Ichthyosaurus

Discovery by Mary Anning, the “Mother of Paleontology”

Ichthyosaurus is a type of marine reptile, similar to the famous Elasmosaurus and Mosasaurus, but it belongs to a distinct group called “Ichthyosaurs” (Fish Lizards).
It was truly a creature that could be described as the “reptilian version of a dolphin.”

A creature that could be described as the “reptilian version of a dolphin”

Fossils of this creature were first discovered in England around 1800.
The discoverer was Mary Anning, who would later be hailed as the “Mother of Paleontology.”
While she would go on to excavate Plesiosaurus and Dimorphodon and receive praise from around the world, her first great achievement was this discovery of Ichthyosaurus.
This discovery served as a stepping stone for her career and holds significant meaning in the development of paleontology.

Streamlined Body and Physical Characteristics

Beautiful Streamlined Shape and Shark-like Tail

The most defining feature of Ichthyosaurus is its beautiful streamlined form, much like a modern dolphin.

A beautiful streamlined form like a dolphin

It possessed a large dorsal fin on its back and a vertical, crescent-shaped tail fin.
Resembling the tail of a modern shark, its shape had completely transformed into a fish-like form.
It is believed they gained speed by swinging this tail, allowing them to swim freely through the ocean.
Also, their skin was smooth, not rugged like typical reptiles.

Evolution of Flippers and Size

Its limbs had evolved into “flippers” perfectly suited for marine life, but the sizes differed between front and back.
The forelimbs were quite developed and large, whereas the hind limbs were very short and small.

The forelimbs were quite developed and large, whereas the hind limbs were very short and small.

Body length ranged from about 2 to 3 meters.
This is roughly the same size as a modern bluefin tuna.
Compared to the giant fish Leedsichthys believed to have lived in the same era, the giant marine reptile Liopleurodon, or ichthyosaurs from later periods, it falls into the rather small category.

Advanced Sensory Organs: “Ears” to Hear Vibrations and “Eyes” to See in the Deep Sea

Ichthyosaurus possessed developed sensory organs to catch prey.
Its mouth was lined with small, sharp teeth typical of carnivores, and it utilized the following abilities to hunt.

“Ears” that Sense Vibration

It possessed very developed, large ear bones.
With excellent hearing, it is believed they could accurately gauge the distance to prey or predators by sensing the slightest vibrations in the water caused by small marine creatures.

They could accurately gauge the distance to prey or predators

“Eyes” that See Through the Deep Sea

Their vision was also exceptional.
Their large eyes were protected by “sclerotic rings,” allowing them to demonstrate superior visual acuity even in the poor visibility of the sea.

Evolution to Viviparity: The Truth of Reproduction Told by Fossils

In the past, because Ichthyosaurus was a reptile, it was thought to “come ashore to lay eggs” like sea turtles.
However, subsequent research and discoveries overturned this established theory.

“Viviparity” Proven by Fetuses in the Womb

The deciding factor was the discovery of fossils containing eggs or fetuses within the abdomen.
This revealed that Ichthyosaurus was “ovoviviparous” (hatching eggs inside the womb) or “viviparous” (giving birth to live young).
They left descendants in the sea without ever going ashore.
It is believed that newborn pups spontaneously swam to the surface to breathe air, adapting as fully aquatic residents from the moment of birth.