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The Dinosaur Origin and Extinction.
A proposal on how the dinosaurs originated and disappeared, and on
their mutual relations.
By
Svend Palm. Lindbjergvej 13, DK 2750
Ballerup, Denmark.
E-mail: palm@post7, tele.dk
The dinosaurs originated from diapside reptiles, which survived the
mass-extinction at the end of the Permian as swimming archosaurs. From those
emerged bipedal archosaurs, among others two groups of bipedal herbivores,
the short-necked ancestors of the ornitischian dinosaurs, and long-necked
ancestors of the saurischian sauropods. Later emerged the short-necked
meat-eaters, ancestors of the carnosaur dinosaurs. From a lineage of small
bipedal, tree-mounting bird-ancestors the various groups of bird-like,
coelurosaurs branched off.
The dinosaurs disappeared as a consequence of growth of forests of deciduous
trees.
Preword.
This essay on the origin and disappearance of the dinosaurs is based
on the supposition, forwarded and argued for in my essay The Origin of Flapping Flight in
Birds,*) that the dinosaurs are offshoots from a lineage
which originated from a group of diapside Permian reptiles leading to the
birds.
The source-group of reptiles, which were very much like the recent
reptile Sphenodon, evolved into birds, the only group of recent bipedal
diapsides, through continuous stages, each stage as for behavioural,
physiological, and anatomical qualities better adapted to live and breed in
the actual environments than the former. Gradually evolved the characters,
which are typical for dinosaurs and the Jurassic pre-bird Archaeopteryx:
The elongated jaws with thecodont teeth and antorbital opening and the
bipedal, narrow-tracked gait. In course of time many offshoots branched off
from this lineage, some of which were the various groups of dinosaurs.
Dealing with the problem of the relation of birds to dinosaurs, and of
the mutual relation of the various groups of dinosaurs, one is presented with
the problem of what is a dinosaur. Much time and space could be wasted on
that, and to avoid that, I prefer to call the entire group archosaurs, and
only those, which commonly are called dinosaurs, i.e. the carnosaurs, the
pro-sauropods and the sauropods, and the four groups of ornitischians for
dinosaurs.
The essay does not pretend to be the TRUTH, but is a proposal of a
coherent theory the validity of which depends on the validity of the basic
evidences and of its consistency, and not if it contradicts other theories or
other interpretations of facts which might be even as valid.
This essay is meant to be published by the internet, this new medium
giving an opportunity to distribute ideas and theories that hardly could be
published by any magazine. That means that I alone am responsible for the
entire work with no editor or others to blame for printing- or other
mistakes.
Ballerup
1998
Svend
Palm.
Introduction.
The skull of the dinosaurs is generally characterised by two temporal
openings behind the eye. As this is also a characteristic trait of a group of
Permian diapside reptiles, very little different from the very unspecialised
resent reptile Sphenodon, these reptiles must be supposed to have been
the stem group of the dinosaurs. The diapside skull is also a characteristic
trait of crocodiles, pterosaurs, and Archaeopteryx, and like the
dinosaurs these also have the particular opening in front of the eye, the
antorbital opening, and they have a single row of teeth in caves of the jaw,
the thecodont dentition. These traits are a general characteristic of the archosaurs
to which also belong quadruped reptiles from the Triassic, the phytosaurs and
the aëtosaurs. The archosaurs therefore emanated from the same diapside
source group.
The narrow gait is a general characteristic of many archosaurs, and bipedality
is the general trait of birds and more groups of dinosaurs.
The dinosaurs are distinguished in two main groups, the ornitischians
and the saurischians, each characterised by a particular structure of pelvis
and dentition.
These two groups of dinosaurs are further distinguished in various
groups, each by its own characteristics. See Fig. 1, C. D. and fig. 3., C. D.
Obviously the origin of the antorbital opening, the thecodont teeth,
the narrow track way and bipedallity, the different pelvic structure as well
as all the other characteristics of the various groups of dinosaurs, are due
to a different manner of life of their ancestors. Thus the ancestors of the
saurischian dinosaurs must have lived differently from the ancestors of the
ornitischians, and the ancestors of the four-footed, long-necked sauropods
must have lived differently from those of the two-footed theropods. And the
forefathers of the heavy, short-necked carnosaurs surely had different
manners of life than those of the light, long-necked coelurosaurs. Also must
the ancestors of the two-legged ornithopods with three toes at each foot have
a fundamental different manner of life from the ancestors of the four-legged
ceratopians, stegosaurs and ankylosaurs with five toes at each foot.
