A study led by Yale University has determined the physical characteristics and behaviour of the first snakes. Accordingly, the original ancestor of snakes was a nocturnal, stealth-hunting predator that had tiny hindlimbs with ankles and toes.
There are more than 3,400 living species of snakes found in a wide range of habitats including land, water, and in trees. Apart from an established understanding about the diversity of snake species, little is known about where and when they evolved, and how their original ancestor looked and behaved. The debate over the evolutionary origin of snakes actually stems from the fact that there are diverse snake species.
To determine the physical characteristics and behaviour of the first snakes, a team of researchers analysed fossils, genes, and the anatomy from 73 snake and lizard species. This analysis involved determining similarities and differences in order to plot a large family tree and illustrate major characteristics that have played out throughout the evolutionary history of snakes.
Results of this analysis suggested that snakes evolved on land and not in the sea, most likely in the warm and forested ecosystems of the Southern Hemisphere or the ancient supercontinent of Laurasia around 128 million years ago or during the Early Cretaceous period. It is important to take note of the fact that the Early Cretaceous period coincided with the rapid appearance of different species of mammals and birds.
“While snake origins have been debated for a long time, this is the first time these hypotheses have been tested thoroughly using cutting-edge methods,” said Allison Hsiang, lead author. “By analysing the genes, fossils and anatomy of 73 different snake and lizard species, both living and extinct, we’ve managed to generate the first comprehensive reconstruction of what the ancestral snake was like.”
Apart from determining a probable period and place, the results of the analysis also suggested that the original ancestor of snakes had tiny hindlimbs with ankles and toes. In addition, this ancient species hunted soft-bodied vertebrate and invertebrate prey that were considerably larger than the common prey target by other ancient lizards that time. The original snake also had not yet developed the ability to kill its prey through constrictions or by wrapping itself around its target.
The original ancestor of snakes was also nocturnal. Although many ancient reptiles were diurnal or most active during daytime, the ancestral snake was most active at night. Diurnal snakes emerged around 45 to 50 million years ago with the appearance of the Colubroidea—the family of snakes that not represents more than 85 percent of all living snake species.
According to the researchers, changing temperatures had influenced the behaviour of earlier snakes. As night temperatures became colder, the nocturnal activity of ancestral snakes or their more recent evolutionary offshoots became severely limited. Thus, the diurnal Colubroidea emerged as more successful among all other snake variants.
Another interesting takeaway from the study is that the success of modern snakes to occupy a range of habitats over their evolutionary history is partly due to their ability to disperse. Snakes are capable of traveling and covering 110,000 square kilometres, about 4.5 times larger than dispersing capability of lizards.
“Our study provides new insights into when, where, and how snakes originated, and presents the most complete picture of the early evolution of snakes to date,” the researchers concluded. “More broadly, we demonstrate the striking influence of including fossils and phenotypic data in combined analyses aimed at both phylogenetic topology inference and ancestral state reconstruction.”
Further details of the study are in the article “The origin of snakes: revealing the ecology, behavior, and evolutionary history of early snakes using genomics, phenomics, and the fossil record” published in 2015 in the journal BMC Evolutionary Biology. Researchers and authors of the study included Allison Y. Hsiang, Daniel J. Field, Timothy H. Webster, Adam D. B. Belk, Matthew B. Davis, Rachel A. Racicot, and Jacques A. Gauthier. Photo credit: Julius Csotonyi