21st January 2018 (Sunday): Herp Walk @Sungei Buloh Wetland Reserve

A large crocodile, that we got to see at our last Herp Walk in April 2017! (Photo by Mahesh Krishnan)

It’s a New Year! But HSS is still here with guided herp walks around Singapore! Sungei Buloh Wetland Reserves play home to many species of herptiles, big and small! The large mangrove ecosystem supports great biodiversity. And we love taking walks there. We’d love it if you could join us for this walk! Herps are often thought of as scary or unnecessary. But in reality, these reptiles and amphibians are important and integral to the Singaporean ecosystem!

This walk will take place on Sunday 21 January 2018, 8.00AM-11.00AM

So what are you waiting for?  Let’s go herping! You can register at this link.

23rd December 2017 (Saturday): Herp Walk @ Bukit Timah Nature Reserve (Holiday Special!)

A gorgeous male Black-bearded Flying Dragon (Draco melanopogon), one of the many lizards that thrive in Bukit Timah Nature Reserve

School’s out and we’re back!

After finishing our gruelling exams and projects, us herpers like nothing better than taking a nice hike up to the summit of Bukit Timah. It’s a nice walk and helps us burn those calories we gained while mugging for the examinations. We’d love it if you could join us for this walk! We want to show you more Herps! These misunderstood creatures are often thought of as scary or unnecessary. But in reality, these reptiles and amphibians are important and integral to the Singaporean ecosystem!

This walk will take place on Saturday 23 December 2017, 8.00AM-11.00AM

So what are you waiting for? It’s the holidays! Let’s go herping! You can register at this link.


30th September 2017 (Saturday): Creepy Crawlies and Herpy Derpies!

Creepy Crawlies and Herps that can be found in Singapore’s green spaces!

Creepy Crawlies, Reptiles and Amphibians are often thought of as scary or dangerous! But nothing could be further from the truth. These creatures are integral aspects of fully functioning ecosystems. Yet, they are regularly overlooked and even shunned by people. So, to show how important and beautiful these creatures really are, HSS and ENSING are joining forces to bring you our first collaborative walk at Venus Loop. So what are you waiting for? Sign up!

This Free Guided Walk is held on Saturday, 30th September 2017, 8.30AM-11.30AM

So, what are you waiting for? Register for the walk at this link! See you there!

13th August 2017 (Sunday): FREE Guided Herp Walk @ Treetop Walk

An uncommon Yellow Striped Tree Skink (Lipinia vittigera) at Treetop Walk!

Yes! We’re back! After the last two months of doing walks at Pulau Ubin, we are resuming our monthly free guided walks. TreeTop Walk is one of our favourite places to herp. So come join us on this walk through Singapore’s Central Catchment Nature Reserve. Learn more about the natural heritage of our tiny island. And if we’re lucky, we might meet some of our scaly friends!

Our coming walk will be held on Sunday, 13 August 2017, 8.00AM-12.00PM

So what are you waiting for? Register for this walk at this link. See you there!

World Sea Turtle Day 2017

One of our members, Rushan is currently undertaking his honours year in Murdoch University, using airborne LiDAR-derived topographic maps to determine the importance of beach topography on nest site selection by flatback sea turtles. He has also been involved in hatchery management, captive-rear and release, and sea turtle nursing in the Maldives, Malaysia, and Singapore. This post was contributed by him to commemorate World Sea Turtle Day

June 16th has been declared as World Sea Turtle Day in honor of Dr. Archie Carr. His work brought the plight of sea turtles to the forefront of our attention, and it was through his work that turned the sea turtles around on their path to extinction towards their recovery.

Dr. Archie Carr placing a satellite tag on a green sea turtle. PHOTO CREDIT: Archie Carr Center for Sea Turtle Research, University of Florida

The fossil record indicates that the oceans were once populated with thousands of species of sea turtles, but this legacy is currently held by seven extant species of sea turtles today. Though there are seven sea turtles species today, each species is naturally  divided into several different populations, either by barriers to migration or movement of currents during their pelagic phase. These populations can be roughly divided into Regional Management Units, which are discrete populations of sea turtles that appear to use different oceans and nesting grounds from other populations of the same species. So different are these different populations, in fact, that their conditions for nest site selection can also greatly vary.

Last year for World Sea Turtle Day, I gave a brief overview of the life cycle of sea turtles, as well as talked about the two most commonly found sea turtles in Singapore. This year, I will talk about each sea turtle species in an easy-to-refer info-style format. Specifically, I will cover the conservation status, distribution, the regional management units, diet, threats, and the most prominent feature for each species.

