End Of The Cretaceous Research Articles

The genome of Shorea leprosula (Dipterocarpaceae) highlights the ecological relevance of drought in aseasonal tropical rainforests

Hyperdiverse tropical rainforests, such as the aseasonal forests in Southeast Asia, are supported by high annual rainfall. Its canopy is dominated by the species-rich tree family of Dipterocarpaceae (Asian dipterocarps), which has both ecological (e.g., supports flora and fauna) and economical (e.g., timber production) importance. Recent ecological studies suggested that rare irregular drought events may be an environmental stress and signal for the tropical trees. We assembled the genome of a widespread but near threatened dipterocarp, Shorea leprosula, and analyzed the transcriptome sequences of ten dipterocarp species representing seven genera. Comparative genomic and molecular dating analyses suggested a whole-genome duplication close to the Cretaceous-Paleogene extinction event followed by the diversification of major dipterocarp lineages (i.e. Dipterocarpoideae). Interestingly, the retained duplicated genes were enriched for genes upregulated by no-irrigation treatment. These findings provide molecular support for the relevance of drought for tropical trees despite the lack of an annual dry season.

Feeding ecology has shaped the evolution of modern sharks

Sharks are iconic predators in today's oceans, yet their modern diversity has ancient origins. In particular, present hypotheses suggest that a combination of mass extinction, global climate change, and competition has regulated the community structure of dominant mackerel (Lamniformes) and ground (Carcharhiniformes) sharks over the last 66 million years. However, while these scenarios advocate an interplay of major abiotic and biotic events, the precise drivers remain obscure. Here, we focus on the role of feeding ecology using a geometric morphometric analysis of 3,837 fossil and extant shark teeth. Our results reveal that morphological segregation rather than competition has characterized lamniform and carcharhiniform evolution. Moreover, although lamniforms suffered a long-term disparity decline potentially linked to dietary "specialization," their recent disparity rivals that of "generalist" carcharhiniforms. We further confirm that low eustatic sea levels impacted lamniform disparity across the end-Cretaceous mass extinction. Adaptations to changing prey availability and the proliferation of coral reef habitats during the Paleogene also likely facilitated carcharhiniform dispersals and cladogenesis, underpinning their current taxonomic dominance. Ultimately, we posit that trophic partitioning and resource utilization shaped past shark ecology and represent critical determinants for their future species survivorship.

Genesis of langrial iron ore of hazara area, khyber pakhtunkhaw, parkistan

The Iron Ore of Hazara area has been studied at seven locations for detail mineralogical and genesis investigations. Thick bedded iron ore have been observed between Kawagarh Formation and Hangu Formation i.e Cretaceous-Paleocene boundary. At the base of Hangu Formation variable thickness of these lateritic beds spread throughout the Hazara and Kohat-Potwar plateau. This hematite ore exists in the form of unconformity. X-Ray Diffraction technique (XRD), X-ray Fluorescence Spectrometry (XRF), detailed petroghraphic study and Scanning Electron Microscope (SEM) techniques indicated that iron bearing minerals are hematite, chamosite and quartz, albite, clinochlore, illite-montmorillonite, kaolinite, calcite, dolomite and ankerite are the impurities present in these beds. The X-ray Fluorescence (XRF) results show that the total Fe2O3 ranges from 39 to 56% and it has high silica and alumina ratio is less than one. Beneficiation requires for significant increase in ore grade. The petroghraphic study revealed the presence of ooids fragments as nuclei of other ooids with limited clastic supply which indicate high energy shallow marine depositional setting under warm and humid climate. The overall results show that Langrial Iron ore is a low-grade iron ore and can be upgraded up to 62% by applying modern mining techniques to fulfill steel requirements of the country.

