Was the Devonian placoderm Titanichthys a suspension-feeder?

Large nektonic suspension-feeders have evolved multiple times. The
apparent trend among apex predators for some evolving into feeding on
small zooplankton is of interest for understanding the associated shifts
in anatomy and behaviour while the spatial and temporal distribution gives
clues to an inherent relationship with ocean primary productivity and how
past and future perturbations to these may impact on the different tiers
of the food web. The evolution of large nektonic suspension-feeders -
'gentle giants’ - occurred 4 times among chondrichthyan fishes (e.g.
whale sharks, basking sharks and manta rays), as well as in baleen whales
(mysticetes), the Mesozoic pachycormid fishes and at least twice in
radiodontan stem group arthropods (Anomalocaridids) during the Cambrian
Explosion. The Late Devonian placoderm Titanichthys has tentatively been
considered to have been a megaplanktivore, primarily due to its gigantic
size and narrow, edentulous jaws while no suspension-feeding apparatus
have ever been reported. Here the potential for microphagy and other
feeding behaviours in Titanichthys is assessed via a comparative study of
jaw mechanics in Titanichthys and other placoderms with presumably
differing feeding habits (macrophagy and durophagy). Finite element models
of the lower jaws of Titanichthys termieri in comparison to Dunkleosteus
terrelli and Tafilalichthys lavocati reveal considerably less resistance
to von Mises stress in this taxon. Comparisons with a selection of
large-bodied extant taxa of similar ecological diversity reveals similar
disparities in jaw stress resistance. Our results therefore conform to the
hypothesis that Titanichthys was a suspension-feeder with jaws ill-suited
for biting and crushing but well suited for gaping ram feeding.