Dinosaur Institute

Los Angeles, CA, United States

Dinosaur Institute

Los Angeles, CA, United States

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O'Connor J.K.,University of Southern California | O'Connor J.K.,Dinosaur Institute | Gao K.-Q.,Peking University | Chiappe L.M.,Dinosaur Institute
Journal of Vertebrate Paleontology | Year: 2010

Basal Ornithuromorpha, until recently, was one of the most poorly documented segments of early avian evolution. The known species diversity of the ornithuromorph clade has increased rapidly with the addition of new discoveries from the Early Cretaceous deposits of northeastern China. Reported in this paper is the discovery of a new bird from the Lower Cretaceous Yixian Formation, Liaoning Province, China. The specimen represents a new species, Longicrusavis houi, but bears similarities to Hongshanornis longicresta from the same formation of Inner Mongolia. The two birds are comparable in size and share an unusual sigmoid mandible and elongate hindlimbs relative to their forelimbs. Together these taxa represent a clade (Hongshanornithidae, new taxon) of specialized 'shorebirds' whose elongate hindlimbs indicate ecological adaptations different from those of other Jehol ornithuromorphs. Phylogenetic relationships of Mesozoic birds are discussed based on the results of a comprehensive cladistic analysis. New morphological information on Ornithuromorpha is provided through the detailed description of the new taxon together with new information on Hongshanornis. © 2010 by the Society of Vertebrate Paleontology.


News Article | October 30, 2015
Site: www.techtimes.com

Could a fossil specimen strengthen the link between dinosaurs and modern birds, and offer unique insight into the evolution of the awe-inspiring extinct creatures? An undergraduate paleontology student from the University of Alberta in Canada discovered and led the study of an Ornithomimus dinosaur showcasing preserved tail feathers and soft tissue, making groundbreaking discovery on the species’ evolutionary adaptation. According to Aaron van der Reest, who was tasked to lead the research since the fossil’s discovery in Dinosaur Provincial Park in 2009, theirs is the first analysis of preserved skin that forms a web from the femoral shaft to the abdomen — something not yet witnessed previously in non-avian dinosaurs. “We now know what the plumage looked like on the tail, and that from the mid-femur down, it had bare skin,” he said. The plumage of the fossil is identical to that of ostriches, which use bare skin for thermoregulation. “We can infer that Ornithomimus was likely doing the same thing,” van der Reest said, referring to the extinct creatures using feathered regions on their body in order to maintain body temperature. Dinosaurs classified as ornithomimids are, in fact, typically called “ostrich mimics.” The research used scanning electron microscopy to address the extremely crushed condition of the preserved feathers. The scan revealed a 3D keratin structure to the tail’ and body’s feathers. The specimen is one of just three feathered Ornithomimus specimens on Earth and offers a glimpse of their evolution to various environments. The findings are deemed useful in forecasting the future adaptation of animals to survive ecological conditions. The paper’s second author, Alex Wolfe, confirmed that their research strengthens the link between dinosaurs and birds, specifically in relation to theropods. He cited the specimen’s morphological parts and the feathers’ chemistry as “indistinguishable” features from modern birds, which were thought to have evolved from a different dinosaur group. According to Luis Chiappe, director of the Dinosaur Institute at Los Angeles’ Natural History Museum, the new findings are important in that they offer details, for instance, on pigmentation that would dictate feather color. He argued, however, that one fossil will not hold all the answers and would make further studies necessary. “It’s about putting together all the pieces,” Chiappe said. Van der Reest, who is now 34 years old and has 10 years of experience with dinosaur fossils, said he will continue to work on the research, adding that he has dreamed of working on such massive fossil find since he was a young boy growing up in Ontario.


