January, 1929 



EVOLUTION 



Page Five 



Rulers of the Ancient Seas 



By FREDERIC A. LUCAS 

 Honorary Director, American Museum of Natural History 



JUST as Greece, Carthage and Rome in turn ruled the seas 

 in the days we call old, so, long before the advent of man, 

 the seas were ruled by successive races of creatures whose bones 

 now lie scattered over the bed of the Mediterranean. For a time 

 the armor-clad fishes held undisputed sway; then their reign 

 was ended by the coming of the sharks, who in turn gave way 

 to the iish-lizards, the Ichthyosaurs and Plesiosaurs. 



Though they were big for reptiles and some were real giants, 

 fifty feet long, they do not merit the adjective "gigantic" so 

 liberally bestowed upon them. They were of many species of 

 assorted sizes. The smaller Ichthyosaurs were, so to speak, rep- 

 tilian porpoises, but provided with four useful paddles instead 

 of just two, in addition to a powerful tail whose shape and use 

 were long unsolved problems. This long tail was bent at a 

 sharp angle to the backbone and this was taken to mean the 



Ichthyosaurus (the fish-lizard) pressed flat on a rock slab. 



— Courtesy Am. Museum Nat. Hist. 



existence of horizontally flattened tail. But when a finely pre- 

 served specimen came to light, lying upon one side and having 

 the tail in place, lo it was much like the tail of a shark, only 

 reversed, the lower lobe being longer than the upper. This 

 means that the reptile came to the surface to breathe, while the 

 shark goes down in search of food and to escape danger. The 

 more perfect specimens also showed an unsuspected high back 

 fin precisely like that of a porpoise. 



The long-necked Plesiosaur was like ''a snake threaded through 

 the body of a turtle", the shell, however, being lacking, as the 

 body was covered by a smooth skin. Despite the snake-like neck, 

 the Plesiosaurs may have been a stiff-necked tribe on account of 

 their biconcave vertebrae. 



Having played their roles of rulers of the seas, Ichthyosaurs 

 and Plesiosaurs in due time passed off the stage of life to give 

 place to the great marine reptiles called Mosasaurs, that extended 

 their empire around the world, from New Zealand to North 

 America. Great they were, but there is a universal tendency 

 to magnify the reptile we never saw as well as the fish that 

 "got away," and the greatest of animals will shrink before a 

 two-foot rule. No animals known to have existed were ever 

 larger than our whales and few Mosasaurs exceeded in size a 

 first-class Crocodile. Very rarely a Mosasaur reached a length 

 of forty feet and even twenty-five feet is large, while the great 

 Mugger, or Man-eating Crocodile, may attain a length of thirty 

 feet, a fit match for most Mosasaurs. 



The first of these sea-reptiles to be discovered now reposes in 

 the Paris Musee d'Histoire Naturelle, after having changed 

 hands several times. The original owner, M. Hoffman, presided 

 for weeks over the arduous task of separating the remains from 

 the surrounding rock. The extraordinary discovery excited so 

 much interest that the canon of the nearby cathedral, as lord of 

 the manor, laid claim to the fossil and succeeded, after a long 

 and harassing lawsuit, in obtaining the precious relic. But dur- 

 ing the French Revolution, the armies of the Republic, advised 

 by a committee of savants, spared from bombardment that part 

 of the city in which the fossil was known to be. Shrewdly sus- 



pecting the reason for the peculiar favor shown his residence, 

 the canon concealed the specimen in a vault; but when the city 

 was taken, he had to give up his ill-gotten prize which was 

 then moved to its present museum location. 



The seas that rolled over western Kansas were the head- 

 quarters of the Mosasaurs and thousands of specimens have been 

 taken from the chalk bluffs of that region, some so well pre- 

 served that we are well acquainted with both internal structure 

 and outward appearance. They were great, overgrown, swim- 

 ming lizards adapted to a roving, predatory life by their power- 

 ful tails and paddle-shaped feet. Their cup-and-ball vertebrae 

 gave great flexibility of body, their sharp teeth helped capture 

 slippery prey and the structure of the lower jaw shows that 

 they bolted their food in great chunks. In snakes, which also 

 swallow their prey entire, the two halves of the lower jaw are 

 loosely over the gape of the mouth. The pelican solves the same 

 problem by the length of his mandibles which bow apart to form 

 a nice, little landing net. In the Mosasaurs each half of the 

 lower jaw was joined so as to bow outward when opened and 

 to add greatly to the swallowing capacity. Extend your arms at 

 full length, the palms touching, and then bend your elbows out- 

 ward and you'll get an idea the action of a Mosasaur's jaw. 



The western sea was a lively place in the day of the great 

 Mosasaurs, for with them swam the king of turtles, Archelon, 

 a dozen feet in length, its head a full yard long. In the shal- 

 lows prowled great fishes with massive jaws and teeth like 

 spikes and the great, toothed diving-bird Hesperornis. Over 

 the waters flew pterodactyls, reptiles with a wing-spread of 

 twenty feet, largest of all flying creatures and very probably 



Tylosaurus ; terror of the Kansas seas. — Am. Mus. Nat. Hist, 

 flesh-eaters too. When all these were seeking their dinners, 

 there were troublous times for smaller fry in that old Kansan sea. 

 Then came a change. To the south, west and north the land 

 was slowly but surely rising, only an inch or two in a century, 

 but still rising. Its area contracted and ridges of the sea-bottom 

 came to the surface as long, low bars that imprisoned the sea- 

 life and subjected it to many risks. The stronger more readily 

 captured the weaker and the fishes gradually died out through 

 the constant freshening of the water. With the death of each 

 considerable group, the balance of food supply was upset and 

 many large species disappeared from the scene. The more 

 omnivorous and enduring long resisted starvation, but finally 

 yielded to inexorable fate — the last was caught in a shallow pool 

 from which his exhausted energies could not extricate him. 



