
"In a cover article published today (23 February 2006) in Science, the team of researchers from Carnegie Museum of Natural History,
Nanjing University, and Chinese Academy of Geological Sciences describe a fossilized skeleton of Castorocauda lutrasimilis
([Castoro] - Latin for beaver, [cauda] - Latin for tail, [lutra] -Latin river otter] and [similis] - Latin for similarity).
Castorocauda had a beaver-like tail, strong arms for digging, and sharp teeth specialized for aquatic feeding, similar to the
modern river otter."
Castorocauda is preserved with a pelt (guard hairs and under furs), making it the most primitive-known mammal to be
preserved with hairs. Carbonized in the fossil, the short and dense under-furs were to keep water from the skin; the longer
guard hairs are preserved as impressions on the fossil slab. Fossilized furs of this animal provide fresh evidence on
phylogenetic evolution of mammalian fur � this kind of specialized pelt developed well before the rise of modern mammals.
All previously discovered fossils with fur belong to the more derived taxa within the Mammalia or mammalian crown group.
"Its lifestyle was probably very similar to the modern day platypus," said Dr. Zhe-Xi Luo, curator of Vertebrate Paleontology
at Carnegie Museum of Natural History. "It probably lived along river or lake banks. It doggy-paddled around, ate aquatic animals
and insects, and burrowed tunnels for its nest."
Dr. Luo pointed out that, perfectly shaped for aquatic life, Castorocauda had a broad and scaly tail that propelled
it through water just like the modern beaver. Its tail vertebrae are also similar to those of beavers and otters. Because
Castorocauda is not related to modern placentals, its adaptation for swimming is a convergent evolution to the modern
beaver and modern river otter, both of which are placentals.
"Uncovered from the Middle Jurassic Jiulongshan Formation of the Inner Mongolia Region, dated approximately 164 million years ago,
Castorocauda is the earliest-known mammal that had specialized skeletal and soft-tissue features for swimming and teeth for
eating fish. This significant fossil offers the first evidence that some Mesozoic mammals occupied the semi-aquatic niche
and that Mesozoic mammals as a whole had a much great ecological diversification than previously thought."
(Text and illustration courtesy Carnegie Museum News)
Answers.com article about Castorocauda
Wikipedia entry for Castorocauda
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Most Mesozoic mammals were tiny, probably nocturnal and insectivorous. They are popularly seen, when thought about at all,
as scampering to keep out of the way of the predatory dinosaurs. One specimen of a small feathered dinosaur,
Sinosauropteryx prima, was found which contained remains of three individuals of small mammals, two Zhangheotherium
and one of the multituberculate Sinobaatar.
Not all Mesozoic mammals were so small, however. Repenomamus, a triconodont known from the
famous fossil beds at Liaoning China
that have produced so many beautiful early birds, is known from several dozen complete specimens. There are two species,
Repenomamus robustus, about the size of the American opossum, and Repenomamus giganticus,
about 50% larger. In Januray 2006, a complete skeleton of R. robustus was prepared and described which contained,
in the area occupied by the stomach, the partial remains of a small herbivourous dinosaur,
Psittacosaurus. The fact that some of the long bones
were found in articulation suggests that "the juvenile Psittacosaurus was dismembered and swallowed as
chunks."

Left: Artists reconstruction of Repenomamus chasing a juvenile Psittacosaurus.
Center: The skeleton of Repenomamus containing the dinosaur remains.
Right: Skeleton of Repenomamus giganticus, the largest known Mesozoic mammal.
Hu, Yaoming, Jin Meng, Yuanqing Wang and Chuankui Li, 2006: "Large Mesozoic mammals fed on young dinosaurs"
Nature Vol. 433(13):149-152
Cretaceous fossil, Maastrichtidelphys meurismeti suggests
transatlantic connection of North American and Europe earlier than previously thought - June, 2005
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"A new mammal more than 66 million years old whose origins are in South Dakota has been identified in the Netherlands.
