Nodosaurid Ankylosaur Research Articles

An ankylosaur femur from the mid-Cretaceous of the peace region of northeastern British Columbia

Dinosaur skeletal material from the mid-Cretaceous of Canada is rare; however, the Cenomanian-aged Dunvegan Formation of northeastern British Columbia and northwestern Alberta is rich with ichnofossils attributed to nodosaurid ankylosaurs. A long bone (Hudson's Hope Museum specimen HH 2017.010.002) collected in 1993 from the Murray River of northeastern British Columbia is identified here as an ankylosaur femur. Femoral measurements of the bone plotted against femoral measurements of major dinosaur clades, combined with observations on femoral features, indicate that the bone belongs to an ankylosaur. The specimen is too damaged to assign to Nodosauridae or Ankylosauridae. HH 2017.010.002 represents the first limb bone material recovered from the Dunvegan Formation; previous ankylosaur material described from the Dunvegan Formation includes associated vertebrae and ribs from British Columbia and osteoderms from Alberta, as well as the presumed nodosaurid footprints Tetrapodosaurus borealis Sternberg, 1932. The Cenomanian is a time of great ecological change in North America, including the possible extirpation of ankylosaurid ankylosaurs. Fossils from the Dunvegan Formation can thus yield important insight into the responses of fauna to this major transition.

A new small-bodied ankylosaurian dinosaur from the Upper Cretaceous of North Patagonia (Río Negro Province, Argentina)

The most representative ankylosaurian remains from Argentina have been found in sediments of the Allen Formation (Campanian–Maastrichtian) in Salitral Moreno, Río Negro Province. Several authors have discussed the identity and history of these remains. In this study, we review all published material along with some new remains in order to summarize all the knowledge about these ankylosaurs. Previously published material includes a tooth, dorsal and anterior caudal vertebrae, a femur and several osteoderms. The new remains include synsacral and caudal elements, a partial femur and osteoderms. The anatomy of the tooth, the synsacrum, the mid-caudal vertebra, the femur and the osteoderms, and the histology of the post-cervical osteoderms, support a nodosaurid identification, as proposed in previous descriptions of the Salitral Moreno material. Patagopelta cristata gen. et sp. nov. is a new nodosaurid ankylosaur characterized by the presence of unique cervical half-ring and femoral anatomies, including high-crested lateral osteoderms in the half rings and a strongly developed muscular crest in the anterior surface of the femur. The ∼2 m body length estimated for Patagopelta is very small for an ankylosaur, comparable with the dwarf nodosaurid Struthiosaurus. We recovered Patagopelta within Nodosaurinae, related to nodosaurids from the ‘mid’-Cretaceous of North America, contrasting the previous topologies that related this material with Panoplosaurini (Late Cretaceous North American nodosaurids). These results support a palaeobiogeographical context in which the nodosaurids from Salitral Moreno, Argentina, are part of the allochthonous fauna that migrated into South America during the late Campanian as part of the First American Biotic Interchange. https://zoobank.org/urn:lsid:zoobank.org:pub:FBA24443-F365-49FD-A959-10D2848C2400

Late Campanian-Early Maastrichtian Vertebrates From The James Ross Basin, West Antarctica: Updated Synthesis, Biostratigraphy, And Paleobiogeography.

The Snow Hill Island Formation (SHIF; late Campanian - early Maastrichtian) crops out in the northeast of the Antarctic Peninsula and constitutes the basal part of the late Campanian-early Maastrichtian sedimentary succession of the James Ross Basin (NG Sequence). Its major exposures occur at the James Ross and Vega islands. Several fossil-bearing localities have been identified in the SHIF providing a valuable fauna of invertebrates and vertebrates, and flora. Our study focuses on the vertebrate fauna recovered at Gamma and Cape Lamb members of the SHIF. The marine vertebrate assemblages include chondrichthyans, actinopterygians, and marine reptiles (elasmosaurid plesiosaurs and mosasaurs). A diverse terrestrial vertebrate assemblage has been reported being characterized by dinosaurs (sauropod, elasmarian ornithopods, nodosaurid ankylosaur, and a paravian theropod), pterosaurs and birds. Most SHIF dinosaurs share close affinities with penecontemporaneous taxa from southern South America, indicating that at least some continental vertebrates could disperse between southern South America and Antarctica during the Late Cretaceous. The Snow Hill Island Formation provides the most diverse Late Cretaceous marine and continental faunas from Antarctica. The present study summarizes previous and new vertebrate findings with the best actualized stratigraphical framework, providing a more complete fauna association and analyzing further perspectives.