Evaluation of environmental impacts of the Covid-19 on the Iran: an updated review

Since December 2019, COVID-19 disease has been spread rapidly in all regions of the world, from cold and dry to hot and humid climates. The results show that after one year (10 May, 2021) infection cases are about 24 times and death cases are about 11 times in the Iran. The ratios are relatively not far from to average data in the other parts of the world. The COVID-19 is a pandemic that affects not only every parts of our life but also different parts of the ecosystems and environment. After one year, ideas about role of this crisis in ecosystem and environment are quite different. Optimists believe that this crisis is the best opportunity to reduce pressure on natural resources and provides time for self-reconstruction of the ecosystems and environment. The pessimist state that the Covid-19 is going to destroy our ecosystem such as catastrophe worse that dinosaur extinction. The most positive impacts of this crisis are reduced pressure on natural resources, decreasing in air pollution and climate change, deeper understanding of the ecosystems and environment saving. The significant negative impacts of this crisis are human infection and death, economic losses, increasing in household consumption, medicine, faces masks and medical gloves and challenge for burial of household and medical waste, reduction in environmental diplomacy, reduction in accuracy of weather forecasts and treat for wildlife infection. The impacts on the ecosystems and environment of Iran are similar to that reported in other parts of the world.

Evolution and dispersal of snakes across the Cretaceous-Paleogene mass extinction

Mass extinctions have repeatedly shaped global biodiversity. The Cretaceous-Paleogene (K-Pg) mass extinction caused the demise of numerous vertebrate groups, and its aftermath saw the rapid diversification of surviving mammals, birds, frogs, and teleost fishes. However, the effects of the K-Pg extinction on the evolution of snakes—a major clade of predators comprising over 3,700 living species—remains poorly understood. Here, we combine an extensive molecular dataset with phylogenetically and stratigraphically constrained fossil calibrations to infer an evolutionary timescale for Serpentes. We reveal a potential diversification among crown snakes associated with the K-Pg mass extinction, led by the successful colonisation of Asia by the major extant clade Afrophidia. Vertebral morphometrics suggest increasing morphological specialisation among marine snakes through the Paleogene. The dispersal patterns of snakes following the K-Pg underscore the importance of this mass extinction event in shaping Earth’s extant vertebrate faunas.

Genesis of Langrial Iron Ore of Hazara area, Khyber Pakhtunkhwa, Pakistan

In this paper, a detailed mineralogical and genesis investigation have been carried out in the seven locations of the Iron Ore in Hazara area. Thick bedded iron ore have been observed between Kawagarh Formation and Hangu Formation i.e, Cretaceous-Paleocene boundary. At the base of Hangu Formation, variable thickness of these lateritic beds spread throughout the Hazara and Kohat-Potwar plateau. This hematite ore exists in the form of unconformity. X-ray diffraction technique (XRD), X-ray fluorescence spectrometry (XRF), detailed petroghraphic study and scanning electron microscope (SEM) techniques indicated that those iron bears minerals including hematite, chamosite and quartz, albite, clinochlore, illite-montmorillonite, kaolinite, calcite, dolomite, whereas ankerite are the impurities present in these beds. The X-ray fluorescence (XRF) results show that the total Fe2O3 ranges from 39 to 56%, with high silica and alumina ratio of less than one. Beneficiation requires for significant increase in ore grade. The petroghraphic study revealed the presence of ooids fragments as nuclei of other ooids with limited clastic supply, which indicate high energy shallow marine depositional setting under warm and humid climate. The overall results show that Langrial Iron Ore is a low-grade iron ore which can be upgraded up to 62% by applying modern mining techniques so as to fulfill steel requirements of the country.

The South American and Antarctic Peninsula fossil record of Salviniales (water ferns): Its implication for understanding their evolution and past distribution

