WFSC 302

      NATURAL HISTORY OF THE VERTEBRATES

                              LECTURE NOTES

          WFSC 302:  Natural History of the Vertebrates  

Course Theme: Adaptive radiation of the vertebrates.  

Vertebrate natural history refers to the study of various aspects of the biology of vertebrate animals:  primarily their taxonomy and classification, evolutionary history (phylogeny), life history, ecology, and geographic distribution.

There are approximately 45,000 known species of vertebrates:

Fish                                                       22,000   (49%)    

Amphibians                                            4,000     (9%)      

Reptiles                                           6,000     (13%)    

Birds                                               9,000     (20%)    

Mammals                                  4,000     (9%)                  

TOTAL:                                         45,000 

 

Classification of Vertebrates: 

The zoological classification system dates from1757 when Linnaeus published the 10th edition of Systema Naturae.    

Linnaeus established the system of binomial nomenclature.

The scientific name of a species is a binomen and is written as follows: Homo sapiens

The primary Linnaean categories are:              

CATEGORY                            EXAMPLE 

Kingdom                     Animal 

Phylum                                     Chordata      

Class                                        Mammalia    

Order                                Primates       

Family                        Hominidae   

Genus                         Homo   

Species                       Homo sapiens 

Other Linnaean categories include: Subphylum,

       subclass, superorder, suborder, superfamily, subfamily, tribe, subgenus, and subspecies (etc.)

METHODS of CLASSIFICATION:

Many aspects of our traditional classification are based upon general similarities of organisms and may include both "grades" and "clades."

Cladistics is a philosophy of classification and phylogeny reconstruction based upon the recognition of shared-derived characters.  The father of the cladistic method of classification was Willi Hennig.  In contrast with traditional classification it is a more objective approach and does not include general similarities (grades) but only branches (clades) defined by synapomorphic characters.

IMPORTANT  DEFINITIONS:

TAXON = any taxonomically recognized group of organisms SISTER TAXON = the closest relative to a taxon

PLESIOMORPHY = a primitive character (present in an ancestor).   

SYNAPOMORPHY = a shared derived character.  AUTAPOMORPHY = a derived character unique to a single taxon. 

MONOPHYLETIC = a group (clade) that includes all the descendants of a single common ancestor.

PARAPHYLETIC = a group that does not include all the descendants of a single common ancestor.

OUTGROUP METHOD = method used to determine whether characters are derived

STRUCTURAL GRADE ‑‑ refers to different organisms from different evolutionary lineages that share broad structural or functional similarities. 

CLADOGRAM = a branching diagram (phylogeny) that represents hypothesized evolutionary relationships. 

 

PHYLOGENETIC CLASSIFICATION METHODS: Traditional classification includes the Order Crocodilia in the Class Reptilia because of general similarities shared by crocodilians and the other living reptiles.  Cladistic classification includes Crocodilia as part of a clade with Class Aves (birds) due to shared derived characters. 

 

Biological Species Concept:  

Some biologists have argued that the only "natural" taxonomic category is the species.  

Definition:          

"All members of a population that are actually or   potentially capable of interbreeding and            producing fertile offspring and are reproductively        isolated from other such populations."                       (After Ernst Mayr)  

MONOTYPIC SPECIES:  a species that has traits or characters that are uniform over its entire range (thus, there are no subspecies designations).

POLYTYPIC SPECIES:  a species that has different traits throughout its range, and shows distinct geographic variation in relation to specific traits (thus, there are typically subspecies designations).

Phylum Chordata

Characteristics:  Shared by all chordates      

1)    Dorsal, hollow nerve chord       

2)    Notochord      

3)    Pharyngeal slits or pouches      

4)    Postanal tail

Phylum Hemichordata      

The sister taxon to the Phylum Chordata

       Hemichordates are filter‑feeders that possess pharyngeal slits. 

       The hemichordates include Acorn worms which are     marine invertebrates that filter feed and live in U-      shaped burrows in the sediment.

Phylum Chordata      

The "Protochordates" which can be described collectively as non‑vertebrate Chordates are marine filter feeders found in two traditional subphyla.

Subphylum Urochordata

Class Ascideacea

Sea squirts or tunicates      

Adults are sessile, Larvae are free swimming.  Tail and notochord are lost during metamorphosis.

