Part I: Evolutionary History

1
Part I Evolutionary History

• Chapter 1
• Tetrapod Relationships Evolutionary Systematics

2
What is Herpetology?

• is it the study of the herpes virus?
• hey this sounds Greek to me!
• The word herpetology is based on the Greek herpes
  or the Latin herpeton, meaning a creeping or
  crawling thing.
• Therefore, Herpetology is the scientific study of
  creepy-crawly things, specifically amphibians and
  reptiles.

3
Systematics

• The two distinct groups are Amphibians and
  Reptiles.
• Both clades arose within the Tetrapoda (Greek for
  four feet).
• Tetrapoda is a clade of bony fish that first
  appeared in the Paleozoic Era. These fish took
  the first step from water to land. And one of
  their earliest divergent groups became the
  Amphibians.
• Another Tetrapod group arrived during the
  Carboniferous, and these animals were called
  Anthracosaurs. They propagated on land in the
  absence of water and were not prone to
  desiccation. Today this group is represented by
  reptiles (including birds) and mammals.

4
The dichotomy of Amphibians Reptiles

• If Amphibians Reptiles are not each others
  closest relatives, why has herpetology continued
  to study these two groups as a single scientific
  pursuit?
• Historical inertia
• Tradition
• Many aspects of the lives and biology of these
  two clades are complementary.
• Can be studied using similar techniques or modes
  of investigation.
• Further the biological similarities of A R have
  made them ideal models in manipulative or
  experimental ecology, etc.

5
Lissamphibia

• Consist of 3 Orders-
• Gymnophiona- Caecilians superficially resemble
  earthworms, and are labeled with the node-base
  name Gymnophiona (naked snake), and the stem base
  name Apoda (without foot).
• All extant caecilians lack limbs, are strongly
  annulated, and have bullet-shaped heads tails.
  This morphology reflects the burrowing lifestyle
  of these tropical amphibians. (33 genera 170
  species)
• Caudata- Salamanders superficially resemble a
  cross between a lizard and a frog. They are
  labeled with the node-based name Caudata (having
  tail) and the stem-based name Urodela (tail
  visible).
• Salamanders have cylindrical bodies, long tails,
  distinct heads and necks, well-developed limbs,
  although a few salamanders have greatly reduced
  limbs or even have lost the hind limbs. Overall
  the salamanders are a fairly diverse group that
  are represented by many ecological types,
  including totally aquatic, burrowing,
  terrestrial, arboreal species. (66 genera
  515 species)

Dermophis mexicanus Caeciliidae, Mexican
Tailless Tropical America, eastern western
equatorial Africa, Seychelles Islands, India,
Burma
Ambystoma tigrinum Ambystomatidae, Mole
Salamanders
NA to the southern rim of the Mexican Plateau
6
Lissamphibia Cont

• Anura- Frogs are given the node-based name Anura
  (without tail) and the stem-based name Salienta
  (jumping).
• They are unlike other vertebrates in having
  robust, tailless bodies a continuous head body
  (no well defined neck) well developed limbs
• The hind limbs are often twice the length of the
  body, and their morphology reflects their bipedal
  jumping. However, not all frogs jump or even
  hop some taxa are totally aquatic and use a
  synchronous hind limb kick for propulsion,
  whereas other species including terrestrial and
  arboreal forms, walk. Among amphibians frogs are
  the most speciose and show the highest
  morphological, physiological, and ecological
  diversity and the broadest geographic occurrence.
  (344 genera 4810 species)

Phyllobates terribilis Dendrobatidae, Poison
Frogs Southern Central America and northern South
America through the Amazonian Basin to Atlantic
forest
7
Extant Reptiles

• The living reptiles consists of 3 clades
  turtles, archosaurs, lepidosaurs. This scheme
  can be further broken down into 5 Orders
• ReptiliagtParareptiliagt
• Testudines (O.)- Turtles
• Cryptodira (subo.)- Hidden-neck turtles
• Pleurodira (subo.)- Side-neck turtles
• ReptiliagtDiapsidagt Sauria
• Archosauria-
• Crocodylia (O.)- Crocodylians
• Aves (O.)- Birds
• Lepidosauria-
• Sphenodonita (O.)- Tuataras
• Squamata (O.)-
• Lacertilia (subo.)- Lizards
• Serpentes (subo.)- Snakes

8
Testudines

• Turtles called by the node-based name Testudines
  (tortoises), like frogs, cannot be mistaken for
  any other animal.
• Classification Reptilia, Parareptilia,
  Testudines
• Body encased with a upper and lower bony shell
  (carapace plastron, respectively)
• Moderately speciose, they range from fully
  aquatic (expect egg deposition) to fully
  terrestrial, from pygmies to giants, from
  herbivores to carnivores. (250-280 species)