We compiled the fossil record of the heterosporous water ferns (Salviniales) including macro- and microfossils from South America and the Antarctic Peninsula. Both extant families, Marsileaceae and Salviniaceae, are well represented and several fossil spore genera that cannot be placed within the extant families are included as Incertae sedis. Marsileaceae is first recorded in the Middle to Late Jurassic. Incertae sedis genera are recorded for first time in the Early Cretaceous while Salviniaceae in the Late Cretaceous. Two diversity spikes are recognized: one spanned the Aptian–Albian (Early Cretaceous) and is linked to an increase in species diversity within Marsileaceae; and the other occurred during the Campanian–Maastrichtian (Late Cretaceous) and it is associated with the diversification at generic level of the entire Salviniales. Two decreases in diversity are recognized: one during the Cenomanian–Santonian and affected Marsileaceae at specific level but not its generic diversity, and the second is related to the Cretaceous–Paleogene mass extinction and affected all Salviniales at generic and specific levels. From the Paleocene onwards there is a steady decline in the fossil record of the group, with most remains belonging to the extant genera. This study suggests that Southern Hemisphere aquatic ferns underwent a sharp radiation during the Late Cretaceous and a deep decline in the Paleocene that parallels that occurred in the Northern Hemisphere. Probably, the temporal co-occurrence of geological and climate events and the availability of suitable lineages promoted the evolutionary changes of the water ferns in the studied area, including the high diversification and distribution in the Cretaceous and the subsequent post-Maastrichtian decline.

A new latest Cretaceous pleurodiran turtle (Testudinata: Dortokidae) from the Haţeg Basin (Romania) documents end-Cretaceous faunal provinciality and selective survival during the K-Pg extinction

Dortokidae is an endemic family of stem-pleurodiran turtles, known exclusively from the Cretaceous and early Paleogene of Europe. Here we describe a new dortokid taxon from the Upper Cretaceous (Maastrichtian) Sînpetru Formation of the southern Haţeg Basin, Romania. The type material of Dortoka vremiri sp. nov. comprises a well-preserved carapace and a nearly complete plastron as well as the in situ right scapula and right pubis. Phylogenetic analyses performed to assess the position and interrelationships of Dortoka vremiri sp. nov. within Dortokidae as well as within the wider Pleurodira recovered the new taxon firmly nested within Dortokidae, and together with other dortokids, placed along the stem lineage of pleurodires. Our analysis provides evidence for allopatric speciation in Dortoka through the presence of two distinct lineages – an eastern and a western European lineage, respectively. A similar east/west disjunct distribution pattern has also been established previously for several vertebrate groups such as other turtles, dinosaurs and mammals, probably resulting from isolation due to the particular palaeogeographical setting of the Late Cretaceous European Archipelago. The phylogeny demonstrates local survival of Dortoka across the K-Pg boundary as the sister-taxon of D. vremiri is D. botanica from the uppermost Paleocene deposits of Romania and points to geographical selectivity, as the western lineage of Dortoka went extinct before the Paleogene. Osteology and novel taphonomical data imply a semi-terrestrial lifestyle for Kallokibotion bajazidi, a turtle occurring in coeval faunas with the aquatic and smaller-sized D. vremiri and most likely going extinct at the K-Pg boundary. Altogether, this pattern is consistent with selective extinction of terrestrial taxa previously observed for other continental vertebrate assemblages across the end-Cretaceous mass extinction with only two other examples from turtles. http://zoobank.org/urn:lsid:zoobank.org:pub:871AD436-9448-40C6-85A4-0213CBC04A29

Clumped-isotope-derived climate trends leading up to the end-Cretaceous mass extinction in northwest Europe

Clumped-isotope-derived climate trends leading up to the end-Cretaceous mass extinction in northwest Europe

Bird neurocranial and body mass evolution across the end-Cretaceous mass extinction: The avian brain shape left other dinosaurs behind.

Birds today are the most diverse clade of terrestrial vertebrates, and understanding why extant birds (Aves) alone among dinosaurs survived the Cretaceous-Paleogene mass extinction is crucial to reconstructing the history of life. Hypotheses proposed to explain this pattern demand identification of traits unique to Aves. However, this identification is complicated by a lack of data from non-avian birds. Here, we interrogate survivorship hypotheses using data from a new, nearly complete skull of Late Cretaceous (~70 million years) bird Ichthyornis and reassess shifts in bird body size across the Cretaceous-Paleogene boundary. Ichthyornis exhibited a wulst and segmented palate, previously proposed to have arisen within extant birds. The origin of Aves is marked by larger, reshaped brains indicating selection for relatively large telencephala and eyes but not by uniquely small body size. Sensory system differences, potentially linked to these shifts, may help explain avian survivorship relative to other dinosaurs.

