We checked one spot in the middle of Kansas, and the answer has two halves. Around 100 million years ago the evidence is loud: hundreds of fossils of sea animals dug up within about 19 km, 60 of them from an age range that overlaps it — and the one rock formation the region still keeps from around then carries both land and sea, which is a clue in itself. But for 3 of the five ages this site checks — 150, 200, 250 million years ago — our sources have nothing for this spot. That may be because no rock of that age was left here, or because nobody has filled that part of the record in; we cannot tell which from what we hold, and saying so is part of the answer.
Five ages in the past of this place, each one a window rather than a day. Each says which witness spoke — and where our evidence cannot answer yet, it says that too.
“Ma” means millions of years ago. The dashed mark means our sources have nothing for that age — which is a finding, not a fault.
One formation, both answers
Witness one — the rock of the region
Across the wider region, the rock from 100 million years ago carries both kinds of environment — parts of it laid down in the sea, parts of it on land. And it is one and the same rock formation, the Dakota Fm, carrying both. That is a statement about roughly 19,000 square kilometres of region, centred about 58 km from the area — not about the ground under one street.
Witness two — the fossils dug up nearby
199 fossils dug up near this part of Kansas have an age range covering 100 million years ago: 60 from the sea, 6 from land, 133 that nobody has classified. The closest of them was found about 19 km away — near the area, never under it.
The regional column spanning 100 Ma is mixed; the fossils dug up near this place whose age range contains 100 Ma are 60 marine, 6 terrestrial and 133 unclassified. These are different claims about different things — a region tens of thousands of km² wide, and individual digs kilometres away — and both are shown. The nearby fossil record is mixed — it holds both sea animals and land animals whose age ranges overlap this age.
Rock piles up slowly, over millions of years. If the edge of a sea moves back and forth across a place during that time, one formation can end up holding layers from both — sea in some, land in others. That is one way geologists read rock like this. Our data alone cannot say it happened that way here; it can only say the formation holds both, so that is where this page stops.
Travel back in time
This ground has moved a very long way. A plate model can wind the continents backwards and say roughly where it was — roughly being the important word.
250
million years agojump to the evidence250 million years ago, the plate model puts this ground almost on the equator. This is one of the ages the models argue about most: published reconstructions put it as much as 5.4° of latitude apart, which is several hundred kilometres. Treat it as one model's answer, not a photograph.
200
million years agojump to the evidence200 million years ago, the plate model puts this ground about 12° north of the equator. Published models agree more closely here, within about 2.9° of latitude, but it is still one model's answer rather than a photograph.
150
million years agojump to the evidence150 million years ago, the plate model puts this ground about 21° north of the equator. Published models disagree by about 4.5° of latitude here — a few hundred kilometres — so it is one model's answer, not a photograph.
100
million years agojump to the evidence100 million years ago, the plate model puts this ground about 34° north of the equator. Published models disagree by about 3.8° of latitude here — a few hundred kilometres — so it is one model's answer, not a photograph.
66
million years agojump to the evidence66 million years ago, the plate model puts this ground about 40° north of the equator. Published models agree more closely here, within about 1.7° of latitude, but it is still one model's answer rather than a photograph.
What was the water doing?
Five ages, oldest first. Each one has two kinds of witness — the rock of the wider region, and the fossils dug up near the area — and they are kept apart on purpose, because they are answers to different questions.
Each age here is a marker on the timeline, not a single day. The evidence that belongs to it comes with an age range of its own that overlaps the marker — so it can tell you what this stretch of time was like, and never what was happening on one exact date.
Our evidence has no witness here
Around 250 million years ago
250 million years ago, the plate model puts this ground almost on the equator. This is one of the ages the models argue about most: published reconstructions put it as much as 5.4° of latitude apart, which is several hundred kilometres. Treat it as one model's answer, not a photograph.
An open question
Neither of the evidence sources we use can answer this one: our regional rock record holds no unit for 250 million years ago at this point, and no fossil dug up nearby covers that age either. That is a real gap in the evidence, not a gap in the past — and saying so is more useful than guessing.
Our evidence has no witness here
Around 200 million years ago
200 million years ago, the plate model puts this ground about 12° north of the equator. Published models agree more closely here, within about 2.9° of latitude, but it is still one model's answer rather than a photograph.
An open question
Neither of the evidence sources we use can answer this one: our regional rock record holds no unit for 200 million years ago at this point, and no fossil dug up nearby covers that age either. That is a real gap in the evidence, not a gap in the past — and saying so is more useful than guessing.
Our evidence has no witness here
Around 150 million years ago
150 million years ago, the plate model puts this ground about 21° north of the equator. Published models disagree by about 4.5° of latitude here — a few hundred kilometres — so it is one model's answer, not a photograph.
An open question
Neither of the evidence sources we use can answer this one: our regional rock record holds no unit for 150 million years ago at this point, and no fossil dug up nearby covers that age either. That is a real gap in the evidence, not a gap in the past — and saying so is more useful than guessing.