Chelus fimbriatus (Matamata Chelidae) Amazon
Drainage
Platemys platycephala platycephala (Twist-neck
Turtle Chelidae) N.SA
9
Archosaurs

• Living Archosaurs include crocodylians and birds.
  Although the archosaur origin of birds has been
  long recognized, it was only recently that their
  true evolutionary classification be depicted,
  thereby promoting birds as reptiles.
• Crocodylians, called by the node-based name
  Crocodylia (lizard), are armored by thick skin
  and osteoderms. The elongate head, body and tail
  dwarf the short strong limbs.
• Crocs are a small group of predaceous, semi
  aquatic reptiles that swim with strong, powerful
  strokes of the tail.

• Their limbs allow for mobility on land, although
  terrestrial activities are usually limited to
  basking and nesting.(18 genera 22-24 species

Paleosuchus palpebrosus Alligatoridae Cuviers
Dwarf Caiman SA, Amazon Drainage
10
Lepidosaurs

• Include the tuatara, snakes, lizards
  amphisbaenians
• Tuatara Classification Reptilia, Diapsida,
  Sauria, Lepidosauria, Sphenodontia
• 2 species of tuataras, referred to by the
  node-based name Sphenodontida (wedge tooth) and
  the stem-based name Rhynchocephalia (nose or
  snout head), are lizard-like but represent and
  early divergence within the lepidosaurian clade.
  Today, the tuataras occur only on islets off the
  coast of New Zealand.

Sphenodon punctatus Northern Tuatara NE coast of
N. Island western Cook Strait, NZ
11
Lepidosaurs Cont

• The node-based name Squamata (scaly) includes the
  lizards, snakes amphisbaenians (420genera
  4800species)
• These groups are the most diverse and speciose of
  the living reptiles, occupying habitats ranging
  from tropical oceans to temperate mountaintops.
  They display a variety of body forms, shapes and
  sizes.
• Most taxa are terrestrial or arboreal, though
  many snakes are semi aquatic. A few snakes are
  totally aquatic, and some are subterranean.
• Snakes are the most successful of limbless or
  reduced limbed lizards.

Chamaeleo calyptratus Chamaeleonidae,
Chameleons Africa, Madagascar, India, Sri Lanka,
Saudi Arabia, S. Spain, the Mediterranean coast
Varanus timorensis Varanidae, Monitors Warm
Temperate and Tropical Africa, Asia Australia
12
Lepidosaurs Cont
Amphisbaena fulginosa Amphisbaenidae Great
Antillies, S. Amer., Africa, Spain, Turkey
13
Lepidosaurs Cont
Cemphora coccinea (Scarlet Snake, SE
US) Colubridae (Colubrinae) Worldwide
Naja nigricollis (Black-necked spitting cobra,
Sub-Saharan Africa) Elapidae (Elapinae Southern
NA to southern SA, Africa, southern Asia to
southern Australia
Sistrurus miliarius (Pygmy Rattlesnake, SE
US) Viperidae (Crotalidae, NW), Worldwide
Bitis gabonica (Gabon Viper, Sub-Saharan
Africa) Viperidae (Viperinae, OW), Wolrdwide
14
Lepidosaurs Cont
Boa constrictor (Common Boa, CS Amer.) Boidae
Western N Amer. to S. subtropical S Amer, West
Indies, C. Africa to South Asia, Madagascar,
southwest Pacific Islands
Python curtus (Blood Python, Indoneisa) Pythonidae
African, India, Indo-Australia)
Eunectes murinus (Green Anaconda,
Amazonian) Boidae Western N Amer. to S.
subtropical S Amer, West Indies, C. Africa to
South Asia, Madagascar, southwest Pacific
Islands Western N Amer. to S. subtropical S Amer,
West Indies, C. Africa to South Asia, Madagascar,
southwest Pacific Islands
Liasis albertisii (Dalberts Python, N. Torres
Is.) Pythonidae Africa, India, Indo-Australia
15
Relationships among Vertebrates

