A new zygodactylid species indicates the persistence of stem passerines into the early Oligocene in North America.

BACKGROUND: The lake deposits of the informal Ruby Paper Shale unit, part of the Renova Formation of Montana, have yielded abundant plant fossils that document Late Eocene - Early Oligocene global cooling in western North America. A nearly complete small bird with feather impressions was recovered from this unit in in 1959, but has only been informally mentioned. RESULTS: Here we describe this fossil and identify it as a new species of Zygodactylus, a stem lineage passerine with a zygodactyl foot. The new taxon shows morphological traits that are convergent on crown Passeriformes, including an elongate hallux, reduced body size, and a comparative shortening of proximal limb elements. The fossil documents the persistence of this lineage into the earliest Oligocene (~ 33 Ma) in North America. It is the latest occurring North American species of a group that persists in Europe until the Miocene. CONCLUSIONS: Eocene-Oligocene global cooling is known to have significantly remodeled both Palearctic and Nearctic mammal faunas but its impact on related avifaunas has remained poorly understood. The geographic and temporal range expansion provided by the new taxon together with avian other taxa with limited fossil records suggests a similar pattern of retraction in North America followed by Europe.

My branch is your branch: Talar morphology correlates with relative substrate size in platyrrhines at Tiputini Biodiversity Station, Ecuador.

Given that most species of primates are predominantly arboreal, maintaining the ability to move among branches of varying sizes has presumably been a common selective force in primate evolution. However, empirical evaluations of the relationships between morphological variation and characteristics of substrate geometry, such as substrate diameter relative to an animal's body mass, have been limited by the lack of quantified substrate usage in the wild. Here we use recently published quantitative data to assess the relationships between relative substrate size and talar morphology in nine New World monkey species at the Tiputini Biodiversity Station, Ecuador. Within this sample, both fibular facet angle (the angle between the fibular facet and the trochlear rims) and body-mass-standardized area of the medial tibial facet decrease as average and maximum relative substrate size increases. Correlations between medial tibial facet area and relative substrate size are driven by the inclusion of callitrichids in this sample. Nevertheless, these findings strengthen the hypothesis that variation in fibular facet orientation and medial tibial facet area are functionally correlated with habitual degrees of pedal inversion. They also strengthen the notion that evolutionarily changing body mass could impact habitat geometry experienced by a lineage and thereby substantially impact major trends in primate morphological evolution. This study highlights the importance of empirical data on substrate use in living primates for inferring functional and evolutionary implications of morphological variation.

Palaeontological evidence for an Oligocene divergence between Old World monkeys and apes.

Apes and Old World monkeys are prominent components of modern African and Asian ecosystems, yet the earliest phases of their evolutionary history have remained largely undocumented. The absence of crown catarrhine fossils older than ∼20 million years (Myr) has stood in stark contrast to molecular divergence estimates of ∼25-30 Myr for the split between Cercopithecoidea (Old World monkeys) and Hominoidea (apes), implying long ghost lineages for both clades. Here we describe the oldest known fossil 'ape', represented by a partial mandible preserving dental features that place it with 'nyanzapithecine' stem hominoids. Additionally, we report the oldest stem member of the Old World monkey clade, represented by a lower third molar. Both specimens were recovered from a precisely dated 25.2-Myr-old stratum in the Rukwa Rift, a segment of the western branch of the East African Rift in Tanzania. These finds extend the fossil record of apes and Old World monkeys well into the Oligocene epoch of Africa, suggesting a possible link between diversification of crown catarrhines and changes in the African landscape brought about by previously unrecognized tectonic activity in the East African rift system.

Effects of substrate and phylogeny on quadrupedal gait in free-ranging platyrrhines.

