By Dorothy Hagmajer
For puzzle-lovers who have mastered 1000-piece jigsaws of blue skies and seek other delightful frustrations: consider paleontology.
Despite the body of knowledge researchers have exhumed, the way our prehistoric neighbors looked — and behaved — is still something of an educated guess. Now, a review published in Biology Letters on the anniversary of the first dinosaur being named (the Megalosaurus, a name which means “great lizard”) encourages researchers to exercise judicious rigor when working backward from the limited pieces of the puzzle that make up a dinosaur skeleton.
“I remember looking at the literature early on and wondering what the rules were,” said Stephanie Baumgart, Ph.D., a postdoctoral researcher in the department of physiological sciences at the UF College of Veterinary Medicine. “It’s difficult to say we’ve arrived at a final conclusion when finding a complete fossil skeleton is rare.”
When dinosaur bones are found, they don’t arrive with a clear, pigmented reference photo. In fact, you’re lucky to have a handful of bones that belong to the same dinosaur at all, Baumgart said.
For context: The case of a fossil like Sue, the largest Tyrannosaurus rex fossil that was also staggeringly well preserved, is rare. Typically, researchers are working with a little over half of a skeleton at best.
“Each new discovery changes the understanding of how this animal could have looked,” Baumgart said. “You can say, ‘Yes, we have 60% of this skeleton, we feel fairly confident assessing how it may have appeared or functioned,’ and then you find 20% more and realize you have to change your hypothesis.”
A guess, however hazarded and educated, needs guardrails, the review points out. Outside of satisfyingly certain observations — like the heft and rigor of powerful jaws that house sharp teeth up to 12 inches indicating a taste for the flesh — conclusions can rapidly become murky.
“Understanding vertebrate structure and how form follows function is a starting point, but the fossils are missing the squishy bits which would have provided a ton of additional data on how the animal lived,” Baumgart said.
The vertebrate paleontologist approaches her research in birds and pterosaurs (the first vertebrates to grow bored of the ground and take to the air) from an anatomical background, having taught comparative anatomy, human gross anatomy, and veterinary anatomy. It’s a common field for paleontologists to work in, another being geology.
“When you consider the wide range of backgrounds paleontologists have, it makes sense that people apply different research methods and arrive at hypotheses with different degrees of certainty,” Baumgart said.
Some of the inferences researchers make regarding dinosaurs are based on access to the animals that still walk among us.
Someone can watch a living animal move and then look at their anatomy and say, confidently, this is why that animal has a very flexible backbone. Here’s precisely what is going on in its skeleton, joints, ligaments and tendons. Then, they can study another animal with a more rigid backbone and note some differences, Baumgart said.
“After examining those two, let’s bring in another animal which also has a less flexible backbone,” she said. “Does this follow the same rules as the previous animal with a rigid backbone? Or is it kind of a weird in-between? Or is it doing something totally different?”
Notes are taken, and the data set continues to grow.
The hope of the paleontologist is to take these rules one notices in living animals, find markers in their bones that are directly related to these rules, and then find the same markers in bones of fossil animals. That connection would provide another piece to the puzzle regarding how dinosaurs lived and breathed when so many pieces are otherwise missing.
Baumgart and her PI, Emma Schachner, Ph.D., looked at different areas of physiology commonly studied by paleontologists, including metabolism, thermoregulation, and cardiovascular and respiratory systems. Together with their team, they looked at what people have done thus far in “dinosaur world.”
Then, they matched it up with some of the physiological data on living animals.
“This comparison is the basis for the claims we can make,” Baumgart said. “And we found that there’s a little bit of a disconnect between the claims being made in paleontology and what can be substantiated by the data from living animals.”
This rigor is necessitated by the contradictions present even in living animals, where the “squishy bits” can throw categorization into a quandary.
For example, take the garden variety tuna fish: Yes, it is mostly cold-blooded, but it also has regional warm-bloodedness. Some of the tuna’s muscles — the ones used for swimming, specifically — will normally have a higher temperature than others.
This kind of detailed information cannot be found in bones.
“Sometimes paleontologists will try and determine something like the core body temperature based on data they collected from fossils,” Baumgart said. “But if that’s hard to do unequivocally with skeletal data from living animals, how can you make a strong claim from sparser fossil data?”
Consequently, Baumgart and co-authors recommend collecting data from at least three to five individuals across each of several species, which will help account for at least some of the normal variation in and between different animal species. Much like having one extremely tall family member among a shorter bunch, this would help to identify how much one can extrapolate to the fossil record.
Nowadays, researchers often use digital imaging like CT scans to study fossils and learn about anatomy and physiology of living animals. But that imaging data should be cross-checked against physical specimens to be sure what the images show is real and not an imaging artifact. Essentially, check your work against what you can, as often as you can.
When it comes to science, it’s the nature of the beast.
“Paleontology is difficult, but we like to do it anyway,” Baumgart said. “We just have to proceed carefully.”