Showing posts with label Cretaceous. Show all posts
Showing posts with label Cretaceous. Show all posts

Tuesday, February 28, 2012

Polysternon isonae, A New Bothremydid Turtle

Researchers at the Institut Català de Paleontologia Miquel Crusafont (ICP), the Museu de la Conca Dellà (MCD) and the Universitat Autònoma de Barcelona (UAB) have published this week in the online edition of the journal Cretaceous Research the discovery and description of a turtle from the end of the age of dinosaurs.   Above left: a reconstruction of Polysternon isonae. (Credit: Oscar Sanisidro)

Josep Marmi, Angel Lujan, Angel Galobart from ICP, Rodrigo Gaete from MDC, and Violeta and Oms Oriol Riera from UAB have named this new species as Polysternon isonae, in recognition of the municipality of Isona I Conca Dellà (Catalonia, Spain), where the fossil remains of the specimen type have been found.

The abundance of dinosaur fossils that lived between 65 and 70 million years ago in the area currently occupied by the Pyrenees It is well known. In this range we find dozens of sites with bones, footprints and eggs of the last dinosaurs that inhabited our planet, the Tremp basin being one of the areas with the highest concentration of fossils.

However, lesser-known are the other organisms that completed the ecosystems at the end of the Cretaceous period, consisting of other vertebrates, invertebrates, plants, fungi, etc. A common feature of these ecosystems were turtles. In the Pyrenean sites, their fossils are relatively abundant and, in general, consist of isolated shell plates or small sets of plates that can help us get a general idea of the morphology and size of the animal. Instead, the entire shell finding is rare and even more exceptional are the findings where parts of the skeleton are preserved within the shell.

In recent years, in the municipality of Isona i Conca Dellà (Catalonia) numerous discoveries of turtle remains have been made, spread over several sites. One of these sites, that of Barranc de Torrebilles, has given fairly complete remains that allowed describing a new species: Polysternon isonae. The remains found consist of dozens of isolated plates derived from the fragmentation of shells through their sutures, and what is more important: a fragment of the ventral side of a shell and an almost entire shell, which without being totally complete, show morphological features of great interest to paleontologists and have allowed to describe this new species. These remains were recovered during two excavation campaigns conducted during the summers of 2008 and 2009.

So far, two species of the genus Polysternon were known : P. provinciale and P. Atlanticum (plus a possible third P. Mechinorum), distributed only in what is know the south of France and the Iberian Peninsula. They were animals adapted to swimming and living in fresh waters, in the deeper areas of rivers and lakes. Specifically, the shell of the new species P. isonae was oval, measuring about 50 centimeters long and 40 wide. The remains were found preserved in a very hard sandstone strata now exposed in the Barranc de Torrebilles. Just over 65 million years ago, when the animal died, this was not a lithified sandstone and consisted of fine sand that was washed away by river streams and that was deposited, along with the remains of other turtles of the Barranc de Torrebilles, at the bottom of one of these rivers.

Unlike other kinds of turtles, it seems that Polysternon did not survive the end of Cretaceous and went extinct with the dinosaurs. The close proximity of the site Barranc de Torrebilles to the geological level that marks the end of the Cretaceous extinction, indicates that Polysternon isonae was possibly one of the last species of the genus Polysternon.

Citation

J. Marmi, Á.H. Luján, V. Riera, R. Gaete, O. Oms, À. Galobart. 2012. The youngest species of Polysternon: A new bothremydid turtle from the uppermost Maastrichtian of the southern Pyrenees. Cretaceous Research; 35: 133 DOI: 10.1016/j.cretres.2011.12.004

Wednesday, February 1, 2012

New 30-foot Fossil Croc from Africa

Aegisuchus witmeri. A 30-foot, flat-headed crocodile. Original art work by Henry Tsai, University of Missouri
A University of Missouri researcher has identified a new species of prehistoric crocodile. The extinct creature, nicknamed "Shieldcroc" due to a thick-skinned shield on its head, is an ancestor of today's crocodiles. Its discovery provides scientists with additional information about the evolution of crocodiles and how scientists can gain insight into ways to protect the species' environment and help prevent extinction.


