Anatomy and Physiology of Herps

allometry

relationship between body size and shape

larval development

larvae can be similar to adults (salamanders)

morphologies can be radically different (anurans)

different amounts of metamorphosis

direct development

hatchlings with fully formed adult morphology

few amphibians

most reptiles

heterochrony

change in timing of growth relative to the ancestral species

paedomorphosis

peramorphosis

peramorphosis vs paedomorphosis

peramorphosis: developmental process in which a trait develops beyond or faster than the state of the ancestral species

paedomorphosis: retention of juvenile traits in adults

***direct development of salamanders is peramorphosis of juveniles

cranial skeleton

supports and protects brain, sense organs, and other tissues

important in orientation, feeding, respiration, etc

cranial skeleton: Lissamphibians

reduced cranium

• parts remain un-ossified throughout life

• bony in reptiles

well developed brachial apparatus

• aquatic forms

• reduced/ lost at metamorphosis in terrestrial taxa

squammates reduced for increased mobility

axial skeleton

framework of the body; support and movement

notochord, vertebral column, ribs, sternum

vertebral column resists torsion; stability and protection

skull no longer attached to pectoral girdle

vertebrae differentiate (neck, trunk, tail, pelvic girdle)

ribs allow for muscular attachment, ventilation, weight of body against gravity

Axial modifications: amphibians

most salamanders are similar to early tetrapod’s

caecilians lost all components of appendicular skeleton

anurans

• robust appendicular skeleton

• urostyle

• sternum united with pectoral girdle

• unique pelvic girdle

Axial modifications: reptiles

increased vertebral differentiation

• cranial kinesis

• ventral projections evolved in some anterior vertebrae for muscle attachment

ribs present through most of body

• attached ventrally to sternum

sternum

• united with parts of pectoral girdle

• absent in turtles and snakes

axial modifications: turtles

trunk and vertebrae ribs fuse with carapace

limb girdles are inside the ribcage and shell

integument outline

boundary/ barrier

water balance

sensory detection

respiration (mostly amphibians)

integument

epidermis

• typically thin

• non living, keratinized

• aids in water retention

dermis

• thicker

• living

• complex tissue matrix with connective tissues, blood vessels, nerves, glands

integument: accessory structures

scales

• plates, scutes, shields

• keratinized

  • alpha: pliable

  • beta: hard and brittle

integument: ecdysis

shedding of skin at one time, regular, whole body

integument: permeability

amphibian skin permeable

• water loss

• cutaneous drinking

• some aquatic can secrete ammonia

• needs to be moist for respiration

• behavior is important component of maintaining water balance for terrestrial sp

reptile scales

• virtually waterproof

• reduced need for association with water

• some can respire through highly vascularized patches of skin

integument: glands

well developed mucous, poison, lipid/ wax in amphibians (conc around head)

reptiles have well developed glands

• mostly lipid/ wax based

• musk glands

• salt excretion

• concentrated in specific areas

integument: coloration

chromatophores: pigment cells

• melanophores (eumelanin, dark)

• iridophores (purines, blues)

• xanthopores (pteridine, yellows & reds)

color change enacted by movement of eumelanin

structure of surface cells can produce colors by refracting light

integument: senses

lateral lines in amphibians

• series of pores responding to currents and prey

• detect water flow as cilia bend

ampullary organs

• electroreceptors in some larval salamanders and caecilians

heat sensory

• pits house IR receptors on scales in some snakes

Ears

one middle ear bone

• stapes

amphibians hear through skull vibrations

• some frogs have tympanum

• salamanders can hear through forelimbs

Eyes

well developed in most taxa

green rod in amphibians

fossorial species eyes are typically reduced, covered, or entirely absent

tastebuds

reduced/ absent in some squammata

olfaction/ nasal organs

vomeronasal organ

-airborne chemical ques (absent in crocs, present in amphibians and reptiles)

respiratory system

get metabolic energy from oxidation of food molecules

O2 needed for oxidation enters and leaves body by diffusion

• gills, lungs, skin

• typically requires ventilation (movement of air)

caudata respriration

salamander larvae retain external gills

• gill morphology varies with size, activity, etc

gills typically lost at metamorphism

• paedomorphism

• ventilatory mechanisms not well studied in terrestrial adult salamanders

anuran respiration

air drawn into nares instead of mouth (pharyngeal muscles)

2 stroke buccal pump (pressure change)

1. glottis closed, nares open, throat sac expands, air comes in

2. glottis opens, nares open, CO2 leaves

3. nares close, glottis open, O2 moves into lungs

4. repeat

gular flutter

• gas exchange across buccal epithelial

• may involve smelling

amniote respiration

ventilate with aspiration pumps

• suction mechanism

some lizards and some turtles use a 2 stroke aspiration pump

crocodilian respiration

aspiration pump and hepatic piston pump

• unique diaphragmatic muscle extends from the liver to the pelvic girdle

circulatory system

O2 enters and CO2 leaves via diffusion

O2 enters and CO2 is transported to/ from target tissues by circulation

other things also need to be transported throughout the body

• heat, hormones, immune cells

3 parts

• pump (heart)

• transport system (blood and lymph vessels)

• supportive tissues/ organs

circulatory transport system

vertebrates have closed circulatory systems (blood in vessels)

arteries

• A away, oxygenated blood goes to the body

veins

• non O2 blood back to the heart

heart

pump

receives blood from veins at low pressure

pumps blood out through arteries at high pressure

frogs: 3 chambered

turtles: 3 chambered, partially separated

birds/ mammals: 4 chambered, separated

amphibian circulatory adaptations

frog heart representative of many lissamphibians

atria completely divided (interior septum)

ventricles undivided

mixing of O2 and CO2 occurs some

when underwater blood bypasses lungs

reptile circulatory adaptations

ventricle partially divided

• interventricular septum

• completely divided in crocs, birds, mammals

blood flow to lungs regulated;

• during lung ventilation left to right shunt

• diving apnea right to left shunt

croc circulatory adaptations

blood shunting more complex

regional blood flow also regulated

• foramen of panizza connects right and left systemic arches, sending deO2 blood to stomach and intestines during diving to preserve O2

Digestive System

breaks down food chemically and absorbs nutrients needed to sustain metabolism

structure an evolution of system reflects adaptations to types of food eaten, metabolic rate, body size

mouth → pharynx → esophagus → stomach → intestine

digestive system in some vertebrates

starch breakdown starts with saliva in mouth

occurs outside the mouth in vipers

digestion in most herps

most digestion and absorption occurs in the stomach and intestine

initial protein digestion in the stomach

intestine is the primary site for digestion and absorption

longer intestines in herbivores

excretory system

kidneys and their ducts

regulates water an salt balance in body

works in conjunction with

• skin

• gills and / or lungs

• special salt excreting glands or salt-absorbing structures

excretion

removal of metabolic waste products

NOT deification

nitrogenous wastes

products of the excretory system

nitrogenous wastes produced as:

• ammonia (aquatic animals)

• urea (many amphibians, mammals)

• uric acid (lizards, snakes, tortoises, a few frogs)

amphibian excretory system

in water function like freshwater fishes - dilute urine

on land - eliminate mostly urea

some highly terrestrial frogs and 1 salt water frog retain urea (water reabsorption)

large distending bladder

• bi-lobed

• stores liquid

• often 20-50% weight in terrestrial species

reptile and amphibian kidneys

reptiles have lobed kidneys

amphibians do not

excretory system

phylogenetic trends in the separation of male urinary and reproductive passages

• ancestral was not separated

• more derived taxa have separate ducts from excretory system