Crocodilians:

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Crocodilians

• The Last of the Ruling Reptiles

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(No Transcript)
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Archosauria a review

• Crocs are one of the earliest archosaurian
  offshoots (at about 250-240 MYBP).
• Truly modern crocodilians first appear in fossil
  record for late Cretaceous (at about 80
  MYBP).
• A wide variety of types

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Taxonomic Confusion Morphology vs. Molecules

• Gharials look a whole lot like tomistomae!
• But all deep-structural morphological taxonomies
  (A) set Gavialis at the base of the crocodilian
  tree ally Tomistoma with the true crocodiles.
• Earliest molecular taxonomies (B) placed
  Alligatoridae at the trees base and linked
  Gavialis Tomistoma as sister groups. But these
  taxonomies were mitochondrial.
• More recent nuclear taxonomies support mtDNA work.

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My guess on how it will sort out

• Alligators broad-snouted, temperate-zone
  animals.
• Caiman Central South American animals
  moderately broad snouts.
• True crocodiles salt glands circumtropical
  small to large mostly slender-snouted animals.
• Gharials large tropical Asian animals w/very
  slender snouts.
• But what about the fossil stuff? ?

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? For example, the terrestrial crocodilians (a
repeated theme) and ?

• Junggarsuchus (above, left) Triassic of China.
  Earliest true crocs were probably terrestrial,
  supported by I-beam backbone.
• Pristichampus (above, right) Eocene of Europe
  and N. America 3m serrated teeth, long running
  legs.
• Numerous other Cenozoic examples existed perhaps
  some SEA island terrestrial crocs become extinct
  lt 1500 years ago.
• Cuban crocs dwarf caiman today.

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and the Terror Crocodilians

• Deinosuchus late Cretaceous of Texas (and
  Sarcosuchus, Cretaceous of Niger).
• 15m (skull 2m).
• Ecologically like Nile croc except this one
  ambushed dinosaurs.
• Other giant crocodilians were narrow-snouted,
  presumed fish-eaters.

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Some characteristics of living crocodilians

• Adults 1.1m-7m 10kg-1000kg.
• Mostly tropical.
• Aquatic predators.
• Reproduction
• all lay eggs
• some dig hole-nests others construct mound
  nests
• most give some care to nests and hatchlings
• all have temperature-dependent sex determination.
• Heavy juvenile losses adults almost
  invulnerable.
• Anatomy (brain, spine, palate, heart, lungs)...

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Internal Anatomy backbone (secondary) hard
palate

• Backbone is built like an I-bream for supporting
  great weight.
• Throat valves and bony palate allow croc to
  breathe while mouth is under water (in aquatic
  profile).

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Importance of strong, flexible backbone.(Slide
shows galloping Australian freshwater croc.)

• Perhaps earliest croc specialization within
  Archosauria.
• Crocodilians are not limited to dragging around.
• When larger animals do high walk, the majority
  of weight is suspended between two distant
  girdles.
• Crocodilians are capable of almost instant
  end-switching, so watch out.

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Internal Anatomy the heart

• Unlike other living reptiles, crocs have
  4-chambered hearts.
• Foramen of Panizza once thought an imperfection.
• But look at the routing of oxygenated blood vs.
  deoxygenated blood.

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Reproductive behavior

• The next 6 slides deal with two different themes
• 1. They show various aspects of crocodilian
  reproductive biology, which is the main thing I
  want to talk about now.
• 2. The slides also illustrate different
  crocodilian species.
• Keep in mind the major steps in crocodilian
  reproduction (which are essentially common for
  all species)
• Pairing
• Mating
• Nest-construction
• Egg-laying
• Nest attendance
• Nest opening
• Hatchling care.

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Pairing

• Differs from species to species some are
  territorial some have dominance hierarchies.
• In at least some species, courtship is initiated
  by either gender.
• Courtship is typically extensive in alligators
  it can last minutes or months.
• Slide shows male alligator bellowing.

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Mating

• Always occurs in water.
• Typically lasts about 5-10 minutes (but can be
  protracted).
• Probably has to occur within narrow temporal
  window (when eggs are in correct ovaducal
  region and sperm are mature).
• In at least some species, multiple paternity is
  possible.
• Picture shows courting alligators.

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Nest building(slides show alligator nests)

• Hole nesters usually dig in sand deposit eggs,
  stay not far away.
• Mound nesters usually construct nests from
  available vegetation often they guard nest by
  lying upon it. (Alligator tales.)
• Nests provide some protection from predators
  also help regulate incubation temperature.
• Position of nest ( of egg in nest) may affect
  temp thereby hatchling gender.

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Attending the nest(slide is Philippine croc)

1. Some mothers never leave nest until hatch(c.
   65-90 days varies by species) thats one cost
   of repro ( one reason most croc females
   reproduce biennially at most).
2. Vigor of nest defense varies by species, size,
   individual, and personal history.

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Opening the nest(slide is mugger crocodile)

• Females of most species open nests, probably cued
  in by sounds (which also encourage babies to
  hatch).
• In some instances, young cannot/will not escape
  nest unless mother opens it.
• In some species mother will open unhatched eggs
  to free babies ( will eat bad eggs).

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Caring for young(slide is Nile croc)

• Extent of care varies by species by individual.
• Sometimes care ceases after nest opening.
• Some mothers will carry young to water (more on
  Nile croc).
• In some species young form a crèche which can
  last for gt a year (w/ varying levels of
  protection).
• Notes on cannibalism.

