timeline for fish evolution by as much as 50 million years.
These fossils demonstrate that vertebrates were already present during the “Cambrian Explosion,” a period of rapid diversification of animal life. This indicates that the emergence of animals with backbones occurred alongside the development of spineless creatures, suggesting a rapid pace of evolution in the oceans during this time. Their existence shows that backboned animals emerged far earlier than previously conceived, providing a more complete picture of life’s early diversification.
Anatomy of Ancient Fish
Based on the fossil evidence, Myllokunmingia and Haikouichthys were small, primitive creatures, around 2.5 cm (1 inch) long. They are characterized as jawless chordates, meaning they possessed a notochord, a flexible rod that provides support, at some stage in their life cycle.
The fossils reveal the presence of gills, though Myllokunmingia shows a more primitive arrangement of these structures. They also exhibited a defined skull, basic fin structures, and segmentation of muscles (myomeres) along their bodies, indicating they were capable of movement through water.
Their morphology suggests a relationship to modern-day jawless fish like lampreys and hagfish. These ancient fish likely inhabited shallow marine environments with muddy bottoms, where their remains were quickly covered and preserved after death, allowing for exceptional fossilization.