• Middle Devonian (380-400 mybp) a fish ancestor
  gave rise to the first tetrapods
• Approx 30-40 mybp, the tetrapods split into 2
  lineages, amphibians anthracosaurs, with gave
  rise to extant tetrapods.
• Plants, like animals, were only beginning to
  radiate into a terrestrial environment from a
  completely aquatic existence.
• Transition from fish to tetrapod occurred in the
  water, the earliest tetrapods were highly
  aquatic.
• However, the proposition that tetrapods evolved
  from fish that used modified fins to escape from
  drying bodies of water is no longer widely
  accepted.
• Limbs probably arose in an aquatic environment,
  perhaps for stalking prey in heavy vegetation, or
  perhaps as props to permit aerial respiration and
  movement in the shallow waters or marshes.
• Tetrapods probably have a freshwater origin owing
  to their kidney structure and overall physiology
  a preponderance of early tetrapod fossils from
  nonmarine sediments.
• A Sarcopterygian ancestor began the movement from
  an entirely aquatic lifestyle to a terrestrial
  one. These prototetrapods, like fish, were
  unable to survive on land.

16
Life in a terrestrial environment

• Aerial Respiration via lungs and possibly skin
  (amphibians)
• Development of well defined limbs
• Increased strength of vertebral column skull
• Pectoral girdle became detached from skull
• Increased skull articulation via the occipital
  condyles atlas. This improved inertial feeding
  and breathing above the waters surface.
• Sense organs shifted from aquatic to aerial
  perception.
• Lateral line only functioned in aquatic stage of
  life cycle or in aquatic species
• Hearing middle ear structures appeared
• Eyes evolved to sharpen their focus for aerial
  vision
• Nasal passage ways became a dual channel, with
  air passages for respiration and portions of the
  surfaces modified for olfaction.
• Epidermis increased its thickness external
  layers undergo keratinization.

17
Life in a terrestrial environment

• The preceding changes represent the major
  anatomical alterations that occurred in the
  transition from fish to tetrapod.
• Many physiological modifications also occurred,
  as we will discuss later in chapter 6
• Reproduction, initially, remained fishlike
  external fertilization, eggs encased in
  gelatinous capsules, and larvae with gills.
• Metamorphosis from aquatic larval to a
  semiaquatic adult stage was a new developmental
  feature.

18
Fish ancestors and early tetrapods

• The earliest tetrapods were terrestrial bony
  fish, that is, members of the sacropterygian
  branch of the bony fish clade.
• However, which early sacropterygian group the
  tetrapods share an immediate ancestor is debated.
  
• This debate has broadened in the last 20 years
  because of 3 reasons 1) the discovery of new
  transitional sarcopterygians, 2) better
  specimens or preparation, 3) different phyletic
  philosophies and analytical approaches.
• Is the tetrapoda monophyletic? Yes, because of
  numerous unique (derived) traits shared by
  members of the group.
• Extinct and extant members share a fenestra
  ovalis into the inner ear, a stapes, a sacrum,
  paired bones in the epipodial segment of the
  limbs, hinged joints between pro- and epipodial
  segments of limbs, digits on the end of limbs, a
  cheek plate of the skull with seven or fewer
  bones, and several other features that are too
  exhausting to list.

19
Fish ancestors and early tetrapods

• One of the earliest tetrapods was Ichthyostega,
  appears much like the osteolepiforms
  Eusthenopteron, even though the former had legs
  and the latter fins.
• The structural similarity of this and other early
  tetrpods supports the osteolepiform-tetrapod
  hypothesis however, other similarities support
  other taxa as possible sister groups.
• Nonetheless, Ichthyostega is not the ancestor of
  either amphibians or reptiles, although it is a
  member of the clade Ichthyostegalia, which is the
  sister group of the Tetrapoda.
• Molecular data suggest that the lungfishes are
  the closest living relative to modern tetrapods.
  This relatedness does not equal a sister group
  relationship because extinct taxa are absent from
  the analysis. In closing the real contenders for
  common ancestry are among the extinct
  sarcopterygians, including older contenders such
  as the osteolepiforms and porolepiforms and newly
  discovered contenders such as Elginerpeton and
  Panderichthys

Ichthyostega
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Evolution of early Amniotes

• Ancient Amphibians
• The ancestor issue cannot be unequivocally
  resolved because of the discovery of new
  transitional taxa (Elginerpeton) or more
  complete, better prepared specimens of older taxa
  (Panderichthys) can significantly alter the
  interpretation of sister-group relationships.
• The ancestor will likely be an extinct member of
  the Temnospondyli clade, such as Eryops.
• There are many interpretations to who and what
  are the Amphibia? The monophyly of living
  amphibians, the Lissamphibia (caecilians, frogs,
  salamanders), seems highly probable, and they are
  the members of the temnospondyl clade.