Sea Turtlesshareablejpg.jpg
Size comparison chart of the extant species of sea turtles and the extinct Archelon. PHOTO CREDIT: National Aquarium




The scales on the sides of the head of Hawksbill Sea Turtles are often snapped an analyzed as these can be used to tell individuals apart. PHOTO CREDIT: Rushan bin Abdul Rahman

Scientific Name: Eretmochelys imbricata
Conservation Status: Critically Endangered
In-water Distribution: Primarily tropical, with lesser extent in subtropical waters of the Atlantic, Indian, and Pacific Ocean.
Nesting Distribution: Tropical (Caribbean, Central America, South America, Africa, Madagascar, India, Maldives, Indonesia, Malaysia, Singapore, Australia)
Regional Management Units: East, West, and Southwest Atlantic; Eastern and Southwest Pacific.
Diet: Primarily feed on sponges, but can also be seen eating small crustaceans.
Threats: The most prominent threat to hawksbill sea turtles is the tortoiseshell trade. The beautiful patterns seen on their carapace are highly prized by consumers for accessories such as combs and bracelets.
Most Prominent Feature: Its beak, hence the name Hawksbill Sea Turtle. The head is long and narrow with a large beak, which allows the sea turtle to reach into tiny crevices within the coral and rip out sponges.

Hawksbill Sea Turtles are often poached for their shells, which are then used to make accessories such as combs, bracelets, and hairbands.



A Green Sea Turtle in the blue waters of the Maldives. PHOTO CREDIT: Chiara Fumagalli

Scientific Name: Chelonia mydas
Conservation Status: Endangered
In-water Distribution: Tropical, with sightings seen as far north as the United Kingdom, but most likely passively drifted there when it was caught in the wrong current stream.
Nesting Distribution: Tropical, as far north as southern Japan and as far south as Southern Madagascar.
Regional Management Units: East, Northwest, South, Central, Southwest, and South Caribbean Atlantic; Northeast, Northwest, Southeast, and Southwest Indian Ocean; Mediterranean; East, North Central, Northwest, South Central, Southwest, West Central, and Western Pacific (i.e. South East Asia, of which Singapore is a part of).
Diet: Green Sea Turtles are omnivorous when they are neonates and juveniles, but switch to an herbivorous diet of sea grass when they recruit into near-shore environments. Adults have been seen eating jelly fish.
Threats: The most prominent threat to Green Sea Turtles is the harvesting of eggs and adults on nesting beaches for food. Some countries allow for the legal take of eggs and adults despite their international conservation status. However, countries that do have legislation protecting nesting beaches of Green Sea Turtles have rampant black markets for Green Sea Turtle products.
Most Prominent Feature: Adult green sea turtles really are very green, which is attributed to their herbivorous diet. They have gentle looking faces, which suits their personality as one of the more gentle sea turtle species in the world.



A juvenile Loggerhead Sea Turtle in Uruguay. PHOTO CREDIT: Alejandro Fallabrino

Scientific Name: Caretta caretta
Conservation Status: Vulnerable
In-water Distribution: Tropical, Sub-tropical, and has been found in some temperate waters
Nesting Distribution: Tropical and temperate waters such as the Gulf of Mexico, Central America, South Africa, Shark Bay in Australia, southern Japan.
Regional Management Units: Northeast, Northwest, and Southwest Atlantic Ocean; the Mediterranean; Northeast, Northwest, Southeast, and Southwest Indian Ocean; and the North and South Pacific.
Diet: Mainly crustaceans.
Threats: Prominent threats are fisheries bycatch and direct take of eggs and adults on nesting beaches.
Most Prominent Feature: Their heads are huge, hence the name Loggerhead Sea Turtle. Their heads are muscular and designed to crush and crack the hard exoskeletons of crustaceans.



A Flatback Sea Turtle on a Port Hedland beach in Western Australia. This particular individual had a very high clearance! PHOTO CREDIT: Linda Reinhold

Scientific Name: Natator depressus
Conservation Status: Needs Updating
In-water Distribution: Only found in the waters of temperate and tropical Australia, from Queensland through the Torres Straits in Northern Territory and Papua New Guinea, the Kimberley’s, Pilbara, Ningaloo Reef and Shark’s Bay.
Nesting Distribution: Queensland, Northern Territory, the Kimberley’s, Pilbara, Eighty Mile Beach, Shark’s Bay.
Regional Management Units: Southeast Indian Ocean and Southwest Pacific Ocean, but more management units may be delineated with additional genetic information.
Diet: Soft-bodied invertebrates
Threats: Currently unclear, though there have been records of direct predation by invasive foxes and feral dogs, habitat degradation, and bycatch.
Most Prominent Feature: True to their name, flatback turtles are indeed very flat turtles.