In the following is proposed a sketchy explanation of what caused the
difference of general structure of the various groups of dinosaurs and, as a
consequence, a proposal of their mutual relations and their extinction.
The previous history.
The dinosaurs emerged in the Triassic. During the previous Permian
period a multitude of vertebrates had arisen, among those the mammalian
ancestors and some lizard-like diapside reptiles, not much different from Sphenodon.
See Fig. 2, A.
During the Permian the climate was generally warm and dry, and by the
end of the period it grew that warm and dry that vast parts of the earth was
desert. Many species were extinct, and at the beginning of the Triassic only
a few survived.
Among the survivors were some of the diapside reptiles, which could
seek shelter from sun and heat under rocks, searching food at dawn and after
sunset, when the temperatures were endurable. From those reptiles the modern
lizards and snakes arose.
In the Early Triassic, when the climate became lesser dry and plants
began to spread, another group of the lizard-like diapsides evolved into the
plant-eating rhynchosaurs, of which many species emerged. They were rather
tall, clumsy reptiles, and they disappeared before the end of the Mesozoic
period.
The dinosaur origin.
The swimming diapsides.
Other diapside reptiles survived by staying at the
waters. They lived on fishes and swam by waving the tail. As an adaptation to
this manner of life their jaws were elongated in order to hold the nostrils
out of the water, which caused the antorbital opening. As a help to catch and
hold fishes in the water they also evolved the solid thecodont dentition.
Fig. 1B, 2B.
The
archosaurs.
On dry land the diapside reptiles originally moved
in the same sprawling manner as lizards, with extended limbs out from the
side of the body, and they moved them in horizontal swings, waving the body
from side to side.
But when they swam, they used to hold the limbs close to the body in
order to minimise the resistance of the water, and when they went out of
water to stay on the banks, they eventually kept the thighs and knees close
to the flanks. And they walked by swinging the lower parts of the hind legs
vertically with the feet beneath the body. They thus evolved a narrow track
way that enabled them to walk on the hind legs alone balancing the forepart
of the body by the heavy, muscular tail. Fig. 2, B. C.
This gait proved advantageous as it does not demand as much muscular
efforts as the sprawling manner of walking, and it caused a general change of
the original breast- and pelvic-skeleton: As the forelegs were relieved from
the burden of the body, the breast-skeleton, apt for the strong musculature
of a four-legged, sprawling reptile, was reduced except in birds where it is
a support for the flight-musculature.
The pelvis consisted of the iliac bone, which was attached to the
spine by a few vertebrae, the pubic bone, which was connected to the iliac
bone and directed forwards, and the iscium, which was directed backwards.
The bipedal, narrow-tracked gait, in which the pelvis alone should
carry the entire burden of the body, needed, however, more vertebrates to
attach the spine to the iliac bone, and consequently this was elongated. The
bipedal gait also caused that the muscles, which in the quadrupedal diapsides
had pulled the sideways-extended thighs downwards, now should pull the
forward extended thighs down- and hind wards and carry the entire
body-weight. As these muscles are attached to the pubic bones, these were
elongated and bend downwards in order to reinforce these muscles. This
structure of the pelvis with the long ilium and the long, downwards directed
pubis is also a characteristic of the bipedal archosaurs and the saurischian
dinosaurs.
As a consequence of the bipedal, narrow-tracked gait, the archosaurs
could develop long hind legs, and later on some of them also lifted the heels
off the ground to become digitigrades, which changed the ankle-joint into a
simple hinge. See
fig. 3
The dinosaurs.
In the Triassic the climate became more humid, and the plants began to
spread. And the bipedal archosaurs followed as they diversified into many
species, some as plant-eaters and some as carnivores. Many of these
archosaurs, however, soon gave up the bipedal walking and supported the
forepart of the body on their forelimbs and thus reassumed the quadrupedal
gait. These four-footed archosaurs, the phytosaurs and the aëtosaurs, many of
which were covered with bony plates and spikes, were rather tallish, but far
from the size of the later dinosaurs. The crocodiles are likely to have
originated from such quadrupedal archosaurs, which have reassumed the
swimming manner.
The
ornitischian.
