BIO 417 - Reptile Lecture Exam

reptilian anatomy

• diverse

• primitive crocodilians

• derived: turtles, lizards, snakes (most derived), and amphisbaenids (worm lizards)

• turtles are primitive and derived (changed greatly and then not much, Devonian)

reptile skin

• rough

• folded epidermis

rough epidermal skin

• horny layer

• become scales

• lose glandular nature, no longer slimy

• aglandular

• tubercles

• epidermis

• dermis

• claws

ecdysis

• “molting”

• over time replaces skin

• done by epidermis, aided by dermis

• several ways they can shed:

  • synchronous

  • inner generation layer

  • outer generation layer

  • oberhautchen (between old and new skin)

synchronous shedding

the entire outer generation is cast off in one synchronous event. This is in contrast to "patchy" shedding seen in chelonians (turtles) or crocodilians, where scales may flake off individually

inner generation layer shedding

this is the "replacement suit" grown underneath. It is a complete duplicate of the epidermis, built cell-by-cell from the stratum germinativum before the old skin is even removed

• separated from outer layer by Oberhäutchen

outer generation layer shedding

this is the current, mature skin exposed to the environment. During ecdysis, it becomes a dead, translucent husk

• separated from inner layer by Oberhäutchen

Oberhäutchen

the outermost sub-layer of both generations. It is arguably the most important part of the shedding process:

• The Blueprint: It contains the microscopic patterns (spines, ridges, or pits) that give the reptile its texture and color.

• The Separation Point: During ecdysis, a "shedding complex" forms between the alpha-keratin of the old Outer Generation and the ________ of the new Inner Generation. This ensures the old skin peels away cleanly without damaging the delicate new surface

skin color

• chromatophores

• iridiphore

• xanthophores

• melanophores

chromatophores

• pigmented cells

• primarily responsible for skin and eye coloration, as well as rapid physiological color changes used for camouflage, thermoregulation, and social signaling

iridiphore

• dermal k mosaic chromatophores

• unlike other chromatophores that use pigments to absorb light, iridophores produce structural coloration by reflecting and scattering specific wavelengths of light

• no pigment → crystals that act as prisms → deflection → various colors → iridescence

xanthophores

• specialized, pigment-containing cells (a type of chromatophore) responsible for the yellow to orange coloration in ectothermic animals

melanophores

• the "dark" pigment cells in the skin of reptiles, amphibians, and fish that are primarily responsible for physiological color change

reptile skull

• deep (stretches up → height, allows for more openings)

• two openings: bilateral symmetric (primitive)

• orbit: eye opening in skull

• external choana: nasal opening (not naris)

• single occipital condyle (primitive)

new skull openings

• temporal region

  • evolutionary conditions (number and location)

foramen

bone opening, through a bone or a membranous partition

fenestra/fenestrum

"window" or opening, often within a bone or a cellular membrane

anapsid

characterized by the absence of temporal fenestrae (openings) behind the eye sockets, considered the ancestral or primitive (plesiomorphic) condition for all amniotes

• first reptile group

• primitive

• turtles

euryapsid

characterized by having a single temporal fenestra (opening) located high on the skull behind the eye socket. This opening is bordered by the postorbital and squamosal bones

• extinct large aquatic reptiles (Ichthyosaurs)

diapsid

defined by the presence of two temporal fenestrae (openings) on each side, located behind the eye socket. These ancestral openings, traditionally referred to as "two arches," provide critical space for larger jaw muscles to expand, resulting in a more powerful bite and greater jaw mobility

• ancestral to turtles

• dinosaurs

• birds

• squamates

• crocodilians

synapsid

defined by a single temporal fenestra (opening) on each side, located behind the eye orbit and low on the skull. This structure is the defining characteristic of the clade Synapsida, which includes modern mammals and their extinct "proto-mammal" ancestors

• ancestral to mammals

acrodont tooth

tooth on top of edge of jaw, small root

thecodont tooth

most sophisticated, large root embedded in jaw

pleurodont tooth

primitive, larger root attached to inside of jaw

basic external reptile anatomy

• head

• neck

• tail

• trunk

• limbs (mostly)

• eyes

• eyelid (mostly)

• nictitating membrane

• external naris (opening)

