How Birds got Their Wings

Did the Permian Extinction Trigger a Shrinkage of Red Blood Cells in the Ancestors of Dinosaurs and Mammals?

Many mammals and birds are remarkable athletes; mice work hard to dig burrows for protection and sparrows fight gravity with each flap of their wings. In order to have the energy to sustain vigorous exercise, the body's tissues need a steady supply of oxygen, and red blood cells (RBCs) are the center of the oxygen delivery system. Size matters, too; athletic mammals and birds have much smaller RBCs than other vertebrates with lesser capacities for exercise. Biologists have long been puzzled over the evolutionary origins of RBC size. Were predecessors of mammals and birds -- including dinosaurs -- athletes and did they have tiny red blood cells? How do you measure the blood of extinct animals?

Now, biologists at the University of Utah and the Natural History Museum of Utah have established a 'fossilizable' indicator of athleticism in the bones of extinct vertebrates.

The study, which published online in Current Biology on Dec. 22, is the first to draw a link between RBC size and the microscopic traces of blood vessels and bone cells inside the bone. The researchers measured the bony channels that deliver oxygen to bone tissue to pinpoint when our mammal ancestors, bird and dinosaur predecessors evolved small RBCs. They found that extinct mammal relatives, or cynodonts, and extinct bird relatives had smaller RBCs and were likely better athletes than earlier terrestrial vertebrates. The timing of RBC-size reduction coincided with the greatest mass extinction event on Earth 252 million years ago, an event that paved the way for the age of the dinosaurs.

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Nasutoceratopsini Ceratopsian From Campanian Cretaceous Alberta, Canada

A basal ceratopsid (Centrosaurinae: Nasutoceratopsini) from the Oldman Formation (Campanian) of Alberta, Canada

Authors:

Ryan et al

Abstract:

A partial skull (CMN 8804) of a ceratopsid from the upper unit of the Campanian Oldman Formation of Alberta is the first Canadian example of the newly established Nasutoceratopsini, a new subclade of Centrosaurinae defined as the stem-based clade of centrosaurine ceratopsids more closely related to Nasutoceratops titusi than to Centrosaurus apertus. The new clade is diagnosed, in part, by having a parietosquamosal frill lacking modified epimarginals; a small nasal horncore; large, rostrolaterally directed postorbital horncores; and a relatively short, deep face. Although the CMN 8804 taxon closely resembles Nasutoceratops, its phylogenetic position within Nasutoceratopsini is unresolved. The CMN 8804 taxon would have been contemporaneous with dinosaurs from the lower portion of the Dinosaur Park Formation 200 km to the northwest in Dinosaur Provincial Park. The presence of the CMN 8804 taxon in Alberta, and the approximately contemporaneous Nasutoceratops in Utah, indicates that the nasutoceratopsins persisted in both north and south Laramidia well after the first appearance (i.e., Coronosaurus brinkmani) of the newly defined Centrosaurini. This stem-based clade is composed of centrosaurine ceratopsids with well-adorned parietosquamosal frills and short postorbital horncores that are more closely related to Centrosaurus apertus than Pachyrhinosaurus canadensis. The rarity of nasutoceratopsins in the well-sampled sediments of Laramidia suggests that they may have had different ecological preferences than centrosaurins, or that their relatively non-diagnostic, fragmentary remains may be misidentified as other centrosaurins. The temporally (∼79–76 Ma) and geographically (Utah to Alberta) large distributions of Nasutoceratopsini weakens the hypothesis of distinct north and south Laramidian provinciality.

