A Vietnam Veteran Collected Fossils for 66 Years. One, Mislabeled 'Child Lamprey,' Made Paleontologists Rethink How Vertebrates Moved From Water to Land

The fossil turned out to be a hatchling of a crocodile-like creature, and it suggests, in keeping with a brand new research, that early animals didn’t use metamorphosis to evolve to dwell on land

Eli Stark-Elster

| AAAS Mass Media Fellow

June 18, 2026

an illustration of two pinkish swimming larvae with small front limbs in front of the snout of a larger crocodile-like creature — Two fossils of juvenile embolomeres—crocodile-like creatures, illustrated right here—recommend that they didn’t bear metamorphosis to change into adults and that the ancestors of as we speak’s birds, mammals, reptiles and amphibians won’t have had a tadpole life section.
Berit Goding

Richard Rock—a Vietnam Battle veteran, a Grasp Gardener and an avid fossil collector—has been selecting up rocks for 66 years. His favored web site is Mazon Creek, a prolific fossil mattress positioned about 70 miles southwest of Chicago. It’s famend not just for its fossils but additionally for the devoted neighborhood of novice scientists who courageous the warmth, poison ivy and Lyme-bearing ticks to gather and catalog artifacts from one of many world’s nice paleontological reservoirs.

In 2023, fellow fossil fanatic Andrew Younger requested Rock if he may {photograph} his collections. Rock “had show instances all through the home and an overloaded storage space within the storage,” Younger recollects. “I went into his research, seemed on the glass cabinets, started to take specimens down, and I noticed one which had a small, laminated label that stated ‘child lamprey.’ And I believed to myself, ‘This isn’t a lamprey.’”

The fossil, it turned out, was one thing way more necessary. In a research revealed as we speak in Science, Subject Museum researchers Arjan Mann and Jason Pardo describe the specimen as a hatchling tetrapod, a member of the four-limbed lineage that gave rise to all residing amphibians, reptiles, birds and mammals. Paired with the same fossil already within the museum’s archives and analyses of dozens of fossilized kin, the hatchling upends the extensively held concept that metamorphosis was important for serving to carry the Earth’s first land-dwelling vertebrates out of the water.

Do you know? The earliest tetrapods

You most likely noticed footage of tetrapods in highschool biology. They had been historic and vaguely lizard-like creatures, initiating vertebrates’ preliminary transition from water to land. For many years, scientists extensively assumed that tetrapods managed this shift by metamorphosis—starting as waterborne tadpoles, very like trendy frogs, then reorganizing their total physique plan to change into partially land-dwelling adults.

This speculation emerged partly as a result of the fashionable animals that look essentially the most like early tetrapods are salamanders that have metamorphosis. However Florian Witzmann, the curator of the fossil fish and amphibian assortment at Berlin’s Pure Historical past Museum who was not concerned within the new analysis, argues that the analogy was all the time flawed. It is sensible, he says, that metamorphosis might need advanced later.

Earlier than Rock’s fossil turned up, Mann and Pardo had spent a number of years analyzing one other specimen from the Subject Museum collections. Whereas working late within the lab, Mann seen that the mysterious fossil had a tiny, budding limb. To determine what creature they had been taking a look at, the researchers, as Mann places it, “went by a listing of candidate animals from the time based mostly on the morphology, slowly eradicated these based mostly on anatomical options, which excluded these teams, till we landed on our prognosis.”

Finally, imagery with a scanning electron microscope allowed the scientists to determine the animal as an embolomere: a crocodile-like predator that dominated ecosystems between 280 million and 350 million years in the past. Rock’s fossil gave the impression to be the identical species. His “specimen exhibits extra of the surface of the physique at a youthful state,” Mann says. “So it augmented the story considerably.”

Importantly, these two hatchlings didn’t present indicators of being in a tadpole-like life section. The embolomere preserved by Rock’s fossil has miniature legs, as an example, and it lacks exterior gills—the feathery appendages that salamander larvae use to breathe underwater earlier than reabsorbing them at metamorphosis. These two fossils “are principally miniaturized variations” of the adults, Mann explains. “They only progressively get larger and larger and larger till you get a large, alligator-sized animal.”

That’s the signature of direct growth—the identical progress technique utilized by mammals, birds, reptiles and even many amphibians as we speak. The research means that early tetrapods adopted this plan quite than metamorphosis, so the water-to-land transition should have initially taken a unique path. Based on Nadia Fröbisch, an evolutionary biologist at Berlin’s Pure Historical past Museum who was not concerned within the analysis, some tetrapod consultants had been anticipating a hatchling fossil with the traits of direct growth to look. “We sort of all have been ready for it,” she says. “We by no means had direct proof, and now Arjan Mann and Jason Pardo discovered the direct proof.”

on a circular piece of rock, a fossil imprint of a thin swimming creature — The tetrapod fossil collected by Richard Rock is lower than an inch lengthy. Subject Museum researchers recognized it as a larval embolomere, an early, crocodile-like animal.

