Prehistoric Marine Life

Basilosaurus:

The one thing about Basilosaurus that instantly causes confusion is its name.‭ ‬When first studied and named by Richard Harlan,‭ ‬he came to the conclusion that it was most likely a marine reptile,‭ ‬and so named it Basilosaurus,‭ ‬or "King lizard"‬.‭ ‬It was not until the remains were studied by Sir Richard Owen that they were confirmed as mammalian. Basilosaurus represents one of the earliest whales, although its actually descended from terrestrial mammals like Ambulocetus.‭ ‬Evidence for this can be seen in the flippers.‭ ‬The front flippers still have an elbow joint,‭ ‬something that today is only seen in seals.‭ ‬The back flippers where the hind legs would have been, in its ancestors, are greatly reduced and although they may have been used to get extra grip on a mate,‭ ‬they would eventually disappear in later whales.‭ ‬The size of its flippers in comparison with the massive bulk of its body means that it was almost certainly an entirely ocean dwelling animal. The large jaws of Basilosaurus housed teeth suitable for catching prey that were fairly large,‭ ‬perhaps smaller whales or large fish that while smaller than Basilosaurus,‭‭ ‬were still too large for most other predators to tackle.

Basilosaurus Size and Location:

Basilosaurus was a large aquatic mammal that grew to lengths of about 18 meters and weighed an estimated 3 tons. It roamed the seas of North America, Egypt, and Pakistan during the Paleogene era, about 38-41 million years ago.

Elasmosaurus:

Today Elasmosaurus is one of the best known Plesiosaurs in the world. It was the long neck of Elasmosaurus that was key to its feeding method.‭ ‬All Elasmosaurus would have to do was swim up to a shoal of fish,‭ ‬possibly from below, so that it could hide its body in the slightly darker depths ‬and use its neck to dart its head in and pluck out a mouthful of fish.‭ ‬Approaching prey like a shoal of fish from below would also silhouette themselves against the brighter surface water,‭ ‬making them easier to define as well as removing the defense method of flashing light off their shiny scales to confuse ‬predators as they turned and swam through the water.‭ ‬Such a method would have been a reasonably efficient form of feeding as Elasmosaurus would just have to move its head and neck and not waste energy swimming after fast moving individuals. Elasmosaurus probably was not a fast swimmer,‭ ‬although if it used stalking tactics to approach its prey from below it would not need to be.‭ ‬The flipper-like limbs were rigid and well suited for providing efficient locomotion through the water.‭ ‬Skeletal elements of the main body such as the pectoral girdles were also well adapted to provide efficient musculature support for the flippers so that that Elasmosaurus could paddle itself through the water with ease.

Elasmosaurus Size and Location:

Elasmosaurus was a large Plesiosaur that grew to about 14 meters long and weighed an estimated 3 tons. It lived in seas of North America during the late Cretaceous period, about 72-84 million years ago.

Ichthyosaurus:

The most well-known of the Ichthyosaurs,‭ ‬Ichthyosaurus itself is almost always included in books about dinosaurs and other prehistoric creatures.‭ ‬While it may look superficially like a prehistoric dolphin,‭ ‬Ichthyosaurus wasn't even close in relation, in fact, ‬Ichthyosaurus wasn't even a mammal like a dolphin is,‭ ‬it was ‬a reptile.‭ ‬Also ‬Ichthyosaurus was not in the same group of reptiles as the dinosaurs,‭ ‬although it did live at the same time as many of them. With its distant ancestors being terrestrial reptiles going back to an aquatic lifestyle,‭ ‬Ichthyosaurus ended up with an extremely different morphology to other land living reptiles.‭ ‬This ‬fish ‬appearance is a result of the fact that the basic fish morphology is the most streamlined and efficient form for submerged locomotion.‭ ‬It also means that Ichthyosaurus was never able to return to the land,‭ ‬instead leading an entirely pelagic life in the oceans. As an ocean going hunter,‭ ‬the main diet of Ichthyosaurus would have been primarily, if not exclusively, piscivorous (fish eater).‭ ‬Study of coprolites has confirmed the presence of both fish and squid in its feeding habits.‭ ‬Although Ichthyosaurus appears to have relied upon its sight for feeding,‭ ‬the solid bone structure of the ear drums suggests that they could have ‬heard ‬their prey from a distance by their vibrations in the water.

Ichthyosaurus Size and Location:

Ichthyosaurus was a small marine reptile that lived in the seas of Europe during the early Jurassic period, around 199-201 million years ago. It grew to lengths of about 2 meters and weighed an estimated 150-200 lbs.

