Download Ecol 483/583 – Herpetology Lab 11

Ecol 483/583 – Herpetology
Lab 11: Reptile Diversity 3: Testudines and Crocodylia
Spring 2010
P.J. Bergmann & S. Foldi
Lab objectives
The objectives of today’s lab are to:
1. Familiarize yourselves with extant diversity of the Testudines and Crocodylia.
2. Learn to identify species of Testundines that live in Arizona.
Today's lab is the final lab on "reptile" diversity, and will introduce you to the Testudines, or
turtles and tortoises, Crocodylia. Although there are no crocodylians in Arizona and the
Testudine diversity is lower than that of the lizards or snakes, there is still a fair amount of
material to learn, so use your time wisely.
Tips for learning the material
At this point in the course, your skills for learning herp diversity should be well honed, so
continue with the strategies you have already learned during the semester. Learn how to
differentiate the three major clades of Crocodylians, and the more numerous Testudine clades.
There is another keying exercise in this lab, focusing on the Testudines.
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Ecol 483/583 – Lab 11: Testudines & Crocs 2010
Exercise 1: Testudines
(Modified from Bonine & Foldi 2008; Bonine, Dee & Hall 2006; Edwards 2002; Prival 2000)
General information
Turtles are probably the most instantly recognizable groups of all reptiles because of their shell
and the ability to withdraw their heads and limbs into this protective structure. Turtles are a
monophyletic group comprising the order Testudines also called Chelonia. Testudines is the
term used to denote all members of the order (extant and extinct) whereas Chelonia is often used
to denote extant turtles. There is some confusion in common terminology used for various
groups of turtles. The term ‘tortoise’ refers to terrestrial species that have high domed shells,
large size and the hind legs are elephantine (columnar). Tortoises belong to the clade
Testudinidae. ‘Terrapin’ is used for freshwater species that are generally harvested and eaten,
however in Britain it is used for all pond turtles. Terrapins belong to more than one clade of the
Testudines.
There are 13 extant families of Testudines, containing about 300 species. Turtles are further
divided into two distinctive clades: the Pleurodira and Cryptodira. These are distinguished by
their method of neck retraction. The Pleurodira, or side-necked turtles, bend their head and neck
to the side (pleuro – Gr. for ‘side’). The Cryptodira withdraw their necks in a vertical plane into
their shell (krypto – Gr. for ‘hidden’). North American turtles all belong to the Cryptodira.
Turtles are found on all continents (with the exception of Antarctica) and reach the greatest
species diversity in two areas of the world: Southeastern United States (35 species) and
Southeastern Asia (about 90 species). In Arizona there are five native species and four
introduced species (all North American species).
The phylogenetic relationships of the
Testudines are shown to the right and in your
textbook. As you go through the material
today, try to think about what sorts of
characteristics make some clades of turtles
more closely related to each other than to
others. A key difference between the
Cryptodira and Pleurodira has already been
discussed.
What is one species of Pleurodira and one
species of Cryptodira that is on display
today?
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Generalized morphology
The turtle shell is comprised of bony plates that are generally covered with keratinized scutes.
These scutes are the portion of the shell that you see, not the actual bones underneath. The shell
is comprised of two general sections, the dorsal carapace and the ventral plastron. The scutes
that cover both halves of the shell are grouped and named. These features are used in species
recognition so it would be good if you familiarize yourself with them. The head is covered with
horny plates whereas the neck generally lacks scales. The limbs may be covered with scales (as
in the desert tortoise) or not (as in the Sonoran mud turtle). In aquatic species the feet are webbed
with clawed toes. In terrestrial species the feet lack webbing.
Label the different scutes on the shells below. Do all species of turtles on display have the
same scutes? Have any species lost some? Which ones?
Pough et al. 2004, Fig. 4-5
Evolutionary trends and conservation
Turtle evolution is the source of much inquiry and debate. The debate is dicussed in some detail
in your textbook and in lecture. Study this for lecture exams, but don’t worry about it for the lab.
The marvelous feature of the shell, from a comparative evolutionary and anatomy standpoint, is
the fact that the shell is comprised of the rib cage and the limb girdles, with the collar bone and
pelvis inside the rib cage. Somehow the ancestral form for the turtles managed this feat and it
has been so successful very few changes have been made to the basic turtle morphology in over
200 million years. In fact, the genus Podocnemis from South America has not changed in shell
morphology for over 60 million years. This evolutionary ‘conservatism’ suggests just how
successful life in a suit of armor is. Turtles have life history strategies that reflect this
morphological success. Most turtle mortality occurs during the egg and hatchling stage, when
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the shell is still soft. Once the shell hardens, turtle survivorship is high. In addition, sexual
maturity is delayed in turtles and reproductive success is highly correlated with increased age.