An Olive Ridley Sea Turtle lumbering on the beach. PHOTO CREDIT: Laura Carruyo-Rincón

Scientific Name: Lepidochelys olivacea
Conservation Status: Vulnerable
In-water Distribution: Tropical
Nesting Distribution: Tropical: Central America, South America, Africa, Sri Lanka and India, Malaysia, and several nesting populations in tropical Australia.
Regional Management Units: East and West Atlantic Ocean; Northeast Indian Ocean; the Northeast Indian arribada Ocean population, and the West Indian Ocean; Eastern Pacific, Eastern arribada Pacific population, and the Western Pacific Ocean population.
Diet: Oceanic jelly fish
Threats: The greatest threat to Olive Ridley Sea Turtles are direct exploitation at nesting beaches. Arribada populations, such as in northern India, see mass nesting of females on single nights, where their eggs or adults are easily picked off.
Most Prominent Feature: The smallest sea turtle in the world, with a round to heart-shaped carapace. They also under arribadas, which is the mass nesting of females. Males appear to stay pelagic throughout their life, only mating with females when en route to breeding waters.



A nesting Kemp’s Ridley Sea Turtle in Rancho Nuevo, Tamaulipas, Mexico in 2017. PHOTO CREDIT: Alejandro Fallabrino

Scientific Name: Lepidochelys kempii
Conservation Status: Critically Endangered
In-water Distribution: The Gulf of Mexico and Northern Atlantic (East Coast of the United States to the West Coast of Europe)
Nesting Distribution: Currently only nesting in the Gulf of Mexico
Regional Management Unit: Only one Regional Management Unit identified, which is the Northwest Atlantic Ocean RMU, which includes the Gulf of Mexico and the entire eastern seaboard of the United States.
Diet: Crustaceans, soft-bodied invertebrates
Threats: Direct take of eggs and adults during their arribada in a single site in the United States has caused the population to plummet. Conservation actions for the Kemp’s Ridley Sea Turtle were relocating nests in the Gulf of Mexico and incubating them on beaches on Padre Island, Texas, as well as releasing juveniles from captive-rear and release programs.
Most Prominent Feature: If you happen to be in the Gulf of Mexico and stumble upon a mass nesting event of sea turtles, it is more than likely that you have come across Kemp’s Ridley Sea Turtles. These sea turtles, like the Olive Ridley Sea Turtles, undertake the arribada, though their nesting populations have plummeted. In addition, their heads are narrower and longer than Olive Ridley Sea Turtles.



From little things to big things: a female Leatherback Sea Turtle nesting adjacent to a hatchling running for the water. PHOTO CREDIT: Linda Reinhold

Scientific Name: Dermochelys coriacea
Conservation Status: Vulnerable
In-water Distribution: Have the widest distribution of all sea turtles, having been seen as far north as Norway and as far south as Patagonia. This is attributed to their size, as they have grown so large that they are able to generate their own heat, and hence are able to tolerate more frigid waters.
Nesting Distribution: Tropical and sub-tropical, with populations in east and west coast of the United States, Caribbean, southern and western Africa, Indonesia, Malaysia, Sri Lanka, and northern Australia.
Regional Management Units: Northeast, Southeast, and Southwest Atlantic Oceans; Northeast and Southwest Indian Oceans; East and West Pacific Ocean.
Diet: Pelagic jellyfish.
Threats: Bycatch and direct take of adults and eggs are direct threats to the populations, while coastal development of their nesting grounds prevents them from nesting and bringing in new recruits into the populations.
Most Prominent Feature: Their size. These are the largest sea turtles in the world and are a phenomenal animal to be in the presence of. Their common and scientific name is also attributed to the fact that leatherbacks do not have a hard carapace, but rather a leathery skin layer.



Hawksbill and green sea turtles have been recorded in Singapore on several occasions, with the former finding nesting areas on the beaches within Singapore. The leatherback sea turtle has only been recorded once in Singapore, with the specimen taken and preserved in the now Lee Kong Chian Natural History Museum.