Temnospondyli Eryops
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Modern Amphibians- The Lissamphibia

• The living Amphibians are thought to share a
  common ancestor.
• The proposed patterns are
• Frogs arose from a different ancestor than
  salamanders and caecilians
• Frogs and salamanders are a sister group and
  caecilians are a sister group to their clade
• Caecilians and salamanders are a sister group,
  and frogs are a sister group to their clade.
• Defining Amphibia by its members-
• The articular surface of the atlas (cervical
  vertebrae is convex
• The exocciptal bones have a suture articulation
  to the dermal roofing bones
• The hand (manus) has four digits and the foot
  (pes) five digits.

22
Modern Amphibians- The Lissamphibia

• Traits that support the monophyly of the
  Lissamphibia.
• All share a reliance on cutaneous respiration,
  but some may also use lungs and gills.
• a pair of sensory papillae in the inner ear
  (stape-basilar opercular-amphibian papillae),
• two sound transmission channels in the inner ear,
• Specialized visual cells in the retina (green
  rods),
• Pedicellate teeth,
• The presence of two types of skin glands (mucous
  granular (poison),
• All have fat bodies
• Frogs and Salamanders are the only vertebrates
  able to raise and lower their eyes. T
• The bony orbit of all amphibians opens into the
  roof of the mouth, with a special muscle
  stretched across the opening which elevates the
  eye.
• The ribs of amphibians do not encircle the body.

23
Tetrapod relationships and Evolutionary
systematics

• Figure 1. Temnospondyl skulls in dorsal view.
• Dendrerpeton acadianum
• Eryops megacephalus
• Tersomius texensis
• D) Melosaurus vetustus
• Abbreviations
• Bc- braincase F- frontal
• In- internasal J- jugal
• L- lacrimal M- maxilla
• N- nasal P- parietal
• Pf- pineal foramen Pm- premaxilla
• Po- postorbital Pof- postfrontal
• Pp- postparietal Prf- prefrontal
• Pt- pterygoid Q- quadrate
• Qj-quadratojugal Sq- squamosal
• St- supratemporal T- tabular.
• Adapted from-
• Steyer Laurin, 2000.

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Evolution of Early AmniotesEarly Tetrapods
Terrestriality

• First terrestrial tetrapods arose in the early to
  middle Mississippian period (360-340 mybp, Lower
  Carboniferous)
• Tetrapod fossils appear with high diversity in
  the late Mississippian and Early Pennsylvanian
  (340-320 myby)
• This diversity includes the 1st radiation of the
  amphibians and the appearance of the
  anthrocosaurs and the earliest amniotes.
• The evolution of terrestrial forms requires
  modifications in anatomy, physiology, behavior,
  and a host of other characteristics.
• These changes did not occur synchronously-some
  were linked and others were not, and some
  required little modification because of
  exaptation (pre-adaptation) and others required
  major reorganization.
• The diversity of changes is reflected in the
  diversity of the Lower Carboniferous amphibians
  and anthracosaurs.
• Amphibians remained close to water and took
  occasional evolutionary ventures toward full
  terrestriality.
• Is this tie to water maladapted or a lower
  evolutionary state? No! This state allow
  amphibians to exploit a different adaptive zone.

25
Early Tetrapods Terrestriality

• As the amphibians diversified in association w/
  aquatic habitats, the anthracosaurs and their
  descendents became increasingly terrestrial in
  all phases of their life.
• The most successful terrestrial group, defining
  success by having descendents still living today,
  was the clade comprising the amniotes (Amniota).
• Full terrestriality required organisms develop in
  the absence of water.
• The evolution of the amniotic egg, which could be
  deposited on land and resisted dehydration,
  occurred at this time.
• The amniotic egg did not appear de novo but in a
  series of steps, each increasing the embryos
  survivorship on land in addition, the amniotic
  egg with its protective extra embryonic membranes
  was not necessarily the first step.
• The evolution of a closed (shelled) egg
  presumably was the first terrestrial egg-step,
  and it had to have been preceded by internal
  fertilization, an exaptation that permitted the
  evolutionary shift from aquatic to terrestrial
  development.

26
Early Tetrapods Terrestriality

• Internal fertilization is not a prerequisite for
  direct development, nor does direct development
  free the parents from seeking an aquatic or
  permanently moist site for egg deposition.
• Internal fertilization, among extant amphibians,
  predominates in caecilians and salamanders, but
  only a few anurans with direct development have
  internal fertilization.
• When eggs are placed in a protective envelope,
  the encasing process must be done inside the
  females reproductive tract, and if sperm is to
  reach the ovum, the sperm must be placed within
  the females reproductive tract as well.
• Sperm delivery and fertilization must precede egg
  encasement.
• Internal fertilization has arisen independently
  numerous times within lissamphibians hence, it
  was an easy evolutionary hurdle for the
  protoamniote anthracosaurs to overcome.

