Ichthyosaurs, why did they become extinct?


This video says about itself:

Prehistoric News: The Ichthyosaur Graveyard

23 June 2014

Dozens of nearly complete skeletons of ichthyosaurs have been uncovered near a melting glacier in southern Chile.

From LiveScience:

An Asteroid Didn’t Wipe Out Ichthyosaurs — So What Did?

by Laura Geggel, Staff Writer

July 23, 2015 08:05am ET

During the dinosaur age, ichthyosaurs — large marine reptiles that look like dolphins — flourished in prehistoric oceans, living in all kinds of watery environments near and far from shore. But as competition in these areas grew, ichthyosaurs lost both territory and species before gradually going extinct, a new study finds.

In fact, the ichthyosaur extinction has stumped scientists for years. Ichthyosaurs likely evolved from land reptiles that dove into the ocean about 248 million years ago, researchers said. After living along the coast for millions of years, they left for the open water. They disappeared about 90 million years ago, going extinct about 25 million years before the dinosaur-killing asteroid slammed into Earth.

So, if the asteroid didn’t kill the ichthyosaurs, what did? To learn more, researchers looked at ichthyosaur fossils and determined what kinds of specialized environments, or niches, the animals likely inhabited. [In Images: Graveyard of Ichthyosaur Fossils Found in Chile]

“In most studies, the niche of the animal is predicted based on a single trait, usually the shape of the teeth,” said lead researcher Daniel Dicks, a doctoral student in paleontology at the Natural History Museum in Stuttgart, Germany. In the new study, the researchers looked at several traits, he said.

For instance, they analyzed the ichthyosaurs’ body sizes and teeth shapes. They also determined each animal’s feeding strategy, such as whether ichthyosaurs were ambush predators (less powerful swimmers) or pursuit predators (fast swimmers), Dicks said.

Ichthyosaur arrangements

After examining 45 ichthyosaur genuses, Dicks and his colleague Erin Maxwell, a vertebrate paleontologist at the museum, used an analysis that grouped the ichthyosaurs into seven categories, called ecotypes.

For instance, the ichthyosauriform genus, Cartorhynchus, is so unique that it has its own ecotype. It was likely a small suction feeder and lived in shallow water, Dicks told Live Science.

Another ecotype represents the majority of the genuses that lived during the Early to Middle Triassic period, he said. Animals of this ecotype were less than 6.5 feet (2 meters) long, and had robust and blunt teeth, suggesting they ate hard-shelled prey, such as coral and shelled mollusks, Dicks said. They didn’t have elongated bodies, so they probably didn’t live in the open water, where they would have needed to swim far distances, he added.

Two genuses — Eurhinosaurus and Excalibosaurus — owe their unique ecotype to their swordfishlike jaws, which indicate they used a slashing method to demolish prey, Dicks said. Their long bodies also indicate they lived in the open water, far from shore, he said.

Not all seven ecotypes existed at once, although five existed simultaneously during the Early Jurassic period, when ichthyosaurs experienced a boom in diversity.

By the Middle Jurassic, the number of ichthyosaur ecotypes decreased. Specialized feeders, such as the swordfishlike Eurhinosaurus, and apex predators, including Temnodontosaurus, went extinct, leaving only two ecotypes, both of which lived in the open water.

These last two ecotypes included ichthyosaur genuses with large bodies and robust teeth for crushing bony fish or hard cephalopods, such as ammonites. The other ecotype was more dolphinlike; it had small teeth and likely ate soft prey, such as squid (also cephalopods), Dicks said.

Ichthyosaur extinction

Ichthyosaurs eventually met their end during the Cenomanian-Turonian extinction event, in which spinosaurs (carnivorous swimming dinosaurs), plesiosaurs (long-necked marine reptiles) and roughly one-third of marine invertebrates (animals without a backbone) also went extinct, Dicks said. [In Images: Digging Up a Swimming Dinosaur Called Spinosaurus]

With only two ecotypes of ichthyosaurs left, they would have been easily wiped out, Dicks said.

“It’s a slow ecological war of attrition, where they become more and more stranded on a single niche, and then the entire [group] is depending on that niche remaining sustainable,” he said. “And if that became unsustainable, then the entire group would become extinct.”

It’s unclear why ichthyosaurs lost their earlier niches, but they were likely “replaced, outcompeted by other species that adapted better,” Dicks said. For instance, plesiosaurs took over many of the near-shore niches, he said.

The study sheds light on ichthyosaurs’ evolution and extinction, said Neil Kelley, a postdoctoral research fellow of paleobiology at the National Museum of Natural History in Washington, D.C., who was not involved in the new research.