As a result, the removal of adults for food, medicine or pet trade can have devastating effects on
wild populations.
Turtle populations everywhere are declining. Although there have been turtle conservation
successes (for example, halts in population declines in some sea turtle populations) the opposite
is the rule. Turtle products are so popular in Asia that three quarters of Asia’s native turtle
populations are considered threatened and two Chinese turtles are thought now to be extinct
(Altyherr and Freyer, 2000, Anon. 2001). During the past century 11 turtle species (out of the
300 known) have gone extinct and 49% are considered threatened by the IUCN (The World
Conservation Union, Turtle Conservation fund, 2002). Demand for turtle products in Asia is so
great that exports of North American turtles to Asia has increased over 1000% in the past 20
years. The pet trade also has been implicated in turtle declines worldwide. This demand
combined with worldwide habitat destruction and lack of conservation laws means that turtles
face considerable threats to their survival. In the U.S., fifteen species are listed for protection
under the Endangered Species Act.
7orth American Turtles
Cheloniidae: Marine Turtles
Content and distribution: 5 genera, 6 species. Worldwide, in temperate and tropical oceans.
Morphology: This family includes all marine turtles with hard shells. Their forelimbs are more
strongly developed than their hind limbs and are shaped like flippers. They cannot retract
their heads inside their shells. Adults vary in size from 70 cm to 1.5 m in length.
Life history: Cheloniids spend their entire lives at sea, except when females come ashore briefly
to lay eggs. They typically eat grasses and invertebrates found on the sea floor. Cheloniids
are known for their extensive migrations between breeding and feeding sites. The female
comes ashore at night to lay eggs, building a nest in the sand above the high tide line.
Females usually exhibit high fidelity toward particular nesting beaches. The clutches are
large, varying from 80-200 eggs. Several clutches may be laid at 2-3 week intervals,
although females usually only reproduce once every two or three years.
Miscellaneous facts: All five cheloniids that occur in U.S. waters are on the Endangered Species
List. Primary threats include the development and destruction of nesting beaches, the
collection of turtle eggs and hatchlings, and the use of outmoded shrimp nets that trap and
drown sea turtles. The use of modified nets that allow turtles to escape are in use by many
countries but not all.
Species in lab:
Caretta caretta – Loggerhead
Chelonia mydas – Green Sea Turtle
Eretmochelys imbricata – Hawksbill Seaturtle
Lepidochelys olivacea – Pacific Ridley Seaturtle
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Chelydridae: Snapping Turtles
Content and distribution: 2 genera, 3 species. Eastern North America, including southern
Canada. Into South America, as far as Ecuador. Platysternon found in southeastern Asia.
Morphology: Chelydrids have a large head and limbs that cannot be fully retracted into the shell,
powerful hooked jaws, a long saw-toothed tail, and a small plastron. They have 11 marginal
scutes per side.
Life history: Chelydrids are highly aquatic freshwater and brackish-water turtles, inhabiting
swamps, ponds, lakes, and streams. However, they are not particularly strong swimmers and
usually get around by walking underwater. They are typically ambush predators, feeding
opportunistically on invertebrates, carrion, aquatic plants, fish, birds, and small mammals.
Eggs are deposited in flask-shaped cavity nests on land, sometimes as far as 0.5 km from
water.
Miscellaneous facts: Macroclemys temminckii is the heaviest freshwater turtle, weighing as
much as 250 pounds (113 kg). Chelydrids are known for their nasty tempers and strong jaws,
so watch your fingers if you encounter them live. Chelydra serpentina is not native to
Arizona, but apparently has been found near Phoenix.
Species in lab:
Chelydra serpentina – Snapping Turtle
What is a ynapomorphy of the Chelydridae that will allow you to identify them from other
testudine clades?
Dermochelyidae: Leatherback Turtles
Content and distribution: 1 species: Dermochelys coriacea. Worldwide distribution in temperate
and tropical oceans.
Morphology: The carapace of dermochelyids is composed of ridged, leathery skin instead of
keratinous scutes. The shell bones found in other turtles are replaced by small, bony plates
embedded in the skin (osteoderms). They cannot retract their head or limbs. Unlike other
marine turtles, dermochelyids lack claws.
Hypothesize as to why leatherback turtles might have a highly reduced shell.