OBJECTIVES: Primate diagonal sequence (DS) gaits are often argued to be an adaptation for moving and foraging in the fine-branch niche; however, existing data have come predominantly from laboratory studies that are limited in taxonomic breadth and fail to account for the structural and ecological variation of natural substrates. We test the extent to which substrate diameter and orientation influence gait sequence type and limb phase in free-ranging primates, as well as how phylogenetic relatedness might condition response patterns. MATERIALS AND METHODS: We filmed quadrupedal locomotion in 11 platyrrhine species at field sites in Ecuador and Costa Rica and measured the diameter and orientation of locomotor substrates using remote sensors. We quantified limb phase values and classified strides by gait sequence type (N = 988 strides). RESULTS: Our results show that most of the species in our sample consistently used DS gaits, regardless of substrate diameter or orientation; however, all taxa also used asymmetrical and/or lateral sequence gaits. By incorporating phylogenetic eigenvectors into our models, we found significant differences in gait sequence patterns and limb phase values among the major platyrrhine clades, suggesting that phylogeny may be a better predictor of gait than substrate diameter or orientation. DISCUSSION: Our field data generally corroborate locomotor patterns from laboratory studies but capture additional aspects of gait variability and flexibility in response to the complexity of natural environments. Overall, our results suggest that DS gaits are not exclusively tailored to narrow or oblique substrates but are used on arboreal substrates in general.

Evolutionary aspects of the development of teeth and baleen in the bowhead whale.

In utero, baleen whales initiate the development of several dozens of teeth in upper and lower jaws. These tooth germs reach the bell stage and are sometimes mineralized, but toward the end of prenatal life they are resorbed and no trace remains after birth. Around the time that the germs disappear, the keratinous baleen plates start to form in the upper jaw, and these form the food-collecting mechanism. Baleen whale ancestors had two generations of teeth and never developed baleen, and the prenatal teeth of modern fetuses are usually interpreted as an evolutionary leftover. We investigated the development of teeth and baleen in bowhead whale fetuses using histological and immunohistochemical evidence. We found that upper and lower dentition initially follow similar developmental pathways. As development proceeds, upper and lower tooth germs diverge developmentally. Lower tooth germs differ along the length of the jaw, reminiscent of a heterodont dentition of cetacean ancestors, and lingual processes of the dental lamina represent initiation of tooth bud formation of replacement teeth. Upper tooth germs remain homodont and there is no evidence of a secondary dentition. After these germs disappear, the oral epithelium thickens to form the baleen plates, and the protein FGF-4 displays a signaling pattern reminiscent of baleen plates. In laboratory mammals, FGF-4 is not involved in the formation of hair or palatal rugae, but it is involved in tooth development. This leads us to propose that the signaling cascade that forms teeth in most mammals has been exapted to be involved in baleen plate ontogeny in mysticetes.

Flight feather attachment in rock pigeons (Columba livia): covert feathers and smooth muscle coordinate a morphing wing.

Mechanisms for passively coordinating forelimb movements and flight feather abduction and adduction have been described separately from both in vivo and ex vivo studies. Skeletal coordination has been identified as a way for birds to simplify the neuromotor task of controlling flight stroke, but an understanding of the relationship between skeletal coordination and the coordination of the aerodynamic control surface (the flight feathers) has been slow to materialize. This break between the biomechanical and aerodynamic approaches - between skeletal kinematics and airfoil shape - has hindered the study of dynamic flight behaviors. Here I use dissection and histology to identify previously overlooked interconnections between musculoskeletal elements and flight feathers. Many of these structures are well-placed to directly link elements of the passive musculoskeletal coordination system with flight feather movements. Small bundles of smooth muscle form prominent connections between upper forearm coverts (deck feathers) and the ulna, as well as the majority of interconnections between major flight feathers of the hand. Abundant smooth muscle may play a role in efficient maintenance of folded wing posture, and may also provide an autonomically regulated means of tuning wing shape and aeroelastic behavior in flight. The pattern of muscular and ligamentous linkages of flight feathers to underlying muscle and bone may provide predictable passive guidance for the shape of the airfoil during flight stroke. The structures described here provide an anatomical touchstone for in vivo experimental tests of wing surface coordination in an extensively researched avian model species.

The evolution of mammal-like crocodyliforms in the Cretaceous Period of Gondwana.

