Late Jurassic Research Articles

Visualization and semi-quantitative analysis of dissolution processes at artificial structures in carbonate rocks using optical, 3D micro-scanning and confocal laser scanning microscopy

The Northern Alpine Foreland Basin in southeast Germany hosts more deep geothermal plants than any other region in the country. Its primary aquifer, the Upper Jurassic, is composed of permeable carbonates containing water with temperatures exceeding 150∘C in the southern margin and low total dissolved solids (≤ 2 g/L) at depths of up to 4000 m. Its sustainable use of geothermal energy depends on an efficient exploitation strategy concerning the entire reservoir, which is influenced by the development of flow paths between production and reinjection wells. The Upper Jurassic’s waters show a carbonate signature with calcium and magnesium often replaced by sodium due to ion exchange along the infiltration pathways. These waters become undersaturated upon cooling, and dissolution around reinjection wells has been previously documented. Assessing short- to medium-term localized dissolution experimentally is challenging. While dissolution kinetics and overall volume changes have been studied in the field, microscopic changes to flow paths remain less under investigation. This study used a time-lapse experiment to evaluate microscopic changes during dissolution in limestone samples exposed to elevated CO2 partial pressure in an autoclave. For an effective observation, we used artificial structures to localize the dissolution effects. Post-treatment analysis included Raman microscopy, 3D micro-scanning, confocal laser scanning microscopy (CLSM), and optical microscopy with image stacking, with a strong focus on the latter three. Each imaging method had distinct strengths and limitations. CLSM provided high-resolution surface roughness assessments but could not capture areas beneath overhangs. Optical microscopy is affordable and user-friendly and was effective for visualizing preferential dissolution pathways but lacked precise roughness information. 3D micro-scanning, despite lower resolution, uniquely resolved overhangs. The dissolution processes led to significant surface roughening, forming micrometer-scale moldic pores and preferential pathways. Artificial structures widened and deformed, with 3D micro-scanning quantifying these changes effectively and CLSM revealing fine-scale roughness details. Increased fracture surface roughness and widening of flow paths enhance water transport and dissolution, potentially accelerating thermal breakthroughs at geothermal plants. Understanding these processes is essential for predicting reservoir behavior, improving geothermal energy extraction efficiency, and exploiting aquifers sustainably.

A new mamenchisaurid from the Upper Jurassic Suining Formation of the Sichuan Basin in China and its implication on sauropod gigantism

The Sichuan Basin has yielded abundant sauropod dinosaurs from the Middle-Late Jurassic, and Mamenchisauridae had predominated the dinosaur faunae during the Late Jurassic in the Sichuan Basin. Here, we describe a new sauropod dinosaur, Tongnanlong zhimingi gen. et sp. nov. from the Upper Jurassic Suining Formation in the Sichuan Basin, southwestern China. The holotype includes three dorsal and six caudal vertebrae, scapula, coracoid, and some hindlimb bones. It is diagnosed by the complex structures of the dorsal and anterior caudal vertebrae compared to other mamenchisaurids. Phylogenetic analysis shows that it is more closely related to Mamenchisaurus than to Omeisaurus. The huge-sized scapula and coracoid also indicate that the specimen belongs to an extremely gigantic individual with a body length approaching about 25 ~ 26 m. The new specimen enriches the diversity of Mamenchisauridae and provides additional information for understanding the evolution and diversity of eusauropod dinosaurs.

Hunting the ghost: phylogenomic analyses reveal divergence, habitat transitions and character evolution of the ghost and mud shrimps (Decapoda: Axiidea).

Understanding when and how habitat transitions occurred is essential for a comprehensive insight into the succession of marine ecosystem and biodiversity. Here we investigated the evolutionary process of an ancient, widespread and ecologically diversified lineage of marine benthic fauna, the ghost and mud shrimps (Decapoda: Axiidea). To reconstruct a robust, time-calibrated phylogeny of this intractable group, we sampled more comprehensively than in previous studies and utilized three types of sequencing data: Sanger, genome-skimming and ultra-conserved elements (UCEs). The UCEs tree supports a monophyletic Axiidea sister to the 'Gebiidea + (Brachyura + Anomura)' clade. Our findings reveal the monophyletic status of Callianideidae and Micheleidae, whereas Axiidae and Strahlaxiidae as presently understood are shown to be non-monophyletic. Axiidae s.s. is now restricted to four genera, Strahlaxiidae to one genus, with most former "axiid" genera reclassified under Calocarididae. We determine that crown axiidean shrimps diverged in the Middle Triassic, with a significant habitat transition from epibenthic to endobenthic during the Middle to Late Jurassic, possibly in response to environmental changes and available ecological niche. We hypothesize that the extreme morphological and behavioural adaptations to the obligate/subsurface burrowing life facilitated the radiation and diversification of ghost shrimps, despite some instances of adaptive convergence.

