Early Evolution Update

Publication Info:

Transcript:

Jason D. Pardo, Direct development of stem tetrapods across the fin-to-limb transition, Science (2026). DOI: 10.1126/science.aeb7635

This Embolomere fossil may be changing everything paleontologists know about the evolution and development of early tetrapods! We may have looked and lived a lot like amphibians, but our early ancestors grew very differently.

Episode 297

Notes:

Is this little fossil proving evolution wrong? Of course not, but it is changing what we know about some of our earliest ancestors that came onto land. Here's your most recent paleontology news almost daily or whenever I get around to it. So, our earliest tetrapod ancestors first kind of worked their way onto land just shy of like 400 million years ago before evolving into what we picture as amphibians and then that evolved into all the groups of tetrapods we have today including mammals and us. Well, the general idea has been that the first limbed animals on land were pretty much amphibians and grew pretty much like amphibians. They hatch from soft eggs, then they have their larval stage, and then they go through metamorphosis to become their full-grown adult form. But apparently with the earliest limbed tetrapods that may not have been the case. If you look at this embolomere fossil from Mazon Creek, you may notice something missing or honestly you may not cuz to the untrained eye it looks a lot more like a fossil banana than the baby of a 10-ft croc-like amphibian. But it doesn't have external gills and that's one of the defining features of the larval forms of amphibians. And yeah, at least in modern list amphibians having external gills in their fully aquatic form is pretty necessary. And they're missing from this baby embolomere meaning that it may just be a baby. The body proportions are different than an adult. It's obviously significantly smaller. It doesn't have the same limbs as the adult, but those are all comparatively normal developmental changes. And according to paleontologists, this is a consistent thing within other groups of early tetrapods at the time. They couldn't find anything resembling a tadpole meaning that even though our earliest ancestors looked a whole lot like amphibians, they didn't really grow and develop like amphibians do. As usual, if you want more information, here's the source.