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Article is published in "Priroda" magazine #5/2017

The Mesozoic butterfly effect,
or Evolution which had not been

Quodcumque retro est.                  
(Everything that has passed is the past.)

M. S. Arkhangelsky,
candidate of geological and mineralogical sciences Saratov Chernyshevsky State University

A. E. Nelikhov



The history does not know a conjunctive mood. What happened – that is happened. Nothing can be altered. This true is banal and indisputable, but it does not prevent absolutely to build forecasts of how our life or even a world history were change if something would go in another way. Many books are published and many entertaining hypotheses are thought up on a theme “what would be, if…”. Probably, the most vivid example is R. Bradbury' novel “A Sound of Thunder” about the travelers into the past. During the dinosaur hunting one tourist had casually crushed the Mesozoic butterfly. Insignificant action had caused global consequences like a small stone inducing an avalanche. In the future basic changes had taken place. Due to this novel in culture and in science the term “the butterfly effect” has appeared. Also the Soviet science fiction writer, well-known paleontologist I. A. Efremov discoursed about alternative paths of history. In 70-th years of XX century he began to write (but has not had time to finish) the novel “Retvizan” - how the history would develop if it would be possible to change the least episode of it: to prevent the captain of Russian ship to receive a contusion during the Russo-Japanese War. In Yellow Sea Retvizan battleship moved to ram attack the Japanese flotilla. The captain wanted to distract the opponent to allow Russian ships to break the encirclement in Port Arthur, but during the bombardment he was wounded. Command had been undertaken by another officer who has cancelled the order about ram attack first of all. Retvizan has returned to Port Arthur which had been surrendered to Japanese army soon. And the chain of dire consequences followed it: defeat in war, disappointment of people in autocracy, revolutions of 1905 and 1917, Civil War, disintegration of empire, re-division of spheres of influences in scale of the whole planet. And all these events, according Efremov’s opinion, are the consequences of a mine splinter which hit captain’s head. If it were possible to change a trajectory of a splinter to only three or four centimeters, the whole history of mankind would develop in different way. Possibly, if Efremov were manage to finish the story, we should speak not about “the butterfly effect”, but about “Retvizan effect”.
What for the alternative history is needed at all? This question has many answers of various degrees of wit. The most general one may be the following: alternative variants of development of events are needed to understand better causes and consequences of history. And certainly because it would be more interesting to study it. The alternative history is applicable to any phenomena. It is so because everything accessible to us in experience develops in time. The organic world of the Earth is not the exception.

* Dixon D. After man. A zoology of future. N.Y., 1981. see also:
Krylov I. N. “Get acquainted: fauna of the future (instead of the review)” // Priroda, 1983. #6, pages 126-128.
** Dixon D. The new dinosaurs. An alternative evolution. Topsfield, 1988.
*** Dixon D., Adams J. The future is wild: A natural history of the future. Firefly Books, 2002

In 1981 D. Dixon's book “After Man: A Zoology of the Future”* had been published, in which the author has tried to represent animals of the far future. This theme appeared new, interesting and fruitful, and in 1988 his next book – “New dinosaurs”** – had been published; it is about how dinosaurs could develop if have not died out at the end of Cretaceous period. Presenting the problem like a game, the book showed the important tendencies of development of biosphere and showed evidently the effect of laws of evolution. Later Dixon has developed this theme and has written the best seller “The Future is Wild”*** upon which the series had been produced.
After that only short time has passed, but the paleontology has already increased volume of the information on various groups of the fossil animals and plants very essentially. It appeared possible to understand evolutionary trends of various groups of organisms deeper to trace general paths in their development.
The interesting new data were received also for the vertebrates inhabited the territory of Volga region in Cretaceous period. The southern edge of shallow Russian Sea had placed here. The large Volga Archipelago had stretched from present day Penza up to Kalach-na-Donu town*.

* Arkhangelsky M.S., Ivanov A.V., Nelikhov A. Е. When Volga had been a sea. Saratov, 2012.

