Blasts from the Past: Mosasaurs, Baryonyx, Zeuglodons, and Ichthyosaurs

Artist’s rendering of a Baryonyx, a prehistoric sea predator. (Troy Therrien)

In 1780 a dinosaur jaw was discovered in a mine near the Maas River in the Netherlands. Napoleon had it carted to France in 1795 where it became the object of much discussion for years, as scientists argued whether it was from a toothed whale, alligator, or lizard. Its resemblance to lizards was finally officially recognized in 1822 when it was given the genus name mosasaurus, which means “Maas River lizard.”

Mosasaurs could reach 40 feet or more in length. They looked very similar to Coleman and Huyghe’s drawing of the classic sea serpent” with a long, alligator-like jaw and strong flippers on a mostly tubular body. One artist’s interpretation of the mososaur known as tylosaurus also shows it with a scalloped dorsal (back) fin, which could provide another explanation of the short humps sometimes seen trailing behind a monstrous head. It lived in a sea that once covered the midsection of North America, and it ate diving birds, fish, and other mosasaurs. Tylosaurus was supposed to have died out 65 million years ago. But did it? The state of Utah has become known for sightings of monsters in Bear, Sevier, Fish, Utah, and Great Salt Lakes. Living things can be tenacious. And Natural History magazine has noted several paleontologists maintain that “snakes and mosasaurs are more closely related to each other than either group is to any other group of lizards.” In that case, calling a mosasaur a “sea serpent” does not seem such a stretch.

Baryonyx was another gator-jawed creature whose fossil skeleton was first discovered in 1983 in a clay pit in the United Kingdom. The lizard-like bones were found about three-quarters complete and would have measured 20 feet long. Evidence shows that Baryonyx was a fish-eater and probably used its oversized, deadly claws to hook its prey. The odds may be less likely that this killing machine has survived until the present without detection, since it would probably wreak noticeable havoc wherever it popped up. Baryonyx would surely be termed a “water monster” if encountered by some unwary fisherman today.

Another ancient species that ranks high on the possible relict popularity scale is not a reptile at all. Zeuglodon was a primitive, toothed whale that lived around 25 million years ago and could reach lengths of 70 feet. Zeuglodon did not look much like modern whales; it was originally named Basilosaurus because it resembled a lizard in some ways. But its later placement in the whale category has also been disputed because it has many characteristics of the seal family, or pinnipeds, as well. Author Dr. Roy P. Mackal has proposed that an unknown creature observed snatching a duck from a watery surface near Vancouver in 1934 matched what we know of Zeuglodons perfectly. “Even a casual comparison,” says Mackal, “. . . reveals the striking agreement with the description of the observed animal.”

The observed animal, according to the duck hunters who saw it, was about 40 feet long and two to three feet wide with a tapering body and a three-foot-long head. The head was described as horse-like, though lacking ears or nostrils, and as dark, grayish brown marked with one horizontal, dark stripe. This is a description that could match many water creature sightings from around the world, making Zeuglodon a prime suspect in the relict category.

Zeuglodon was also tapped to explain one of the most famous sea serpent sightings ever—that of the H.M.S Daedalus in August 1848, off St. Helena, a British island in the South Atlantic Ocean. That monster was described by one witness as “a blunt-nosed animal with a neck carried about four feet above the water, which was so long as to present the appearance of a serpent . . . Two or three years after this, on reading the description of a Zeuglodon cetoides . . . it struck me that the animal seen from the Daedalus may have been a descendent of the order to which Zeuglodon belonged; and I have ever since watched with interest for reports of the ‘great sea-serpent.’ ”

While there are probably innumerable prehistoric creatures that resembled traditional sea serpents, with many still possibly undiscovered, one other is often inserted into the lineup of suspected sea monsters: the ichthyosaur, which means “fish-lizard.” The first ichthyosaur skull was found and recognized off Southern England in 1811. Ichthyosaurs varied in size and appearance from three to over 30 feet long, and from early, eel-shaped species to later versions that looked like dolphins with long, sharp beaks full of teeth. Ichthyosaurs, like mosasaurs, were reptiles, and needed to come to the surface to breathe. But they were more ancient than the mosasaurs, making it even less likely that some of them might have survived until present times.