Class Thaliacea      

Salps

Adults similar to adult tunicates except incurrent and excurrent siphons at opposite ends.  These are small, planktonic creatures some of which are bioluminescent.

Class Larvacea      

Retain larval characters (tail) throughout life.      

Never metamorphose but mature sexually.

Neoteny is a term for the retention of larval characters in adults.

Subphylum Cephalochordata      

"Amphioxus" ‑‑most fish‑like of all protochordates   Spends most of its time partially buried in sand.  Filter feeds in a way that is similar to that of larval lamprey eels.  Cilia are used to pump water through pharynx.  Food particles are trapped and entrained in mucous.  Although very similar to vertebrates, cephalochordates are not thought to be vertebrate ancestors.  They do, however, date to Cambrian times as exemplified by the fossil Pikaia from the Burgess Shale formation. 

CRANIATA

(A new taxon created when the hagfish were removed from the vertebrates.  It does not correspond to any Linnaean category.)

The morphological feature that defines the Craniata is the cranium.  This is a skeletal structure that encases and protects the brain.  It forms part of the skull in advanced vertebrates.

ORDER MYXINIFORMES

Family Myxinidae 

(hagfish; 40 species, all marine) first appeared during Carboniferous, feed primarily on invertebrates; may feed on dead fish caught in nets/traps; considered to be the sister taxon to vertebrates

 CHARACTERISTICS:

1)    Skin naked, many mucous glands present for antipredator defense

2)    Body elongate, eel-like

3)    Cartilaginous skeleton

4)    No vertebrae

Hagfish can be described as non-vertebrate craniates.

SUBPHYLUM  VERTEBRATA  

Characteristics:

1) Brain present--this is an enlargement of the              anterior end of the dorsal hollow nerve chord.

3) Endoskeleton, including vertebrae, present--      functions for protection and support.

 

 

SUPERCLASS AGNATHA 

       Characters:

       1)    Jawless

       2)    No paired fins

       3)    Early forms had external bony armor (exoskeleton)

       Geological range: Cambrian to Recent     OSTRACODERMS (earliest vertebrates) includes 4 extinct Orders which originated in late Cambrian and early Ordovician.  Ostracoderms were mostly filter feeders but used a "muscular pump" feeding mechanism instead of current created by cilia as in protochordates.

This improved mode of filter feeding allowed collection of larger food items and led to evolution of increased body size (up to 30 cm).  These animals also had improved mobility due to their vertebral columns and flexible skeletons.

Examples of ostracoderms included:

Jamoytius--possibly a parasitic form and ancestral to             the living lampreys.

Pteraspis--a pelagic, filter feeder.  The elongated          rostrum probably provided lift.

Arandaspis--Among the earliest known vertebrates (Ordovician).  It was very primitive with stabilizing fins.  Bottom feeder, probably swam in tadpole-like fashion.

Hemicyclaspis--a dorso-ventrally flattened ostracoderm with fin-like flaps that were scale covered.  Probably a bottom feeder.

The above four taxa represent the four recognized orders of ostracoderms.

 

CLASS CEPHALASPIDIMORPHA

ORDER PETROMYZONTIFORMES

Family Petromyzontidae (lamprey eels)

Lamprey eels first appeared during the Carboniferous Period.  Today, both marine and freshwater species are known.  They have reportedly destroyed the lake trout fishing industry in the Great Lakes (due to construction of the St. Lawrence seaway that includes a series of locks and a canal that allows ocean‑going vessels to have access to the upper Great Lakes.

CHARACTERISTICS:

1)    Skin naked

2)    Body elongate, eel-like

3)    Some species are anadromous

4)    Ammocoete larvae

Uncertain Status:  Conodonta

Conodonts are marine organisms that existed from Late Cambrian - Late Triassic (300 million years).  Fossilized remains include tooth-like microfossils 0.2 - 2 mm long, rarely as large as 14 mm.  Conodonts are important in biostratigraphy as indicators of age and rock strata.  Conodont fossils are also used to determine the thermal history of the sediment and chemistry of the oceans in which they lived.  Conodonts were first reported in 1856 but details of their soft anatomy remained unknown until 1983. Today based on new fossil information we know that conodonts are elongate, laterally compressed and eel-like, and were probably swimming carnivores. Finely preserved fossils give evidence of a notochord and caudal fin rays.  No jaws or paired fins are present.