Fossil crocodyliforms discovered in recent years have revealed a level of morphological and ecological diversity not exhibited by extant members of the group. This diversity is particularly notable among taxa of the Cretaceous Period (144-65 million years ago) recovered from former Gondwanan landmasses. Here we report the discovery of a new species of Cretaceous notosuchian crocodyliform from the Rukwa Rift Basin of southwestern Tanzania. This small-bodied form deviates significantly from more typical crocodyliform craniodental morphologies, having a short, broad skull, robust lower jaw, and a dentition with relatively few teeth that nonetheless show marked heterodonty. The presence of morphologically complex, complementary upper and lower molariform teeth suggests a degree of crown-crown contact during jaw adduction that is unmatched among known crocodyliforms, paralleling the level of occlusal complexity seen in mammals and their extinct relatives. The presence of another small-bodied mammal-like crocodyliform in the Cretaceous of Gondwana indicates that notosuchians probably filled niches and inhabited ecomorphospace that were otherwise occupied by mammals on northern continents.

Macroevolutionary developmental biology: Embryos, fossils, and phylogenies.

The field of evolutionary developmental biology is broadly focused on identifying the genetic and developmental mechanisms underlying morphological diversity. Connecting the genotype with the phenotype means that evo-devo research often considers a wide range of evidence, from genetics and morphology to fossils. In this commentary, we provide an overview and framework for integrating fossil ontogenetic data with developmental data using phylogenetic comparative methods to test macroevolutionary hypotheses. We survey the vertebrate fossil record of preserved embryos and discuss how phylogenetic comparative methods can integrate data from developmental genetics and paleontology. Fossil embryos provide limited, yet critical, developmental data from deep time. They help constrain when developmental innovations first appeared during the history of life and also reveal the order in which related morphologies evolved. Phylogenetic comparative methods provide a powerful statistical approach that allows evo-devo researchers to infer the presence of nonpreserved developmental traits in fossil species and to detect discordant evolutionary patterns and processes across levels of biological organization.

Qualitative skeletal correlates of wing shape in extant birds (Aves: Neoaves).

BACKGROUND: Among living fliers (birds, bats, and insects), birds display relatively high aspect ratios, a dimensionless shape variable that distinguishes long and narrow vs. short and broad wings. Increasing aspect ratio results in a functional tradeoff between low induced drag (efficient cruise) and increased wing inertia (difficult takeoff). Given the wide scope of its functional effects, the pattern of aspect ratio evolution is an important factor that contributes to the substantial ecological and phylogenetic diversity of living birds. However, because the feathers that define the wingtip (and hence wingspan and aspect ratio) often do not fossilize, resolution in the pattern of avian wing shape evolution is obscured by missing information. Here I use a comparative approach to investigate the relationship between skeletal proxies of flight feather attachment and wing shape. RESULTS: An accessory lobe of the internal index process of digit II-1, a bony correlate of distal primary attachment, shows weak but statistically significant relationships to aspect ratio and mass independent of other skeletal morphology. The dorsal phalangeal fossae of digit II-1, which house distal primaries VIII and IX, also show a trend of increased prominence with higher aspect ratio. Quill knobs on the ulna are examined concurrently, but do not show consistent signal with respect to wing shape. CONCLUSIONS: Although quill knobs are cited as skeletal correlates of flight performance in birds, their relationship to wing shape is inconsistent among extant taxa, and may reflect diverging selection pressures acting on a conserved architecture. In contrast, correlates of distal primary feather attachment on the major digit show convergent responses to increasing aspect ratio. In light of the diversity of musculoskeletal and integumentary mophology that underlies wing shape in different avian clades, it is unlikely that a single skeletal feature will show consistent predictive power across Neoaves. Confident inference of wing shape in basal ornithurine birds will require multiple lines of evidence, together with an understanding of clade-specific evolutionary trends within the crown.

Examining the Dimensions of the Bicipital Groove: A Human Cadaveric Study.

