Four-Legged Snake Fails as a Transitional Form and Perhaps Even as a Snake

News to Know

by on

Controversy over the identity of a four-legged snake fossil raises important questions.

  • The four-legged snake fossil discovered last year is not a transitional form between modern legless snakes and their supposed lizard-like ancestors.
  • Scientists debate whether the four-legged snake fossil is even a snake.
  • Scientists demand that scientific conclusions be based on testable, repeatable observations, yet they continue to believe in unobservable evolutionary biology.
  • Snakes are legless because a regulatory gene governing their embryonic limb development is missing a 17-base-pair DNA sequence.

Last year scientists reported discovery of a fossilized four-legged snake—the first ever found. Evolutionists disagree as to whether snakes evolved from marine lizards or legged terrestrial lizards, so this discovery weighs heavily on that debate. Hailed as a transitional form between modern snakes and their supposed terrestrial lizard ancestors, Tetrapodophis amplectus is now the subject of heated controversy.

Another group of scientists told a standing-room-only crowd at this year’s meeting of the Society for Vertebrate Paleontology that the little four-legged animal was just a lizard, not a snake in transition to leglessness. “Tetrapodophis doesn’t show any of those features that you would expect to see in a snake,” says Michael Caldwell, who led the newer study.1 Caldwell says, “Every single character that was identified in the original manuscript as being diagnostic of a snake was either not the case or not observable.”2

But David Martill and the other scientists who originally reported that Tetrapodophis is a snake stand by their study. Martill maintains, “In virtually every single respect [it] looks like a snake, except for one little detail—it has arms and legs.”3 His coauthor Nicholas Longrich asserts Caldwell’s “highly creative”4 analysis is biased toward his belief that snakes evolved from marine lizards. And after the fossil’s mysterious disappearance from a German museum, paleontologists everywhere were in an uproar because there was no way for them to repeatedly analyze the specimen to test their conclusions.

Snake? Maybe. Transitional Form? Nope.

For evolutionists, the question is not merely whether Tetrapodophis was a snake, but whether it was a transitional form showing that snakes evolved from burrowing lizards.

Evolutionary scientists are ever on the hunt for transitional forms. Transitional, or intermediate, forms are animals having unusual characteristics that make them appear—to those with an evolutionary worldview—to be intermediates between different kinds of animals. And evolutionary scientists are generally convinced snakes evolved from lizards. If Tetrapodophis was only a lizard with legs too scrawny to support its weight—perhaps an unusual marine lizard as Caldwell asserts—then it could not have been the hoped-for transitional form.

Just to be clear, despite claims that intermediate forms represent transitions between one kind of animal and a more complex kind of animal, evolutionists have never actually found any fossil that can be demonstrated to be an evolutionary intermediate. Such evolutionary transitions-in-action are not observable in fossils or in living animals, no matter what odd collection of characteristics they have. They are just animals with interesting traits.

Observable, Testable, Repeatable

Beyond discovering its true identity, the controversy concerning Tetrapodophis expanded to include its inaccessibility for further scientific observations. Did its private collector reclaim it? Was it illegally smuggled out of Brazil to its German museum home in the first place? Where was Tetrapodophis hiding, and why? Speculation about the sudden disappearance of the slippery snake abounded.

The paleontologists who disputed its claim to snake-ness wanted to go back for another look. They say that Martill was all wrong about its snake-like traits. For instance, Martill and colleagues said Tetrapodophis possessed the uniquely long jawbone that snakes use to unhinge and open their mouths so very wide. Caldwell says it has an ordinary lizard-like jaw with a C-shaped bone surrounding its hearing apparatus just like all squamate lizards.5 Martill’s team said the fossil’s teeth hooked backward like a snake’s, but Caldwell says the teeth were merely displaced after death. Caldwell said the dinner remnants in the fossil’s gut were likely just fish because he believes the fossil was a marine lizard, but Martill’s colleague Longrich points out that those remains contain leg bones. Martill’s team described a number of skull and skeletal features unique to snakes in the fossil, but Caldwell says he could not find any of those snake traits. Then when Caldwell returned to the German museum to re-examine the fossil, it was no longer available.

Paleontologists—both Caldwell and those who wished to add their own observations to the debate—were furious because Tetrapodophis was nowhere to be seen. Science standards demand observations be repeatable and testable, they pointed out. For instance, University of Cambridge paleontologist Jason Head, who was also denied access to the fossil, exclaimed, “Tetrapodophis is no longer science. . . . It’s not repeatable, it’s not testable.”6 Yale University paleontologist Jacques Gauthier echoed this concern, saying, “Science requires repeatability.”7 And they are correct.