News Article | February 14, 2017
Site: www.csmonitor.com

—Live birth: Most mammals do it, some lizards and snakes do it, but archosaurs – a reptilian group that includes crocodiles and birds – don't... or so biologists thought. When a long-necked, marine archosauromorph died some 245 million years ago in what is now China, she was pregnant, according to a paper published Tuesday in the journal Nature Communications. And now paleontologists are hailing this fossil as evidence that archosaurs might not have always been strict egg-layers. "We commonly think of these aspects of animal biology as static or 'fixed' throughout evolutionary time, and cases like this demonstrate just how labile the evolution of animal form and biology can be," Dr. Nathan Smith, an associate curator at the Dinosaur Institute at the Natural History Museum of Los Angeles, who was not involved in the study of this new specimen, writes in an email to The Christian Science Monitor. Egg-laying, or oviparity, is thought to be the ancestral reproductive strategy, with live birth, or viviparity, evolving later in some lineages. Viviparity isn't just the placenta-nourished embryonic development of mammals. It has also frequently evolved independently among lizards and snakes in a variety of forms, sometimes with babies hatching from eggs incubated inside their mothers. So viviparity was known in mammals and lepidosaurs (the vertebrate group including lizards and snakes), explains study co-author Michael Benton, a paleontologist at the University of Bristol in Britain. But "nobody had ever discovered, in any of the living or fossil forms, any evidence that archosaurs could adopt live birth." When the new specimen was first discovered and the researchers saw the small bones preserved within the larger animal's ribcage, they didn't want to jump to any conclusions. After all, this could have simply been this animal's last meal. As the team examined the fossil, they realized that the two animals were indeed the same species. But it still could have been a case of cannibalism, Dr. Benton says in a phone interview with the Monitor. The researchers are pretty sure that Dinocephalosaurus, as this animal is called, fed on fish because it has a small mouth and a long, thin neck, perfect for gulping down the long, slippery bodies of fish. Swallowing a chunky baby of its own species would have been quite the feat. Not only that, but the little bones didn't display any evidence of acid digestion, as would be expected for such a meal. Furthermore, what Benton says is "quite strong evidence" against cannibalism is the position of the little animal within the bigger one. The big Dinocephalosaurus likely would have had to swallow the baby head first so it went down easily, but the little animal is oriented the wrong way. Finding a little version of the bigger animal in the abdominal region "is about as close as you can get in the fossil record to direct evidence of reproductive mode," Christian Sidor, a paleobiologist at the University of Washington who was not involved in the research, says in a phone interview with the Monitor. Daniel Blackburn, a biologist at Trinity College in Hartford, Conn., whose own research has focused on viviparity in reptiles, is convinced. "Based on the state of development of the embryo and its position in the body of the adult, it almost certainly is a developing fetus," he writes in an email to the Monitor. "Given the absence of any trace of an eggshell, as well as its advanced state of development, the embryo seems unlikely to be laid as an egg. Thus, the adult specimen is almost certainly a pregnant female with a developing fetus." "Viviparity has previously been documented in only a few groups of extinct reptiles, notably ichthyosaurs, the giant mosasauroid lizards, and plesiosaurs," Dr. Blackburn says. "The authors' analysis extends live-bearing habits to an entirely new reptilian group, one in which it had not previously been suspected." That may not be entirely true, says Xiao-chun Wu, a palaeobiologist at the Canadian Museum of Nature who was not involved in the new research. In 2010, Dr. Wu and colleagues reported evidence of viviparity in a choristoderan reptile. But there has been some debate around whether the choristoderans are lepidosauromorphs or archosauromorphs, he explains. And Wu asserts that these reptiles actually belong among the archosaurs. Still, Wu says, this finding is significant because it increases the diversity of reproductive patterns among this group of reptiles. And, Dr. Sidor says, even if choristoderan reptiles are viviparous archosaurs, Dinocephalosaurus is still the oldest example of live birth in an archosauromorph, as the choristoderans lived tens of millions of years later. This pregnant Dinocephalosaurus could help corroborate a dominant idea about what makes a reptile stop laying eggs and start birthing live young: that viviparity is an adaptation necessary for reptiles to move to a fully aquatic lifestyle. "Because eggs of reptiles (and birds) cannot be laid in water, aquatic reptiles have two choices: they either must come to land to lay their eggs (like sea turtles) or they must be viviparous (like ichthyosaurs and certain sea snakes)," Blackburn explains. "Dinocephalosaurus is highly specialized for aquatic life and probably could not come onto the land to lay its eggs." "It's nice to see that we've got a pattern developing," Sidor says. According to that pattern, it fits that Dinocephalosaurus gave birth to live young. "It's nice to see that the fossil record is giving us glimpses of what we expected," he says. And, Sidor adds, "it's nice to see a fossil like this come along that reminds us that evolution has developed this feature many times, and it's not something that is particularly special to [placental and marsupial] mammals." Benton expects this discovery of live birth in archosauromorphs to open up many broad questions about why some groups have evolved to lay eggs and others give birth to live young. This might even lead to questions like why don't humans lay eggs, he says with a laugh.