Prognathodon:

Prognathodon was a late Mosasaur that specialized in eating tough shelled prey like shellfish, ammonites and turtles.‭ ‬The diet of Prognathodon was for a long time just speculation, based upon the teeth and jaw construction,‭ ‬but two discoveries in Canada in the early years of the 21st century not only revealed the full body shape of Prognathodon but the diet as well.‭ Prognathodon had a robust and heavy jaw that would have been capable of withstanding a high bite force supplied by powerful jaw muscles.‭ ‬However it’s the teeth that should receive special note as not only are they strong and well adapted for crushing,‭ ‬they have serrations which can be seen under much more detailed inspection.‭ ‬This makes the teeth specialized for a dual purpose,‭ ‬destroying the protective shells of prey while shearing the flesh within.‭ ‬Another specialization is the presence of bony rings around the eye sockets.‭ ‬This is seen as a deep water adaptation for the eyes to better withstand the higher water pressure of deep water,‭ ‬something which may have often been necessary when diving for ammonites.

Prognathodon Size and Location:

Prognathodon was a larger member of the Mosasaur family that grew to lengths of about 13-14 meters and weighed around 2-3 tons. It stalked the seas of North America and Europe during the late Cretaceous period, about 72-84 million years ago.

Shastasaurus:

Shastasaurus was what is now termed a primitive Ichthyosaur.‭ ‬Key to this is what appears to be a lack of a dorsal fin,‭ ‬something which is clearly seen in advanced Ichthyosaurs but is lacking in basal forms.‭ ‬The lack of a dorsal fin bone does not necessarily mean that a dorsal fin was not present‭, ‬it just may have existed in the form of softer tissue such as cartilage which rapidly decomposes in sea water.‭ ‬Still without more direct evidence the wider assumption is that Shastasaurus did not have a dorsal fin.‭ The tail fluke of Shastasaurus may not have been as well formed as in later Ichthyosaurs either.‭ ‬The rear of the body that grew into the tail is seen to have strongly arced downwards indicating that the lower tail‭ ‬lobe was larger and more developed than the upper‭ ‬lobe.‭ ‬This suggests that Shastasaurus was better at cruising rather than active pursuit of prey. Shastasaurushas one of the most specialised mouths of‭ ‬all‭ ‬known ichthyosaurs in that the jaws are both short and toothless.‭ ‬This toothless adaptation is also seen in the similar Shonisaurus although this ichthyosaur has comparatively longer jaws.‭ ‬Why Shastasaurus should have such short jaws has puzzled many,‭ ‬but analysis of the skulls,‭ ‬particularly the attachments for the jaw opening muscles has given rise to the theory‭ that Shastasaurus was a suction feeder.‭ ‬Like some fish Shastasaurus opening its mouth wide so fast that it would have created a point where the space and existing water inside its mouth would be reduced to such a low pressure it would create a vacuum inside its mouth.

Shastasaurus Size and Location:

The addition of new fossil material has made Shastasaurus the largest currently known marine reptile at 21 meters long with weight estimates are at about 75 tons. This thing was huge! It lived in the waters of North America and Asia during the mid Triassic period, about 228-235 million years ago.

Dunkleosteus:

Dunkleosteus is one of the largest predatory prehistoric fish known in the fossil record.‭ Dunkleosteus was an apex predator capable of taking down pretty much anything it could clasp its jaws around. Although Dunkleosteus had a powerful bite it was not the strongest among fish,‭ ‬that title goes to the gigantic shark Megalodon that lived several hundred million years later.‭ ‬Still,‭ ‬with a bite force estimated at almost 2 metric tons,‭ ‬Dunkleosteus could still use its sharp jaws to shear through any prey item it chose. The actual hunting and feeding style of Dunkleosteus is also a popular subject of interest.‭ ‬With the heavy plates around the head,‭ ‬Dunkleosteus was probably not a fast swimmer,‭ ‬but still would have had powerful muscles developed from just swimming around with the weight.‭ ‬This meant that Dunkleosteus either preferred slower prey,‭ ‬or used ambush tactics to try and take its prey off guard.‭ ‬Another thing to consider is that the jaws of Dunkleosteus could open exceptionally fast within a fraction of a second.‭ ‬This would create a sudden void inside the mouth of Dunkleosteus,‭ ‬creating a vacuum that sucked the water and the prey that was swimming in it into its mouth.‭ ‬This means that Dunkleosteus did not have to physically catch its prey,‭ ‬just get close enough to open its mouth.