According to the study, “[ichthyosaurs] get more and more confined to a specialized lifestyle,” Kelley said. “Ultimately, they can never seem to re-evolve some of these more transitional lifestyles and body types that you see early on.”

However, the study takes a broad view encompassing roughly 158 million years, so it loses some nuance in how these animals lived and why they went extinct, Kelley told Live Science. Furthermore, “just one weird fossil could totally rewrite that picture of what happened,” by adding another ecotype, Kelley said.

The study was published online July 8 in the journal Biology Letters.

Plesiosaur discovery in Alberta, Canada


Plesiosaur skeleton

In Alberta, Canada, a fossil plesiosaur from the Cretaceous age has been discovered in November 2011: here.

Talking about fossils: Oldest Hairy Microbe Fossils Discovered.

Biggest ever Swiss dinosaur skeleton discovered


This video is called My Plateosaurus Tribute + my favorite Plateosaurus Pictures!

From swissinfo in Switzerland:

Triassic park: oldest Swiss dinosaur skeleton found

July 1, 2015 – 18:55

The largest dinosaur skeleton ever found in Switzerland has been uncovered in a clay pit in northern Switzerland. The eight-metre skeleton of a plateosaurus is thought to have been around 25 years old when it died.

“This herbivore lived 210 million years ago and was discovered in the Upper Triassic geologic layer,” said Ben Pabst, who has been leader of the dig in Frick, canton Aargau, since 1976. The dinosaur’s head has yet to be found.

Plateosaurus was a bipedal herbivore with a small skull on a long, mobile neck, sharp but plump plant-crushing teeth, powerful hind limbs, short but muscular arms and grasping hands with large claws on three fingers, possibly used for defence and feeding.

Unusually for a dinosaur, instead of having a fairly uniform adult size, fully grown individuals ranged from 4.8-10 metres long and weighed 600-4,000 kilograms.

The site in Frick is known around the world for the density of dinosaur skeletons.

“We have here an unbelievably large site. So far we have been able to determine an area with a diameter of three kilometres,” Pabst explained on Wednesday, adding that one hectare will yield some 500 animals and that for every 100 herbivore dinosaurs there is one carnivore.

Museum

Around 210 million years ago, Frick was flat, very hot, tropical and criss-crossed with rivers. Pabst assumes that at various times a range of dinosaurs, which weighed several tons, got stuck in the boggy land and died of thirst.

Since many complete skeletons of legs have been found, he believes the animals were mummified by the heat.

The theory that the dinosaurs sank in mud was strengthened by the fact that the plateosaurus in question was found with its legs spread.

The Frick site has an annual budget of CHF50,000 ($52,800) and the work is heavily reliant on volunteers. The latest find is too big for the Frick dinosaur museum, so a renovation is being considered.

Cambrian fossil spiky worm discovery


Illustration showing the many legs and spikes covering the early Cambrian creature, Collinsium ciliosum. Credit: Javier Ortega-Hernández

From LiveScience:

Armored Spiky Worm Had 30 Legs, Will Haunt Your Nightmares

by Laura Geggel, Staff Writer

June 29, 2015 03:00pm ET

A spiky, wormlike creature with 30 legs — 18 clawed rear legs and 12 featherlike front legs that likely helped it filter food from the water — once lived in the ancient oceans of the early Cambrian period, about 518 million years ago, a new study finds.

The critter is one of the first known animals on Earth to develop protective armor and to sport specialized limbs that likely helped it catch food, the researchers said. This newfound species lived during the Cambrian explosion, a time of rapid evolutionary development, they said.

“It’s a bit of a large animal for this time period,” said one of the study’s lead researchers, Javier Ortega-Hernández, a research fellow in paleobiology at the University of Cambridge. “The largest specimen is just under 10 centimeters [4 inches], which, for a wormy thing, is quite mighty.” [See Images of the Spiky Worm & Other Cambrian Creatures]

The creature likely used its rear clawed legs to anchor to sponges or other penetrable surfaces, and waved its feathery front limbs to and fro in the current to catch nutrients in the water, Ortega-Hernández said. This technique is still used by modern animals, such as bamboo shrimp, that capture passing meals with their fanlike forearms.

But, because the Cambrian critters were “soft and squishy,” it’s likely they waved their limbs in a gentle motion, Ortega-Hernández told Live Science. “I don’t imagine they would have quick muscle control.”

A squishy creature that didn’t move quickly needed a steadfast defense strategy, and that’s likely why it had so many spikes, he said. Other Cambrian wormlike creatures, such as the bizarre Hallucigenia, also sported spines.

