Diversity of Living Amphibians and Reptiles - Lecture notes

From Then to Now: Diversity of Living Amphibians and Reptiles

Phylogeny of the Amniotes

• The phylogeny of a group of organisms is its evolutionary tree.
• Key amniote groups include:
  • Synapsids
  • Reptilia
    • Diapsids
      • Archosaurs
        • Crocodilians
        • Pterosaurs
        • Dinosaurs
          • Ornithischian dinosaurs
          • Saurischian dinosaurs (including birds)
      • Lepidosaurs
        • Tuatara
        • Squamates
    • Parareptiles
    • Turtles
  • Plesiosaurs
  • Ichthyosaurs
  • Mammals

Skull Fenestration and Amniote Phylogeny

• Skull fenestration patterns are important in understanding the phylogeny of amniotes.

Monophyletic Groups

• A monophyletic group includes all the descendants of a common ancestor and ONLY those descendants.
• Monophyletic groups are a natural product of evolution.
• "Reptiles" are NOT monophyletic if birds are excluded.
• Therefore, the term "non-avian Reptiles" is used to refer to reptiles excluding birds.

Diversity of Living Non-Avian Reptiles

• Four major groups:
  • Lepidosauria
    • Squamata (lizards, snakes, & amphisbaenians) - Approximately 11671 species
    • Rhynchocephalia (tuatara) - 1 species
  • Archosauria
    • Crocodylia (crocodiles and alligators) - Approximately 27 species
  • Testudines (turtles and tortoises) - Approximately 361 species; membership in Archosauria is questionable.
• Species numbers are based on data from www.reptile-database.org.

Testudines: Turtles, Terrapins, Tortoises

• Approximately 361 species.
• Unique anatomy, including:
  • Shoulder girdle inside the rib cage.
  • Bony and keratinous shell encasing the body.
  • Loss of teeth, replaced by a horny beak.
• Diverse habitats and anatomies:
  • Terrestrial (tortoises) - herbivorous.
  • Freshwater (terrapins) - varying degrees of ties to water, mostly carnivorous.
  • Marine (sea turtles) - entirely marine except for egg-laying, herbivorous or carnivorous
• Ancestor freshwater

Testudines: Clades

• Basal clades:
  • Cryptodira – neck bends vertically.
  • Pleurodira – neck bends laterally.

Crocodylia: Crocodiles and Relatives

• Approximately 27 living species, worldwide in tropics.
• Extant crocs are large, semi-aquatic predators, morphologically conserved except for snout shape.
• Often apex predators in their environment.
• Examples:
  * Alligator – Alligator mississippiensis
  * Saltwater crocodile – Crocodylus porosus
  * Gharial – Gavialis gangeticus
• Egg layers with advanced parental care (shared with dinosaurs and birds).
• 4-chambered heart

Lepidosauria: Scaled Reptiles

• Approximately 11672 living species.
• Extensive fossil record over approximately 200 million years.
• Two basal lineages:
  • Rhynchocephalia – tuataras – one species restricted to New Zealand, the last survivors of a diverse group with an extensive fossil history.
  • Squamata – lizards, snakes, amphisbaenians – the remaining approximately 11671 species.

Rhynchocephalia: Sphenodon, the Tuatara

Squamata: Snakes, Lizards, Amphisbaenians

• Lizards (Sauria): approximately 7598 species; morphologically and ecologically highly diverse, often conspicuous.
• Snakes (Serpentes): approximately 4073 species; morphologically fairly diverse, ecologically highly diverse, usually cryptic.
• Amphisbaenia: approximately 202 species; morphologically conserved, small, fossorial, highly cryptic.
• Many new species are still being discovered – >200/yr over the last few years!
• Extreme diversity of morphology, ecology, behavior, and life history.
  • Smallest lizard (dwarf gecko) to 5 cm, < 1 g
  • Largest lizard (Komodo dragon) to 3 m, 100 kg
  • Smallest snakes to 10 cm, < 1 g
  • Largest snakes to 10 m, >> 100 kg
• Most lizards and amphisbaenians feed on small invertebrate prey.
• Herbivory is uncommon in lizards and unknown in snakes.
• Snakes are mostly large prey specialists, consuming few large meals.
• Phylogeny of Squamata:
  • Wide diversity of old “lizard” groups.
  • Snakes (Serpentes) are a particularly successful group.
  • Lizards are non-monophyletic if snakes and amphisbaenians are excluded.
  • In Squamata, everything is LIZARD.

