Photo and illustration of the fossil of Jeanerpeton mazonensis.
Credit: Allison Sefcovic. © Field Museum.
One of the recurring problems for young-Earth creationism is that Earth’s history contains so much life before the supposed beginning of Earth’s history. A newly recognised fossil species from Illinois adds another example: a small, amphibian-like animal that lived approximately 309 million years ago, when the area around modern Chicago was a swampy river delta. That places it more than 300 million years before the creation event that biblical literalists insist accounts for all life on Earth. Explaining away a discrepancy of that magnitude requires rather more than pointing to an uncertainty in a scientific paper.
The animal is Jeanerpeton mazonensis, described by Allison J. Sefcovic, Payton J. Kohlberg and colleagues in a new paper in the Journal of Vertebrate Paleontology. Its recognition resulted from a fresh examination of a fossil already held in a museum collection. Previously assigned to Amphibamus grandiceps, the specimen proved sufficiently different in its skull and skeleton to warrant a genus and species of its own. The authors also suggest that other known specimens conceal more diversity among these early amphibamiforms than has previously been recognised.
The fossil comes from the exceptionally productive Mazon Creek deposits. Its preservation includes a body outline, scales, tiny abdominal skeletal elements called gastralia, and even impressions of the eyes. The genus honours the two student lead authors’ mothers, both named Jean. This is a reminder that important discoveries can begin with someone taking a closer look at a specimen collected long ago.
Left: Allison Sefcovic and Payton Kohlberg hold epoxy sculptures of their new species, Jeanerpeton mazonensis.
Photo credit: Arjan Mann. © Field Museum.
There is also a useful lesson here about how science works. An earlier identification was a conclusion open to revision. Re-examining the evidence has revealed diversity that the old classification obscured. Creationists may welcome the admission that scientists have changed their minds, but the revision offers no support for their preferred alternative. Recognising a different branch of an ancient evolutionary family tree does not make that tree disappear.
Nor does rapid burial provide an escape into the story of Noah’s Flood. The museum describes sediment accumulating rapidly over organisms in a river delta—a local setting capable of preserving unusual detail. Rapid burial and a recent, worldwide catastrophe are entirely different claims; evidence for the former does not establish the latter. What this fossil offers is another opportunity to reconstruct a world hundreds of millions of years older than the young-Earth narrative allows.
Mazon Creek — a window into a 309-million-year-old world. The Mazon Creek deposits of north-eastern Illinois are among the world’s outstanding fossil sites. Their fossils occur mainly in the Francis Creek Shale, approximately 309 million years old, from the late Carboniferous Period. At that time, this part of North America lay near the equator. The rocks record a tropical coastal landscape undergoing changes in sea level and climate, rather than anything resembling modern Illinois.The paper in the Journal of Vertegrate Paleontology was accompanied by a news item from the Field Museum.:
What lived there?
The deposits preserve hundreds of species, including tree ferns, giant clubmoss relatives, horsetails, insects, spiders, millipedes, crustaceans, worms, molluscs, fish and early tetrapods. They therefore reveal much more than the history of one amphibian-like animal: they help reconstruct the communities and habitats surrounding it. Among the most celebrated inhabitants is the peculiar Tully monster, Tullimonstrum gregarium, whose evolutionary relationships remain disputed.
Why is the preservation so exceptional?
Many fossils are enclosed in concretions—rounded masses of sediment cemented by the iron-carbonate mineral siderite. Burial and early mineral formation around organic remains helped preserve details normally destroyed during decay or crushed as sediment compacted. Mazon Creek can consequently preserve soft-bodied animals and delicate anatomical features, as well as bones, shells and leaves. Some plant specimens even retain three-dimensional cellular detail. A fossil deposit with exceptional preservation of this kind is called a Konservat-Lagerstätte.
Several habitats, rather than one mixed collection
Palaeontologists traditionally distinguish the Braidwood assemblage, rich in land plants and animals alongside freshwater and brackish-water organisms, from the more marine Essex assemblage. These represent different parts of an ancient coastal system; land organisms could also wash into aquatic environments.
A recent analysis of 283,821 concretions supported this broad distinction and recognised two subdivisions within the Essex assemblage. The distribution of fossils therefore carries ecological information: different communities occupied different environments across the ancient coastline.
A record of environmental change
The fossil-bearing shale overlies the Colchester Coal, formed from accumulated peat. According to the Illinois State Geological Survey, rising sea level inundated the peat-forming lowlands as the region passed from a glacial interval towards an interglacial. The succession records changing environments—peat accumulation followed by inundation and sediment deposition—within a much longer geological history.
Why old collections still matter
Many specimens were recovered by amateur collectors, particularly from material exposed by coal mining, and later entered museum collections. Those collections remain active research resources. The recognition of Jeanerpeton mazonensis shows how re-examining a familiar fossil can reveal previously overlooked diversity. Fossils do not exhaust their scientific value when they are collected or first given a name.
