Skip to content

Nature

Monitoring lizard dispersal and evolution

by Dave Armstrong 18 Jul 2012
Monitoring lizard dispersal and evolution

The varanid lizards, such as the very large water monitor, Varanus salvator speciated in Asia, Africa and Australia, in this case, about 17 million years ago - Monitor Lizard; Credit: © Shutterstock

Snakes, iguanas and the lizards are squamate reptiles, sharing an ancestry back into the Oligocene period and beyond. Many of the lizards originated in Laurasia but the varanids or monitors have a disputed origin.

Africa, Arabia, Australia and Asia hold the present-day species, with the most ancient Varanus spp. coming from the Late Eocene of Africa.

This means the Asian monitors or this African fossil species could have started off the line in the Cenozoic or a Gondwanan relative could have been their ancestor at the Jurassic/Cretaceous interface. (note Gondwana at the bottom left of the maps)

As the continents spread out, the monitors were developing in Eurasia. With the opening of the Atlantic, they were excluded from North America, but managed to cross later into Africa and then Australia. The Australian plate moves upward (with the small green area of India) after the sequence shown till it collides with Asia

Credit: © Shutterstock

Reference Above: As the continents spread out, the monitors were developing in Eurasia. With the opening of the Atlantic, they were excluded from North America, but managed to cross later into Africa and then Australia. The Australian plate moves upward (with the small green area of India) after the sequence shown till it collides with Asia.

The regular modus operandi in genetic mapping now is to check DNA and RNA of representative species (in this case, 54, in all). A whole genome is not necessary to give all the clues needed about relationships between a Class such as the Reptilia or even the Order Squamata here.

Nicolas Vidal et al of the Departement Systematique et Evolution, Museum National d'Histoire Naturelle, in Paris, used probabilistic approaches which they call ML (maximum likelihood) and built up a perfect phylogeny of the whole group.

Identical trees were formed by two methods. With a split between New and Old World types in the early Cretaceous, 100 million years ago, the varanids simply become an African niloticus group and two other groups based on an Indo-Asian and an Indo-Australian biogeography.

Most species-rich groups have developed recently, but one or two date back to before the formation of the Atlantic, such as the Helodermatids (gila monsters) These groups have very few species in them.

Gila monster image

Gila monster image; Credit: © Shutterstock

The gila monster above (Heloderma suspectum), here in Arizona, and its Mexican relative, Heloderma horridum are examples of a lizard family that developed early, with these two modern (Miocene) species, but many fossil relatives. The family date as far back as the early Cretaceous dinosaurs.

The monitors seem to have originated in Asia and may have used Iran as a route - stop on the way to Africa. As the intriguing Madagascar fauna lacks varanids, some support is available for later colonisation of the African continent, between 49 and 33 mya.

Varanus Acanthurus

The spiny-tailed monitor (Varanus acanthurus) © Freek Vonk

This only leaves Australia to be considered. Between 39 and 26 mya, the late Eocene saw blindsnakes, pythons, agamids and geckos reach the continent, and it seems the monitors travelled there within the same time-limits, before its collision with the Asian plate.

The large Komodo dragon would have developed since then, along with the other larger monitors in both Australia and Asia, during the Miocene and Pliocene. The detailed paper with all 54 species tagged on a family tree can be found in Biology Letters today.


Trending Eco-Friendly Clothing

Love My Planet Women's Relaxed Fit Hoodie
Earth
Quick Add
Close
Notify me
Notify me
Love My Planet Women's Relaxed Fit Hoodie
Love My Planet women's eco-friendly relaxed fit hoodieSize Guide Centimeters 8 10 12 14 16 18 Bust 84 88 92 97 103 108 Waist 66 70 75 80 85 91 Hips 91 95 99 104 109 116 Bust: Measure around the fullest part of...
£38.00
£38.00
Close
Notify me
Notify me
Penguins Hate Push-Ups Men's Pullover Hoodie
Earth
Quick Add
Close
Notify me
Notify me
Penguins Hate Push-Ups Men's Pullover Hoodie
Penguins Hate Push-Ups men's eco-friendly pullover HoodieSize Guide Centimeters XS S M L XL XXL Height 171 175 179 183 189 195 Chest 86 93 99 104 116 129 Waist 71 76 81 89 99 112 Chest: Measure all round your chest just below...
£38.00
£38.00
Close
Notify me
Notify me
Lightning Bolt Kids Long Sleeve T-Shirt
Earth
Quick Add
Close
Notify me
Notify me
Notify me