Physical characterization of a simulated impact-vapor plume using laser ablation of Chicxulub sediments

An asteroid impacted the Yucatan carbonate platform in the Southern Gulf of Mexico about 66 million years ago. The ejecta and impact-vapor plume introduced massive amounts of gases and dust into the atmosphere causing major global environmental effects that led to the Cretaceous-Paleogene mass extinction. The physical parameters of the Chicxulub impact-vapor plume are not completely known and are important to constrain its evolution and the aftermath of the event. Here we reconstruct the impact-vapor plume by laser ablation of target sediments recovered from the Yaxcopoil-1 borehole in the Chicxulub impact crater. The ablation experiment was performed under a reconstructed late Cretaceous atmosphere composed of 0.16% CO2, 30% O2, and 69.84% N2 at 1000 ​mbar. The initial propagation velocities of the shockwave and impact-vapor plume were ~4.5 ​km ​s−1 and ~2.3 ​km ​s−1, respectively. The temperature and electron density of a simulated Chicxulub impact-vapor plume were determined using calcium emission lines. The initial temperature and electron density were estimated to be ~1.8(±0.1)×104 ​K and ~5.9(±0.7)×1017 ​cm−3, respectively. The plume expanded adiabatically with a specific heat ratio of 1.31 ​± ​0.03. Its initial pressure was computed to be ~103 ​bar. These parameters are required in gas dynamic codes to develop chemical models to study the evolution of the simulated impact-vapor plume and predict the fluxes and nature of gases, vapors and mineral phases injected in the atmosphere. Such chemical models will allow scaling from laboratory to planetary conditions to better constrain the chemical effects to the environment and the biosphere by the asteroid impact.

End-Cretaceous to middle Eocene events from the Alpine Tethys: Multi-proxy data from a reference section at Kršteňany (Western Carpathians)

Early Paleogene events of the Alpine Tethys were considerably upgraded for the Western Carpathians. The Kršteňany KRS-3 core section provides high-resolution data from the Cretaceous-Paleogene (K/Pg) transition to Lutetian/Bartonian boundary. The Upper Cretaceous sequence started from terrestrial red-beds superposed by transgressive sediments with Abathomphalus mayaroensis. The K/Pg transition is inferred in a horizon with reworked Maastrichtian microfossils and earliest Danian species of Globigerinidae. Multiple redeposition with eugubina-rich clasts implies a storm erosion and resuspension of the post K/Pg sequence during P0 - Pα Zones (approx. 300 kyr). The early Danian microfauna was initially impoverished, later enriched by first praemuricids, and after the Latest Danian Event (LDE) diversified to angulate morozovellids, igorinids and fasciculiths. Paleocene bioevents and polarity chrons imply a radiation of planktic foraminifera during transgressive cycles in the late Danian (P1, C28n), Middle Selandian (P3b, C26r/n) and late Thanetian (P4c/P5, C25n/C24r), and vacant P/C zones either in regressive cycles or during unconformities in the early Danian (P1a/C28r), Danian/Selandian transition (P2/P3a, C27r/n) and middle Thanetian (P4b/C25r). The late Thanetian transgression (Th-2) led to replacement of Assilina-rich beds (SBZ 4) by Nummulites-bearing marls (SBZ 5) at the base of Ilerdian (= LFT). The Paleocene – Eocene transition is marked by Acarinina-rich marlstones with densely muricate species (Ac. acarinata) and excursion taxa (Ac. sibaiyaensis, D. araneus), which correspond to the Paleocene-Eocene Thermal Maximum (PETM). This horizon implies a warm-water productivity, eutrophication, humidity and upwelling activity (pteropods, diatoms). The hyperthermal conditions culminated at the beginning of the Early Eocene Climatic Optimum (EECO) with demise of morozovellids, intensification of hydrological cycles and enhanced continental input of siliciclastics, which progressed by accumulation of Ypresian nummulite banks and terminated by pelagic deposition with recovery of hispid morozovellids (E5 – E7 Zones, chron C23n - C22r). The lower Lutetian sequence reveals a post-EECO cooling by predominance of deep-dwelling habitats (subbotinids, turborotaliids, catapsydracids) and appearance of subtile morozovellids (M. gorrondatxensis), earliest globigerinathekids and another marker species of the E7 – E8 Zones (chron 22n - C21r). Late Lutetian warming (LLTM) is indicated by increased plankton productivity of mixed-layer habitats like strongly muricate species of anguloconical acarininids (Ac. topilensis, Ac. medizzai) and gracile species of morozovelloids (M. coronatus). The youngest part of the Kršteňany section belongs to the E11 Zone, indicating prior conditions of Middle Eocene Climatic Optimum (MECO) warming.

