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Article is published in "Priroda" magazine #5/2017
The
Mesozoic butterfly effect,
or Evolution which had not been
| Главная | Неоцен |
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.)
Horace
M. S. Arkhangelsky,
candidate of geological and mineralogical sciences Saratov Chernyshevsky
State University
Saratov
A. E. Nelikhov
Moscow
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”.
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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.
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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.
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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.
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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.
Birds. 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].
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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.
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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
2017
