A sketch of 19 fossilized dinosaurs have constitute that one species had teeth when youthful , but lost them in maturity . The species involved was concern to modern birds , and may help start the line of descent of the beak .
Dr Shuo Wangof the Capital Normal University in China has been examining a collection of theropod dinosaurs with the marvelous nameLimusaurus inextricabilis .
Wang began meditate juvenileL. inextricabilisfossils 15 years ago . When he first come upon grownup specimens , he did n’t distinguish them as the same species . “ ab initio , we believe that we found two different ceratosaurian dinosaurs from the Wucaiwan Area , one toothed and the other toothless , and we even started to describe them separately , ” he said in astatement .
In the course of elaborated examination , however , Wang and his fellow note that , dentition aside , these brute looked remarkably similar . Another 77 developmental differences have been identified between the adults and their young , Wang report inCurrent Biology , but they nevertheless amount from a unmarried species that did not grow new teeth after misplace their childhood single .
alas for theL.inextricabilis , their habitat in northwestern China in the Upper Jurassic take mucky trap in which animals of all ages became stuck . Wang has foundL.inextricabilisspecimens in three depositary , two from roughly the same time and the other from somewhat later . He has found fossils at six microscope stage of development , from hatchlings and juveniles to subadults and adults . The paper describes this as “ one of the considerably - documented increase series for an nonextant theropod coinage . ”
As useful as man find dentition , some live species lose them as a natural part of growing up , not include cases where tooth decay or glue disease affects an inauspicious someone . However , this is both the first fossil record of a species that lost its teeth in adulthood and the first case we know of in a reptile . Moreover , forward-looking coinage that lose their teeth in this way , such as the platypus , do n’t usually have a in full formed set to commence with , whereasL.inextricabilishad at least 21 full tooth at age one .
The source trust the youngL.inextricabilismust have consumed a unlike dieting to their elder , most likely being omnivorous , before develop to a purely plant - ground diet as adults . Isotopic analysis of grownup specimen farm similar results to other herbivores , but the younger animals are much more varied , suggest the nestling ' dieting were unlike , perhaps vary with the seasons .
It ’s still not exculpated why the adultL.inextricabilisfound teeth an evolutionary drawback . The absence of teething in Bronx cheer is usually attributed to the need for fly fauna tominimizetheir baggage allowance , butL.inextricabiliswas a reason - dweller . Nevertheless , further study may assist excuse why hens ' tooth today are in such short supply .
Other change we have observed with years admit the growing of a shallower head , longer finger bones , and stone in the digestive system to grind up unchewed food .
A comparison of Limusaurus inextricabilis ' mouthparts when a juvenile and an adult . George Washington University