Dr. James Martin (Geol71), professor emeritus, geology and geological engineering, identified the mammals while conducting
research for the School of Mines Museum of Geology. Two amateur collectors from the Netherlands, Roland Meuris and Frans Smet,
discovered the fossil, which consists of a tooth. When paleontologists at the Natural History Museum of Maastricht showed a
photograph to Martin, he was able to identify it because of his experience with fossils at the School of Mines Museum of Geology.
The Museum of Geology is an epicenter for the study of fossils, both regionally and worldwide. Although the museum has a collection
of fossils from around the world, specimens from South Dakota make up a majority of the collections. Based upon these specimens,
Dr. Martin was able to recognize the mammal. In addition to the museum�s library of fossils, Dr. Martin was able to draw on
his personal experience with them. Some of the fossils that he collected in his senior year of college at the School of Mines
helped him in identifying the new specimen. The new species has been named after its discoverers and is called Maastrichtidelphys
meurismeti, which means the �Maastricht opossum of Meuris and Smet.�
The fossil�s closest relative is found in western South Dakota in Meade County. This relative suggests that these mammals
were able to travel across a before unknown trans-Atlantic route. �This find has world-wide implications,� Dr. Martin said.
�It changes the way we look at the history of climates and animal distribution.� According to Martin, paleontologists had
assumed that these mammals had not made the crossing from North America until the Eocene epoch, which was 10 million years
after the extinction of dinosaurs. The new fossil find suggests that during the end of the Cretaceous period, which was the
end of the Age of Dinosaurs, temporary trans-Atlantic land bridges existed. The new find is so important because it changes
views on the timeline of the distribution of animals through history."
The description of Maastrichtidelphys appears in the Journal of Mammalian Evolution. The complete reference is:
Martin, J.E., Case, J.A., Jagt, J.W.M., Schulp, A.S. & Mulder, E.W.A. (2005). �A New European Marsupial Indicates
a Late Cretaceous High-latitude Transatlantic Dispersal Route.� Journal of Mammalian Evolution vol. 12, Nos. 3/4, 495-511.
Source of news article.
Phoberomys pattersoni, huge South American rodent
announced September, 2003
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World's Largest Rodent: Buffalo-Size Fossil Discovered
By John Roach
for National Geographic News
September 22, 2003
The fossil remains of a giant rodent that weighed an estimated 1,500 pounds (700 kilograms) is helping scientists form a
clearer image of what northern South America was like some eight million years ago.
Heralded as the world's largest rodent, Phoberomys pattersoni looked more like a giant guinea pig (Cavia porcellus)
than an oversized house rat (Rattus rattus) and it apparently flourished on a diet of vegetation, not scraps dropped on the
kitchen floor.
"Phoberomys was most likely a herbivore, and I seriously doubt it was a pest," said Marcelo S�nchez-Villagra,
a paleontologist at the University of T�bingen in Germany. "When thinking of Phoberomys, think guinea pig, not rat."
Orangel Aguilera, a zoologist with the Universidad Francisco de Miranda in Venezuela, together with a colleague,
Ascanio Rincon, discovered the Phoberomys fossils in 1999 in the Urumaco Formation, a desert region near the
northwest coast of Venezuela.
S�nchez-Villagra and Ines Horovitz, a professor of organismic biology, ecology, and evolution at the University of California,
Los Angeles, together with Aguilera, performed detailed studies of the fossils beginning in 2002. The team's report was
published in the September 19, 2003 issue of the journal Science.
"It's really an exciting find," said Louise Emmons, a field biologist who specializes in neotropical mammals at the
Smithsonian Institution in Washington, D.C.
Original article in Science (abstract only)
Australian cave fossils include a complete skeleton of the marsupial lion
Thylacoleo carnifax,
July, 2002
|
 Thylacoleo carnifex skeleton and reconstruction
Interior of Nullabor cave
Illustrations courtesy Western Austrailan Museum
An astonishing collection of fossil animals from southern Australia is reported by scientists.
The creatures were found in limestone caves under Nullarbor Plain and date from about 400,000-800,000 years ago.
The palaeontological "treasure trove" includes 23 kangaroo species, eight of which are entirely new to science.
Researchers tell Nature magazine that the caves also yielded a complete specimen of Thylacoleo carnifex,
an extinct marsupial lion.