Cretaceous–Paleogene transition interval in the north flank of the Alborz Mountains (N Iran); Planktic foraminiferal biostratigraphy and stable isotopes evidence

A Cretaceous/Paleogene (K/Pg) boundary interval in the north flank of Alborz Mountains (Aboksar section), northern Iran, has been studied to investigate the biological and geochemical variations of this event in the eastern Tethys. Abathomphalus mayaroensis at the late Maastrichtian, Pα (Parvularugoglobigerina eugubina), P1a (Parasubbotina pseudobulloides) and P1b (Subbotina triloculinoides) at the early Danian are the recognized planktic foraminiferal biozones and subzones in the studied area. The Plummerita hantkeninoides subzone at the uppermost Maastrichtian and P0 Biozone at the base of Danian were not defined in the studied section. This proposes a short-term hiatus and sedimentary discontinuity at the base of Paleocene and probably uppermost Maastrichtian, which most likely caused by winnowing of sediments after a cooling phase and development of bottom current in the Albors Basin. The K–Pg transition in the Aboksar section is characterized by a bloom in the Guembelitria cretacea, evolution of first Danian species (Pv. eugubina, Pv. longiapertura), δ13C negative shift (about 0.5‰), and a gentle Ir anomaly (0.1 ppb). Planktic foraminifera were diverse and abundant during the late Maastrichtian of studied section in a warm (relatively lower δ18O contents) and well stratified environment. Bloom of the opportunist species, G. cretacea, and decrease of planktic foraminiferal abundance and diversity at the base of Paleocene interval propose an abnormal stressful environment in this time probably after the asteroid impact and its following temperature decline. The appearance of more complete species with more specialized shells and larger sizes, such as Globoconusa daubjergensis, Parasubbotina pseudobulloides, Eoglobigerina eobulloides and Subbotina triloculinoides in the P1a and P1b subzones and return of carbon isotope diagram into the pre-boundary values testify an environmental recovery and optimization of ecosystem conditions.

Revisiting Russell’s troodontid: autecology, physiology, and speculative tool use1

Dale Russell described the osteology, morphology, and ecology of the small theropod “Stenonychosaurus inequalis” in two papers, speculating on its life habits, brain power, vision, movement, feeding, and hand capabilities. Russell even pondered a tool-using dinosauroid, the hypothetical troodontid descendant if the lineage had survived the Cretaceous–Paleogene extinction event. We revisit the life habits of the North American troodontids Troodon formosus and Latenivenatrix mcmasterae in part by reviewing various trace fossils of T. formosus discovered in Montana. These fossils include egg clutches, a nest, and recently discovered regurgitalites. We also contemplate the possibility of dinosaur tool use. Troodon likely constructed earthen nests in the same way that ratites and other birds did to create their nesting scrapes through backward hindlimb kicks. The more complex clutch architecture suggests dexterous movement of the eggs, potentially requiring manual manipulation. Functionally, reproductive traces support elevated body temperatures and a metabolic output that approach but do not equal that of modern birds. Brooding would require very high energy investment from the adult. The regurgitalites largely contain multi-individual aggregations of the marsupialiform Alphadon and support Russell’s hypotheses of troodontids as crepuscular to nocturnal, intelligent, small game hunters with elevated metabolism and enhanced vision. Tool use in a few crocodilians and widely among extant birds suggests a reasonable possibility of this behavior in nonavian dinosaurs. Whether an avian-comparable encephalization quotient and freed forelimbs would make North American troodontids good candidates for exhibiting such behavior remains an open and speculative question. However, given the minimal modification made to tools by modern archosaurs, recognition of fossil tools poses a challenging problem.