Hallucigenia has two sets of spines per leg,” Ortega-Hernández said. “This one has up to five, which means it was a much more heavily armored creature.”

Collins’ monster

Researchers have dubbed the new creature Collinsium ciliosum, or Hairy Collins’ Monster, named after Desmond Collins, a paleontologist who discovered a fossil of a similar Cambrian wormlike creature in Canada in the 1980s. Since then, researchers have found five species of Collins’ Monster (in the family Luolishania), including one from Australia.

But, unlike earlier fossils, the newfound specimens offer researchers a spectacular view of the prehistoric creature. One fossil displays much of Collinsium ciliosum’s body, including its digestive tract and even the delicate, featherlike structures on its front limbs. Based on the fossils, when it was alive, the worm likely didn’t have any eyes or teeth, Ortega-Hernández said.

Over the past three years, scientists at Yunnan University in China and the University of Cambridge have uncovered and studied 29 C. ciliosum fossils from the early Cambrian Xiaoshiba biota, a deposit in southern China that contains a rich collection of fossilized Cambrian creatures, he said.

An analysis of C. ciliosum‘s anatomy indicates it’s a distant ancestor of modern-day velvet worms, also known as onychophorans — a small group (just 180 species) of squishy worms that live in tropical forests, shoot slime at their prey and resemble legged worms.

Interestingly, the Collins’ Monsters were likely a more diverse group that “came in a surprising variety of bizarre shapes and sizes” than today’s onychophorans, Ortega-Hernández said in a statement.

This isn’t the first time that an ancestral group has displayed more diversity than its modern-day relatives. Sea lilies (crinoids) and lamp shells (brachiopods) also follow this trend. But Collins’ Monsters are the first example of this evolutionary pattern playing out in a mostly soft-bodied group, the researchers said. [See Images of Another Bizarre Cambrian Creature]

The study is “a superb description based on absolutely exquisite fossils,” said Greg Edgecombe, a researcher of arthropod evolution at the Natural History Museum in London, who was not involved in the new study.

The new finding drives home that Cambrian wormlike animals such as Hallucigenia and the new Collinsium are the ancestors of Onychophora, Edgecombe said.

“That means they are more closely related to Onychophora than to any other living groups (such as arthropods or tardigrades),” Edgecombe told Live Science in an email. “Rather than floating around on the tree of life without an exact home,” these creatures can be pinpointed to a living group, Edgecombe said.

The findings were published online today (June 29) in the journal Proceedings of the National Academy of Sciences.

See also here.

Triassic turtle evolution, new research


This video says about itself:

Evolution of the Turtle Shell (Illustrated)

30 May 2013

Evolution of the turtle shell based on developmental and fossil data. This animation is based on the work of Dr. Tyler Lyson, currently at the Smithsonian Institution.

The animation shows how various fossils, particularly Eunotosaurus and Odontochelys, bridge the morphological gap between a generalized animal body plan to the highly modified body plan found in living turtles.

The paper, published in Current Biology, can be found here.

Animation by Stroma Studios.

From the Washington Post in the USA:

How the turtle got its shell, a not-so ‘Just So’ story

By Sarah Kaplan

June 25 at 5:22 AM

Long, long ago, in a time so far in the past it preceded the dinosaurs and the continents, lived a tiny creature named “grandfather turtle.” It had many of the qualities of the turtles we know and love today: a boxy body, plodding legs, a long neck topped by a small, round head.

It was only missing one thing: a shell.

Thanks to the newly discovered fossil of that tiny creature, scientists say they have solved the story of how the turtle got its shell. But this is no Rudyard Kipling fable. It’s science.

The not-so “Just So” story, published in the journal Nature on Wednesday, tracks the evolution of the turtle body plan through millions of years of history. By examining fossils that spanned millennia and continents, researchers were able to figure out how the modern turtle’s unique shell evolved from what was just a brief expanse of belly bones about 240 million years ago.

The origin of the turtle shell has long bewildered scientists (this was, apparently, the one natural phenomenon Kipling hadn’t written a story to explain). Though they had fossils of turtle predecessors from the beginning and the end of the Triassic period, there was little evidence of what happened to ancient turtles during the intervening years. The bones of the 260 million-year-old Eunotosaurus, a reptilian creature found in South Africa, had wide, flat ribs and a sprawling, turtle-like figure, but it was far from the armor-encased animal we know today.

The next time a turtle ancestor popped up in the fossil record, the Odontochelys about 220 million years before present, it had a fully developed belly plate called a “plastron” that would eventually expand to enclose the turtle’s whole body, protecting it from attacks from above and below. (The first turtle with a true shell wouldn’t appear on the scene until about 6 million years after that.)