27
Early Tetrapods Terrestriality

• The evolution of the shelled egg presents a
  greater hurdle, and its explanation requires a
  speculative scenario because it has left no
  traces in the fossil record.
• Some common scenarios suggests that naked
  amniotic eggs with direct development were laid
  in moist areas.
• Selection to reduce predation by microorganisms
  drove the replacement of gelatinous capsules by
  the deposition of a fiberous envelope that was
  the precursor to the thicker calcareous shell
  that allowed a shift of laying eggs in drier
  environments.
• Others suggest the private pool scenario and have
  directed attention to the development of the
  extra embryonic membranes and their encapsulation
  of the egg or embryo
• Each hypothesis provides a facet from
  evolutionary history but none provide a full
  explanation of events, therefore, these are
  probable theories.
• In any case we cannot determine without actual
  evidence whether the amniotic membranes evolved
  in embryos held within the females oviduct or
  whether they evolved in externally shed eggs.
• Either scenario is equally parsimonious from the
  available data on other extant vertebrates.

28
Early Tetrapods Terrestriality

• Other modifications for life in a terrestrial
  environment include
• Changes in skin structure
• Lung changed in several ways-
• Increase in size and internal partitioning
  (increase in vascularization), and these changes
  apparently occurred in the protoamniotes.
• Modification to ribs and presence of thoracic
  basket (rib cage)
• The rib cage appears incomplete in most
  anthracosaurs and seymouriamorphs, so those
  groups probably were still largely dependent on
  the buccal force pump.
• The rib cage of diadectomorphs (pre-amniotes)
  extends further ventrally although it still
  appears incomplete, this contradiction may mark
  the transition from buccal to thoracic
  ventilation.
• Anthracosaurs and early amniotes lacked otic
  notches, denoting the absence of eardrums
  although they were not deaf, they were
  insensitive to high frequency sound.
• The olfactory sense was highly developed in the
  earliest of amniotes.
• Changes in the postcranial skeleton
• Vertebral structure changed to produce a more
  robust supporting arch.
• Modification to limb and girdle skeleton
• Skull became more compact and tightly linked
• Modification to the skull in association with the
  inner ear.

29
Early Amniotes Allies

• Anthracosaurs are the ancestral stock that gave
  rise to the amniotes, and some may have had eggs
  similar to amniotes.
• The anthracosaurs, seymouriamorpha,
  diadectomorpha, and early amniotes do share some
  features.
• Multipartite atlas-axis
• Have a large single pleurocentrum for each
  vertebrae.
• Possess five toed forefeet with a phalangeal
  formula of 2,3,4,5
• Seymouriamorphs compose an early divergent group
  of anthracosaurs
• These small tetrapods may be the sister group to
  diadectomorphs or to the protoamniote taxa.
• They probably had external development and
  required water for reproduction.
• They have been incorrectly called amphibians
• They are not amniotes
• Their fossil history does not begin until the
  Late Pennsylvanian

30
Early Amniotes Allies

• Diadectomorphs share a number of specialized
  (derived) features with early amniotes-traits
  that are not present in their predecessors.
• Both groups lost temporal notches from their
  skulls,
• Have a fully differentiated atlas-axis complex
  with fusion of the two centra in adults
• Possess a pair of sacral vertebrae
• They share a large, platelike supraoccipital bone
  and a number of small cranial bones
  (supratemporal, tabulars, and postparietals) that
  are lost in advanced reptiles.
• The stapes of both were stout bones with large
  footplates, and apparently eardrums were absent.
  These latter features do not suggest that they
  were deaf, but that their hearing was limited to
  low frequencies.
• Their development probably included preamniotic
  changes, such as partitioning of the fertilized
  egg into embryonic and extra embryonic regions or
  even a full amniotic state.