• eardrum

• teeth in both jaws (minus turtles)

crocs have

webbed feet

reptile vent

perpendicular

total length

less important than SVL

croc skeleton

• axial

  • cervical vertebrae (ribs on them)

  • diapsid skull

  • ribs circle around body (have sternum for more support)

  • gastralia: abdominal ribs

  • more sacral vertebrae (2-3)

  • thoracic region (2 ribs)

  • many caudal

• appendicular

  • 4-5 toes

  • variation

turtle skeleton

• derived

• shell

  • dermal elements

  • epidermal elements - scale

  • two halves:

    • carapace: dorsal end (back)

    • plastron: flat ventral side (flat, “stomach”)

  • vertebrae column fused to carapace (dermal bone)

    • only non-fused → cervical and caudal

  • scutes: outermost layer of shell on top

• appendicular

  • girdle

  • limb bones

dewlap

in lizards, flexible skin connected to hyoid apparatus

lizard scales

overlap

lizard cloaca/vent

• localized glands in males for pheromones

  • femoral

  • cloacal

turtle skull

• anapsid skull (lost fenestra)

• eyes and nose hole

• beak

• temporal region

scutes

bony epidermal

osteoderms

bony dermal

lizard skin

• skin and modified ribs

• spines

• gular pouch (can be folded back, not a dewlap)

• claws

• thorns

• crest

lizard skeleton

similar to crocs

snake external anatomy

• head

• tail (starts after cloaca)

• trunk (no limbs)

• no eyelid

• lack tympanum

• heat pits

• external naries

• forked tongue (cylindrical)

snake hind limbs

vestigial, primitive

snake scale names

• dorsal: triangular

• ventral: rectangular

• tail ventrally: divided scales

• keeled scale: not smooth

snake skeleton

• large number of vertebrae and ribs

• highly modified skull

  • cranial kinesis

snake venom

• salivary → venom

• teeth → injection

reptile heart

• 3 chambers (crocs 4 chambers)

  • 2 atria (2 atria)

  • 1 ventricle (2 ventricles)

reptile evolution

from stem Tetrapoda, end of Paleozoic (370 mya, right after the first true amphibians)

• then Reptilomorpha

  • early amphibians

  • first group in line to reptiles

reptile radiation

• very quick “adaptive radiation”

• ancient reptiles dominated during Mesozoic, Jurassic, and Cretaceous

• punctuated equilibrium

Mesozoic

age of reptiles

• includes Triassic, Jurassic, Cretaceous

Jurassic and Cretaceous

age of dinosaurs

Reptilomorpha to reptiles

primitive to derived:

• Anthracosaurs

• Captorhinomorph

• Cotylosauria

Anthracosaurs

an extinct group of reptile-like amphibians that flourished during the Carboniferous and early Permian periods (roughly 345 to 245 million years ago). They are considered the "ancestral stock" that eventually gave rise to amniotes (reptiles, mammals, and birds)

• first group after Reptilomorpha

• anapsid

Captorhinomorph

primitive group of extinct "stem reptiles" (early amniotes) that lived during the Late Carboniferous and Permian periods. Historically classified under the order Cotylosauria, they are traditionally considered the basal stock from which most other reptile lineages evolved

• anapsid

Cotylosauria

a group of extinct, primitive tetrapods historically known as "stem reptiles." They flourished from the Late Carboniferous to the Triassic periods and were traditionally considered the ancestral stock for all later amniotes (reptiles, birds, and mammals)

reptile key adaptations

• skeletal

  • deeper skull

  • one occipital condyle

• integumentary

  • thicker skin

• reproductive

  • internal fertilization (copulatory organ)

  • dehydration resistant egg (Cleidoic egg)

reptile egg

Extraembryonic layers:

• yolk sac

• allantois

• chorion

• amnion

• shell

Embryonic layers:

• ectoderm

• mesoderm

• endoderm

fish and amphibian eggs have

• yolk sac

• allantois

• chorion

• NO amnion or shell!

ectoderm

form the skin and nervous system

mesoderm

form the muscles and bone

endoderm

forms the linings of digestive tract and some organs

allantois

acting as both a respiratory organ and a storage site for metabolic waste

yolk sac

acting as the embryo's primary fuel tank and nutrient delivery system

leathery egg shell

a semi-permeable protective barrier that was the key evolutionary "invention" allowing vertebrates to transition from water to land

chorion

outermost extraembryonic membrane, acting as the "protective envelope" that encases the embryo and all other internal membranes (amnion, yolk sac, and allantois)

amnion

innermost extraembryonic membrane that directly surrounds the developing embryo, creating a private "aquatic environment" that is essential for survival on dry land, insulation

classifying reptiles

• controversial

• classified by number and location of skull openings

• possibly 4 clades:

  • 1) Anapsida (turtles)?

