The total turtle count - two hundred and thirty species - doesn't seem like an irresistible horde compared to the several thousand mammals in today's global ecosystem. However, turtles have scored quite an impressive ecological triumph in one very important role, that of freshwater predator-omnivore... All through the Temperate Zone, otters delight the naturalist and the lay public. But how many other freshwater, semi-aquatic mammal predators can you name? Mink, of course. Relatives of otters on one hand, land weasels on the other, mink do hunt in streams. How many others? If you caught the excellent BBC series "Life on Earth", you saw footage of the swimming shrew, the Desman of the Pyrenees, a molelike furball that dives for aquatic worms and other freshwater small fry. Our own New England star-nosed mole goes hunting in water, using its starburst-shaped snout tip to feel out wriggling prey. Andean streams flowing through Preu are host to the fish-spearing mouse, Ichthyomys, that impales prey on its projecting front teeth. But if we go to a tropical lake or sluggish river, is it full of otters, mink, and paddling shrews? No, it is full of turtles.
American paleontologist
Robert Thomas Bakker (born March 24, 1945) is an American paleontologist who helped reshape modern theories about dinosaurs, particularly by adding support to the theory that some dinosaurs were endothermic (warm-blooded). Along with his mentor John Ostrom, Bakker was responsible for initiating the ongoing "dinosaur renaissance" in paleontological studies, beginning with Bakker's article "Dinosaur Renaissance" in the April 1975 issue of Scientific American. His special field is the ecological context and behavior of dinosaurs.
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By themselves, brontosaur gizzards don't indicate how much or what these dinosaurs ate each day; other lines of evidence must be employed to explore these questions. But brontosaur gizzards and teeth together indicate what brontosaurs did not eat. They didn't eat soft, mushy vegetation. Birds that subsist entirely on soft fruits don't possess muscular gizzards and don't use hard pebbles for their gizzard linings. Soft, watery food requires only a short, simply constructed gut - with just enough contractile force to squeeze out all the juices.
Brontosaur teeth, moreover, confirm the heretical idea that they ate a tough vegetable diet. If the brontosaurs dined only on soft water plants, then very little wear would be found on their teeth. But in fact the teeth of Camarasaurus, Brachiosaurus, and their kin manifest very severe wear, which could only have been produced by tough or gritty food.
The message from the tropics is unambiguous: To be a successful big land animal, you must cope with mammals, and to cope with mammals you must be a mammal yourself, or at least have metabolism as high as a mammal's. And big mammals have suppressed big reptiles in our tropics for the last sixty-five million years. So how can the dinosaurs' success over mammals' be explained? By assuming that dinosaurs had low-energy metabolic styles? Not very likely.
Up to eight feet long and as heavy as a lioness, the adult Komodo dragon brandishes steak-knifelike teeth - sharp, recurved blades with serrated cutting edges. Showing the same sagacity found in veteran Nile crocodiles, fully adult dragons know their hunting territory from years of experience. They know where to lie along hilly game trails, awaiting the light footsteps of a deer. Attacks are instant successes or failures because the ora has no stamina, and if it misses on the first short rush, it has little sustained speed for a long pursuit. When an attack succeeds, the cruel rows of slashing teeth cut fearful wounds on the rump and thigh of ambushed animals and the stricken prey may die of massive infection days later even if it manages to break free from the dragon's mouth. Tethered livestock suffer truly terrible cuts across the legs when an ora slinks into the compound under cover of the warm Indonesian nights. Several humans, both native and European visitors, have died in savage daylight attacks. The victims simply had no warning sign that the ora was waiting patiently a few feet from the trail's edge.
Even 'Jurassic Park III' tried to jump on the avian-dino bandwagon by making a brave attempt to adorn Velociraptor with a feathery hair-piece. (The result looked like a roadrunner's toupee- don't blame the effects-artists; it's notoriously difficult to render feathers in computer graphics animation, so we'll have to wait for 'JP IV' for a more thoroughly rendered avian pelage.)
Without doubt the most dangerous devices for active defense among the Dinosauria emerged in Triceratops. The scene has been portrayed in paintings, drawings, and illustrations hundreds of times, but it remains thrilling. Tyrannosaurus, the greatest dinosaur toreador, confronts Triceratops, the greatest set of dinosaur horns. No matchup between predator and prey has ever been more dramatic. It's somehow fitting that those two massive antagonists lived out their co-evolutionary belligerence through the very last days of the very last epoch in the Age of Dinosaurs. Tyrannosaurus stood over twenty feet tall when fully erect, and a large adult was as heavy as a small elephant - five tons. No predatory dinosaur, no predatory land animal of any sort, had more powerful jaws. Withstanding a Tyrannosaurus's attack required either tanklike armor – the approach taken by Ankylosaurus – or most powerful defensive weapons - the approach taken by Triceratops.
Dinosaurs are not lizards, and vice versa. Lizards are scaley reptiles of an ancient bloodline. The oldest lizards antedate the earliest dinosaurs by a full thirty million years. A few large lizards, such as the man-eating Komodo dragon, have been called "relicts of the dinosaur age", but this phrase is historically incorrect. No lizard ever evolved the birdlike characteristics peculiar to each and every dinosaur. A big lizard never resembled a small dinosaur except for a few inconsequential details of the teeth. Lizards never walk with the erect, long-striding gait that distinguishes the dinosaurlike ground birds today or the birdlike dinosaurs of the Mesozoic.
The sum of evolutionary evidence is thoroughly damning. In nearly every modification of the evolutionary process made in the duckbills as they developed from their dryosaur ancestors, the duckbills suffered a diminution of their swimming potential. Their fore- and hind paws became shorter and more compact, not longer and more widely spread. Their tails got weaker and stiffer. Far from being the best, the duckbills must have been the clumsiest and slowest swimmers in all the Dinosauria. If pressed, they probably could paddle slowly from one riverbanck to another. The central theme of their bodily evolution was indeed specialized - orthodox theory was right on that point - but the direction of specialization was landward. These dinosaurs were specialized for a totally terrestrial existence.
Plants and plant-eaters co-evolved. And plants aren't the passive partners in the chain of terrestrial life. Hence today's Pop Ecology movement is quite wrong in believing that plants are happy to fill their role as fodder for herbivores in a harmonious and perfectly balanced ecosystem. A birch tree doesn't feel cosmic fulfillment when a moose munches its leaves; the tree species, in fact, evolves to fight the moose, to keep the animal's munching lips away from vulnerable young leaves and twigs. In the final analysis, the merciless hand of natural selection will favor the birch genes that make the tree less and less palatable to the moose in generation after generation. No plant species could survive for long by offering itself as unprotected fodder.
Duckbills were supposedly croc-style swimmers, moving by strong, easy, side-to-side flexures of their tail. Therefore, the optimal design would feature vertical tail spines. But duckbill spines all slanted strongly backward, exactly as in land-living lizards, not in swimmers.
Another problem in the duckbill's swimming equipment lies in the profile of the tail. The deepest part of the croc's tail is close to the end, because the end swings through a wider arc than does the base in moving side to side. Thus the tail is deepest where it can do the most good in pushing against the water. All powerful tail-scullers have such deep tail ends. But duckbill tails were deepest at the hips and become progressively narrower from top-to-bottom toward the tip - another caudal feature nearly totally maladapted for its primary function.