Temnospondyli

These animals lived a long time ago.

They lived in water and on land. Some were very big. They look like crocodiles.

Many had scales on their skin. Some even had hard bone plates. They could be tiny or giant.

Their bones tell us how they lived. They were some of the first to live on land. It is fun to study their old bones.

Temnospondyls were a group of ancient animals.

They lived a very long time ago. Some lived on every continent. They lived in water and on land. Some were small like salamanders. Others were giant. Some had skulls over one meter long.

These big ones could be several meters long.

Their name means "cut vertebrae." This is because their spine bones had many parts. Most animals have one main bone in their spine. Temnospondyls had two main parts. These parts were the intercentrum and the pleurocentrum.

These bones helped them move. Some had strong limbs for life on land. Others had weaker backs for life in water.

Many had hard plates on their skin called osteoderms. Some had large teeth like tusks. Their skulls often had pits and ridges. These might have helped them breathe on land. Scientists still study them today. They want to know if they are the ancestors of modern frogs. Some think they died out without any living relatives.

Temnospondyls were a diverse group of ancient animals.

They lived for about 210 million years. This group flourished during the Carboniferous, Permian, and Triassic periods. They lived on every continent on Earth. Some species lived into the Jurassic and Early Cretaceous periods. However, all of them were gone by the Late Cretaceous. They were some of the first vertebrates fully adapted to life on land.

These animals lived in many different places. Some stayed in freshwater. Others lived in coastal marine environments. Most were semiaquatic, meaning they lived partly in water and partly on land. Some were almost fully terrestrial. They only returned to the water to breed.

Their bodies changed to fit their homes. Some had strong limbs and backbones for walking on land. Others had weaker backbones for life in the water. This shows how they adapted to many habitats.

Scientists have studied them since the early 19th century.

At first, people thought they were reptiles. They used different names for them like batrachians or labyrinthodonts. These names are rarely used now. In the early 20th century, experts grouped them together. They did this based on the structure of their vertebrae. The name Temnospondyli means "cut vertebrae." This refers to how their spine bones were divided into parts.

Temnospondyls came in many different sizes. Some were small and looked like salamanders. Others were huge and looked like crocodiles.

The largest ones were called stereospondyls. These giants had skulls longer than one meter. The whole animal could be several meters long. For comparison, the largest living amphibian is about 1.8 meters long. Many had large teeth called tusks or fangs. Some even had holes in their skulls for these teeth to poke through.

There is a big mystery about where they fit in history.

Experts disagree on their relationship to modern amphibians. Modern amphibians include frogs, salamanders, and caecilians. Some think temnospondyls are the ancestors of these animals. Others think the whole group died out without any descendants. Most studies suggest a group called amphibamiforms is the closest relative. They share similar teeth, skulls, and hearing structures. Scientists continue to study fossils to find the answer.

Temnospondyli refers to a diverse order of ancient tetrapods that lived for approximately 210 million years.

These animals are often classified as primitive amphibians. They flourished globally during the Carboniferous, Permian, and Triassic periods. Fossils of these creatures have been discovered on every continent. While some species survived into the Jurassic and Early Cretaceous, the entire group went extinct by the Late Cretaceous. They represent some of the first vertebrates to become fully adapted for life on land.

The name Temnospondyli comes from Greek words meaning "cut vertebrae." This describes their unique spinal structure. In most living tetrapods, the main body of a vertebra is a single bone called a centrum. However, temnospondyl vertebrae were divided into multiple parts. These parts included the intercentrum and paired pleurocentra, along with the neural arch.

Scientists recognize two primary types of these vertebral structures. The first type is called rhachitomous vertebrae. In these, the intercentra are large and wedge-shaped. The small pleurocentra fit between them to support the spine. The second type is stereospondylous vertebrae. In this version, the pleurocentra are greatly reduced or lost. The intercentrum becomes the enlarged main body of the vertebra. This weaker backbone suggests these animals spent more time in the water.

Temnospondyls occupied a wide variety of ecological niches. Many species were semiaquatic, meaning they split their time between land and water. Some were almost entirely terrestrial and only returned to water to breed. Others lived in freshwater or even coastal marine environments.

Their physical features changed based on these lifestyles. Terrestrial species often had strong limbs and robust backbones for walking. Aquatic species, such as the stereospondyls, often had more specialized features for swimming. Some even possessed sensory sulci. These are canal-like grooves in the skull. They were part of a lateral line system used to detect vibrations in the water. This is a trait seen in modern fish and certain amphibians.

The anatomy of a temnospondyl skull was often quite complex. Many skulls were shaped like a triangle or a parabola when viewed from above. The surface of the skull was frequently covered in pits and ridges. This created a honeycomb-like pattern known as dermal ornamentation. One hypothesis suggests these pits supported blood vessels. These vessels might have helped transfer carbon dioxide to the bones. This could have helped neutralize acid buildup in the blood while the animal was on land.

Many also had an indentation at the back of the skull called an otic notch. Scientists believe this structure may have supported a tympanum, which is an eardrum used for hearing.

Temnospondyls varied immensely in size and appearance. Some species were small and resembled modern salamanders. Others were massive and looked similar to crocodiles.

The largest were the Mesozoic stereospondyls. These giants could have skulls exceeding one meter in length. The entire animal could reach several meters in length. For comparison, the largest living amphibian, *Andrias*, is only about 1.8 meters long. Many temnospondyls also had specialized teeth. Some possessed large teeth called tusks or fangs. In certain species, these lower jaw tusks were so long they pierced through openings in the top of the skull.

Our understanding of these animals has evolved since the early 19th century. Initially, researchers thought temnospondyls were reptiles. They were described using various names, such as batrachians, stegocephalians, or labyrinthodonts. These terms are rarely used by modern scientists. It was not until the early 20th century that they were grouped into a distinct taxon. This classification was based specifically on their unique vertebral structure.

Today, scientists use different methods to define the group. Some use a branch-based definition involving the relationship to the genus *Eryops*. Others use a node-based definition involving specific species like *Edops craigi* and *Mastodonsaurus giganteus*.

A major scientific debate concerns the ancestry of modern amphibians. Modern amphibians, known as lissamphibians, include frogs, salamanders, and caecilians. Experts disagree on whether temnospondyls are the direct ancestors of these animals. Some hypotheses suggest lissamphibians evolved from a specific group of temnospondyls called amphibamiforms. Others suggest they may have descended from a different group called lepospondyls. Some even propose they descended from both groups.

While the exact lineage remains a mystery, similarities in teeth and hearing structures keep the connection under intense study.