News Article | February 14, 2017
Site: www.csmonitor.com

—Live birth: Most mammals do it, some lizards and snakes do it, but archosaurs – a reptilian group that includes crocodiles and birds – don't... or so biologists thought. When a long-necked, marine archosauromorph died some 245 million years ago in what is now China, she was pregnant, according to a paper published Tuesday in the journal Nature Communications. And now paleontologists are hailing this fossil as evidence that archosaurs might not have always been strict egg-layers. "We commonly think of these aspects of animal biology as static or 'fixed' throughout evolutionary time, and cases like this demonstrate just how labile the evolution of animal form and biology can be," Dr. Nathan Smith, an associate curator at the Dinosaur Institute at the Natural History Museum of Los Angeles, who was not involved in the study of this new specimen, writes in an email to The Christian Science Monitor. Egg-laying, or oviparity, is thought to be the ancestral reproductive strategy, with live birth, or viviparity, evolving later in some lineages. Viviparity isn't just the placenta-nourished embryonic development of mammals. It has also frequently evolved independently among lizards and snakes in a variety of forms, sometimes with babies hatching from eggs incubated inside their mothers. So viviparity was known in mammals and lepidosaurs (the vertebrate group including lizards and snakes), explains study co-author Michael Benton, a paleontologist at the University of Bristol in Britain. But "nobody had ever discovered, in any of the living or fossil forms, any evidence that archosaurs could adopt live birth." When the new specimen was first discovered and the researchers saw the small bones preserved within the larger animal's ribcage, they didn't want to jump to any conclusions. After all, this could have simply been this animal's last meal. As the team examined the fossil, they realized that the two animals were indeed the same species. But it still could have been a case of cannibalism, Dr. Benton says in a phone interview with the Monitor. The researchers are pretty sure that Dinocephalosaurus, as this animal is called, fed on fish because it has a small mouth and a long, thin neck, perfect for gulping down the long, slippery bodies of fish. Swallowing a chunky baby of its own species would have been quite the feat. Not only that, but the little bones didn't display any evidence of acid digestion, as would be expected for such a meal. Furthermore, what Benton says is "quite strong evidence" against cannibalism is the position of the little animal within the bigger one. The big Dinocephalosaurus likely would have had to swallow the baby head first so it went down easily, but the little animal is oriented the wrong way. Finding a little version of the bigger animal in the abdominal region "is about as close as you can get in the fossil record to direct evidence of reproductive mode," Christian Sidor, a paleobiologist at the University of Washington who was not involved in the research, says in a phone interview with the Monitor. Daniel Blackburn, a biologist at Trinity College in Hartford, Conn., whose own research has focused on viviparity in reptiles, is convinced. "Based on the state of development of the embryo and its position in the body of the adult, it almost certainly is a developing fetus," he writes in an email to the Monitor. "Given the absence of any trace of an eggshell, as well as its advanced state of development, the embryo seems unlikely to be laid as an egg. Thus, the adult specimen is almost certainly a pregnant female with a developing fetus." "Viviparity has previously been documented in only a few groups of extinct reptiles, notably ichthyosaurs, the giant mosasauroid lizards, and plesiosaurs," Dr. Blackburn says. "The authors' analysis extends live-bearing habits to an entirely new reptilian group, one in which it had not previously been suspected." That may not be entirely true, says Xiao-chun Wu, a palaeobiologist at the Canadian Museum of Nature who was not involved in the new research. In 2010, Dr. Wu and colleagues reported evidence of viviparity in a choristoderan reptile. But there has been some debate around whether the choristoderans are lepidosauromorphs or archosauromorphs, he explains. And Wu asserts that these reptiles actually belong among the archosaurs. Still, Wu says, this finding is significant because it increases the diversity of reproductive patterns among this group of reptiles. And, Dr. Sidor says, even if choristoderan reptiles are viviparous archosaurs, Dinocephalosaurus is still the oldest example of live birth in an archosauromorph, as the choristoderans lived tens of millions of years later. This pregnant Dinocephalosaurus could help corroborate a dominant idea about what makes a reptile stop laying eggs and start birthing live young: that viviparity is an adaptation necessary for reptiles to move to a fully aquatic lifestyle. "Because eggs of reptiles (and birds) cannot be laid in water, aquatic reptiles have two choices: they either must come to land to lay their eggs (like sea turtles) or they must be viviparous (like ichthyosaurs and certain sea snakes)," Blackburn explains. "Dinocephalosaurus is highly specialized for aquatic life and probably could not come onto the land to lay its eggs." "It's nice to see that we've got a pattern developing," Sidor says. According to that pattern, it fits that Dinocephalosaurus gave birth to live young. "It's nice to see that the fossil record is giving us glimpses of what we expected," he says. And, Sidor adds, "it's nice to see a fossil like this come along that reminds us that evolution has developed this feature many times, and it's not something that is particularly special to [placental and marsupial] mammals." Benton expects this discovery of live birth in archosauromorphs to open up many broad questions about why some groups have evolved to lay eggs and others give birth to live young. This might even lead to questions like why don't humans lay eggs, he says with a laugh.