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Life history: Like the cheloniids, the dermochelyids are completely marine, only the females
come ashore to lay eggs. Dermochelyids primarily eat jellyfish and are incapable of chewing
hard prey due to their weak jaws. Their esophagus has many backwards-pointing, stiff spines
which may aid in swallowing soft-bodied marine invertebrates. Reproduction is similar to
that of cheloniids. The clutches are large, varying from 50-170 eggs.
Miscellaneous facts: This endangered species is the largest turtle in the world, reaching over
seven feet in length and weighing almost a ton. Dermochelys coriacea probably also has a
larger geographical range than any other reptile.
Species in lab: None.
Emydidae: Semi-aquatic Pond and Marsh Turtles
Content and distribution: 12 genera, 40 species. The Americas, Europe, W Asia, NW Africa.
Morphology: As is often the case with large families, easily recognized synapomorphies are few.
All have a bony shell covered with keratinous scutes and well-developed limbs. Most have
solid plastrons, but three genera have single-hinged plastrons.
What adaptive value would a platron with a hinge have?
Life history: Emydids are aquatic, semiaquatic, and terrestrial. They are mostly omnivorous, but
a few are carnivorous. Females dig a flask-shaped nest/cavity in which eggs are laid.
Reproductive activity is strongly correlated with precipitation in many species.
Miscellaneous facts: Commercial collectors, especially in the eastern U.S, have harvested
Emydid populations heavily. Trachemys scripta is not native to Arizona, but populations
have become established here and throughout the world as a result of the pet trade.
Species in lab:
Actinemyss marmorata – Pacific Pond Turtle
Chrysemys picta – Painted Turtle
Clemmys guttata – Spotted Turtle
Glyptemyss insculpta – Wood Turtle
Deirochelys reticularia – Chicken Turtle
Graptemys geographica – Common Map Turtle
Graptemys nigrinoda – Black-knobbed Map Turtle
Graptemys pseudogeographica – False Map Turtle
Graptemys versa – Texas Map Turtle
Pseudemys concinna (P. floridana) – Coastal Plains Cooter
Terrapene carolina – Eastern Box Turtle
Terrapene ornata – Ornate Box Turtle
Trachemys scripta (Pseudemys scripta) – Pond Slider
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Kinosternidae: Musk and Mud Turtles
Content and distribution: 3 genera, 22 species. North, Central, and South America.
Morphology: Kinosternids have a carapace covered by overlapping horny shields. The plastron,
which may be greatly reduced, is either singly or doubly hinged. They have paired musk
glands near the bridge that secrete foul smelling fluids when handled. They have barbels
(nipple-like projections) on the chin and neck, a short tail, and 23 marginal scutes (most other
turtles have 25).
Life history: These turtles are either fully aquatic or semi-aquatic but are not strong swimmers;
instead they are bottom walkers. They are found in and around the edges of lakes, streams,
and ponds, preferring slow-moving water with abundant vegetation. All kinosternids are
opportunistic feeders, primarily carnivorous, feeding on invertebrates, fish, and frogs.
Miscellaneous facts: “Kinosternon” means moveable chest.
Species in lab:
Kinosternon baurii – Striped Mud Turtle
Kinosternon flavescens – Yellow Mud Turtle
Kinosternon hirtipes – Rough-footed Mud Turtle
Kinosternon sonoriense – Sonora Mud Turtle
Kinosternon subrubrum – Eastern Mud Turtle
Sternotherus carinatus – Razor-backed Musk Turtle
Sternotherus odoratus – Stinkpot
How would you distinguish K. flavescens from K. sonoriense?
Testudinidae: Tortoises
Content and distribution: 11 genera, ~40 species. Worldwide distribution in tropical and
temperate zones except northern North America, northern Eurasia, and Australia.
Morphology: Testudinids have high domed shells; heavily scaled, strong legs; flattened
forelimbs with claws; and unwebbed feet. They are able to fully retract their head and limbs
into their shell.
Life history: All testudinids are terrestrial and occur in habitats ranging from extremely arid
desert regions to tropical rainforests. Most tortoises are herbivorous, but a few are
omnivorous. Some species use their flattened forelimbs to dig burrows. Most lay fairly
small egg clutches.
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Miscellaneous facts: Two of the three U.S. species are endangered. Gopherus agassizii is
federally protected in CA, NV, and UT and state protected in AZ.
Species spotlight: The Desert tortoise is federally listed as a threatened species in the Mojave
Desert of Nevada and California. These populations have experienced rapid declines
associated with the occurrence of upper respiratory tract disease (URTD). The spread of
URTD in wild populations has likely been accelerated by the escape or release of captive, pet
tortoises. Additional factors in their decline include loss of habitat to residential and
agricultural development, roadkill, and habitat alteration by off road vehicles and grazing.
