ch. 17 - archosaurs (crocodilians)

what are the 2 synapomorphies of archosaurs

1. hindlimb modifications, direct foot forward

2. mandibular fenestra: opening in lower

how does the mandibular fenestra in archosaurs help them? 

lightens skull + provides space for more jaw muscles

how does hindlimb structure in archosaurs differ from hindlimb in lepidosaurs?

lepidosaurs = sprawling posture

archosaurs = set stage for upright limb posture, direct foot forward

name 3 extant crocodilian groups + characteristics discussed about each group

1. alligators/caimen - freshwater

• broad snout

• teeth of lower jaw fit into pits in upper jaw (not visible when mouth closed

2. crocodiles - fresh/saltwater

• teeth of lower jaw fit into grooves outside of upper jaw (both sets of teeth visible when mouth closed)

3. gharial/gavilidae - freshwater (S + SE Asia)

• very narrow snouts, specialized for fish feeding

• both sets of teeth visible when mouth closed

how do the snouts of the three living crocodiles differ?

crocodiles - V-shaped

gharials - narrow + long 

alligators/caimen - broad + U-shaped 

name the general crocodilian characteristics

• strong eyesight, hearing + smell

• very strong jaw closing muscles + weak jaw opening muscles

• indeterminate growth: grow throughout lifetime

what are the 3 forms of terrestrial locomotion seen in crocodilian?

1. crawl - sprawling location

2. high walk - slower walking for longer distances

3. gallop - only in crocodiles

bony palate 

separates food + air passages in mouth to allow breathing while eating 

• analogous to mammalian bony palate)

hepatic piston

“diaphragmatic” muscle pulls back on liver to increase chest volume

• analogous to diaphragm

know the features of the crocodilian respiratory system

costal breathing w/ intercostal muscles

• parabronchial lung, unidirectional air flow

• faveoli continuously exposed to fresh, oxygenated air

how does the hepatic piston work

“diaphragmatic” muscle pulls back liver to increase chest volume

• aids in inspiration of both lungs when walking

know the feature of the crocodilain circulatory system

4-chambered heart (analogous to mammalian heart)

• prevents mixing of oxygenated + deoxygenated blood

• able to perform right-to-left shunt of blood outside heart

• usually higher pressure in systemic compared to pulmonary

describe roles of blood vessels in heart when crocodile is active

pulmonary artery - always deoxygenated blood from RV going to lungs

right aorta - alway oxygenated blood from LV to body

• oxygenated blood flow from LV into left aorta via foramen of panizza when pressure is high

what type of ESD are crocodilians 

type II 

• males hatch at intermediate temps. 

• females at extremes

how does right-to-left shunting work?

pressure is higher in pulmonary compared to systemic

• some deoxygenated blood flows from RV into left aorta

• body receives mix of deoxygenated and oxygenated blood

when would a right-to-left shunt occur in crocodilian hearts

diving + resting/basking in sun

how does right-to-left shunting benefit crocodiles

• warms body faster

• if diving, can’t breathe O2, so send blood to body instead of pulmonary circuit

• CO2-rich blood brought to stomach can aid in digestion of large meals

how doees shunting of blood in crocodilians differ from that in turtles + lizards 

croc - 4 chambers

• separation of blood flow to either systemic or pulmonary circuit 

• divert blood from RV to left aorta 

turtle + lizard - 3 chambers 

• less efficient compared to controlled process of crocodilaians