The largest dinosaurs had individual cells more than 30 meters long. How did such things develop? Read on! Illustration from Wedel (2012: fig. 2).

Here’s something that’s been in the works for a while: a popular article in Scientific American on stretch growth of axons in large, fast-growing animals:

Smith, Douglas H., Rodgers, Jeffrey M., Dollé, Jean-Pierre, and Wedel, Mathew J. 2022. Giraffes vs. blue whales vs. dinosaurs: contest reveals which one builds its nervous system fastest to evade predators. Scientific American,

This one started a few years ago, when Doug Smith at the University of Pennsylvania saw my ‘long nerves in dinosaurs’ paper (Wedel 2012) and reached out to me to ask about the growth of nerve cells in giant dinosaurs. Among his many other interests in neurobiology, Doug has worked on the stretch growth of axons (Smith et al. 2001, Smith 2009, Purohit and Smith 2016).

As a reminder, the axon is the “sticky-out bit” of the neuron. In unipolar neurons like the one in the cartoon above, the axon transmits signals away from the nerve cell body or soma. Most primary sensory neurons — the ones that actually receive stimuli from the environment — are pseudounipolar, meaning that the axon extends in both directions, with the soma sitting off to the side like a teardrop on a tightrope.

Also worth noting is that almost all drawings of neurons are hilariously compressed and oversimplified. I drew that cartoon neuron, above, with a few dozen synapses. Here is an actual neuron from the cerebellum, drawn from a stained specimen by Spanish anatomist Santiago Ramón y Cajal in the late 1800s:

In my hand drawn neuron cartoon, the length of the axon is only three or four times the diameter of the soma. You have motor neurons that run from your lower back to your feet, in which the axon is 10,000 times as long as the soma is wide (~1 meter vs 0.1 millimeters). The difference is even more pronounced for primary sensory neurons, some of which run from your toe-tips to your brainstem, and which have somata as small as 0.02 millimeters across, or 1/100,000th of the length of their axons. In a 20-meter whale or sauropod, the axon of a primary sensory neuron could be 1 million times longer than the soma.

How do such ridiculously elongated cells develop? One method is stretch growth, and that’s what Doug has been studying for more than two decades now. Once an axon has found its innervation target, it’s stuck, like a grappling hook trailing a rope. As the body parts between the soma and the axon terminals grow, the axon is forced to grow in length to keep up (in the grapping hook analogy, playing out more rope). This can be done in the lab, by getting neurons to connect to two plates, and then cranking the plates apart.

How fast can axons possibly grow by stretching? For that we have to look at the maximum linear growth rates of the largest and fastest-growing mammals and dinosaurs. Doug and I and our coauthors wrote a whole article about that, and it’s short. Check it out — here’s that link again.


This is the first 3D print of a dinosaur bone that I ever had access to: the third caudal vertebra of MWC 8028, the ‘new’ Haplocanthosaurus specimen from Snowmass, Colorado (Foster and Wedel 2014, Wedel et al. 2021). I’ve been carrying this thing around since 2018. It’s been an aid to thought. I touched on this before, in this post, but real sauropod vertebrae are almost always a giant pain to work with, given their charming combination of great weight, fragility, and irreplaceability. As opposed to scaled 3D prints, which are light, tough, and endlessly replaceable.

This was brought home to me again a couple of weeks ago, when I visited the Carnegie Museum, in Pittsburgh, Pennsylvania, and Research Casting International, in Trenton, Ontario, Canada. I was at each place to have another look at their haplocanthosaur specimens. The Carnegie is of course the home of CM 572, the type of H. priscus, and CM 879, the type of H. utterbacki (which has long been sunk into H. priscus, and rightly so — more on that another time, perhaps). RCI currently has CMNH 10380, the holotype of H. delfsi, for reprepping and remounting before it goes back to the Cleveland Museum of Natural History.

Caudals 1 through 6 of CM 572, the holotype of Haplocanthosaurus priscus.

The caudals of CM 572 and CM 879 aren’t that different in size — the centra max out at about 20cm (8in) in diameter, and the biggest, caudal 1 of CM 572, is 50cm (20in) tall. Still, given their weight and the number of thin projecting processes that could possibly break off, I handled them gingerly.