Dunkleosteus Size and Location:

Dunkleosteus was a very large armored fish, also known as a Placoderm, that grew to lengths of about 10 meters and weighed an estimated 4 tons. It prowled the ancient seas of North America, Europe and Africa during the late Devonian period, about 359-375 million years ago.

Kronosaurus:

If you think present day Australia is full of creatures that are extremely deadly, well prehistoric Australia was no different. Kronosaurus is one of the more famous fossil discoveries to come from Australia,‭ ‬and as a huge short-necked Pliosaur,‭ ‬Kronosaurus would have been the apex predator of the waters it swam in.‭ ‬The teeth of Kronosaurus are conical and up to 30 centimeters long. ‬Interestingly the teeth of Kronosaurus are quite different to other Pliosaurs in that they are not serrated.‭ ‬The teeth may suggest that despite its large size Kronosaurus may have seized smaller to medium sized prey which could then be manipulated to be swallowed.‭ ‬The only way that Kronosaurus could have fed from larger prey would be to clamp on with its jaws and then use brute strength from its body to tear off a chunk of flesh by twisting or rolling.‭ ‬Either way it seems that Kronosaurus may have eaten in a similar manner to a crocodile.‭

Kronosaurus Size and Location:

Initial size estimates for Kronosaurus placed it at just under 13 meters long.‭ ‬However further study, combined with a better understanding of pliosaur remains in general, resulted in a reduction in this estimate to somewhere in the region of 9-10 meters long.‭ ‬This estimate is universally accepted as being more accurate,‭ ‬and although the upper size is reduced to 10 meters,‭ ‬Kronosaurus was still big for a pliosaur and was much bigger than Liopleurodon which is often incorrectly credited as the biggest pliosaur ever. Weight estimates for Kronosaurus come in at about 12 tons. Kronosaurus lived in the waters of Australia during the mid Cretaceous period, around 113-125 million years ago.

Tylosaurus:

Whereas Tyrannosaurus is dubbed "THE" ‬land predator of the late Cretaceous,‭ ‬Tylosaurus would have equally been "THE" ‬predator of the late Cretaceous seas,‭ ‬specifically the Western Interior Seaway that once submerged the central portion of the United States and Canada.‭ ‬The large size of Tylosaurus meant that it easily attained apex predator status and as such absolutely nothing was off the menu.‭ ‬Fossil evidence supports this as stomach contents for Tylosaurus are well known and include fish,‭ ‬sharks,‭ ‬flightless birds like Hesperornis,‭ ‬large marine reptiles such as Plesiosaurs and even other Mosasaurs. There is also evidence to suggest that Tylosaurus fed upon dinosaurs,‭ ‬as evidenced by bones associated with a Hadrosaur that have puncture marks that are very similar to the tooth size and arrangement of Tylosaurus. The snout is also reinforced making it stronger than other marine reptiles.‭ ‬Additionally some Tylosaurus snouts show signs of compression damage that seem to have been caused by a violent impact.‭ ‬These all point to Tylosaurus relying upon brute force to ram prey at high speeds. Tylosaurus was one of the most deadly sea predators of all time.

Tylosaurus Size and Location:

Tylosaurus is the second largest known Mosasaur, behind Mosasaurus itself. Tylosaurus grew to lengths of about 15 meters long and weighed around 20 tons. It dominated the waters of North America during the late Cretaceous period, about 66-72 million years ago.

Leedsichthys:

This thing was big! The secret to the large size of Leedsichthys is probably down to its lifestyle as a filter feeder. This method of feeding requires very little effort, other than opening the mouth and cruising near the surface of the water. Such a method of feeding only requires a slow metabolism as it is not actively hunting for prey. Its large size however may mean that it was possibly gigantothermic (doesn't need to eat very much) like many of the large fish we know today.

Leedsichthys Size and Location:

Because of the fragmentary nature of recovered remains, the exact size has been open to much speculation. Most researchers agree that a size of 9-10 meters long is realistic, but also recognize isolated remains that are larger than they appear in more complete specimens. This in turn has pushed the maximum estimate to a potential 16 meters long. In contrast, the largest living fish today is the whale shark with a maximum recorded body length being just over 12 and a half meters. Some estimates have further pushed the maximum size of Leedsichthys to beyond 20 meters. Weight estimates are around 2 tons. It lived in the waters of South America and Europe during the late Jurassic period, about 157-164 million years ago.