Egg size was dinos ultimate undoing

Artist's impression of Massospondylus and babies hatching(Source: Julian Csotonyi/)

The fact that land-bound dinosaurs laid eggs is what sealed their fate of mass extinction 65 millions of years ago, says scientist.
In a new explanation for mammals' evolutionary victory over dinosaurs, researchers claim a mathematical model has shown that infant size was the clincher.
Given physical limitations to egg size, dinosaurs had comparatively small young. Some came out of the egg weighing as little as two to 10 kilograms, yet had to bulk up to a hefty 30 or 50 tonnes.
Growing up, the youngsters had to compete in several size categories with adults of other animal groups for food, says University of Zurich scientist Marcus Clauss.
This meant that all the small and medium animal size categories supported by the natural environment were "occupied", leaving no room for smaller dinosaur species in which to thrive, according to the findings published in Biology Letters.
"There is a lot of room in the ecosystem for small species, but (in such a scenario) that room is taken up by the young ones of the large species," says Clauss.
"That was not a problem for 150 million years but as soon as something happens that takes away all the large species so that only small species remain, if there are no small species to remain you are gone as a whole group."
The catastrophic event that wiped out all larger life forms some 65 million years ago meant the end for terrestrial dinosaurs.

Mammals best equipped

Scientists disagree on whether the scaly reptiles died out before or after a meteorite smashed into Earth in what is known as the Cretaceous-Tertiary impact, causing billions of tonnes of wind-borne ash and dust to filter out light from the Sun and triggering a "nuclear winter" that cooled the planet and withered vegetation.
Mammals did not have the same limitations in size spread, says Clauss, because their young were not born as comparatively small and did not need to compete with other species for food, instead suckling on their mothers.
This meant there were smaller mammal species able to cope with the new post-catastrophe environment and evolve into new species alongside birds, which are also dinosaurs.
"The question that haunted some people including me is ... why did the mammals survive and why did the dinosaurs not. I think we have a very good answer for that," says Clauss.
The researchers says egg size is constricted by upper limits to the thickness of shells, which have to allow oxygen through to the embryo.
The average forty-tonne titanosaur, the largest type of vertebrate that ever lived, was 2500 times heavier than its newborn. A modern-day elephant mother weighs 22 times more than her calf.
Scientists say all animals with a bodyweight of more than about 10 to 25 kilograms died in the mass extinction event.

Some dinos in decline when space rock hit

Tyrannosaurus rex was part of one group of dinosaurs that maintained a stable level of biodiversity leading up to the mass extinction (Source: J Brougham/AMNH)

Large, plant-eating dinosaurs were already in decline by the time a space rock smashed into Earth 65 million years ago and ended their reign, according to a new study.
The findings by scientists in the United States and Germany do not dispute the mass extinction that so dramatically ended the Cretaceous era.
But they suggest the dinosaur kingdom, or at least some of its species, was not struck down in its prime as is often hypothesised. The findings are published in the journal Nature Communications.
"A lot of the time people think of the dinosaurs going extinct: 'oh, you know, an asteroid did it ... the dinosaurs were doing just fine, an asteroid came along and killed them all off'," says Steve Brusatte, a palaeontologist at the American Museum of Natural History.
"I think now we can say it was probably more complicated than that. You had some dinosaurs that were doing just fine, but you had others like these big plant eaters that were maybe in trouble.
"This was a world that was undergoing a lot of changes before the asteroid hit. It wasn't quite such a nice, easy story as we might like to think."