       Recent studies (1992) using modern microscopic analysis of conodont fossils indicate the tooth-like structures possessed enamel and cellular bone.  These are clearly vertebrate characters and thus conodonts have been moved from the Phylum Conodonta to the vertebrates.  (Vertebrate hard tissues include cellular bone, acellular bone, enamel, and dentine--these are found in no other animal groups). This reanalysis of conodont relationships will likely spark renewed interest in the relationships of the earliest vertebrates--the Agnatha.

 

 

SUPERCLASS GNATHOSTOMATA

Jawed fishes with paired fins.

Jaws (derived from anterior gill arch) enable animal to grasp and manipulate objects, and thus allowed exploitation of new sources of food (which resulted in carnivory).  Carnivorous species have teeth with sharp, cutting edges.  Herbivorous fish have flattened teeth for grinding.

CLASS PLACODERMI (armored fishes)

First jawed fishes.  They possessed paired fins.

Placoderms first appeared at the end of Silurian and became extinct by early Carboniferous. 

Subclass Arthrodira  

Ancestral to the Chondrichthys.

Predaceous forms reached 30 feet in length (example Dunkleosteus).  Ctenurella was similar in many ways to a chimaera, including possessing claspers.

Subclass Acanthodii ("spiny‑finned fishes")

Ancestral to bony fish.  Most were small, schooling fish such as Climatius (3 inches) and Acanthodes (1 foot).  Sometimes considered as Bony Fish (Osteichthys).

 

Characters of Acanthodii:

1)    Pectoral fins with large spines.

2)    Small finlets in rows between pectoral and pelvic fins.

3)    Bony operculum in some species, but doesn't cover all gill slits.

4)    Ganoid scales.

 

Class Chondrichthys      

Approximately 625 living species. 

Middle Devonian‑Recent.

Characteristics:      

1)    Cartilaginous skeleton      

2)    Second gill arch (hyoid) involved in jaw suspension

3)    Males with claspers

 

Subclass Elasmobranchii      

Sharks, skates, rays      

Protacrodus ‑ early shark with some dermal bone.

Order Carcharhiniformes            

Hammerhead      

Order Orectolobiformes            

Nurse shark, Whale shark      

Order Pristiformes            

Sawfish

Order Torpediniformes

Electric ray

 

Characteristics of Elasmobranchii:

1)    5‑7 gill openings

2)    Dermal placoid scales usually present

3)    Spiracle present

Subclass Holocephali      

Order Chimaeriformes            

Ratfish or Chimaeras

These are slow moving bottom feeders that feed on hard shelled prey.  Most are found in very deep water.  

Characteristics:      

1)    Fleshy operculum covers four gill slits      

2)    Skin naked      

3)    No spiracle      

4)    Flattened, grinding teeth

 

 

 

Adaptations of Chondricthys

The largest chondrichthyans are filter- feeders

Whale shark Rincodon            

Up to 50' in length            

Feeds mostly on small schooling fish.  Takes large mouthfuls of water, drains oral cavity, expels water and swallows food 

 Basking shark Cetorhinus             

Up to 30' in length            

Large mouth, long gill rakers             

Filter feeds plankton

Manta ray Manta or Devil fish            

Up to 20' long            

Also filter feeds

All the above species are harmless to man

Buoyancy in chondrichthyans      

No swim bladder, neutral buoyancy maintained by liver which is large (25% of body wt.) 

Fats and oils in liver determine specific gravity

Cookie‑cutter shark ‑ maintains neutral buoyancy,

Slowly approaches prey, takes bite out of large fish or whales.

Osmoregulation      

Chondrichthyans use urea to maintain body fluids isotonic to sea water. Terms: isosmotic, hyperosmotic, hypo-osmotic

Class Osteichthys

About 22,000 species of Bony Fishes

Chondrichthys ‑ cartilagenous fish

Osteichthys ‑ bony fish

Chondrostei ‑ fish with bone and cartilage

Holostei ‑ entirely bony fish

Teleostei ‑ final bony fish

This series of names implies a gradual increase in bone during evolution -- we now know this was not the case. 

Characteristics of bony fish:      

Few characters because of diversity of group

        1)    All have some true bone            

2)    Skulls have sutures (sharks have a single block of cartilage)        

3)    Teeth fused to mandibles            

4)    Swim bladder or lungs usually present

5)    Bony operculum present

Subclass Actinopterygii      

Ray‑finned fishes

Characteristics:

1)    Scales ganoid, cycloid, ctenoid or none.

