The smooth amphibians are not the ancestors of reptiles

History · Published 18 October 2026 Swipe more like this →

In short: For a long time, the evolutionary path of amphibians was shrouded in mystery. While they were among the first animals to transition from water to land, their place in the tree of life is often misunderstood. They are a distinct lineage, not a stepping stone to modern reptiles.

Lissamphibia, the group containing all modern frogs, salamanders, and caecilians, represents a unique evolutionary branch. While they were pioneers of terrestrial life appearing roughly 340 million years ago, they are not the ancestors of reptiles. Instead, they diverged into a separate lineage. This distinction is crucial for understanding vertebrate evolution: while some amphibian traits might resemble those of reptilian ancestors, the two groups represent independent paths from their common aquatic origins.

The internal relationships of lissamphibians are still a subject of intense scientific debate. While most scientists agree that frogs, salamanders, and caecilians are closely related, their exact branching order is contested. Molecular studies suggest a Late Carboniferous divergence between the caecilian lineage and the frog/salamander lineage, with the latter splitting in the early Permian. However, some paleontologists remain skeptical about whether Lissamphibia is a 'natural' group at all, noting that many of their defining skeletal characteristics—such as cylindrical vertebrae and specific skull bones—are also found in various Paleozoic amphibians.

The origin of these 'smooth amphibians' may lie in a process of paedomorphosis and miniaturization from earlier tetrapods. Evidence for this includes the 2023 description of Funcusvermis, a stem-caecilian that retained features of dissorophoid temnospondyls. This suggests that the transition to the modern lissamphibian form involved a complex mix of shrinking in size and retaining juvenile traits, a survival strategy that allowed them to thrive in diverse environments for hundreds of millions of years.

General information, not professional advice. Spotted an error? Flag the card or see corrections and complaints.

Intellect Plus is a visual educational discovery platform for exploring fascinating facts and ideas. Brain Food, Not Brain Rot. What is Intellect Plus?

Related

• Were these giant, crocodile-like amphibians the true ancestors of every modern frog and salamander?
• Reptiliomorpha: The ancient bridge between water-bound amphibians and the masters of dry land.
• Were these ancient, diverse tetrapods the true ancestors of modern amphibians and reptiles?
• Frogs make up about 88 percent of living amphibians
• The 230-million-year evolution of the world's most diverse vertebrates
• How archaeology bridges the gap between ancient scripture and physical history
• Modern technology and ancient dust are rewriting the history of empires
• Exploring the world's most significant archaeological breakthroughs
• The strange case of the 1930s underpants found in an ancient Sumerian city
• The genetic bottleneck of the first Americans
• Ancient metallurgical secrets revealed through the analysis of a single Liao Dynasty gold cup
• The Levallois technique allowed ancient humans to master stone tool efficiency through complex pre-planning.

More in Animals · More in History · Latest · A–Z · All topics