The Sonoran Desert population of the desert tortoise is not federally listed, but is of special
concern in Arizona and is fully protected throughout its range. URTD is found in Sonoran
populations but similar die-offs have not been observed. In Arizona, loss of habitat to
residential development is probably the greatest immediate threat to the species.
The basic activity cycle identified in the Sonoran Desert is peak activity during the summer
monsoons. By late august, breeding occurs as males pursue females in courtship rituals. A
male may stay with a single female for several days before searching for another. Adult
males that come into contact during this time may combat for dominance, but this behavior
may be less common in Sonoran populations than in Mojave populations (Niblick et. al.
1994). As winter approaches (late October/early November) tortoises generally move
upslope to winter hibernacula (Bailey 1992). Females store sperm over the winter and
follicles may develop in the spring (Murray et. al. 1996). Males are generally not active
during the winter or spring and stay in hibernation or aestivation until the summer rains
occur. Females may take advantage of warm weather and bask or feed during winter or
spring to boost metabolism needed for reproduction. Not all females necessarily lay eggs in
a given year. Typically, only 30-70% of females in Sonoran populations will lay eggs
(Averill-Murray 2000). Female desert tortoises in the Sonoran Desert have been observed to
defend nests since the eggs are vulnerable to predation by Gila monsters, ringtails, and
skunks.
Species in lab:
Geochelone pardalis – Leopard Tortoise
Geochelone sulcata – African Spurred Tortoise
Gopherus agassizii – Desert Tortoise
Examine the specimens of G. agassizii on display. How would you distinguish males from
females? Give at least two distinguishing characteristics.
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Trionychidae: Soft-shelled Turtles
Content and distribution: 14 genera, ~27 species. North America from S. Canada to N. Mexico
(except for NW U.S), Africa, the Middle East, India and East Asia.
Morphology: Trionychids have nearly circular, flat, flexible shells that are covered in a leathery
skin that lacks keratinous scutes. Trionychids have carapace bones that are greatly reduced
in addition to the lack of shell scutes. They have long necks, fleshy lips instead of a beak, a
fleshy proboscis on the snout, and fully webbed paddle-like limbs.
Life history: Trionychids are completely aquatic and strong swimmers. They are carnivores
which either ambush or actively seek prey. They are capable of cutaneous gas exchange, but
often use their long snouts as snorkels. Females lay eggs in a nest on land near water.
Miscellaneous facts: Apalone spinifera has been introduced into the Lower Colorado and Gila
River systems in Arizona.
Species in lab:
Apalone mutica (Trionyx muticus) – Smooth Softshell
Apalone spinifera (Trionyx spiniferus) – Spiny Softshell
Clades not found in 7orth America but with specimens in lab
Chelidae: Chelus fimbriatus – Matamata
Pelomedusidae: Podocnemis unifilis – Yellow-spotted Amazon River Turtle
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Exercise 2: Crocodylia
(Modified from Bonine & Foldi 2008; Edwards 2002; Prival 2000)
General information
The Crocodylia is a monophyletic group. They
are the sister group to dinosaurs + birds, making
up the Archosauria with those taxa. Crocs have
been around since the mid-Triassic (~215 mya).
There are three main clades, with 7 genera and
23 species currently recognized. The
phylogenetic position of the members of the
Gavialidae are under contention, with molecular
and morphological data conflicting. Pictured to
the left (Pough et al. Fig. 4-39) is the most
widely accepted phylogeny. Crocs are found in
tropical and subtropical areas throughout the
world.
Generalized morphology
Crocodilians have elongate, powerful, heavilyarmored bodies with four short, powerful limbs; a long snout with thecodont teeth; and a long,
muscular tail. They have several adaptations for their aquatic habitat, including webbed feet,
nostrils that can be closed by valves, and a secondary palate that enables the crocs to breathe air
through their nostrils while their mouths are open underwater. Some other derived crocodilian
respiratory features include a four-chambered heart (other reptiles have three-chambered hearts),
a diaphragm-like membrane between the pectoral and abdominal cavities, and lungs with welldeveloped alveoli. Cloacal slit is longitudinal (compared to the transverse cloacal slit of the
Squamata).
Examine a crocodilian skull on display.
What is meant by thecodont teeth?
What is a secondary palate and how does it allow crocs to breath with their mouths full
(hint: do we have a secondary palate?)
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Generalized life history
Crocodilians are closely tied to water, but can also get around quite well on land. They are
strictly carnivorous and eat a wide variety of animals, including about 2,000 humans per year.
The three main clades have a close association between diet and cranial morphology.