2)    Membranous fins supported by fine bony rays.

3)    Caudal fins highly variable.

Infraclass Chondrostei

Characteristics:

1)    Spiracle present.

2)    Heterocercal tail in some.

3)    Ganoid scales.

Order Accipenseriformes

Sturgeons, Beluga, Paddle fish

Ganoid Scales on tail, dermal bony plates on back.

Accipenser ‑ sturgeons

Important economically for meat and Caviar.

Huso ‑ beluga      

Largest of the sturgeon group, from Caspian Sea, Up to 3,300 lbs.  The finest black caviar in the world comes from this species ($5 per gram).

Polydon ‑ paddlefish      

Includes two species, one in the US (including Texas) and one in China.  Weighs up to 200 lbs. 

Order Polypteriformes      

Have lungs, lobed fins, found in Africa, ganoid scales cover body

Polypterus – bichir or African rope-fish

Calamoichthys ‑ reedfish      

Infraclass Neopterygii

Series Holostei            

Order Semionotiformes            

Lepisosteus ‑ gars           

Body covered with Ganoid scales.

Swim bladder aids in respiration.

Long snout with many teeth, voracious predators on small fish.  Restricted to North America.

Order Amiiformes      

Amia ‑ bowfin            

Cycloid scales cover body.

Predator on smaller fish.

Also use swim bladder for respiration.

The one living species (Amia calva) is restricted to the Mississippi drainage of North America but fossils are known from Europe.

Characteristics of Holostei:      

1)    Modified heterocercal tail.    

2)    Scales ganoid (gars) or Cycloid (bowfin).

3)    Swim bladder connected to pharynx aids in respiration.

Series Teleostei      

Characteristics:             

1)    Tails homocercal in most species.

2)    Scales cycloid or ctenoid, not ganoid.

3)    Swim bladder present in most species.

There are 24 Order of teleost fishes, some of which will be covered in Lab.  Taxonomy is not presented in lecture.

Life History Strategies of Teleosts      

Extremely varied      

Desert pupfish ‑ live in isolated permanent springs in Western U.S. deserts.        

Antarctic ice fish ‑ lives in water so cold that it does not need hemoglobin to bind oxygen.

Life histories of the salmon and cisco      

Family Salmonidae            

Includes:  salmon, trout, whitefish, cisco, etc.   Many species with anadromous life history

Anadromous ‑ fish that spawn in freshwater but spend most of their lives in marine waters.

Catadromous ‑ Opposite of anadromous.  Spawn in ocean but live in freshwater. Example--the freshwater eel Anguilla.

Salmon, such as the sockey (Oncorhynchus nerka) begin life as fertilized egg in freshwater stream.  After hatching they stay in fresh water usually until the next spring when the rains wash them to a nursery lake where they grow for a year (sockeye), or else directly to sea.  They spend up to 4 years at sea before becoming sexually mature, return to natal stream to spawn and then die. There are four species of Pacific salmon (sockeye, silver, chum, king, and pink)

Arctic cisco (Coregonus autumnalis) spawn in the Mackenzie River system of North America but live most of their lives in the near-shore low-saline waters of the Beaufort sea.  It over-winters in deep pools at the mouths of large rivers such as the Mackenzie and Colville.  This species is thought to be at risk because of oil industry related activities at Prudhoe Bay.  A native Alaskan fishery exists at the Colville R. in Alaska.  Young of the year must migrate past Prudhoe Bay to reach the Colville R.

Subclass Sarcopterygii      

Fleshy‑finned fishes      

7 living species      

Superorder Dipnoi      

Lungfish 6 sp.

Characteristics of Lungfish:      

1)    Internal nares. 

2)    Lungs ‑ for aerial respiration.

3)    Fleshy paired fins.

4)    No dorsal fins (in living forms).

Lepidosiren ‑ South America

Protopterus ‑ Africa

Neoceratodus ‑ Australia

S. Am. and African lungfish have reduced gills and will drown in water if not allowed to breathe air! African lungfish ‑‑ forms cocoon and aestivates when rivers dry up in dry season.

Australian lungfish

Reduced lungs ‑‑ will die out of water.      

