The marine iguana (Amblyrhynchus cristatus), also known as the Galápagos marine iguana, is a species of iguana found only on the Galápagos Islands (Ecuador) that has the ability, unique among modern lizards, to forage in the sea, making it a marine reptile. This iguana feeds almost exclusively on algae and large males dive to find this food source, while females and smaller males feed during low tide in the intertidal zone. They mainly live in colonies on rocky shores where they warm after visiting the relatively cold water or intertidal zone, but can also be seen in marshes, mangrove and beaches.
Plotosaurus at the Natural History Museum of Los Angeles.
Plotosaurus was a genus of Mosasaur from late Cretaceous (Maastrichtian) California. It has two known species, P. bennisoni (the species mounted in the photo) and P. tuckeri.
Plotosaurus is also considered to be one of the most derived Mosasaurs, and perhaps one of the fastest swimmers as well. It’s caudal (tail) fin was larger in comparison to it’s body size than other Mosasaurs, it’s flippers were a lot thinner, and it’s body was a lot more streamlined.
Here’s a project that never came to fruition, but it was still a fun idea to illustrate.
When I was a kid, I always wondered what type of dinosaurs roamed the San Francisco Bay Area. I recently found out that dinosaurs never existed in the Bay Area, but what inhabited my hometown were prehistoric marine reptiles, fish and ammonite. For the most part, SF was submerged thousands of feet underwater during the Mesozoic.
“The cause of nearly all strandings on this island, the largest
Ruptorsaurs swim around the shore for prey of all sorts, attacking
nearly anything they spot in the water, even smaller members of their
kind. They come at a pinnacle size comparable to that of an orca whale,
any larger and they risk death. Few reach that size due to how
aggressive the species is towards itself, along with living in such a
hostile ecosystem. Only the truly tenacious Ruptorsaurs earn the right
to be so massive.
It’s turtle Tuesday! This loggerhead sea turtle was spotted in Flower Garden Banks National Marine Sanctuary. Loggerheads’ powerful jaws enable them to feed on hard-shelled prey, such as whelks and conch. Adults can reach up to 250 pounds!
Numerous groups of reptiles have “returned to the water” and become aquatic over the last three hundred million years, but tracing their direct ancestry can be surprisingly difficult. Highly modified and specialized anatomy, lack of transitional forms, and similar features convergently evolving multiple times can all obscure relationships, making it hard to properly classify them.
We’re only just starting to figure out the true origin of turtles (they’re probably archosauromorphs), and they’re a marine reptile group with living members.
Some of the extinct ones are even more uncertain. For example: mosasaurs. (Represented here by the eponymous Mosasaurus.)
While some semi-aquatic early mosasaurs are known, and they seem to be closely related to aigialosaurs and dolichosaurs, their exact placement within the squamates is a lot less clear. Traditionally they were regarded as the sister group to snakes, but some studies have found them to be closer to monitor lizards instead, and others have even placed them as much more basal scleroglossans. Their classification in phylogenetic analyses is “highly unstable”, changing depending on what other reptile groups are included, so there’s no real current consensus.
(And even if they are most closely related to snakes, that doesn’t necessarily help much – the exact origin and evolution of snakes is still very poorly known, too!)
“Shore Iguanadon are the first encounters of many of those stranded on
this island, other than the hungry marine reptiles in the water. Around
the size of a large cow, these often lazy reptiles rarely move, chewing
on seaweed and coral they’ve aquired in the water. Their time spent
digesting makes them noisy and smelly, "burping” every so often in a
10. ANOMALOCARIS (~ 525 Ma) This one metre long invertebrate surely deserves to be included on the list, being one of the first complex oceanic predators to ever have existed. Anomalocaris stalked the Cambrian oceans, viewing the world with a deadly new evolutionary innovation - eyes. Complex eyes allowed this creature to storm its way to the top of the food chain, and with powerful appendages covered in spines it had no trouble devouring prey with tough carapaces. Whilst Anomalocaris is dwarfed by the other contenders on this list, it was still over 10 times larger than any other animal of its time.
9. KRONOSAURUS (125-99 Ma) Kronosaurus, a Cretaceous mosasaur, is named after the Greek titan, Cronus. Its name is well deserved as this ancient beast was a remarkably powerful being. Kronosaurus could reach up to 10 metres long and had a mouth full of sharp, conical teeth. Unlike most other mosasaurs its tail was relatively short, however, evidence shows that Kronosaurus has immensely powerful fins and a pectoral girdle making it an impressive swimmer and hunter.
8. HELICOPRION (290-250 Ma) Helicoprion has astounded scientists since its discovery over 100 years ago. It is iconic for its bizarre spiral of teeth, there are still debates on where exactly these teeth where on the shark with proposals stating they were inside the mouth, on the tip of the tail, the dorsal fin or hanging under the jaw. The most commonly accepted location of the teeth is inside the lower jaw enabling Helicoprion to cleanly slice its prey into pieces.