News Article | February 14, 2017
Site: www.csmonitor.com

—Live birth: Most mammals do it, some lizards and snakes do it, but archosaurs – a reptilian group that includes crocodiles and birds – don't... or so biologists thought. When a long-necked, marine archosauromorph died some 245 million years ago in what is now China, she was pregnant, according to a paper published Tuesday in the journal Nature Communications. And now paleontologists are hailing this fossil as evidence that archosaurs might not have always been strict egg-layers. "We commonly think of these aspects of animal biology as static or 'fixed' throughout evolutionary time, and cases like this demonstrate just how labile the evolution of animal form and biology can be," Dr. Nathan Smith, an associate curator at the Dinosaur Institute at the Natural History Museum of Los Angeles, who was not involved in the study of this new specimen, writes in an email to The Christian Science Monitor. Egg-laying, or oviparity, is thought to be the ancestral reproductive strategy, with live birth, or viviparity, evolving later in some lineages. Viviparity isn't just the placenta-nourished embryonic development of mammals. It has also frequently evolved independently among lizards and snakes in a variety of forms, sometimes with babies hatching from eggs incubated inside their mothers. So viviparity was known in mammals and lepidosaurs (the vertebrate group including lizards and snakes), explains study co-author Michael Benton, a paleontologist at the University of Bristol in Britain. But "nobody had ever discovered, in any of the living or fossil forms, any evidence that archosaurs could adopt live birth." When the new specimen was first discovered and the researchers saw the small bones preserved within the larger animal's ribcage, they didn't want to jump to any conclusions. After all, this could have simply been this animal's last meal. As the team examined the fossil, they realized that the two animals were indeed the same species. But it still could have been a case of cannibalism, Dr. Benton says in a phone interview with the Monitor. The researchers are pretty sure that Dinocephalosaurus, as this animal is called, fed on fish because it has a small mouth and a long, thin neck, perfect for gulping down the long, slippery bodies of fish. Swallowing a chunky baby of its own species would have been quite the feat. Not only that, but the little bones didn't display any evidence of acid digestion, as would be expected for such a meal. Furthermore, what Benton says is "quite strong evidence" against cannibalism is the position of the little animal within the bigger one. The big Dinocephalosaurus likely would have had to swallow the baby head first so it went down easily, but the little animal is oriented the wrong way. Finding a little version of the bigger animal in the abdominal region "is about as close as you can get in the fossil record to direct evidence of reproductive mode," Christian Sidor, a paleobiologist at the University of Washington who was not involved in the research, says in a phone interview with the Monitor. Daniel Blackburn, a biologist at Trinity College in Hartford, Conn., whose own research has focused on viviparity in reptiles, is convinced. "Based on the state of development of the embryo and its position in the body of the adult, it almost certainly is a developing fetus," he writes in an email to the Monitor. "Given the absence of any trace of an eggshell, as well as its advanced state of development, the embryo seems unlikely to be laid as an egg. Thus, the adult specimen is almost certainly a pregnant female with a developing fetus." "Viviparity has previously been documented in only a few groups of extinct reptiles, notably ichthyosaurs, the giant mosasauroid lizards, and plesiosaurs," Dr. Blackburn says. "The authors' analysis extends live-bearing habits to an entirely new reptilian group, one in which it had not previously been suspected." That may not be entirely true, says Xiao-chun Wu, a palaeobiologist at the Canadian Museum of Nature who was not involved in the new research. In 2010, Dr. Wu and colleagues reported evidence of viviparity in a choristoderan reptile. But there has been some debate around whether the choristoderans are lepidosauromorphs or archosauromorphs, he explains. And Wu asserts that these reptiles actually belong among the archosaurs. Still, Wu says, this finding is significant because it increases the diversity of reproductive patterns among this group of reptiles. And, Dr. Sidor says, even if choristoderan reptiles are viviparous archosaurs, Dinocephalosaurus is still the oldest example of live birth in an archosauromorph, as the choristoderans lived tens of millions of years later. This pregnant Dinocephalosaurus could help corroborate a dominant idea about what makes a reptile stop laying eggs and start birthing live young: that viviparity is an adaptation necessary for reptiles to move to a fully aquatic lifestyle. "Because eggs of reptiles (and birds) cannot be laid in water, aquatic reptiles have two choices: they either must come to land to lay their eggs (like sea turtles) or they must be viviparous (like ichthyosaurs and certain sea snakes)," Blackburn explains. "Dinocephalosaurus is highly specialized for aquatic life and probably could not come onto the land to lay its eggs." "It's nice to see that we've got a pattern developing," Sidor says. According to that pattern, it fits that Dinocephalosaurus gave birth to live young. "It's nice to see that the fossil record is giving us glimpses of what we expected," he says. And, Sidor adds, "it's nice to see a fossil like this come along that reminds us that evolution has developed this feature many times, and it's not something that is particularly special to [placental and marsupial] mammals." Benton expects this discovery of live birth in archosauromorphs to open up many broad questions about why some groups have evolved to lay eggs and others give birth to live young. This might even lead to questions like why don't humans lay eggs, he says with a laugh.


