The Amniotes
Traditional groupings: all reptiles, birds, mammals
First amniotes appear by late Paleozoic (during
Carboniferous [350-290 MYA] and Permian [290-250
MYA]) through Mesozoic (250-65 MYA)
First amniote – about 340 MYA
Life on land – required major adjustments, such as…..
A. Strengthening of axial system – support
- zygapopheses – processes on vertebrae,
convert spine to stiff rod that withstands
bending and twisting
B. Reduction of cutaneous water loss
- cutaneous respiration – amphibians, but
very, very few amniotes
- reduce permeability by having (a) lipids in
skin & (b) keratinized epidermis
C. Ability to reproduce away from water Why? fewer predators; new niches
Amniotic egg = “land egg”? Extra membranes
(chorion, allantois, amnion) and shell
(leathery or calcareous) evolved to reduce
water loss? MAYBE NOT!
Large eggs (> 10 mm diameter) have difficulty
(a) exchanging gas (thus, allantois), and (b) avoiding
collapse
Large body size
large egg
amniotic egg
Cleidoic (“closed” or “locked”) egg = birds only
D. Skull elongation – associated with feeding
- suction feeding in water/grasping on land
- elongation of tongue (manipulation)
- salivary glands
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E. New musculature – support & maintenance of posture
- rectus abdominus – pectoral to pelvic girdle
(“washboard”)
F. Ventilation – ribs and associated costal muscles
G. Modification to appendicular skeleton
- Pelvic girdle – fused to vertebral column
ilium (attachment), ischium and pubis
- Pectoral girdle = free of cranium and
vertebral column (except pterosaurs)
scapula, coracoid, clavicle (connects scapula
to sternum)
- Jointed limbs: knee (forward), elbow (backward),
wrist, ankle, carpals, tarsals, digits
Fxn of limbs = support, propulsion (not so in
most fish [lift, steering])
H. Massive changes to cardiovascular, respiratory and
excretory systems (to be discussed later….lots of good
stuff!!!)
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Phylogeny of the
amniotes
Anthracosaurs – “reptilomorphs” (350-250 MYA)
Ancestral to all amniotes.
Rich diversity of Paleozoic amniotes
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Major divisions among amniote lineages very old…..these
included:
a. Split between synapsids (mammal-like reptiles and
mammals), & sauropsids (all reptiles and birds) at
about 310-300 MYA, followed by…
b. Split of parareptiles (some extinct reptiles and turtles
[TESTUDOMORPHA]) and eureptiles
(thecodonts, dinosaurs, pterosaurs, crocodilians,
and birds [ARCHOSAUROMORPHA] and,
lizards and snakes [LEPIDOSAUROMORPHA)
a little over 300 MYA.
c. Split of Lepidosaurs from Archosaurs about 270 MYA
d. Ancestry and timing of split between birds and
other reptiles…debated!
By end of Carboniferous (290 MYA) all major amniote lines exist
Some derived features of sauropsids that distinguish them
from synapsids:
(a) skull fenestration,
(b) color vision
(c) harder keratin (beta keratin in all
sauropsids)
Some derived features of lepidosaurs that distinguishes them
from archosaurs:
(a) forked tongue
(b) shedding skin in one piece
(c) hemipenes = paired, bifurcate penes
Some derived features of archosaurs that are unique among
eureptiles:
(a) muscular gizzard
(b) strong tendency towards bipedality
(c) larger, more complexly subdivided lungs
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Class Reptilia (Linnaean System)
Mesozoic – maximum diversity and abundance
Only 4 extant orders of 22 orders known to exist
- Subclass Mesosauria
- Parareptilia
Order Testudinata – Suborder Chelonia
- Subclass Synapsida
Order Pelycosauria
Order Therapsida
- Subclass Eureptilia
Infraclass Lepidosauromorpha
Superorder Lepidosauria
Order Sphenodonta
Order Squamata
Superorder Sauropterygia
Order Plesiosauria
- Subclass Eureptilia (cont.)
- Infraclass Ichthyopterygia
- Infraclass Archosauromorpha
Superorder Archosauria
Order Thecodontia
Order Crocodylia
Order Pterosauria
Order Saurischia
Order Ornithischia
Principal differences between this and cladistic analysis???
Placement of birds!!!
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Subclass Mesosauria
Late Permian (290 MYA), but probably earlier. Gone
by about 270 MYA.
Anapsids
All secondarily aquatic (paddle-shaped feet, laterally
compressed tail, long neck)
Jaw – elongate; bristled with long, sharp teeth; fish
and/or crustaceans
Subclass Parareptilia
Order Testudinata – turtles
- Only surviving members; all anapsids
- Probable ancestor: Pareiasaurs (cow-sized
anapsids from late Permian)
-First fossil record – about 210-220 MYA (late Triassic)
All extinct and extant species have carapace and
plastron
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- Carapace – dorsal shell composed of fused and expanded
ribs and surface skin plates (scutes)
- Dermal bone grows from 59 separate centers of
ossification; 8 of 59 fused to vertebrae
- Ribs – external to pectoral and pelvic girdles;
unique among tetrapods
- Plastron – ventral shell composed of fused bony pieces;
- Dermal ossifications, but clavicles also fused with
plastron
- Shell kinesis – hinging
- Restricted mostly to plastron
Epidermal scutes
Dermal bone
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Two major divisions within turtles
1. Pleurodira – retract head by bending neck
horizontally; all southern hemisphere
- 66 species in 3 families
2. Cryptodira – retract head into shell by bending
neck in a vertical S-shape; worldwide,
including oceans (all marine turtles)
- 195 species in 10 families
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Alligator Snapper
Loggerhead Sea Turtle
Galapagos
Tortoise
Most uniformgroup of vertebrates:
- low metabolism; most herbivorous
- all oviparous
- no parental care (other than nest construction)
- life history characterization: long life and low
reproductive rate; low rate of population
growth
- migration – to isolated beaches
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Subclass Eureptilia
Infraclass Ichtyosauria
- Triassic to Cretaceous of Mesozoic
- “porpoise-like” body, but fish-like movement of tail
(side-to-side); paddle fins; numerous teeth
- entirely marine; piscivorous
- birthing? Live-birth or egg-laying?
Infraclass Lepidosauromorpha
Order Pleiosauria
- Jurassic to Cretaceous of Mesozoic
- all marine; fore- and hind-limbs flattened that
functioned as oars
- dorsoventrally flattened trunk; many (but not all) with
long neck; piscivorous
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Infraclass Lepidosauromorpha – extant taxa
Superorder Lepidosauria
Order Sphenodonta – tuataras
2 species; relics from Triassic; New Zealand
Extant forms:
-length of 60 cm
- nocturnal
- low body temp
- share burrows with seabirds
- feed largely on invertebrates
associated with seabirds
-parietal eye; maxilla and palatine
teeth
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