Herpetology = “crawling thing” + “study of” (Greek)

‘Herps’ comprise two groups: (grouped together because of history and biology)

Amphibian = “double life” (Greek) ‘Reptile’ = “to creep” (Latin)

(not monophyletic)

Carl Von Linné(Swedish Naturalist)

On Reptiles:“The foul and loathsome animals aredistinguished by a heart with a single ventricle and a single auricle, doubtfullungs and double penis.”On Amphibians:“Most amphibia are abhorrent because of their cold body, pale color, cartilaginousskeleton, filthy skin, fierce aspect, calculating eye, offensive smell, harshvoice, squalid habitation, and terriblevenom; and their creator has not exertedHis powers (to create) very many of them.”

Systema Naturae 10th ed., 1758

Some herps get a lot of press

Herps in History

1. Alexander the Great (356 B.C.)

2. Aesculapius (2000 yrs ago) - Caduceus

3. Religion, Coins, Mythology 4. Linnaeus (binominal nomenclature; 1700’s)

- ‘Foul and Loathsome’ - lumped verts that weren’t mammals or birds

5. Science - large amphibian eggs (e.g., Xenopus) - ectotherms and fever- behavior- ecology

- medicines etc.

Reasons to Study Herpetology

1. Unique anatomy, physiology, ecology, behavior

2. Insight into aspects of biology of extinct groups (e.g., dinosaurs)

3. Important members of food webs 4. Economic importance

Introduced pests, Leather, Curios, Jewelry, Aphrodisiacs, Food, Medicine

5. Many rare/threatened/endangered 6. Fascination

Studies of amphibians, reptiles

• Have played key roles to understanding:– Developmental biology

• Frog development

– Ecology• Diurnal activity patterns of lizards

– Physiology• Freezing frogs

– Medicine• Stress proteins first identified in salamanders

The Most Important Reason to Study Herps

Pseudacris crucifer (Spring Peeper)

Relative DiversityOf Vertebrates

Fishes------------30,000 speciesAmphibians------4,500 speciesReptiles-----------6,600 speciesBirds--------------8,700 speciesMammals---------3,500 species

Modern Approachesto Herpetology

(1) Functional—genetics, physiology, ecology, behavior

(2) Levels of Organization—molecular, cellular, organismal, populational, etc.

The Roots of HerpetologyAre Two-fold

(1) Taxonomy(2) Systematics

Anura ‘frogs’

Urodela salamanders

Gymnophiona caecilians

Mammalia

Testudines turtles

‘Lizards’

‘Lizards’

Amphisbaenia

Serpentes snakes

‘Lizards’

‘Lizards’

Rhynchocephalia tuatara

Crocodylia crocs etc.

Aves birdsSee Fig 2-1 (Pough et al., 2001)

To F

ishes

and A

nce

stor

Lissamphibia

Amniota

Diapsida

Reptilia

Tetrapoda

Lepid

osa

uri

a

SquamataExtant Herp

Groups

Archosauria

Synapsida

Phylogenetic Systematics- Apomorphy

derived character - Synapomorphy*

shared derived character - Autapomorphy

derived character in only one lineage - Plesiomorphy

shared ancestral characters no information on relationships, but inform

biology - Convergence

similar character but two (or more) separate origins

Phylogenetic Systematics (con’t) Phylogenetic Diagrams = Cladograms

- constructed by postulating sequence of changes in characters that will produce distribution of characters seen in taxa of interest

Parsimony - often used to decide among possible sequences - smallest number of changes from ancestral to derived condition

Sister Groups/Lineages - two adjacent branches

Outgroups - lineages outside the clade in question

Operational Characters

Amphibians (~4,600 species)

Three extant groups (Anura, Urodela, Gymnophiona) - Smooth skin without scales - Skin permeable to water (and gases)

dehydration, absorption, social, defense

- Anamniotic Egg

Reptiles (~6,600 species; excluding birds)

- Epidermal Scales - Lacking Hair or Feathers

- Amniotic Egg

Lissamphibia (Amphibians; 4,600 spp.) 1. Urodela (Salamanders)

-loss of lungs (~hyoid apparatus) -paedomorphosis (heterochrony)

2. Anura (Frogs and Toads) -no tail -short body, large head -limb proportions ~ locomotion -metamorphosis (aquatic tadpole -> terrestrial adult)

3. Gymnophiona (Caecilians) -burrowing -legless ~tropical -some with fetal teeth

Ambystoma californiense

Rana pipiens

Typhlonectes sp.