31
The first Amniotes

• 1st Amniote fossils are from the Middle
  Pennsylvanian, but they are not primitive
  amniotes in the sense of displaying numerous
  transitional traits.
• These 1st amniotes are Archaeothyris (a
  synapsid), Hylonomus (a reptile), and Paleothyris
  (a reptile) already the divergence of the
  synapsids and reptilian stocks was evident.
• The Synapsida is the clade represented today by
  mammals and in the past they have been commonly
  called mammal-like reptiles, an inappropriate and
  misleading name.
• The pelycosaurs were the first major radiation of
  synapsids and perhaps gave rise to the ancestor
  of the Therapsida, the line leading to modern
  mammals.
• Divergence among the basal reptiles apparently
  occurred soon after the origin of the synapsids,
  but there is some controversy about the early
  evolutionary history of reptiles.
• The major controversy surrounds the origin of
  turtles and whether the Parareptilia is
  paraphyletic or monophyletic. The Parareptilia
  includes the millerettids, pareiasaurs,
  procolophonoids, and turtles.
• Another interpretation considers the turtles as
  diapsids and suggests a moderately close
  relationship to lepidosaurs.
• Molecular data support the diapsid relationship
  yielding a turtle-archosaur (crocodylian bird)
  sister group relationship or a turtle-crocodylian
  one.
• Note that the molecular data only yield a simple
  phylogeny of living taxa and do not show the
  relationships of extinct taxa or their history of
  divergence.

32
Radiation of Diapsids

• Diapsida is a diverse clade of reptiles, its
  content is generally accepted with only minor
  controversy (excluding the disagreement regarding
  turtles).
• Modern diapsids include lizards, snakes, birds,
  crocodylians extinct diapsids include dinosaurs,
  pterosaurs, ichthyosaurs, and other extinct
  groups.
• The stem based name Diapsida is derived from the
  presence of a pair of fenestrae in the temporal
  region of the skull diapsids also have
  suborbital fenestra, and occipital condyle
  lacking an exocciptal component, and a
  ridged-grooved tibioastragalar joint.
• The earliest known divergence yielded the
  araeoscelidians and the saurians
• The araeoscelidians were small (40 cm TBL)
  diapsids of the Late Carboniferous and were an
  evolutionary dead end. In contrast the saurian
  lineage gave rise to all subsequent diapsid
  reptiles.
• Members of the saurians share over a dozen unique
  osteological features, including a reduced
  lacrimal with nasal-maxillary contact, no
  caniniform teeth maxillary teeth, an
  interclavicle with distinct lateral processes,
  and a short, stout fifth metatarsal.

33
Radiation of Diapsids

• The Euryapsida apparently arose from an early
  split in the Sauria clade (fig. 1.11).
• They comprised a diverse group of mainly aquatic
  (marine) reptiles, ranging from the fishlike
  ichthyosaurs to the walruslike placodonts and the
  sea-serpent plesiosaurs.
• Individually these taxa and collectively the
  Euryapsida have had a long history of uncertainty
  in their position within the phylogeny of
  reptiles.
• In the late 1980s their diapsid affinity gained a
  consensus, although their basal relationship is
  still debated.
• For example, are they a sister group of the
  lepidosauromorphs or a sister group of the
  lepidosauromorph-acrhosauramorph clade? Is the
  Ichthyosauria a basal divergence of the
  euryapsids or perhaps not an euryaspid. (fig.
  1.11).
• Two clades Archosauromorpha and the
  Lepidosauromorpha, compose the other lineages of
  the Sauria.
• Both clades have living representatives,
  crocodylians and birds in the former and
  tuataras, lizards and snakes in the latter.
• Both clades have had high diversity in the deep
  past, although the dinosaurs focus attention on
  the diversity within the archosauromorphs,
  specifically on the archosaurs.

34
Radiation of Diapsids

• The Archosauria had earlier relatives (e.g.
  rhyncosaurs, protorsaurs, proterosuchids), and
  furthermore, the archosaurs are much more than
  just dinosaurs.
• The Archosaurs encompass two main lineages, the
  Crocodylotarsi and the Ornithodira they share a
  rotary cruruotarsal ankle, an antorbital
  fenestra, no ectepicondylar groove or foramen on
  the humerus, a fourth trochanter on the femur,
  and other traits.
• The Ornithodira includes the Pterosauria and
  Dinosauria
• The pterosaurs were an early and successful
  divergence from the lineage leading to the
  dinosaurs however, they never attained the
  diversity of modern birds or bats but were a
  constant presence from the Late Triassic to the
  end of the Cretaceous.
• The dinosaurs attained a diversity that was
  unequaled by any other Mesozoic group of
  tetrapods (ornithischian and saurischian)

35
Dinosaur Evolution

• Dinosaur evolution has been well studied outside
  the province of herpetology but relevant to the
  evolution of living reptiles.
• Birds (Aves) are feathered reptiles and
  Archaeopteryx is often considered the
  missing-link that has a mixture of reptilian
  and avian characteristics.
• Although few would argue that Archaeopteryx is
  not a bird, a controversy exists over the origin
  of birds.
• The current consensus places the origin of birds
  among the theropod dinosaurs however, three
  other hypothesis have current advocates, although
  all hypotheses place the origin of birds within
  the Archosauria. The theropod dinosaur
  hypothesis has the weight of cladistic evidence
  in its support. The others are mentioned below
  
• An early crocodyliform
• Among the basal ornithodiran archosaurs, and
• Megalanocosaurus, another basal archosaur taxon
  (see pg 20, fig. 1.12).
• Although these later interpretations represent
  minority positions, the cladistic near-relatives
  (birdlike theropods) of birds occur much later
  (lt25mybp) in the geological record than
  Archaeopteryx.