Rapid burial helps explain the preservation of individual organisms, but it does not establish a worldwide flood. Mazon Creek’s scientific importance lies in the combination of anatomy, fossil distribution, sedimentary setting and geological succession—all evidence that must be explained together.
Mother of amphibians: New species of proto-amphibian described by two student scientists, named in honor of their moms
309 million years ago, long before the dinosaurs, the area around Chicago was a swampy river delta swarmed with early land-dwellers, giant insects, and strange swimming animals. What once was a hot bed for new forms of life to flourish and evolve, became one of today’s richest Carboniferous period fossil deposits. Two student-scientists from the Field Museum have just described the latest animal discovered at this location—and they named it after their mothers, who both happen to be named Jean.
Meet Jeanerpeton mazonensis, meaning “Jean’s crawler from Mazon Creek." Described in the Journal of Vertebrate Paleontology, J. mazonensis is an early ancestor of today’s amphibians. Think of a salamander, but make it squat and chubby like a frog.
Because the Mazon Creek area was a river delta during the Carboniferous period, sediment was quickly deposited on dead animals and plants. That’s a perfect recipe for fossilization. Today, Mazon Creek is home to one of the world’s best fossil sites, with fossils that preserve records of soft tissues and fine details that are normally lost.
What's really cool about Mazon Creek is that it preserves all of these unusual details—things like toe pads and body outlines. In the fossil of Jeanerpeton, we can see some of the scales on its back and tiny ‘belly ribs’ called gastralia. You can even see the eye impressions! It's so cool to see.
Allison J. Sefcovic, co-lead author.
Negaunee Integrative Research Center
Field Museum of Natural History
Chicago, Illinois, U.S.A.
These findings point to a 309-million-year-old origin of classic traits we see in today’s frogs and salamanders.
The fossil specimen was found many years ago by an amateur collector and donated to the Field Museum. At a glance, the fossil was classified as another species with a well-established presence in the region, Amphibamus grandiceps.
Sometimes, poorly-understood specimens are lumped together into what scientists call a “waste bin taxon,” which serves as a metaphorical dumping ground for specimens that seem related but haven’t been well-studied yet.
What we're finding from the Field Museum’s collection are a bunch of things that historically were grouped together into this waste bin taxon known as Amphibamus grandiceps. Jeanerpeton is one of those species. And now, we’ve found enough evidence to support it being an anatomically distinct animal. With this publication, we officially pull Jeanerpeton out of this waste bin taxon.
Dr Cam So, co-author
Negaunee Integrative Research Center
Field Museum of Natural History
Chicago, Illinois, U.S.A.
The study’s co-lead authors, Payton Kohlberg and Allison Sefcovic, were part of last year’s cohort of Women in Science Interns at the Field Museum, a program that champions young women to pursue careers in science and museums. They, along with So, are all part of the lab group of Arjan Mann, the Field’s assistant curator of fossil fishes and early tetrapods in the Negaunee Integrative Research Center.
Before working in the Mann Lab, I didn’t know much about paleontology. My experience at the Field and in the Women in Science program has made me more confident in my abilities to try something new. It is scary to take on a project when you feel like you don’t know as much as you should, but I learned with my practical experience that it is possible to overcome that fear with hard work.
Payton J. Kohlberg, co-lead author.
Negaunee Integrative Research Center
Field Museum of Natural History
Chicago, Illinois, U.S.A.
The description of J. mazonensis opens a door for researchers as they continue to chronicle the biodiversity that once lived in Mazon Creek. Together, their discoveries make a detailed mosaic of what life looked like in Illinois more than 300 million years ago.
Publication:
Jeanerpeton mazonensis illustrates how our understanding of evolution becomes more detailed as scientists return to the evidence with fresh questions. A specimen once assigned to a familiar species has revealed another branch of the early tetrapod family tree. Revising its classification does not undermine evolution; it improves our understanding of the diversity that evolution produced. The fossil has not changed, but our ability to interpret it has advanced.
For young-Earth creationism, the chronological problem remains insurmountable without rejecting the geological evidence. This animal inhabited a functioning ecosystem approximately 309 million years ago, alongside plants and other animals with evolutionary histories of their own. Its burial belongs within the history of an ancient coastal landscape. The fact that rapid burial helped preserve its remains provides no justification for replacing that history with a recent global flood.
Nor does recognising amphibian-like features require us to imagine evolution working towards modern frogs and salamanders. Jeanerpeton was an animal living in its own environment, not a preliminary model awaiting a designer’s improvements. Its particular combination of characteristics helps researchers investigate evolutionary relationships, without requiring either a predetermined destination or a claim that it was the direct ancestor of any living species.
The contrast is straightforward. Science can revisit a museum drawer, question an inherited identification and recover information that previous researchers overlooked. Creationism begins with an answer that the evidence must be made to accommodate. Here, as so often, the productive questions concern how ancient organisms lived, diversified and were related—not how to squeeze hundreds of millions of years into a chronology devised long before anyone understood the rocks.
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