MESOZOIC REPTILESInvader of Land
Presented by
Wynn Haupt
Contents
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Intoduction
Mesozoic Reptile Classification
Defining the Mesozoic Era
Common Ancestor (Thecodonts to Dinosaurs)
Order Saurischia
Suborder Theropoda Characteristic features
Suborder Theropoda Unique Characteristic features
Order Ornithischia
Suborder Ornithopoda
Suborder Ornithopoda
Suborder Stegosauria
Suborder Ankylosauria
Suborder Ceratopsia
Reference List
Introduction
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In this presentation I will discuss the diversity of the land
dwelling reptiles of the Mesozoic era.
I will show how they are unique and what makes them
unique.
Basically land dwelling dinosaurs evolved from a
common ancestor and divided into two orders based on
their pelvic structures.
Mesozoic Reptile Classification
Kingdom – Animalia
Phylum – Chordata
Class – Reptilia
Subclass – Diapsida
Super order – Archosauria
Order – Saurischia
Ornithischia
Defining the Mesozoic Era
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The Mesozoic era was about 248-65Million Years
Ago. The Mesozoic era is divided into three periods,
Triassic 245 - 208 MYA, Jurassic 208 -146 MYA,
and the Cretaceous 146 - 65 MYA. Mesozoic means
"middle animals" this was the time when most
modern plants, invertebrates and fish started
evolved. The land was dominated by Mesozoic
reptiles, the ocean dominated by large marine
reptiles and the air ruled by Pterosaurs. Warm and
tropical climate at the time was mostly experienced.
Mesozoic era was around when, all the worlds’
continents were joined to form the supercontinent
called Pangea.
(www.palaeos.com/mesozoic/mesozoic.htm)
Defining the Mesozoic Era Cont.
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Mesozoic reptiles invaded the land water and
ocean. The fossil records tell use the story of the
Mesozoic era. Fossils are the mineralized remains
of animals and plants or the trace such as footprints.
The totality of fossils is their place in rock formation
and the sedimentary layers is known as the fossil
records. (www.en.wikipedia/org/wiki/fossils)
Common Ancestor (Thecodonts to
Dinosaurs)
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Dinosaurs evolved from a group of socket toothed reptiles the
thecodonts, which appeared about 225 million years ago (Lambert,
1983).
Early thecodonts were sprawling, crocodile-like called
proterosuchians (“earlier crocodile”) (Lambert, 1983).
Many thecodonts bodies where equipped them for hunting life spent
mostly in the water (Lambert, 1983).
They swam using their long, deep tails, but their hind limbs gave
them their powerful forward thrust, their hind limbs where longer and
stronger than there forelimbs (Lambert, 1983).
Thecodonts that went to live on land could thrust theirwhole limbs
down and back, giving them a longer stride than other reptiles of
their size (Lambert, 1983).
Thecodonts divided into two main groups the saurischian and
ornithischian dinosaurs.
Common Ancestor (Thecodonts to
Dinosaurs) Cont.
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Most could walk upright like a dog and raised their bodies off the ground
(Lambert, 1983).
Pseudosuchian (sham crocodiles) thecodonts walked on all fours, but short
front legs made running difficult, so they sprinted on their long hind legs and
balanced with their long, strong tail (Lambert, 1983).
In time there were many sizes of these flesh-eating pseudosuchians, the
thecodont speed could of help with their rise in abudance (Lambert, 1983).
By 205 million years ago pseudosuchians gave rise to the first flesh eating
dinosaur (Lambert, 1983).
Soon there were large and small dinosaurs, including those with teeth
designed to eat leaves (Lambert, 1983).
By 193 million years ago, flesh eating dinosaurs replaced thecodonts, and
nearly all big herbivores were dinosaurs (Lambert, 1983).
Source Unkown
Order Saurischia
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One of two distinct orders of dinosaur, distinguished from each other
by differences in structure (Microsoft Encarta 98).
Saurischian (lizard-hipped) dinosaurs had a pelvic structure similar
to that of extant (surviving) reptiles (Microsoft Encarta 98).
Its hip girdle has three main bones, the pubis (front bone) faces
forward in most saurichia (Lambert, 1983).
They had teeth around the entire jaw, or only at the front, and
included both carnivores (meat-eaters) and herbivores (plant-eaters)
(Microsoft Encarta 98).
The two main saurischia suborders evolved, the two legged, flesh
eating theropods and the four legged, mostly plant eating
sauropodomorphs (Lambert, 1983).
Saurischians thrived all three periods of the Mesozoic Era, but as
the age of the dinosaurs came to an end saurischians were
outnumbered by the other major group of dinosaurs: the
ornithischians (Lambert, 1983).
Source unknown
Suborder Theropoda
Characteristic features
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Theropods fall under the order saurischia.
Theropods have a reduced or the complete loss, of the outer finger
of the hand (Farlow & Brett-Surman, 1997).
They are flesh eaters, most have lade like teeth, which are serrated
(Farlow & Brett-Surman, 1997).
Claws are often recurved and taper to sharp points especially on the
hand (Farlow & Brett-Surman, 1997).
Theropods are slender, long legged, bipedal animals that are built to
move quickly (Farlow & Brett-Surman, 1997).