A new vertebrate fauna from the Lower Cretaceous Holly Creek Formation of the Trinity Group, southwest Arkansas, USA.

We present a previously discovered but undescribed late Early Cretaceous vertebrate fauna from the Holly Creek Formation of the Trinity Group in Arkansas. The site from the ancient Gulf Coast is dominated by semi-aquatic forms and preserves a diverse aquatic, semi-aquatic, and terrestrial fauna. Fishes include fresh- to brackish-water chondrichthyans and a variety of actinopterygians, including semionotids, an amiid, and a new pycnodontiform, Anomoeodus caddoi sp. nov. Semi-aquatic taxa include lissamphibians, the solemydid turtle Naomichelys, a trionychid turtle, and coelognathosuchian crocodyliforms. Among terrestrial forms are several members of Dinosauria and one or more squamates, one of which, Sciroseps pawhuskai gen. et sp. nov., is described herein. Among Dinosauria, both large and small theropods (Acrocanthosaurus, Deinonychus, and Richardoestesia) and titanosauriform sauropods are represented; herein we also report the first occurrence of a nodosaurid ankylosaur from the Trinity Group. The fauna of the Holly Creek Formation is similar to other, widely scattered late Early Cretaceous assemblages across North America and suggests the presence of a low-diversity, broadly distributed continental ecosystem of the Early Cretaceous following the Late Jurassic faunal turnover. This low-diversity ecosystem contrasts sharply with the highly diverse ecosystem which emerged by the Cenomanian. The contrast underpins the importance of vicariance as an evolutionary driver brought on by Sevier tectonics and climatic changes, such as rising sea level and formation of the Western Interior Seaway, impacting the early Late Cretaceous ecosystem.

An ankylosaurian dinosaur from the Cenomanian Dunvegan Formation of northeastern British Columbia, Canada

Abstract. Fragmentary but associated dinosaur bones collected in 1930 from the Pine River of northeastern British Columbia are identified here as originating from an ankylosaur. The specimen represents only the second occurrence of dinosaur skeletal material from the Cenomanian Dunvegan Formation and the first from Dunvegan outcrops in the province of British Columbia. Nodosaurid ankylosaur footprints are common ichnofossils in the formation, but the skeletal material described here is too fragmentary to confidently assign to either a nodosaurid or ankylosaurid ankylosaur. The Cenomanian is a time of major terrestrial faunal transitions in North America, but many localities of this age are located in the southern United States; the discovery of skeletal fossils from the Pine River demonstrates the potential for the Dunvegan Formation to produce terrestrial vertebrate fossils that may provide important new data on this significant transitional period during the Cretaceous.

An exceptionally preserved armored dinosaur reveals the morphology and allometry of osteoderms and their horny epidermal coverings.

Although the evolution and function of “exaggerated” bony projections in ornithischian dinosaurs has been subject to significant debate recently, our understanding of the structure and morphology of their epidermal keratinized coverings is greatly limited. The holotype of Borealopelta, a new nodosaurid ankylosaur, preserves osteoderms and extensive epidermal structures (dark organic residues), in anatomic position across the entire precaudal length. Contrasting previous specimens, organic epiosteodermal scales, often in the form of horn-like (keratinous) sheaths, cap and exaggerate nearly all osteoderms, allowing for morphometric and allometric analyses of both the bony osteoderms and their horny sheaths. A total of 172 osteoderms were quantified, with osteoderm spine length and height being positively allometric with respect to basal length and width. Despite tight correlations between the different measures amongst all other osteoderms, the large parascapular spines represent consistent outliers. Thickness and relative contribution of the keratinized epiosteodermal scales/sheaths varies greatly by region, ranging from 2% to 6% for posterior thoracics, to ∼25% (1.3×) for the parascapular spines—similar to horn sheaths in some bovid analogues. Relative to the bony cores, the horny portions of the spines are strongly positively allometric (slope = 2.3, CI = 1.8–2.8). Strong allometric scaling, species-specific morphology, and significant keratinous extension of the cervicoscapular spines is consistent with elaboration under socio-sexual selection. This marks the first allometric analysis of ornithischian soft tissues.