One formation, both worlds
Around 100 million years ago
100 million years ago, the plate model puts this ground about 34° north of the equator. Published models disagree by about 3.8° of latitude here — a few hundred kilometres — so it is one model's answer, not a photograph.
The rock of the region
Across the wider region, the rock from 100 million years ago carries both kinds of environment — parts of it laid down in the sea, parts of it on land. And it is one and the same rock formation, the Dakota Fm, carrying both. That is a statement about roughly 19,000 square kilometres of region, centred about 58 km from the area — not about the ground under one street.
The fossils dug up nearby
199 fossils dug up near this part of Kansas have an age range covering 100 million years ago: 60 from the sea, 6 from land, 133 that nobody has classified. The closest of them was found about 19 km away — near the area, never under it.
The regional column spanning 100 Ma is mixed; the fossils dug up near this place whose age range contains 100 Ma are 60 marine, 6 terrestrial and 133 unclassified. These are different claims about different things — a region tens of thousands of km² wide, and individual digs kilometres away — and both are shown. The nearby fossil record is mixed — it holds both sea animals and land animals whose age ranges overlap this age.
Only the fossils speak
Around 66 million years ago
66 million years ago, the plate model puts this ground about 40° north of the equator. Published models agree more closely here, within about 1.7° of latitude, but it is still one model's answer rather than a photograph.
The rock of the region
No rock layer from 66 million years ago survives in the regional record here, so the rock has nothing to say about this age.
The fossils dug up nearby
One fossil dug up near this part of Kansas has an age range covering 66 million years ago: 1 from the sea, 0 from land. It was found about 61 km away — near the area, never under it.
What was dug up nearby?
Only one of the five ages has fossils binned to it at all — every other age on this page has none. Each fossil below was found somewhere near here, never underneath, so each one comes with the distance to where it was actually dug up.
Around 100 million years ago
An Elasmosauridae — its group, Reptilia, is reptiles and their extinct relatives; this broad group includes animals such as lizards, snakes, turtles, crocodilians and many prehistoric reptiles — from 100 million years ago was dug up about 27 km from here, in Ellsworth County.
A Megacephalosaurus eulerti — its group, Reptilia, is reptiles and their extinct relatives; this broad group includes animals such as lizards, snakes, turtles, crocodilians and many prehistoric reptiles — from around this time (its own age range is 89.8–93.9 million years) was dug up about 57 km from here, in the Greenhorn Limestone.
A Xiphactinus audax — its group, Osteichthyes, is bony fishes and their relatives — most of the familiar fish a child could name belong here — from 100 million years ago was dug up about 52 km from here, in the Greenhorn Limestone (Lincoln Limestone), Russell County.
A Squalicorax falcatus — its group, Chondrichthyes, is the sharks, rays and their relatives, whose skeletons are made of cartilage rather than bone — from 100 million years ago was dug up about 27 km from here, in the Greenhorn Limestone (Lincoln Limestone), Ellsworth County.
A Praescabrotrigonia emoryi — its group, Bivalvia, is the two-shelled animals, like clams, oysters and mussels — from around this time (its own age range is 100.5–113.2 million years) was dug up about 14 km from here, in the Kiowa, Ellsworth County.
A Cardita belviderensis — its group, Bivalvia, is the two-shelled animals, like clams, oysters and mussels — from around this time (its own age range is 100.5–113.2 million years) was dug up about 14 km from here, in the Kiowa, Ellsworth County.
A fossil the database records without an accepted name from around this time (its own age range is 100.5–113.2 million years) was dug up about 14 km from here, in the Kiowa, Ellsworth County.
We show these places to the nearest few kilometres rather than pinning them exactly. The scientists who recorded them know the spot far better than that — the full record is one click away in the Paleobiology Database, and it is free for anyone to read. We round them here because a map made for children is not a map for digging things up, not because anything is being hidden.
One of the animals that swam in that sea
The fossils above were dug up near this spot. This one was not — it came from Logan County, about 200 kilometres west of here, and it is in the Smithsonian’s collection today. It is worth showing anyway, because it is one of the long-necked sea reptiles whose family the rock around here also holds: a real animal, from this state, from the sea this page is about.
Real photographBones of Thalassiosaurus ischiadicus, a long-necked sea reptile of the family Elasmosauridae, dug up in Logan County, Kansas in 1927.Found in Logan County, western Kansas — about 200 km from the place this page is about, not underneath it.USNM V11910, collected by George F. Sternberg in Logan County, western Kansas, in 1927. The museum record gives its family as Elasmosauridae and its age as Late Cretaceous.Smithsonian National Museum of Natural History (USNM V11910), CC0 · CC0-1.0 · Museum record
What changed?
The ground itself travelled. The plate model puts it almost on the equator 250 million years ago and near 40° north today — the whole width of the tropics, carried by the plate it sits on.
The rock at the surface here today is what the geological map of this exact point returns: Mesozoic sedimentary rocks (Late Cretaceous), Late Cretaceous sedimentary (Late Cretaceous), Loess (Cenozoic).