A new hybodontiform shark (Strophodus Agassiz, 1838) from the Upper Jurassic of Switzerland

The hybodontiform shark-like Strophodus was a large durophagous predator with highly specialized crushing-type dentition that mainly inhabited Mesozoic marine environments for more than 130 million years, with a fossil record spanning from the Middle Triassic to the Lower Cretaceous. Strophodus was a geographically widespread taxon with 13 species reported from Africa, Asia, Europe, India and South America. Here, we describe a new species of Strophodus, which we name Strophodus timoluebkei sp. nov. based on three teeth from the same individual in semi-articulated position. The holotype was collected in the Prealpine Sulzfluh Limestone Formation (Middle Oxfordian to Late Tithonian), Central Switzerland. Strophodus timoluebkei sp. nov. currently is the only vertebrate species reported from this geological unit, and its presence suggests that this durophagous shark likely played an important role as predator of the invertebrate fauna in this ancient Tethyan tropical coastal ecosystem. The new discovery sheds additional light onto the hybodontiform paleodiversity during the Upper Jurassic.

On the Incompleteness of the Coelacanth Fossil Record

This study conducted a spatiotemporal review of the coelacanth fossil record and explored its distribution and diversity patterns. Coelacanth research can be divided into two distinct periods: the first period, which is based solely on the fossil record, and the second period following the discovery of extant taxa, significantly stimulating research interest. The distribution and research intensity of coelacanth fossils exhibit marked spatial heterogeneity, with Europe and North America being the most extensively studied regions. In contrast, Asia, South America, and Oceania offer substantial potential for future research. Temporally, the coelacanth fossil record also demonstrates significant variation across geological periods, revealing three diversity peaks in the Middle Devonian, Early Triassic, and Late Jurassic, with the Early Triassic peak exhibiting the highest diversity. With the exception of the Late Devonian, Carboniferous, and Late Cretaceous, most periods remain understudied, particularly the Permian, Early Jurassic, and Middle Jurassic, where the record is notably scarce. Integrating the fossil record with phylogenetic analyses enables more robust estimations of coelacanth diversity patterns through deep time. The diversity peak observed in the Middle Devonian is consistent with early burst models of diversification, whereas the Early and Middle Triassic peaks are considered robust, and the Late Jurassic peak may be influenced by taphonomic biases. The low population abundance and limited diversity of coelacanths reduce the number of specimens available for fossilization. The absence of a Cenozoic coelacanth fossil record may be linked to their moderately deep-sea habitat. Future research should prioritize addressing gaps in the fossil record, particularly in Africa, Asia, and Latin America; employing multiple metrics to mitigate sampling biases; and integrating a broader range of taxa into phylogenetic analyses. In contrast to the widespread distribution of the fossil record, extant coelacanths exhibit a restricted distribution, underscoring the urgent need to increase conservation efforts.

Региональные закономерности распределения смол и асфальтенов в нефтях Западной Сибири

The paper studies the spatial distribution patterns of resins and asphaltenes in the main regional oils reservoirs of the West Siberian megabasin. The studies on schematic maps for the main regional reservoirs (Lower and Middle Jurassic in general, Upper Jurassic, Neocomian, Aptian-Albian-Cenomanian) show that, from the central regions in the northern, northeastern and southeastern directions, a decrease in the content of resins and asphaltenes in oils is observed. In the central part of Western Siberia, oils with a relatively high content of resins and asphaltenes, formed in deep-sea sediments with hydrogen sulfide contamination, are localized in Jurassic and Cretaceous deposits. In the northern regions of Western Siberia, where less reducing conditions existed in marine sediments and there was a significantly higher level of catagenesis, low-resin, virtually asphaltene-free, light oils are localized in Jurassic and Neocomian deposits. The constructed maps-schemes of distribution of resins and asphaltenes in oils can be used in forecasting the quality of oils, in assessing the prospects of oil and gas potential of the West Siberian megabasin.

