Convergent with mysticetes, one of the largest arthrodire placoderms enters the LRT with one of the smallest

Earlier
tiny latest Silurian Bianchengichthys (Fig 1) entered the large reptile tree (LRT, 2102 taxa) as a phylogenetically miniaturized taxon at the base of the arthrodire clade of placoderms.

Today
a very large, rather flat arthrodire placoderm from the Early Devonian, Heterosteus (Asmuss 1856, Fig 2), nests in the LRT alongside tiny Bianchengichthys (Fig 1).

Heterosteus ingens
(= Heterostius Asmuss 1856, Agassiz 1844; Early Devonian, ~6m total length, 60cm skull length; Fig 2) is one of the largest arthrodires. The jugal and preopercular were not preserved and are restored here. These once ossified, now soft tissues may have acted like baleen to filter out each mouthful of plankton-rich water.

A smaller. closely related Early Devonian arthrodire placoderm,
Yinostius major (Wang and Wang 1984; Fig 3) may be reconstructed like Heterosteus (Fig 2) and different than originally reconstructed by restoring the missing (= soft) jugal + preopercular (gray areas).

Yinostius and Hetersteous
both appear to be open water filter feeders, like whale sharks, engulfing vast amounts of sea water and filtering out tiny to large suspended planktonic animals while expelling exhaled water through gills and soft lateral lips, acting like baleen, as the wide mouth opened and closed for respiration and food acquistion.

This appears to be a novel hypothesis
of observation and interpretation. If not, please provide a citation so I can promote it here.

Speaking of ‘whales’…
ResearchGate.net sent a note saying ‘The Triple Origin of Whales” had reached 900 downloads.

References
Asmuss HM 1856. Das vollkommenste Hautskelet der bisher bekannten Thierreiche. An fossilen Fischen des Alten Rothen Sandsteins aufgefunden und aus ihren Resten erläutert: Abhandlung.
Wang JQ and Wang NZ 1984. New Material of Arthrodira from the Wuding Region, Yunnan. Institute of Vertebrate Palaeontology and Palaeoanthropology, Academia Sinica, Beijing.

wiki/Heterosteus
wiki/Bianchengichthys
wiki/Yinostius