Introduction Understanding the mechanisms and risk factors associated with bicipital groove (BG) morphology is essential for optimizing patient outcomes. Despite interest in the topic of BG morphology, there remains a lack of clarity and consensus on the parameters of BG morphology due to significant methodological limitations in the existing research. The purpose of this study is to explore the dimensions of BG morphology with a methodology rooted in recent research findings to better understand the human anatomy, potentially underpinning various shoulder pathologies.  Methods The right shoulders of seventeen cadavers (nine male and eight female; median age of death: 88.0 years; age of death range: 66.0 - 97.0 years) were included in this cadaveric study. Dissection was done by removing the deltoid musculature and reflecting the long head of the biceps tendon to expose the BG. Measurements for BG morphology included BG width (millimeters, mm), depth (mm), and length (mm). Statistical comparisons were done between male and female measurements using the independent-samples Mann-Whitney U test due to the small sample size.  Results The median width of the BG at the narrowest point was 4.3 mm (mean: 4.7 ± 1.4 mm; range: 3.0 - 7.7 mm) with male cadavers having a significantly wider BG as compared to female cadavers (median: 5.0 mm versus 3.7 mm; p=0.006). The median depth of the BG was 5.1 mm (mean: 5.0 ± 0.7 mm; range: 3.8 - 6.3 mm) with no statistically significant difference between male and female cadavers (median: 4.8 mm versus 5.3 mm; p=0.370). The median length of the BG was 25.1 mm (mean: 25.1 ± 3.3 mm; range: 18.1 - 31.3 mm) with no statistically significant difference between male and female cadavers (median: 25.4 mm versus 23.9 mm; p=0.673). Conclusion The width of the BG at the narrowest point was significantly larger in male cadavers as compared to female cadavers in this study. However, there was no difference between male and female cadavers in terms of depth and length of the BG. This study contributes to the understanding of BG morphology by exploring the dimensions for width, depth, and length of the BG, which may contribute to biceps tendon pathology in clinical practice. Future research should focus on reducing measurement variability and exploring the possible relationship between BG morphology and biceps tendon conditions to further enhance the understanding of this complex relationship.

Intraskeletal consistency in patterns of vascularity within bat limb bones.

Bats are the only mammals to have achieved powered flight. A key innovation allowing for bats to conquer the skies was a forelimb modified into a flexible wing. The wing bones of bats are exceptionally long and dynamically bend with wingbeats. Bone microarchitectural features supporting these novel performance attributes are still largely unknown. The humeri and femora of bats are typically avascular, except for large-bodied taxa (e.g., pteropodid flying foxes). No thorough investigation of vascular canal regionalization and morphology has been undertaken as historically it has been difficult to reconstruct the 3D architecture of these canals. This study augments our understanding of the vascular networks supporting the bone matrix of a sample of bats (n = 24) of variable body mass, representing three families (Pteropodidae [large-bodied, species = 6], Phyllostomidae [medium-bodied, species = 2], and Molossidae [medium-bodied, species = 1]). We employed Synchrotron Radiation-based micro-Computed Tomography (SRµCT) to allow for a detailed comparison of canal morphology within humeri and femora. Results indicate that across selected bats, canal number per unit volume is similar independent of body size. Differences in canal morphometry based on body size and bone type appear primarily related to a broader distribution of the canal network as cortical volume increases. Heavier bats display a relatively rich vascular network of mostly longitudinally-oriented canals that are localized mainly to the mid-cortical and endosteal bone envelopes. Taken together, our results suggest that relative vascularity of the limb bones of heavier bats forms support for nutrient exchange in a regional pattern.

Anatomy and Ontogeny of the Mandibular Symphysis in Alligator mississippiensis.

Crocodylians evolved some of the most characteristic skulls of the animal kingdom with specializations for semiaquatic and ambush lifestyles, resulting in a feeding apparatus capable of tolerating high biomechanical loads and bite forces and a head with a derived sense of trigeminal-nerve-mediated touch. The mandibular symphysis accommodates these specializations being both at the end of a biomechanical lever and an antenna for sensation. Little is known about the anatomy of the crocodylian mandibular symphysis, hampering our understanding of form, function, and evolution of the joint in extant and extinct lineages. We explore mandibular symphysis anatomy of an ontogenetic series of Alligator mississippiensis using imaging, histology, and whole mount methods. Complex sutural ligaments emanating about a midline-fused Meckel's cartilage bridge the symphysis. These tissues organize during days 37-42 of in ovo development. However, interdigitations do not manifest until after hatching. These soft tissues leave a hub and spoke-like bony morphology of the symphyseal plate, which never fuses. Interdigitation morphology varies within the symphysis suggesting differential loading about the joint. Neurovascular canals extend throughout the mandibles to alveoli, integument, and bone adjacent to the symphysis. These features suggest the Alligator mandibular symphysis offers compliance in an otherwise rigid skull. We hypothesize a fused Meckel's cartilage offers stiffness in hatchling mandibles prior to the development of organized sutural ligaments and mineralized bone while offering a scaffold for somatic growth. The porosity of the dentaries due to neurovascular tissues likely allows transmission of sensory and proprioceptive information from the surroundings and the loaded symphysis. Anat Rec, 302:1696-1708, 2019. © 2019 American Association for Anatomy.