An Exceptionally Preserved Three-Dimensional Armored Dinosaur Reveals Insights into Coloration and Cretaceous Predator-Prey Dynamics

Predator-prey dynamics are an important evolutionary driver of escalating predation mode and efficiency, and commensurate responses of prey [1-3]. Among these strategies, camouflage is important for visual concealment, with countershading the most universally observed [4-6]. Extant terrestrial herbivores free of significant predation pressure, due to large size or isolation, do not exhibit countershading. Modern predator-prey dynamics may not be directly applicable to those ofthe Mesozoic due to the dominance of very large,visually oriented theropod dinosaurs [7]. Despite thyreophoran dinosaurs' possessing extensive dermal armor, some of the most extreme examples of anti-predator structures [8, 9], little direct evidence of predation on these and other dinosaur megaherbivores has been documented. Here we describe a new, exquisitely three-dimensionally preserved nodosaurid ankylosaur, Borealopelta markmitchelli gen. et sp. nov., from the Early Cretaceous of Alberta, which preserves integumentary structures as organic layers, including continuous fields of epidermal scales and intact horn sheaths capping the body armor. We identify melanin in the organic residues through mass spectroscopic analyses and observe lighter pigmentation of thelarge parascapular spines, consistent with display, and a pattern of countershading across the body. With an estimated body mass exceeding 1,300kg, B.markmitchelli was much larger than modern terrestrial mammals that either are countershaded or experience significant predation pressure as adults. Presence of countershading suggests predation pressure strong enough to select for concealment in this megaherbivore despite possession of massive dorsal and lateral armor, illustrating a significant dichotomy between Mesozoic predator-prey dynamics and those of modern terrestrial systems.

Wear Pattern, Dental Function, and Jaw Mechanism in the Late Cretaceous Ankylosaur Hungarosaurus

ABSTRACTFeeding in thyreophoran dinosaurs is poorly understood. Although the group existed for over 130 million years, only the Early Jurassic basal thyreophoran Scelidosaurus harrisonii and the Late Cretaceous ankylosaurid Euoplocephalus tutus have been studied from this perspective in detail. In contrast to the earlier, conservative hypothesis of a simple “orthal pulping” feeding mode with no or limited tooth–tooth contact, recent studies have demonstrated precise dental occlusion with differing jaw mechanisms in these two species. Here, we describe the first detailed study of feeding related characters in a nodosaurid ankylosaur, Hungarosaurus tormai, from the Late Cretaceous of Hungary. Dental wear patterns comprising small, apical, and low‐angled facets on the maxillary and steep, extended, and bowl‐like facets on the dentary teeth reveal sophisticated tooth–tooth contact in this basal nodosaurid. The presence of two different scratch generations (vertical and low‐angled) on the dentary teeth unambiguously demonstrate a multiphasic powerstroke, which is further supported by the morphology of the quadrate‐articular and mandibular symphyseal joints and by the architecture of the reconstructed jaw adductors. Chewing started with an initial slicing phase associated with orthal movement that was followed by a retractive powerstroke with significant occlusal contact. Because of the curved tooth rows, these movements were probably facilitated by some mediolateral translation and/or axial rotation of the mandibles to produce precise shearing along the whole tooth row. These results demonstrate that complex jaw mechanisms and dental occlusion were more widespread among thyreophorans than thought previously and that palinal movement was present in at least two ankylosaurian lineages. Anat Rec, 297:1165–1180, 2014. © 2014 Wiley Periodicals, Inc.

Wear Pattern, Dental Function, and Jaw Mechanism in the Late Cretaceous Ankylosaur Hungarosaurus