The impacts of diagenesis on bioturbated ramp deposits: A study of Arab-D outcrops in Wadi Malham, Central Saudi Arabia

Understanding how bioturbation influences diagenetic processes is critical for predicting final rock textures and their petrophysical properties. This study investigates how diagenesis alters bioturbated, mud-dominated carbonates in the upper part of the Late Jurassic Jubaila Formation, central Saudi Arabia—a unit characterized by extensive dolomitization. The studied 7.8-meter-thick interval contains 22 beds. Most beds (54%) consist of burrowed, mud-dominated intraclastic floatstones and rudstones (LF1), interpreted as middle ramp deposits. Two thin grain-dominated beds (LF2 and LF3), each ∼15 cm thick and together comprising only 4%, are interpreted as storm-event deposits. The dolomitized lithofacies include burrowed dolomitic limestones (LF4, 30%) and burrowed dolostones (LF5, 12%). LF1 contains dolomitized Thalassinoides unrelated to stratigraphic surfaces, whereas LF4 and LF5 exhibit surface-controlled Glossifungites ichnofacies. In LF4, dolomitization is largely restricted to burrow fillings, decreasing downward in intensity, paralleling bioturbation intensity. Sparse dolomite crystals appear in the host matrix. LF5 contains dolomite crystals in both burrows and matrix, showing non-fabric-preserving textures. Petrographic and geochemical data indicate dedolomitization (calcitized dolomite) in LF5, with calcitization intensity decreasing from bed tops downward. These findings suggest bioturbation significantly influenced dolomitization through: (1) passive burrow fillings acting as permeability pathways for dolomitizing fluids, or (2) dolomite formation triggered by organic matter degradation and microbial activity under anoxic conditions. Dedolomitization may follow similar pathways, with intercrystalline porosity in burrow fillings allowing calcium-rich fluids to calcitize dolomite. Since dolomitization improves porosity and permeability in these mud-rich lithofacies, understanding the spatial distribution of dolomite and its formation mechanisms is essential for predicting reservoir quality. These insights have implications for both hydrocarbon reservoir development and assessing the potential of such formations for subsurface geological storage, including carbon sequestration and hydrogen storage.

New name for the Jurassic dinoflagellate cyst species Gonyaulacysta longicornis (Deflandre, 1938) Riding et al., 2022

ABSTRACT One of the taxonomic actions in a recent review of the Jurassic dinoflagellate cyst genus Gonyaulacysta, was the elevation of the subspecies Gonyaulacysta jurassica subsp. longicornis Deflandre, 1938 to species rank, as Gonyaulacysta longicornis (Deflandre, 1938) Riding et al., 2022. In doing so, the authors of this review inadvertently created an illegitimate junior homonym of Gonyaulacysta longicornis (Downie, 1957) Sarjeant, 1969. To remedy this situation, we propose the new name Gonyaulacysta nasuta as a substitute for Gonyaulacysta longicornis (Deflandre, 1938) Riding et al., 2022, thus preserving the integrity of this important index taxon for the late Callovian to middle Oxfordian (Middle–Late Jurassic) of the Northern Hemisphere.

Meso-Cenozoic episodic uplift and exhumation of the Zhangguangcai Range, Northeast China: Insights from low-temperature thermochronology

Northeast China has undergone a complex tectonic history since the Mesozoic driven by its tectonic interaction with the Paleo-Pacific/Pacific plate. This history has been recorded across the Zhangguangcai Range making it a key region for investigating orogenic processes associated with Pacific plate subduction. Previous studies have identified multiple Mesozoic thermo-tectonic events without quantifying the precise timing and rates of crustal cooling and exhumation, and the mechanisms and driving forces behind the tectono-thermal evolution remain poorly understood. In this study, we present new zircon and apatite (U-Th)/He, as well as apatite fission track age data of Mesozoic granitic plutons constraining the regional thermal history to below 200 °C. Combined with thermal history modeling, our new data reveal periods of increased cooling in the Late Jurassic (165−140 Ma) at ∼2.8 °C/m.y. and Late Cretaceous (85−70 Ma) at ∼1.6 °C/m.y. We interpret the Late Jurassic rapid cooling phase to be linked to the closure of a pre-existing oceanic basin, the Mudanjiang Ocean, driven by the NNW subduction of the Paleo-Pacific plate. Similarly, the Late Cretaceous rapid cooling phase is thought to be associated with a more westward shift of the direction (NNW-NW) of Paleo-Pacific plate subduction. Notably, the activities of the Yilan-Yitong and Dunhua-Mishan faults played a significant role in regional orogenic events; they induced the regional differential uplift and terrane boundary (microplates) interactions. During the Cenozoic, the subduction of the Pacific plate predominantly influenced uplift and exhumation events along the plate margin, however, with only minor crustal responses in the Zhangguangcai Range. Overall, the subduction system of the Paleo-Pacific plate has provided the driving force for the regional stress fields, tectonic deformation, and magmatism in the upper plate since the Mesozoic, ultimately leading to the formation of a basin-and-range system in Northeast China.

