Amphibians are ancient. Most people don’t realize that not only have amphibians existed since before the dinosaurs, they’re actually the ancestors of all reptiles, including many dinosaurs. There are also many more incredible amphibians alive today than most people have ever heard of!
The first ancient amphibians evolved from lobe-finned fish around 370 million years ago. The first ancient reptiles evolved from ancient amphibians around 310 million years ago, and modern-day amphibians first began appearing around 290 million years ago, followed by modern reptiles 260 million years ago.
The history of amphibians is far more fascinating, and more important to the history of our world, than many people realize. So many of the animals alive today would not exist without ancient amphibians.
What Were the Earliest Amphibians?
Roughly 370 million years ago, the first amphibians appeared. The earliest amphibians evolved from lobe-finned fishes, such as the Coelacanth and lungfish. These species, while still fish, had the first fins that began to resemble limbs, allowing their descendants to eventually leave the water (Vences, 2010).
Early amphibians looked a lot more like our modern idea of reptiles than the amphibians we know and love today. However, these amphibians lived over 100 million years before the first reptiles, and over 130 million years before the first dinosaur. In fact, ancient amphibians are the ancestors of most dinosaurs!
One group of ancient amphibians, called the temnospondyls, are believed to have been the ancestors of our modern day amphibians. Temnospondyls displayed a massive size range, with some growing only to a few centimeters, and others growing to six meters or more in length. Temnospondyls laid gelatinous, aquatic eggs, similar to most modern day amphibians (Nishank, undated).
Another group of ancient amphibians, the reptilimorphs, were the ancestors of modern day reptiles. While the name reptilimorph may make you think they themselves were reptiles, they were actually still amphibians. They were simply amphibians with more reptile-like characteristics, whose descendants later became the first true reptiles.
Reptilimorph amphibians were the first organism on Earth to lay the shelled, amniotic eggs we associate today with modern birds and reptiles.
What Were the First Modern Amphibians?
The first modern-day amphibians to appear were Anura (frogs and toads) and Caudata (salamanders and newts), both around 290 million years ago. They were joined by Gymniophona (caecilians) about 235 million years ago. These three modern orders together are called Lissamphibia.
Early frogs were actually the first vertebrates to vocalize on land. They quickly adapted unique calls for breeding purposes, helping frogs of the same species find each other. This unique communication has been carried on and passed down for 290 million years!
Early salamanders showed many similarities to modern salamanders. In fact, it’s believed that all 10 living families of salamanders have existed for at least 100 million years.
Caecilians were the last of the modern amphibians to develop. These unique amphibians are rarely seen due to all species being either fully aquatic, or burrowers. While they may resemble earthworms, they are definitely not! Caecilians are amphibians just like frogs and salamanders, with spines and teeth.
Caecilians’ presence near the equator around the world gives support to the theory that early amphibian groups began to separate even before Pangaea separated into our modern continents (San Mauro et al. 2005).
What Amphibians are Alive Today?
Three orders of amphibians exist today – Anura, or the frogs and toads, Caudata, or the salamanders and newts, and Gymniophona, or the caecilians.
While all share the amphibian characteristics of being ectothermic (cold-blooded) vertebrates with moist, smooth, permeable skin, each order has distinct differences as well.
As of November 24, 2022, AmphibiaWeb lists 8,516 known species of amphibians. Of these, 7,523 (88.3% of all amphibian species) are frogs, 778 (9.1%) are salamanders, and just 215 (2.5%) are caecilians.
Frogs and toads are an order of amphibians defined by their very short spines made up of just a few vertebrae, and long, powerful hind legs for jumping. In some frog species, the hind legs may be up to double the length of the torso when fully extended. These muscular legs can sometimes allow frogs to jump more than 10 times their body length.
There is also extensive diversity within the order Anura as well. Toads, for example, are a specialized family of frogs with drier, bumpier skin, and shorter legs better suited to walking than to jumping.
Tree frogs have specially adapted toe pads for climbing nearly any surface, and many have excellent camouflage to hide in the leaves of the trees they climb.
Pipidae, the family of tongueless frogs, are fully aquatic and eat through suction and by pushing food into their mouths with long, thin fingers. All are frogs, even if they may seem incredibly different!
Salamanders and newts are an order of amphibians with body shapes very similar to lizards. They have long spines and very short legs compared to frogs. Many terrestrial salamanders spend most their adult lives burrowed underground, and a larger percentage of salamanders remain aquatic as adults than frogs.
Newts are a family with salamanders that almost exclusively remain aquatic as adults, however many newts have a terrestrial “teenage” or eft stage between the aquatic larval and adult stages.
Many salamander species display neoteny, in which the animal retains juvenile characteristics, such as gills and an aquatic habitat, into adulthood. While the axolotl is the best known example of neoteny in salamanders, they are far from the only species with this adaptation.
Caecilians are the little-known third order of amphibians. While they are frequently mistaken for invertebrates such as earthworms, caecilians being amphibians means that they are vertebrates.
A large part of the reason caecilians are so relatively unknown is their small range of habitats compared to other amphibians, and their discrete nature. Caecilians exist only around the equator, in parts of Africa, South and Central America, and Asia. Additionally, all caecilians, depending on their species, live either fully underwater or fully underground.
This article was written in collaboration with another Master Herpetologist certified by the Amphibian Foundation.
San Mauro, D., Vences, M., Alcobendas, M., Zardoya, R., & Meyer, A. (2005). Initial diversification of living amphibians predated the breakup of Pangaea. The American Naturalist, 165(5), 590–599. https://doi.org/10.1086/429523
Nishank, S. S. (n.d.). Origin of amphibians – utkal university. Utkal University. Retrieved November 14, 2022, from https://utkaluniversity.ac.in/wp-content/uploads/2022/06/amphibians-evolution-2021.pdf
Vences, M. (2010). Reconstructing the roots of the amphibian tree. BioScience, 60(6), 470–471. https://doi.org/10.1525/bio.2010.60.6.12