‘Reptilia’(not monophyletic; ~ 6,600 spp.) 1. Testudines (Chelonia, Turtles)

-duh -shell shape ~ ecology -no arboreal or gliding forms

2. Squamata (‘Lizards’ and Snakes and Amphisbaenians) -lizards not monophyletic -repeated loss of limbs -very diverse

Terrapene ornata ornata

Elgaria kingii

Crotaphytus collaris

‘Reptilia’(not monophyletic; ~ 6,600 spp.) 3. Crocodylia (Crocodiles, Alligators, Caiman)

-threatened (21 spp. remain)

-snout shape ~ diet -related to archosaurs (birds and dinosaurs)

4. Rhynchocephalia (Sphenodontida, Tuatara)

-2 extant species -islands of New Zealand -operate at ~cold

temperatures

Sphenodon sp.

Crocodylus siamensis

To Think About

Ancestral vs. Primitive as description of ‘old’ characters Why do we want to know about phylogenetic relationships? Why are there so many species of small reptiles and amphibians? Why do many herps operate at temperatures that are lower than optimal?

Ancestral vs. Primitive as description of ‘old’ characters (‘primitive’ implies something negative or bad, prefer to use ‘ancestral’) Why do we want to know about phylogenetic relationships? (to understand processes of evolution, understand/predict characters, apply to ecology, etc…) Why are there so many species of small reptiles and amphibians? (energetically possible, ecological ‘space’ devoid of endothermic competitors) Why do many herps operate at temperatures that are lower than optimal? (e.g., nocturnal, niche availability, survival)

Earth almost 5 billion years old, 3.5 bya ago cyanobacteria (unicellular)

Precambrian comprises ~85% of geologic time Phanerozoic Paleozoic Cambrian - origin of many invertebrate phyla and classes - first vertebrate remains Ordovician - first jawless fishes - first land plants Silurian - radiation of jawless fishes - first jawed fishes Devonian - radiation of bony fishes - disappearance of many jawless fishes - first tetrapods (early amphibians)

Biogeological Time Scale

Phanerozoic Paleozoic (con’t)

Cambrian Ordovician Silurian Devonian

Carboniferous Mississippian- radiation of amphibians

- abundant sharks Pennsylvanian - first reptiles

- many specialized amphibians Permian - radiation of reptiles

- displacement of amphibians - first archosaurs (early crocodylia, aves) - lots of extinctions at end of period - Pangaea (single continent)

Phanerozoic Mesozoic

Triassic - first Angiosperms - first ‘dinosaurs’ replace mammal-like

reptiles - first turtles and crocodilians - first appearance of true mammals - Pangaea splits

Jurassic - first salamanders, frogs, rhynchocephalians

- reptile diversity high - first birds

Cretaceous - climax of giant land and marine reptiles - then MASS EXTINCTION (66MaBP) - modern lizards (and later snakes)

Phanerozoic Cenozoic

TertiaryPaleocene - first caecilians

- first placental mammals Eocene - radiation of placental

mammals Oligocene - first apes, monkeys, whales Miocene - grazing mammals are

abundant Pliocene - large carnivores

Quaternary Pleistocene - early humans Holocene - (aka Recent) modern humans

Fig. 2-1 Pough et al. 2001

Major Groups of

Extant Tetrapods

Actinopterygii (fin-rayed fishes)

Sarcopterygii

Major Groups of Extant Tetrapods and Relatives From Fig. 2-1 (Pough et al. 2001)

6 = Actinopterygii (fish) - bony fishes with fins supported by rays and extrinisic muscle

2 = Sarcopterygii - from fish-like ancestors - vertebrates with fins/limbs supported by internal bone and intrinsic muscle - enamel on teeth

Major Groups of Extant Tetrapods and Relatives

From Fig. 2-1 (Pough et al. 2001) Extant Groups of Sarcopterygii:

7 = Actinistia (Latimeria = Coelocanth)

- 2 extant species - symmetrical three-lobed

tail 8 = Dipnoi

- 3 genera of extant lungfishes

3 = Tetrapoda - common ancestor of

lissamphibians and amniotes

(does not include stem tetrapods such as

Acanthostega and Ichthyostega

- developed pectoral girdle free from skull roof

- developed ankle and wrist joints

Extinct Tetrapod Relatives (attach on branch3) Stegocephalians (almost tetrapods on up…) - clade including Tetrapoda and all taxa more closely

related to them than to Panderichthyes - non-tetrapod stegocephalians are the stem tetrapods - includes temnospondyls and anthracosaurs

