Hadrosaurid Dinosaur Research Articles

A new ‘duck-billed’ dinosaur (Ornithischia: Hadrosauridae) from the upper Campanian of Texas points to a greater diversity of early hadrosaurid offshoots

We describe a previously unrecognized genus and species of basally-branching hadrosaurid dinosaur, Malefica deckerti, from the middle- to upper Campanian upper shale member of the Aguja Formation in Big Bend National Park, southwestern Texas, USA. This taxon is represented by a partial left maxilla. The hadrosaurid maxilla is particularly useful in differentiating species, and, despite the incomplete nature of the material, this new taxon is diagnosable by several autapomorphies and a unique combination of character states. Phylogenetic analysis places M. deckerti within Hadrosauridae but outside Saurolophidae, the major hadrosaurid clade consisting of the solid-crested or unadorned Saurolophinae and the hollow-crested Lambeosaurinae. When considered with the other known non-saurolophid hadrosaurids, this species adds to the growing evidence a hitherto unrecognized diversity of early hadrosaurid offshoots spanning the upper Santonian through the Maastrichtian and widespread throughout Eurasia and North America.

Taphonomy and taxonomy of a juvenile lambeosaurine (Ornithischia: Hadrosauridae) bonebed from the late Campanian Wapiti Formation of northwestern Alberta, Canada.

Hadrosaurid (duck-billed) dinosaur bonebeds are exceedingly prevalent in upper Cretaceous (Campanian–Maastrichtian) strata from the Midwest of North America (especially Alberta, Canada, and Montana, U.S.A) but are less frequently documented from more northern regions. The Wapiti Formation (Campanian–Maastrichtian) of northwestern Alberta is a largely untapped resource of terrestrial palaeontological information missing from southern Alberta due to the deposition of the marine Bearpaw Formation. In 2018, the Boreal Alberta Dinosaur Project rediscovered the Spring Creek Bonebed, which had been lost since 2002, along the northern bank of the Wapiti River, southwest of Grande Prairie. Earlier excavations and observations of the Spring Creek Bonebed suggested that the site yielded young hadrosaurines. Continued work in 2018 and 2019 recovered ~300 specimens that included a minimum of eight individuals, based on the number of right humeri. The morphology of several recovered cranial elements unequivocally supports lambeosaurine affinities, making the Spring Creek sample the first documented occurrence of lambeosaurines in the Wapiti Formation. The overall size range and histology of the bones found at the site indicate that these animals were uniformly late juveniles, suggesting that age segregation was a life history strategy among hadrosaurids. Given the considerable size attained by the Spring Creek lambeosaurines, they were probably segregated from the breeding population during nesting or caring for young, rather than due to different diet and locomotory requirements. Dynamic aspects of life history, such as age segregation, may well have contributed to the highly diverse and cosmopolitan nature of Late Cretaceous hadrosaurids.

Description and rediagnosis of the crested hadrosaurid (Ornithopoda) dinosaur Parasaurolophus cyrtocristatus on the basis of new cranial remains.

For nearly 60 years, skulls of Parasaurolophus species have been differentiated primarily on the basis of crest shape rather than on unique morphologic characters of other cranial elements. Complicating matters is the fact that crests dramatically change shape throughout ontogeny. Without a complete growth series, it has become difficult to assess the taxonomic distinctness of each species through the lens of allometric growth. Parasaurolophus cyrtocristatus has proven to be especially troublesome to assess because of the poorly preserved nature of the type and only skull. A new, partial skull from the Fossil Forest Member of the Fruitland Formation—the same geologic unit as the type specimen—is the first opportunity to re-diagnose this species as well as redefine the genus with many new traits. An undescribed, short-crested subadult skull from the Kaiparowits Formation of Utah previously assigned to cf. P. cyrtocristatus allows detailed comparisons to be made between the unnamed Utah taxon and the material of this species from the type locality. We find that several characteristics of the squamosal, supraoccipital, and premaxilla shared between the referred skull and the type skull are unique to P. cyrtocristatus (senso stricto) within the genus, irrespective of the overall crest shape. A phylogenetic analysis that includes six new characters posits that P. cyrtocristatus and P. tubicen are sister taxa, and that the latter does not share a closest common ancestor with the long-crested P. walkeri as previously hypothesized. This result helps to explain why both taxa are found in northeastern New Mexico, USA and in sequential geologic units (Fruitland Formation and Kirtland Formation, respectively). Additionally, the exquisitely preserved new skull provides the first opportunity to unequivocally identify the osteological make-up of the Parasaurolophus cranial crest. Unlike in previous reconstructions, the crest composition in Parasaurolophus follows what is seen in other lambeosaurines such as Corythosaurus, where the dorsal process of the premaxilla dominates the crest, with the nasal forming 80% of the ventral paired tubes, and the lateral premaxillary process acting a lateral cover between the dorsal and ventral tubes. The skull of P. cyrtocristatus is still incompletely known, so more complete material will likely reveal new features that further differentiate this species and aid in determining the pace of ornamental crest evolution.