It lives in well oxygenated rivers.

Dipterus - Fossil Devonian lungfish

Superorder Crossopterygii      

Lobe‑finned fishes

Order Actinistia

Characteristics:      

1)    Two dorsal fins.

2)    Fleshy paired fins.

3)    Internal nares.

4)    Vestigial lungs.

Latimeria chalumnae is the only living species.  It was first caught by fishermen off the east coast of Africa, in 1938.  Previously this group was believed extinct since the Mesozoic (60 million years ago).  About 80 specimens have since been collected.  The "coelacanth" gets up to 2 m. in length and lives at the bottom in 230‑300 m of water.  Recently, new populations have been found in Indonesia and South Africa.  Coelacanths have well developed electric sense that is associated with the curious behavior of orienting with head down and tail up.  They have recently been studied from a submersible.

 Macropoma - Cretaceous fossil coelacanth   

 

Order Osteolepiformes

Sometimes referred to by the old name of Rhipidistia. 

Thought to be ancestral to Amphibians, had Labyrinthodont teeth like those of early amphibians.

Example: Osteolepis

Class Amphibia  

Upper Devonian ‑ Recent  

Ichthyostega and Acanthostega are the earliest known amphibians, from Devonian rocks in Greenland.

Characters:      

1) Labyrinthodont teeth ‑ Synapomorphic Character shared with osteolepiformes      

2) Relict of Operculum      

3) Caudal fin with dermal fin rays      

4) Small bony scales present      

5) Similarity of tetrapod limb & osteolepiform fin

6) Internal Nares  

 

The origin of tetrapods (amphibians, reptiles, birds, mammals).

1) Originate in Devonian.

2) Single continental land mass – Pangeae.

3) Tropical Climate ‑ swamp‑like habitats.

4) Abundant terrestrial flora & fauna.

Advantages to invasion of land.

1) New Food resources.

2) Avoid aquatic predators and competitors.

3) Oxygen is abundant in the atmosphere.

Disadvantages (Obstacles).

1) Water is a limiting factor in terrestrial distribution.

2) Gravity necessitates new morphological designs.

Characteristics of Amphibians       

1) Presence of well developed lungs.

2) Strengthened pelvic & pectoral girdles.

3) Strengthened ribs.

4) Flexible neck, the pectoral girdle not attached to the skull.

5) Development of tetrapod limbs.

6) Skin is naked in most living amphibians, some extinct forms were armored.

Amphibians ‑ "tied to water"       

1) for reproduction, anamniote eggs

2) for respiration 

Class Amphibia  

Subclass Labyrinthodontia    

Included Ichthyostega, Acanthostega, Platyhystrix, Eryops

Some as large as crocodiles.

Gave rise to reptiles

Devonian - Jurassic 

Subclass Lepospondyl:     

Small, mostly aquatic, such as boomerang‑head Diplocaulus

Carboniferous - Permian

Subclass Lissamphibia    

Modern amphibians

Triassic - Recent

Order Apoda       

Caecelians ‑ No legs, dermal scales.

Tropical, About 158 species   

Mostly burrowing species, some aquatic.

Order Caudata       

Salamanders and Newts, tailed amphibians

Aquatic, semi‑aquatic, terrestrial - in some respects most primitive tetrapods‑‑e.g. locomotion.

About 300 species, some lungless.

Family Plethodontidae (lungless salamanders)

Desmognathus wrightii - Very small, completely terrestrial species - High surface/volume ratio provides adequate surface for gaseous           exchange to take place across the skin.  No lung is needed.  

Order Anura       

Frogs, toads, and their relatives      

3,500 species 

Characteristics:       

1) No tail      

2) Hind limbs elongated for hopping      

3) Vertebral column short and inflexible      

4) Pelvic girdle enlarged, strengthened and anchored to vertebral column      

5) No ribs 

Amphibian Diversity       

F. Ranidae ‑ True Frogs

Leopard frog Rana  pipiens       

F. Pipidae

Africa and S. America, Aquatic   

examples: suriname toad Pipa pipa, African clawed frog, Xenopus

       F. Hylidae         

Tree frogs         

Toe pads for climbing         

example: Agalychnis colorful, tropical tree frog example: Hyla boulengeri cryptic coloration for sitting on tree bark. 