Dallasaurus:

Dallasaurus was‭ ‬a‭ ‬fascinating discovery,‭ ‬especially for lovers of the marine reptiles, the Mosasaurs.‭ ‬The skeletal features of Dallasaurus have‭ ‬helped to further cement the theory that the mosasaurs evolved from terrestrial‭ ‬reptiles like monitor lizards during the early/mid Cretaceous.‭ ‬Dallasaurus is seen as a transitory link because while its body and tail show adaptation for swimming,‭ ‬the legs still have a greater development for walking on land.‭ ‬This would suggest that Dallasaurus lived in coastal waters,‭ ‬perhaps estuarine waters‭ where they could take advantage of an abundant supply of aquatic prey but still had to return to the land,‭ ‬either to rest or possibly to hunt in different waters such as coastal lagoons.‭ ‬Roaming behaviour like this would lead to an oceanic expansion so that Dallasaurus could have access to an even greater number of prey.‭ ‬In later mosasaurs the legs would develop fully into flippers to support a completely aquatic life.

Dallasaurus Size and Location:

Dallasaurus is the smallest member of the Mosasaur family reaching only about 1 meter in length. It lived in the waters of North America during the mid Cretaceous period, around 90-94 million years ago.

Livyatan:

When first described, Livyatan was actually named Leviathan after the biblical sea monster.‭ ‬Unfortunately Leviathan had already been used to name a mastodon now known as Mammut‭ (‬Leviathan is actually a synonym to this genus,‭ ‬but still cannot be used)‬.‭ ‬As such the Hebrew word for Leviathan,‭ ‬Livyatan,‭ ‬is now used to refer to this ancient whale.‭ ‬The species name,‭ ‬L.‭ ‬melvillei is in honor of the author Herman Melville,‭ ‬the man who wrote the world famous novel, ‬Moby Dick‭‬. Not only was Livyatan an apex predator like the giant shark ‬Megalodon,‭ ‬it probably fed upon the same prey animals. ‬Smaller juvenile Livyatan may have preferred proportionately smaller prey items like the smaller cetaceans or even large fish.‭ ‬With teeth that were 36 centimeters long,‭ ‬Livyatan had the dentition to take down large prey items.‭ ‬In fact not only were the teeth of Livyatan considerably larger than Megalodon teeth,‭ ‬they are considered to be the largest known teeth for the purpose of eating. How Livyatan hunted is still a matter of debate,‭ ‬but given its large mouth and teeth it may have used a similar method to kill smaller whales as Megalodon did.‭ ‬This could be approaching from the bottom and slamming into its target from underneath.‭

Livyatan Size and Location:

Because only the skull is known,‭ ‬Livyatan is often compared to the modern day sperm whale ‬when piecing together the rest of the body.‭ ‬This has yielded size estimates of 13 and a half meters with upper estimates reaching 17-18 meters long and a max weight estimate is at around 50 tons.

Liopleurodon:

Liopleurodon was an apex predator of the Jurassic seas. With a skull, and jaws taking up one fifth of the total length of the animal it had a powerful bite. The 20 centimeter teeth buried deep into the jaws further reinforce this idea. Liopleurodon had a typical Pliosaur limb arrangement and although not as efficient as an Ichthyiosaur (more fish-like) layout, this arrangement of 4 flippers provides excellent acceleration. The nostrils are very interesting in that the arrangement suggests a directional sense of smell. This would enable Liopleurodon to find its prey while still well out of visual range, perhaps even sensing the blood of fresh kills from other predators like sharks do today.

Liopleurodon Size and Location:

Sizing estimates for Liopleurodon have been changing for the entire time we have known it existed. One thing that is clear is that it was never the 25 meter behemoth it was shown to be in the BBC documentary series Walking with Dinosaurs. The most complete specimen was estimated at just over 6 meters long, with a skull 1 meter long. Analysis of all specimens suggest that adult Liopleurodon would range somewhere between 5-7 meters long. It prowled the seas of Europe during the late Jurassic, possibly into the early Cretaceous, about 145-152 million years ago.