Paleontologists have found numerous fossils of marine reptiles (ichthyosaurs, plesiosaurs, mosasaurs) and animals inhabited the islands of archipelago (aquatic flightless hesperornitid birds, flying pterosaurs, dinosaurs). This community of organisms had existed for about 60 million years with few changes and had finally disappeared at the end of Cretaceous, in the time of “great extinction of dinosaurs”. The reasons of this catastrophe remain mysterious. Most likely, there were some of them, according the Russian proverb “the trouble does not come alone”.

Hypothetical neoichthyosaurus.

Here and below pictures by A. A. Smentzarev

Intensive phases of orogenesis and global anoxic events, climatic changes and the appearing of deciduous forests, the increased activity of volcanos and fall of the level of World ocean. Some kind of a final point, probably, had been put by falling of asteroid. Based upon a huge crater in Gulf of Mexico, the impact was of enormous force. If this asteroid has missed by the Earth, evolution of Mesozoic organisms, probably, would proceed plenty more millions years.
The modern level of knowledge of the inhabitants of Russian Sea and Volga Archipelago enables to draw a hypothetical picture of how descendants of Mesozoic animals could look if they managed to live to our time (at preservation of geographical conditions existed in Cretaceous in this region).
Ichthyosaurs. In Mesozoic seas they occupied the ecological niche similar to one that belongs to dolphins now. They had basically been predators of medium and rather large size, from one and a half up to five meters. According the morphology of teeth and contents of stomachs, they fed on medium-sized fish and cephalopods.
In due course of evolution at the advanced representatives of group the powerful tail fin had developed, which had performed the main locomotor function. The large back fin had appeared also. Front flipper limbs had strongly extended and had turned to the original hydrofoils playing the part of stabilizing rudder [1]. The widest and longest front fins were at cretaceous ichthyosaurs of Platypterygius genus.
Some ichthyosaurs were deep-water divers and, according to huge eye orbits of skull and sclerotic rings, they hunted in dark. A number of features indicates that they used echolocation like modern cetaceans.
Later ichthyosaurs from genus Leninia and some species of genus Platypterygius had very lengthened thin jaws similar to scissors. These ichthyosaurs had also double nasal apertures which functional value is not completely clear. Probably, ichthyosaurs had flowing nasal system similar to one supposed for plesiosaurs. Water could enter to choanae, flow via nasal chambers and leave from external nasal apertures. It is possible, that one pair of nostrils emitted water, and another pair had been used for breath [2].
At descendants of cretaceous ichthyosaurs these features could develop further and result in unique specialization of the nocturnal hunter for giant mollusks.
In diet of ichthyosaurs cephalopods, including ammonites, took the significant place. In due course of evolution ammonites increased their size and amplified the protection of shell: thickness of its walls increased, the number of spikes and powerful ridges was increased (an example is shown by representatives of genus Parapuzosia). Possible neoammonites would reach the size of children carousel. Thick strong shells covered with thorns protected mollusks reliably from predators. Neoichthyosaurs should attack these giants very quickly to give them no time to retract head into the shell. In case of successful attack the predator has cut off tentacles of a mollusk by thin jaws. Loss would not become fatal for neoammonites. All cephalopods have high abilities of regeneration and can restore the lost extremities quickly.
Giant neoammonites, probably, would make daily migrations, and, like modern day Humboldt squids, rose to sea surface at night. Because of it neoichthyosaurs should become nocturnal hunters. Giant eyes and additional pair of external nasal apertures providing the ablution of olfactory epithelium with a current of water would help them to find enormous mollusks in darkness. Thus front flippers of neoichthyosaurs would increase in great degree, as it is observed at a modern humpback whale.
Plesiosaurs. Representatives of this group of marine reptiles had thickened spindle-like body and powerful flipper extremities. Some forms had long neck and rather small head (Elasmosauridae and Cryptoclididae). At others, on the contrary, neck is very short, and head grows to giant size (Pliosauridae) [3]. The diet of these animals differed in great degree, depending on the size and morphological features: from small fishes and cephalopods up to large reptiles. Some long-necked plesiosaurs (Mortuneria, Tatanectes, Kaiwhekea) supposedly ate krill: their thin long teeth formed a lattice which kept small fry in mouth during the water filtering [4].
The carried out computer modelling has shown that for moving under water plesiosaurs used so-called underwater flight like modern penguins. They moved by making flapping movements by large front flippers. Rear extremities had almost not taken part in movement. This advanced type of swimming allowed plesiosaurs to develop significant speed.
For the majority of groups of plesiosaurs the evolutionary tendency to increase of the body size was peculiar. At some of them, for example, at elasmosaurs, neck was much extended, and the head became rather small relating to body. Despite of the huge size (up to 15 м), these plesiosaurs hunted only small fish and cephalopods. Probably, these reptiles floated slowly in thickness of water, seizing from time to time the prey lost vigilance.
It is possible to assume, that at fish-eating neoelasmosaurs the trend to the further increase of a cervical part of spinal column could be kept. As a result the sizes of their trunks would not exceed 1/5 of general lengths of animals. The super-long neck would allow hunting while remaining almost at the same place.
Thinning and lengthening of teeth of other elasmosaurids would transform them into huge passive filtrating organisms as it is supposed for some Jurassic and Cretaceous plesiosaurs. Very thin awl-shaped teeth could form an analogue of baleen. Active hunting even for the tiniest pelagic animals would become impossible. Necks of these sea reptiles could become shorter a little bit, and heads would grow larger. Filtering neoelasmosaurs would evolve to original “marine vacuum cleaners” which suck in shrimps, algae, sea horses and young squids. Both ecological types of enormous neoelasmosaurids would inhabit shallow waters where large predators are absent.