Provenance and tectonic settings of late Triassic–Jurassic deposits in the Southwestern Yangtze block: evidence from the geochemistry, SW China

During the Late Triassic to Jurassic, the western Yangtze Block transitioned from marine carbonate deposits to terrestrial detrital deposits. There are different views on the orogen evolution of the western margin of the Yangtze Block, such as whether the Longmenshan Thrust Belt was uplifted in the Late Triassic or Early Jurassic, and when the Yangtze Block began to receive the source from Yidun Terrane. In this paper, whole-rock elemental compositions and zircon U–Pb ages and Hf isotope data from the Upper Triassic to Jurassic successions are introduced. The whole-rock elemental compositions reveal that the clastic rocks were deposited in a collisional setting and were derived mainly from intermediate–felsic magmatic rocks and recycled sediments. The Upper Triassic zircon sample shows a single age peak at ~ 831 Ma. The three Jurassic samples show similar age patterns with four main age populations (e.g., 200–500 Ma, 788–834 Ma, 1863–1875 Ma, and 2462–2531 Ma). The results revealed that the Kangdian Palaeo-land was the main provenance area in the Late Triassic. In contrast, in the Early Jurassic (~ 198.7 Ma), the Longmenshan was massively uplifted, and the recycled sediments from the Longmenshan, Songpan–Ganzi Terrane and Yidun Terrane provided large amounts of detrital material to the southwestern Yangtze Block. Volcanic rocks from the Yidun Terrane also provided a partial source for the southwestern Yangtze Block. In the Middle Jurassic, owing to the weathering and erosion of the Longmenshan Thrust Belt in the Early Jurassic, the provenance supply in Longmenshan decreased, and the provenances from the Yidun Terrane and the Songpan–Ganzi Terrane increased. In the Late Triassic to the Early Jurassic, the tectonic setting of the southwestern Yangtze Block may have changed from a passive continental margin to a foreland basin.

Diagenetic and sequence stratigraphic controls on reservoir quality in the Upper Jurassic Smackover Formation, southern Arkansas, USA

Diagenetic and sequence stratigraphic controls on reservoir quality in the Upper Jurassic Smackover Formation, southern Arkansas, USA

Internal structure of the Upper Jurassic subsurface carbonate buildups of the northern Tethys shelf in southern Poland – integration of seismic forward modeling and outcrop analogs

Internal structure of the Upper Jurassic subsurface carbonate buildups of the northern Tethys shelf in southern Poland – integration of seismic forward modeling and outcrop analogs

Chemostratigraphy of the Upper Jurassic (Kimmeridgian–Tithonian) Pałuki Formation of central Poland and its correlation to organic matter rich deposits of Western Europe

Geochemical data derived from fine-grained, organic rich deposits of the Pałuki Formation of central Poland, which are coeval with those of the Kimmeridge Clay of England, are presented here. Precise biostratigraphical dating and correlations show strict simultaneity of occurrences of major (≤ 10.7 wt.%) and minor (≤ 5.2 wt.%) organic rich horizons of the Pałuki Formation from the higher Eudoxus–Pseudoscythica zone interval with their equivalents known from the NW Europe. This coincidence is despite a partially different sequence stratigraphic framework of the Pałuki Formation. The calculated chemical redox and palaeoproductivity indices show predominant subooxic and more oligotrophic settings in the lower part of the Pałuki Formation, which are followed by a gradual change of the depositional parameters to more anoxic and eutrophic ones. The uppermost portion of the studied strata is, however, characterized by a decrease in organic matter content and an increase in calcium carbonate content. This phenomenon is interpreted as a result of gradual climate aridification, being in agreement with local and regional geochemical proxies of weathering intensity. The chemostratigraphical data reported point to orbital forcing of the latest Jurassic climate of NW and central Europe and to synchronicity of its high-amplitude variations.

