Our Oldest Jawed Ancestor Was A Spiky Shark

The shark in question dates back 439 million years – a shock since earlier scientists had dated the oldest acanthodian 15 million years younger.

This Paleozoic fossil was found in the bone bed of the Rongxi Formation in the Shiqian County of Guizhou Province of South China. It was gathered along with numerous other skeletal fragments and pieced back together.

Scientists named the specimen Fanjingshania renovata, and say the fish wrapped in bony armor and paired fin spines would have looked very distinct from the sharks we know today.

The authors of the study released a statement that went into the insights they were able to glean from the fossil.

“This is the oldest jawed fish with known anatomy. The new data allowed us to place Fanjingshania in the phylogenetic tree of early vertebrates and gain much needed information about the evolutionary steps leading to the origin of important vertebrate adaptations such as jaws, sensory systems, and paired appendages.”

They also say that the fish is remarkable because even though they belong to the chondrichthyans, which are known for their cartilage, Fanjingshania shows traits more often seen in bony fish or even mammals.

“This level of hard tissue modification is unprecedented in chondrichthyans, a group that includes modern cartilaginous fish and their extinct ancestors. It speaks about greater than currently understood developmental plasticity of the mineralized skeleton at the onset of jawed fish diversification.”

The discovery primarily lends itself to the idea that jawed fish started to evolve 455 million years ago, during the Ordovician.

“The new discovery puts into question existing models of vertebrate evolution by significantly condensing the timeframe for the emergence of jawed fish from their closest jawed ancestors. This will have profound impact on how we assess evolutionary rates in early vertebrates and the relationship between morphological and molecular change in these groups.”