Quantitative microanatomy of jaw muscle attachment in extant diapsids.

Muscular reconstructions in vertebrate paleontology have often relied heavily on the presence of "muscle scars" and similar osteological correlates of muscle attachment, a practice complicated by the fact that approximately half of tendinous muscle attachments to bone in extant vertebrates do not leave readily interpretable scars. Microanatomical and histological correlates of tendinous muscle attachment are much less ambiguous. This study examines the microanatomical correlates of muscle attachment for the mandibular adductors in six species of diapsids. Most prominent tendinous or aponeurotic muscle attachments display a high density of extrinsic fibers (similar to Sharpey's fibers). There is also some indication that the density of extrinsic fibers at an attachment may be directly related to the amount of stress exerted on that attachment. The presence of comparable densities of extrinsic fibers in fossil tissue constitutes strong and readily interpretable positive evidence for the presence of adjacent fibrous connective tissue in life. Microanatomy and histology provide reliable data about muscle attachments that cannot be gleaned from gross observation alone. These additional data, when coupled with existing muscular reconstruction techniques, may be essential to the resolution of ambiguous character states, and will provide more severe tests for long-standing hypotheses of musculature in extinct diapsids. Increasing the accuracy and precision of muscular reconstructions lends greater strength to any phylogenetic, paleobiological, or paleoecological inferences that draw upon these reconstructions as important lines of evidence.

Structure of white rhinoceros (Ceratotherium simum) horn investigated by X-ray computed tomography and histology with implications for growth and external form.

The nasal and frontal horns of two individuals of Ceratotherium simum were examined by x-ray computed tomography (CT scanning), gross observation of sectioned horn, and light microscopy of histological sections of the horn tissue. CT scans of both sets of horns reveal a periodic banding pattern that is evident upon gross observation of sections as darker bands of tissue. The overlap of these bands in both histological and CT slices suggests the presence of both a photoabsorbent component (melanin) and a radiodense component (calcium phosphate salts, most likely hydroxyapatite or octocalcium phosphate). The distribution of these two components in the horns is hypothesized to contribute to the differential wear patterns that produce the characteristic sweeping conical shape of rhinoceros horn from what otherwise (in the absence of wear and UV exposure) would be cylindrical blocks of constantly growing cornified papillary epidermis. Although extant rhinocerotids are unique in possessing a massive entirely keratinous horn that approximates the functions of keratin-and-bone horns such as those of bovid artiodactyls, the tissue structures that make up the horn are strikingly convergent with other examples of papillary cornified epidermis found in horses, artiodactyls, cetaceans, and birds.

Aquatic Habits of Cetacean Ancestors: Integrating Bone Microanatomy and Stable Isotopes.

The earliest cetaceans were interpreted as semi-aquatic based on the presence of thickened bones and stable oxygen isotopes in tooth enamel. However, the origin of aquatic behaviors in cetacean relatives (e.g., raoellids, anthracotheres) remains unclear. This study reconstructs the origins of aquatic behaviors based on long bone microanatomy and stable oxygen isotopes of tooth enamel in modern and extinct cetartiodactylans. Our findings are congruent with published accounts that microanatomy can be a reliable indicator of aquatic behaviors in taxa that are obligatorily aquatic, and also highlight that some "semi-aquatic" behaviors (fleeing into the water to escape predation) may have a stronger relationship to bone microanatomy than others (herbivory in near-shore aquatic settings). Bone microanatomy is best considered with other lines of information in the land-to-sea transition of cetaceans, such as stable isotopes. This study extends our understanding of the progression of skeletal phenotypes associated with habitat shifts in the relatives of cetaceans.