The Chicxulub impactor: comet or asteroid?

Abstract Steve Desch, Alan Jackson, Jessica Noviello and Ariel Anbar assess the evidence for what type of object caused the end–Cretaceous extinction and suggest best practices for writing and reviewing inter–disciplinary papers

New interpretation of the cranial osteology of the Early Cretaceous turtle Arundelemys dardeni (Paracryptodira) based on a CT-based re-evaluation of the holotype.

Arundelemys dardeni is an Early Cretaceous paracryptodire known from a single, incomplete, but generally well-preserved skull. Phylogenetic hypotheses of paracryptodires often find Arundelemys dardeni as an early branching baenid. As such, it has a central role in understanding the early evolution of the successful clade Baenidae, which survived the Cretaceous–Paleogene mass extinction, as well as the diversification of Paracryptodira into its subclades, which recent research suggests to perhaps include helochelydrids, compsemydids, pleurosternids, and baenids. Computer tomography scans of the holotype material that were produced for the initial description of Arundelemeys dardeni reveal several errors in the initial anatomical description of the species, which we correct based on element-by-element segmentation. In addition, we provide entirely novel anatomical information, including descriptions of several previously undescribed cranial bones, the endosseous labyrinth, and the cranial scutes, the latter of which are unknown for most paracryptodires. We provide an interpretation of cranial scutes which homologizes the scutes of Arundelemys dardeni with those of other stem turtles.

Current extinction rate in European freshwater gastropods greatly exceeds that of the late Cretaceous mass extinction

The Cretaceous–Paleogene mass extinction event 66 million years ago eradicated three quarters of marine and terrestrial species globally. However, previous studies based on vertebrates suggest that freshwater biota were much less affected. Here we assemble a time series of European freshwater gastropod species occurrences and inferred extinction rates covering the past 200 million years. We find that extinction rates increased by more than one order of magnitude during the Cretaceous–Paleogene mass extinction, which resulted in the extinction of 92.5% of all species. The extinction phase lasted 5.4 million years and was followed by a recovery period of 6.9 million years. However, present extinction rates in European freshwater gastropods are three orders of magnitude higher than even these revised estimates for the Cretaceous–Paleogene mass extinction. Our results indicate that, unless substantial conservation effort is directed to freshwater ecosystems, the present extinction crisis will have a severe impact to freshwater biota for millions of years to come.

Mammaliaform extinctions as a driver of the morphological radiation of Cenozoic mammals

Adaptive radiations are hypothesized as a generating mechanism for much of the morphological diversity of extant species.1-7 The Cenozoic radiation of placental mammals, the foundational example of this concept,8,9 gave rise to much of the morphological disparity of extant mammals, and is generally attributed to relaxed evolutionary constraints following the extinction of non-avian dinosaurs.10-13 However, study of this and other radiations has focused on variation in evolutionary rates,4,5,7,14 leaving the extent to which relaxation of constraints enabled the origin of novel phenotypes less well characterized.15-17 We evaluate constraints on morphological evolution among mammaliaforms (mammals and their closest relatives) using a new method that quantifies the capacity of evolutionary change to generate phenotypic novelty. We find that Mesozoic crown-group therians, which include the ancestors of placental mammals, were significantly more constrained than other mammaliaforms. Relaxation of these constraints occurred in the mid-Paleocene, post-dating the extinction of non-avian dinosaurs at the K/Pg boundary, instead coinciding with important environmental shifts and with declining ecomorphological diversity in non-theriimorph mammaliaforms. This relaxation occurred even in small-bodied Cenozoic mammals weighing <100 g, which are unlikely to have competed with dinosaurs. Instead, our findings support a more complex model whereby Mesozoic crown therian evolution was in part constrained by co-occurrence with disparate mammaliaforms, as well as by the presence of dinosaurs, within-lineage incumbency effects, and environmental factors. Our results demonstrate that variation in evolutionary constraints can occur independently of variation in evolutionary rate, and that both make important contributions to the understanding of adaptive radiations.

