The question of whether trees or sharks appeared first on Earth requires understanding what defines a “tree” and an “ancient shark” ancestor. The answer reveals the complexity of the planet’s evolutionary timeline. This comparison between a land-dweller and an ocean predator shows that some life forms considered ancient are younger than others. Trees are relative newcomers compared to certain marine groups.
The Early Evolution of Vascular Plants
The journey toward the first tree began with the colonization of land by plants. The earliest known plants with a true internal plumbing system, called a vascular system, were small organisms of the genus Cooksonia. These species first appeared in the Middle Silurian period, with fossils dated back to around 433 to 425 million years ago. Cooksonia was only a few centimeters tall and lacked true leaves, roots, or wood, but its xylem tissue allowed it to transport water and nutrients and stand upright.
This initial terrestrial foothold set the stage for diversification in the subsequent Devonian Period. Over millions of years, these small vascular plants evolved into larger forms, developing the woody tissue that defines a tree. The first true forests were created by plants like Archaeopteris, which emerged during the Late Devonian, with fossils dating to approximately 385 million years ago. Archaeopteris possessed a large, woody trunk and an extensive root system, giving it the structure associated with modern trees, despite reproducing with spores rather than seeds.
The appearance of Archaeopteris transformed the global environment by creating the first deep, stable soils and altering atmospheric carbon dioxide levels. This plant, a type of progymnosperm, was widespread and could grow up to 40 meters tall. The development of true wood, formed by secondary growth, made these organisms the first to fully embody the tree habit and establish forest ecosystems.
The Appearance of Cartilaginous Fish
The lineage leading to modern sharks began in the oceans, far earlier than the first woody plant ventured onto land. The group known as Chondrichthyes, which includes sharks, rays, and chimaeras, is defined by its skeleton primarily composed of cartilage rather than bone. The earliest unambiguous fossil evidence places their origin in the Early Silurian period, around 439 million years ago. These early cartilaginous fish were among the first jawed vertebrates to appear in the fossil record.
While some dermal denticles suggest an earlier origin, the 439 million-year-old fossils provide a concrete anchor for the timeline of the Chondrichthyes class. This initial appearance means that the foundational body plan of the cartilaginous fish existed before simple vascular plants fully colonized the land. The success of this early design has endured through five major mass extinction events.
The fossil record of these early shark ancestors is often limited to teeth, fin spines, and dermal denticles because cartilage rarely preserves well. By the Devonian Period, often called the “Age of Fishes,” more complete shark-like forms had diversified, including genera such as Cladoselache and Doliodus. These marine predators established a basic body plan that has shown remarkable longevity, allowing them to patrol the oceans to the present day.
Comparing the Two Timelines
Synthesizing the geological data provides a clear answer to the evolutionary comparison. The earliest unambiguous ancestors of sharks, belonging to the class Chondrichthyes, first appeared approximately 439 million years ago during the Early Silurian period. In contrast, the first organisms that meet the structural definition of a true tree, possessing a woody trunk and extensive root system, were genera like Archaeopteris, which emerged much later, around 385 million years ago in the Late Devonian period.
This difference of more than 50 million years means that the direct cartilaginous fish ancestors of sharks were swimming in the oceans for tens of millions of years before the first true trees grew on land. Simple, non-woody vascular plants like Cooksonia did appear around the same time as the earliest sharks, at about 433 to 425 million years ago. Therefore, basic plant life on land and the shark lineage arose nearly simultaneously.
However, the question centers on the “tree” form, which requires the complex woody structure that defines forest ecosystems. The evolution of this woody form came significantly after the development of the cartilaginous fish body plan. Ultimately, the lineage that led to the shark is older than the lineage that led to the tree, confirming that the ocean predator holds the greater claim to seniority in this evolutionary contest.