The discovery was published this week in the journal PLoS ONE (Public Library of Science). "Aegisuchus witmeri or 'Shieldcroc' is the earliest ancestor of our modern crocodiles to be found in Africa," said Casey Holliday, co-researcher and assistant professor of anatomy in the MU School of Medicine. "Along with other discoveries, we are finding that crocodile ancestors are far more diverse than scientists previously realized."

Shieldcroc is the newest discovery of crocodile species dating to the Late Cretaceous period, approximately 95 million years ago. This period is part of the Mesozoic Era, which has been referred to as the "Age of the Dinosaurs;" however, numerous recent discoveries have led to some scientists calling the era the "Age of the Crocs," Holliday said.

Holliday identified Shieldcroc by studying a fossilized partial skull specimen, which was discovered in Morocco and held by the Royal Ontario Museum of Toronto for several years before Holliday analyzed it. By analyzing blood vessel scarring on the bone, Holliday determined that the crocodile would have had a structure on top of its head, resembling a shield. The dents and bumps on the bone indicate veins delivered blood to a circular mound of skin, something never before seen in a crocodile. He said the shield was likely used as a display structure to attract mates and intimidate enemies and possibly as a thermo-regulator to control the temperature of the animal's head.

Holliday compared Shieldcroc's skull to those of other crocodilians. By comparing slopes of various bones, he found that the new species had a flatter skull than other known species. With this information, he believes it is unlikely that Shieldcroc wrestled dinosaurs on or near the shoreline. Instead, Holliday said the fossil indicates that Shieldcroc had thin jaws, likely used to catch fish.

"We believe Shieldcroc may have used its long face as a fish trap," said co-author Nick Gardner, an undergraduate researcher at Marshall University, who collaborated with Holliday on the study. "It is possible that it lay in wait until an unsuspecting fish swam in front of it. Then, if it was close enough, Shieldcroc simply opened its mouth and ate the fish without a struggle, eliminating the need for strong jaws."

In addition, Holliday analyzed Shieldcroc's skull and brain to estimate the overall size of the reptile. He said scientists often use head size of an animal to estimate its total length. Using several parameters, Holliday and Gardner estimate that this specimen had a 5-foot long head and was 30 feet long.

"Scientists often estimate body size of crocodilians based on the size of the skull," Gardner said. "However, estimating the body size of Shieldcroc was difficult, due to the enormous size of the skull compared to other crocodilians. To make a size estimate, we compared several features of the bone to many different species."

Although Shieldcroc lived more than 90 million years ago, Holliday said scientists can use information about the animal to gain a better understanding of today's crocodiles. He said this insight grows in importance as humans encroach on ecosystems.

"Today's crocodiles live in deltas and estuaries, the environments put under the most stress from human activity," Holliday said. "By understanding how these animals' ancestors became extinct, we can gain insight into how to protect and preserve the ecosystems vital to modern crocodiles."

The Shieldcroc fossil studied by Holliday and Gardner is being returned to the Royal Ontario Museum, where it will be put on display later this year.

Citation
Holliday, CM & Gardner NM. A New Eusuchian Crocodyliform with Novel Cranial Integument and Its Significance for the Origin and Evolution of Crocodylia. PLoS ONE, 2012; 7 (1): e30471 DOI: 10.1371/journal.pone.0030471

Saturday, September 17, 2011

Feathers from Canadian Dinosaurs

A feather trapped in Amber. University of Alberta 
The following is a press release from the University of Alberta.

(Edmonton) Secrets from the age of the dinosaurs are usually revealed by fossilized bones, but a University of Alberta research team has turned up a treasure trove of late Cretaceous feathers, which have been discovered trapped in tree resin.

The resin turned to resilient amber preserving some 80-million-year-old protofeathers, possibly from non-avian dinosaurs, as well as plumage that is very similar to modern birds, including those that can swim under water.