An arboreal rhynchocephalian from the Late Jurassic of Germany, and the importance of the appendicular skeleton for ecomorphology in lepidosaurs

Abstract Here, we describe a new species of Jurassic rhynchocephalian from the Solnhofen Archipelago, Sphenodraco scandentis gen. et sp. nov., and highlight the importance of the postcranial anatomy for ecomorphological studies in the rhynchocephalian clade. The holotype of Sphenodraco scandentis is divided into a main slab, which has been mentioned in the literature and previously assigned to Homoeosaurus maximiliani, and a counterslab containing most of its skeletal remains. This new taxon shows an exclusive combination of osteological features that differs from previously described rhynchocephalians. Sphenodraco was recovered in our phylogenetic analysis as a component of a clade including Homoeosaurus and Kallimodon. To evaluate the ecomorphology of the new taxon, we compare fossil rhynchocephalians with the extant tuatara and squamates. We quantify the diversity of body proportions in lepidosaurs systematically, inferring lifestyle for extinct rhynchocephalians. Our analysis suggests that fossil rhynchocephalians had a diverse array of substrate uses, with some categorized as good climbers, and with Sphenodraco showing the extreme condition of limb elongation found in strictly arboreal lizards. This new taxon is here regarded as the first predominantly or even strictly arboreal rhynchocephalian. Furthermore, our analysis shows that the diversity of fossil rhynchocephalians might still be underestimated.

Convergent evolution among non‐carnivorous, desert‐dwelling theropods as revealed by the dentary of the noasaurid Berthasaura leopoldinae (Cretaceous of Brazil)

Abstract The Cretaceous witnessed the establishment of many desertic landscapes across the globe, including the Early Cretaceous Caiuá palaeodesert, in south‐central Brazil, and those of several Late Cretaceous deposits of the Gobi Desert. Although separated in time and space, their faunas share the presence of medium‐sized, edentulous theropods (e.g. oviraptorids and Berthasaura leopoldinae) which depart from the typically carnivorous diet of the group. Here, we report a new dentary of the latter taxon, which bears alveolar vestiges, suggesting that its teeth were lost during ontogeny, as previously reported for another noasaurid, Limusaurus inextricabilis, from the Late Jurassic of China. In addition, we used geometric morphometrics to quantitatively analyse the shape of theropod jaw bones, revealing a significant morphological convergence signal for the dentary of Be. leopoldinae and oviraptorids, which are dorsoventrally deep, and bear a large mandibular fenestra. This probably resulted from adaptations to feed on the tough parts of xerophytic plants, which are important food sources in desertic environments.

Schlagintweitella inopinata, a new genus and species of Dasycladales (green algae) from the Upper Jurassic limestones of Romania

Within the Upper Jurassic deposits of the Cioclovina-Băniţa area (Southern Carpathians), an outcrop was identified that most likely corresponds to a cavern fill. In several clasts of this fill, including black-pebbles, we found a dasycladalean alga whose morphological features differentiate it from all other Jurassic-Cretaceous dasycladalean algae with two orders of laterals. This alga is described in the present work as a new species of a new genus: Schlagintweitella inopinata nov. gen., nov. sp.

Erratum to: redescription of the Upper Jurassic Aeshna antiqua Vander Linden, 1827 in the anisopteran family Protolindeniidae (odonata)

The authors of the paper found some mistakes in the publication ‘Redescription of the Upper Jurassic Aeshna antiqua Vander Linden, 1827 in the Anisopteran family Protolindeniidae (Odonata)’.

