Are sharks really older than trees?

The popular claim that sharks are older than trees holds only under a broad definition of shark. If the word includes shark-like fishes and their ancestors, the lineage goes back roughly 400 million years or more, before the first trees. If it means the modern sharks alive today, the group is younger than trees. John Maisey, a fossil fish curator emeritus at the American Museum of Natural History, summed it up to Live Science: the shark lineage generally goes back further than trees, but it depends on how shark is defined. [1]

Live Science reports that experts generally place the first trees in the Middle Devonian, around 380 million to 390 million years ago. Cindy Looy, a paleobotanist at the University of California, Berkeley, called the timing of the first trees not very controversial. Archaeopteris, regarded as the first true tree, is known from a 385 million-year-old fossil forest near Cairo, New York, and had a tall woody trunk, leaves and deep roots. Eospermatopteris and Calamophyton appear at about 390 and 393 million years ago. [1]

Other sources give later dates. The Smithsonian and CK-12 place the first trees at about 350 million years ago, and Forbes says the late Devonian, roughly 350 million years ago. Conservation International says about 390 million years ago. These figures differ, and the Live Science account, based on named fossil sites, supports the earlier range. [2] [3] [4] [5] [1]

Narrow definition: modern sharks. Live Science says these first emerged around 195 million years ago, in the Jurassic, with fossils traceable to living lineages such as Hexanchiformes, the sharks with six or seven gills and a single dorsal fin. On this view sharks are not older than trees. [1]

Broad definition: shark-like fishes and their ancestors. Maisey points to extinct relatives such as hybodonts, spiny fishes with tessellated calcified cartilage, which he calls a hallmark of most shark-like fishes and their ancestors. Using this trait, sharks appeared around 400 million years ago, before trees. He has studied the early Devonian spiny fish Doliodus problematicus. Tooth-like skin scales called dermal denticles appear in the fossil record around 450 million years ago, which is why some sources, including the Horniman Museum and Conservation International, cite 450 million years. [1] [6] [5]

Maisey describes the transitional fossils as a gray area, since ancient forms have no living counterparts to compare with. Many sources repeating the claim use the broad definition without stating it. The results do not say which view most specialists hold, but the Live Science experts treat the answer as dependent on definition. [1]

Both dates rest on incomplete evidence. Many shark fossils are fragments such as a single tooth, so scientists are still working out when and how sharks arose. Looy adds that fossils clearly showing parts of a tree are rare and finding a fossil forest takes luck, though there is little sign that trees existed before the Middle Devonian. [1]