Feeding in thyreophoran dinosaurs is poorly understood. Although the group existed for over 130 million years, only the Early Jurassic basal thyreophoran Scelidosaurus harrisonii and the Late Cretaceous ankylosaurid Euoplocephalus tutus have been studied from this perspective in detail. In contrast to the earlier, conservative hypothesis of a simple "orthal pulping" feeding mode with no or limited tooth-tooth contact, recent studies have demonstrated precise dental occlusion with differing jaw mechanisms in these two species. Here, we describe the first detailed study of feeding related characters in a nodosaurid ankylosaur, Hungarosaurus tormai, from the Late Cretaceous of Hungary. Dental wear patterns comprising small, apical, and low-angled facets on the maxillary and steep, extended, and bowl-like facets on the dentary teeth reveal sophisticated tooth-tooth contact in this basal nodosaurid. The presence of two different scratch generations (vertical and low-angled) on the dentary teeth unambiguously demonstrate a multiphasic powerstroke, which is further supported by the morphology of the quadrate-articular and mandibular symphyseal joints and by the architecture of the reconstructed jaw adductors. Chewing started with an initial slicing phase associated with orthal movement that was followed by a retractive powerstroke with significant occlusal contact. Because of the curved tooth rows, these movements were probably facilitated by some mediolateral translation and/or axial rotation of the mandibles to produce precise shearing along the whole tooth row. These results demonstrate that complex jaw mechanisms and dental occlusion were more widespread among thyreophorans than thought previously and that palinal movement was present in at least two ankylosaurian lineages.

The Basal Nodosaurid Ankylosaur Europelta carbonensis n. gen., n. sp. from the Lower Cretaceous (Lower Albian) Escucha Formation of Northeastern Spain

Nodosaurids are poorly known from the Lower Cretaceous of Europe. Two associated ankylosaur skeletons excavated from the lower Albian carbonaceous member of the Escucha Formation near Ariño in northeastern Teruel, Spain reveal nearly all the diagnostic recognized character that define nodosaurid ankylosaurs. These new specimens comprise a new genus and species of nodosaurid ankylosaur and represent the single most complete taxon of ankylosaur from the Cretaceous of Europe. These two specimens were examined and compared to all other known ankylosaurs. Comparisons of these specimens document that Europelta carbonensis n. gen., n. sp. is a nodosaur and is the sister taxon to the Late Cretaceous nodosaurids Anoplosaurus, Hungarosaurus, and Struthiosaurus, defining a monophyletic clade of European nodosaurids– the Struthiosaurinae.

A New Nodosaurid Ankylosaur from the Chaochuan Formation of Dongyang, Zhejiang Province, China

Abstract:Dongyangopelta yangyanensis gen. et sp. nov. from the Chaochuan Formation (Albian – Cenomanian) of Dongyang, Zhejiang Province, China is characterized: the convex anterior surface of the first presacral rod centrum strongly inflates laterally and slightly curves posteriorly; the fused pelvic shield composes of larger pebble‐shaped bosses, defined by smaller tubercles or flat stretches of bone; most osteoderms are heavily roughened with notches and grooves for dermal attachment along the edge; domed triradiate osteoderm is present; sigmoid curvature of the dorsal surface of the ilium is present; the preacetabular process curves lateroventrally at the anterior end and has a shallow groove in the edge of the lateral and anterior ends and strong lateromedial expansion of the distal femur. The femoral head is well separated from the greater trochanter, indicating that Dongyangopelta is a nodosaurid ankylosaur, the second from southeast China. Phylogenetic analysis also positions this taxon in the Nodosauridae clade. Dongyangopelta differs from Zhejiangosaurus in the characters of presacral rod, ilium, and femur. Dongyangopelta represents the first ankylosaur outside North America and Europe that definitively possesses a pelvic shield with fused armor.

Sympatry of two ankylosaurs (Hungarosaurus and cf. Struthiosaurus) in the Santonian of Hungary

A complete and well-preserved right ankylosaurian humerus from the Upper Cretaceous (Santonian) Csehbánya Formation of Iharkút, western Hungary is described here. Based on its osteological features and 21.5 cm adult length, the new specimen is markedly different from the slender humerus of Hungarosaurus, the previously known ankylosaur from the locality, and more similar to that of Struthiosaurus. Thus, the new Hungarian specimen is tentatively assigned here to cf. Struthiosaurus thereby dating back the first occurrence of this genus to the Santonian. The new fossil demonstrates the sympatric co-existence of two different nodosaurid ankylosaurs (a smaller, robust form with 2–2.5 m total body length and a larger, cursorial form with 4–4.5 m body length) in the Iharkút fauna. This also suggests that the pattern of the European ankylosaur diversity was more complex than previously thought.