There are several conservation actions being taken in Singapore. For example, Sisters’ Islands has recently been declared as a Marine Park, with plans to establish a sea turtle hatchery on the island. Considering that Singapore coastlines and beaches are constantly used by visitors, translocating sea turtle nests to a hatchery far away from the hustle and bustle of urban Singapore may be a much needed relief and safe haven for incubating nests.

It is coming to the peak nesting period for the local RMU, so if you happen to be on a beach at night, you may come across a nesting sea turtle. As excited as you may be, this is a very delicate process, which can easily be disrupted with the flashing of cameras and squealing of people. If you happen to come across a nesting sea turtle on any of our beaches, please follow these simple guidelines:

  1. Call the National Parks Board on their hotline at 1800 471 7300. Take note of your location (barbecue pit number, the zone you are in, etc.) so they are able to come down to the site.
  2. Do not approach a sea turtle emerging onto the beach to nest; sea turtles are incredibly sensitive to movement and lights, and may abort the entire procedure if they feel the slightest inclination that they are being threatened.
  3. Do not touch sea turtle hatchlings that are emerging from the ground as this is a very sensitive part of their life cycle. Give them plenty of space to go into the water, and maybe even remove trash that would be in their way.

Thanks for reading, and have a turtley awesome day!

HSS at Pesta Ubin!

Pesta Ubin is happening in full swing! Check out all the action on the Pesta Ubin Blog! The Friends of Ubin Network (FUN) have organized this amazing 10-week long celebration to showcase this amazing island to Singapore!

Pesta Ubin 2017

HSS is joining the fun as well! For the next few weeks, we will be collaborating with Strix Wildlife Consultancy and the Vertebrate Study Group to do guided walks at Pulau Ubin!
So far, we have done a few walks already. Check out these pictures from our last few walks!

Looks like fun? Join us on the following dates and see what biodiversity Ubin has to offer:
Saturday 24th June 2017, 6.30PM-9.30PM
Saturday 1st July 2017, 6.30PM-9.30PM
Saturday 8th July 2017, 9.00AM-12.00PM
Saturday 15th July 2017, 5.00PM-8.00PM

Each walk will cost $15 per pax, with payment made on the spot! There is no need to register. Simply meet at the Assembly Area (In front of the Ubin NParks Office) 30 minutes before the walk starts! Here’s a handy map that you can use to find the meeting point!

We will resume our regular herp walks in August! See you on Ubin!

Snakes – Why No Legs?

One of our members, Jonathan Tan, recently wrote an essay on why snakes have evolved to be legless. We’ve invited him to share it here to help our readers better understand their fascinating evolutionary history. 

Disclaimer: our understanding of the evolution of snakes is itself continuously evolving, so this essay may contain points of contention. 

What causes a new trait to evolve in an organism? When a character becomes fixed, it is usually because it provides a selective advantage that increases that organism’s fitness over competitors’. Many characters also affect fitness only within particular niches, not universally; evolving wings for instance, would probably be less useful in the water than on land.  But tracing the original selective advantage of characters is not simple, as they can subsequently be adapted and repurposed for completely different uses such as how the wings of penguins are used as flippers. This is especially so for taxa with a wide variety of habitats and lifestyles, such as snakes. Today, snakes can be found in aquatic (both freshwater and marine), terrestrial, fossorial, and even arboreal environments. The defining character of snakes to most people is often their lack of legs. But having diversified extensively into so many different niches, the adaptive advantages, selection pressures, and environment that first resulted in their evolution of limblessness can be difficult to figure out. To do so, we must first identify the original conditions in which the very first snakes lived.

What sort of habitat did the first snakes live in?

There are two main hypotheses for the form of the last common ancestor of snakes: a terrestrial burrower, or a marine swimmer[1]. Phylogenetic reconstruction using snake fossils as well as extant species can tell us which is likelier. A reconstruction[2] found it certain that the ancestors of both crown group and total group snakes were terrestrial, but not necessarily fossorial. Analysis [1] of the inner ear vestibular shapes of modern snakes correlating them with habitat type led to the deduction that both Dinilysia patagonica, a Cretaceous era snake sister to all modern snakes, as well as a hypothetical ancestor of all modern snakes had burrowing lifestyles (Figure 1). Furthermore, most basal snake clades are burrowers[3], as can also be seen from Figure 1. Evidence for the fossorial origins of snakes can also be found in the morphology of other limbless squamates. There are two main ecomorphs: the short-tailed (tail at most half body length) and long-tailed (tail about 1.5 times body length). Short-tailed limbless squamates such as amphisbaenians and legless skinks are all burrowers; long-tailed ones such as legless anguids all live on the ground surface[4]. Snakes fall morphologically into the former group, making it highly likely that the ancestral snake was also a burrower, and that its non-fossorial descendants retained this body plan when they recolonised surface niches. Other parts of snake anatomy also suggest their fossorial origins. Snakes have unique eye structures[5] and optic nerves[6] that are the result of the restructuring of original squamate eyes[7]. This secondary re-evolution of visual acuity would be expected if snakes descended from a fossorial ancestor, as most limbless tetrapods have poor vision with reduced eyes due to their subterranean lifestyles[7]. The loss of external ear openings and inability to hear sounds above 1500 Hz in snakes also correlates with the poor hearing of other fossorial limbless squamates compared to surface dwelling forms[8]. Both phylogenetic evidence and morphological comparisons with other limbless squamates thus suggest snakes first evolved in a fossorial habitat.


