Excellent shot ! Really highlights how much longer this marmoset's teeth are than those of most Callithrix , perfect for gnawing through tree bark to get to the exudate sap.
@Onychorhynchus coronatus
That's a canine you can see (left upper).
Marmosets use their incisors to gouge bark, usually in an upward motion - leaving tell-tale round holes.
@Andrew Swales Yes , I know this , I meant the teeth in general are much longer with Callithrix jacchus than the other species. I work with a conservation NGO that works to conserve two of the more endangered of the Callithrix species and this little guy in the picture is unfortunately one of our biggest and most enduring problems.