A partial articulated hadrosaurid skeleton from the Maastrichtian (Upper Cretaceous) of the Ganzhou area, Jiangxi Province, China

ABSTRACT We describe the first partial articulated skeleton from the Ganzhou area, Jianxi Province, China. This basin has not been forthcoming in yielding hadrosaurid remains. The new specimen consists of an articulated rib cage belonging to a relatively large (no less than 9 m in length) hadrosaurid. It was collected from Maastrichtian strata of the Hekou Formation. This is the first partial skeleton of a large hadrosaurid dinosaur recovered from South southern China and confirms the presence of relatively large members of the clade previously suggested by ichnological evidence.

Over 13,000 elements from a single bonebed help elucidate disarticulation and transport of an Edmontosaurusthanatocoenosis.

Over twenty years of work on the Hanson Ranch (HR) Bonebed in the Lance Formation of eastern Wyoming has yielded over 13,000 individual elements primarily of the hadrosaurid dinosaur Edmontosaurus annectens. The fossil bones are found normally-graded within a fine-grained (claystone to siltstone) bed that varies from one to two meters in thickness. Almost all specimens exhibit exquisite preservation (i.e., little to no abrasion, weathering, and breakage), but they are disarticulated which, combined with our sedimentological observations, suggests that the bones were remobilized and buried after a period of initial decay and disarticulation of Edmontosaurus carcasses. Because of the large number of recovered fossil elements, we have been able to gain deeper insight into Edmontosaurus biostratigraphy including disarticulation and transport of skeletal elements. The most common postcranial elements in the bonebed are pubes, ischia, scapulae, ribs, and limb bones. By contrast, vertebrae, ilia, and chevrons are rare. The most common craniomandibular bones include dentaries, nasals, quadrates, and jugals, whereas the premaxillae, predentaries, and braincase bones are underrepresented. Thus, overall, chondrocranial and axial elements, as well as distal elements of the limbs, are distinctly underrepresented. We hypothesize that following decay and disarticulation, hydraulic winnowing removed the articulated sections (e.g., vertebral columns) and the small, distal-most elements before, or at the same time, the remaining bones were swept up in a subaqueous debris flow that generated the deposit. Comparison of the HR Bonebed with other widely dispersed Upper Cretaceous hadrosaurid-dominated bonebeds reveals many shared attributes, which suggests similar processes at work in the formation of these bonebeds across space and time. This in turn reflects similar behavior by populations of these species around the world resulting in similar modes of death, becoming interred in similar depositional settings.

Integumentary structure and composition in an exceptionally well-preserved hadrosaur (Dinosauria: Ornithischia).

Preserved labile tissues (e.g., skin, muscle) in the fossil record of terrestrial vertebrates are increasingly becoming recognized as an important source of biological and taphonomic information. Here, we combine a variety of synchrotron radiation techniques with scanning electron and optical microscopy to elucidate the structure of 72 million-year-old squamous (scaly) skin from a hadrosaurid dinosaur from the Late Cretaceous of Alberta, Canada. Scanning electron and optical microscopy independently reveal that the three-dimensionally preserved scales are associated with a band of carbon-rich layers up to a total thickness of ∼75 microns, which is topographically and morphologically congruent with the stratum corneum in modern reptiles. Compositionally, this band deviates from that of the surrounding sedimentary matrix; Fourier-transform infrared spectroscopy and soft X-ray spectromicroscopy analyses indicate that carbon appears predominantly as carbonyl in the skin. The regions corresponding to the integumentary layers are distinctively enriched in iron compared to the sedimentary matrix and appear with kaolinite-rich laminae. These hosting carbonyl-rich layers are apparently composed of subcircular bodies resembling preserved cell structures. Each of these structures is encapsulated by calcite/vaterite, with iron predominantly concentrated at its center. The presence of iron, calcite/vaterite and kaolinite may, independently or collectively, have played important roles in the preservation of the layered structures.

