Scaled Reptiles (Squamates)

Squamata, or scaled reptiles, is the largest recent order of reptiles, including over 9,200 species of lizards and snakes (Daza, 2014). This order includes the suborders of Serpentes (snakes), Lacertilia (lizards), and Amphisbaenia (worm lizards) (Cox, 2014).

Image 1: A scaly snake catching its prey

Image 1: A scaly snake catching its prey

They originated around 193 million years ago in the Jurassic Period. Squamates are found on all continents except Antarctica, inhabit a diverse variety of habitats, and can live up to very high latitudes  (Daza, 2014). Members of the order are distinguished by their skins, which bear scales or sheilds. They also possess movable quadrate bones, making it possible to move the upper jaw relative to the braincase.

Squamates are extremely diverse in size and diet. They vary in length from a few millimeters to several meters. Squamates can be herbivores, insectivores, omnivores, or predators. To see a video with examples of the diverse variety of squamates and some fun facts,  check out this cool video–>AWESOME SQUAMATE VID!!

Image 2: A leopard gecko is a colorful squamate

Image 2: A leopard gecko is a colorful squamate

 

Phylogeny

Squamata is a subgroup of Lepidosauria. Squamates give rise to a number of groups such as snakes, chameleons and lizards.

Squamates Tree

Squamates as Model Organisms

Squamates are commonly used as model organisms to study viviparity as well as evolutionary radiation (Blackburn, 2006). However, with the application of new genetic assays and techniques, these scaled reptiles have become an emerging model organism for limb development and morphology as well as developmental patterning (see below). As seen in the “Tail Regeneration in Lizards” page by mmichaels, squamates (particularly the leopard gecko) are also being used in regeneration studies due to the unique physical ability of certain species.

Some species have unique regeneration abilities. Many can voluntary shed their tail and develop complete replacement appendages.

Some species have unique regeneration abilities. Many can voluntary shed their tail (often to escape predation) and develop complete replacement appendages.

 

Control of Segment Number in Embryos

The number of somites, and hence of vertebrae, is highly variable among vertebrates. For instance, frogs have 10 vertebrae, whereas humans have 33 and snakes can have more than 300. To investigate the mechanisms controlling somite numbers in vertebrates, Gomez et al. compared somitogenesis in the corn snake, which makes a large number of somites (315), with that in three other vertebrate species that make far fewer: zebrafish (31), chicken (55) and mouse (65).

Vertebrate segments are formed during early embryogenesis, when vertebrae precursors, called somites, bud off in a rhythmic fashion from the anterior part of the presomitic mesoderm (PSM).

Pathways in PSM involved:

  • Notch
  • Wnt
  • Fibroblast growth factor (FGF)

 

Image 3: Two wild squamates in the grass!

Image 3: Two wild squamates in the grass!

Online Resources:

http://en.wikipedia.org/wiki/Squamata

References:

Blackburn, Daniel. “Squamate Reptiles as Model Organisms for the Evolution of Viviparity“.  Herpetological Monographs 2006 20 (1), 131-146

Daza, J.D. “What’s So Special About Squamates?.” Anatomical Record 297.3 (2014): 341-343. Scopus®. Web. 23 Apr. 2014.

Cox, C.L. ( 1 ), S.M. ( 2 ) Boback, and C. ( 3 ) Guyer. “Spatial Dynamics Of Body Size Frequency Distributions For North American Squamates.” Evolutionary Biology 38.4 (2011): 453-464. Scopus®. Web. 23 Apr. 2014.

Gomez et al. (2008) Control of segment number in vertebrate embryos. Nature 454:335-339.

“Squamates An Instructional Movie 2010 08 sound” by acetten1. https://www.youtube.com/watch?v=E7IzaxvDqSc

Image 1: Origin unknown. Public domain. Courtesy of “Wallpapers HIDE”. http://wallpapershide.com/snake-wallpapers-full-hd-wallpaper-search.html

Image 2: “Leopard Geckos as Pets” Image credit to Grace Lydia https://salmanspets.wordpress.com/category/leopard-geckos/

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