eastern grey(?) kangaroo (macropus giganteus) ✸ sex unknown, juvenile (joey) ✸ 11.3cm
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kangaroo teeth have growth lines on them as they continue to grow over the course of a kangaroo's life. yearly growth lines are present in two regions of kangaroo incisors, providing a record of age. we can also take a look at their molars to determine their age as well - kangaroo molars move forward in the jaw over time. the older, worn teeth are pushed forward and fall out, making way for new, unworn teeth. (here's a super cool study about it!) and you can see some examples on the diagram to the left there. |
now! lets take a look at my skull. on the left, i have a partial adult eastern grey's mandible, and on the right is our joey's mandible.
there's some notable differences; first, of course, the adult's incisors are worn and chipped. you can see how much more drastic that first molar is growing over the ridge, and if you open the image and zoom in, you can see how much more worn down that one is! had this kangaroo lived longer, it would have fallen out and been replaced by the next one in line. now, comparing that to the joey on the right, we see there is no molars growing over that ridge yet, the teeth are much smaller and less formed than the adult's, and there isn't a lot of signs of wearing. now if we didn't have the adult to compare it to, we might think that this could be a wallaby or some other small marsupial, however! if we have a look in the very back of the joey's mandible, we can see some new molars that didn't get the chance to erupt! this would not be present in an adult's skull, as their teeth would have grown in fully. the left image is of the mandible, and the right image is of the maxilla, which also has some unerupted molars! though the second image is also a good example of some other indications of this joey's age - there's some sections that aren't quite fused together yet, which typically would be in adults.