Figure 1 Phylogeny of snakes (nested within squamates) showing habitat type and corresponding vestibule shapes[1]. E indicates the hypothetical common ancestor of crown group snakes (70.1% probability burrowing type), F indicates D. patagonica (93.4% probability burrowing type). The more basal snake clades, represented by R. caecus and T. jamaicensis, and A. scytale, are burrowers.

Why did snakes evolve to live in fossorial habitats?

What might have made fossorial habitats such promising environments that snakes evolved to occupy it? Firstly, they provide excellent concealment and protection from predators that lack similar burrowing abilities[9]. A surface predator would be unable to spot snakes concealed in the soil or leaf litter, and if it were to dig for them, a snake could still escape by quickly burrowing away or going deeper. Even today, save for non-fossorial snakes, almost all limbless tetrapods such as amphisbaenids or caecilians burrow in soil or take shelter in crevices for safety[7]. Fossorial habitats also contain a wide variety of small prey items (e.g. rodents and invertebrates) which seek refuge in leaf litter and subterranean environments[9], making it attractive for small carnivores such as snakes. Although many snakes of today take on prey larger than their own heads due to their highly kinetic skulls[9], ancestral state reconstruction[2] suggests the first snakes targeted smaller prey.  Fossorial snakes of today continue to specialise in eating small animals such as rodents, other snakes, or in the extreme case of scolecophidians, ant/termite larvae[10]. Finally, the opportunity to exploit a new niche in the face of competition from other squamates may also have driven snakes underground. Competition with closely related taxa often drives evolution of novel characters to occupy new niches[11], and sometimes in distinct, determinative patterns. For instance, the very same combination of different ecomorphs evolved in anoles independently on four separate Caribbean islands[12]. Similarly, where there is an empty fossorial niche, a limbless squamate is likely to evolve, an event that has happened at least 20 times[4]; even small isolated patches of new fossorial habitat can give rise to novel limblessness evolution, such as the Calyptommatus lizards endemic to the Sao Francisco sand dunes[13]. The presence of so attractive an unfilled niche meant that snakes adapted to fill it; and in the process they became limbless.

How does limblessness help in fossorial habitats?

So how did limblessness benefit snakes when they were adapting to fossorial habitats? Primarily, this had to do with ease of movement. Serpentine body plans, characterised by elongated bodies and limblessness, are very effective for movement through dense herbaceous foliage and loose soil[9]. Fossil evidence shows that snakes became elongated before losing their legs[14]. Elongation – reduction of body diameter to length ratio –  allowed them to access a larger proportion of crevices while expending less energy trying to squeeze through[7]. When they then lost their limbs, snakes further reduced their effective body diameter, improving their ability to hunt for prey in narrow tunnels and small cracks, as well as flee from predators into the soil/leaf litter or find shelter amongst rocks. Elongation also preadapted them to evolving reduced limbs, as it provided the additional vertebrae necessary for lateral undulation to replace walking and the need for functional limbs. Lateral undulation may be more energy efficient than quadrupedal movement because there is no need to lift the body against gravity[15]; retaining extraneous legs that affected the body’s streamlining would also have reduced the efficiency of this new form of movement. Lateral undulation being common in limbless tetrapod lineages (Table 1) which are almost all fossorial, it likely had strong functional advantage in fossorial habitats where there is little space for limbs to work. With legs having lost their main function to be replaced by lateral undulation, even becoming a hindrance in tight spaces and when slithering through substrate, limblessness would have helped snakes better occupy their fossorial niche.



