Dunkleosteus Downsized

[dinofelid]

Despite this, the model predicts the lengths of placoderms really well:

(@dinofelid I believe this is the graph you specifically requested!)

Thanks, and also thanks for mentioning the paper is viewable in full online, I hadn't noticed the "download" button. I'm a little confused about the graph vs. the equation here, can anyone with more knowledge of statistics help me with this? The graph seems to show that that for an orbit-opercular length (OOL) of 1 cm, the best-fit prediction for the total length (TL) would be less than 10 cm, but the equation they give is log[TL] = 1.9008 + 0.99619*log[OOL], if you plug in OOL=1, then since log[1]=0 the equation should reduce to log[TL] = 1.9008 which is equivalent to TL = 79.58. In whatever statistical method they're using here, is there something like a constant factor you have to divide the lengths in cm by before you plug them into the equation, or is there some other trick here? I'm also confused by why they say in the text that the best-fit line has "a log-transformed slope of 0.947", 0.947 is said to be the r-squared value but from the equation it seems like the slope of the line on the log-log plot should just be 0.99619.

edit: if anyone else is curious, I found the answer to the first part on a reddit thread about the paper--it turns out there's a mistake in the equation given in the graph, they write the logarithms as being in base 10 but if you look at table 1 they give the equation as Ln(TL)=0.9962 x Ln(OOL) + 1.9008, where Ln is the standard symbol for the natural logarithm.

[andrewsaurus rex]

i'm not sure about the reasoning at all.  The author is comparing extant animals to extinct placodermi.  While the relationship between OOL and total length may be valid for extant fishes, can it be assumed it is also valid for extinct ones?  Especially ones as different in body form as the placoderms?  It's not like there are oodles of full length placoderm fossils around to test the ratio on.

[stargatedalek]

They did include a decent amount of placoderm examples, none of which ended up being outliers.

[dinofelid]

They did include a decent amount of placoderm examples, none of which ended up being outliers.

It probably wasn't an outlier in the sense of being outside the 95% confidence interval, but they do say on p. 23 that the method understimates the body length of the placoderm Amazichthys trinajsticae whose full body was fossilized:

In contrast to coccosteomorphs, OOL tends to underestimate length in the aspinothoracidan Amazichthys trinajsticae and the basal arthrodire Holonema westolii. However, Amazichthys, at the very least, shows a body plan that suggests some degree of axial elongation has occurred, similar to extant mackerels (see "Body Shape of Arthrodires", below). No complete body fossils are known for dunkleosteoids like Dunkleosteus, but given the phylogenetic position and anatomy of Dunkleosteus the head–body proportions of this taxon might be expected to be intermediate between aspinothoracidans and coccosteomorphs (i.e., D. terrelli neither shows signs of axial elongation in its armor proportions nor the overhanging head of coccosteomorphs).

And a little more on the reasoning of why they think Amazichthys being an outlier doesn't cast doubt on the Dunkleosteus estimate on p. 39:

Despite Amazichthys' elongate body shape, this taxon still has pelvic fins located immediately posterior to the end of the ventral armor, and the pelvic girdle is still located approximately midway between the pectoral fin and base of the caudal fin [21]. This supports the idea that these patterns are present across all arthrodires, even those with atypical body shapes. Amazichthys maintains the close relationship between the pelvic girdle and ventral armor seen across arthrodires despite its elongate body plan due to having a highly elongate ventral shield. This suggests that thoracic armor shape is indicative of body shape in arthrodires, and other arthrodires with Amazichthys-like body plans can be identified in the fossil record based on elongate ventral shields. Such a feature is not present in Dunkleosteus, where the ventral shield is unusually short compared to the rest of the armor. Thus, the morphology of Amazichthys trinajsticae is not suggestive of a more elongate shape and longer body for Dunkleosteus terrelli. Indeed, in some respects (e.g., in the correlation between armor shape or pelvic fin placement and body shape) the anatomy of A. trinajsticae actually supports the short, deep body plan for D. terrelli recovered here.

[Gwangi]

I'm all aboard the Chunkleosteus train. 

[andrewsaurus rex]

well, this is very interesting.  I'll be interested to read rebuttals to this paper.  I learned from my reaction to the discovery that Spinosaurus had short legs to not dismiss new theories and discoveries just because they are vey different from what I am used to and I don't like them.  I was sure short legged Spinosaurus was bunk, or an anomaly of some kind.  It wasn't.  So now I keep an open mind, even if I don't like it.

[Faelrin]

Just caught wind of this even though it was published last month, through the 2023 Paleo rewind event going on now. Anyways Engelman himself wrote another paper explaining why the Dunk was Shrunk:

https://www.researchgate.net/publication/375755857_What_Shrunk_the_Dunk_Explaining_the_Science_Behind_a_Major_Update_to_the_Appearance_of_a_Prehistoric_Icon

I haven't read it yet of course, just found it now, but honestly despite my initial push back to the new reconstruction, it has definitely grown on me this past year (no doubt because of the many amazing and funny reconstructions and memes of it out there).

Also have yet to watch this, but this may also be of interest:

[Over9K]

Looks like he thoroughly explains why the head for the new reconstruction is smaller than the older reconstruction, despite using the same specimen at 11min 35sec into the video. Basically, the previous reconstruction is based on erroneous measurements, and he explains.

[Faelrin]

I've watched most of the vid and wow I had no idea Dunkleosteus was so poorly studied. Also absolute props to this madlad going through and figuring this stuff as best he can. It all makes so much more sense to me now.

Also glad he explained the different body parts of the armor and how they fit into how it should be taken into account for its overall body porportions. The talks about its ecology in the video also show that figuring out this aspect, the body size, also helps explain a lot of other things about the species (if not overall genus). I'll have more to say tomorrow on this. Probably.

Edit: Need to give my burned thumb time to heal first. Will come back to this later.