GEOLOGICAL HORIZONS. 



145 



Recent. 

 I Quaternary. 



Tapir. Peccary, Bison. 

 Bos, Equus, Tapirus, Dicoti 



, Megatherium, Mylodj 



I Pliocene. 



; Equus Beds. 

 Plioluppus Beds. 



Equus, Tapirus, Elephas. 



\Pliohippus, Tapiravus, Mastodon, Procamelus. 



(Aceratherium, Bos, Morotherium, PlatygonuK. 



, Miohippus Beds. 

 Miocene. Oreodon Beds. 



Brontotheriuin Bed; 



Miohippus, Diceratherium, Thinohyus, Protoceras. 

 (Oreodon, Eporeodon, Sycenodon, Moropus, Ictops. 

 (ECyracodon, Agnochcerus, Colodon, Leptochcerus. 

 \ Brontotherium, Brontops, AUops, Titanops, Titano- 

 t therium, Mesohippus, Ancodus, Entelodon. 



Diplaeodon Beds. 

 Dinoceras Beds. 

 Heliobatis Beds. 

 Coryphodon Beds. 



Diplaeodon. Epihippus, Amynodon, Eomeryx. 

 sDinocei-as, Tinoceras, VintatheHum, Palceo&yops. 

 I Orohippus, Hyrachyus, Colonoceras, JSomacodon. 

 Heliobatis, Amia, Lepidostetis, Asineops, Clupea. 

 \ Coryphodon, Eohippus, Eohyus, Etyracops, Earahyus. 

 ^Lemurs, Ungulates, Tillodonts. Rodents, Serpents. 



Ceratops Beds of 

 Laramie Series. 



Ceratops, Triceratops, Claosaurus, Ornithomimus, 

 Mammals, Cimolomys, Bnpriodon, Selenacodon, 

 Xanomyops, Stagodon. Birds, Cimolopteryx. 



Cretaceous. 



Fox Hills Group . 



Colorado Series, or 

 Pteranodon Beds. 



Dakota Group. 



Birds with Teeth. Sesperornis, Ichthyornis, Apatornis 

 Mosasaurs, Edestosaurus, Lestosaurus, Tylosaurus. 

 Pterodactyls, Pteranodon. Plesiosaurs, Turtles. 



H Jurassic. 



Atlanto^aurus Beds 

 Baptanodon Beds. 

 Hallopus Beds. 



'arboniferous 



Coal Measures, or 

 Eosaurus Beds. 



Subcarbonif erou s , 

 i or Sauropus Beds. 



; Dinosaurs, Brontosaurus, Morosaurus. Eiplodacus, 



Stegosaurus, Camptosaurus, Ceratosaurus. Mam- 



{ mals, Dryolestes, Xtylacodon, Tinodon, Ctenacodon. 



First Mammals, Dromatherium. First Dinosaurs, 

 AncJiUauti.cs, Ammosaurzis, Bathygnathus, Clepsy- 

 saurus. Many footprints. Crocodiles, Belodon. 



Fishes, Catopterus, Ischypterus, Ptycholepis. 



First Reptiles ( 1) Eosaurus. Amphibians, Baphetes, 

 Dendrerpeton, Sylonomits, Pelion. Footprints, 

 Anthracopus, Allopus, Baropus, Dromopus, Sylo- 

 pus, Limnopus, Xasopus. 



First known Amphibians (Labyrinthodonts). 

 Footprints, Sauropus, Thenaropus. 



Dinichthys Beds. 

 Lower Devonian. 



Dinichthys, Acanthodes, Bothriolepis, Chirolepis, Cla- 

 dodus, Eipterus, Titanichthys. 



Silurian. 



Upper Silurian. 



Lower Silurian. 



First known Fishes. 



r~?jg£5^^sf Cambrian. Primordial. 



No Vertebrates known. 



Fig. 1. — Geological Horizoxs of Vertebrate Fossils in North America. 

 16 GEOL, FT 1 10 