An unusual ‘shovel-billed’ dinosaur with trophic specializations from the early Campanian of Trans-Pecos Texas, and the ancestral hadrosaurian crest

We describe a new genus and species of hadrosaurid dinosaur, Aquilarhinus palimentus, from the lower shale member of the Aguja Formation (lower Campanian) of Big Bend National Park, south-western Texas. This species is characterized by several autapomorphies of the facial skeleton and mandible, including a crest composed of broadly arched nasals. Notably, the symphyseal processes of the dentary are elongated and reflected dorsally, causing the dentaries to meet with a ‘W’-shaped anterior profile. A hypothesized shovel-shaped ‘bill’, associated with widening of the skull, in A. palimentus might have been used in shovelling out and scooping up semiaquatic vegetation. This animal is otherwise superficially similar to kritosaurins like Gryposaurus but differs in the retention of key plesiomorphic character states in the maxilla and jugal. Phylogenetic analysis reveals Aquilarhinus to be a non-saurolophid hadrosaurid allied to Latirhinus from the late Campanian of Mexico, which bears a similar broadly arched nasal. The recognition of this lineage adds to the diversity of non-saurolophid hadrosaurids and points to the existence of a hitherto unknown diversity of ‘duck-billed’ dinosaurs outside of the saurolophine-lambeosaurine radiation. Cranial crests were ancestral for early hadrosaurids and evolved before the saurolophid radiation. Ancestrally, crests were ‘solid’, and consisted of arched nasals. These were retained among kritosaurins and subsequently modified into the diverse crest morphologies observed among derived saurolophines. Lambeosaurine ‘hollow-crested’ crest morphology departed from the ancestral, ‘solid-crested’ pre-saurolophid condition early following the origin of that clade.http://www.zoobank.org/urn:lsid:zoobank.org:pub:F7CE1BE7-1A76-4628-8510-93C37A1A807E

Maiasaura (Dinosauria: Hadrosauridae) Tibia Osteohistology Reveals Non-annual Cortical Vascular Rings in Young of the Year

Annually, tetrapod vertebrate bone apposition is briefly interrupted, which typically coincides with the yearly environmental nadir. The temporary appositional hiatus is histologically recorded in bone cortex as a hypermineralized ring termed a line of arrested growth (LAG). One paleohistology study used this known LAG periodicity to quantify ontogenetic ages and growth rates in a dataset of fifty tibiae from the hadrosaurid dinosaur Maiasaura. In addition to LAGs, unusual cortical rings resulting from localized changes in vascular diameter were also noted in the tibiae, but not investigated further. The fifty Maiasaura tibiae from that study were histologically reexamined here to explore and document the composition, frequency, and cortical extent of localized vascular changes (LVCs) to assist with the recognition of similar structures in the cortices of other extinct taxa. This assessment reveals that the Maiasaura LVC is comprised of one or more laminae of primary osteons forming a ring of vascular canal diameters either uniformly larger or smaller than those of primary osteons adjacent to the vascular ring. With one exception, LVCs are only found prior to the first LAG in Maiasaura. However, LVC frequency is variable, ranging from specimens with no LVCs to as many as five prior to the first LAG. Because of their inconsistent frequency and restricted location within the cortex, LVCs likely do not have an annual periodicity in Maiasaura. Instead, LVCs may signal times of temporary but repeated stress. As both growth rates and mortality rates were highest during the first year in Maiasaura, illness or starvation seemed to have the greatest impact on growth during that time. A subadult tibia presenting with a pathologic directional cortical outgrowth is the only instance within the sample in which LVCs were found beyond the first LAG. Unfortunately, LVCs are under-explored in extant taxa, so the underlying cause(s) for Maiasaura LVCs cannot be established. As LVCs may provide yet another histological method for interpreting extinct vertebrate biology, foundational investigations of LVCs in extant vertebrates should be pursued.

Feeding traces attributable to juvenile Tyrannosaurus rex offer insight into ontogenetic dietary trends.