Family Bufonidae ‑ Toads      

Poison skin secretion, some species can kill dogs  e.g. Bufo alvarius--Colorado River toad

 Paratoid gland present, dry, warty skin      

Terrestrial, little or no webbing on feet 

Family Rhinophrynidae      

Rhynophrynus dorsalis  Mexican burrowing frog                   Weak hind legs, doesn't hop      

Burrows in termite nests, rotten logs               Usually collected at ponds when breeding.         Male calls while floating in middle of pond 

Family Dendrobatidae      

Arrow‑poison frogs ‑ Neotropical      

Ex. Dendrobates tinctorius Dye frog      

Brightly colored, highly poisonous

Reportedly used to change color of parrots      

Ex. Phyllobates terribilis      

Found in Colombia ‑ golden yellow in color

skin scretions deadly poisonous

Indians use this species to tip blow gun darts 

Amphibian Reproduction      

Amphibians are anamniotes.

Most lay eggs in water, external fertilization, aquatic larvae.

Metamorphosis:  controlled by balance of thyroxin and prolactin.

Neoteny:  retention of larval characters in adult‑‑found in many species especially salamanders.

Reversible:  tiger salamander Ambystoma tigrinum.    Irreversible:  mudpuppy Necturus maculosus.

Reproduction in caecelians.  

Males with intromittant organ for internal fertilization,

some species are oviparous, aquatic breeders. Some species are viviparous: young feed on "Uterine milk".

 Reproduction in Caudata.

Internal fertilization via spermatophore: gelatinous cap containing sperm is picked up by the cloaca of the female.

Salamanders are oviparous.

Liebespiel - in Ambystoma maculatum

Reproduction in Anura

External Fertilization in most.

Elaborate advertisement vocalization in males (species specific calls).

Amplexus: male grasps female from behind, stimulates oviposition.       

Amplexus = sexual embrace without true sexual intercourse. 

Terms to describe modes of reproduction.

Oviporous‑lay eggs.

Ovoviviparous‑retain egg within womb, no extra nourishment besides yolk.

Viviparous‑retain young within womb, provide nourishment through placenta or by other means (Uterine milk, etc.).

 

Class Reptilia

Carboniferous - Recent

Characters of Reptiles 

1) Amniote (cleidoic) egg

All reptiles lay eggs on land.

Terrestrial egg is perhaps the most important    adaptation of reptiles.

Reptiles not "tied to water" for purposes of    reproduction or respiration.

Amniote Egg, calcarious shell, four

extraembryonic membranes (amnion, chorion, allantois, and yolk sac).             

Embryo excretes uric acid‑‑not as toxic as    ammonia excreted by amphibians.

Albumin‑protein source and holds water.

2.    More effective jaw. 

Greatest strength when nearly closed, for       crushing prey. 

3.    Skeletal structure improved; greater strength and agility, improved locomotion due to rotation of limbs to support body 

4.    Skin tough, leathery, and covered with scales. The dry skin of reptiles is resistant to desiccation and serves no respiratory function. 

5.    Well developed lungs in all reptiles.

Classification of Reptiles 

Higher level classification of reptiles is based largely on the structure of skulls and position of temporal fenestra.  Anapsid, synapsid, and diapsid skull types define the major groups of reptiles: Anapsida, Synapsida, Diapsida.

Subclass Anapsida       

Order Captorhinida

Also called cotylosaurs or stem reptiles.

Hylonomus Carboniferous, first known reptile.

Pareiasaurus 8 ft. long, herbivore, Permian.

Mesosaurus first aquatic reptile, 3 ft., Permian.

Earliest reptiles‑ancestral group to all others.      

Order Testudines    

Traditionally considered direct descendants of cotylosaurs and the only living group of Anapsida.  However, a recent proposal was made to place them in the Diapsida.

Triassic ‑ Recent 

Turtles, tortoises etc. ca. 180 sp.       

Proganochelys the oldest known fossil turtle, from the Triassic of Germany--had teeth, well-developed shell, but could not retract head beneath shell

Characters of Testudines:       

1.    Shell produced by dermal plates fused to ribs and vertebrae.

2.    Shell overlaid with scales (scutes).       

3.    Pectoral girdle lies within ribcage.

4.    Teeth absent, jaws covered by keratinized "beak".

Suborder Pleurodira            

"Side‑necked turtles"            

S. America, Africa, Australia       

Example Chelus the Mata Mata

Suborder Cryptodira            

"Hidden‑necked turtles"            

N. America, Europe, Asia, S. America, Africa.

Marine, freshwater, and terrestrial habitats.