As the earth was grown with plants, some of the
bipedal archosaurs supplied their carnivore diet with plants and eventually
became plant-eaters. The foliage trees did not yet exist, and a sort of
trees, which were abundant, was ferns and the 2 - 3 meter tall, palm-like
cycads, and to reach the sappiest shoots of these trees some of the bipedal
archosaurs attained the habit of raising the forepart of the body to a
steeple angel, turning the thigh as long to the rear as possible, almost
perpendicular to the spine. As an adaptation to his habit, their iliac-bone,
which attached the pelvis to the spine, was further elongated, and the
downward-directed pubic bone was bend in behind and came to lie parallel to
the ischium. This reinforces the muscles, which pull the thighs in behind and
maintain the steeple position. See fig. 3, D.
To adapt further as plant-eaters they evolved front teeth in the
upper-jaw and a tooth-less "pre-jaw" at the lower jaw, which made
them better apt to bite plants off. Eventually their back teeth changed to be
fit for chewing plants, thus improving their digestion. Thus did the
ornitischian group of dinosaurs arise, and as an improvement of their ability
to walk, the pubic bone evolved a forward branch, almost parallel to the
ilium.
The bipedal ornitischians.
The original group of bipedal ornitischians supported on the entire
sole of their five-toed foot, but gradually they evolved digitigrady, and the
number of toes was reduced to three. This group, the ornithopods,
evolved into many species. In the Cretaceous many new kinds of plants arose,
and many ornithopods arose which were adapted to eat this plants. A group of
ornithopods, the hadrosaurs had rather broad mouths without front teeth, and
most of them developed spectacular crests on the top of the head. The purpose
of these ornaments is hard to explain, but their close connection to the
nasal passage points to a site for olfactory sense.
The quadrupedal ornitischians.
The stegosaurs and the ankylosaurs.
Some of the ornitischians specialised in eating
lower parts of the plants and gave up the habit of raising the body. Instead
they supported the forepart of their body on the forelimbs and retained a
quadrupedal manner of walking. They did not evolve digitigrady and maintained
the five toes at each foot. Those were the stegosaurs and the ankylosaurs,
which were provided with bony knots on the back. The stegosaurs had bony
spears and vertical bony plates along the back, and the ankylosaurs had bony
plates, which covered the neck and back almost as a shield. It seems
reasonably that this was evolved to protect these low creatures against tall
carnivores.
The ceratopians.
The four-footed ceratopians originated from
bipedal ornitischians, which had acquired digitigrady, but gave up the
bipedallity before the number of five toes at each food was reduced. They
evolved a big bone collar, which covered the neck, and they are generally
characterised by tall bony horns projecting from the front of the head in a
rhinoceros fashion. This was surely a protection they had acquired after they
had reassumed the quadrupedal manner of walking.
The
saurischians.
The quadrupedal sauropods.
Instead of rising at their hind legs to reach high parts of the plants
as the ornitischians did, another group of bipedal plant-eating archosaurs
evolved a long neck. Thus they maintained the original structure of pelvis
with the pubic bone pointing forward and downward. See fig. 2, D.
They evolved a peculiar manner of digesting: Instead of chewing their
food, they swallowed stones, which grinded the vegetable parts in their
stomach. This manner of digestion is to be found in birds.
These long-necked archosaurs soon gave up the bipedal manner of
walking and supported the forepart of the body on the forelimbs, and they
became the four-footed sauropods. They never acquired digitigrady and
maintained the five toes at each foot.
As four-legged plant-eaters with the narrow gait, they could assume gigantic
size.
They evolved very long tail as a flexible balance to the long neck,
but it might also have been useful as a gigantic whip for protection.
The bipedal theropods.
The carnosaurs.
As the plants were abundant and many herbivores
arose, plant-eating archosaurs as well as the plant-eating rhynchosaurs,
there was basis for carnivores to establish, and some of the bipedal
archosaurs took advantage of this. The short-necked Ornithosuchus of
Triassic is surely such an early carnivore archosaur.
They hardly chased to kill, but lurked about, and their main course
was most likely dead, weakened, or damaged herbivore ornitischians and
sauropods. As these tall victims had a thick and though hide, and as long,
strong and sharp teeth were necessary to bite through that, and as long teeth
demand tall jaws with strong muscles, the carnivore, bipedal archosaurs got
big heads on large bodies. They became the tall carnivore carnosaurs.
The carnosaurs moved bipedal at the hind legs and evolved digitigrady.
The number of toes was reduced into three toes at each foot. Their forelimbs,
which they did not use for walking, were reduced and became extremely small.