A FEATHERED Dinosaur Tail Found Trapped in Amber From Cenomanian Cretaceous Myanmar

A Feathered Dinosaur Tail with Primitive Plumage Trapped in Mid-Cretaceous Amber

Authors:

Xi et al

Abstract:

In the two decades since the discovery of feathered dinosaurs, the range of plumage known from non-avialan theropods has expanded significantly, confirming several features predicted by developmentally informed models of feather evolution. However, three-dimensional feather morphology and evolutionary patterns remain difficult to interpret, due to compression in sedimentary rocks. Recent discoveries in Cretaceous amber from Canada, France, Japan, Lebanon, Myanmar, and the United States reveal much finer levels of structural detail, but taxonomic placement is uncertain because plumage is rarely associated with identifiable skeletal material. Here we describe the feathered tail of a non-avialan theropod preserved in mid-Cretaceous (∼99 Ma) amber from Kachin State, Myanmar, with plumage structure that directly informs the evolutionary developmental pathway of feathers. This specimen provides an opportunity to document pristine feathers in direct association with a putative juvenile coelurosaur, preserving fine morphological details, including the spatial arrangement of follicles and feathers on the body, and micrometer-scale features of the plumage. Many feathers exhibit a short, slender rachis with alternating barbs and a uniform series of contiguous barbules, supporting the developmental hypothesis that barbs already possessed barbules when they fused to form the rachis. Beneath the feathers, carbonized soft tissues offer a glimpse of preservational potential and history for the inclusion; abundant Fe2+ suggests that vestiges of primary hemoglobin and ferritin remain trapped within the tail. The new finding highlights the unique preservation potential of amber for understanding the morphology and evolution of coelurosaurian integumentary structures.

Early Dinosaurs (and Relatives) had Highly Variable Growth Rates

Look out your window, and you may see people of all ages and sizes roaming the street: a 6-foot-5-inch man walking beside a 4-foot-6-inch boy, for example, or a sprouting teen-ager who is much taller than a full-grown adult.

Virginia Tech geoscientists Christopher Griffin and Sterling Nesbitt discovered that this sort of variation in growth patterns in people despite their ages also occurred among early dinosaurs, and may have provided an advantage in surviving the harsh environment at the end of the Triassic Period approximately 201 million to 210 million years ago.

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A New Dinosauromorph & Carnivorous Sauropod Ancestor Fossils Discovered in Norian/Rhaetian Triassic Brazil

A Unique Late Triassic Dinosauromorph Assemblage Reveals Dinosaur Ancestral Anatomy and Diet

Authors:

Cabreira et al

Abstract:

Dinosauromorpha includes dinosaurs and other much less diverse dinosaur precursors of Triassic age, such as lagerpetids [1]. Joint occurrences of these taxa with dinosaurs are rare but more common during the latest part of that period (Norian-Rhaetian, 228–201 million years ago [mya]) [2, 3]. In contrast, the new lagerpetid and saurischian dinosaur described here were unearthed from one of the oldest rock units with dinosaur fossils worldwide, the Carnian (237–228 mya) Santa Maria Formation of south Brazil [4], a record only matched in age by much more fragmentary remains from Argentina [5]. This is the first time nearly complete dinosaur and non-dinosaur dinosauromorph remains are found together in the same excavation, clearly showing that these animals were contemporaries since the first stages of dinosaur evolution. The new lagerpetid preserves the first skull, scapular and forelimb elements, plus associated vertebrae, known for the group, revealing how dinosaurs acquired several of their typical anatomical traits. Furthermore, a novel phylogenetic analysis shows the new dinosaur as the most basal Sauropodomorpha. Its plesiomorphic teeth, strictly adapted to faunivory, provide crucial data to infer the feeding behavior of the first dinosaurs.

A Fossilized Dinosaur Brain was Found

An unassuming brown pebble, found more than a decade ago by a fossil hunter in Sussex, has been confirmed as the first example of fossilised brain tissue from a dinosaur.

The fossil, most likely from a species closely related to Iguanodon, displays distinct similarities to the brains of modern-day crocodiles and birds. Meninges - the tough tissues surrounding the actual brain - as well as tiny capillaries and portions of adjacent cortical tissues have been preserved as mineralised 'ghosts'.