36
Crocodylotarsi

• Crocodylotarsi, the other major clade of
  archosaurs, has an abundance of taxa and a broad
  radiation in the Mesozoic and Early Tertiary.
• The Crocodylia, a group including the most recent
  common ancestor of the extant Alligatoridae,
  Crocodylidae, and Gavialidae (Gavialis) and its
  descendants, remains a successful group but shows
  only one aspect of crocodylotarsian radiation.
• The earliest radiations in the middle and Late
  Triassic included phytosaurs, aetosaurs, and
  rauisuchids.
• Another lineage, the Crocodyliformes, which
  include the later-appearing Crocodylia, also
  appeared in the Middle Triassic and yielded the
  diversity of Jurassic and Cretaceous taxa.
• The crocodyliformes had members that were small
  wolflike, large bipedal tyrannosaurus-like, giant
  marine crocodylian-like, and a variety of other
  body forms.

37

• The Lepidosauromorpha, the archosauromorphs
  sister group, consists of several basal groups
  and the lepidosaurs.
• All share derived traits such as a lateral ridge
  of the quadrate supporting a large tympanum, no
  cleithrum in the pectoral girdle, and
  ectepicondylar foramen rather than a groove in
  the humerus, and a large medial centrale in the
  foot.
• The earliest basal group is the Younginiformes
  from the Upper Permian and Lower Triassic.
• The Lepidosauria is a strongly supported clade
  with a wealth of derived features that are
  shared.
• Teeth attached loosely to the tooth-bearing bones
• Fusion of the pelvic bones in late development
• Hooked fifth metatarsals, and
• Paired copulatory organs (Hemipenes Rudimentary
  in Sphenodon)
• Of the two sister groups within the Lepidosauria,
  only two species of tuatara (sphenodontians)
  survive.
• The Sphenodontida has acrodont dentition and a
  premaxillary enameled beak. It was moderately
  abundant in the Late Triassic and Jurassic, and
  largely disappeared from the fossil record
  thereafter.
• The squamates are the sister group of the
  sphenodontians and are more abundant and
  speciose than the latter group from their first
  appearance in the Late Jurassic to today.
• The squamates apparently split early into two
  major lineages, Iguania (Iguanidae, Agamidae,
  Chamaeleonidae) and Scleroglossa (all other
  lizards, including Amphisbaenia and snakes).

38
Systematics- Theory and Practice

• What is systematics?
• It is the practice and theory of biological
  classification.
• Modern systematists attempt to discover the full
  diversity of life, to understand the processes
  producing the full diversity of life, and to
  classify the diversity in a manner that expresses
  phylogenetic relationships (i.e., evolutionary
  history)
• How does systematics mesh with what we do on a
  daily basis?
• Whether unraveling the inter-workings of a cell,
  tracing the epidemiology of a disease, or
  conserving a fragment of natural habitat, we must
  know the organisms with which we are working.
• Similarly, correct identification of an organism
  allows correct decisions in research and
  conservation.
• Further, correct identification provides
  immediate access to previously published
  information on that species, and knowledge of its
  classification-and hence its evolutionary
  relationships-opens a wider store of information
  because related species likely function
  similarly.

39
Basic Concepts

• Evolution, the concept of descent with
  modification, is the glue that unites the diverse
  aspects of modern biology. Therefore, our
  classification of organisms should reflect
  evolutionary history as closely as possible.
• Each name identifies an organism or group of
  organisms and provides an index to information
  associated with that name.
• Biological classification is traditionally
  hierarchical (a system of nested sets), with each
  ascending level potentially containing more
  subgroups and characterized by the shared
  similarities of the included subgroups (e.g.,
  TestudinesgtgtReptiliagtgtVertebrata)
• Species are the basic units of classification and
  the only real units, existing not as artificial
  categories but as real entities.
• The principal rule is that the grouping of
  organisms is monophyletic (a unique history of
  descent) and thus represents a single
  evolutionary group containing the ancestor and
  all descendants (i.e., clade).
• This would seem easily achieved if the members of
  the group are adequately known or studied
  however, aside from the difficulty in estimating
  relationships of divergent species, there is
  difficulty of tradition (see gorzugi pg 22, fig
  1.15)
• Presently we are making a conceptual shift from
  the traditional Linnean, non-evolution-based
  classification to an evolution-based one.