U of A paleontology graduate student Ryan McKellar discovered a wide range of feathers trapped in amber in collections at the Royal Tyrrell Museum and in the private collection of the Leuck family in Medicine Hat.

“Most of the feather specimens were probably blown into contact with the sticky surface of the resin and encapsulated by subsequent resin flows,” said McKellar.

The 11 feather specimens used by the U of A team were all found near the community of Grassy Lake in southern Alberta. The research specimens are described as the richest amber feather find from the late Cretaceous period.

“The amber preserves microscopic detail of the feathers and even their pigment or colour,” said McKellar. “I would describe the colours as typically ranging from brown to black.”

During the late Cretaceous, southern Alberta was a warm coastal region. “The trees that produced the resin were probably comparable to the redwood forests of the Pacific Northwest,” said McKellar.

No dinosaur or avian fossils were found in direct association with the amber feather specimens, but McKellar says comparison between the amber and fossilized feathers found in rock strongly suggest that some of the Grassy Lake specimens are from dinosaurs. The non-avian dinosaur evidence points to small theropods as the source of the feathers.

McKellar says that some of the feather specimens can take on water, enabling the bird to dive more effectively and are very similar to those of modern birds like the Grebe, which are able to swim underwater.

“The preservation of microscopic detail and pigmentation has provided a unique snapshot of feathers and their uses in the late Cretaceous forests of Alberta,” said McKellar.

The U of A team’s research was published Sept. 15, in the journal Science.

Monday, March 7, 2011

The Oldest Pteranodon?

The following is a press release from Southern Methodist University.

Fossilized bones discovered in Texas from a flying reptile that died 89 million years ago may be the earliest occurrence of the prehistoric creature known as Pteranodon.

Previously, Pteranodon bones have been found in Kansas, South Dakota and Wyoming in the Niobrara and Pierre geological formations. This likely Pteranodon specimen is the first of its kind found in Texas, according to paleontologist Timothy S. Myers at Southern Methodist University in Dallas, who identified the reptile. The specimen was discovered north of Dallas by an amateur fossil hunter who found various bones belonging to the left wing.

Pteranodon was a type of pterosaur that lived about the same time as some dinosaurs, about 100 million to 65 million years ago. The only reptiles to dominate the ancient skies, pterosaurs had broad leathery wings and slim torsos.

Adult pterosaur, toothless variety with about a 12-foot wing span
The specimen identified by Myers is an adult pterosaur of the toothless variety and while larger than most birds, wasn't among the largest pterosaurs, Myers said, noting it had a wing span between 12 and 13 feet, or 3.6 to 4 meters. It was discovered in the Austin Group, a prominent rock unit in Texas that was deposited around 89 million years ago, early in the geological time period called the Late Cretaceous.

Pterosaurs, many of which survived on fish, lived at a time when a massive ancient sea cut across the central United States. The Western Interior Seaway was a shallow body of water that split North America in half from the Arctic Ocean to the Gulf of Mexico.

More than a thousand Pteranodon fossils have been unearthed from the middle part of the seaway.

No definitive Pteranodon specimens have emerged from the southern part that is now Texas.

The SMU specimen, if it is Pteranodon, would be the first discovered so far south in the Western Interior Seaway, said Myers, a postdoctoral researcher in SMU's Huffington Department of Earth Sciences.

Myers reported and described the specimen in "Earliest Occurrence of the Pteranodontidae (Archosauria: Pterosauria) in North America; New Material from the Austin Group of Texas" in the Journal of Paleontology.

Left wing suggests Pteranodon; cause of death a mystery
Key to identifying the SMU fossils as Pteranodon is a humerus of 5.7 inches, or 14.5 centimeters. The humerus is the uppermost bone in the wing and attaches to the torso. The humerus of the SMU specimen, while complete, did suffer some damage during fossilization when it became compressed and distorted through millions of years of compaction.

"If it wasn't crushed so badly, it would be possible to determine if it really is Pteranodon," Myers said. "These bones are easily flattened. They are hollow inside, because they have to be lightweight to allow a pterosaur to fly. So they compress like a pancake as they're embedded in layers of rock."