The results are reported in a Special Publication of the Geological Society of London, published in tribute to Professor Martin Brasier of the University of Oxford, who died in 2014. Brasier and Dr David Norman from the University of Cambridge co-ordinated the research into this particular fossil during the years prior to Brasier's untimely death in a road traffic accident.

The fossilised brain, found by fossil hunter Jamie Hiscocks near Bexhill in Sussex in 2004, is most likely from a species similar to Iguanodon: a large herbivorous dinosaur that lived during the Early Cretaceous Period, about 133 million years ago.

Finding fossilised soft tissue, especially brain tissue, is very rare, which makes understanding the evolutionary history of such tissue difficult. "The chances of preserving brain tissue are incredibly small, so the discovery of this specimen is astonishing," said co-author Dr Alex Liu of Cambridge's Department of Earth Sciences, who was one of Brasier's PhD students in Oxford at the time that studies of the fossil began.

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Triopticus primus: a Triassic Archosauromorph Convergent With Pachycephalosaur Dinosaurs

A Dome-Headed Stem Archosaur Exemplifies Convergence among Dinosaurs and Their Distant Relatives

Authors:

Stocker et al

Abstract:

Similarities in body plan evolution, such as wings in pterosaurs, birds, and bats or limblessness in snakes and amphisbaenians, can be recognized as classical examples of convergence among animals [1, 2, 3]. We introduce a new Triassic stem archosaur that is unexpectedly and remarkably convergent with the “dome-headed” pachycephalosaur dinosaurs that lived over 100 million years later. Surprisingly, numerous additional taxa in the same assemblage (the Otis Chalk assemblage from the Dockum Group of Texas) demonstrate the early acquisition of morphological novelties that were later convergently evolved by post-Triassic dinosaurs. As one of the most successful clades of terrestrial vertebrates, dinosaurs came to occupy an extensive morphospace throughout their diversification in the Mesozoic Era [4, 5], but their distant relatives were first to evolve many of those “dinosaurian” body plans in the Triassic Period [6, 7, 8]. Our analysis of convergence between archosauromorphs from the Triassic Period and post-Triassic archosaurs demonstrates the early and extensive exploration of morphospace captured in a single Late Triassic assemblage, and we hypothesize that many of the “novel” morphotypes interpreted to occur among archosaurs later in the Mesozoic already were in place during the initial Triassic archosauromorph, largely non-dinosaurian, radiation and only later convergently evolved in diverse dinosaurian lineages.

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Structure and homology of Psittacosaurus tail bristles

Structure and homology of Psittacosaurus tail bristles

Authors:

Mayr et al

Abstract:

We examined bristle-like appendages on the tail of the Early Cretaceous basal ceratopsian dinosaur Psittacosaurus with laser-stimulated fluorescence imaging. Our study reveals previously unknown details of these structures and confirms their identification as integumentary appendages. For the first time, we show that most bristles appear to be arranged in bundles and that they exhibit a pulp that widens towards the bristle base. We consider it likely that the psittacosaur bristles are structurally and developmentally homologous to similar filamentous appendages of other dinosaurs, namely the basal heterodontosaurid Tianyulong and the basal therizinosauroid theropod Beipiaosaurus, and attribute the greater robustness of the bristles of Psittacosaurus to a higher degree of cornification and calcification of its integument (both skin and bristles). Although the psittacosaur bristles are probably homologous with avian feathers in their origin from discrete cell populations, it is uncertain whether they developed from a follicle, one of the developmental hallmarks of true feathers. In particular, we note a striking resemblance between the psittacosaur bristles and the cornified spine on the head of the horned screamer, Anhima cornuta, an extant anseriform bird. Similar, albeit thinner keratinous filaments of extant birds are the ‘beard’ of the turkey, Meleagris gallopavo, and the crown of the Congo peafowl, Afropavo congensis. All of these structures of extant birds are distinct from true feathers, and because at least the turkey beard does not develop from follicles, detailed future studies of their development would be invaluable towards deepening our understanding of dinosaur filamentous integumentary structures.