New teeth of nodosaurid ankylosaur from the Lower Cretaceous of Southern England

We present new nodosaurid teeth from the Valanginian of Bexhill, Sussex and the Barremian of the Isle of Wight, the first from the Lower Cretaceous of the United Kingdom. Teeth found during the mid-1800s from the Valanginian and ascribed to the nodosaurid Hylaeosaurus are probably from sauropod dinosaurs. The Isle of Wight tooth could possibly be referred to Polacanthus foxii, the teeth of which are unknown. These new English nodosaurid teeth are similar to those of North American and European Jurassic to Late Cretaceous nodosaurids, especially the American Gastonia, Texasetes, Mymoorapelta, Gargoyleosaurus, and the European Hungarosaurus.

The First Hatchling Dinosaur Reported from the Eastern United States: Propanoplosaurus marylandicus (Dinosauria: Ankylosauria) from the Early Cretaceous of Maryland, U.S.A.

Abundant and diverse dinosaur footprints have been discovered recently on bedding surfaces of the Lower Cretaceous Patuxent Formation of Maryland and Virginia. Found along with those ichnofossils is a fossil preserved partially as natural casts and partially as natural molds of a baby nodosaurid ankylosaur so small as to justify interpreting it as a hatchling. Despite the rather unusual type of preservation, the find is properly termed a body fossil and not an ichnite, per se, because it records not the action of an organism, but the body form and bone structure (including partial articulation) of a dinosaur. We here name it Propanoplosaurus marylandicus and provide a description of its diagnostic characteristics. Although actual skeletal remains referable to P. marylandicus have not been found in the Patuxent Formation, other nodosaurids recognized from skeletal remains are known from both the Lower and Upper Cretaceous strata of the Western Interior of North America and Europe. P. marylandicus represents the only diagnostic nodosaurid from the Early Cretaceous of the eastern U.S.A., provides information on growth patterns among nodosaurids, and is the first direct evidence of a dinosaur hatchling and, deductively, nesting, on the entire eastern seaboard.

New remains of Hungarosaurus tormai (Ankylosauria, Dinosauria) from the Upper Cretaceous of Hungary: skeletal reconstruction and body mass estimation

Hungarosaurus tormai is a medium-sized nodosaurid ankylosaur that was described on the basis of four partial skeletons from the Santonian (Upper Cretaceous) of Hungary. In this paper, a new fifth skeleton and several isolated remains are described which greatly improve our knowledge of this primitive nodosaurid ankylosaur. Isolated cranial remains referred to juvenile individuals provide new information on the development of cranial ornamentation in nodosaurid ankylosaurs. Apart from both preserved mandibles with in situ dentition, the fifth partial skeleton contains several previously unknown limb elements (humerus, ulnae, radius) that indicate unusual limb proportions for Hungarosaurus compared with other ankylosaurs. On the basis of the five partial skeletons and the isolated remains, a skeletal and dermal armor reconstruction is attempted. Body mass calculations using three different methods yield an estimate of 650 kg for H. tormai.

Ankylosaurs from the Price River Quarries, Cedar Mountain Formation (Lower Cretaceous), east-central Utah

ABSTRACT A new large nodosaurid ankylosaur, Peloroplites cedrimontanus, is described from a partial skull and postcranial skeleton found at the PR-2 Quarry located at the base of the Mussentuchit Member of the Cedar Mountain Formation in central Utah. The specimen is about the same size as the contemporary nodosaurid Sauropelta edwardsorum from the Cloverly Formation of Montana, and is of an individual approximately 5–5.5 m long. The skull of Peloroplites differs from that of Sauropelta in the vertical orientation of the suspensorium, non-domed cranium and broad, square premaxillary beak. The quarry is near and roughly at the same level as the CEM Quarry that produced the holotype of the ankylosaurid Cedarpelta bilbeyhallorum. The postcrania of Cedarpelta is described and illustrated based on the paratype and new material. These elements clearly establish that Cedarpelta is closer to Ankylosaurus than to Sauropelta. As a primitive ankylosaurid, there is no a priori reason to assume that the tail club was present. Based on recent finds in China, a hypothesis is presented that the tail club is a derived feature in non-shamosaurine (i.e., ankylosaurine) ankylosaurids.

Palaeoenvironmental controls on the distribution of Cretaceous herbivorous dinosaurs

Previous attempts to determine palaeoenvironmental preferences in dinosaurs have generally been qualitative assessments based upon data from restricted geographical areas. Here, we use a global database of Cretaceous herbivorous dinosaurs to identify significant associations between clades and broad palaeoenvironmental categories ('terrestrial', 'coastal', 'marine'). Nodosaurid ankylosaurs and hadrosaurids show significant positive associations with marine sediments, while marginocephalians (Ceratopsia, Pachycephalosauria), saurischians (herbivorous theropods, Sauropoda) and ankylosaurid ankylosaurs are significantly positively associated with terrestrial sediments. These results provide quantitative support for the hypothesis that some clades (Nodosauridae, Hadrosauridae) were more abundant in coastal and/or fluvial environments, while others (e.g. Marginocephalia, Ankylosauridae) preferentially inhabited more distal environments.