Shrinking diversity

The study compared the skeletal structure of 150 different species of land-bound dinosaurs to see how they changed over time, the idea being to see if a species was up, down or stable in survival terms.
By this benchmark, the large herbivores -- specifically, horned and duckbilled dinosaurs -- were becoming less and less diverse during the last 12 million years of the Cretaceous.
The four-footed giants "were becoming more similar to each other, they were losing variability," says Brusatte. "Usually when you see these big decreases in the anatomy like this, that means that a group is in trouble."
Groups that show an increase in variety boost their chances of survival because they can fill new habitat niches or adapt to changing conditions, he says.

T-rex thriving

But if big herbivores were on the skids towards the end of the Cretaceous, carnivorous dinosaurs and medium-sized herbivores were thriving, say the researchers.
"What we can say for certain now is when the asteroid hit and when these volcanoes began erupting, they didn't hit a world that was totally OK, they didn't hit a static world," says Brusatte.
"At the time, dinosaurs, at least some of them, were undoing major evolutionary changes and at least these plant eaters were declining."
The reason for their downward spiral is unclear but "was probably something ecological," he says.
AFP

One-tonne 'feathered tyrant' found in China

An artist impression of Yutyrannus huali, meaning "beautiful feathered tyrant".
(AFP/Nature/ Brian Choo)

Palaeontologists in China have uncovered a species of giant feathered dinosaur that was an ancient relative of Tyrannosaurus rex. 

Scientists have known for over a decade that some small dinosaurs had bird-like feathers.

But a report in the journal Nature says the new species of tyrannosaur, which was 9 metres long and weighed about 1.5 tonnes, provides direct evidence of the existence of gigantic feathered dinosaurs and has implications for early feather evolution.

The theropod, which was an ancient relative of Tyrannosaurus rex, was 40 times larger than any previously known feathered dinosaur.

It has been given the name Yutyrannus huali, a combination of Latin and Mandarin, which means "beautiful feathered tyrant".

The paper's lead author, Professor Xu Xing from Beijing's Institute of Vertebrate Palaeontology and Palaeoanthropology, says the new species is based on three beautifully preserved specimens.
"The feathers of Yutyrannus were simple filaments," Professor Xu said.

"They were more like the fuzzy down of a modern baby chick than the stiff plumes of an adult bird."

Dinosaur graveyard

The almost complete skeletons were found near each other in a quarry in the famous dinosaur fossil beds of Liaoning Province in north-eastern China.

They date back to the lower Cretaceous period between 130 and 125 million years ago.

At the time the area was an anoxic lake bed.

The lack of oxygen helped preserve the animals that died there, and prevented bugs and scavengers from destroying the remains.

The two smaller specimens are thought to be juveniles and were fully articulated, meaning their skeletons were positioned as they would be if the animals were still alive.

They weighed about half a tonne each and were found together, on their sides and with their necks arched backward.

Feather blanket

Professor Xu and colleagues believe the large size of Yutyrannus and the downy structure of its feathers would have made flight an impossibility, but they argue that the feathers may have provided the animals with insulation keeping them warm.

Palaeontologist Dr Eric Roberts from James Cook University in Queensland, says it was thought that large dinosaurs did not need feathers to keep warm because their huge body mass to surface area allowed them to retain most of their heat.

"In fact for big dinosaurs, getting rid of excess heat was the problem," Dr Roberts said.

But he points out that while the Cretaceous was generally very warm, Yutyrannus lived at a time when Liaoning Province was much cooler due to its latitude and elevation.

"The fossils are also interesting because they include a combination of primitive features compared to other tyrannosauroids," he said.

"These include having three rather than two fingers on each hand, having different muscle attachment ridges on the bones and showing growth patterns which appear to be more similar to Allosaurus than T rex."

"This is exciting stuff, providing palaeontologists with a greater insight into the evolution of dinosaurs."
 

Dinosaurs dug for mammalian prey

Mounting evidence suggests dinosaurs preyed upon our mammalian ancestors (Source: brotherxii/Flickr)

Larry O'Hanlon
Discovery News

Fossilised mammal burrows that appear to have been clawed out by a predator suggests dinosaurs dug into mammal dens to get furry morsels.

