![Oviraptor eggs, late Cretaceous, Mongolia, China](https://a4.pbase.com/g9/43/815143/3/153359376.R13V7Sit.jpg) Oviraptor eggs, late Cretaceous, Mongolia, China |
![Precursor to the horse, Protorohippus venticolus, from the Fossil Butte Member of the Eocene, Green River Formation, WY](https://a4.pbase.com/g9/43/815143/3/152612482.QXwg9lnQ.jpg) Precursor to the horse, Protorohippus venticolus, from the Fossil Butte Member of the Eocene, Green River Formation, WY |
![Bass, Priscacara liops, Eocene Green River Formation, Kemmerer, WY](https://a4.pbase.com/g1/43/815143/3/130430198.4Rqqc29B.jpg) Bass, Priscacara liops, Eocene Green River Formation, Kemmerer, WY |
![Keichousauris hui, late Triassic, Guanling Fm., Xingiji, Guizhou, China](https://a4.pbase.com/g9/43/815143/3/153359585.oWMC7hKP.jpg) Keichousauris hui, late Triassic, Guanling Fm., Xingiji, Guizhou, China |
![Herring, Knightia alta, Eocene Green River Formation, Kemmerer, WY](https://a4.pbase.com/g1/43/815143/3/130433095.u84iloUJ.jpg) Herring, Knightia alta, Eocene Green River Formation, Kemmerer, WY |
![Fossil Sting Ray, Asterotrygon maloneyi, Fossil Butte Member of the Eocene Green River Formation, WY](https://a4.pbase.com/g9/43/815143/3/152612667.2KiLcHaE.jpg) Fossil Sting Ray, Asterotrygon maloneyi, Fossil Butte Member of the Eocene Green River Formation, WY |
![Fossil fish and palm fronds, Fossil Butte Member of the Eocene Green River Formation, Fossil, WY](https://a4.pbase.com/g9/43/815143/3/152612685.MYMvebYA.jpg) Fossil fish and palm fronds, Fossil Butte Member of the Eocene Green River Formation, Fossil, WY |
![Fossilized skull of a Mosasaur, a marine reptile of the Cretaceous Period, from Morocco.](https://a4.pbase.com/g9/43/815143/3/152612602.Oxf69Txc.jpg) Fossilized skull of a Mosasaur, a marine reptile of the Cretaceous Period, from Morocco. |
![Trilobite: Paradoxides, Cambrian, Anti-Atlas Mountains, Morocco](https://a4.pbase.com/g1/43/815143/3/130427536.e0mha4hK.jpg) Trilobite: Paradoxides, Cambrian, Anti-Atlas Mountains, Morocco |
![Trilobites in a mating assemblage: Homotelis bromidensis, Ordovician Bromide Formation, Carter County, OK](https://a4.pbase.com/g1/43/815143/3/130426604.HMOEj5Uz.jpg) Trilobites in a mating assemblage: Homotelis bromidensis, Ordovician Bromide Formation, Carter County, OK |
![Trilobites: Phacops rana, Devonian Silica Shale, Sylvania, OH](https://a4.pbase.com/g1/43/815143/3/130426798.499mIlkE.jpg) Trilobites: Phacops rana, Devonian Silica Shale, Sylvania, OH |
![Ammonite replaced by pyrite](https://a4.pbase.com/g9/43/815143/3/152626368.9j3jeNb4.jpg) Ammonite replaced by pyrite |
![Trilobite: Elrathia kingii, Cambrian Wheeler Shale, Millard County, UT](https://a4.pbase.com/g1/43/815143/3/130433100.g50oCoq6.jpg) Trilobite: Elrathia kingii, Cambrian Wheeler Shale, Millard County, UT |
![Crinoid, Mississippian, Montgomery County, IN](https://a4.pbase.com/g1/43/815143/3/130465432.1zfy9nmt.jpg) Crinoid, Mississippian, Montgomery County, IN |
![Conophyton Stromatolite structures in Precambrian Helena Formation, Glacier National Park, MT](https://a4.pbase.com/g9/43/815143/3/152595155.xCp9J7pJ.jpg) Conophyton Stromatolite structures in Precambrian Helena Formation, Glacier National Park, MT |
![Ammonite, Madagascar](https://a4.pbase.com/g9/43/815143/3/152626313.xBMHTqOV.jpg) Ammonite, Madagascar |
![Trilobite: Asaphus cornutus, Ordovician, St. Petersburg, Russia](https://a4.pbase.com/g1/43/815143/3/130427017.yOg3vsBD.jpg) Trilobite: Asaphus cornutus, Ordovician, St. Petersburg, Russia |
![Ammonite assemblage, Lower Jurassic, North Yorkshire, U.K.](https://a4.pbase.com/g9/43/815143/3/153358061.InhAprP7.jpg) Ammonite assemblage, Lower Jurassic, North Yorkshire, U.K. |
![Trilobites: Asphus punctata, cast and mold, middle Ordovician, St. Petersburg, Russia](https://a4.pbase.com/g9/43/815143/3/153358063.FC0Hdz3q.jpg) Trilobites: Asphus punctata, cast and mold, middle Ordovician, St. Petersburg, Russia |
![Cross section of an ammonite, Madascar](https://a4.pbase.com/g9/43/815143/3/152625165.NdY86BW0.jpg) Cross section of an ammonite, Madascar |
![Dragonfly, Carduluganphus tuberculatus, Crato Fm., lower Cretaceous, Ceara, Brazil](https://a4.pbase.com/g9/43/815143/3/153359519.l9K5cFWu.jpg) Dragonfly, Carduluganphus tuberculatus, Crato Fm., lower Cretaceous, Ceara, Brazil |
![Shrimp, Solenhoffen Limestone, Jurassic, Germany](https://a4.pbase.com/g9/43/815143/3/153359553.yyhJccDc.jpg) Shrimp, Solenhoffen Limestone, Jurassic, Germany |
![Ammonite](https://a4.pbase.com/g1/43/815143/3/130422766.39iOVbde.jpg) Ammonite |
![Trilobite: Thysanopeltis speciosa, middle Devonian, Zerg, Morocco](https://a4.pbase.com/g9/43/815143/3/153362669.S8IUpBo3.jpg) Trilobite: Thysanopeltis speciosa, middle Devonian, Zerg, Morocco |
![Opalized Ammonite,](https://a4.pbase.com/g9/43/815143/3/157485138.Mqp23UvB.jpg) Opalized Ammonite, |
![Devonian Trilobite, Phacops rana, Silica shale, Sylvania, Ohio](https://a4.pbase.com/g12/43/815143/3/172640834.Bt4Bc5IB.jpg) Devonian Trilobite, Phacops rana, Silica shale, Sylvania, Ohio |
![Selenopeltis, Ordovician Trilobite](https://a4.pbase.com/g12/43/815143/3/172643954.XsRNnar5.jpg) Selenopeltis, Ordovician Trilobite |