The dinosaurs' extinction.
As for the extinction of the dinosaurs the only solid fact is that no trace
of dinosaur has been found after the Cretaceous. This calls for ideas of
their sudden disappearence, and a great numbers of theories have been
proposed, many of which with a preference for the dramatic.
It should be emphasize, however, that their is no reason to think that
the dinosaurs disappeared suddenly. And there is neither any reason to
think that they disappeared because they all died! All animals die, but
extinction happens because lesser new are born than die.
The dinosaurs were a very great succes and the superiors of their time
with no competition from other vertebrates. The mammals, which did exist
during the entire dinosaurian period, were small nocturnal animals which
played only little or no role to the dinosaurs.
At the beginning of the Triassic various other groups of reptiles, which
had survived the great extinction, took their place in the ecological
system of the Mesozoic. Those were the diapside reptiles which evolved into
the quadrupedal, sprawling lizards, and the herbivore rhynchosaurs, but the
former stayed small, and the latter were slow, clumsy animals which died
out during the Mesozoic. The birds arose during the rign of the dinosaurs,
and also did the flying reptiles, the pterosaurs, but non of these met the
dinosaurs with any kind of competition, neither did the amphibian
archosaurs, phytosaurs and crocodiles, and nor the various species of
sea-living reptiles, the ichthyosaurs and the plesiosaurs. From the Middle
Triassic the stage was entirely set for the dinosaurs, and they constituted
almost exclusively an eco-system of their own.
This system was based on the tall plante-eaters, the sauropods, the
various ornitischians, and eventually on the bird-like, plante-eating
ornithomimians. These plant-eaters drifted in hosts over the landscapes and
consumated enormeous amounts of plants, which they transformated into
enormeous amounts of meat.
These hosts of plante-eaters were escorted by the meat-eaters, the tall
carnosaurs and the lesser bird-like coelurosaurs which profitated from the
vast amounts of meat to be served when a tall plante-eater died, fell ill,
or was wounded. Occasionally they might have attached and killed a prey,
presumably young or invalid ones which could be overtaken, but there is no
reason to imagine the meat-eating dinosaurs as active, chasing predators.
More likely they should be imagined as scavengers, equipped with large
teeth and sharp claws for cutting through thick and tough hide and for
carving the meat, rather than for killing a living prey.
The dinosaurs owed their superiority to the narrow gait which they had
achieved from the swimming and bipedal ancestrial archosaurs.
This gait made them able to evolve long legs and to move in a manner
which demands much lesser energy than the original sprawling gait and the
semi-improved gait of the pre-mammals. Besides it made them able to acquire
Due to this superiority the dinosaurs in general did not need to evolve
neither essential physiological improvements nor essential improvements of
senses and breeding as did the contemporary mammals. Some dinosaurian
species might have improved their digestion and have developed a higher
metabolic rate with some degree of endothermy, and some might have attained
some kind of youth-care. And it is the most likely the bird-like
coelurosaurs of Late Jurassic and Cretaceous, defectors from the
bird-lineage, were warm-blooded and had a rather high metabolism as well as
an advanced activity. But in general the dinosaurs remained reptiles with
low metabolism and low activity-level, and with humble ability to
orientate.Their ability to recognize objects of their surroundings were
surely poor and confined to eye-sight, and only to a very small degree to
hearing. The ornamental crests in the late ornithopods may have given these
some ability to orientate by smelling, but there is in general no reason to
think of the dinosaurs as particular active and agile, not to say
intelligent, and no more than any modern reptile or bird.
During the Mesozoic the dinosaurs evolved into a great number of
species, each adapted to its niche, and by the end of Cretaceous the entire
dinosaurian world was one great, complicated, delicate ecosystem.
Their generally tall size, compared to other animals of their time, and
their long legs confined the dinosaurs to the open, flat, and firm lands,
and - like the modern tall, long-legged plain-living mammals - unsuited for
rocks, swamps, and dense forrests. During the greater part of Mesozoic the
latter was, however, no disadvantage as the herds of plant-eating dinosaurs
on their all-consumating wanderings over the landscapes bit down all green
plants and prevented any dense, tall vegetation to grow.
The dinosaurian world was based on the herds of tall plant-eaters which
lived mostly on ferns and conifers, which trees cannot stand to have the
green parts bitten off. So when a host of dinosaurs had passed, the ground
was left with bare, dying, and crushed trunks and heaps of dungs. Then new
plants could grow up until the next herd of plant-eating dinosaurs came
along, followed by their meat-eating compagnions.
But in the Cretaceous the foliage plants and the foliage trees evolved.
These plants could stand to have the green leaves bitten off; they grew new
foliage and grew on. Thus great areas eventually became forrest, and the
space for the dinosaurs was gradually reduced.
The dinosaurs did not die from this, but the balance of the ecosystem
was upset, and the number of plant-eaters decreased, slowly at the
beginning, faster later on as the forrests extended. This further minimized
the space for the dinosaurs which decreesed, and so on to an increasing
degree. By the end of Cretaceous the entire eco-system collapsed. Due to
their specialization as plain-dwellers with restricted physiology and
sences the dinosaurs were unable to adapt themselves to the new situation.
In a realtively short time they disappeared, leaving the earth to be
covered with forrest.
This had its consequenses: The amount of carbon-dioxide, CO2, in the
atmosphere is lesser than 1 %, but the plants live on it and tie it as
cellulose, thereby removing it from the atmosphere. But as the herds of
dinosaurs eat almost any plant, the tied CO2 was released to the atmosphere
all the time. But when the forrests began to spread, the great amounts of
tied CO2 were no more released, and the CO2-amount of the atmosphere
In the sea, the algeas also depended on the CO2. During Cretaceous
enormeous amounts of CO2 were consumated by the algeas which tied it and
diposed it as chalk. But as the increasing forrests tied still larger
amounts of CO2 and the atmospheric amount of CO2 fell, the algeas of the
sea decreased which upset the ecological balance of the sea too: The algeas
were food for other sea-organisms, which were food for fishs and other
see-animals, which also decreased, why the lope-finned fishs and the
see-reptiles, ichthyosaurs, plesiosaurs, mesosaurs ect. consequently
These factors, and surely many others, brought the world of the
dinosaurs to an end, leaving a world covered with foliaged forrests, and
the possibility for the small, warm-blooded mammals to evolve.
* * * * * * * * *
*)As most readers with interest for the subject are supposed to be
familiar with relevant evidences, this essay deliberately is not garnished
with numerous references.
Only for the proposal of the pro-avian lineage should be refered the
author's small book, Palm, Svend, (1997) The Origin of Flapping Flight in
Birds. Ballerup. (ISBN 87 - 986364 - 0 - 5). As for the question of
dinosaurs warm-bloodedness is refered to Palm, Svend, (1997) The
Warm-blooded Dinosaurs? Ballerup. (ISBN 87 - 986710 - 0 - 6). Each can be
required by E-mail: palm@post7, tele.dk.
* * * * * * * * *
Attached: Illustrations, fig. 1 - 4 and 5.