The famous carnosaur Tyrannosaurus rex, as big as an elephant, had
forelimbs only the size of a man’s arm. But the small forelimbs, which in Tyrannosaurus
had only two fingers with sharp claws, had a strong musculature and were
not totally reduced, most likely because they were necessary when the big,
heavy male mounted the female to mate.
The coelurosaurs.
At an early stage some long-necked plant-eating
archosaurs, ancestors of the long-necked sauropods, added small living prey
to their vegetable diet, and their long legs and long necks made them fit for
fast moving and rapid snatching. Their sharp-pointed, thecodont teeth,
evolved for fish eating, were also advantageous for them as ground-living
predators, and they evolved digitigrady and long metatarsals. These bipedal
predators evolved into numerous species, which never became especially tall,
but rather agile.
At an early stage, before the original breast-skeleton was yet not
reduced, some very small ones of these bipedal, long-necked archosaurs
initiated the habit of climbing tree-trunks to stay in the tree-crowns. Those
were the birds’ ancestors, the pro-avians.
The tree-mounting pro-avians.
The trees, which the pro-avians used to climb, were not branched trees
like present day trees, but palm-like cycads the flat crowns of which was
suited for the small bipedal archosaurs to lay their eggs. Here they were in
safe from egg-robbers, and their hatchlings, which were endangered by
predators on the ground, were reasonably in secure.
The pro-avians performed tree-mounting by step-by-step walking,
hooking by the claws while clinging to the trunk by the claws of their
outstretched forelimbs. See fig. 4.
This use of the forelimbs demanded strong efforts of the pectoral
musculature, and therefore the pectoral skeleton was not reduced as in the
other bipedal archosaurs, but was maintained and developed. And as an
adaptation to the tree-mounting behaviour, their forelimbs were elongated and
transformed into three-fingered hands with sharp claws and wrists to flex to
the rear only in the lateral plane. This forelimb structure, which is found
in birds as the skeletal framework of the wings, is also to be found in the
later coelurosaurs.
As the ultimate adaptation to the tree-mounting behaviour the pro-avians
evolved the flying capacity and became the birds.
The life in the tree-crowns.
The laying of eggs in the crowns of the cycads gave
the small pro-avians and their hatchlings a great advantage, but also a
disadvantage as they were exposed to sun heating with little possibility to
seek shadow and in great danger of overheating. As a means to stay as long as
possible in the safe place of the tree-top, their small knobbed scales
evolved into a plumage, which yielded some protection against the rays of the
sun, and as a means to reduce the body-temperature they evolved air sacs
connected with the lungs to cool when they breathed.
Besides they were forced to assume the optimal body-temperature of 42o
C., which, however, was disadvantageous when they sought food in shady,
cooler places on the ground. To maintain the high optimal body-temperature
they increased their metabolic rate to produce body heating and thus acquired
the ability to maintain a constant body-temperature and became warm-blooded.
The bird-like coelurosaurs.
The agile, warm-blooded pro-avians split into may species, and many of
these eventually abandoned the tree-mounting manner to live solely on the
ground as bipedal creatures. The breast-musculature, which was maintained for
tree mounting, was then reduced, the more reduced, the more time elapsed from
giving up tree climbing.
Those defectors from the bird’s lineage are the very bird-like
coelurosaurs, most of which have reduced the breast-skeleton, but some, Oviraptor
and Velociraptor have retained a part of the clavicle.
The long three-fingered hands with the sharp claws, the longer the
more close the coelurosaurs were to the birds before they abandoned the
tree-climbing manners, were retained for other purposes despite of the
peculiar construction of the wrists.
As these offshoots from the avian lineage no more needed to climb,
they could be taller, and they split into many species of various size, all
with the shape of theropod dinosaurs, though they were more lightly built and
long-necked, and generally more bird-like of appearance. The descendants of
those which gave up the climbing at an early stage were lesser bird-like than
those which did it at later, and they had yet not evolved the long hands and
fingers.
The middle-sized Coelophysis, Saltopus and Procompsognatus
from the end of Triassic are surely descendants of early offshoots from the
bird’s lineage. Those which gave up the climbing behaviour later in the
bird-evolution, were much more bird-like. The small, feathered Archaeopteryx
from Jurassic with its long tail and toothed mouth was surely a close
pro-avian offshoot which had not yet reduced the fused clavicles and
breastbone, whereas the small Compsognatus of Jurassic were an earlier
and more distant pro-avian offshoot.
