Scaling issues - a minor irritation?

Scaling issues - a minor irritation?

The Super Spinosaurus? post produced some interesting conversation; in particular Marco asked a good question about whether using the skull of the South American spinosaurid Irritator would have a material impact on the size of the animal. Let's take a quick look at Irritator's skull, and then a broader look at how these sorts of questions do (or don't) impact mass estimates.

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Super Spinosaurus?

spinosaurus size comparison.jpg

In the past I have been skeptical of claims of 50+ foot Spinosaurus specimens - and with how little we know about the tail length in Spinosaurus there is still reason for caution.

That said, science is always based on data, and sometimes the data isn't what you expected. I was reminded of this once again recently after I tweaked the scaling of elements in my Spinosaurus skeletal reconstruction. The "main" skeletal seen above (the fully restored version is in the theropod gallery) is based on a composite skeletal of the type specimen and other various referred bits. Previously I'd had the mandible scaled up too much by about 6%. After correcting I measured and sure enough, a nice 14m (46 foot) long beast.

Now please use some caution here: as you can see the composite skeletal is missing large swaths of bones. I have filled those in with bones from other relatives (e.g. Baryonyx and Suchomimus), but there's definitely some uncertainty here. Of particular note, tail length varies quite a bit in dinosaurs (as demonstrated recently by Dave Hone), and I would feel a lot better about estimating the length if we had some more Spinosaurus tail vertebrae.

Still, unless you restore an almost comically long tail the type specimen of Spinosaurus was less than 50 feet. Ah, but that's not the largest specimen! The biggest specimen referred to Spinosaurus is MSMN V4047, a giant snout that Dal Sasso et al described in 2005.

Assuming that the composite is scaled correctly and that the giant MSMN specimen scales up isometrically (which seems probable) then it would be in the range of 15.6 meters (51 feet) give or take. That's one long theropod we are looking at! Given our margin of error it's entirely possible that the MSMN specimen is actually 48 feet (or 55 feet!), but assuming it had proportions similar to that of other spinosaurids, then it seems clear that 50 foot lengths were most likely attained.

Of course length is just one estimate of size, and mass is generally considered more important. And here things get interesting. Check back this weekend for a closer look at how much Spinosaurus may have tipped the scales in life.

The problem with Puertasaurus

Puertasaurus reuili

Puertasaurus reuili

When I released my Thunder Lizards  size comparison I was asked why a few of the largest animals were rendered in gray, and when I would be making the actual skeletal available. Using gray silhouettes solved an aesthetic concern (the image was threatening to get too busy), but it turns out that those critters have another problem: they are not known from very incomplete remains.

So here is the skeletal of Puertasaurus in all its "glory". I have a fully restored version as well, but it's not going to be making a public appearance, as frankly I don't want it to be separated from the rigorous version, as that could give off the impression that the animal is better known. In fact even this version is somewhat misleading, as the two tail vertebrae were reported but not figured or described - I don't actually know how big they were!

That's not to say the reconstruction is a fantasy - it's status as a lognkosaur seems secure, and we have very good remains of some of its relatives. And the neck and back vertebrae actually provide a pretty reasonable basis for scaling the largest parts of Puertasaurus. That said, I feel it's important for scientists (and scientific illustrators) not to inadvertently mislead people about the level of inference involved.

So enjoy the skeletal, but please do so responsibly!