But there was nothing in the yawning 40 million-year void between the two ancient species to explain where that plastron came from.

“Hopefully we’ll find more,” Robert Reisz, a paleontologist at the University of Toronto, told National Geographic after the Odontochelys was first found in 2008. “We’re closing the gap, but there is still a big morphological gap between this turtle and its non-turtle ancestors.”

Enter Pappochelys, the hero of our story, ready and willing to fill that gap.

Pappochelys, whose name means “grandfather turtle,” lived about 240 million years ago in a warm sub-tropical lake, Hans-Dieter Sues, a co-author of the Nature study and curator at the Smithsonian Museum of Natural History in D.C., told NPR. Discovered in a limestone quarry near Stuttgart, Germany, it is the precise chronological and morphological midpoint between the two previously known fossils: about eight inches from tip to tail, it had slender legs and an oddly boxy body with a rib cage that looked like the beginnings of a “little bony house.”

This physiological setup was good for protection and also worked as “bone ballast,” according to Smithsonian, allowing the animal to control its buoyancy in the water.

In addition, the Pappochelys had a series of hard, shell-like bones lining its belly — the beginnings of the plastron that would turn up 20 million years later.

“It has real beginnings of the belly shell developing, little rib-like structures beginning to fuse together into larger plates and then ultimately making up the belly shell,” Sues told NPR.

Sues’s co-author, Rainer R. Schoch, a paleontologist at the Staatliches Museum für Naturkunde in Stuttgart, called Pappochelys a “transitional creature,” one that illustrates how ancient lizards became modern turtles.

“Transitional creatures are the most important contribution that paleontology can make to the study of evolution,” Schoch told Voice of America. “They are often unexpected and show surprising features.”

And, in Pappochelys case, they tell pretty good stories.

Cambrian fossil Hallucigenia, new study


This video says about itself:

Hallucigenia: The worm with the missing head

The remains of an ancient worm species called ‘Hallucigenia’ were so bizarre looking that scientists originally reconstructed it upside down and back to front. Now Martin Smith reveals the most complete picture so far of this peculiar marine worm.

Read the Nature paper ‘Hallucigenia’s head and the pharyngeal armature of early ecdysozoanshere.

Find out more about Hallucigenia and other finds from the Burgess Shale at www.burgess-shale.rom.on.ca.

24th June 2015

From daily The Independent in Britain:

Hallucigenia: Significance of bizarre extinct creature revealed as it finally bares its teeth

The fossil’s bizarre appearance had mystified scientists for more than a century

Steve Connor, Science Editor

Wednesday 24 June 2015

A bizarre extinct creature that has mystified scientists since its 500m-year fossil was first unearthed more than a century ago has finally revealed its teeth – placing it centre stage in the evolution of many complex life-forms living today.

Hallucigenia, which owes its name to its unworldly appearance, was so odd that scientists initially confused its top from its bottom and its head from its tail. However, a study has now unequivocally identified its mouth, complete with a fearsome ring of sharp teeth.

Researchers from the University of Cambridge have also identified a pair of simple eyes on Hallucigenia’s head and have determined that it was a close relative of the last common ancestor of everything from tiny velvet roundworms to huge lobsters.

“The early evolutionary history of this huge group is pretty much uncharted. While we know that the animals in this group are united by the fact that they moult, we haven’t been able to find many physical characteristics that unite them,” said Martin Smith of Cambridge University, the lead author of the study in Nature</em>.

Read more: Bat-like dinosaur fossil found after 160 million years

176-million-year old dinosaur vertebra discovered in Yorkshire

New Jurassic-era dinosaur species discovered in Wales

“Prior to our study there was still some uncertainty as to which end of the animal represented the head, and which the tail,” Dr Smith said.

“A large balloon-like orb at one end of the specimen was originally thought to be the head, but we can now demonstrate that this actually wasn’t part of the body at all, but a dark stain representing decay fluids or gut contents that oozed out as the animal was flattened during burial,” he said.

Film Jurassic World’s depiction of dinosaurs criticized


This video says about itself:

Jurassic Park was ahead of its time. Jurassic World is not.

10 June 2015

A lot has changed in paleontology since Jurassic Park first came out in 1993.

For more information about this topic:

National Geographic: A Velociraptor Without Feathers Isn’t a Velociraptor

The Guardian: Siberian dinosaur spreads feathers around the dinosaur tree

Science Mag: Earliest dinosaurs may have sported feathers

See also here.