How the land rose, or where the water went, is not something our datasets answer — so this page does not say.
Try it yourself
The animals whose fossils turn up in these fields swam in water. Water like it is still going round the cycle, and some of it is in the tap in your kitchen. Work out how much of your next glass has been through a dinosaur.
457 fossils have been dug up near this spot from around 100 million years ago — and 133 of the 199 closest in age have never been sorted into sea or land at all.
One rock formation here records both land and sea, which is a puzzle worth sitting with.
For 3 of the five ages on this page — 150, 200, 250 million years ago — our sources have nothing of either kind.
For three of the five ages, our sources have nothing for this spot. That is not the same as nobody knowing. Is “we have not looked here yet” a scientific answer? What would you go and look for?
How sure are we?
Column facts describe an area of thousands to tens of thousands of km², centred tens of kilometres from the town coordinate. They are claims about a region, never about the rock beneath the town.
Fossil facts are a bounding-box sample around the town, each with its own distance from it; a fossil is never "here". The absence of fossils is not evidence of the absence of life — only of the absence of a recorded, published dig in this box.
Positions are model outputs, not observations. Independent plate models disagree by hundreds of kilometres at these ages, and that spread is the honest size of the uncertainty.
The land/sea question is answered only by the regional rock and the local fossils, separately, and never by the reconstruction — which says where this ground was and cannot say whether it was wet. There is deliberately no single field holding a one-word answer, because answering in one word would require merging a regional claim with a local one (CLAUDE.md rule 5). The nearby fossils are reported as a census of what has been found — which kinds are present, and how many of each — and never counted into a verdict: occurrence records are not statistically equivalent observations, so a plurality of them cannot establish an environment (science review, 2026-08-30).
Fossils are binned to their nearest slice age by age-range midpoint, with boundaries at the inter-slice midpoints 83, 125, 175 and 225 Ma. Those boundaries are an editorial choice, not a published stratigraphic scheme; a reviewer may prefer stage boundaries. Every occurrence keeps its own age range so the choice can be re-examined.
Sources
Macrostrat — the rock of the regionRead from version 2.3.9 of its data service on 27 August 2026.Peters, S.E. et al. Macrostrat: a platform for geological data integration and deep-time research. https://macrostrat.org, accessed on (date)Palaeogeography: Wright, N., Zahirovic, S., Müller, R. D., and Seton, M. Towards community-driven paleogeographic reconstructions: integrating open-access paleogeographic and paleobiology data with plate tectonics. Biogeosciences 10:1529-1541
The Paleobiology Database — the fossils dug up nearbyPBDB publishes no dataset version string; the data-service path (data1.2) and the datainfo access_time bound this claim.Fossil occurrence data from the Paleobiology Database (https://paleobiodb.org), released under CC0 1.0.Palaeo-coordinate cross-check (Paleobiology Database `pgm=gplates`): Wright et. al., 2013; Towards community-driven paleogeographic reconstructions.Palaeo-coordinate cross-check (Paleobiology Database `pgm=scotese`): Scotese, C.R., 2021. An Atlas of Paleogeographic Maps: The Seas Come In and the Seas Go Out, Annual Reviews of Earth and Planetary Sciences, v. 49, p. 669-718.Palaeo-coordinate cross-check (Paleobiology Database `pgm=seton`): Seton et. al., 2012; Global continental and ocean basin reconstructions since 200 Ma.
The EarthByte plate model — where this ground used to beMULLER2019 version 3.0, run with pyGPlates 1.0.0, licensed CC BY 4.0.GPlates: Müller, R. D., Cannon, J., Qin, X., Watson, R. J., Gurnis, M., Williams, S., Pfaffelmoser, T., Seton, M., Russell, S. H. J., Zahirovic S. (2018). GPlates: Building a virtual Earth through deep time. Geochemistry, Geophysics, Geosystems, 19, 2243-2261. https://doi.org/10.1029/2018GC007584Reconstructions computed with the GPlates Web Service (EarthByte Group, The University of Sydney).Plate model: Müller, R. D., Zahirovic, S., Williams, S. E., Cannon, J., Seton, M., Bower, D. J., Tetley, M. G., Heine, C., Le Breton, E., Liu, S., Russell, S. H. J., Yang, T., Leonard, J., and Gurnis, M. (2019), A global plate model including lithospheric deformation along major rifts and orogens since the Triassic. Tectonics, vol. 38, https://doi.org/10.1029/2018TC005462. Licensed CC BY 4.0.Plate model: Zahirovic, S., Eleish, A., Doss, S., Pall, J., Cannon, J., Pistone, M., Tetley, M. G., Young, A., & Fox, P. (2022). Subduction kinematics and carbonate platform interactions. Geoscience Data Journal, 9(2), p.371-383. Licensed CC BY 4.0.Coastline and static-polygon data by the EarthByte Group, licensed CC BY 3.0 Unported.
This record was assembled on from the datasets above. The ancient positions are reconstructions from a published plate model, not observations.