Caudals 1 through 5 of CM 10380, the holotype of Haplocanthosaurus delfsi.

The caudals of H. delfsi are a whole other kettle of fish. Caudal 1 has a max diameter of 36cm (14in) and a total height of 85cm (33.5in). I didn’t handle that one by myself unless I absolutely had to. Fortunately Garth Dallman of RCI helped a lot with the very literal heavy lifting, as did fellow researcher Brian Curtice, who was there at the same time I was.

Back to my beloved MWC 8028, the Snowmass haplocanthosaur. My colleagues and I are still working on it, and there will be more papers coming down the pike in due time (f’rinstance). I’m pretty sure that the main reason we’ve been able to get so much mileage out of this mostly incomplete and somewhat roadkilled specimen is that we’ve had 3D prints of key bones to play with. Now, I joke all the time about being a grownup who gets paid to play with dinosaur bones, but for once I’m not writing in jest when I say ‘play with’. That 3D printed caudal is basically a dinosaurian fidget toy for me, and I think it’s probably impossible to play with anatomical specimens without getting interested in their nooks and crannies and bits and bobs.

Another nice thing about it: I can throw it in my luggage, take it Oklahoma or Utah or Pennsylvania or Canada, and just plop it in someone’s hand and say, “Look at this weird thing. Have you ever seen that before?” I have done that, in all of those places, and it’s even more convenient and useful than showing CT slices on my laptop. I’ve watched my friends and colleagues run their fingers over the print, pinch its nearly non-existent centrum, poke at its weird neural canal, and really grokk its unusual morphology. And then we’ve had more productive conversations than we would have otherwise — they really Get It, because they’ve really handled it.

When I started writing this post, the title was a question, but that’s tentative to the point of being misleading. Three-D prints are obviously useful for sauropod workers because with very few exceptions our specimens are otherwise un-play-with-able. And playing with dinosaur bones turns out to be a pretty great way to make discoveries, and to share them.

(And yes, we’ll be publishing the CT scans and 3D models of MWC 8028 in due time, so you can play with it yourself.)


Years ago, when I was young and stupid, I used to read papers containing phylogenetic analyses and think, “Oh, right, I see now, Euhelopus is not a mamenchisaurid after all, it’s a titanosauriform”. In other words, I believed the result that the computer spat out. Some time after that, I learned how to use PAUP* and run my own phylogenetic analysis and realised how vague and uncertain such result are, and how easily changed by tweaking a few parameters.

These days good papers that present phylogenetic analysis are very careful to frame the results as the tentative hypotheses that they are. (Except when they’re in Glam Mags, of course: there’s no space for that kind of nuance in those venues.)

It’s common now for careful work to present multiple different and contradictory phylogenetic hypotheses, arrived at by different methods or based on different matrices. For just one example, see how Upchurch et al.’s (2015) redescription of Haestasaurus (= “Pelorosaurus“) becklesii presents that animal as a camarasaurid (figure 15, arrived at by modifying the matrix of Carballido at al 2011), as a very basal macronarian (figure 16, arrived at by modifying the continuous-and-discrete-characters matrix of Mannion et al. 2013), and as a basal titanosaur (figure 17, arrived at by modifying the discrete-characters-only matrix from the same paper). This is careful and courageous reporting, shunning the potential headline “World’s oldest titanosaur!” in favour of doing the work right.) [1]

But the thing that really makes you understand how fragile phylogenetic analyses are is running one yourself. There’s no substitute for getting your hands dirty and seeing how the sausage is made.

And I was reminded of this principle today, in a completely different context, by a tweet from Alex Holcombe:

Some of us lost our trust in science, and in peer review, in a journal club. There we saw how many problems a bunch of ECRs notice in the average article published in a fancy journal.