In total, 69 vertebrate species have been identified in three chambers the scientists now call the Thylacoleo Caves.
These include mammals, birds and reptiles. The kangaroos range from rat-sized animals to 3m (nearly 10ft) giants.
Story from BBC News
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Eomaia scansoria, earliest eutherian mammal discovered in China - April, 2002
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Earliest Known Ancestor of Placental Mammals Discovered
By John Roach
for National Geographic News
April 24, 2002

Researchers today announced the discovery of the earliest known ancestor of the group of mammals that give birth to live young.
The finding is based on a well-preserved fossil of a tiny, hairy 125-million-year-old shrewlike species that scurried about in
bushes and the low branches of trees.
"We found the earliest ancestor, perhaps a great uncle or aunt, or perhaps a great grandparent�albeit 125 million years removed�to
all placental mammals," said Zhe-Xi Luo, a paleontologist at the Carnegie Museum of Natural History in Pittsburgh, Pennsylvania.
"It is significant because a vast majority of mammals alive today are placentals." Cows, rats, monkeys, lions, tigers, and pandas are placentals. Dogs, rhinoceroses, tree sloths, horses, and whales are placentals.
And, of course, humans are placentals.
The fossil of the animal, named Eomaia scansoria, was found in the fossil-rich region of Liaoning Province in China, which has
also produced ancient evidence of feathered dinosaurs and primitive birds. Eomaia, which means "ancient mother" in Greek, was
five inches (14 centimeters) long and weighed no more than 0.9 ounces (25 grams). the discovery in the April 25 issue of Nature.
The finding indicates that the earliest extinct relatives of placentals had a much greater diversity than previously thought,
Luo said, and "tells us about the ancestral morphology from which all placentals would have descended."

Full article can be found online at
National Geographic News
Abstract from the article in Nature:
"The skeleton of a eutherian (placental) mammal has been discovered from the Lower Cretaceous Yixian Formation of northeastern
China. We estimate its age to be about 125 million years (Myr), extending the date of the oldest eutherian records by about 40�
50 Myr. Our analyses place the new fossil at the root of the eutherian tree and among the four other known Early Cretaceous
eutherians, and suggest an earlier and greater diversification of stem eutherians than previously known (the latest molecular
estimate of the diversification of extant placental orders is 104�64 Myr). The new eutherian has limb and foot features that are
known only from scansorial (climbing) and arboreal (tree-living) extant mammals, in contrast to the terrestrial or cursorial
(running) features of other Cretaceous eutherians. This suggests that the earliest eutherian lineages developed different
locomotory adaptations, facilitating their spread to diverse niches in the Cretaceous."
Full article is in Nature: pdf format
Note: Wible, Rougier and Novacek (2005) commented on Eomaia as follows: "The oldest known eutherian skull is that of Eomaia
(Ji et al., 2002) but it is badly damaged and preserved mostly as molds and impressions providing few details."
Hadrocodium wui, smallest known Mesozoic mammal,
discovered in 2001
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Researchers discover fossil of tiny mammal from Early Jurassic
Discovery provides important new evidence on the earliest evolution of mammals
Pittsburgh... An international team of researchers led by Carnegie Museum of Natural History Vertebrate Paleontologist
Dr. Zhe-Xi Luo has discovered a 195-million-year-old fossil mammal. The new mammal is the smallest known for the Mesozoic
Era and represents a new branch on the mammalian family tree.
In an article published today in the prestigious journal Science, the team of American and Chinese scientists described
this new mammal as having a precociously large brain and the middle ear of modern mammals. It suggests that these two features
may have evolved together.
Previously, these important mammalian traits could only be traced to the late Jurassic (approximately 150 million years ago).
This discovery pushes back their origins by some 45 million years to the Early Jurassic.
The new species is named Hadrocodium wui for its exceptionally large brain ([hadro] � Greek for "large and full" and
[codium] � Greek for head). The fossil has widespread implications to scientists piecing together the earliest mammalian
evolutionary history.
"Mammals differ from non-mammalian vertebrates by possessing a very large brain and an advanced ear structure," said Dr. Luo.
