L17(2) - Turtles: Building a Shell From Ribs

rowing vs flapping

forelimb swimming strokes

rowing

slider

• humerus swing = 107

• humerus updown= -8

flapping

loggerhead

• humerus fore-aft swing = 38

• humerus up-down = -51 depression

hybrid rower-flipper

pig-nosed turtle

• humerus fore-aft swing = 97

• humerus up-down = 31 (excursion)

flipper does not equal

flapping

• the pig-nose turtle has flipper-shaped limbs but still mostly rows

partly shaped muscle control - some shoulder muscle keep their

firing pattern; the deltoid switches role

cryptodira - neck retraction

vertical S-bend; modified joint between the 8th cervical and 1st thoracic vertebrae

cryptodira - jaw0muscle pulley

tendon runs over the otic chamber

cryptodira - pelvis

mobile; toatesc 18* when walking

cryptodira - living range

nearly worldwide; land, fresh water, sea

• 11 families

pleurodira (“side-necked”) - neck retraction

sideways fold; mid-neck kink

pleurodira (“side-necked”) - jaw-muscle pulley

tendon runs over a pterygoid process

pleurodira (“side-necked”) - pelvis

sutured to carapace and plastron; no movement

pleurodira (“side-necked”) - living range

southern freshwaters

• 3 families

pleurodira (“side-necked”) - hide the head

neck bends sideways; head tucks under the shell edge beside a forelimb

cryptodira - way to hide the head

neck folds in a vertical S; head pulls straight back

neck retraction - ancestral

a lateral head tuck in stem turtles

neck retraction - independent

each crown lineage specialized separately

• so “retraction evolved independently” is only half right

neck retraction - jaw link

both lineages evolved a jaw-muscle pulley that clears space for the neck

chelidae =

snake-necked turtles

pelomedusoids =

side-necks of Africa and S. America

trionychia =

soft shells, pig-nosed turtle

testudinoidea =

tortoises, pond turtles

americhelydia =

sea, snapping, mud turtles

the crown turtle tree is

stable; its dates are not

pleurodires - past

widespread, even marine

• giants

pleurodires - today

restricted to freshwaters of South America, Africa, Madagascar, and australisa

pleurodires - lesson

a living range can hide a much wider fossil range

modern diversity -

364 living species

• 493 species + subspecies

• 14 families

• 10 taxa extinct

modern diversity -cavet

speci

modern diversity range

richest in the tropics but diverse in temperature zones; leatherbacks reach Newfoundland, Labrador, and north Norway

alabama is one of the world's

richest turtle watersheds

oviparous

all turtles lay eggs, even fully marine sea turtles, which must return to beaches to nest

nesting

females dig a nest in soil or sand, bury the eggs, and usually leave

sperm storage

painted turtles fertilized eggs with sperm stored for up to 3 years

hatchlings tend to emerge from

the nest together, which may swamp predators

TSD -

temperature-dependent sex determination: incubation temperature, not sex chromosomes, sets sex

temperature sets sex - pattern 1a

males at cool temperatures, females at warm

• the most common

temperature sets sex - pattern II

females at both extremes, males in between

temperature sets sex - pattern 1b

females cool, males warm

temperature sets sex when

the thermosensitive period is roughly the middle third of incubation

temperature sets sex - how

warmth => calcium influx → activated STAT3 protein switches off kdm6b

sex chromsomes - ancestral state

TDS; genotypic sex determination evolved at least 5 times

sex chromosomes - two system

XX/XY - males carry two different chromosomes

• ZZ/ZW females so

temperature sets sex - old and stable

the soft-shell ZZ/ZW system is shared across the family

temperature sets sex - conservation

in TSD species, warming nest shift sex ratios

turtles are the most

threatened large vertebrate group

why turtles are so vulnerable? slow life history

• late maturity

• populations depend on high adult survival

• protecting nests cannot offset steady adult losses

why turtles are so vulnerable? temperature-set sex

• in TSD species, nest temperature determines sex

why turtles are so vulnerable? human pressures

• harvest for food, medicine, and pets

• habitat loss

• hot, dry nests also raise scute defects

outcomes span extinction to

recovery

outcomes - Yangtze giant soft-shell

• functionally extinct

• two or three individuals known

• search now uses environmental DNA from lake water

outcomes - Burmese star tortoise

• 175 founders → 14,000 in assurance colonies

• captive breeding plus releases

outcomes - green sea turtles

• international union for conservation of nature (IUCN) red list: endangered → least concern

• Raine island subpopulation still at risk

recoveries are real but

rare, and each depended on sustained, targeted effort

turtle placement

diapsids, sister to archosaurs; their closed skull is secondary

turtle shell

mostly ribs and vertebrae redirected by carapacial ridge; plastron first, carapace later

turtle body plan

shoulder enclosure, abdominal breathing, a shunting three-compartment heart, scutes, and limbs are separate modules

two crown lineages

cryptodires and pleurodires solved neck, jaw and pelvis problems differently

reproduction

all turtles lay eggs; nest temperature sets sex in most species, and sex chromosomes evolved at least 5 times

conservation -

over half of turtle species are threatened, most heavily tortoises, soft shells, and tropical asian species

alabama - the mobile basin is one

of the two richest turtle watersheds on Earth