SUMMARY OF MESOZOIC HISTORY 279 



TABULAR SUMMARY OF MESOZOIC LIFE — Continued 



Molluscoids 



Mollusks 



Arthropods 



Vertebrates 



Bryozoans: 

 Present. 



Brachiopods : Only 

 a few genera and 

 species remain, 

 and these are of 

 pretty modern as- 

 pect. 



Pelecypods and Gastro- 

 pods: Abundant and sim- 

 ilar to Jurassic, but more 

 modern. 



Cephalopods: Still very 

 abundant and much like 

 those of the Jurassic with 

 uncoiled to even straight 

 Ammonoids (e.g. Bacu- 

 lites) common. Ammo- 

 noids become nearly ex- 

 tinct. Dibranchs com- 



Eucrustaceans: Much 

 like Jurassic, but 

 Brachyurans (Crabs) 

 greatly increased. 



Insects: Much like 

 Jurassic but even 

 more modern types 

 appear. 



Fishes: Selachians abun- 

 dant; Dipnoans rare; 

 Ganoids common; Tele- 

 osts predominate. 



Amphibians : Very sub- 

 ordinate. 



Reptiles: Abundant and 

 much like Jurassic; first 

 Snakes. 



Birds: Much increased. 



Mammals: Simple, rare. 



Bryozoans: 

 Present. 



Brachiopods: Still 

 more diminished 

 and not many spe- 

 cies. 



Pelecypods: Similar to 

 Triassic, but increased. 



Gastropods: Ditto. 



Cephalopods: Nautiloids 

 of coiled forms only and 

 common; Ammonoids 

 (e.g. Ammonites) culmi- 

 nate, with development 

 of some uncoiled to even 

 straight forms ; Di- 

 branchs become profuse 

 (e.g. Belemnites). 



Eucrustaceans : Ma- 

 crurans (e.g. Lob- 

 sters) common, and 

 Brachyurans (e.g. 

 Crabs) first appear, 

 though rare. 



Insects: Abundant 

 and diversified; first 

 appearance of high- 

 est forms, e.g. Flies, 

 Ants and Bees. 



Fishes: Selachians com- 

 mon; Dipnoans rare; 

 Ganoids common; Tele- 

 osts first appear, but 

 rare. 



Amphibians: Fossils? 



Reptiles: Much like Tri- 

 assic, but more common 

 and varied. 



Birds: First appear (e.g. 

 Archeopteryx) . Mam- 

 mals: Simple, rare. 



Bryozoans: 

 Present. 



Brachiopods: 

 Greatly dimin- 

 ished and those 

 with curved-hinge 

 lines prevail for 

 the first time. 



Pelecypods and Gastro- 

 pods: Prominent and as- 

 sume more distinctly 

 modern aspect. 



Cephalopods: . Nautiloids 

 common, with straight 

 forms (Orthoceras) be- 

 coming extinct; Ammo- 

 noids common, with com- 

 plex sutures (e.g. Cera- 

 tites and Ammonites) ; 

 Dibranchs first appear. 



Eucrustaceans: Ma- 

 crurans (e.g. Lob- 

 sters) first appear. 



Insects: Common 

 and mostly simpler 

 forms but first Bee- 

 tles appear. 



Fishes: Selachians, Dip- 

 noans and Ganoids much 

 as in late Paleozoic time. 



Amphibians: Declining 

 but large. 



Reptiles: Abundant and 

 varied, e.g. Enaliosaurs, 

 Dinosaurs, and Ptero- 

 saurs; first Turtles and 

 Lizards. 



Mammals: First and rare. 



Among plants the Ferns, Cycads, and Conifers predominated 

 during the earlier Mesozoic, but later in the era the Angiosperms, 

 including both Monocotyledons and Dicotyledons, first appeared 

 and very soon predominated. 



Among animals the absence of certain characteristic Paleozoic 

 groups should be noted, such as Cystoids, Blastoids, Trilobites, 

 and Eurypterids. Other Paleozoic groups continued into the early 

 Mesozoic and then either became extinct or very greatly diminished 

 such as the ancient Corals (Tetracoralla), Brachiopods, Orthoceras, 

 and Amphibians. Some of the more important groups which made 

 their first appearance in the Mesozoic were modern Corals (Hexa- 

 coralla), modern Echinoids (e.g. Sea-urchins), modern Eucrusta- 

 ceans (e.g. Lobsters and Crabs), highest Insects, Teleost Fishes, 



