含羞草传媒

鈥淥ur goal as paleontologists is to bring these animals back to life, 鈥 says Associate Professor Mary Silcox (photo by Ken Jones)

Darwinius fossil: longer in the tooth than we thought?

More like a lemur than a monkey when it comes to teeth, new model shows

A famous fossil of an early primate has more in common with modern lemurs than researchers previously thought based on how its teeth erupted, 含羞草传媒 researchers say.

PhD student Sergi L贸pez-Torres and Associate Professors Mary Silcox and Michael Schillaci of U of T Scarborough developed a new model that re-examines the interpretation of Darwinius, the best preserved fossil primate known to exist. 

By looking at the sequence in which adult teeth come in 鈥 known as dental eruption 鈥 in primates, they found it had more in common with lemurs than squirrel monkeys, the model species used by the researchers who discovered Darwinius. Since Darwinius died before reaching adulthood, the fossil offers clues about the sequence in which its teeth erupted.   

鈥淓very species has a particular pattern by which their teeth come in and this allows us to estimate the age of fossils that died before their adult teeth could emerge,鈥 says L贸pez-Torres. 鈥淚t seems that the pattern of dental eruption for Darwinius is more similar to that of lemurs than to that of monkeys.鈥

Before looking at Darwinius, L贸pez-Torres did a large study of 97 living and fossil primates in order to get a clearer picture of how different species compare through patterns of dental development. He found that the three most primitive ancestors 鈥 the ancestor to lemurs and lorises, the ancestor to monkeys, apes, and tarsiers, and the ancestor to all primates 鈥 share the same eruption sequence with each other. That pattern shares some similarities with the dental eruption sequence found in Darwinius.   

head shot of PhD studentThe major difference is we found that anthropoids (ancestors to monkeys, apes and humans) are characterized by a late eruption of the third molar, which is something Darwinius clearly doesn鈥檛 show,鈥 says L贸pez-Torres (pictured at left). 鈥淥ne idea that still stands links Darwinius to anthropoids, but since it doesn鈥檛 show this late eruption, it looks more like a modern lemur.鈥 

Their model also suggests Darwinius was a little older at the time of death and would have weighed slightly less as an adult than the original estimates predicted. 

The team that originally discovered Darwinius argued the 47-million-year-old fossil was more closely related to haplorrhines, the group that includes anthropoids (monkeys, apes, and humans) and tarsiers.

Subsequent studies by the same group suggested Darwinius was specifically related to anthropoids, the primate lineage in which humans belong. But other researchers argue that Darwinius is more likely a strepsirrhine, meaning it belongs to the opposite branch of the primate family tree, closer to lemurs and lorises.

鈥淥ur findings don鈥檛 entirely support the strepsirrhine hypothesis, but it鈥檚 certainly consistent with it,鈥 says L贸pez-Torres. 鈥淲e can say for certain it鈥檚 not consistent with the anthropoid hypothesis.鈥   

While the new model proposes only a slight change in adult weight and age at death 鈥 622-642g and 1.05-1.14 years compared to original estimates of 650-900g and nine to 10 months 鈥 the findings are significant in terms of figuring out what Darwinius was actually like. 

鈥淚t may seem trivial going from 9 or 10 months to a little over a year, but if you consider that, for example, some species of lemur can reproduce at a year old, this difference could mean a major change in what the life of this animal was like,鈥 notes L贸pez-Torres. 

Silcox says: 鈥淥ur goal as paleontologists is to bring these animals back to life. It鈥檚 the best preserved fossil primate. It even has stomach contents, so there鈥檚 a lot of potential for understanding its biology. 

鈥淲e want to be able to answer broader evolutionary questions, but we also need to have a nuanced view of what this particular animal was like.鈥 

The model is explained in a new research published online in the journal Royal Society Open Science

image of fossil

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