  • 2) Synapsida (mammals)

  • clade Diapsida

    • 3) Archosauria (primitive diapsida)

    • 4) Lepidosauria (derived diapsida)

Anapsida

• ancestral condition from Reptilomorphs?

  • no temporal fenestra

  • produced turtles

  • oldest fossil turtles: Triassic

    • Proanochelys quenstedti

      • most ancient turtle in Germany

      • lower (earlier) Triassic

Synapsida

• Captorhinomorpha (no temporal fenestra)

  • primitive reptiles

• Pelycosauria (synapsida)

  • one lower temporal fenestrum

  • eventually lead to mammals

    • Dimetrodon

Euryapsida

• originally misinterpreted

• derived diapsida

• no living descendants, extinct Cretaceous end

• marine carnivores

• Ichthyosauria, plesiosaurs

• very successful

• not dinosaurs

• dolphin/seal-like

Diapsida

• 2 temporal openings

• Archosauria (ancient reptiles)

• Lepidosauria (scaly reptiles)

  • Mosasaurus: looks like Euryapsida but not, not true dinosaurs

Lepidosauria

• diapsid

• likely from Archosauria

• appeared early Mesozoic

• Squamata: most derived

  • squamous: “scaly/shingled”

Archosauria

• diapsid

• dinosaurs, crocodilians, birds

• extinct Diapsida

  • dinosaurs = terrestrial

  • Pterosaurs: flying reptiles (not dinosaurs)

extinct diapsida

• Archosauria (4 clades)

  • Crocodylia

  • Pterosauria

  • Ornithischians*

  • Saurischians *

Ornithischians

• “bird-like hip bones”

• true dinos → didn’t lead to birds

• no descendants

• appeared in Triassic, extinct at end of Cretaceous

• small and large diverse forms

• ischium towards tail

• herd forming, cooperative hunting, vocalization, parental care, homeothermia?

• examples:

  • Stegosaurus

  • Triceratops

  • Ankylosaurus

  • Pachycephalosaurus

  • Parasaurlophus

Saurischians

• “lizard-like hip bones”

• true dinos → lead to aves

• appeared in Triassic, extinct at end of Cretaceous

• small and large diverse forms

• bird hips evolved to look more like Ornithischia

• ischium towards tail

• herd forming, cooperative hunting, vocalization, parental care, homeothermia?

• examples:

  • Apatosaurus

  • Velociraptor

  • Tyrannosaurus Rex

dinosaurs

“giant lizard”

• most famous fossils

• largest animals known

• quadra or bipedal

  • first to develop bipedal locomotion

Stegosaurus

• Ornithischians

• from the Late Jurassic period, roughly 155 to 145 million years ago. It is famous for the two rows of upright, kite-shaped plates along its back and the four formidable spikes on its tail

Triceratops

• Ornithischians

• lived during the Late Cretaceous Period, approximately 68 to 66 million years ago. It was one of the last non-avian dinosaurs to walk the Earth before the Cretaceous-Paleogene (K-Pg) mass extinction

Apatosaurus

• Saurischians

• lived during the Late Jurassic period

Velociraptor

• Saurischians

• lived during the Late Cretaceous period

homeothermia

maintaining body temperature in narrow limits under normal conditions

poikilothermic

body temperature can significantly fluctuate throughout life

• bats and bears when hibernating

dinosaur extinction

• mass extinction, asteroid impact

• geologic continental changes with unusually active volcanic activity

• climactic changes

• mammalian competition

• likely combo of all

• Mesozoic to Cenozoic transition

Extant Reptilia

• reptiles and birds

• Testudines, Crocodylia, Rhynchocephalia, Squamata

Order Testudines

Monophyletic

• unique body plan (strongly conserved)

• Anapsida

• supraoccipital crest

• jaws without teeth (serrated, sheer-like)