Since there were no large mammal predators 80 million years ago, the most likely candidates are theropod dinosaurs.

Making the connection even stronger is that claw marks in the burrows are a pretty good match to the claws of dinosaur fossils found in rocks nearby, though slightly later in time.

"It's pretty tight," says palaeontologist Professor Edward Simpson of Kutztown University of Pennsylvania. "We can't say whether it's a troodont or a velociraptor," because the claw bones of those found nearby have lost their nails, or cuticles. But otherwise the match is a good one, he says.

Simpson and his students have published their 'trace fossil' discovery - that is, fossilised evidence of animal behaviours rather than the animals themselves - in the August issue of the journal Geology.

"To me there is almost no doubt," says trace fossil expert Professor Anthony Martin of Emory University. "It's very good circumstantial evidence."

No actual mammal bones or teeth have been found, though the burrows match the complexity of those of other mouse- or shrew-like mammals of that time and their present-day counterparts.

The criteria for calling something a fossilised mammal burrow were laid out a few years ago in a separate paper by Martin.

Other evidence

With that criteria in mind, the team feels confident that they did find a mammal's subterranean abode. The researchers could go even further to make their case.

"One of the things we could do is to take the burrows and cut them up," says Simpson. There might be mammal teeth in them, which make an even stronger case.

But, he's hesitant to do that since it's a destructive process. There is also only a very small chance they will find any mammal bones or teeth.

So far Simpson and his students haven't even extracted the fossil burrow from the cliff in southern Utah in which it was found.

As for the dinosaur involved, it probably wasn't very big, judging by the claw marks in the burrows, says Martin.

Other evidence that has been reported to support the dinosaurs-bites-mammal story include the specialised jaw, teeth and skulls of some dinosaurs; mammal bones with bite marks; fossilised gut content; and faeces and trackways.

This case is different in that it points directly at how the dinosaurs hunted rather than just the fact that they ate mammals.

"This is an excellent example of how trace fossils can reveal animal behaviour," says Martin.

Dino demise supersized the mammals

Abbie Thomas
ABC

The demise of the dinosaurs kick-started a growth spurt in mammals that would see them become supersized within a mere 25 million years, new research has found.

The international team led by Felisa Smith from the University of New Mexico publish its findings today in the journal Science.

The mass extinction event at the end of the Cretaceous period, 65 million years ago, wiped out all the non-flying dinosaurs virtually overnight, as well as many other animals, plants and insects.
Suddenly there was room and resources for the mammals to flourish.

The researchers tracked how mammal body size changed over time by identifying the largest mammal from each geological period since the end of the Cretaceous. All major mammal groups including elephants, cats and horses were included.

For the extinct animals, often only fossil teeth were available. To work out how large the body might have been, researchers used modern day animals as a comparison. They calculated the ratio of tooth size to body size for these modern species, and then extrapolated this to extinct mammals.

When size was tracked over time, it was revealed that mammals eventually grew to a thousand times larger than they had been when they shared the Earth with dinosaurs.

The pinnacle of land mammal size was achieved by the bizarre Indricotherium, a hornless rhinoceros-like herbivore that lived around 34 million years ago. At 17 tonnes and standing five and a half metres at the shoulder, it would have dwarfed today's African elephant.

This pattern of increasing size in mammals after the demise of the dinosaurs repeated itself across all continents, including North America, Africa, Eurasia and to a lesser extent, South America, say the researchers.

So how did the dinosaurs keep the mammals at bay for so long?

Keeping mammals at bay

"It was most likely competition for resources [rather than direct predation]," says Dr Alistair Evans, a palaeontologist at Monash University in Melbourne and a co-author on the paper.

"The dinosaurs were there first, so they were able to fill the ecological niches very effectively, for example feeding on plants and carnivory: They could do it better than the mammals could," says Evans. "So there would have been limited opportunity for these smaller mammals to evolve into larger sizes."