40
Systematic Analysis

• Types of Characters-
• Anatomical (skeletal)
• Physiological (resting metabolic rate)
• Biochemical (DNA or RNA)
• Ecological (biophysical habitat parameters)
• For the above characters to be useful for
  systematics, a characters state generally have
  lower variation within samples (i.e., population,
  species, etc) than among samples.

41
Methods of Analysis

• Numerical Analysis-
• The initial analysis examines the variation of
  single characters within each sample using
  univariate statistics (i.e., mean, median, mode,
  sd, frequency distributions, central tendency
  statistics).
• The next phase compares individual characters
  within samples, the relationship of characters to
  one another within samples, and character states
  of one sample to the those of another sample
  using bivariate statistics (i.e., ratios
  proportions, regression correlation, ANOVA,
  nonparametric statistics)
• The final phase usually is the comparison of
  multiple characters within and among samples
  using multivariate analysis (PCA, Cononical
  Correlation, Discriminant Function Analysis, and
  Cluster Analysis)
• Phylogenetic Analysis-
• The preceding numeric techniques do not provide
  estimates of phylogenetic relationships rather,
  they summarize the level of similarity.
• Hennigs approach to systematics (mid-1960s) gave
  repeatability to systematic practices and is
  broadly known as cladistics.
• The basic tenets of phylogenetic systematics are
  
• Only shared similarities that are derived are
  useful in deducting phylogenetic relationships.
• Speciation produces two sister species and
  speciation is recognizable only if the divergence
  of two populations is accompanied by the origin
  of a derived character state.

42
Nonmenclature

• Nonmenclature is another important aspect of
  systematics- also known as taxonomy.
• Why is nonmenclature important?
• All biologists must correctly identify the
  organism being studied and then must use the
  correct taxonomic name in reporting the results
  of their study.
• Failure to provide the correct scientific name
  will prevent other biologists from recognizing
  that the results are important or it may cause
  others to inappropriately compare data from
  unrelated species.
• Brief History- Our formal system of animal
  classification dates from the Linnaeuss 10th
  edition of Systema Naturae in 1758. Importantly,
  it was the 1st publication to consistently use a
  two-part name (a binomial of genus species).
• To avoid confusion, the botanical and zoological
  communities separately developed codes for the
  practice of nonmenclature. The most recent code
  for zoologists is the International Code of
  Zoological Nomenclature, Fourth Edition (the
  Code), published in 1999.

43
The Code - Rules and Practice

• The Code has 6 major tenets
• All animals extant or extinct are classified
  identically, using the same rules, classification
  hierarchies, and names where applicable.
• Although the Code applies only to the naming of
  taxa at the family level and below, all names
  formalized in Latin. All except the specific and
  subspecific epithet are capitalized when used
  formally these latter two are never capitalized.
  
• To ensure that a name will be associated
  correctly with a taxon, a type is designated-
  type genus for a family, type species for a
  genus, and type specimen for a species. There
  are several kinds of types recognized by the
  Code. The holotype is the single specimen
  designated as the name-bearer in the original
  description of the new species or subspecies, or
  the single specimen on which a taxon was based
  when no type was designated.
• Only one name may be used for each species.
• Just as for a species, only one name is valid for
  each genus or family.
• When a revised Code is approved and published,
  its rules immediately replace those of the
  previous edition.

44
Evolution-Based Taxonomy

• The preceding rules illustrate the typological
  approach of Linnean taxonomy, most especially the
  emphasis on named categories and fixed levels
  within the hierarchy.
• The adoption of cladistics as the major practice
  of current systematics has increased the advocacy
  for a taxonomy that is based on the principle of
  decent.
• A consequence of this change is how a taxon is
  named.
• In the Linnean system, a taxon is defined in
  terms of its assumed category in contrast, the
  evolution-based system defines a taxon in terms
  of its content, that is, the clade containing the
  most recent ancestor of X and all its
  descendants.
• A result of the latter practice is a
  classification in which a species has a
  hierarchical position equivalent to a clade with
  dozens of species in several lower level
  clades.
• Another consequence is the abandonment of
  category labels such as family, order, or class.