Ichthyosaurs

 

Ichthyosaur is Greek for ‘fish lizard’, and is the name for a group of large extinct marine reptiles. They lived during the time of the dinosaurs, but formed a separate group from them and may not have been closely related.

Ichthyosaurs thrived during much of the Mesozoic era. Based on fossil evidence, they appeared about 250 million years ago, and at least one species survived until about 90 million years ago, during the Late Cretaceous. During the early Triassic period, ichthyosaurs evolved from some unidentified land reptile that returned to the sea. In a case of convergent evolution, they gradually came to resemble modern dolphins and whales, which evolved from land-dwelling mammals millions of years after the ichthyosaurs returned to the ocean. These ‘fish lizards’ were abundant until the later Jurassic and Cretaceous periods, when they were replaced as the top aquatic predators by the Plesiosauria, another marine reptilian group.

Ichthyosaurs averaged 2-4 meters (6.6 to 13.1 ft) in length. Some specimens were as short as 1 ft, while other species were much larger. During the Triassic, the Shonisaurus popularis was about 15 meters (49 ft) long. The Shastasaurus sikanniensis was estimated in 2004 to have been 21 meters (69 ft) long. Some lower jaw fragments found in England indicated a length between 20 and 25 meters (66 to 82 ft).

Weight estimates indicate a 2.4 meter (8 ft) Stenopterygius weighed around 163-168 kg (359-370 lb), while a 4 meter (13 ft) Ophthalmosaurus icenicus weighed 930-950 kg (2,050-2,090 lb). That would be a lot of tuna! Or salmon.

The earliest members of the ichthyosaur lineage were eel-like, but later members resembled more typical fishes or dolphins. Their limbs had been fully transformed into flippers, and some species had a fin on their backs and a more vertical fin at the rear of a rather short tail.

Their heads were pointed, and the jaws often came equipped with conical teeth to catch smaller prey. Some species had larger, bladed teeth to attack large animals. Their eyes were very large and the neck was short. Later species had a stiff trunk with a more vertical tail fin, which made for a powerful propulsive stroke. Ichthyosaurs were air-breathing, warm-blooded and bore live young. It’s possible they had a layer of blubber for insulation.

They may have looked like fish, but they were not. They were reptiles. They adapted so well to their environment that some of them developed dorsal fins and vertical tail fins without their ancestors having had anything there to be adapted.

 

https://en.wikipedia.org/wiki/Ichthyosaur

Rhynchosaurs

Imagine a reptilian pig with a hammerhead, no visible ears, and a parrot-like beak, and you'll have a pretty good mental picture of a rhynchosaur.

Rhynchosaurs were herbivores that in some fossil localities account for 40 to 60% of the specimens found, making them the most abundant plant eaters on land. They were reptiles with stocky bodies and a powerful beak.

Early forms were small, less than a meter long, and typically lizard-like in build. They had narrow, wedge-shaped skulls with a few small, blunt teeth for eating plants.

Later versions grew up to two meters in length. The skull in these later forms were short, broad and triangular, becoming much wider than long, giving them a somewhat hammer-head appearance, although the eyes were set close together, near the top of the beak. The broad skull accommodated powerful jaw muscles that enabled the rhynchosaurs to cut up tough plant material. The teeth were modified into broad tooth plates, and the lower jaw fit into a groove on the upper jaw, enabling the ‘cutting’ of plant fibers.

The hind feet were equipped with massive claws, presumably for digging up roots and tubers, although digging claws are usually found on the front feet. Like many animals of their time, they spread all across Pangea, and thus across the world.

And that seems to about all there is to say about the rhynchosaurs. They lived during the Triassic era (251 to 199 million years ago), dying out just before herbivore dinosaurs appeared.

I think I would have found rhynchosaurs terrifying, particularly the larger ones, even though they were basically reptilian cows or deer. Let’s face it, the larger ones were as long as a man is tall, and who’s to say they wouldn’t try munching on this new plant called human that invaded their space, even if it didn’t sit still like other plants?

What do you think? If you had a time machine, would you venture back to visit them up close and personal?

 

https://ucmp.berkeley.edu/taxa/verts/archosaurs/rhynchosauria.php

https://en.wikipedia.org/wiki/Rhynchosaur

Dimetrodon

First, the dimetrodon was not a dinosaur. It went extinct some 40 million years before the first dinosaurs came into being, so it wasn’t even a contemporary of dinosaurs. However, it is often mistaken as a type of dinosaur, probably because life that long ago is all jumbled up in people’s minds.

Having said that, the dimetrodon lived around 295-272 million years ago. Its most prominent feature was a large neural spine sail on its back, formed by elongated spines extending from the vertebrae. Without the spine, it resembled a lizard, as it walked on 4 legs and had a tail. Its tall, curved skull had teeth of different sizes in the jaws. Most dimetrodon fossils have been found in southwestern United States, specifically from a deposit called the Red Beds of Texas and Oklahoma. However, there have been some fossils found in Germany. There are over a dozen species within the dimetrodon genus.

Although reptile-like in appearance, the dimetrodon is more closely related to mammals than to modern reptiles, although it is not a direct ancestor of mammals. It is assigned to the group ‘synapsids’, a group traditionally called ‘mammal-like reptiles’.

It was probably one of the apex predators of its time, feeding on fish, reptiles and amphibians. Smaller dimetrodon species may have had different roles in their ecological niche. The back sail may have been used to stabilize its spine or to heat and cool its body. Some recent studies argue that the sail would have been ineffective at removing heat, as large species have been discovered with small sails, and small species having large sails. This would appear to rule out heat regulation as its main purpose. It is proposed that the sail was most likely used in a courtship display, such as threatening rivals or showing off to potential mates.

Most species of dimetrodon range from 6 to 15 ft, and are estimated to have weighed between 60 to 550 lbs. The largest known species is about 13 ft. The smallest is 2 feet.

I remember seeing sail-backed giant lizards in a few movies. Always, they were supposed to be at least as tall as a man at their shoulder. Something that could easily eat a man without giving it much thought. This article only gave their length, not their height at their shoulder, so I can’t tell how much the movies may have ‘blown up’ their size. Considering they were most likely using a modern lizard with an fx sail glued to their back, the film crew probably got very close to make them look a threatening size.

How about you? Seen any good dimetrodon movies lately?

 

 

https://en.wikipedia.org/wiki/Dimetrodon#:~:text=Dimetrodon%20(%2Fda%C9%AA%CB%88m,member%20of%20the%20family%20Sphenacodontidae.