A new nodosaurid ankylosaur (Dinosauria: Ornithischia) from the Paw Paw Formation (Late Albian) of Texas

ABSTRACT Pawpawsaurus campbelli gen. et sp. nov. from the Paw Paw Formation (late Albian), Tarrant County, Texas, appears more primitive than other pre-Campanian nodosaurids, Silvisaurus condrayi and Sauropelta edwardsi. New cranial synapomorphies for the Nodosauridae are prominent W-shaped basioccipital tubera, anteriorly concave and anteroposteriorly flattened quadrate, and transversely continuous and straight posterior margin of the pterygoid aligned with the quadrate shaft. These synapomorphies are closely related to the downward orientation of the nodosaurid head in life. A pair of bony eyelids recovered with the skull are the first discovered for the Nodosauridae. Other Paw Paw Formation nodosaurid remains, including new postcranial elements and a baby nodosaurid, are taxonomically indeterminate.

On the first partial skull of an ankylosaurian dinosaur from the Lower Cretaceous of the Isle of Wight, southern England

AbstractThe specimen is identified as the partial cranium of a nodosaurid ankylosaur (Ornithischia: Thyreophora) on the basis of the presence of bone which is fused to the dorsal surface of the skull and has secondarily closed the upper temporal fenestrae. The only unequivocally nodosaurid material recovered from the Isle of Wight to date comes from Wealden facies, and has been referred to the genus Polacanthus; it is considered highly probable that this new skull is referable to the same genus. Despite having undergone abrasion, through post-emergence water-rolling, the skull and cranial walls have proved to be relatively informative of the general anatomy of the braincase and the neural and vascular anatomy of this part of the head. The anatomy of the braincase of most ankylosaurs (with the notable exception of the juvenile specimens of the ankylosaurid Pinacosaurus) is surprisingly poorly known, despite the relative abundance of cranial material in North American and Asian collections.The cranial neural and vascular anatomy is well shown in this specimen and enables the first detailed description of nodosaurid endocranial structures. The general form of the brain can be outlined from the structure of the endocast and the principal lobes can be identified; the majority of the cranial nerves have been identified, and a significant component of the associated vascular system is also visible. In most respects the endocast shows a neural anatomy which is common to that known in most dinosaurs. When compared to their nearest relatives, the ankylosaurid ankylosaurs (Euoplocephalus), the nodosaurid endocranial cast shows a more pronounced cerebral flexure, a forebrain which is broader and more expanded dorsally, and a more prominent cerebellum (although there is no evidence for a floccular lobe); there are minor differences in the arrangement of the cranial nerves, and the dorsal portions of the vascular system are better shown.Because of erosion, the olfactory lobes of this specimen of cf. Polacanthus are not preserved, and cannot be compared to those of ankylosaurid ankylosaurs; the latter are unusual in the strong separation of the lobes (reflected in the divergent olfactory stalks); this feature may be associated with the very complex passages within the nasal region of the skull, which are lacking in the nodosaurids described to date.

The Dinosaurs of the Niobrara Chalk Formation (Upper Cretaceous, Kansas)

ABSTRACT The dinosaurian fauna of the Niobrara Chalk Formation constitutes the best known assemblage from the middle Santonian-early Campanian interval of the Late Cretaceous of North America. The fauna consists of both hadrosaurid ornithopods and nodosaurid ankylosaurs. The nodosaurid specimens from the Smoky Hill Chalk Member of the Niobrara Chalk Formation include the holotype of Hierosaurus sternbergii (here regarded as nomen dubium), material of “Hierosaurus” coleii (herein designated the type species of the new genus Niobrarasaurus) and two specimens that may belong to N. coleii, but are better interpreted as Nodosauridae incertae sedis. Claosaurus agilis, the sole hadrosaurid from the Niobrara Chalk Formation, constitutes a poorly known, but distinct species having a basal relationship among remaining hadrosaurids.