Theropod dinosaur feeding traces and tooth marks yield paleobiological and paleoecological implications for social interactions, feeding behaviors, and direct evidence of cannibalism and attempted predation. However, ascertaining the taxonomic origin of a tooth mark is largely dependent on both the known regional biostratigraphy and the ontogenetic stage of the taxon. Currently, most recorded theropod feeding traces and bite marks are attributed to adult theropods, whereas juvenile and subadult tooth marks have been rarely reported in the literature. Here we describe feeding traces attributable to a late-stage juvenile Tyrannosaurus rex on a caudal vertebra of a hadrosaurid dinosaur. The dimensions and spacing of the traces were compared to the dentition of Tyrannosaurus rex maxillae and dentaries of different ontogenetic stages. These comparisons reveal that the tooth marks present on the vertebra closely match the maxillary teeth of a late-stage juvenile Tyrannosaurus rex specimen histologically determined to be 11–12 years of age. These results demonstrate that late-stage juvenile and subadult tyrannosaurs were already utilizing the same large-bodied food sources as adults despite lacking the bone-crushing abilities of adults. Further identification of tyrannosaur feeding traces coupled with experimental studies of the biomechanics of tyrannosaur bite forces from younger ontogenetic stages may reveal dynamic dietary trends and ecological roles of Tyrannosaurus rex throughout ontogeny.

Vertebrate tracks from the Paso Córdoba fossiliferous site (Anacleto and Allen formations, Upper Cretaceous), Northern Patagonia, Argentina: Preservational, environmental and palaeobiological implications

The Paso Córdoba fossiliferous site (Río Negro, Northern Patagonia) is one of the first Mesozoic fossiliferous localities studied in Argentina. There, turtle, crocodile and dinosaur remains as well as dinosaur and bird tracks have been recorded. Recently, a new locality with vertebrate tracks, the Cañadón del Desvío, has been discovered in Paso Córdoba. Six track-bearing layers were located in outcrops belonging to the Anacleto (lower to middle Campanian, Neuquén Group) and Allen (middle Campanian-lower Maastrichtian, Malargüe Group) formations. The Cañadón del Desvío locality reveals that vertebrate trace fossils are distributed in two distinct environments, floodplains of a meandering fluvial to shallow lacustrine system and a wet interdune deposit that is associated to an aeolian setting. Also, in the logged section several soft sediment deformation structures were found. In regard of this, a sedimentary facies analysis is provided in order to assess the palaeoenvironmental implications of this new record. The analysed tracks are preserved in cross-sections, on bedding-planes and as natural casts. When it is possible, the tracking surface, true tracks, undertracks and overtracks/natural casts have been identified and the track preservation and the formation history of the tracksite are discussed. Only two tracks preserve enough anatomical details to relate them with their trackmakers, in this case hadrosaurid dinosaurs. The stratigraphical, facial and palaeoenvironmental data of this study support the idea of a transitional passage between the Anacleto and Allen Formation in Paso Córdoba. The presence of hadrosaurid dinosaur tracks suggests that the upper part of the log, where this kind of tracks were found, likely belong to Allen Formation due to this dinosaurs appear in the Southern Hemisphere in this epoch. The sum of osteological and ichnological remains improve the Paso Córdoba palaeofaunistic knowledge. The presence of six different levels in which the trackmakers walked reflects the abundance of vertebrates in the transition between Anacleto and Allen formations.

Large hadrosaurid dinosaur from the San Juan Basin, New Mexico

Hadrosaurid dinosaur diversity in the San Juan Basin of New Mexico has been difficult to determine due, in part, to poor preservation of specimens compared to those found in northern North America. A reexamination of a collection of hadrosaurid material from the Hunter Wash Member of the Kirtland Formation in San Juan County, New Mexico, excavated in 1922 by Charles H. Sternberg, has revealed some well‐preserved specimens. Among these specimens is a large hadrosaurid humerus that is 860 millimeters in length, with a humeral shaft diameter of 176 millimeters. The proportional size of the deltopectoral crest in relation to the humeral shaft indicates that the humerus comes from a saurolophine hadrosaur.Previously recognized hadrosaurid diversity in the lower Kirtland Formation has been restricted to the lambeosaurine, Parasaurolophus cyrtocristatus, and the saurolophine, Kritosaurus navajovius. Recent studies of hadrosaurid elements in this Sternberg collection have indicated that there are additional, as yet unnamed, saurolophine taxa in the San Juan Basin with strong affinities to the Kritosaurini, but distinct from K. navajovius. The large humerus is significantly larger than that of any of the previously known hadrosaurid taxa from the lower Kirtland Formation, including the newly described kritosaurine material. Morphometric analysis of the humerus suggests an element with proportions similar to those of Shantungosaurus, one of the largest hadrosaurs, and dissimilar to any of the previously known San Juan Basin hadrosaurid taxa. The robust construction of the humeral shaft is reflected by a shaft volume to humeral length ratio that greatly exceeds most other hadrosaurid taxa, resulting in a humerus with greater loading capacity. Though it is an isolated element, this humerus provides evidence that there were large hadrosaurids, potentially from a new species, living in the San Juan Basin, expanding the diversity of the San Juan Basin hadrosaurid dinosaur fauna.