Petrogenesis of Late Jurassic–Early Cretaceous Granitoids in the Central Great Xing’ an Range, NE China

The Great Xing’ an Range is located in the eastern part of the Xing’ an-Mongolian Orogenic Belt, which is an important component of the Central Asian Orogenic Belt. To determine the emplacement age and petrogenesis of the granitoids in the Gegenmiao and Taonan areas of the central Great Xing’an Range, and to investigate its tectonic setting, petrographic studies, zircon U-Pb geochronology, whole-rock Sr-Nd isotopic analysis, zircon Hf isotopic analysis, and detailed geochemical investigations of this intrusion were carried out. The results indicate the following, in relation to the granitoids in the study areas: (1) The zircon U-Pb dating of the granitic rocks in the study areas yields ages ranging from 141.4 ± 2.0 Ma to 158.7 ± 1.9 Ma, indicating their formation during the Late Jurassic to Early Cretaceous; (2) the geochemical characteristics indicate that these rocks belong to the calc-alkaline series and peraluminous, classified as highly fractionated I-type granites with adakite features; (3) the Sr-Nd isotopic data show that the εNd(t) values of Gegenmiao granitic rocks are 2.8 and 2.1, while those of Taonan granitic rocks range from −1.5 to 0.7; (4) the Zircon εHf(t) values of the granitic rocks from Gegenmiao and Taonan vary from 2.11 to 6.48 and 0.90 to 8.25, respectively. They are interpreted to have formed through partial melting of thickened lower crustal material during the Meso-Neoproterozoic. The Gegenmiao and Taonan granitic rocks were formed in a transitional environment from post-orogenic compression to extension, which is closely associated with the Mongolia–Okhotsk tectonic system.

First Paleomagnetic and Geochronological Results From the Early Cretaceous Volcanic Rocks in the Western Tethyan Himalaya: Contribution to the Breakup of Eastern Gondwana and the Paleogeography of Neo‐Tethys Ocean

Abstract The temporal‐spatial relationships of widely distributed latest Jurassic–Early Cretaceous igneous rocks in the Tethyan Himalaya (TH) are crucial for understanding the breakup of eastern Gondwana and the paleogeography of the Neo‐Tethys Ocean. However, no paleomagnetic data are available from the Early Cretaceous volcanic rocks in the central‐western TH. Here, we report the first paleomagnetic and geochronological results from Early Cretaceous volcanic rocks, dated at ∼144‒142 Ma, in the western TH. The tilt‐corrected site‐mean direction for 31 sites is Ds = 303.9°, Is = −58.7° with α95 = 4.3°, yielding a mean pole at 1.9°N, 303.2°E (A95 = 5.0°) and a paleolatitude of 40.8 ± 5.0°S for the Zhongba area. Positive fold and reversal tests support pre‐fold primary magnetizations. Our paleomagnetic and geochronological results, combined with those from the eastern TH, northeastern India, and southwestern Australia, reveal that the latest Jurassic–Early Cretaceous volcanic rocks were emplaced across a paleolatitudinal range from approximately 40.8°S to 55.5°S, with a central paleolatitude of about 48.2°S, which is consistent with the present‐day latitude of the Kerguelen Mantle Plume (KMP). This, along with the affinity of these rocks to the KMP‐related magmatic rocks supports that the latest Jurassic–Early Cretaceous TH igneous rocks originated from the KMP, and that the KMP contributed to the breakup of eastern Gondwana. Comparison of Early Cretaceous paleolatitudes observed from the western TH and Lhasa terrane shows that the latitudinal width of the Neo‐Tethys Ocean was ∼6,600 km at ∼144–142 Ma.

Enigmacursor mollyborthwickae, a neornithischian dinosaur from the Upper Jurassic Morrison Formation of the western USA

Although their remains have been known since the 1870s, the small, bipedal ornithischian dinosaurs from the Upper Jurassic Morrison Formation of the western USA remain poorly known. The historic type specimens are incomplete and poorly preserved and have recently been designated as nomina dubia. Here, we describe a recently collected, partial but three-dimensionally preserved skeleton of a new small-bodied ornithischian from the Morrison Formation of Colorado, USA, that we name Enigmacursor mollyborthwickae gen. et sp. nov. The skeleton includes substantial portions of the axial and appendicular skeleton and, when scored into a phylogenetic analysis, is shown to be a non-cerapodan neornithischian, whose closest relative is Yandusaurus hongheensis from the Late Jurassic of China. The discovery of Enigmacursor enhances the diversity of ornithischian dinosaurs from the Morrison Formation and provides new information on their anatomy. In addition, it demonstrates that there is additional cryptic diversity of small-bodied Morrison Formation ornithischians, suggesting they were a more diverse component of these Late Jurassic ecosystems than was previously realized.