Evolutionary Trends in Squamata

• Cranial kinesis.
• Loss of limbs (at least 25 times).
• Viviparity (at least 100 times).

Diversity of the Squamata - UK Lizards

• Zootoca vivipara – Viviparous lizard
• Lacerta agilis – Sand lizard
• Anguis fragilis – Slow worm

Viviparous Lizard – Zootoca vivipara

• Widespread in the UK and Ireland.
• Common along woodland edges, heathlands, coastal dunes, sea cliffs, moorland.
• Widespread in NW Wales.
• Viviparous.

Sand Lizard – Lacerta agilis

• Southern and NW England, N and W Wales
• Sandy heathlands (in South), coastal sand dunes (Wales, NW England).
• Oviparous – requires warm, bare sand for egg incubation.
• European Protected Species, a license is required to disturb (photograph, survey for).

Slow Worm – Anguis fragilis

• Widespread in Great Britain, patchy in Ireland.
• Very common in N. Wales, even in Bangor!
• Variety of habitats – gardens, woodland edges, heathlands, seems tied to soil type.
• Only UK legless lizard.
• Viviparous, gives birth to live young in late summer.
• Typically found under warm stones; roofing felt or tin is used to survey for them in the 3rd year!

Introduced Squamata Species in the UK

• Podarcis muralis - Wall lizard (Introduced Dorset)
• Lacerta bilineata - Green lizard (Introduced Dorset)

Diversity of the Squamata - UK Snakes

• Vipera berus – adder – venomous
• Natrix helvetica – grass snake – harmless
• Coronella austriaca – smooth snake – harmless, endangered

Adder (Vipera berus)

• Britain’s only venomous snake
• Widespread but declining in Great Britain
• Found in heaths, moorland, clifftops, woodland edges, dunes
• Viviparous, mates April-May, birth Aug- Sep
• “Dance” of adders during spring mating: male rivalry
• Bite – fatalities exceptional (last UK in 1975) but significant emergency

Barred Grass Snake (Natrix helvetica)

• Widespread England & Wales
• N. Wales: mostly S. of Snowdonia
• Usually near water – heaths, ponds, meadows, woodland edges
• Largely amphibian-feeding
• Oviparous, often lays eggs in garden compost heaps
• Recognizable through black and yellow collar

Smooth Snake (Coronella austriaca)

• Heathlands in southern England only
• Viviparous
• European Protected Species, license required for surveys, disturbance etc.
• Usually under refugia
• Mostly reptile feeder

Aesculapian Snake (Zamenis longissimus)

• A North Wales Special!
• Introduced from Central and Southern Europe
• Colony around Welsh Mountain Zoo in Colwyn Bay
• Large (150 cm), rodent-eating
• Juveniles resemble grass snakes
• Usually found along hedges, woodland edges, or in and around buildings
• Bangor has been involved in intensive research of the N Wales population for decades

Conservation of Amphibians and Reptiles

• Reptiles and amphibians are especially vulnerable due to:
  • Low capacity for movement (climate change, habitat changes).
  • Susceptibility to disease (especially amphibians).
  • Human beliefs and superstition about many species (food, traditional medicine).

Threatened Amphibians

• Numerous species threatened by chytrid fungus (likely spread by human activity).
• Highly vulnerable to climate change.
• Vulnerable to pollution.
• 38. 5% threatened
• 37% non-threatened
• 38. 5% unknown

Threatened Reptiles

• 21. 1% of species estimated to be threatened.
• Only approximately 35% of species have been assessed!
• Causes:
  • Habitat destruction.
  • Climate change.
  • Invasive species (especially on islands).
  • Overexploitation for food, skin and superstition (a.k.a. traditional “medicine”) (e.g., Asian chelonians, crocodiles, some snakes).

Take-Home Messages

• Amphibians and reptiles contribute over 50% of land vertebrate species diversity (85% if birds included!).
• Great diversity of life histories (reproduction, morphology, behavior).
• Excellent models for evolutionary and ecological research.
• Conservation concern.