Turtle supraoccipital crest

“Pointed” part on back of skull sticking out

Testudines history

• changed little in ~210 million years

• Triassic origin

• extensive fossils

• Thoracic skeleton fused

  • 8 vertebra, ribs, sternum

  • form protective shell

• pull limbs, head, and tail inside

  • some reduced skeletons (Softshell turtles)

  • some heavy elaborated (Box turtles)

Turtle shell

• Carapace (dorsal)

• Plastron (ventral)

• Bridge (connects carapace and plastron)

• Scutes (superficial keratinous plates)

• Osteoderms (deeper dermal, bony plates, differ in # and shape)

• Fused vertebrae (thoracic, lumbar, sacral)

• Free vertebrae (cervical (8), caudal)

• Fused ribs and sternum

• Long necks

• 4 well-developed limbs

Turtle shell implications/tradeoffs

• Protection

• Limited radiation

• Added weight

• Breathing constraints

• Limited movement

Domed turtle shell

Terrestrial

Flat turtle shell

Aquatic

Turtle limb types

• Stump-like (elephantine)

• Webbed (fresh water)

• Flipper-like (marine)

Turtle ecology

• cosmopolitan (minus poles)

• high density in SE US and SE Asia

• many terrestrial (tortoises)

• some burrow (gophers)

• aquatic (mud, pond, snapping, sliders)

Turtle feeding

• mostly omnivorous

• carnivorous

• herbivorous

• many scavengers

• some specialists (some feed exclusively on jellyfish)

Turtle reproduction

• internal fertilization

• oviparous (1-100+) only (rare in other animals)

• sexual dimorphism

  • size (generally females bigger)

  • plastral shape (many terrestrial males concave)

  • plastral spurs (near face, males use to fight other males)

  • tail length

  • claws

• males compete for females

• courtship may be elaborated

  • “dances”, caressing, head shaking

• copulatory organ

• females make nests

• temperature sex determination (TSD)

• no parental care

Turtle classification

330+ spp, 99 genera, 14 families, 2 suborders

Pleurodira

• suborder of turtles

• pleuro = thorax, folding neck

• 3 families, 21 genera, ~90 species

• most primitive

• side-necked turtles

• primitive

• 13 plastral scutes

• 9-11 plastral bones

• pelvic bones fused to skull

• exotic

  • Africa, Madagascar

  • SA

  • Australia

• all aquatic, freshwater

Cryptodira

• suborder of turtles

• crypto = hidden

• 11 families, 80+ genera, ~203 species

• “hidden”, “S-vertical neck”

• complete head retraction

• more diverse

  • morphologies

  • all environments

• vertical-necked turtles

• S-shape neck folding

• advanced

• 11-12 plastral scutes

• 8-9 plastral bones

• pelvic bones free inside shell

• familiar

Family Chelidae

• Suborder Pleurodira

• 14 genera, 61 species

• medium to small (12-50 cm)

• flattened, large emarginated skull

• wide cheek bones

• flattened shells

• webbed feet

• GSD*

• freshwater

• bottom walker

• omnivorous, opportunistic carnivores

• Chelus suction feeds (Mata mata)

Family Chelydridae

• Suborder Cryptodira

• mostly E US, some central America + northern SA

• 2 genera, 4 species

• second smallest turtle family

• large size + heads

  • cannot fully retract head

• bottom dwellers

• freshwater

  • opportunistic carnivores

• contains largest turtle in NA

• tongue adaptation

• TSD Type II

  • trimodal

  • low incubation temps = all females

  • high incubation temps = all females

  • mid incubation temps = all males

Family Kinosternidae

• Suborder Cryptodira

• NA to N SA

• 4 genera, 25 species

• mud and musk turtles

• small turtles

• elongated shells (egg shaped, unusual for aquatic)

  • plastron may be reduced

  • singly or double hinged

• musk glands in cloaca

  • aquatic

  • carnivorous

• GSD (also TSD)

• 2 hinges in Kinosternon genus

Family Testudinidae

• Suborder Cryptodira

• super widespread

• Africa, Asia, S NA, SA

• tortoises

• 15 genera, 60 species

• largest on land

• temperate and tropical

• high domed shells

• head and limbs fully withdrawn

• stout limbs

• herbivorous/omnivorous

• kinixys: hinged carapace genus

• Island Gigantism

• Gopher tortoise: keystone species, many species use their burrows, SE US