These characteristics are not unique to theropods, even though they
are significant aspects of their appearance (Farlow & Brett-Surman,
1997).
Suborder Theropoda Unique
Characteristic features
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But uniquely theropods always have hollow limb bonesand also
have a tendency towards air-filled bones in the front of its body
(Farlow & Brett-Surman, 1997).
Bone in front of eye extends onto the top of skull (Farlow & BrettSurman, 1997).
Extra joint in lower jaw (Farlow & Brett-Surman, 1997)
Elongated prezygapophyses found on tail (Farlow & Brett-Surman,
1997).
Scapula is strap-like (Farlow & Brett-Surman, 1997).
Hand is elongated with loss of outer finger (Farlow & Brett-Surman,
1997).
Expansion on the distal end of pubis (Farlow & Brett-Surman, 1997).
These are some of the unique characteristics of theropods.
Order Ornithischia
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The other distinct order of dinosaurs are, distinguished from each
other by differences in structure (Microsoft Encarta 98).
Ornithischian (bird-hipped) dinosaurs had forward and backward
projecting extensions to the pubic bone of the pelvis, superficially
resembling the pelvic structure of a bird (Microsoft Encarta 98).
The front of the jaws developed into a horny beak, with powerful
grinding teeth, cheek pouches and lattice of bony tendons
reinforcing the spine (Lambert, 1983).
. All known ornithischians were herbivores (plant-eaters) (Microsoft
Encarta 98).
They also had an extra bone forming the tip of the lower jaw
(Lambert, 1983).
They were two legged, four legged plated, horned and armored
dinosaurs (Lambert, 1983).
The four suborders which fall under the order of
ornithischian dinosaurs. Source unknown
Suborder Ornithopoda
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Only ornithopods that were able to walk or run on their hind legs
(Lambert, 1983).
“bird-footed” bird-hipped bipeds were dinosaur equivalents of
browsing mammals like deer and gazelles (Lambert, 1983).
They were herbivorous, existed from the earliest Jurassic to the end
of the Cretaceous period and were the first herbivores to have
multiple tooth rows cheek pouches, true mastication and the first to
engage in selective feeding (Farlow & Brett-Surman, 1997).
They lacked horns and armor (Farlow & Brett-Surman, 1997).
Walk on their toes, have five functional fingers on the hand and
three on its foot, the pre-pubic bone projects forward and away from
the midline of the body (in contrast to theropods) (Farlow & BrettSurman, 1997).
Considered to be the stem group of the order due to its lack of
horns, armor and spikes (Farlow & Brett-Surman, 1997).
Suborder Ornithopoda cont.
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Ornithopods are diagnosed as follows: premaxillary teeth are on a
lower level than the maxillary teeth, jaw joints lower than tooth rows
so jaw comes together like nutcrackers, the premaxillary bone has a
process that extends backward towards the orbit, and there is a
large fourth trochanter on the femur for the attachment of the
caudifemoralis muscle group (Farlow & Brett-Surman, 1997).
Suborder Stegosauria
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Known as the plated dinosaur (Lambert, 1983).
Bony spikes or plates, or both, which are embedded into its thick
skin, it guarded the neck, back, and tail and could have been used
for to shed unwanted body heat (Lambert, 1983).
They walked on all fours unless they browsed on trees then it would
stand on its rear legs (Lambert, 1983).
They could only feed on soft lush plants because of short, weak
teeth (Lambert, 1983).
Under attack they might have swung its spiky tail, but their flanks
would become vulnerable (Lambert, 1983).
Suborder Ankylosauria
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Ankylosaurs (fused lizzards) were short limbed, four legged, armor
plated dinosaurs with long wide body (Farlow & Brett-Surman,
1997).
Most prominent armor, or scutes consisted of keeled or unkeeled
plates of bone embedded into the skin of the dinosaur (Farlow &
Brett-Surman, 1997).
This armor protect exposed part of the body (Lambert, 1983).
The scutes were sometime repaced by spines or spikes on the body
and tail (Farlow & Brett-Surman, 1997).
In at least one group you would find a bone club at the end of its tail
(Farlow & Brett-Surman, 1997).
They had weak jaws and small teeth, which meant they ate soft, low
growing plants, but might live on insects (Lambert, 1983).
Suborder Ceratopsia
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Known as horned dinosaurs were one of the last to evolve (Lambert,
1983).
They were the largest and most abundant group of dinosaurs
(Lambert, 1983).
Mostly four legged, with massive heads armed with formidable horns
(Lambert, 1983).
They had a bony frill jutting backward from the skull which masked
the neck and provided an anchor for powerful muscles that worked
jaw ending in a massive “parrot’s beak” (Lambert, 1983).
Browsed on tough leaved plants and used its horn to ward off
attacks by carnivores (Lambert, 1983).
In modern time they could be categorized as rhinoceroses or cattle
(Lambert, 1983)
Reference List
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Brett-Surman. M and Farlow. J, The Complete Dinosaur, (1997),
Indiana University Press, Bloomington and Indanapolis
Lambert. D, A Field Guide to Dinosaurs,(1983), Avon Books, New
York
(www.palaeos.com/mesozoic/mesozoic.htm)
(www.en.wikipedia/org/wiki/fossils)