-Upper Devonian (360 MaBP) -Carnivores -6-8 digits/limb

Ichthyostega still had labrynthine pattern of dentition, lost in later Stegocephalians“Labyrinthodontia”

Fig. 2-1 Pough et al. 2001

Major Groups of

Extant Tetrapod

s

Panderichthyida,

then Stegocephalia,

then Tetrapoda

Major Groups of Extant Tetrapods and Relatives From Fig. 2-1 (Pough et al. 2001)

3 = Tetrapoda - common ancestor of lissamphibians and

amniotes (does not include stem tetrapods such as

Acanthostega and Ichthyostega- developed pectoral girdle free from skull

roof - developed ankle and wrist joints

9 = Lissamphibia - we will discuss synapomorphies later

4 = Amniota - amniotic egg - internal fertilization - loss of complex folding of dentine in teeth (labyrinthine pattern)

Extinct Tetrapod Relatives (attach on branch3) Panderichthyida (365 MaBP)

before Stegocephalians - less fish-like group - resemble tetrapods with paired fins - eyes dorsal on crocodile-like skull - flattened body - no dorsal or anal fins (why?) - frontal bones in skull- labyrinthodont dentition - probably shallow water predators tetrapod-like body and other features appeared BEFORE limbs

Osteolepiformes

Panderichthyida

(Ancestral to Panderichthyida)

Acanthostega

Acanthostega

Acanthostega

Acanthostega

Ichthyostega

Ichthyostega

Ichthyostega

Origins of Tetrapods Some Whys and Hows

The stegocephalians were still semi-aquatic. Transition from being fish-like to terrestrial tetrapod involved modification of structure

and function.

What changes would you expect to see and why?

Body Support

Moving from water to land requires different support system

Tetrapod origins

Ancestors of Stegocephalians were large (1-2m long) and therefore weighed a lot. Not a problem in water because float. But on land, had to modify structures to better fight gravity. Pectoral and pelvic fins were modified into limbs. Distal bone elements became more complex (e.g., wrist and ankle, digits). Proximal limb elements became more robust.

(fore: humerus, radius, ulna. hind: femur, tibia, fibula) Muscles of limbs increase in size and complexity. Muscles to lift body up, other muscles move body forward.

Body Support (con’t)

Moving from water to land requires different support system

Tetrapod origins

Pectoral girdle lost connection to skull -> mobility of head and shoulders. Pelvic girdle becomes more firmly attached to the vertebral column (~sacrum), initially to only one vertebrae. Helps support hindlimbs. Skull flattens, broadens, and snout elongates. Eyes become more dorsal. Dorsal and anal fins lost.

Locomotion

Walking/running replace swimming (water bouyant)

Tetrapod origins

In fish, body-wall muscles provide most of the locomotor force, and fins are used for maneuvering. In tetrapods, the body and tail muscles are less developed, whereas the muscles of limbs are greatly enlarged. Fish swim by lateral undulation. First tetrapods retain this bending, and use it to move limbs forward. Vertebrae develop zygapopheses, which limit movement dorsoventrally, and prevent sagging of the body. Vertebrae generally better ossified.

Respiration

Moving from water to air requires gills --> lungs

Tetrapod origins

Stegocephalians inherited lungs (modified swim bladder???) from fish. Also had gills (as evidenced by presence of opercular bones indicating gill slits found in adult stem tetrapods like Ichthyostega) Gills of fish will collapse in air, so even though there is more oxygen in air than in water, fish will suffocate. Had to switch to ventilating the lungs, which meant developing muscles of the rib cage. Note that modern amphibians use buccal pumping (~air swallowing) and cutaneous respiration, rather than negative pressure from expanding rib cage.

Related to Respiration

How to excrete nitrogenous waste?

Tetrapod origins

Gills used to excrete nitrogenous waste (e.g. ammonia, urea) in fish. Plenty of water for dilution. On land, must develop kidney’s ability to remove and excrete nitrogenous waste. Must also concentrate waste to conserve water.

Water Balance

Living on land requires conserving precious water.

