Stegosaurid size

[Deleted]

Discuss stegosaurid sizes here.

A recent paper estimates the mass of the skeletally-immature Stegosaurus specimen NHMUK R36370 at ~1560 kilograms.

Charlotte A. Brassey, Sussannah C. R. Maidment, Paul M. Barett, 2015, "Body mass estimates of an exceptionally complete Stegosaurus (Ornithischia: Thyreophora): comparing volumetric and linear bivariate mass estimation methods"

May 27, 2015 20:49:09 GMT 5 theropod said:

Based on the skeletal and the femur length in the SMA’s files, it’s about 5.15m. At least Sophie/Sarah is the only complete Stegosaurus skeleton at the NHMUK that I’m aware of…

Then scaling this up gives ~8326 kilograms for a ~9-meter Stegosaurus armatus. That was unexpectedly massive, I thought S. armatus would have been closer to ~5ish tonnes.

[spinodontosaurus]

I don't know if this thread is entirely needed - there already exists an Ornithischian Size thread on here, it's nearly a year old and only a page long but most of the discussion on there is about Stegosaurus and Dacentrurus anyway. Then again, I'm not opposed to a stegosaur-focussed thread.

I guess I'll leave that decision to the mods though.



As blaze mentions in the ornithischian thread, the largest Stegosaurus femur is some 1.35 meters long, although I don't know if this is actually the largest specimen outright. The Dacentrurus type specimen has one 1.23 meters long, so I scaled a couple of skeletals to see how big they were.


Click text for full size version.

(EDIT: oops, forgot the scale bar a couple other things, will update the image)

Tip-to-tip lengths of the Dacentrurus is, ignoring the tail spines, 7.2 meters, the big Stegosaurus is 8.25 meters while the little sub-adult is only 4.3 meters. The Stegosaurus looks a lot bigger but then we can't see the ridiculously wide pelvis of Dacentrurus from this angle.

[theropod]

For comparison purposes, the femur length of what would later become the NHMUK specimen was given as 34in=86.36cm here→^{(zip-download warning)}

This implies a body mass short of 6t for the owner of the 135cm long femur.

[Deleted]

That Dacentrurus' underside seems to flat imo. I'll try to make one using the ~1.5-meter wide pelvis if I have the time.

Anything about Stegosaurus armatus? If S. stenops could already get that large, and S. armatus is often implied to be even larger...

[spinodontosaurus]

I think that the 1.5 meter wide pelvis belongs to the holotype, the same specimen I've scaled it to on the chart.

Looking at the paper linked previously, the skeleton in Figure 1 should allow us to infer how wide the pelvis of a Stegosaurus with a 1.35 meter femur would be. From what I can deduce, in that figure the pelvis is about as wide as the femur is long (both seem to be 60 pixels in the full size version). However, Gregory S. Paul's skeletal contradicts this:
blog.press.princeton.edu/2010/10/01/pgs-daily-dinosaur-stegosaurus-stenops/

In his skeletal, the femur is 27.4% longer than the pelvis is wide. His skeletal apparently represents an animal ~6.5 meters long, which would suggest to me it is a better guide for the proportions of giant Stegosauurs specimens than the little 5 meter sub-adult described above.

Either way, Dacentrurus' pelvis is most likely wider, which would go some way to make up for it's torso seemingly being shallower. If I was to make a crude estimate for a second, if we base Stegosaurus' proportions on Greg Paul's skeletal then Dacentrurus has a pelvis 46% wider, but Stegosaurus' torso is 49% deeper while their total lengths are roughly the same. This would suggest an overall size roughly the same between the two of them, which is also implied by their femurs being almost identical in width.
If we instead base Stegosaurus proportions on Scott Hartman's skeletal, then it's torso is only 37% deeper than Dacentrurus', but is also around 15% longer than it. If it's pelvis stays as wide as it is in Paul's skeletal, then again this would imply the two to be of fairly similar overall size.

Also about the species I used, I don't actually know what species YPM 853 is referred too, I just put S. stenops as the label on the chart mostly out of habit. Hartman's skeletal that I used is definitely S. stenops though.

[creature386]

Gonna post something I posted on CF:

The most common track morphotype from Quarry 5 ichnofacies range are wider medio-laterally than deep anterio-posteriorly, tridactyl with blunt digits ending in squared, hoof-like claws. Combined, these characters point to the pes of a single genus: Stegosaurus. Stegosaurus-morphotype tracks range in size from hatchling (estimated body mass 3kg) to adult animals (estimated body mass 6-8 tons). One talus block demonstrates adult stegosaur pedal track partially crushing a juvenile Stegosaurus-morphotype track, implying social behavior amongst juvenile and adult stegosaurs.

gsa.confex.com/gsa/2010AM/finalprogram/abstract_182427.htm
When I read this first, I thought 8 t are unimaginable for a Stegosaurus (even at 9 m), but looking at broly's calculation (and my own one), it looks like I have to change my mind.

[blaze]

YPM 1853 is currently referred to S. ungulatus but it was origninally referred to S. armatus, current consensus seems to be that the type of S. armatus is undiagnostic (so no other specimen can be referred to it) and there's a petition to change Stegosaurus type specimen to the holotype of S. stenops.

Accordng to Owen (1875) the ilium of Dacentrurus is 104cm long, in your size chart it's only 79cm, it seems Headden's reconstruction has scaling problems, the pubis is also too big compared to the pelvis and the scale between the radius and humerus.

Also Paul's S. stenops reconstruction is based on USNM 4934, which is only about 5.5m, he scales it up to 6.5m in his book (and promo material) because of a larger specimen.