Quantitative assessment of tarsal morphology illuminates locomotor behaviour in Palaeocene mammals following the end-Cretaceous mass extinction.

Mammals exhibit vast ecological diversity, including a panoply of locomotor behaviours. The foundations of this diversity were established in the Mesozoic, but it was only after the end-Cretaceous mass extinction that mammals began to increase in body size, diversify into many new species and establish the extant orders. Little is known about the palaeobiology of the mammals that diversified immediately after the extinction during the Palaeocene, which are often perceived as ‘archaic’ precursors to extant orders. Here, we investigate the locomotor ecology of Palaeocene mammals using multivariate and disparity analyses. We show that tarsal measurements can be used to infer locomotor mode in extant mammals, and then demonstrate that Palaeocene mammals occupy distinctive regions of tarsal morphospace relative to Cretaceous and extant therian mammals, that is distinguished by their morphological robustness. We find that many Palaeocene species exhibit tarsal morphologies most comparable with morphologies of extant ground-dwelling mammals. Disparity analyses indicate that Palaeocene mammals attained similar morphospace diversity to the extant sample. Our results show that mammals underwent a post-extinction adaptive radiation in tarsal morphology relating to locomotor behaviour by combining a basic eutherian bauplan with anatomical specializations to attain considerable ecomorphological diversity.

The postcranial skeleton of Cerrejonisuchus improcerus (Crocodyliformes: Dyrosauridae) and the unusual anatomy of dyrosaurids.

Dyrosauridae is a clade of neosuchian crocodyliforms that diversified in terrestrial and aquatic environments across the Cretaceous-Paleogene transition. The postcranial anatomy of dyrosaurids has long been overlooked, obscuring both their disparity and their locomotive adaptations. Here we thoroughly describe of the postcranial remains of an unusually small dyrosaurid, Cerrejonisuchus improcerus, from the middle-late Paleocene Cerrejón Formation of Colombia, and we provide a wealth of new data concerning the postcranial anatomy of the key dyrosaurids: Congosaurus bequaerti and Hyposaurus rogersii. We identify a series of postcranial autapomorphies in Cerrejonisuchus improcerus (an elliptic-shaped odontoid laterally wide, a ulna possessing a double concavity, a fibula bearing a widely flattened proximal end, a pubis showing a large non-triangular distal surface) as well as functionally-important traits such as a relatively long ulna (85% of the humerus’ length), short forelimb (83% of hindlimb’s length), or thoracic vertebra bearing comparatively large lateral process (with widened parapophysis and diapophysis) along with strongly arched thoracic ribs allowing a more sturdy and cylindrical rib cage. These indicate a more terrestrial lifestyle for Cerrejonisuchus compared to the derived members of the clade. We also built a dataset of 187 traits on 27 taxa, that extensively samples the cranial and postcranial architectures of exemplar crocodyliforms. We analyze these data in via Principal Coordinate Analysis (PCoA) to visualize the postcranial morphospace occupation of Dyrosauridae, Thalattosuchia, and Crocodylia. Our data reveal the existence of a distinctive postcranial anatomy for Dyrosauridae that is markedly distinct from that of crocodylians. As a result, modern crocodylians are probably not good functional analog for extinct crocodyliformes. Postcranial data should also be more widely used in phylogenetic and disparity analyses of Crocodyliformes.