Tetrapods: Origins & RadiationPART II

VERTEBRATE ZOOLOGY (VZ Lecture10 – Fall 2012 Althoff - reference PJH Chapters 8 &9)

Moving on Land• Locomotion on land is energetically more costly

than in water. Walking on land takes more energy than flying which takes more than swimming

• Most tetrapods accomplish locomotion by moving diagonal pairs of legs together (see Fig. 8-7, p174).

Even humans retain “some” of this (e.g., right arm forward when left leg strides forward)

• Primitive mode exhibited by modern day salamanders: forces comes from ______ muscles, _____________ muscles

• Much advanced: swimming, walking, & jumping modes by frogs highly specialized ____ muscles

Advancements: Primitive tetrapods Amniotes

• Amniotes first to have “the _____”…where each limb moves independently in succession, usually with 3 feet on the ground at a time

• The ______ is a sped-up walk….only 1 or 2 feet on the ground at a time.

• ______ is faster movement yet, involves diagonal pairs of limbs moving together.

• Then, a new faster mode is the ________—found in some mammals. Jumping off hind legs and landing on forelegs with flexion of the back contributing to the length of the stride.

Eating on Land

• Early tetrapods: wide, flat skulls and elongated snout resulting in most of tooth row in front of eyes

• ________: Fishes small and bony Tetrapods large and muscular…

increasing manipulation of food

--some (frogs, lizards salamanders) can project tongue to capture prey

• ______________: only in terrestrial vertebrates advantagemoisten “dry” food, start digestion. Other specializations for some species (i.e., venom: lizards/snakes

Changes in Branchiomeric Musculature(from ancestral pharyngeal arches)

• With loss of gills, much of musculature of associated with gill movement has been lost in tetrapods

• Exception: gill levers. In fishes, the muscle mass is a single unit (the cucullaris). In tetrapods, it becomes the tapezius (runs from top of the neck and shoulders to the shoulder girdle)

• Major branchiomeric muscles of tetrapods are associated with feeding and feeding only. This mean those associated with the mandibiles (ex. crushing food in some tetrapods) and hyoid arches (help open mouth and aids in swallowing food)

(see Fig. 8-10, p179 for generalized tetrapod condition)

Breathing Air: changes from nonamnioticto amniotic tetrapods

• Nonamniotic tetrapods: uses __________-pressure buccal pump to inflate lungs. Lungs are “simple”

• Amniotic tetrapods: use ____________-pressure aspiration pump.Inhalation: rib cage expands by hypaxial

muscles sucking air in Exhalation: compression of, mainly achieved

by elastic return of rib cage, reductionof lung capacity

• Amniotes: lungs subdivided, usually complex resulting in significant increase in _____________ for gas exchange

Breathing:INSPIRATION

• Rib cage moves up & out

• Diaphragm contracts and moves down

• Pressure in lungs decreases—air rushes in.

• Rib cage moves down and in

• Diaphragm relaxes and moves up

• Pressure in lungs increases and air is pushed out

Breathing:EXPIRATION

Pumping Blood Uphill & Double Circulation

• In H20, blood is weightless…only significant challenge to the heart is fluid resistance

• Circulation more difficult for terrestrial animals: a) blood tends to pool in low spotsb) must be forced through the veins, back up to

the heart--this requires ________ blood pressure

• Another tetrapod advancement: double-circuit cardiovascular system:a) __________ circuit rich O2 blood to bodyb) ____________ circult low O2 blood to lungs

Fig. 8-11 p180 PJH

Atrium always completed dividedVentricle sometimes “fixed” barrier division

Sensory System Advancements

• Switch is from “liquid” transmission medium to “air”

• Lateral line system of fishes won’t work in air medium because air is not dense enough to stimulate the mechanical receptors there

• If molecules light enough to be suspended in air, then chemical systems work fine for sense of smell

• Vision and hearing in air can offer advantages over those in a liquid medium

• Vision: easier on land because light is transferred through air with less disturbance than through H2O

• Vision: most tetrapods re-shape lens to focus(snakes move lens to focus eye…like fishes)

Fig. 8-15 p186 PJH

Hearing

• “middle ear” in tetrapods serves to amplify sound

• Fluids of inner ear compressed, with the waves stimulating hair cells in organ of Corti (within lagena… cochlea in mammals)

• ___________ much enlarged in tetrapods

lagena

lagena

FROG

LIZARD

Fig. 8-16 p186 PJH

• Some sensitivities up to 1 million trillion (1015) part of air

• Mammals…with very highly developed olfaction…aided by presence of _____________: thin bone lined with olfactory epithelium

• vomeronasal organ(Jacobson’s

organ)

Olfaction

maxilloturbinates

GENERALIZED MAMMAL CONDITION

UNGULATE CONDITION

vomeronasal organ

Dry Environments: Must conserve H20

• Losses through body surfaces (skin) and respiratory system…and through the kidney

• Partially overcome rapid skin water loss with increased thickness (in amniotes compared to fishes and amphibians) of ___________________ (keratinized epidermal cells)

• These keratinized cells are:a) insoluble in water (providing some “water-

proofing”b) resist physical wear

• However, lipids in skin most responsible for limiting evaporative water loss

Fig. 8-18 p189 PJH

The Energy “Game”: 4 major “external”influences

________________________

________________________

________________________

________________________

the impactof all of

these can beaddressed bythe animals

behavior….!!