The scientific method requires scientists be able to repeat their tests and observations. Is Tetrapodophis a snake or not? The discrepancies between the observations made by the two teams of scientists are substantial. We will not know whether this animal was an unusual snake or a lizard until these differences have been resolved. For a scientific observation to be observable, testable, and repeatable, it must be possible for scientists to replicate the measurements and anatomical observations made by others. As Head explained during the clamor before the missing fossil surfaced, “We’re never going to know whether or not the original analysis was right or wrong, or whether or not Dr. Caldwell’s work was right or wrong, because we can’t replicate either observation.”8

Unobservable, Untestable, Unrepeatable

The unavailability of the fossil for further examination could have forever prevented us from knowing whether Tetrapodophis is a four-legged snake or not. However, it turns out the owner had temporarily removed it from the museum to assess the damage sustained during CT scanning at a French facility. Tetrapodophis will return to the museum and be accessible in future for in-house examination only. Nevertheless, even with the fossil in hand, some of the assertions concerning it cannot be tested or observed. “Origins science” is not observational science. The supposed evolutionary rise of snakes can never be replicated, tested, or observed.

What these scientists do not acknowledge is that they themselves cling to many unobservable, untestable scientific beliefs concerning this fossil and many others.

What these scientists do not acknowledge is that they themselves cling to many unobservable, untestable scientific beliefs concerning this fossil and many others. For instance, how do scientists know Tetrapodophis is really 110 million years old? How do they know that legless snake fossils Michael Caldwell discovered in early 2015 are 143–167 million years old? They do not. Those ages are based upon a series of unverifiable assumptions affecting the interpretation of radiometric dating methods. (See “Doesn’t the Order of Fossils in the Rock Record Favor Long Ages?” and “Radiometric Dating: Problems with the Assumptions.”)

And then there is the evolutionary significance of the little four-legged fossil. Evolutionists assume that snakes evolved from a completely different kind of animal, some sort of lizard. They simply seek fossil proof of the path it took. But can that path be tested? Can it be observed? Can the origin of the snake be repeated for scientists to observe? No! Evolutionary transitions from one kind of animal to another have never been observed. The origin of the snake has already happened. Fossils can be described, the anatomy of snakes and lizards can be compared, and the genomes of living animals can be scrutinized and subjected to tests determining the functions of the genes that govern their embryonic development in the present. But the origin of snakes cannot be repeated, observed, or subjected to scientific tests.

Suppose for a moment that the missing fossil really is a four-legged snake as originally claimed. Does that make it a transitional form? No! Even if Tetrapodophis was a snake, it was not the transitional form Martill and Longrich claim it was. It was just a functional animal with some unusual characteristics, such as stubby legs useful for hugging prey or perhaps a mate, but not for lifting its belly off the ground. The idea that the four-legged snake represents an evolutionary transition, an intermediate form, is not a scientific fact. It is a worldview-based assumption rooted in the unbiblical presupposition that all living things have an evolutionary origin.

Losing Is Not Gaining

If Tetrapodophis really were a snake—something we will not know until it is scrutinized by more scientists—then it was a variety of legged snake that still had to crawl about on its belly. Based on its anatomy, its legs could not have supported its weight on land and presumably therefore had other functions. And losing the ability to walk or to even develop legs over time is not the same thing as evolving the information to develop new complex anatomical structures and abilities, as evolutionists believe happened over and over again to produce all the living things we see today.

Furthermore, a snake is not just a lizard minus the legs. Snakes and lizards differ in ways that cannot be accounted for by loss of information in a snake-ward direction. In fact, our biological roster of interesting creatures includes legless lizards—the legless worm lizards that burrow in dirt around the world. The presence or absence of legs does not dictate whether an animal is a snake or a lizard.

Snakes and lizards each have unique characteristics. For instance, snakes possess specially designed vertebral bones and jaws. Snakes and lizards are different created kinds of animals, not biological cousins. We should not therefore view snakes as specialized descendants or evolutionary progeny of lizards. As we pointed out when the four-legged fossil first achieved fame in 2015, nothing about the unusual extinct snakes with two external limbs9 or the four-legged snake Tetrapodophis—if it is a snake—has opened a window to observe lizard-to-snake evolution but has, at most, only shown that some leggy snakes once slithered in this biodiverse world.

The Secret Limbs of Snakes

Whether or not Tetrapodophis was a snake, the genomes and embryos of snakes may contain the clues explaining why adult snakes living today do not have legs. Two recent studies suggest that snakes lack legs due to a large mutation in their genome. When compared to other animals, the snake genome lacks a 17-base-pair segment in an important regulatory gene.

All vertebrates that develop legs do so as embryos under the direction of genetic switches—regulatory genes—that turn on the genes for leg development. One of these regulatory genes, Sonic hedgehog (SHH), plays a regulatory role in the embryonic development of limbs, fins, and wings as well as the nervous system in mammals, fish, and birds.

Scientists have found that the DNA sequence known as ZRS regulates the all-important Sonic hedgehog gene’s regulatory role in leg development. And in snake DNA, ZRS is missing a 17-base-pair segment, when compared to the DNA of typical legged vertebrates. To test whether the absence of this bit of DNA is responsible for leglessness, scientists replaced the ZRS of mice with the ZRS DNA sequence from snakes. The mouse embryos failed to develop proper legs. Then they genetically engineered the snake ZRS to replace the 17 base pairs and placed that into the mouse genome. This new-and-improved snake ZRS was able to make mouse embryos grow legs like normal.