News Article | February 14, 2017
Site: www.csmonitor.com

—Live birth: Most mammals do it, some lizards and snakes do it, but archosaurs – a reptilian group that includes crocodiles and birds – don't... or so biologists thought. When a long-necked, marine archosauromorph died some 245 million years ago in what is now China, she was pregnant, according to a paper published Tuesday in the journal Nature Communications. And now paleontologists are hailing this fossil as evidence that archosaurs might not have always been strict egg-layers. "We commonly think of these aspects of animal biology as static or 'fixed' throughout evolutionary time, and cases like this demonstrate just how labile the evolution of animal form and biology can be," Dr. Nathan Smith, an associate curator at the Dinosaur Institute at the Natural History Museum of Los Angeles, who was not involved in the study of this new specimen, writes in an email to The Christian Science Monitor. Egg-laying, or oviparity, is thought to be the ancestral reproductive strategy, with live birth, or viviparity, evolving later in some lineages. Viviparity isn't just the placenta-nourished embryonic development of mammals. It has also frequently evolved independently among lizards and snakes in a variety of forms, sometimes with babies hatching from eggs incubated inside their mothers. So viviparity was known in mammals and lepidosaurs (the vertebrate group including lizards and snakes), explains study co-author Michael Benton, a paleontologist at the University of Bristol in Britain. But "nobody had ever discovered, in any of the living or fossil forms, any evidence that archosaurs could adopt live birth." When the new specimen was first discovered and the researchers saw the small bones preserved within the larger animal's ribcage, they didn't want to jump to any conclusions. After all, this could have simply been this animal's last meal. As the team examined the fossil, they realized that the two animals were indeed the same species. But it still could have been a case of cannibalism, Dr. Benton says in a phone interview with the Monitor. The researchers are pretty sure that Dinocephalosaurus, as this animal is called, fed on fish because it has a small mouth and a long, thin neck, perfect for gulping down the long, slippery bodies of fish. Swallowing a chunky baby of its own species would have been quite the feat. Not only that, but the little bones didn't display any evidence of acid digestion, as would be expected for such a meal. Furthermore, what Benton says is "quite strong evidence" against cannibalism is the position of the little animal within the bigger one. The big Dinocephalosaurus likely would have had to swallow the baby head first so it went down easily, but the little animal is oriented the wrong way. Finding a little version of the bigger animal in the abdominal region "is about as close as you can get in the fossil record to direct evidence of reproductive mode," Christian Sidor, a paleobiologist at the University of Washington who was not involved in the research, says in a phone interview with the Monitor. Daniel Blackburn, a biologist at Trinity College in Hartford, Conn., whose own research has focused on viviparity in reptiles, is convinced. "Based on the state of development of the embryo and its position in the body of the adult, it almost certainly is a developing fetus," he writes in an email to the Monitor. "Given the absence of any trace of an eggshell, as well as its advanced state of development, the embryo seems unlikely to be laid as an egg. Thus, the adult specimen is almost certainly a pregnant female with a developing fetus." "Viviparity has previously been documented in only a few groups of extinct reptiles, notably ichthyosaurs, the giant mosasauroid lizards, and plesiosaurs," Dr. Blackburn says. "The authors' analysis extends live-bearing habits to an entirely new reptilian group, one in which it had not previously been suspected." That may not be entirely true, says Xiao-chun Wu, a palaeobiologist at the Canadian Museum of Nature who was not involved in the new research. In 2010, Dr. Wu and colleagues reported evidence of viviparity in a choristoderan reptile. But there has been some debate around whether the choristoderans are lepidosauromorphs or archosauromorphs, he explains. And Wu asserts that these reptiles actually belong among the archosaurs. Still, Wu says, this finding is significant because it increases the diversity of reproductive patterns among this group of reptiles. And, Dr. Sidor says, even if choristoderan reptiles are viviparous archosaurs, Dinocephalosaurus is still the oldest example of live birth in an archosauromorph, as the choristoderans lived tens of millions of years later. This pregnant Dinocephalosaurus could help corroborate a dominant idea about what makes a reptile stop laying eggs and start birthing live young: that viviparity is an adaptation necessary for reptiles to move to a fully aquatic lifestyle. "Because eggs of reptiles (and birds) cannot be laid in water, aquatic reptiles have two choices: they either must come to land to lay their eggs (like sea turtles) or they must be viviparous (like ichthyosaurs and certain sea snakes)," Blackburn explains. "Dinocephalosaurus is highly specialized for aquatic life and probably could not come onto the land to lay its eggs." "It's nice to see that we've got a pattern developing," Sidor says. According to that pattern, it fits that Dinocephalosaurus gave birth to live young. "It's nice to see that the fossil record is giving us glimpses of what we expected," he says. And, Sidor adds, "it's nice to see a fossil like this come along that reminds us that evolution has developed this feature many times, and it's not something that is particularly special to [placental and marsupial] mammals." Benton expects this discovery of live birth in archosauromorphs to open up many broad questions about why some groups have evolved to lay eggs and others give birth to live young. This might even lead to questions like why don't humans lay eggs, he says with a laugh.