Wiehenvenator albati (aka the Monster von Minden): a new Megalosaurid Theropod From Callovian Jurassic Germany

A new megalosaurid theropod dinosaur from the late Middle Jurassic (Callovian) of north-western Germany: implications for theropod evolution and faunal turnover in the Jurassic

Authors:

Rauhut et al

Abstract:

Fragmentary remains of a large, robustly built theropod dinosaur were recovered from the marine middle Callovian Ornatenton Formation of north-eastern Northrhine-Westphalia, Germany. The specimen includes a premaxilla, maxilla, lacrimal, postorbital, dentary, several caudal vertebrae, ribs, fibulae, astragalus, and partial calcaneum. It is here described as a new species of megalosauroid, Wiehenvenator albati n. gen. n. sp., diagnosed by a strongly reduced maxillary antorbital fossa on the base of the ascending process of the maxilla, a very short anterior ramus of the lacrimal with an additional pneumatic depression anteroventral to the lacrimal fenestra, a transversely expanded orbital facet in the postorbital, and a laterally flexed proximal end of the ascending process of the astragalus. Phylogenetic analysis recovers Wiehenvenator as a megalosaurine megalosaurid, sister taxon to the Late Jurassic genus Torvosaurus. It thus adds to the considerable diversity of megalosauroids in the Middle Jurassic. A time-calibrated phylogeny of theropods indicates a rapid radiation of averostran theropods between the Toarcian and the Bathonian. This radiation was probably triggered by the Pliensbachian-Toarcian extinction event, which might have been more important for theropod evolution than the Triassic-Jurassic extinction. The fossil record indicates a faunal turnover from megalosauroid dominated Middle Jurassic to allosauroid / coelurosaur dominated Late Jurassic faunas. However, differences in the Middle and Late Jurassic theropod fossil records both in respect to geographic distribution of localities, as well as sampled environments make this inference problematic, at least in respect to allosauroids. An analysis of environmental preferences of allosauroids and megalosauroids indicates that the former preferred inland environments, whereas the latter are more common in nearshore environments.

Were There two Species of Agujaceratops in Cretaceous West Texas?

New specimens of horned dinosaurs from the Aguja Formation of West Texas, and a revision of Agujaceratops

Authors:

Lehman et al

Abstract:

Most horned dinosaur remains recovered from the Aguja Formation in West Texas are referable to the endemic chasmosaurine Agujaceratops mariscalensis. One specimen, however, differs sufficiently to justify its designation as the holotype of a new species, Agujaceratops mavericus sp. nov. This specimen and an isolated postorbital horncore from the same vicinity are stratigraphically the highest found in the Aguja Formation. A well-preserved juvenile specimen exhibits some unique features, and others compatible with A. mavericus, but due to its immature condition cannot be identified with certainty. A parietal referred to A. mariscalensis is the most complete thus far known, and shows that the frill of this taxon is more elaborately ornamented than previously believed, bearing a set of large horn-like spikes at the posterolateral corners. These two species share features of the premaxilla and squamosal, which warrant their inclusion in the same genus. However, characters thought to distinguish the two species vary in a manner similar to that found in other chasmosaurines, where debate persists as to their taxonomic significance. A consensus species concept has yet to be adopted for ceratopsid genera, of which most are monotypic. As a result, the two Agujaceratops species could be interpreted as arbitrary anagenetic stages in a single lineage, end-members in a spectrum of ontogenetic and sex-associated variation in that lineage, or two sympatric lineages that occupied separate niches in the same range.