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Feeding

• In general, crocodilians eat any animal of
  appropriate size that they can catch. The list
  of alligator foods is very long.
• Head shape gives clues about diet.
• Smaller crocs (smaller species smaller
  individuals) eat smaller material.
• Most hatchling crocs begin life eating mostly
  invertebrates, fish, and small amphibians.
• The next 4 slides will offer opportunity to
  discuss species and diets.

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Small animals, small food items(Slide is
juvenile common caiman.)

• Depending on species, hatchling crocs are about
  15-30cm.
• Many eat large, aquatic invertebrates or frogs,
  but fish are probably most common food.
• Small animals usually snap at movement, day or
  night.
• Larger juveniles sometimes eat smaller juveniles
  (or are eaten by still larger crocs).

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Head shape often gives clues about species
diets. (Slide is African slender-snouted
crocodile.)

• Narrow-snouted crocs are usually fish eaters.
• Broad, shovel-shaped snouts are often used for
  touch-feeding in murky water bottom muck.
• But remember, all crocs are opportunists will
  not refuse a food item just because its not on
  some books list.

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Big prey!

• Large crocs often take large prey (but seldom
  refuse more modest prey if its convenient).
• Most prefer prey 5-20 of crocs body weight.
  (Few feeding attacks on people by alligators lt 3m
  long.)
• Most feeding is at night in water (but).
• Saltwater croc biggest.
• But Nile croc is specialized for land hunting.

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Cooperative hunting feeding. (Slide shows Nile
crocs.)

• All crocs hunt alone most of the time.
• Some will defend prey item against conspecifics.
• But many crocs will share very large prey.
  (Relate observations in Hwange National Park.)
• Sometimes this is useful for dismembering prey.
• There are a few reliable observations of
  cooperative hunting among Nile crocs.

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A few species accounts

• Many crocodilians look alike, even to experts, so
  why show all? The next 9 photo-slides depict a
  selection of crocodilian species.
• The taxonomic and geographical coverage is rather
  broad.
• Remember
• Family Alligatoridae 4 genera, 7 species mostly
  neotropical.
• Family Gavialidae 2 genera, 2 species tropical
  Asian.
• Family Crocodylidae 2 genera, about 14 species
  mostly circumtropical.

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Alligator

• Southeastern USA, mostly coastal plain.
• Females adult at about 2m males at about 2.5m
  age depends on locale food can be 10-20
  years.
• Courting in spring nesting egg-laying in
  June-July.
• 30-50 eggs per clutch variation depends on a
  number of factors.
• Endangered in 40s-70s now well recovered.
• Biggest wild animal in South Carolina.

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Chinese alligator (Alligator sinensis)

• Linked to Alligator mississippiensis by fossils.
• One of the most cold-tolerant crocodilians.
• A confirmed burrower.
• In the wild, this is one of the most endangered
  crocodilians. But it is prospering in captivity.

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Common Caiman

• Central America tropical South America.
• Extremely abundant in some areas highly
  adaptable to a variety of habitats.
• Females to about 1.6m, males to about 2.2m (less
  in many populations).
• Time to maturity varies but can be as little as 4
  years!!!
• Probably the worlds most abundant crocodilian.
• Note eyeshines.

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Black Caiman

• A large (to gt 4m) alligator-looking caiman of
  South American big rivers.
• Not well known in the wild.
• Various reports of disposition.
• Skin valuable highly endangered (people keep
  hunting after this animal reaches commercial
  extinction).

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Dwarf caiman

• 2 species one in Piedmont-looking creeks and one
  in rainforest streams both tropical South
  American.
• Exceedingly slow to mature probably over 20
  years for both sexes.
• Probably more terrestrial than other living
  crocs.
• Apparently territorial.
• Rainforest species never gets as warm as crocs
  like to be nesting adaptations.

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Gharial

• Very large (to at least 6m) fish-eating croc of
  big south-Asian rivers note long, slender snout.
• Family once more widespread (South Carolina
  fossils).
• Demography unknown.
• Apparent fishing strategy.
• Thermoregulation in snow-melt rivers.
• One of the worlds most endangered crocodilians.

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Tomistoma(false gharial)

• Southeast Asia (mostly Malaysia Indonesia).
• Very large (to 6m).
• Taxonomic status
• appearance like gharial
• internal anatomy like crocodiles
• genetics like gharial??
• Poorly known in the wild
• probably endangered
• breeding biology essentially unobserved
• arguments over food habits.

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Dwarf Crocodle

• African rainforest.
• Two species look almost identical-- but split is
  very ancient.
• Females to about 1.2m males to almost 2m.
• Natural history is almost entirely unknown
  perhaps is similar to dwarf caiman.
• Mound-nester and burrower.
• Heavily exploited for food but probably not
  endangered.

On nest, at night
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Saltwater crocodile

• Tropical Papua-Aust., Indonesia.
• Most nearly marine of all living crocs big river
  estuaries.
• Largest living reptile (to 7m, but Bayliss
  says...).
• Along with Nile croc, the most dangerous
  person-eater.
• Extensively studied in Australia.
• Some commercial ranches and farms.

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Cuban crocodile

• Swampy areas in Cuba Isla de la Juventud.
• To about 2.5m.
• Probably the most terrestrial of the true
  crocodiles (stories from Cuba).
• Disposition of a chainsaw.
• Endangered over-hunting in past habitat
  destruction and interbreeding today.

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• Today most species of crocs are endangered-- for
  a variety of reasons
• skins are valuable
• some species are dangerous
• some species live in habitats that people also
  like
• other habitats are threatened by pollution
• But several species have proved that populations
  can recover from low levels.
• It would be a shame to lose the last of the
  Ruling Reptiles!