Fostering curiosity in kids (and their parents) since 2011

Update to a Past Caterpickle: “Did dinosaurs have belly buttons?”

A young girl highfives a museum worker in a t-Rex costume

The then Six-Year-Old interview a gentle dinosaur at the Field Museum in Chicago. No record exists of this conversation, so we can neither confirm nor deny that it touched on the vexing matter of belly buttons. (Photo: Shala Howell)

News broke this week of particular interest to us here at Caterpickles Central, because it touches on a ten-year-old question of ours: Did dinosaurs have belly buttons?

Ten years of life and a century’s worth of history* have passed since we first investigated this question here at Caterpickles, so I think a refresher is in order.

The Origins of the Issue

In 2012, I took my then five-year-old daughter on a trip to the Boston Museum of Science. While examining the skeleton of Cliff the Triceratops, she asked, “Mommyo, did dinosaurs have belly buttons?”

My first impulse was an instinctive, no. Belly buttons are a thing mammals have because a belly button is the scar the umbilical cord leaves when it drops off after birth.

But my daughter had learned by then that my medical knowledge is sadly incomplete, so she wanted to examine all of the evidence at hand before taking my word for it. Fortunately, we were in the museum’s dinosaur exhibit so there was a fair amount of evidence at hand to go through.

A photo of a dramatically lit triceratops skeleton.
Cliff the Triceratops at the Boston Museum of Science may have inspired the question, but he was no help in answering it. (Photo: Shala Howell, 2012)

I won’t relive the experience for you, but I will sum it up. After looking at the footprints, skeletons, and models available to us, we concluded reluctantly that what we really needed was a dinosaur mummy. The only one of those we knew about in 2012 was Leonardo, a mummified 77 million year old juvenile duck-billed dinosaur housed at the Phillips County Museum in Montana. At the time, I cold-heartedly refused to take The (then) Five-Year-Old there for our next Mommyo-Daughter play date.

Given the lack of readily available fossilized belly skin and my firm stand against The (then) Five-Year-Old’s proposal to set up an incubator in the guest bedroom to grow her own clutch of dinosaurs at home, we had no choice but to venture into the perilous field of comparative anatomy.

Feel free to read the past episode if you like (it’s one of our enduring favorites), but the upshot was that we decided that if dinosaurs had a belly button, it would have been like the scar baby birds have upon first hatching from their eggs. Those scars, which often fade over time, are what’s left of the connection between the developing bird embryo and its yolk sac.

Pending further investigation, we decided that newly hatched dinosaurs could also have had some version of a belly button, but that, like birds, a dinosaur’s belly button scar would have faded or disappeared altogether by the time they were full-grown.

“Further investigation” came three years later, when we had a chance to tour Dr. Paul Sereno’s lab at the University of Chicago

In the fall of 2015, my daughter and I had the chance to tour Dr. Paul Sereno’s paleontology lab at the University of Chicago. He had all sorts of marvelous things in there, including a dinosaur mummy, complete with a long swatch of skin.

Brown stone containing a ripply patch of fossilized dinosaur skin.
A portion of Dr. Sereno’s dinosaur mummy. There may be a dinosaur belly button here, but I can’t see it. (Photo: Shala Howell, Mummy: Dr. Paul Sereno & his team at University of Chicago)

Dr. Sereno was very excited about the potential that swatch raised for resolving the long-standing dispute about whether dinosaurs sported scales or skin, but my mind was buzzing with another question entirely.

I think you know what it was.

“Dr. Sereno, did dinosaurs have belly buttons?”

That’s right. Put me in a room with a world-famous paleontologist and I will have him talking about belly buttons faster than you can say Suchomimus.

In a testament to the effectiveness of what must have been hours and hours of absolutely grueling media training, Dr. Sereno managed not to laugh me out of his lab. He simply answered the question.

No. Belly buttons are a mammalian structure. They are the scar left when the umbilical cord that connected the fetus with the placenta during pregnancy detaches at birth. The scars baby birds have are a remnant of their connection to the yolk sac in its egg, but not true belly buttons. True belly buttons require a placenta, which creatures hatched via eggs never develop.

This week’s update: Paleontologist think some dinosaurs may have had the reptilian equivalent of a belly button

This week, news broke that scientists have discovered a Psittacosaurus fossil that sports a scar that they think is the reptilian version of a belly button. In case you, like me, had forgotten what a Psittacosaurus was, it’s an early member of the Ceratopsian family. Cliff the Triceratops, by the way, is also a Ceratopsian. It seems fitting that if Cliff couldn’t provide the answer to the question his skeleton inspired, that his great-great-great-…-great Uncle Psitty would.

Artist’s illustration of Psittacosaurus, a mummified fossil of which appears to sport the dinosaur equivalent of a belly button. Although this dinosaur’s neck frill is so small I can’t see it in this image, I am assured by the Encyclopaedia Britannica writers that it is in fact there. Just as importantly, Psittacosaurus clearly has the all important upper beak bone, called a rostral, unique to the members of the Ceratopsian family. (Source: Psittacosaurus, Encyclopædia Britannica, last accessed June 23, 2022)

After reading the Smithsonian article about the discovery, I no longer feel bad about not spotting the reptilian version of a belly button on Dr. Sereno’s mummy with my bare eyes. Dr. Phil Bell from University of New England and his team used a modified version of Laser-Stimulated Fluorescence (LSF) to spot changes in the pattern of the skin and scales that marked the umbilical scar. LSF uses intensified lasers to highlight fine details of each scale, wrinkle, and pattern on their Psittacosaurus mummy.

I do not have modified laser beams installed on my glasses, so of course I wouldn’t have spotted the umbilical scar while browsing Dr. Sereno’s fossil collection on a school tour. Of course, even if I could have spotted it, I likely wouldn’t have recognized it. I would have been looking for something round, like the belly button on a human child. The artist’s rendition of the belly button in the Smithsonian article reveals that a dinosaur’s umbilical scar would have been long and skinny.

Are we done now?

Ten years on, can I finally treat this question as settled?

Ten years ago, my daughter and I decided that if dinosaurs had had belly buttons, they would have been structures similar to those found on baby birds. She was fine with that answer then. So fine she had forgotten that she’d ever asked the question in the first place when Dr. Sereno politely explained to me that belly buttons are not a thing reptiles have, technically speaking.

Nonetheless, if this new study is to be believed, it looks like our original supposition was close to correct. This dinosaur’s umbilical scar is more permanent than we had expected it to be, based on our baby bird model. And of course, as we learned from Dr. Sereno, a dinosaur belly button isn’t a true belly button like mammals have.

But, yes, some dinosaurs had the reptile equivalent of a belly button, and now paleontologists have a specimen and a paper proving it.

If any other paleontologists out there would like my daughter and me to speculate wildly and imaginatively on their area of expertise well in advance of the evidence, my comment field is open.

Related Links:

*It feels dissonant at best to post about something like this after the past few weeks, and I almost didn’t. I almost posted something about Dobbs, but in the end, decided to keep Caterpickles a politics-free zone. I want to keep Caterpickles a place where we can focus on our common interests, and put our differences on pause for a little while. I need a mental break from politics and fear-mongering, perhaps you do too.

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