New and improved galleries!

New and improved galleries!

For those of you wondering why the pace of content has slowed down, it's because I entered a PhD program in paleontology at the University of Wisconsin-Madison this fall, and I lost what was left of my free time. But that's not to say that there hasn't been substantial work going on behind the scenes of SkeletalDrawing.com!

First and foremost, there is a new skeletal gallery featuring some of my non-dinosaur reconstructions.  "Non-dinosaurs" is admittedly a pretty broad category, and indeed it features everything from the proto-dinosaur Silesaurus to crocodylomorphsturtlesmammals, and even the basal tetrapod Ichthyostega.

 

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Mass estimates: North vs South redux

Mass estimates: North vs South redux

I have good news and bad news - the bad news is today is not the day you get a general estimate of the mass of Spinosaurus. I know, I know, and I'm sorry. Here's the good news - in preparation for a deeper look at the challenges of estimating the mass of Spinosaurus, I've produced far more rigorous mass estimates of Tyrannosaurus and Giganotosaurus from GDI, and I got some surprising results.  Jump below the fold to see who is bigger (and why I think this is so).

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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.

Transitional series

Transitional series

I'm often asked about what I think of "transitional fossils". Here's the thing: it's a red herring. Not because we can't see important transitions everywhere in the fossil record, but because a single fossil can't show a transition by definition. If you want to see a transition you need a series of related animals, generally organized by who is related to whom.

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