#placoderms

#RETROVEMBER2025: 6. Dunkleosteus (2000s)

dunk design for a pal

Is that why he hid for so long

Bothriolepis

Oh my god I love and hate this thing why does it have so many species

Prehistoric Reef Cam Footage: Field Notes

A series of Horizontal Baited Remote Underwater Video Stations (H-BRUVS) were lowered into the sea over the Late Devonian Canning Basin reef system, in what is now the Kimberley region of Western Australia. The purpose of this research study was to understand grouping and trophic interactions within the Canning Basin Biota. Screenshots of the footage from the third camera (file name HBRUVS_Cann_03.mp4) are shown here to present some select interactions observed during the day's recording session. The BRUVS was baited with chopped Bothriolepis.

Slide 1: After being lowered into the water at 10am, the bait bag draws a small group of Mimipiscis toombsi that begin to feed on the bait. Placoderms Rolfosteus canningensis and Camuropiscis laidlawi are observed swimming among the stromatoporoid corals, seeming disinterested in the bait bag. Acuticryphops trilobites are visible on the seafloor and ammonites (likely Ponticeras sp.) swim slowly suspended in the water column.

Slide 2: The bait bag has drawn a larger group of Mimipiscis, the gathering has been disrupted by the presence of Mcnamaraspis kaprios. The placoderm is larger and has a stronger bite than the Mimipiscis, and claims feeding privileges while they keep their distance. Materpiscis attenboroughi is briefly visible in the lower left of the frame, and slowly drifted along the sand before disappearing off frame. One Rolfosteus individual continues to swim around the stromatoporoids.

Slide 3: The feeding session is interrupted by a large Eastmanosteus calliaspis as it attacks the bait bag, startling the Mimipiscis and Mcnamaraspis into fleeing. This was the only Eastmanosteus individual observed in the week since beginning video surveys, and their usual habitat is still unknown. A dramatic and exciting encounter for the team upon rewatching today's footage.

Slide 4: This slide is indicative of the rest of the footage until the thirds BRUVS was recovered at 17:00. With the bait bag torn off by the Eastmanosteus, no further fish were drawn to the camera and activity in the area was limited. This slide does, however, show a rare sighting of the predatory Onychodus jandemarrai toward the background, likely hunting. Materpiscis is visible sheltered at the base of the reef, and the small saltwater lungfish Rhinodipterus kimberleyensis can also be seen.

Field notes for future reference:

- Use heavier weights on the BRUVS to prevent motion

Ti. clarki is among the largest known placoderms we have fossil record off, remains of their jaws, skull and shield bones are found scattered but some complete specimens offer a complete view of this peculiar and possible first large filter feeding vertebrate from the late devonian. AMNH 7315 or AMNH FF 7134 (IDK why the different ID from Engelman reference) represent one of the biggest known specimens recovered alongside the Moroccan Ti. termieri, having a head length of 75 cm and extended flat a breadth of 1.4 meters.

Engelman paper on Dunkleosteus body calculation used the measurements of this specimen alongside the smaller but quite complete CMNH 5768 implementing OOL giving on both specimens a body size of 3.7 and 4.15 meters respectively, making this one of the few placoderms that can rivalice in length to Dunkleosteus.

Reconstructing Titanichthys

If you are wondering about some details on this reconstruction looking this way, proportions, shape of the head and the strange "fang" on the front that lacks many recons is because I spend some time trying to check how to reconstruct properly this armored fish, which ended up with this skeletal reconstruction

This already comes from what I tried to do several months ago with the need to properly reconstruct this placoderm since the available figures and references seem not to expose several elements, even those that we do know exist which are not often highlighted in the paper skeletal reconstructions. in this case the base of everything is mostly from CMNH 50319, perhaps one of the most complete Titanichthys with material described online (scale bar 1 m)

I was not just comfy about doing this reconstruction based only in sketches, so instead on assuming proportions by digital sketches in a 2D way, I spend few weeks working my way into blender and modeling each pieces I did build a basic model from most of the bone that forms the whole skull and thoracic shield bones, the model for the moment is not available anywhere, and I don't think I could share it online for the moment.

Every minor thing that is not know is being filled with other of its relatives such as Bungartius and Tafilalichthys, both species the most close relatives on few cladistic trees. Unlike the filter feeder, these two are known to might have been hard prey eaters, they are relatively more complete and better preserved so they work out as a reference base being one of the most useful aspects the lacking elements of the jaw.

Probably is important to remark a lot of mounts that are used as references are pretty incomplete in the front, with also the lower jaw being backwards, the extreme of the jaws should be touching in V shape and the notch probably was filled with cartilage called a meckel's cartilage.

In general picking Bungartius as a sample the upper jaw possess the complete set of superognathal plates, the upper jaw bones that exist on all placoderms, in many species vary in size and shape, which even Titanichthys there is some evidence of a Posterior Supergnathal Plate along the complete specimen (PSG, see above), but not the Anterior (MG or ASG), inferring from the position of both supergnathal and the articulation of the cheek bone where the inferognathal fits, this hypothetically could mark how these bones configurated in the skull.

Eye with this, my reconstruction is speculative, based on how these bones articulates on other specimens, new evidence and more material could provide a more accurate conclusion.

Compared to Dunkleosteus is amazing that level of diversity these reached on the last days of the Devonian, both belonging to two totally different radiations of Arthrodira they grew to become the giants of their time, though currently with this body reconstruction Dunk remains very robust on body shape compared to the more compact shaped Titan.

Dang, fossil placoderms are a bit of a gap in my paleo knowledge. I'd have to default to Dunkleosteus because its shearing jaw plates being direct extensions of its skull is absolutely metal.

I'm also a big fan of Sacabambaspis, which while not a placoderm, is still an interesting early fish species from the Ordovician. It looks so alien when compared to more modern fish groups.

I just also think the name is funny because Sacabambaspis sounds like a very technical and elaborate species descriptor, but it literally just means "Fish from Sacabamba."