The very bird-like coelurosaurs from the Late Jurassic and Cretaceous,
the toothless ornithomimosaurs, such as Struthiomimus, Gallimimus,
and Ornithomimus are descendants from late, more distant pro-avian
offshoots, which had adopted a running, plant-eating manner of life. The
deinonychosaurs, among those Deinonychosaurus, Dromaeosaurus, Velociraptor,
Ornitholestes, Oviraptor and other very bird-like coelurosaurs
with teeth and sharp claws, and long forelimbs and hands with a very
bird-like structure of the wrist, are surely descendants of late off-shoots
from pro-avians which had taken up a running, meat-eating manner of life. The
large, sharp scythe-shaped claw on the second toe, which Deinonychosaurus
and others were furnished with, most likely served as a means to cut the
tough skin and carve the meat of a fallen prey.
Dinosaurs’ mutual relations.
The dinosaurs originate from a Triassic group of reptiles, the
archosaurs, which had elongated jaws with thecodont dentition and antorbital
opening. Many archosaurs had a narrow-tracked gait and a bipedal manner of
walking.
From those arose short-necked and the long-necked herbivores.
The short-necked ones had a general change of the pelvis, and a
dentition apt to chew the food. They became the ornitischian dinosaurs, which
split up in the ornithopods, which remained bipedal, whereas the stegosaurs
and ankylosaurs soon assumed quadrupedality, and the ceratopsians did it
later on.
The long-necked herbivores were ancestors of the tallish, bipedal
prosauropods, some of which were the ancestors of the huge quadrupedal
sauropods. Some early ancestors of the long-necked herbivores were also the
root of the bird-lineage, the long-necked, light-builded pro-avians. From the
lineage of pro-avians the early coelurosaurs branched off, and eventually the
ornithomisaurs and deinonychosaurs defected from the bird-lineage.
From the bipedal archosaurs the tall, short-necked meat-eating
carnosaurs emanated separately. See fig. 5.
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 disappearance, and a great numbers of theories have been
proposed, many of which with a preference for the dramatic.
It should be emphasise, however, that there 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 success 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 reign of the dinosaurs, and
also did the flying reptiles, the pterosaurs, but none 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 plant-eaters, the sauropods, the
various ornitischians, and eventually on the bird-like, plant-eating
ornithomimians. These plant-eaters drifted in hosts over the landscapes and
consummated enormous amounts of plants, which they transformed into enormous
amounts of meat.
These hosts of plant-eaters were escorted by the meat-eaters, the tall
carnosaurs and the lesser bird-like coelurosaurs, which made use of the vast
amounts of meat to be served when a tall plant-eater died, fell ill, or was
wounded. Occasionally they might have attached and killed a prey, presumably
young or invalid ones that 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 ancestral 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
large size.
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 that 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 recognise objects of their surroundings were surely poor and
confined to eyesight, 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 forests. During the greater part of Mesozoic the
latter was, however, no disadvantage as the herds of plant-eating dinosaurs
on their all-consummating 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 dung. Then
new plants could grow up until the next herd of plant-eating dinosaurs came
along, followed by their meat-eating companions.
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 forest, 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 forests extended. This further minimised the space for
the dinosaurs, which decreased, and so on to an increasing degree. By the end
of Cretaceous the entire eco-system collapsed. Due to their specialisation as
plain-dwellers with restricted physiology and senses the dinosaurs were
unable to adapt themselves to the new situation. In a relatively short time
they disappeared, leaving the earth to be covered with forest.
This had its consequences: 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 forests began to spread, the great
amounts of tied CO2 were no more released, and the CO2-amount
of the atmosphere decreased.
In the sea, the algae also depended on the CO2. During
Cretaceous the algae that tied it and disposed it as chalk consummated
enormous amounts of CO2. But as the increasing forests tied still larger
amounts of CO2 and the atmospheric amount of CO2 fell,
the algae of the sea decreased which upset the ecological balance of the sea
too: The algae were food for other sea-organisms, which were food for fishes
and other see-animals, which also decreased, why the lope-finned fishes and
the see-reptiles, ichthyosaurs, plesiosaurs, mesosaurs and others,
consequently disappeared.
These factors, and surely many others, brought the world of the
dinosaurs to an end, leaving a world covered with foliated forests, 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 referred 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 referred to Palm, Svend, (1997) The
Warm-blooded Dinosaurs? Ballerup. (ISBN 87 - 986710 - 0 - 6).
* * *
* * * * * *
Comments and questions to Dinosaur Origin and Extinction.
February 2000.
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