To Romanian hystorians this weapon, is known more as
"sica" version, and in this country is accepted that it has evolved directly from the agricultural implements, likely a sickle. Normally "sica" is accepted as being the short, or one hand falx but I think little distinction was made in size than it is paraded now.
The
THRAEX, a classic type of gladiator impersonating the Thracian warrior (the Dacians were of course of Thracian familly) character from the gladiator arenas of Roman Empire was carrying a well sized
sica curved dagger as main weapon. As a side note the famous Spartacus was one of these, a Thracian himself from the southern parts.
Peasant rebelions were known as far 18th century in Romania to use agricultural tools as weapons and according to sources quite succesfully from sickles to bills. Specially when serfs were not allowed to carry or own weapons.
Manolo, you should try to find lectures of Hadrian Daicoviciu or Constantin Daicoviciu, like chapters on Dacian weaponry on their books. I'll se what I can dig for you but its hard being away from the homeland's libraries and museums.
If you want more graphic (and real contemporary with the times) you should look for an album or "googlise" on
Trajan's Column (known to us Romanians as the
Columna lui Traian) from Rome. It is a monument in Rome erected by the Trajan himself in 113 to comemorate his conquest of Dacia and Sarmisegetusa (the capital), his great victory against local king Decebalus.

Is that you on that furious reenactment picture, taking a plunge in the poor Roman shield ? If thats you, you should grow a beard, tie some "opinci" and youre a true Dacian, my brother!