Andrew Younger

Nonetheless, these two fossils alone didn’t rule out metamorphosis throughout tetrapods. Maybe the embolomeres had been a department that simply occurred to evolve towards direct growth. However Mann and Pardo examined 1000’s of juvenile fossils from different early tetrapod kin, and so they discovered no proof in any of them of metamorphosis. “It’s not one species,” Pardo says. “We are able to go to each stem group tetrapod, each animal that’s a part of this fin-to-limb transition—each animal that we discover within the Mazon Creek assemblage that falls into that class lacks something that might level to metamorphosis.”

Fröbisch thinks that there’s little to debate about Mann and Pardo’s conclusion. “I can not consider anyone who would say this … doesn’t match into the evolutionary image in any respect,” she says. Witzmann agrees. “The fossils are very lovely,” he says. “You’ve so many mushy elements preserved—cartilage, bone, pores and skin. I’d make the identical interpretation.”

This pristine preservation is a uncommon characteristic of the fossils present in Mazon Creek. In most different places, discovering specimens of hatchling animals is tough or not possible. Infants are small, and their skeletons are partly manufactured from cartilage, which degrades quickly after loss of life. It takes a selected set of circumstances to protect the minuscule packages of soppy tissue left behind by juveniles.

overhead view of a rocky peak with six people standing on the side, looking small — Individuals working in Arjan Mann’s laboratory on the Subject Museum and members of the Earth Science Membership of Illinois search for fossils at Mazon Creek on Could 8, 2025, in Braceville, Illinois.

Audrey Richardson / Chicago Tribune / Tribune Information Service through Getty Photographs

Happily, Mazon Creek was as much as the duty. Roughly 309 million years in the past, the area was an unlimited river delta, swept by seasonal floods that dragged thick, iron-rich mud into the sediment and buried many unfortunate crops and animals beneath it. In different places, micro organism would have damaged down these organisms fully. There, nevertheless, the dissolved iron within the mud surrounding the carcasses reacted with the carbon dioxide launched by micro organism. This turned the mud into siderite, an iron carbonate mineral. Inside days or even weeks of an organism’s loss of life, it will be encased in a tough mineral nodule, typically earlier than mushy tissue had time to rot away.

This geochemical course of left behind thousands and thousands of concretions: “little egg-shaped stones,” as Younger describes them, that collectors can smash or freeze-thaw to disclose the fossils inside. Normally, collectors would have needed to dig into the bottom to get well these orbs. However within the mid-Twentieth century, the coal mining trade started to strip-mine Mazon Creek, which made the concretions readily accessible within the uncovered shale.

Over the previous eight many years, Mazon Creek has garnered consideration from collectors and citizen scientists. “You’ve a coal mining web site close to a significant inhabitants throughout a time interval when folks socialized in rock swaps and had a penchant for accumulating stuff,” says Younger, who serves as a bridge between the Mazon Creek citizen-scientist neighborhood {and professional} researchers on the Subject Museum. At present, a few of these fans go to Mazon Creek a number of instances every week to gather extra concretions. “These are such sensible and educated folks,” Pardo says. “They know what they’re taking a look at higher than I do typically.”

five people stand around a table with fossils in a case — Richard Rock and Subject Museum researchers, together with Arjan Mann and Jason Pardo, meet to debate the tetrapod fossil donation and particulars of the continued research on June 14, 2024.

Andrew Younger

Since 1960, Rock has been a pre-eminent member of this neighborhood of citizen scientists. Impressed by fossil ferns at a science truthful, he went to Mazon Creek for the primary time in center college, along with his dad. He “confirmed me what a superb concretion was and confirmed me that you may smash it with a hammer,” Rock says. “So I began accumulating.”

A number of years later, his dad determined to depend what number of fossils Rock had introduced residence. “I needed to go someplace,” Rock recollects. “I got here again 4 or 5 hours later, and my dad was sitting at my desk, and I stated, ‘Effectively, did you get achieved?’ And he stated, ‘No … I stop at 50,000.’ And he stated he had created a monster.”

Rock doesn’t keep in mind selecting up the child tetrapod. However as soon as he’d heard Mann and Pardo’s ideas on the specimen, he knew he wanted to donate it to the museum. “I spotted in a short time that it was an especially necessary fossil,” Rock says. Within the museum’s collections quite than his personal, he provides, the article may “assist us study one thing concerning the previous that we don’t know.”

If metamorphosis didn’t type the evolutionary bridge from water to land, then another set of traits should have achieved the job. For now, nobody is aware of the entire story. “Generally it’s a must to destroy as a way to create,” Mann says. “We’ve simply torn down a longstanding speculation. Now we’ve got to start out from scratch.”

As for Rock, he’s happy that his 66 years of accumulating may contribute one thing to the enterprise. The fossil he discovered is “the dimensions of a dime,” he recollects. “My spouse stated, ‘How may you ever even see to choose it up?’ And as I advised her, I choose all the pieces up—doesn’t matter what it’s—since you don’t know what it’s till you get a while to look.”