Table 1 Locomotion methods of limbless vertebrates. Note that all the tetrapods share lateral undulation as a form of movement[7]


Limblessness evolved as an outcome of the adoption of a previously unfilled fossorial niche by early snakes, giving them an even greater adaptive advantage in foraging and avoiding predators in an environment where already food was abundant and predators few. But while this accounts for the initial evolution of limblessness, it does not answer why many modern snakes continue to be limbless even as they diversified into new habitats, as they clearly retain the ability to re-evolve legs (e.g. Tethyan snakes from the Cretaceous[16] ). Instead, snakes seem to have evolved a variety of means to overcome the limitations of being limbless in non-fossorial habitats, such as rectilinear motion to climb trees, or sidewinding in deserts[9]. Perhaps there are secondary benefits to limblessness in these new niches, such as camouflage or stealth; or legs on such an elongated body may just be ineffective as a mode of locomotion. While we can understand under what conditions they lost their legs, why losing them was beneficial at the time, and even the process of losing them relative to other traits, we still do not fully understand why they continue to lack them. For now at least, snakes will continue to remain just a little bit of a mystery.


[1] – Yi, H. & Norell, M. A. (2015) The burrowing origin of modern snakes. Science Advances. 1 (10), 19 March 2017. Available from: http://advances.sciencemag.org/content/1/10/e1500743 [Accessed 19 March 2017].

[2] – Hsiang, A. Y., Field, D. J., Webster, T. H., Behlke, A. D. B., Davis, M. B., Racicot, R. A. & Gauthier, J. A. (2015) The origin of snakes: revealing the ecology, behaviour, and evolutionary history of early snakes using genomics, phenomics, and the fossil record. BMC Evolutionary Biology. 15 (87), 19 March 2017. Available from: http://bmcevolbiol.biomedcentral.com/articles/10.1186/s12862-015-0358-5 [Accessed 19 March 2017].

[3] – Zug, G. R., Vitt, L. J. & Caldwell, J. P. (2001) Herpetology: an introductory biology of amphibians and reptiles. 2nd edition. San Diego, CA, Academic Press.

[4] – Wiens, J. J. & Brandley, M. C. (2009) The evolution of limblessness. In: Hutchins, M. (ed.).Grzimek’s Animal Life Encyclopedia. Internet edition. Farmington Hills, Michigan, Gale Cengage.

[5] – Walls, G. L. (1942) The vertebrate eye and its adaptive radiation. Bloomfield Hills, Michigan, The Cranbrook Institute of Science.

[6] – Northcutt, R. G. & Butler, A. B. (1974) Retinal projections in the northern water snake Natrix sipedon sipedon (L.). Journal of Morphology. 142 (2), 117-135.

[7] – Gans, C. (1975) Tetrapod limblessness: evolution and functional corollaries. American Zoologist. 15 (2), 455-467.

[8] – Wever, E. G. (1967) Tonal differentiation in the lizard ear. The Laryngoscope. 77 (11), 1962-1973.

[9] – Parker, H. W. & Grandison, A. G. C. (1977) Snakes – a natural history. 2nd edition. Ithaca, New York, Cornell University Press.

[10] – Parpinelli, L. & Marques, O. A. V. (2015) Reproductive biology and food habits of the blindsnake Liotyphlops beui (Scolecophodia, Anomalepididae). South American Journal of Herpetology. 10 (3), 205-210.

[11] – Schulter, D. (2000) The Ecology of Adaptive Radiation. Oxford, United Kingdom, Oxford University Press.

[12] – Losos, J. B., Jackman, T. R., Larson, A., de Queiroz, K. & Rodriguez-Schettino, L. (1998) Contingency and determinism in replicated adaptive radiations of island lizards. Science. 279 (5359), 2115-2118.

[13] – Wiens, J. J., Brandley, M. C. & Reeder, T. W. (2006) Why does a trait evolve multiple times within a clade? Repeated evolution of snakelike body form in squamate reptiles. Evolution. 60 (1), 123-141.

[14] – Martill, D. M., Tischlinger, H. & Longrich, N. R. (2015) A four-legged snake from the Early Cretaceous of Gondwana. Science. 349 (6246), 416-419.

[15] – Chodrow, R. E. & Taylor, C. R. (1973) Energetic cost of limbless locomotion in snakes. Federation of American Societies for Experimental Biology. 32, 422.

[16] – Leal, F. & Cohn, M. J. (2016) Loss and re-emergence of legs in snakes by modular evolution of Sonic hedgehog and HOXD enhancers. Current Biology. 26 (21), 2966-2973.