some sort of tiny beetle -- probably a juvenile. Found a dozen of them on a leaf
On looking again at your pictures, I think that the insect pictured there is a bug, not a beetle.
By
“bug”, I mean a true bug, an insect of the order
Hemiptera. The shape looks about right for a true bug, certainly more so than for a beetle. Beetles, by the way, are of the order
Coleoptera. I do think this is an immature form, as it does not appear to have wings.
By the way, here's an interesting little bit of taxonomic information. True bugs, if they have
“bug” as part of their common name,
“bug” is treated as a separate word. For example, the stink bug, and the assassin bug. Insects that are not true bugs, if they have
“bug” as part of their name, it's not treated as a separate word; it's appended to the rest of the name without an intervening space. For example, the ladybug or doodlebug or pillbug (which isn't even an insect at all).
A similar convention pertains to the word
“fly”. True flies are of the order
Diptera. A house fly is a true fly, as is a blow fly, a robber fly, and a crane fly. A butterfly is not a true fly, and neither is a firefly or a dragonfly.