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When does a tooth become a tusk? It’s a pretty intricate puzzle!

To better understand how tusks developed, researchers collected broken parts of suspected tusks or teeth from dicynodonts, or highly early animals, held at several institutions in Africa and the United States. The stars of a paleontological dig are usually entire skeletons and petrified remains, but fragmented relics can reveal vital information about ancient species as well.

These tooth and tusk-like features from early mammals, which existed before dinosaurs, are assisting researchers in determining how and when the species developed. Researchers gathered broken parts of putative tusks or teeth from dicynodonts, exceptionally early animals, held at various organizations in Africa and the United States for a study published in Proceedings of the Royal Society B. And they returned to the lab with the tusk-like bones to examine their composition under the microscope.

They were trying to find out if the preserved bits were tusks or teeth. And, if they were tusks, does this new finding change our knowledge of when tusks first appeared in the animal kingdom? As a result, the researchers recognized they needed to provide a rigorous description of what a tusk is.”It’s simply one of those things that everyone believes we know,” says Megan Whitney, a Harvard zoology researcher and principal author on the study.

“There wasn’t a plenty of stuff out there on [tusks] in terms of a diagnosable anatomical nature.” Whitney and her colleagues discovered three distinct features of tusks. A tusk had to be constantly developing, protrude from the mouth, and be formed of dentine, the substance within a tooth, and couldn’t include enamel, the material that makes up the tooth’s outer coating. When the team examined the broken fragments they had gathered from the field, they discovered that these fragmented portions were ideal for this type of study. Whitney and her colleagues had to split them further to investigate them.

“A large part of our effort was gathering a large number of specimens that we could sample destructively,” Whitney explains. To better look at these specimens, the researchers utilized specialized saw equipment to create small slices in the ancient material, then immersed them in a polyester resin mixture for grinding and crushed them down to a consistency suitable for seeing under a microscope.

From there, the researchers were able to determine a variety of parameters, including their age and whether it was dentine or enamel, which was especially significant for this study. And what they discovered astounded Whitney. The researchers found several specimens that fit the newly defined criteria of a tusk. However, not all of these tusks came from the same period or the same progenitor. Instead, they appeared to evolve on distinct timeframes for different organisms, a phenomenon is known as convergent evolution by evolutionary scientists.

“I anticipated we’d discover more animals with real tusks,” Whitney adds, “and I was surprised to see that [tusks] evolved convergently at least a few times.” Furthermore, the study found that specific features, such as flexible tooth ligaments and lower rates of teeth repairing themselves after falling out, were required for tusks to evolve, which helps researchers comprehend today’s mammalian tusks.

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