Tracing the Origin & Evolution of Bird Reproduction in Dinosaurs

What really did come first--the chicken or the egg? Birds' reproductive biology is dramatically different from that of any other living vertebrates, and ornithologists and paleontologists have long wondered how and when the unique features of bird reproduction originated. A new Review in The Auk: Ornithological Advances examines answers from three sources--modern birds, fossils of primitive birds, and fossils of the dinosaurs from which birds are descended--to shed new light on the subject.

All modern birds share certain reproductive features, such as a single functional ovary and the practice of incubating their eggs through direct contact. Analysis of the bird family tree also suggests that early birds built simple, open nests on the ground and that their young were "precocial," meaning they were well-developed and almost ready to fend for themselves when they hatched. Those dinosaurs close to the ancestry of birds shared some of these traits, but they had two functional reproductive tracts, and their eggs were smaller relative to their body size and more elongated than those of modern birds.

Fossils of primitive birds and eggs from the Mesozoic era place them midway between their dinosaur ancestors and their modern descendants, with eggs between those of pre-avian dinosaurs and modern birds in term of size and shape. In this way, David Varricchio and Frankie Jackson of the Montana State University are able to trace the evolution of bird reproduction through a series of distinct stages, from pre-avian dinosaurs to the birds of today.

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A Giant Abelisaurus Theropod Foot Print Found in Bolivia

A footprint measuring over a metre wide has been discovered in the southern American country of Bolivia. It's thought to have been made by an Abelisaurus, a meat-eating dinosaur that walked the Earth millions of years ago. Palaeontologist Sebastian Apesteguia went to the site of the discovery.

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Were Heterodontosaurs Arboreal?

A newly described specimen of a tiny plant-eating dinosaur shows features indicating that it may have been able to climb around in branches -- an ability so far unknown in any dinosaurs except birds.

Dinosaurs were enormously successful vertebrates that dominated terrestrial ecosystems for almost the entire Mesozoic Era. The dinosaur family tree can be divided into three major branches: the theropods, mostly carnivorous bipeds (including birds); the sauropods, usually enormous long-necked herbivores; and the ornithischians, an incredibly diverse assemblage of beaked herbivores. Commonly known onithischians include (but are not limited to) armored dinosaurs, horned dinosaurs, bone-headed dinosaurs, and duck-bills. One of the earliest groups of ornithischians to appear in the fossil record are the heterodontosaurids, small bipeds recognizable by the long tusk-like teeth in their upper and lower beaks. Heterodontosaurids are known from the Upper Triassic to the Lower Cretaceous rocks in Africa, Asia, Europe, and North and South America and include the namesake Heterodontosaurus from the Early Jurassic of South Africa as well as the famous filament-covered Tianyulong from the Early Cretaceous of China.


In June, researchers described a new specimen of a heterodontosaurid found in Lower Jurassic rocks from Argentina dated to about 180 million years ago. The specimen, which consists of portions of the left and right foot, several toe bones, and some tail vertebrae comes from the Cañadón Asfalto Formation in near the town of Cerro Condor, Chubut Province. The authors think it’s likely that the remains belong to Manidens condorensis, a pigeon-sized heterodontosaurid found from the same location. Unfortunately the only known specimen of Manidens lacks its feet, so there are no overlapping parts that would make the assignment definitive.

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Cenozoic Theropod Dinosaurs in South America Revisited

Cenozoic dinosaurs in South America – revisited

Authors:

Molnar et al

Abstract:

Of course there were Cenozoic dinosaurs (theropods) in South America, phorusrhacid (‘terror’) birds among others, but that is not the subject here. Why did anyone think there were Cenozoic (non-avian) theropods in South America? Because of a misinterpretation of Ameghino’s belief that derived mammals lived along with dinosaurs in Late Cretaceous Argentina. But also because isolated theropod teeth were found associated with derived (Eocene) mammal fossils. These turned out to be the teeth of Sebecus icaeorhinus. This is a small crocodylomorph, skull length c. 450 mm. More recently discovered sebecosuchians were substantially larger: Barinasuchus arveloi had an (estimated) skull length of c. 1000 mm, similar to that of Daspletosaurus (1000 mm). These crocodylomorphs are generally believed to have been terrestrial animals, presumably preying on large mammals. Thus, although there were no large non-avian theropods in Cenozoic South America, there were crocodylomorphs that seem to have been ecological vicars of large theropods. The reconstruction of terrestrial trophic networks for large terrestrial tetrapods after the Cretaceous-Paleogene extinctions seems to have been slower than often supposed. At (or near) the Cretaceous-Paleogene boundary, large herbivores turned over from archosaurs to mammals, but turnover of large carnivores was slower. In South America, dinosaur-size crocodylomorphs lived as late as the Miocene. Thus modern terrestrial ecosystems do not, trophically, reflect those of even the Early Neogene in some southern continents. Sebecosuchians, at least in South America, seem to have been unaffected by the Cretaceous-Paleogene extinctions.

Ceratopsian Tooth Found in Cretaceous Mississippi

Paleontologists have discovered Mississippi's first horned dinosaur fossil in a creek bed in New Albany.

According to George Phillips, the Paleontology Curator at the Museum of Natural Science, paleontologists were searching for fossils of prehistoric crabs and mollusks, when they came across the tooth of a Ceratopsidae, or horned dinosaur. These dinosaurs were essentially unknown to eastern North America until a jawbone was discovered in North Carolina.

Phillips says the tooth is only the second of these fossils ever found east of the Mississippi River in North America.

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Murusraptor barrosaensis: a new megaraptorid Theropod From Cretaceous Argentina

A new species of megaraptorid dinosaur discovered in Patagonia may help discern the evolutionary origins of the megaraptorid clade, according to a study published July 20, 2016 in the open-access journal PLOS ONE by Rodolfo Coria from the Consejo Nacional de Investigaciones Científicas y Técnicas, Argentina, and Phillip Currie from the University of Alberta, Canada.

The Patagonian region of Argentina has previously proven to be rich in fossils from the Late Cretaceous epoch, including a number of megaraptorids, a clade whose carnivorous diet gave rise to their name meaning 'giant thieves'. These medium-sized theropod dinosaurs, including South American genera Megaraptor, Orkoraptor, and Aerosteon as well as genera from Australia and Japan, have characteristically large claws and air-filled, birdlike bones.

The fossilized partial skeleton of a megaraptorid dinosaur analyzed in this study was discovered in Sierra Barrosa, in northwest Patagonia and represents one of the most complete megaraptorids found, with an unusually intact braincase. With unique skull features, the dinosaur, which they named Murusraptor barrosaensis, is a new species in the megaraptorid clade. This specimen appears to be immature, but the authors suggest that the species is larger and slenderer than Megaraptor and comparable in size with Aerosteon and Orkoraptor. While sharing many features with the other species, Musuraptor has distinctive facial features not previously seen amongst megaraptorids, as well as unusually shaped hip bones.

While phylogenetic analysis could not clearly determine evolutionary relationships, the authors note that these fossils provide new anatomical information which might help to resolve current debates as to whether the megaraptorids are a clade of the allosauroid or the coelurosaurid theropods.

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Why Were Ornithopod Dinosaurs so Successful?

here has been a long debate about why dinosaurs were so successful. Say dinosaur, and most people think of the great flesh-eaters such as Tyrannosaurus rex, but the most successful dinosaurs were of course the plant-eaters.

A new study from the University of Bristol, led by Masters of Palaeobiology student Eddy Strickson, has presented clear evidence about how plant-eating dinosaurs evolved.

In the rich dinosaur deposits of North America, hundreds of skeletons of plant-eaters are found for every T. rex. But how did they survive and proliferate? Was it down to innovation or stimulus by plant evolution?

Eddy Strickson said: "The plant-eating ornithopods showed four evolutionary bursts; one in the middle of the Jurassic, and the other three in a cluster around 80 million years ago in the Late Cretaceous. This was down to innovation in their jaws and improved efficiency."