7. XIPHACTINUS (~110-70 Ma) Xiphactinus was an extraordinary fish that lived during the Cretaceous. It was an esteemed predator that could reach an incredible 6 metres in length and specimens are renowned for their stunning preservation. One such example was 4 metres long and found with another exceptionally well preserved fish just short of 2 metres inside it implying that this particular Xiphactinus individual died shortly after its last feast. Xiphactinus had immensely sharp, slim teeth and an unmistakable underbite which was a possible aid when snaring creatures from below.
6. TYLOSAURUS (86-75 Ma) Tylosaurus is considered a mosasaur and was a vivacious predator all be it smaller than its relative Mosasaurus. Tylosaurus could reach up to 15 metres in length and was one of the apex predators of its day. Fossilised stomach contents of Tylosaurus contain fish, sharks, turtles and other marine reptiles. Despite having an impressive set of teeth, the frontal areas of the jaws exhibit a large reduction in tooth size as well as a more heavily reinforced snout in comparison to other mosasaurs suggesting that Tylosaurus may have rammed into victims with immense force damaging prey internally.
5. MOSASAURUS (70-66 Ma) The mosasaurs ruled the Cretaceous oceans and Mosasaurus was no exception. It could reach up to 17 metres long, longer than most other mosasaurs. Mosasaurus had a strong jaw packed with numerous conical teeth, bite marks of which have been found in huge prehistoric turtles and ammonites suggesting that Mosasaurus was a formidable hunter capable of catching large prey. Mosasaurus was a profound swimmer with strong paddle-like limbs and a huge tail capable of rapidly accelerating the animal when required.
4. DUNKLEOSTEUS (382-358 Ma) Dunkleosteus terrorised the oceans around 370 million years ago and was part of a dynasty known as the placoderm fish (meaning armoured). Dunkleosteus could reach a whopping 6-10 metres in length and probably weighed over a ton. The skull was made up of huge, solid bony plates giving unrivalled protection allowing them to dominate the oceans. Placoderm fish were some of the first organisms to have a mobile jaw, as can be seen in Dunkleosteus’ impressive shearing plates which were used to slice cleanly through prey. Despite an revolutionary jaw, Dunkleosteus could not chew and several fossilised regurgitated remains of its meals have been found that the giant fish simply could not stomach.
3. DAKOSAURUS (157-137 Ma) Dakosaurus was the largest of a group of marine reptiles that were distant relatives of crocodiles. Dakosaurus could reach up to 5 metres long and had a streamlined body with large paddle-like fins and a long muscular tail implying that is was a very efficient swimmer. The diet of Dakosaurus consisted mostly of fish. The teeth of Dakosaurus are lateromedially compressed and serrated which is a similar morphology to modern killer whales indicating that Dakosaurus was an apex predator of the Jurassic oceans. Skull fenestrae provides evidence that Dakosaurus had very large adductor muscles (which are responsible for the jaw closing) and so it was certainly capable of a forceful bite.
2. LIOPLEURODON (160-155 Ma) Liopleurodon stormed the Jurassic oceans, its huge 7 metre long frame effortlessly cruised through the water. The skull itself could reach a massive 1.5 metres long with a jaw that was packed with teeth up to 10cm long and was capable of an immense bone-crushing force. Liopleurodon was a remarkable hunter with the ability to swim with its nostrils open and so could use its powerful sense of smell to track prey from afar, much like sharks do. Liopleurodon most likely had good camouflage such as a lighter underside and a darker topside so it would blend in with the water to prey above and below.
1. MEGALODON (~16-2.6 Ma) Megalodon rightfully deserves the top position of the greatest prehistoric ocean predators, ruling the seas for an incredible 14 million years. Megalodon has been estimated to reach up to 18 metres in length and weighing over 40 tonnes. Megalodon is known for its huge 6 inch teeth which were serrated on both sides for an efficient slicing action. Fossils of Megalodon’s prey have also been found, the shark appeared to have adapted its hunting tactics for different sized prey; for smaller prey they would just use their bone crushing bite to pulverise internal organs, but for larger prey they would bite or rip flippers off of creatures to immobilise them and then go in for the kill. The exact bite force of Megalodon has been estimated at around 110,000 N which was more than enough to shatter even the most robust bones. The hunting methods of Megalodon will unfortunately remain a mystery but it was been hypothesised that they swam at great depths and used short bursts of speed to swim up and tear into their preys vulnerable underbelly. Sharks have existed for over 420 million years and still continue to be some of the most successful predators alive, Megalodon is a perfect example of how deadly they can be.
When Charles Darwin was off observing wildlife in the Galápagos Islands, he wasn’t just looking at finches. In fact, one of the most striking creatures that Darwin found was the Marine Iguana (Amblyrhynchus cristatus). To Darwin, this species was strikingly…stupid.
Marine Iguanas are necessarily dumb, but when Darwin and his fellow shipmates reached the Galápagos, the iguana species was so far removed from human contact that it didn’t consider them a threat. One of my favorite Darwin anecdotes is about the famed naturalist repeatedly throwing a single iguana into the ocean, only to have it swim right back to rest in the same place.
These are huge, huge lizards, reaching over a meter in length, so the idea of one being tossed into the sea is a bit of a strange one. It really does make one wonder what other animal species might be like without the constant threat of predation or disturbance.