Bonapartesaurus rionegrensis, a new hadrosaurine dinosaur from South America: implications for phylogenetic and biogeographic relations with North America

ABSTRACT The Gondwanan hadrosaurid dinosaur record is relatively poorly known and very complicated. A new hadrosaurid, Bonapartesaurus rionegrensis, gen. et sp. nov., from the late Campanian–early Maastrichtian of the Salitral Moreno site, Argentina, is characterized by the following combination of characters: the ratio between the height of the neural spines and that of the centrum of the sacral vertebrae greater than 3.5; neural spines of the anterior section of the caudal vertebrae extremely long and evenly expanding distally; a preacetabular process of the ilium slightly deflected ventrally, with the angle greater than 150°; the ratio between the maximum dorsoventral depth of the posterior end of the preacetabular process and the dorsoventral distance from the pubic peduncle to the dorsal margin of the ilium less than 0.50; the ratio between the dorsoventral height and anteroposterior length of the iliac blade 0.8 or greater; asymmetrical lateral profile of the supraacetabular process; the posterior portion of the postacetabular process markedly thicker mediolaterally as a result of the dorsomedial twist of the postacetabular process; an anteriorly expanded cnemial crest restricted to the proximal end of the tibia; and articular surface of the astragalus for the internal malleolus of the tibia moderately expanded medially, articulating with only part of the ventral surface of the tibial internal malleolus. Our phylogenetic analysis indicates that Bonapartesaurus is located within the Tribe Saurolophini. Paleobiogeographically, its presence suggests at least two saurolophine dispersal events from North America, one toward South America and another toward Asia, no later than the late Campanian. http://zoobank.org/urn:lsid:zoobank.org:pub:1ADEDB71-1FD6-4081-915D-6C73D8389408 SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP Citation for this article: Cruzado-Caballero, P., and J. Powell. 2017. Bonapartesaurus rionegrensis, a new hadrosaurine dinosaur from South America: implications for phylogenetic and biogeographic relations with North America. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2017.1289381.

Anatomy and osteohistology of the basal hadrosaurid dinosaur Eotrachodon from the uppermost Santonian (Cretaceous) of southern Appalachia.

The cranial and postcranial anatomy of the basal hadrosaurid dinosaur Eotrachodon orientalis, from the uppermost Santonian of southern Appalachia (southeastern U.S.A.), is described in detail. This animal is the only known pre-Campanian non-lambeosaurine hadrosaurid, and the most complete hadrosauroid known from Appalachia. E. orientalis possesses a mosaic of plesiomorphic and derived characters in the context of Hadrosauroidea. Characters shared with basal hadrosauroids include a short and sloping maxillary ectopterygoid shelf, caudally prominent maxillary jugal process, one functional tooth per alveolus on the maxillary occlusal plane, a jugal rostral process with a shallow caudodorsal margin and medioventrally facing articular facet, a vertical dentary coronoid process with a poorly expanded apex, and tooth crowns with accessory ridges. Derived characters shared with other hadrosaurids include a circumnarial depression compartmented into three fossae (as in brachylophosaurins and Edmontosaurus), a thin everted premaxillary oral margin (as in Gryposaurus, Prosaurolophus, and Saurolophus), and a maxilla with a deep and rostrocaudally extensive rostrodorsal region with a steeply sloping premaxillary margin (as in Gryposaurus). Eotrachodon orientalis differs primarily from the other hadrosauroid from the Mooreville Chalk of Alabama, Lophorhothon atopus, in having a slender and crestless nasal whose caudodorsal margin is not invaded by the circumnarial depression. Hadrosaurus foulkii, the only other known hadrosaurid from Appalachia, is distinct from E. orientalis in having dentary teeth lacking accessory ridges and a dorsally curved shaft of the ischium. A histological section of the tibia of the E. orientalis holotype (MSC 7949) suggests that this individual was actively growing at the time of death and, thus, had the potential to become a larger animal later in development.

