A proposal on how the dinosaurs originated and disappeared, and on their mutual relations.

1998

Svend Palm Publishing Ballerup, Denmark. ISBN 87 - 986710 - 1 - 4


The Dinosaur Origin and Extinction.

By Svend Palm

© Svend Palm 1998 ISBN 87 - 986710 - 1 - 4

Published and distributed by Svend Palm Publishing Lindbjergvej 13 DK 2750 Ballerup, Denmark E-mail: palm@post7.tele.dk

Distributed by internet only. Rekvisition by e-mail: palm@post7.tele.dk


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 hervivores, the short-necked ancestors of the ornitischian dinosaurs, and long-necked ancesors 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 consequense of growth of forrests of deciduous trees.

  Attached: Illustrations, z/fig1.gif z/fig2.gif z/fig3.gif z/fig4.gif and z/fig5.gif.


Preword.

  This essay on the origin and disapperance 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. I 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 dinosaurs. Much time and space could be vasted on that, and to avoid that, I prefere 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 THRUTH, 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 ment to be published by the internet, this new medium giving an opportunity to distribute ideas and theories which hardly could be published by any magazine. That means that I alone is responsible for the entire work with no editor nor others to blame for printing- or other mistakes.
Ballerup 1998
Svend Palm.


Introduction.

  The skull of the dinosaurs is generally characterized 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 unspecialized 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 quadrupedal reptiles from the Triassic, the phytosaurs and the aėtosaurs. 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 characterized by a particular structure of pelvis and dentition.
  These two groups of dinosaurs are further distinguished in various groups, each by its own characteristics.
  Obviously the origin of the antorbital opening, the thecodont teeth, the narrow trackway and bipedality, 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 differenly 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-fooded theropods. And the forefathers of the heavy, short-necked carnosaurs surely had different manners of life than those of the light, long-necked coelurosaus. 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 concequence, 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 arosen, among those the mammalian ancestors and some lizard-like diapside reptiles, not much different from Sphenodon.
  (Fig. 2, A.)

diapside reptiles

Fig. 2 The principle of the
archosaur evoltion.
A.
Quadrupedal diapside (Sphenodon).
B. Swimming archosaur. C. Early bipedal
herbivore archosaur, E. Early short-necked
Bipedal herbivore archosaur.

  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, seaching 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 fishs 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 fishs in the water they also evolved the solid thecodont dentition. (Fig. 1B, 2B.)

Fig. 1 Principle of evolution of
archosaur skull.

A. Diapsid (Sphenodon), B. Early archosaur,
C. Saurischian dinoseur, D. Ornitischian dinosaur.
a. o.: antorbital opening. p. j.: pre-jaw.

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 minimize 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 hindlegs vertically with the feet beneath the body. They thus evolved a narrow trackway which enabled them to walk on the hindlegs 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 sideway extended tighs downwards, now should pull the forward extended tighs down- and hindwards 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 consequense of the bipedal, narrow-tracked gait, the archosaurs could devellop long hindlegs, and later on some of them also lifted the heels off the ground to became digitigrade, which changed the ankle-joint into a simple hinge.
  See fig. 3

archosaur pelvis

Fig. 3. Principle of evolution of
archosaur pelvis.
A.
Quadrupedal diapside (Sphenodon). B.
Early bipedal archosaur, C. Saurischian dinosaur,
D. Ornitischian dinosaur. Pb.: Pubic bone

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 aėtosaurs, 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 parallelly to the ischium. This reinforce the muscles which pull the thighs in behind and maintain the steeple posisition. See fig. 3, E.
  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 were changed to be fit for thewing 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 ornithopodes, 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 olfactury sense.

The quadrupedal ornitischians.

The stegosaurs and the ankylosaurs.

  Some of the ornitischians specialized 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 aquired digitigrady, but gave up the bipedality 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 characterized by tall bony horns projecting from the front of 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 raising at their hindlegs 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 thewing 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 aquired 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 usefull 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 bipedally at the hindlegs 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 extreemely small. The fameous carnosaur Tyrannosaurus rex, as big as an elefant, 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.

pro-avis

Fig. 4. Climbing pro-avis.
A.
Mounting pro-avis, B. Descending pro-avis.

  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 develloped. And as an adaption to the tree-mounting behaviour, their fore-limbs were elongated and transformed into three-fingered hands with sharp clawes and wrists to flex hindways only in the lateral plane. This fore-limb 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 adaption 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 sunraids, and as a means to reduce the body-temperature they evolved air sacs connected with the lungs to coole when they breathed.
  Besides they were forced to assume the optimal body-temperature of 42° C. which, however, was disadvantageous when they seeked 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 clawes, 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 middlesized Coelurophysis, 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-evolusion, 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 Jurasic were an earlier and more distant pro-avian offshoot.
  The very bird-like coelurosaurs from the Late Jurassic and Cretaceous, the toothless ornithomimimosaurs, such as Struthiomimus, Gallimimus, and Ornithomimus are descendants from late, more distant pro-avian offshoots which had adopted a running, plante-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 scyte-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 af 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 the long-necked herbivores.
  The short-necked ones had a general change of the pelvis, and a dentition apt to thew the food. They became the ornitischian dinosaurs which split up in the ornithopodes, which remained bipedal, whereas the stegosaurs and ankylosaurs soon assumed quadrupedality, and the ceratopsians did it later on.
  The long-necked herbivore 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 ornithomimimosaurs and deinonychosaurs defected from the bird-lineage.
  >From the bipedal archosaurs the tall, short-necked meat-eating carnosaurs emanated separately. See fig. 5.

dinosaurs and birds
Fig. 5. Proposed relation of dinosaurs and birds.

The dinosaurs' extinction.


Attached: Illustrations, z/fig1.gif z/fig2.gif z/fig3.gif z/fig4.gif and z/fig5.gif.

Links

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