Ontogenetic changes – the changes in anatomy that appear during the lifetime of an individual – are not particularly liked among paleontologists. The reason is simple – they make the research more difficult. You simply don’t know if you are working on one species or more.
And when you’re working on the Late Jurassic theropod Limusaurus, the ontogenetic changes are a pure nightmare.
Limusaurus inextricabilis was a small, approximately 1.5 m (5 feet) long theropod dinosaur that was first described in 2009. It lived some 160 million years ago in what is now the northern part of the Xinjiang autonomous region of China. Limusaurus belonged to the Ceratosauria and was initially thought to be differing from its close relatives – among others – in that it lacked the teeth.
A new study published by a team of scientists led by Shuo Wang from the Capital Normal University shows that the dinosaur was even more interesting than the original description suggested.
The researchers looked at 19 individuals, from juveniles to adults, and identified at least 78 traits that were variable ontogenetically. Among those, the most striking change concerned the teeth.
The youngest individuals of Limusaurus had at least 42 teeth. As the animal was growing, the number of teeth was reducing, resulting in toothless jaws in adults. The changes also affected the jaw bones which became curved downward. That might have led to the development of a beak.
These modifications naturally led to shifts in diet. Analyses of stable carbon and oxygen isotopes showed that youngsters inclined towards meat-eating and adults were most likely.
Following these fascinating findings, an interesting question arises – was Limusaurus a result of unique evolutionary changes or did he belong to an as yet unidentified clade of ceratosaurs? Hopefully, we will find out soon.
Featured image © Yu Chen.