The Smoky Hill Member of the Niobrara Chalk in Kansas (USA) has yielded the remains of numerous members of the Hesperornithiformes, toothed diving birds from the late Early to Late Cretaceous. This study presents a new taxon of hesperornithiform from the Smoky Hill Member, Fumicollis hoffmani, the holotype of which is among the more complete hesperornithiform skeletons. Fumicollis has a unique combination of primitive (e.g. proximal and distal ends of femur not expanded, elongate pre-acetabular ilium, small and pyramidal patella) and derived (e.g. dorsal ridge on metatarsal IV, plantarly-projected curve in the distal shaft of phalanx III:1) hesperornithiform characters, suggesting it was more specialized than small hesperornithiforms like Baptornis advenus but not as highly derived as the larger Hesperornis regalis. The identification of Fumicollis highlights once again the significant diversity of hesperornithiforms that existed in the Late Cretaceous Western Interior Seaway. This diversity points to the existence of a complex ecosystem, perhaps with a high degree of niche partitioning, as indicated by the varying degrees of diving specializations among these birds. © 2015 Bell, Chiappe. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.


Chiappe L.M.,Dinosaur Institute | Gohlich U.B.,Naturhistorisches Museum Wien
Neues Jahrbuch fur Geologie und Palaontologie - Abhandlungen | Year: 2010