Tetrapod origins

Most living vertebrates are ~70% water. Fish skin not well adapted to conserving water. Replaced dermal scales in fish with stratum corneum, keratin, and mucous glands. Mucous glands function as osmotic seal. Dead outer layer shed periodically (ecdysis).

Hearing

Sound vibrations in water and bodies (mostly water) similar. Sound in air mostly bounces off of bodies.

Tetrapod origins

Tetrapods modified the hyomandibula bone (for jaw support) into the stapes - becomes a bone in the middle ear. Later this bone modified into more efficient sound transducer at least three times (amphibians, Reptilia, mammals). Stapes connects outer ear (e.g., tympanum) to inner ear allowing sound conduction. Fish had lateral line system - groups of mechanoreceptors that sense changes in pressure from vibrations of sound waves, or water currents. Retained in earliest Stegocephalians, but since lost in most living adult tetrapods; retained in larvae and a few adult amphibians.

Other Senses Tetrapod origins

Nasal passages became a dual channel for respiration and olfaction. Vision sharpened and modified for aerial use.

Feeding

Suction feeding replaced by elaboration of tongue.

Tetrapod origins

In water, prey acquisition often via suction feeding. On land, early tetrapods had to develop ability to grab food with tongue and jaws. Maybe not such a difficult transition, as we see extant salamanders that switch seasonally between aquatic suction feeding and terrestrial ‘tongue feeding’.

Fig. 2-1 Pough et al. 2001

We just discussed many synapomorphies of Tetrapoda (3),

Now on to Lissamphibia (9), Amniota (4), and Reptilia (5)

Lissamphibian Origins Anura, Urodela, Gymnophiona

Osteolepiformes Panderichthyes Stegocephali (including Acanthostega, Ichthyostega)

30 million years (explosion of tetrapod diversity)

Lissamphibia (first fossil 245 MaBP, lower Triassic)

Debate about lissamphibian relatives. Temnospondyls or Lepospondyls (incl. microsaurs). True ancestor influences how we think Anura, Urodela, and Gymnophiona are related, but still monophyletic.

Lissamphibian Monophyly Anura, Urodela, Gymnophiona

1. Pedicellate and bicuspid teeth 2. Ear with stapes and operculum (caecilians different) 3. Stapes directed dorsolaterally

Pough et al. 2001

Lissamphibian Monophyly Anura, Urodela, Gymnophiona 4. Fat bodies develop from germinal ridge 5. Skin with mucous and poison (granular) glands 6. Green rod receptor cells in eye (lost in caecilians) 7. Levator bulbi muscle to elevate eye (no hard palate) 8. Cutaneous respiration, buccopharyngeal pump 9. Short, straight ribs that do not encircle body 10. Two occipital condyles where skull articulates with atlas 11. Reduction in skull bones (from paedomorphosis)

METAMORPHOSIS!

from Stebbins and Cohen, 1995

Fig. 2-1 Pough et al. 2001

Lissamphibia (9)

Fig. 2-1 Pough et al. 2001

Tetr

apoda

Lissamphibian Origins Anura, Urodela, Gymnophiona

Osteolepiformes Panderichthyes Stegocephali (including Acanthostega, Ichthyostega)

30 million years (explosion of tetrapod diversity)

Lissamphibia (first fossil 245 MaBP, lower Triassic) (Triadobatrachus)

Debate about lissamphibian relatives. Temnospondyls or Lepospondyls (incl. microsaurs). True ancestor influences how think Anura, Urodela, and Gymnophiona are related, but still monophyletic.

Lissamphibian Relationships ((Urodela + Gymnophiona) Anura)

Uncertainty surrounding Temnospondyls vs. Lepospondyls (incl. microsaurs), alters what characters are synapomorphic and thus alters the hypothesed relationships of extant Lissamphibia.

Urodela

Urodela

GymnophionaAnura

Gymnophiona Anura

Batrachia

Comprehensive molecular and morphological analyses support this hypothesis

Procera

Temnospondyls or Lepospondyls

Temnospondyls or Lepospondyls

Paedomorphosis Helps Explain Lissamphibian Origins (paedo = child, morph = form)

e.g., some adult salamanders retain gills •Type of Heterochrony (Change in timing of development) •Retention of juvenile characters in adult stages •Gonads mature while have juvenile characters

‘Evidence’: - missing skull bones that are last to form in

ancestor - large orbits (sensory organs develop early) - bicuspid pedicellate teeth (juvenile char. in ancestor)