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

AbstractTiny 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 asParvitubulites striatusn. 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 striatusprovides 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.

The late-surviving ‘duck-billed’ dinosaur Augustynolophus from the upper Maastrichtian of western North America and crest evolution in Saurolophini

AbstractWe amend the taxonomy and provide new anatomical information on the hadrosaurid dinosaur Saurolophus morrisi (upper Maastrichtian Moreno Formation, central California, USA) derived from full preparation of the referred skull roof. The cranial morphology of this species is distinct enough to justify the new combination Augustynolophus morrisi gen. nov. The morphology of the nasals and surrounding cranial bones indicates that A. morrisi sported a solid nasal crest ending in an elongate triangular plate that extended above the skull roof. Autapomorphies include a crescentic base of the frontal caudodorsal process and extension of the process caudal to the frontal ‘dome’; distal end of nasal crest with knob-like process inflected rostrally; circumnarial depression lightly incised and weakly emarginated, adjacent to caudolateral margin of nasal and occupying two-thirds the width of lateral surface of distal region of crest; and caudal surface of distal nasal crest subrectangular. We formally establish the new tribe Saurolophini consisting of Prosaurolophus, Augustynolophus and Saurolophus. Saurolophin synapomorphies include a premaxilla with broad arcuate contour of rostrolateral region of thin everted oral margin and flat and steeply inclined occlusal surface of dentary dental battery, among other characters. Saurolophin crests evolved towards increasing caudodorsal length, along with caudal extension of the circumnarial fossa and involvement into the crest of adjacent facial elements. Augustynolophus is the second described genus of North American late Maastrichtian hadrosaurids. Its recognition implies a greater diversity among late Maastrichtian dinosaur faunas than previously recognized and is congruent with hypotheses of endemism and/or provinciality during Late Cretaceous time.

A juvenile Edmontosaurus from the late Maastrichtian (Cretaceous) of North America: Implications for ontogeny and phylogenetic inference in saurolophine dinosaurs

The anatomy of an articulated juvenile specimen of the saurolophine hadrosaurid dinosaur Edmontosaurus annectens, LACM 23504, is described in detail. This individual consists of a partial skull and nearly complete articulated postcranium, collected from upper Maastrichtian strata of the Hell Creek Formation of Montana, USA. This study aims to help understand the ontogenetic morphological changes occurring in the cranium and postcranium of saurolophine hadrosaurids using E. annectens as a case study. Emphasis is placed on those morphological attributes that are ontogenetically variable via comparative osteology between the juvenile and the available adult specimens. It is observed that much of the cranial ontogenetic variation relates to the elongation of the skull and mandible. In the postcranium, most of the ontogenetic variation concentrates in the pectoral and pelvic girdles and the stylopodia. Not all the identified patterns of ontogenetic variation may be generalized to all hadrosaurids. The impact of ontogenetic variation on phylogenetically informative characters of saurolophine hadrosaurids is evaluated. It is concluded that, at least for Edmontosaurus annectens (and perhaps other saurolophine hadrosaurids), most characters used in phylogenetic inference of these animals are not affected by ontogeny. Thus, juvenile specimens are still a source of substantial character data suitable for use in phylogenetic analyses of saurolophine relationships. Nevertheless, it is recommended that ontogenetically variable characters are left as missing data in a character–taxon matrix when only juvenile material is available for a given saurolophine taxon. Scoring those characters based solely on juveniles is likely to decrease the accuracy of the phylogenetic inference.

A Mummified Duck-Billed Dinosaur with a Soft-Tissue Cock’s Comb

Among living vertebrates, soft tissues are responsible for labile appendages (combs, wattles, proboscides) that are critical for activities ranging from locomotion to sexual display [1]. However, soft tissues rarely fossilize, and such soft-tissue appendages are unknown for many extinct taxa, including dinosaurs. Here we report a remarkable "mummified" specimen of the hadrosaurid dinosaur Edmontosaurus regalis from the latest Cretaceous Wapiti Formation, Alberta, Canada, that preserves a three-dimensional cranial crest (or "comb") composed entirely of soft tissue. Previously, crest function has centered on the hypertrophied nasal passages of lambeosaurine hadrosaurids, which acted as resonance chambers during vocalization [2-4]. The fleshy comb in Edmontosaurus necessitates an alternative explanation most likely related to either social signaling or sexual selection [5-7]. This discovery provides the first view of bizarre, soft-tissue signaling structures in a dinosaur and provides additional evidence for social behavior. Crest evolution within Hadrosaurinae apparently culminated in the secondary loss of the bony crest at the terminal Cretaceous; however, the new specimen indicates that cranial ornamentation was in fact not lost but substituted in Edmontosaurus by a fleshy display structure. It also implies that visual display played a key role in the evolution of hadrosaurine crests and raises the possibility of similar soft-tissue structures among other dinosaurs.