We provide a detailed study of the morphology of the holotype of Juravenator starki from the Late Jurassic of the Solnhofen area of southern Germany. The incompletely ossified surface of multiple bones and lack of several skeletal fusions indicate that Juravenator starki is based on an immature specimen. Nonetheless, numerous unique morphologies and bone proportions distinguish this taxon from Compsognathus longipes, the only previously named non-avian theropod dinosaur from the Late Jurassic of the Solnhofen Archipelago. Yet, its skeletal anatomy is most similar to that of Compsognathus and other theropods that have often been regarded as closely related to the latter sometimes within a monophyletic Compsognathidae. Juravenator is characterized by having a small size (~ 0.75-meter-long in the holotype) with few maxillary teeth, lack of a premaxillary-maxillary diastema, an antorbital fenestra subequal in length to orbit, an elongate scapula that is narrowest at its neck, a proportionally short humerus and high and abruptly tapered manual claws, and bowlike zygapophysial articulations in the mid-caudal vertebrae. Portions of the epidermis preserved mainly along the tail provide the only glimpse of the morphology of the skin of basal coelurosaurs, and structures newly revealed under UV light hint at the possibility of filamentous integumentary structures - akin to those interpreted as proto-feathers in other basal coelurosaurs - also covering the body of this dinosaur. The discovery of Juravenator has provided evidence of morphologies - from details of the skull to the epidermis - that are poorly known in other theropods interpreted as at or near the base of Coelurosauria, and thus contributes significantly to our understanding of the evolutionary history of this clade. The exquisitely preserved holotipic skeleton adds significantly to the meager record of small-bodied Late Jurassic theropods. © 2010 E. Schweizerbart'sche Verlagsbuchhandlung, Stuttgart, Germany.


Brocklehurst N.,Leibniz Institute For Evolutions Und Biodiversitatsforschung | Upchurch P.,University College London | Mannion P.D.,Leibniz Institute For Evolutions Und Biodiversitatsforschung | Mannion P.D.,Imperial College London | And 2 more authors.
PLoS ONE | Year: 2012

Many palaeobiological analyses have concluded that modern birds (Neornithes) radiated no earlier than the Maastrichtian, whereas molecular clock studies have argued for a much earlier origination. Here, we assess the quality of the fossil record of Mesozoic avian species, using a recently proposed character completeness metric which calculates the percentage of phylogenetic characters that can be scored for each taxon. Estimates of fossil record quality are plotted against geological time and compared to estimates of species level diversity, sea level, and depositional environment. Geographical controls on the avian fossil record are investigated by comparing the completeness scores of species in different continental regions and latitudinal bins. Avian fossil record quality varies greatly with peaks during the Tithonian-early Berriasian, Aptian, and Coniacian-Santonian, and troughs during the Albian-Turonian and the Maastrichtian. The completeness metric correlates more strongly with a 'sampling corrected' residual diversity curve of avian species than with the raw taxic diversity curve, suggesting that the abundance and diversity of birds might influence the probability of high quality specimens being preserved. There is no correlation between avian completeness and sea level, the number of fluviolacustrine localities or a recently constructed character completeness metric of sauropodomorph dinosaurs. Comparisons between the completeness of Mesozoic birds and sauropodomorphs suggest that small delicate vertebrate skeletons are more easily destroyed by taphonomic processes, but more easily preserved whole. Lagerstätten deposits might therefore have a stronger impact on reconstructions of diversity of smaller organisms relative to more robust forms. The relatively poor quality of the avian fossil record in the Late Cretaceous combined with very patchy regional sampling means that it is possible neornithine lineages were present throughout this interval but have not yet been sampled or are difficult to identify because of the fragmentary nature of the specimens. © 2012 Brocklehurst et al.


Bell A.,Dinosaur Institute | Chiappe L.M.,Dinosaur Institute
Journal of Systematic Palaeontology | Year: 2015

Despite extensive discoveries across the globe over the past two centuries, little phylogenetic work has been done on the Hesperornithiformes. Spanning the late Early to Late Cretaceous, hesperornithiforms are one of the most diverse groups of Mesozoic birds in terms of both their geographical distribution and the wide differences in body size and diving specializations. This study presents the first phylogenetic analysis of the Hesperornithiformes that includes a majority of the described taxa, enabling the first detailed look at evolutionary relationships within the clade. The results of this study support the monophyly of the Hesperornithiformes, which is recovered as the sister clade to the avian crown group, Neornithes. Within the Hesperornithiformes, the Brodavidae and Hesperornithidae are monophyletic while the Baptornithidae are polyphyletic. Little evidence of species-level taxonomic differentiation is found within Hesperornis, with many species indistinguishable from Hesperornis regalis. Evolution within the Hesperornithiformes provides a fascinating example of progressive development of specialized diving adaptations in birds. The acquisition of these diving specializations appears to be uncorrelated to the independent evolution of multiple large increases in body size. © The Trustees of the Natural History Museum, London 2015. All Rights Reserved.

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