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 Con’t • 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 • Reptilia>Parareptilia> • Testudines (O.)- Turtles • Cryptodira (subo.)- Hidden-neck turtles • Pleurodira (subo.)- Side-neck turtles • Reptilia>Diapsida> 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. 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 Archosaurs Paleosuchus palpebrosus Alligatoridae Cuvier’s 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 Con’t Chamaeleo calyptratus Chamaeleonidae, Chameleons Africa, Madagascar, India, Sri Lanka, Saudi Arabia, S. Spain, & the Mediterranean coast • 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. Varanus timorensis Varanidae, Monitors Warm Temperate and Tropical Africa, Asia & Australia

12. Lepidosaurs Con’t Amphisbaena fulginosa Amphisbaenidae Great Antillies, S. Amer., Africa, Spain, Turkey

13. Lepidosaurs Con’t 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 Con’t Boa constrictor (Common Boa, C&S 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 (Dalbert’s 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

20. 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

21. 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.

24. 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 embryo’s 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 female’s reproductive tract, and if sperm is to reach the ovum, the sperm must be placed within the female’s 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 female’s 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 (<25mybp) 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 archosauromorph’s 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., Testudines>>Reptilia>>Vertebrata) • 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 character’s 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 Linnaeus’s 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.