"It has been a challenge for scientists to trace the origins of these important mammalian features in the fossil record."
The newest addition to the mammalian family tree also happens to be the tiniest mammal known from the Mesozoic Era and
one of the smallest mammals ever. Based on the size of its well-preserved skull, it is estimated that the whole animal weighed
only two grams, less than the weight of a paper clip. With such a tiny body, its diet was likely limited to very small insects
and small worms. Its enlarged brain and very small body also tell scientists that the animal had a very high metabolism, forcing
it to continuously eat.
Co-existing with the extremely small Hadrocodium in the Early Jurassic were several other primitive mammals with much larger
body size. "This tiny creature greatly stretches the range of body size for the earliest known mammals," added Dr. Luo.
Hadrocodium is a distant and extinct relative of living mammals such as the platypus, kangaroos and primates. It is more
closely related to mammals that exist today than the primitive cynodonts or "mammal-like reptiles."
Hadrocodium was discovered in the famous Lufeng Basin in Yunnan Province, southwestern China. It is one of the most prolific
sites for early Jurassic land vertebrates. The Mesozoic Redbeds of the Lufeng Basin have yielded many vertebrate fossils.
Among the fossils that have been unearthed are the carnivorous dinosaur Dilosphosaurus, the prosauropod Lufengosaurus, crocodiles,
and lizard-like animals, herbivorous mammal-like reptiles, and some of the earliest mammals ever discovered.
Dr. Luo's research team includes Alfred W. Crompton of Harvard University and Ai-Lin Sun of the Chinese Academy of Sciences.
Funding for this research was provided by the National Science Foundation, National Geographic Society, Carnegie Museum of
Natural History's Putnam Funds and Museum of Comparative Zoology at Harvard University.
(Text and illustrations courtesy Carnegie Museum News)
Left: Reconstruction of Hadroconium wui. Right: Dr. Zhe-Xi Luo is holding up the tiny skull of Hadrocodium
for a close look.
Sea-going sloths from Peru
announced May, 1995
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(Above) The skull of Thalassocnus yaucensis, the youngest species of the aquatic sloth. (Journal of Vertebrate Paleontology)
Image used by permission of the artist, Bill Parsons
"GROUND sloths (Gravigrada, Xenarthra) are known from middle or late Oligocene to late Pleistocene in South America
and from late Miocene to late Pleistocene in North America. They are medium to gigantic in size and have terrestrial
habits. Discovery of abundant and well preserved remains of a new sloth (Thalassocnus natans), in marine Pliocene
deposits from Peru drastically expands our knowledge of the range of adaptation of the order. The abundance of
individuals, the absence of other land mammals in the rich marine vertebrate fauna of the site, and the fact
that the Peruvian coast was a desert during the Pliocene suggest that it was living on the shore and entered the
water probably to feed upon sea-grasses or seaweeds. The morphology of premaxillae, femur, caudal vertebrae
(similar to those of otters and beavers) and limb proportions are in agreement with this interpretation." [Nature 375, 224 - 227
(18 May 1995)]
The research was reported by C. de Muizon and H. Greg McDonald in
Nature.
In 2004, de Muizon, McDonald, Salas and Urbina reported on the evolution of the feeding strategy of the sloths:
"The aquatic sloth Thalassocnus is represented by five species that lived along the coast of Peru from the late Miocene
through the late Pliocene. A detailed comparison of the cranial and mandibular anatomy of these species indicates different
feeding adaptations. The three older species of Thalassocnus (T. antiquus, T. natans, and T. littoralis)
were probably partial grazers (intermediate or mixed feeders) and the transverse component of mandibular movement was very minor, if any.
They were probably feeding partially on stranded sea weeds or sea grasses, or in very shallow waters (less than 1 m) as
indicated by the abundant dental striae of their molariform teeth created by ingestion of sand. The two younger species
(T. carolomartini and T. yaucensis) were more specialized grazers than the three older species and had a distinct
transverse component in their mandibular movement. Their teeth almost totally lack dental striae. These two species were probably
feeding exclusively in the water at a greater depth than the older species."
[Journal of Vertebrate Paleontology: Vol. 24, No. 2, pp. 398�410.
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