Which dinosaurs lived at the same time?
Of the 4,851 possible pairs among the 99 genera on this site, 1,412 have fossil ranges that overlap by at least part of a stage. Another 331 pairs meet exactly at a stage boundary, and the other 3,108 are separated by a gap of time. Overlap in time is the weaker test, though. Two genera can share a stage and still have lived on different continents. The stronger evidence is a single fossil collection that holds both.
How overlap is counted
Every range on FossilRange runs from the base of one geological stage to the top of another (see How to read a dinosaur fossil range). Two ranges overlap when they share at least one stage. When one range ends at exactly the boundary where the other begins, the pair “meets”: the data puts them in neighbouring stages and cannot say whether they were alive at the same moment.
Overlaps pile up where many genera share a stage. The five busiest stages on this site are:
| Stage | Genera alive | Pairs inside the stage |
|---|---|---|
| Campanian | 39 | 741 |
| Maastrichtian | 32 | 496 |
| Tithonian | 22 | 231 |
| Kimmeridgian | 19 | 171 |
| Sinemurian | 9 | 36 |
A genus counts in every stage of its range. “Pairs inside the stage” is the number of two-genus combinations among the genera alive in it.
The Campanian and Maastrichtian together account for most of the overlapping pairs, because so many of the genera here come from those last two stages of the Cretaceous. That is a feature of the fossil record and of this site’s selection, which holds genera with at least 12 records. It is not a measure of how crowded the Late Cretaceous really was.
Same time, same rocks
The Paleobiology Database groups fossils into collections: the finds from one site and one rock layer. When two genera are listed in the same collection, they were buried in the same deposit. FossilRange counts these shared collections for every genus, keeping each genus’s eight most frequent companions. Across the site that gives 327 distinct pairs. These ten are found together most often:
| Pair | Ranges (Ma) | Shared collections |
|---|---|---|
| Allosaurus and Camarasaurus | 154.8–145 / 154.8–145 | 76 |
| Allosaurus and Stegosaurus | 154.8–145 / 154.8–145 | 53 |
| Camarasaurus and Stegosaurus | 154.8–145 / 154.8–145 | 53 |
| Saurornitholestes and Troodon | 83.6–66 / 83.6–66 | 50 |
| Camarasaurus and Diplodocus | 154.8–145 / 154.8–145 | 46 |
| Allosaurus and Diplodocus | 154.8–145 / 154.8–145 | 42 |
| Apatosaurus and Camarasaurus | 154.8–145 / 154.8–145 | 39 |
| Allosaurus and Apatosaurus | 154.8–145 / 154.8–145 | 37 |
| Diplodocus and Stegosaurus | 154.8–145 / 154.8–145 | 37 |
| Allosaurus and Camptosaurus | 154.8–145 / 154.8–145 | 31 |
Where the two genera’s own counts differ slightly (synonyms are counted per genus), the higher figure is shown.
9 of the ten pairs are made of genera recorded in the Morrison Formation, the Late Jurassic rock unit of the western United States. The Morrison holds 15 of the genera on this site, and 13 of them have exactly the same range, 154.8–145 Ma. For the Morrison genera, overlap in time and shared collections tell the same story.
Tyrannosaurus and Triceratops
The most famous pair on the site also has one of the clearest records. Both ranges are 72.1–66 Ma, and the database lists them together in 24 collections. That is 29% of the 82 collections that hold Tyrannosaurus, and 15% of the 161 that hold Triceratops. Triceratops is the most frequent companion of Tyrannosaurus; the most frequent companion of Triceratops is Edmontosaurus, in 27 collections.
Same age, different continents
Of the 1,412 overlapping pairs, 557 have no country in common at all. Those genera were never found in the same collection, however closely their ranges match. Tarbosaurus has the same range as Tyrannosaurus, but its records come from Mongolia, China and Russia, while those of Tyrannosaurus come from the United States, Canada and Mexico. Kentrosaurus, a plated dinosaur from Tanzania, shares the Tithonian with Stegosaurus, whose records are from the United States, Portugal and China.
Country names are present-day borders. In the Mesozoic the continents sat in different positions, so two sites that are far apart today were not necessarily as far apart then, and the reverse. The point stands either way: the fossils of these pairs have not turned up together.
Overlap can also be partial. Spinosaurus (100.5–93.9 Ma) sits inside the longer range of Carcharodontosaurus (121.4–93.9 Ma), and the two are listed together in 20 collections. Carcharodontosaurus is by far the most frequent companion of Spinosaurus: the next, Baryonyx, appears with it in 1 collection.
Check a pair yourself
The compare tool gives the overlap or gap for any two of the 99 genera, the share of the shorter range they have in common, and the number of shared collections where the data lists one. To see everything alive at one moment, type a number of millions of years into Who lived when. Try Allosaurus and Camarasaurus, the pair found together most often, or Tyrannosaurus and Tarbosaurus, two genera of the same age with no shared country.
Sources
- The Paleobiology Database (paleobiodb.org), data service v1.2, licensed CC BY 4.0; retrieved 2026-10-27. All counts, ranges and pairs in this article are calculated by FossilRange from that download.
- International Commission on Stratigraphy, International Chronostratigraphic Chart: stage names, base ages and colours.
- FossilRange, Data & method: which genera are included and how ranges are derived.