What do fish scales have to do with tooth enamel? More than you would think.

Who knew our teeth were so fishy?

Apparently, the enamel that covers our teeth originated from the scales of ancient fish that lived more than 400 million years ago, scientists say.

Enamel – white, shiny, and resilient to cavity – is the hardest tissue our bodies can produce, and it isn’t just found in teeth. While most vertebrates have enamel teeth, some have enamel scales. Sharks, for instance, have "dermal denticles” or little tooth-like scales on their skin to help them swim faster.

To researchers, this posed the question: Which came first, teeth enamel or skin enamel? In July, researchers from Uppsala University in Sweden and the Institute of Vertebrate Palaeontology and Palaeoanthropology (IVPP) in Beijing used data from both palaeontology and genomics to determine that enamel was first part of the skin and colonized the teeth much later.

"This is important because it is unexpected," paleontologist Per Erik Ahlberg of University of Uppsala told Tech Times. "In us, enamel is only found on teeth, and it is very important for their function, so it is natural to assume that it evolved there."

Professor Ahlberg is one of four authors in a collaborative study published Wednesday in the journal Nature. The first component of the study looked at the bony fish gar (Lepisosteus) from North America, whose scales were covered with not enamel but an enamel-like tissue called "ganoine."

Tatjana Haitina, a researcher of organismal biology at Uppsala University, investigated the genome of Lepisosteus discovered that it contains genes for two out of humans’ three enamel matrix proteins.

Ahlberg, along with his colleagues Qingming Qu and Min Zhu from IVPP, studied two other fossil fishes – Psarolepis from China and Andreolepis from Sweden, both of which are more than 400 million years old. They found that the Psarolepis had enamel-covered scales and face denticles but none on the teeth; the Andreolepis only had scales that carried enamel. This suggests that enamel came first from outside of the body before growing on teeth.

Courtesy of Qingming Qu and Min Zhu/Reuters

An undated illustration shows the Early Devonian bony fish called Psarolepis romeri found in south China. Scientists said on Wednesday that fossil and genetic evidence indicates enamel did not originate in the teeth but in the scales of ancient fish that lived more than 400 million years ago, and only later became a key component in teeth. The two fossil pieces, one of the dermal skull (top l.) and the other of a lower jaw, are bearing teeth. However, these teeth lack enamel, unlike our teeth, according to new research published in the journal Nature. This fish is a key piece of evidence showing that enamel did not evolve together with vertebrate teeth, but appeared much later in more derived bony fishes, according to researchers.

“Together, the positive molecular identification of ganoine as enamel and the recognition of restricted enamel distribution in Andreolepis and Psarolepis provide important evidence for the evolution of [enamel],” the authors write in the study.

According to an Uppsala University press release, the study is the first tissue evolution analysis to combine both palaeontological and genomic data. The research group will continue exploring the origin of vertebrate tissues using this approach.

This report contains material from Reuters.