Tag: Mesozoic

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Crocodilomorphs of mesozoic seas

Dakosaurus maximus skull
Dakosaurus maximus skull

In the Mesozoic Era crocodilomorphs lived on Earth; they had lots of simillarities with modern crocodiles, but their body was very adapted for marine life and looked like fishes’ one. Their tails had fins, some of them had limbs, that were transformed into fins, and their body was far more gidrodynamical, than body of modern days land and freshwater living crocodiles. Most of crocodilomorphs was fish hunters, but there were big species, that hunted on other marine reptiles; dakosaurus ( from Greek words, that “biting lizard” ) was one of them. Their teeth was flat and serrated, such form is not adapted for small fishes hunting and was adapted for hunting on big reptiles, that has comparable sizes to dakosaurus themselve. Many of the crocodilomorphs had grooves in skulls, in which salt glands resided. Salt glands is organ, that helps marine animals to remove from themselves excess of salts, that accumulates in them due to constant contact with salt water. For now there are no direct proves, that crocodilomorphs had exactly salt glands in these grooves, but their presence in them is the most probable assumption. Modern day crocodiles are adapted for ambushes tactics on hunting, but crocodilomorphs of mesozoic seas was far more active hunters : their fast body says about this and they had need to swim to surface for air breaths and there is no possibility to do this without leaving cover.

Dacosaurus maximus
Dacosaurus maximus

In most of areas of mesozoic seas different species of crocodilomorphs lived on one territory and occupied different ecological niches. Their fossils are found in many countries of the world : in England, France, Switzerland, Germany, Polland, Russia, Argentine and Mexico. Crocodilomorphs was very adapted for living in seas and for now it is not clear whether they oviposited eggs on land or gave birth to already formed posterity. From one side : they were able to move on land on their fins, like turtles ( but their body made them vulnerable to big land carnivores and they were unable to hide in shell, like turtles ); from other side : they were able to develop viviparity, like their contemporaries ichthyosaurus and modern days whales and dolphins. So, untils nests and eggs of crocodilomorphs or evidences of viviparity of crocodilomorphs are found : this question is still open. Species was first described in 1856 year by paleontologist Friedrich August von Quenstedt.

Ichthyosaurus

Ichthyosaurus skeleton
Ichthyosaurus skeleton

Ichthyosaurus ( from Greek words fish and lizard ) are marine reptiles, that lived in Mesozoic Era, almost in all its time span 250 – 90 millions years ago. Ichthyosaurus reached in length 2 – 20 meters ( members of their family was the biggest marine reptiles, that lived on Earth to date ); their skin was scaleless; they were warm-blooded; and had very big eyes, this says, that ichthyosaurus hunted at night time or dived deep in Mesozoic seas. As all reptiles, they had lungs and had need to swim to surface to make air breathes. They were unable to lay eggs in seas and their body was not adapted for land walking, so they developed viviparity, like modern dolphins have. Ichthyosaurus are very similar to modern whales and dolphins in their shape and way of life, this is the result of convergent evolution, when animals of different species develop similar shapes and way of life in close living conditions. Ancestors of whales and dolphins made the same way, as ancestors of ichthyosaurus did 200 millions years before them.

Ichthyosaurus skeleton
Ichthyosaurus skeleton

For now no transitional forms between land reptiles and ichthyosaurus are found : the earliest of know already lived in seas. Previously it was thought, that they originated straight from amphibia, but later studies show, that they originated from reptiles, whose ancestors were amphibia. Ichthyosaurus was the most diverse in late Triassic Period, they occupied lots of ecological niches : from biggest marine predators to small fish hunters. In Jurassic their diversity was still high, but there were no such big species, like in previous period. Probably, this was caused by increased competition from sharks and first plesiosaurs. Previously it was thought, that in early Cretaceous Period amount of ichthyosaurus species abruptly decreased, but new studies show, that they were still diverse at that time. And only at the middle of Cretaceous they went extinct from Earth’s surface.

Ichthyosaurus
Ichthyosaurus

Ichthyosaurus had 4 limbs with big amount of phalanges, that were completely transformed into fins. Many species had back and tail fins, that were not present in any form in their ancestors – reptiles. Earlier scientists reconstructed ichthyosaurus without back and tail spins, because there are no bones, that support them. But later fossils were found, which contain prints of fins and animals were reconstructed from that time with these parts of bodies. Ichthyosaurus had circle of bone plates in each eye, that protected eyes from high pressure of deep waters. They had the biggest eyes from all vertebrates in both relative and absolute meanings. Their hearing was weakly developed, but smelling was advanced and, probably, they had some kind of bio electricity sensors on surface of their skin. Earlier it was thought, that their skin had colors, like modern dolphins have : dark on top and light at bottom to camouflage them closer to water surface; but new studies show, that they had dark pigment all around surface of their skin. This camouflaged them in deep waters and helped to perform thermoregulation. First fossilized bones of ichthyosaurus were found at the end of 18th century and during 19th and 20th centuries amount of found fossilized bones increased each year.

Allosaurus

Allosaurus skeleton
Allosaurus skeleton

Allosaurus ( “strange dinosaur” ) are carnivorous dinosaurs from theropod family, they lived in Jurassic Period 155 – 145 millions years ago. They was named so, because their vertebrae was very different from vertebrae of other dinosaurs, that was know at that time. Allosaurus reached 11 – 12 m in length and 2,5 – 3 m in height ; their maximal weight was 1 – 2 tons. They were biggest predators of their time and hunted on plant-eating dinosaurs, like stegosaurus and iguanodons. Fossils of allosaurus were found in North America, Europe, Africa and Australia; in total there were found 60 fossilized skeletons of allosaurus. First almost complete skeleton of allosaurus was found by farmer M. P. Felch in 1883 year in Colorado, USA. Dinosaur was described first time by paleontologist O. C. Marsh in 1877 year.

Allosaurus Fragilis
Allosaurus Fragilis

They moved on their 2 legs, their forelegs was small and mainly used for hunting. They were able to run fast on their legs, despite their big size and weight, because there were found lots of allosaurus skeletons with ribs, that were broken during falls at high speed running. Also, their vertebrae had special holes, that allowed them to breath through skin at high physical exercise; modern birds also has such adaptations in their skeletons. Probably, allosaurus lived and hunted in groups, because there are lots of their fossilized footprints found together. Their brain was big relative to their body size; and allosaurus was able to perform social interactions and care about their youth. Their inner ear was relatively big and they was able to perceive low frequencies; but they had problems in perceiving high frequencies. Their smelling was developed to high level and they was able to use it for hunting and to determine other animals of their kind.