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Gualicho shinyae: a Neovenatorid Carcharodontosaurian Theropod With a Tyrannosaur-like Hand From Cenomanian Cretaceous Argentina

An Unusual New Theropod with a Didactyl Manus from the Upper Cretaceous of Patagonia, Argentina

Authors:

Apesteguía et al

Abstract:

Background

Late Cretaceous terrestrial strata of the Neuquén Basin, northern Patagonia, Argentina have yielded a rich fauna of dinosaurs and other vertebrates. The diversity of saurischian dinosaurs is particularly high, especially in the late Cenomanian-early Turonian Huincul Formation, which has yielded specimens of rebacchisaurid and titanosaurian sauropods, and abelisaurid and carcharodontosaurid theropods. Continued sampling is adding to the known vertebrate diversity of this unit.

Methodology/ Principal Findings

A new, partially articulated mid-sized theropod was found in rocks from the Huincul Formation. It exhibits a unique combination of traits that distinguish it from other known theropods justifying erection of a new taxon, Gualicho shinyae gen. et sp. nov. Gualicho possesses a didactyl manus with the third digit reduced to a metacarpal splint reminiscent of tyrannosaurids, but both phylogenetic and multivariate analyses indicate that didactyly is convergent in these groups. Derived characters of the scapula, femur, and fibula supports the new theropod as the sister taxon of the nearly coeval African theropod Deltadromeus and as a neovenatorid carcharodontosaurian. A number of these features are independently present in ceratosaurs, and Gualicho exhibits an unusual mosaic of ceratosaurian and tetanuran synapomorphies distributed throughout the skeleton.

Conclusions/ Significance

Gualicho shinyae gen. et sp. nov. increases the known theropod diversity of the Huincul Formation and also represents the first likely neovenatorid from this unit. It is the most basal tetatanuran to exhibit common patterns of digit III reduction that evolved independently in a number of other tetanuran lineages. A close relationship with Deltadromaeus from the Kem Kem beds of Niger adds to the already considerable biogeographic similarity between the Huincul Formation and coeval rock units in North Africa.

pop sci write up.

Evidence of Parasites in Hadrosaurs From Campanian Cretaceous Canada

Trace fossils of possible parasites inside the gut contents of a hadrosaurid dinosaur, Upper Cretaceous Judith River Formation, Montana

Authors:

Tweet et al

Abstract:

Tiny sinuous trace fossils have been found within probable gut contents of an exceptionally preserved specimen of a hadrosaurid dinosaur, Brachylophosaurus canadensis, from the Judith River Formation of Montana. Approximately 280 examples of the trace fossils were observed in 19 samples of gut region material. The tubular structures typically are about 0.3 mm across. Many have thin calcareous linings or layers, and some exhibit fine surficial striae. At least two dozen of these trace fossils share walls with adjacent tubular traces, and this association can extend for several millimeters. While the trace fossils share some characteristics with fine rhizoliths, these features are most consistent with tiny burrows, or possibly body impressions, of worms (vermiform organisms) of uncertain biologic affinity. Such trace fossils have not been reported previously, and herein described as Parvitubulites striatus n. gen. n. sp. Either autochthonous (parasites) or allochthonous (scavengers) worms may have created the trace fossils, but taphonomic factors suggest that autochthonous burrowers are more likely. Several lines of evidence, such as constant diameters and matching directional changes, suggest that the paired trace fossils were made by two individuals moving at the same time, which implies sustained intraspecific contact. Parvitubulites striatus provides a rare record of interactions between terrestrial, meiofaunal-sized, soft-bodied invertebrates and a dinosaur carcass. The evidence that the worms may have parasitized a living hadrosaur and subsequently left traces of intraspecific behavior between individual worms adds unique information to our understanding of Mesozoic trophic interactions.