Platecarpus:

Research into Platecarpus has arguably advanced our understanding of the Mosasaurs more than any other of its kind,‭ ‬part of this being down to the number of known Platecarpus fossils.‭ Some of these specimens of Platecarpus are so well preserved that they actually reveal impressions of soft tissue of body parts like the internal organs. Platecarpus was long suspected of having a tail fluke similar to the primitive Ichthyosaurs,‭ ‬something which was confirmed in a later discovery when a new Platecarpus specimen was discovered with soft tissue impressions that revealed it had a crescent shaped tail fluke.‭ ‬This discovery alone turned the study of Mosasaurs upside down as the long held reconstruction of Mosasaurs gave them all long eel like tails that trailed behind their bodies. The fact that Platecarpus was developing a stronger swimming tail suggests that this was a Mosasaur that was developing an increasing reliance upon speed in its hunting behavior.‭ ‬Clearly this represents a shift towards fish as a primary prey source which makes Platecarpus different from other Mosasaurs that had a large prey preference.‭ ‬It‭’‬s possible that the Mosasaurs that went after larger and slower prey may have retained eel like tails,‭ ‬only needing to use a sudden burst of speed for ambushing tactics.

Platecarpus Size and Location:

Platecarpus was one of the smaller members of the Mosasaur family. It grew to lengths of about 4-5 meters and weighed around 1 ton. It lived in the waters of North and South America, as well as Australia during the later part of the Cretaceous period, about 84-86 million years ago.

Edit: My Other Prehistoric Posts:

Large Theropods: https://imgur.com/a/oKGjI
Medium Sized Theropods: https://imgur.com/a/Epvid
Raptors: https://imgur.com/a/4CVWe
Sauropods: https://imgur.com/a/UUs9iva
Ceratopsians: https://imgur.com/a/U29NBik
Ankylosaurs: https://imgur.com/a/MHb8oJf
Pterosaurs: https://imgur.com/a/hD4tS2t
Hadrosaurs: https://imgur.com/a/EqpRMQa
Stegosaurs: https://imgur.com/a/uKvjLtt
Tyrannosaurs: https://imgur.com/a/BMgGpYq
Oviraptosaurs: https://imgur.com/a/ZDN6wxl
Ornithomimosaurs: https://imgur.com/gallery/9n58gUk
Spinosaurs: https://imgur.com/a/RqTuj3D
Carcharodontosaurs: https://imgur.com/a/W0BCmTt
Abelisaurs: https://imgur.com/a/xHONtTp
Allosaurs: https://imgur.com/a/9HFW3gv
Rauisuchians: https://imgur.com/a/YUMvoMz
Prehistoric Marine Life: https://imgur.com/a/QtroooW
Prehistoric Marine Life Part 2: https://imgur.com/a/qEQomBt
Plesiosaurs: https://imgur.com/a/X5ZXSSG
Pliosaurs: https://imgur.com/a/QrJcjNR
Mosasaurs: https://imgur.com/a/y0dMm78
Prehistoric Mammals: https://imgur.com/a/IYBMhMb
Prehistoric Mammals Part 2: https://imgur.com/a/bPU4wNI
Prehistoric Mammals Part 3: https://imgur.com/a/yEjSwc2
Pre-Dinosaur Wildlife: https://imgur.com/a/zq3Y2SI
Prehistoric Birds: https://imgur.com/a/iwobJEp
Prehistoric Nopes: https://imgur.com/a/YzmuOoM
Prehistoric Sharks: https://imgur.com/a/YVImZXu
Prehistoric Crocodiles: https://imgur.com/a/wD6cI2m
Prehistoric Cats: https://imgur.com/a/SuCKxTN
Prehistoric Fish: https://imgur.com/a/Bty8rgu
Prehistoric Dogs: https://imgur.com/a/2CrsVl5
Prehistoric Whales: https://imgur.com/a/yxN2w0a
Feathered Dinosaurs: https://imgur.com/a/s6vpNHj
Dinosaurs from North America: https://imgur.com/a/EZ7D4z4
Dinosaurs from South America: https://imgur.com/a/9JFgRUN
Dinosaurs from Africa: https://imgur.com/a/KrdTEnO
Dinosaurs from Europe: https://imgur.com/a/xOSpTMX
Dinosaurs from Asia: https://imgur.com/a/XRjwx4v
Dinosaurs from Australia and Antarctica: https://imgur.com/a/2mSXj8f
The Largest Carnivores: https://imgur.com/a/OXPAJrI
The Largest Sauropods: https://imgur.com/a/qu3Qi5M
The Largest Herbivores: https://imgur.com/a/Eoxdut1
The Largest Pterosaurs: https://imgur.com/a/V3MaqxF
The Largest Prehistoric Marine Life: https://imgur.com/a/NMB2xo5
The Largest Prehistoric Mammals: https://imgur.com/a/Wa5Itxd
The Smallest: https://imgur.com/a/TSn8JfQ

Source for prehistoric pics: prehistoric_wildlife.com and google.