While it's difficult to narrow the humerus definitively to a specific genus and species, some features clearly identify the specimen as part of the Pteranodontidae family, most likely the genus Pteranodon. It exhibits, for example, the prominent warped deltopectoral crest that is characteristic of members of the Pteranodontidae family, called pteranodontids, he said.

Discovered along with the humerus were parts of the elongated fourth finger that in pterosaurs forms the wing. The SMU specimen's metacarpal — at 20 centimeters — is incomplete, missing an estimated 37 percent of its length.

The fossils do not solve the mystery of the reptile's cause of death, Myers said. But it appears the animal probably died in flight over the sea and then fell into the water. Its carcass probably floated for some time, so that when the flesh decomposed the bones separated at the joints, known as "disarticulation," before they settled to the sea floor and were buried.

"We know it was disarticulated when it was buried because the bones weren't preserved in correct anatomical position," Myers said. "Abrupt truncation of the broken end of one of the bones and infilling of the break with sediment also indicates that the breakage and disarticulation took place prior to burial."

May be oldest Pteranodon in world
If the specimen represents Pteranodon, Myers said, it would be the oldest one in North America by 1 million to 2 million years, and the second oldest pteranodontid in the world.

Pterosaurs were alive from the Late Triassic — more than 200 million years ago — to the Late Cretaceous, evolving from small-bodied creatures to some of the largest animals to ever inhabit the skies, Myers said. An older pteranodontid specimen, belonging to the genus Ornithostoma, previously was identified in England.

"Any pterosaur material is fairly rare to find unless you have exceptional preservation conditions. They are frail, fragile bones, and they require rapid burial to be well preserved," Myers said. "The SMU specimen was deposited relatively far offshore in deep water, perhaps 50 to 80 feet deep. It's fairly exceptional because of the number of elements. Typically you'll only find one piece, or one part of a piece in the local rock."

During the Early Cretaceous, many types of pterosaurs lived around the world, Myers said. The earliest ones had thin, razor-sharp teeth. In the transition from Early to Late Cretaceous, the toothed variety disappear from the fossil record and toothless forms, like the SMU specimen, become more common, he said.

Dallas area specimens illustrate pterosaur evolution
North Texas is fortunate to have had both the toothed and toothless kinds discovered in the area, illustrating the evolutionary transition, noted Myers.

Besides the toothless specimen just identified by Myers, an older toothed pterosaur, Aetodactylus halli, previously was discovered in the Dallas area. Aetodactylus, also identified by Myers, lived 95 million years ago.

"This new specimen adds a lot more information about pterosaurs in North America," Myers said. "It helps constrain the timing of the transition from toothed to toothless because there's only a few million years separating this specimen and Aetodactylus."

Amateur fossil collector Gary Byrd of Rockwall, Texas, discovered the new SMU pterosaur fossils about 10 years ago. A roofing contractor who keeps an eye out for fossils, Byrd made the find after stopping to look at two freshly excavated culverts while driving through a new subdivision in Collin County. Using a hammer and pick he dug out the bones and brought them to SMU paleontologists Louis Jacobs and Dale Winkler. Jacobs and Winkler indicated the fossils were likely a pterosaur. Byrd donated the fossils to SMU's Shuler Museum of Paleontology.

"I found a couple parts of a fish, and then when I saw these my initial thought was that they weren't fish," Byrd recalled. "I kind of knew it was something different — a birdlike thing. It's very rare you find those thin, long bones."

This isn't the first time Byrd has hit it lucky finding fossils. In 1994 he discovered dinosaur bones that he donated to SMU's Shuler Museum. The specimen was identified as a rare primitive duck-billed dinosaur and named Protohadros byrdi after Byrd. — Margaret Allen

Citation:
Myers. T. S. 2010. Earliest Occurrence of the Pteranodontidae (Archosauria: Pterosauria) in North America: New Material from the Austin Group of Texas. Journal of Paleontology, 84 (6): 1071 DOI: 10.1666/09-082.1