Hypothetical fish-eating neoelasmosaurus.

Hypothetical filter-feeding neoelasmosaurus.

Hypothetical neopliosaurus.

Another evolutionary strategy could develop at pliosaurids with large heads and very prolonged snouts. Their powerful teeth were adapted to tearing of large prey and had been located in jaws at the significant distance from each other, as at modern toothed whales. The length of animals reached 10 m. Probably, pliosaurs were deaf ones, that is indicated by features of the structure of some bones of scull base. Probably, during the hunting they relied on sight and the special sensitive bodies similar to pressure receptors (neuromasts) on muzzle of crocodile. These sensors allowed them to feel the vibration emanating from animals appeared in water even at the great distance.

Hypothetical neomosasaurus.

According another version, pliosaurs had rather original acoustic apparatus. The matter is that in water the specialized organ of hearing (middle ear) is not necessary, like on land, because sound waves spread well in the liquid and are transferred through scull bones directly into an internal ear. Thus, the whole body could serve to pliosaurs as an ear.
Possible descendants of pliosaurs would be able to occupy an ecological niche of sperm whales, becoming the deep-water divers ransacking in searches of prey in dark abyss. Their strong muzzles would extend even more to locate on it the huge number of neuromast sensors. These receptors would have a leading role in search of prey. Sight sense of neopliosaurs could worsen, and in forward part of head the fat bag would appear: it would help to adjust buoyancy of an animal at diving and ascent, and also would amortize impacts during the courtship battles for females. Similar functions are performed by spermaceti organ at sperm whale.
Mosasaurs. These sea lizards are prospective relatives of monitor lizards. They were the last group of the reptiles managed to develop World ocean. The advanced representatives of mosasaurids had lengthened bodies, rather small flipper-like extremities and also tail fin. Their anatomy allows us to assume that they swam waving their bodies in a horizontal plane, i.e. had “eel-like” locomotion.
The length of the majority of mosasaurs did not exceed 5 m; they fed on fish. But at the end of their evolutionary way the group has given rise to giant forms – Hoffmann mosasaurus (Mosasaurus hoffmanni) and tylosaurins (Tylosaurinae), which length reached 17 m. These giants had powerful dagger-like teeth, hunted smaller congeners, turtles and sharks [5].
Also specialized мозазавры of genus Goronyosaurus with canine-like teeth and massive skull are known; they resemble more a crocodile, rather than a lizard [6]. Some mosasaurs (Pannoniasaurus) probably lived in fresh water [7].
Bodies of neomosasaurs could extend considerably; tail fins could increase in size, and heads may become even more robust and massive. In strong jaws differentiated teeth would grow: rounded ones for crushing bones and shells in back part, and sharp ones for prey tearing – in front part. Something similar was observed at Prognathodon mosasaur [8].
At certain neomosasaurs poisonous glands could appear like at modern Comodo monitor lizard. Victims of an attack of these sea reptiles would die both from wounds, and from effect of toxins.
Some neomosasaurs would hunt in muddy coastal waters or swim up the rivers, and others would take giant size and would occupy polar latitudes. Gigantothermy (inertial endothermy) – a constancy of the body temperature of 20-25°С connected only to the huge size – would allow them to swim in cold water.

