Dear Guys,
I recently found the triangle bone in dolomite erratic of Varena town, South Lithuania, it is 4 mm length.
It has the wider growths in the lower sides and straight blunt bony growth in the top. The dolomite also has poorly visible calcified lenses (maybe oncolites?).
The erratic is typical to Triassic arid conditions and should belong to Late Triassic epoch because frogs from Early Triassic are found only in Madagascar island.
Here is the link in frog omosternum:
http://scienceblogs.com/tetrapodzoology/2010/08/27/blombergs-toad-and-buddies/