do they display cannibalistic behavior?
Yes, sexual cannibalism
Mantis
Sexual cannibalism is common among most predatory species of mantises in captivity. It has sometimes been observed in natural populations, where about a quarter of male-female encounters result in the male being eaten by the female. 
what is the predator of a praying mantis Mantises are generalist predators of arthropods what family or species is this a part of? Mantidae ("mantids") are there any fossils of this found? Yes, from Siberia
wiki:57007
Mantis [SEP] Sexual cannibalism
Sexual cannibalism is common among most predatory species of mantises in captivity. It has sometimes been observed in natural populations, where about a quarter of male-female encounters result in the male being eaten by the female. Around 90% of the predatory species of mantises exhibit sexual cannibalism. Adult males typically outnumber females at first, but their numbers may be fairly equivalent later in the adult stage, possibly because females selectively eat the smaller males. In "Tenodera sinensis", 83% of males escape cannibalism after an encounter with a female, but since multiple matings occur, the probability of a male's being eaten increases cumulatively.