He says, the researchers found that larger animals evolved whenever the Earth got cooler. A big body helps conserve heat, last longer without food and travel further to find it.

But mammals can't keep growing forever. The researchers say that mammal body size will always be limited by environmental temperatures and available land area.

Being big also means slower reproduction rates and a certain vulnerability to changes in the environment.

"We're talking over tens of millions of years, but it may be that if the world gets warmer in the future, the larger mammals may well go extinct again, because they are adapted to cooler climates," says Evans.

How the world's biggest mouth evolved

Blue whales are the largest creatures that have ever lived (Source: Carl Buell)

Anna Salleh
ABC

An Australian palaeontologist has figured out a missing step in the evolution of giant filter-feeding mouths characteristic of blue whales.

Dr Erich Fitzgerald from Museum Victoria in Melbourne reports his argument in today's issue of Biology Letters.

"You could fit an average garden-variety kombi van in the mouth of a blue whale," says Fitzgerald, adding that blue whales are the largest animal ever known to inhabit the earth.
They have no teeth but, like other such whales, live on a diet of krill and other marine organisms that they filter out from seawater, using bristles on the roof of their mouths, called baleen.
Central to this baleen whale filter-feeding system is a cavernous mouth with a wide upper jaw and an elastic lower jaw that can open up wide to allow more than the whale's own bodyweight in sea water to enter in one gulp.

"[Modern baleen whales] have extremely mobile lower jaws, which is quite frankly bizarre because no other mammals have that sort of specialisation," says Fitzgerald.

This elastic lower jaw, in which the left and right hand sides are able to stretch apart, was until now believed to be a feature of all baleen whales, even fossil ones.

Scientists have long wondered how ancestral baleen whales, which used their teeth to catch large prey (like killer whales do) evolved into toothless filter feeders.

"This is a huge evolutionary jump," says Fitzgerald.

He now believes he has found the evolutionary missing link in the story.

Missing link

Fitzgerald has found the first fossil evidence of a toothed baleen whale that has no elastic lower jaw.
The newly-described jaw belonged to a tiny 25 million-year-old primitive baleen whale called Janjucetus hunderi, which was at most just three metres long, the size of a bottlenose dolphin.

"This is the clearest evidence yet that the earliest baleen whales could not filter feed and that's interesting because it had previously been thought that all baleen whales were filter feeders," says Fitzgerald.

He first analysed and named this creature in 2006, but at that stage he only had an incomplete lower jaw.

Fitzgerald then came across missing lower jaw bones in the collection of an amateur fossil hunter, by the name of Brian Crichton, who originally found them in the 1970s on a beach near Torquay in Victoria.

These new bones showed that the two halves of the lower jaw bone in Janjucetus hunderi were fused, and unable to open up to allow filter feeding.

Yet, Fitzgerald had previously found the animal had evolved another feature thought to be essential for the filter feeding - a wide upper jaw that creates a large space inside the mouth.

So why did this toothed whale evolve a wide upper jaw?

Suction feeding

Fitzgerald finds a clue in the mouths of modern dolphins, which also lack an elastic lower jaw. Those with really wide upper jaws feed by sucking in large individual prey, he says.

"They generate a vacuum [helped by the wide upper jaw] and hoover up fish and squid, sucking them in through a relatively small opening at the front of their mouths," says Fitzgerald.

"I argue that the big mouth of baleen whales possibly originally evolved to enhance the ability to generate suction."

He says it would be less of an evolutionary leap to go from baleen whales that catch large prey with their teeth to those that suction feed, than directly to those that filter feed of lots on tiny organisms.
After being decimated by past whaling the numbers of blue whales remain low with only about 10,000 individuals left, mainly in the Southern Ocean, says Fitzgerald.

Although they are now protected, he says they remain under threat due to changes in the ocean ecosystem that may affect levels of krill.