Evolution in Surfaces: Interaction of Topography with Contact Pressure During Wear of Composites Including Dinosaur Dentition

A two-parameter elastic foundation model is used to predict the coupled evolution of contact pressure and wear of multicomponent composite surfaces. The iterative model predicts the evolution of surface shape for an initially flat multicomponent surface under uniform applied pressure; where the components of the composite surface are different materials of different wear rates. The model is applied to elucidate the chewing surface morphology of the dentition in a hadrosaurid dinosaur using wear rates measured from fossilized dental tissues. Additionally, to further illustrate the predictive capabilities of the coupled contact pressure and wear model, a two-component polymer sample was fabricated and experimentally evaluated through laboratory wear experiments. Data obtained from the abrasive wear testing of a laboratory multicomponent polymer sample was compared to model predictions using measured system and material parameters. Differences between the measured and predicted surface profiles were on the same order as the sample’s surface roughness (Ra ~3 µm).

Cranial Endocast of the Lambeosaurine Hadrosaurid Amurosaurus riabinini from the Amur Region, Russia

Information on the structure of the brain of the lambeosaurine hadrosaurid dinosaur Amurosaurus riabinini, from the Late Maastrichtian of Blagoveschensk, Far Eastern Russia, is presented based on endocranial casts. The endocasts are compared with physical and digital endocasts of other dinosaurs. The olfactory tract was large. The cerebral hemispheres are enlarged and round, illustrating the important development of this part of the brain in hadrosaurids. The pituitary body is enlarged as well, perhaps prefiguring the large size attained by hadrosaurids. The EQ of Amurosaurus was similar to that of the lambeosaurine dinosaur Hypacrosaurus altispinus and was relatively larger than in most extant non-avian reptiles, including sauropod and ceratopsian dinosaurs. However, it was apparently relatively smaller than those of most theropod dinosaurs. The relatively large size of the cerebrum is consistent with the range and complexity of social behaviors inferred for lambeosaurine dinosaurs.

Ontogeny in the tube-crested dinosaurParasaurolophus(Hadrosauridae) and heterochrony in hadrosaurids

The tube-crested hadrosaurid dinosaur Parasaurolophus is remarkable for its unusual cranial ornamentation, but little is known about its growth and development, particularly relative to well-documented ontogenetic series for lambeosaurin hadrosaurids (such as Corythosaurus, Lambeosaurus, and Hypacrosaurus). The skull and skeleton of a juvenile Parasaurolophus from the late Campanian-aged (∼75.5 Ma) Kaiparowits Formation of southern Utah, USA, represents the smallest and most complete specimen yet described for this taxon. The individual was approximately 2.5 m in body length (∼25% maximum adult body length) at death, with a skull measuring 246 mm long and a femur 329 mm long. A histological section of the tibia shows well-vascularized, woven and parallel-fibered primary cortical bone typical of juvenile ornithopods. The histological section revealed no lines of arrested growth or annuli, suggesting the animal may have still been in its first year at the time of death. Impressions of the upper rhamphotheca are preserved in association with the skull, showing that the soft tissue component for the beak extended for some distance beyond the limits of the oral margin of the premaxilla. In marked contrast with the lengthy tube-like crest in adult Parasaurolophus, the crest of the juvenile specimen is low and hemicircular in profile, with an open premaxilla-nasal fontanelle. Unlike juvenile lambeosaurins, the nasal passages occupy nearly the entirety of the crest in juvenile Parasaurolophus. Furthermore, Parasaurolophus initiated development of the crest at less than 25% maximum skull size, contrasting with 50% of maximum skull size in hadrosaurs such as Corythosaurus. This early development may correspond with the larger and more derived form of the crest in Parasaurolophus, as well as the close relationship between the crest and the respiratory system. In general, ornithischian dinosaurs formed bony cranial ornamentation at a relatively younger age and smaller size than seen in extant birds. This may reflect, at least in part, that ornithischians probably reached sexual maturity prior to somatic maturity, whereas birds become reproductively mature after reaching adult size.