Subclass Diapsida

Order Ichthyosauria 

Dolphin‑like reptiles

Ichthyosaurus fish lizard, fed on fish and cephlopods

Fossils showed these animals to be viviparous

Order Plesiosauria  

Elasmosaurus 46 ft., probably swam at surface            Liopleurodon 40 ft., short neck, fast swimmer,      probably the top predator in the ocean.  Plesiosaurs like Elasmosaurus are thought to have nested on beaches similarly to living sea turtles.            

Order Placodontia                  

Probably mollusk feeders similar to walrus. 

Henodus possessed a large, turtle-like shell.

 

Lepidosauromorpha, "scaly reptiles"       

There are several extinct orders, and two extant orders, all with diapsid skulls.

Order Rhyncocephalia  

2 species, found in New Zealand

tuatara (Sphenodon punctatus, S. guntheri)

During Mesozoic this order was very diverse.       

Greatest diversity was during the Triassic.

In the past century, 10 of 40 populations have become extinct.

Characters:            

1) Well developed Parietal eye.

2) Lowest active body temperature of any reptile = 13⁰C.

 

Order squamata 

ca. 6,000 sp.       

Suborder Lacertilia ‑ lizards            

Mostly insectivorous, e.g. geckoes.

Some herbivorous: e.g. Iguana.

Some carnivorous: e.g. Komodo dragon (worlds largest living lizard, 10 ft. long, Family Varanidae), Megalania--extinct Pleistocene varanid from Australia 26 ft. long.

Most species of lizards are diurnal but some are nocturnal: ex. geckoes  F. Gekkonidae.

Diurnal species: ex. Anolis F. Polychrotidae.

Some legless, burrowing species, ex. glass lizard Ophisaurus F. Anguinidae.

Most lizards are terrestrial but a few are aquatic such    as the marine iguana of the Galapagos Islands and the     extinct Mesozioc marine lizards called Mosasaurs.

Some lizards have a predator escape mechanism called        tail autotomy and some escape by allowing their skin   to easily tear away.

Suborder Amphisbaenia – Insectivorous.

Amphisbaenians ‑ some consider to be lizards.  Mostly legless, burrowing, tropical Ex.  Rhineura floridana worm lizard.

Suborder Serpentes ‑ snakes       

Legless ‑ all insectivores or carnivores 

Characters:       

1) No legs‑vestigial limbs in male Boidae.

2) Jaw loosely connected to skull by ligament ‑ can stretch to open gape larger than diameter of body.    

3) Lower jaw not fused at midline ‑ held by ligament.

4) No eyelids ‑ scale covers eye.

5) No ear openings.

Snakes have two highly specialized means of capturing prey. Some species are constrictors, which means they dispatch their prey by suffocation.  Some species use venom to poison their prey.  Venomous snakes include viperids (rattlesnakes and their relatives) which have long retractable fangs in the front of the mouth, elapids (coral snakes and their relatives) which have short non-retractable fangs in front, and colubrids (such as the vine snake) which have fangs in the rear of the mouth (most species of colubrids are nonpoisonous).  Venoms are classified as to their mode of action as hemotoxic and neurotoxic.  Venoms serve both to dispatch (and partially digest) prey as well as an anti-predator mechanism.

Archosauromorpha       

"Ruling Reptiles".

Diapsid skull.

Order Thecodontia

Earliest Archosaurs, ancestral to dinosaurs, crocodilians, and pterosaurs.

Example Longisquama--elongated scales possibly   represent early stage in the evolution of feathers.

Order Ornithischia, "Bird‑hipped dinosaurs" herbivores               Example:  Stegosaurus, Tricerotops, Parasaurolophus Ankylosaurus, Pachycephalosaurus, Maiasauria,

Order Saurischia, "Lizard‑hipped dinosaurs"

       Example:  Tyrannosaurus, Deinonychus, Velociraptor Apatosaurus, Diplodocus, Compsognathus

Order Pterosauria

Extinct flying reptiles: Pteranodon 23 ft.

Quetzalcoatlus 39 ft wingspan--largest flying animal.

Order Crocodilia