“This is one of many components of the DNA instructions needed for making limbs in humans and, essentially, all other legged vertebrates. In snakes, it's broken,” explains geneticist Axel Visel, in whose laboratory the ZRS snake connection was made.10

Another study looking at the lack of legs in snakes from a different angle has drawn similar conclusions. Scientists have long known that some snakes, like boas and pythons, have tiny bones, presumed limb remnants, buried within their muscles. Martin Cohn of the University of Florida College of Medicine found that python embryos have a “pulse of sonic hedgehog transcription . . . in just a few limb bud cells,”11 but after this abortive attempt to switch on limb development, the process is discontinued due to the inability of ZRS to keep Sonic hedgehog switched on. Cohn explains, “Python ZRS proved to be very inefficient, turning on transcription for a short time in a few cells,” never allowing limb development to get off the ground.12

Loss of information is not the same as evolution of new information.

Do these studies prove snakes once expressed the genetic information to grow legs? Did they lose it due to a mutational deletion of 17 base pairs in ZRS? Or were snakes simply designed without those 17 base pairs in ZRS, leaving their Sonic hedgehog genes free to perform their other functions while leaving snakes forever legless by design. We cannot know for sure, but it is quite possible the 17 absent base pairs apparently responsible for the snake’s signature slithery nature departed the snake genome sometime after snakes were created. But if so, was this evolution? No! Loss of information is not the same as evolution of new information. Excellent examples of this are found in the recently discovered history of hagfish and among blind cavefish. (See “Discovery of Hagfish Eyes Debunks Claim About Eye Evolution” and “How Cavefish Went Blind, and Why It Matters” to learn more.) Each has lost the eyes it once had; they have not evolved anything new. Similarly, snakes might have lost the ability to develop legs, but they did not have to acquire new information to make this change. At most, they simply lost information they previously possessed.

Sorting out the Serpent’s Past

God cursed the serpent to move on its belly (Genesis 3:14) after Adam and Eve sinned. Many Bible-believing scholars believe this portion of Scripture indicates that God made a dramatic change in the snake’s body plan after man’s Fall into sin. This was, at the least, a permanent visual reminder of the serpent’s role in Satan’s deception of Eve, the prelude to the first couple’s rebellion against God and the subsequent punishment for sin that fell upon all mankind. If so, did God switch off certain genes to bring about this change? Did He use a mutation?

Mutations are generally random genetic changes. Mutations do not create new genetic information of the type required for the evolution of more complex kinds of animals. Mutations do, however, sometimes result in a loss of genetic information. The inability of the snake genome to express whatever information it might possess for limb development might be due to a mutation in the ZRS genetic switching mechanism. Therefore, these discoveries about the role of snake ZRS in producing the legless snakes we see today may have given us a peek into genetic events through which God may have implemented the Curse He spoke upon the serpent in Genesis 3:14, though we cannot be dogmatic about this.

As we ponder the significance of the mysterious four-legged whatever-it-is as well as the recent discoveries about the genetic underpinning of the snake’s lack of legs, we should remember that nothing about these discoveries demonstrates an evolutionary origin for snakes. They are, however, completely consistent with what we learn from the Word of God, the Creator of all, and the only eyewitness to our origins.

Further Reading

For More Information: Get Answers

Remember, if you see a news story that might merit some attention, let us know about it! (Note: if the story originates from the Associated Press, FOX News, MSNBC, the New York Times, or another major national media outlet, we will most likely have already heard about it.) And thanks to all of our readers who have submitted great news tips to us. If you didn’t catch all the latest News to Know, why not take a look to see what you’ve missed?

(Please note that links will take you directly to the source. Answers in Genesis is not responsible for content on the websites to which we refer. For more information, please see our Privacy Policy.)


  1. Laura Geggel, “Mistaken Identity? Debate Over Ancient 4-Legged Snake Heats Up,” Yahoo, November 7, 2016,
  2. Carolyn Gramling, “‘Four-Legged Snake’ May Be Ancient Lizard Instead,” Science 354, no. 6312 (2016): 536, doi:10.1126/science.354.6312.536
  3. Ibid.
  4. Michael Greshko, “Famous ‘Four-Legged Snake’ May Really Be Dino-Era Lizard,” National Geographic, November 2, 2016,
  5. Carolyn Gramling, “‘Four-Legged Snake’ May Be Ancient Lizard Instead.”
  6. Ibid., 537.
  7. Ibid.
  8. Laura Geggel, “Mistaken Identity? Debate Over Ancient 4-Legged Snake Heats Up.”
  9. For example, a fossil snake with two external hind limbs articulated with its vertebral column was reported in 2006. Sebastián Apesteguía and Hussam Zaher, “A Cretaceous Terrestrial Snake with Robust Hindlimbs and a Sacrum,” Nature 440 (2006): 1037–1040, doi:10.1038/nature04413.
  10. Laura Geggel, “Snakes Used to Have Legs and Arms . . . Until These Mutations Happened,” Live Science, October 21, 2016,
  11. Ibid.
  12. Ibid.


Get the latest answers emailed to you or sign up for our free print newsletter.

Answers in Genesis is an apologetics ministry, dedicated to helping Christians defend their faith and proclaim the gospel of Jesus Christ.

Learn more

  • Customer Service 800.778.3390