Alex relays (with permission) this anecdote from an anonymous student in his Good Science, Bad Science class :

In the introduction of the article, the authors lay forth four very specific predictions that, upon fulfillment, would support their hypothesis. In the journal club, one participant actually joked that it read very much as though the authors ran the analysis, derived these four key findings, and then copy-pasted them in to the introduction as though they were thought of a priori. I’m not an expert in this field and I don’t intend to insinuate that anything untoward was done in the paper, but I remember several participants agreeing that the introduction and general framework of the paper indeed felt very “HARKed“.

Here’s the problem: as the original tweet points out, this is about “problems a bunch of ECRs notice in the average article published in a fancy journal”. These are articles that have made it through the peer-review gauntlet and reached the promised land of publication. Yet still these foundational problems persist. In other words, peer-review did not resolve them.

I’m most certainly not suggesting that the peer-review filter should become even more obstructive than it is now. For my money it’s already swung way too far in that direction.

But I am suggesting we should all remain sceptical of peer-reviewed articles, just as we rightly are of preprints. Peer-review ain’t nuthin’ … but it ain’t much. We know from experiment that the chance of an article passing peer review is made up of one third article quality, one third how nice the reviewer is and one third totally random noise. More recently we found that papers with a prestigious author’s name attached are far more likely to be accepted, irrespective of the content (Huber et al. 2022).

Huber et al. 2022, figure 1.

We need to get away from a mystical or superstitious view of peer-review as a divine seal of approval. We need to push back against wise-sounding pronouncements such as “Good reporting would have noted that the paper has not yet been peer-reviewed” as though this one bit of information is worth much.

Yeah, I said it.



  1. Although I am on the authorship of Upchurch et al. (2015), I can take none of the credit the the comprehensiveness and honesty of the phylogenetics section: all of that is Paul and Phil’s work.


UPDATE: Y’all came through! I’m very happy to announce that Vicki’s scholarship is fully funded, and we’ll be able to give out the first scholarship in the spring of 2023 — and every year thereafter. Thank you, thank you, thank you!! 

When my partner, Vicki Wedel, passed away unexpectedly last year, the whole community at Western University of Health Sciences pulled around London and me. One of the most touching things that happened is that my then dean, Paula Crone, DO (now interim provost of the university), got to work right away with University Advancement to set up the Vicki Wedel PhD Memorial Scholarship:

The scholarship will be awarded to a first year WesternU College of Osteopathic Medicine of the Pacific student with a GPA of or greater than 3.0, with demonstrated financial need who excelled in first-year anatomy classes.

I’m happy to report that the scholarship is nearly fully-funded, at which point it will generate at least one scholarship for a deserving student, every year in perpetuity. We’ve had a very kind offer of a matching gift challenge: an anonymous donor will contribute matching funds to get the scholarship to full funding, if the other half of the remainder is donated by next Tuesday, September 6, which is WesternU’s annual Giving Day. At this point, we’re just a few hundred dollars short of that goal.

Other than very infrequent notices about crowdfunding projects, we don’t put any financial solicitations on this blog, but I’m making an exception in this case. It’s a good cause, to fund a scholarship to help a deserving student with demonstrated financial need pursuing medical training at a non-profit health sciences university. And it’s particularly important to me, because I knew Vicki best, and she was always actively looking for ways to support students. I had no idea how many lives she had touched until after she passed — for weeks I was receiving testimonials from students and former students that she helped and encouraged. Vicki’s memorial scholarship is special to me because I can’t think of a better way to honor her legacy.

I need to give a special thank you to Vicki’s parents, Terry and Carla Cooper, who celebrated their 50th wedding anniversary this summer. They kindly asked guests at their celebration to donate to Vicki’s scholarship fund in lieu of giving them gifts, and we’re so close to the finish line because of that act of generosity.

If you’re interested in learning more about Vicki’s memorial scholarship, please follow this link. And if you’re interested in donating, thank you, sincerely. You’ll have the option to be recognized for your donation, or to donate anonymously, whichever you prefer. Every dollar counts, and every dollar is appreciated.

If you’re reading this post sometime after September 6, 2022, and you’re interested in donating, please feel free! It’s still a good cause, and if the scholarship fund gets large enough, it may be possible to either increase the size of the scholarship, or to give more than one.