Hypothetical neoazhdarchid.

Pterosaurs. At the end of Cretaceous at the islands of Volga Archipelago representatives of the last group of pterosaurs – azhdarchids (Azhdarchidae) – nested. Representatives of this group of flying reptiles did not have teeth in beaks and had rather narrow wings [9].
In due course of evolution necks of azhdarchids turned longer, and the overall sizes of animals increased. Some giant azhdarchids (Quetzalcoatlus), probably, could not fly any more and became giant sized pedestrians. They hunted lizards and small dinosaurs, gathered carrion and ravaged nesting sites of other reptiles. By some estimations such pterosaurs were comparable in height to giraffes, and their weight could reach 250 kg [10].
Volga region neoazhdarchids also could turn completely flightless. Life on islands where there are no natural enemies would promote it. In appearance and way of life they would resemble storks and herons and could earn a livelihood by hunting small reptiles, fish and invertebrates.
Toothed Hesperornis birds had evolved in second half of Cretaceous. They are notable for a long neck, and their sizes were comparable to growth of the adult human. Hesperornis birds resembled great auks and penguins and fed on fish. They were heavy and not able to fly, but swam under water quickly [11].

Hypothetical neohesperornis

Their probable descendants could completely make a break not only with the air element, but also with land, becoming completely aquatic animals like marine reptiles. Thus they could become much larger, but, probably, would lose the ability to dive. Neohesperornises would swim in waves and, like swans, lowered superlong necks into depth, gathering crustaceans and seaweed from the bottom. They could gather to numerous colonies and drift silently along the islands of Volga Archipelago like giant flocets. They would creep on land only to lay eggs in hot sand like modern leatherback turtles.
Dinosaurs. Dinosaurs were the most mysterious inhabitants of Volga Archipelago. For now very few of their rests are found. The most significant find is a series of vertebrae of large titanosaurid from Ulyanovsk region.
Titanosaurs (Titanosauria) are among the largest ground-dwelling creatures for all history of the planet. They reached length of 40 m and weight of 35 tons. It is the latest group of long-necked sauropods. For them the tendency to tail shortening and also wide position of limbs [12] are noted.
Neotitanosaurs lived on islands of Volga Archipelago, could decrease in size (like Magyarosaurus from deposits of Maastricht of Romania [13]), pass to amphibious way of life and spend almost all the time in a coastal zone, feeding on algal meadows. Their tail, probably, would become very short. Lengthened claws having an anchor functions would help them to stay in surf-shaken zone. On their heads special glands removing surplus of salts would appear. Such glands are present at modern marine iguana Amblyrhynchus which eats seaweed. Titanosaur descendants could constantly “sneeze out” salty slime like Amblyrhynchus. With their “sneezing” the herd of neotitanosaurs would make earsplitting noise – the loudest sound of Volga Archipelago.
This archipelago would exist until now at the place of present day Saratov, Penza, Ulyanovsk and Samara towns if the history of a planet developed under the different scenario.

Hypothetical neotitanosaurid.

Authors thank the experts who have shared their supervision and hypotheses: A. O. Averyanov (Zoological institute of the Russian Academy of Sciences and the St.-Petersburg State University), R. Benson (University of Oxford, Great Britain), D. V. Grigoriev (Zoological institute of the Russian Academy of Sciences), N. G. Zverkov (Lomonosov Moscow State University), N. V. Zelenkov (Borissiak Paleontological Institute of Russian Academy of Sciences), S. Sax (Museum of Natural History of Bielefeld, Germany), I. M. Stenshin (Ulyanovsk regional museum of study of local lore), D. Surmik (University of Silesia, Poland).


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Translated by Pavel Volkov