Pough et al. Fig. 4-38
Gavialis and Tomistoma have long and very thin snouts with which they slash laterally into
schools of small fish. Alligator and Paleosuchus have relatively broad, short and heavy snouts
and often specialize in eating turtles. Members of the genera Crocodylus and Caiman have
snouts of moderate length and intermediate breadth and are generalized predators. Drowning is
often used as a method of killing large prey. Low-frequency calls are used to communicate with
other crocs of the same species and are also important in parental care for communication
between nestlings and between young and their mother. They become quite territorial during the
breeding season. All crocodilians have internal fertilization and are oviparous. Crocs lack
differentiated sex chromosomes and developing embryos have temperature-dependent sex
determination. Eggs are laid in nests near water and are guarded by the parents. In several
species, the female assists with digging up the nests, hatching, and transports the young to water
in her mouth. Hatchlings may remain with the female for a few weeks. These are some of the
few examples of well-developed parental care in reptiles. Crocs are generally inactive during the
winter, spending those months in burrows or quiet water.
How might a broad snout be adaptive for subduing turtles?
How would internal fertilization be adaptive for animals like crocodylians?
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Conservation
Hunting (for leather and meat) and habitat destruction are the main threats faced by crocodilians
today. Many species have declined significantly over the last 200 years as a result of these
pressures, and at least 17 of the world’s 23 croc species receive some kind of governmental
protection. Experimental efforts to control hunting by creating croc farms and using incentives
to encourage sustainable harvest of wild populations are underway, but according to some, these
efforts are failing the species most in need (see Thorbjarnarson 1999). Several species will
probably become extinct in the near future.
7orth American Families
Alligatoridae: Alligators and caimans
Content and distribution: 3 genera, 8 species. SE U.S., Central and South America, and east
China.
Morphology: Alligatorids have broad snouts that hide the lower teeth when the jaw is closed.
Some species can reach at least 6 meters in length.
Life history: Most inhabit fresh water, but Alligator mississippiensis can occasionally be found in
marine coastal water.
Miscellaneous facts: Alligator mississippiensis is the only native U.S. alligatorid, but Caiman
crocodilus has been introduced into southern Florida. Alligator mississippiensis was
extensively hunted in the U.S. from around 1800 to 1962 for the leather trade, resulting in
widespread population declines and local extirpations. Following protection in the 1960’s,
the species rebounded well in the U.S. and is currently probably more abundant than any
other crocodilian. Today, South American caimans are the main source of crocodilian
leather, endangering several species.
Species in lab:
Alligator mississippiensis – American alligator
Caiman spp. – Caiman
Crocodylidae: Crocodiles
Content and distribution: 2 genera, 13 species. Distributed worldwide in tropical and subtropical
areas.
Morphology: Crocodylids usually have narrower snouts than alligatorids and the 4th tooth of the
lower jaw is visible when the mouth is closed. One species can reach about 7 meters in
length.
Life history: Some species inhabit brackish and salt water, others inhabit fresh water.
Miscellaneous facts: Crocodylids face essentially the same threats as alligatorids. The
Australasian Crocodylus porosus and African Crocodylus niloticus are the crocodilian
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species that tend to eat people relatively often. The only crocodylid in the U.S. is Crocodylus
acutus, where it is restricted to only a few protected areas in southern Florida.
Species in lab: None.
Exercise 3: Keying Turtles
In going through the specimens on display today, you probably noticed that some turtles can be
tricky to identify - they all have shells and the same general body plan. As you know, a
taxonomic key can help you with this. On display are six unidentified specimens that you should
key out. Don't forget to write down the steps you took to arrive at each identification.
A. Steps: _________________________
Species: _______________________
B. Steps: __________________________
Species: ________________________
C. Steps: _________________________
Species: _______________________
D. Steps: __________________________
Species: ________________________
E. Steps: _________________________
Species: _______________________
F. Steps: __________________________
Species: ________________________
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REFERE7CES
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Tortoise Newsletter, 3: 13-14.
Averill-Murray, R.C. 2000. Reproduction and activity of desert tortoises at Sugarloaf Mountain, Arizona.
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Bailey, S.J. 1992. Hibernacula use and home range of the desert tortoise (Gopherus agassizii) in the San
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Murray, R.C., C.R. Schwalbe, S.J. Bailey, S.P. Cuneo and S.D. Hart. 1996. Reproduction in a population
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mating system of the desert tortoise, Gopherus agassizii. Herpetological Monographs, (8): 124132.
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Thorbjarnarson, J. 1999. Crocodile tears and skins: international trade, economic constraints, and limits
to the sustainable use of crocodilians. Conservation Biology 13(3): 465-470.
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