A comparison of postnatal arterial patterns in a growth series of giraffe (Artiodactyla: Giraffa camelopardalis).

Nearly all living artiodactyls (even-toed ungulates) possess a derived cranial arterial pattern that is highly distinctive from most other mammals. Foremost among a suite of atypical arterial configurations is the functional and anatomical replacement of the internal carotid artery with an extensive, subdural arterial meshwork called the carotid rete. This interdigitating network branches from the maxillary artery and is housed within the cavernous venous sinus. As the cavernous sinus receives cooled blood draining from the nasal mucosa, heat rapidly dissipates across the high surface area of the rete to be carried away from the brain by the venous system. This combination yields one of the most effective mechanisms of selective brain cooling. Although arterial development begins from the same embryonic scaffolding typical of mammals, possession of a rete is typically accompanied by obliteration of the internal carotid artery. Among taxa with available ontogenetic data, the point at which the internal carotid obliterates is variable throughout development. In small-bodied artiodactyls, the internal carotid typically obliterates prior to parturition, but in larger species, the vessel may remain patent for several years. In this study, we use digital anatomical data collection methods to describe the cranial arterial patterns for a growth series of giraffe (Giraffa camelopardalis), from parturition to senescence. Giraffes, in particular, have unique cardiovascular demands and adaptations owing to their exceptional body form and may not adhere to previously documented stages of cranial arterial development. We find the carotid arterial system to be conserved between developmental stages and that obliteration of the giraffe internal carotid artery occurs prior to parturition.

Cross sectional geometry of the forelimb skeleton and flight mode in pelecaniform birds.

Avian wing elements have been shown to experience both dorsoventral bending and torsional loads during flapping flight. However, not all birds use continuous flapping as a primary flight strategy. The pelecaniforms exhibit extraordinary diversity in flight mode, utilizing flapping, flap-gliding, and soaring. Here we (1) characterize the cross-sectional geometry of the three main wing bone (humerus, ulna, carpometacarpus), (2) use elements of beam theory to estimate resistance to loading, and (3) examine patterns of variation in hypothesized loading resistance relative to flight and diving mode in 16 species of pelecaniform birds. Patterns emerge that are common to all species, as well as some characteristics that are flight- and diving-mode specific. In all birds examined, the distal most wing segment (carpometacarpus) is the most elliptical (relatively high I(max) /I(min) ) at mid-shaft, suggesting a shape optimized to resist bending loads in a dorsoventral direction. As primary flight feathers attach at an oblique angle relative to the long axis of the carpometacarpus, they are likely responsible for inducing bending of this element during flight. Moreover, among flight modes examined the flapping group (cormorants) exhibits more elliptical humeri and carpometacarpi than other flight modes, perhaps pertaining to the higher frequency of bending loads in these elements. The soaring birds (pelicans and gannets) exhibit wing elements with near-circular cross-sections and higher polar moments of area than in the flap and flap-gliding birds, suggesting shapes optimized to offer increased resistance to torsional loads. This analysis of cross-sectional geometry has enhanced our interpretation of how the wing elements are being loaded and ultimately how they are being used during normal activities.

The facial integument of centrosaurine ceratopsids: morphological and histological correlates of novel skin structures.

The horned dinosaur Pachyhinosaurus possesses rugose bony bosses across the skull roof in lieu of the projecting bony horn cores seen in most ceratopsians. This elaboration of typical ceratopsian ornaments provides an opportunity to test hypotheses of ceratopsian facial skin morphology and function. We analyze bone morphology and histology associated with several classes of skin features in extant amniotes using a classification tree analysis. We isolate key osteological and histological correlates for unpreserved skin structures, including both a pattern of pitting and resorption characteristic of muskox (Ovibos) frontal horn boss, and a pattern of metaplastic ossification characteristic of rhinoceros nasal horn boss. We also describe correlates for other skin features, such as epidermal scales and horn sheaths. Dermatocranial elements from centrosaurine ceratopsians are then examined for the same osteological and histological correlates. From this comparison we propose that the rugose bosses that replace horn cores in many centrosaurine dinosaurs, most notably Achelousaurus and Pachyrhinosaurus, were covered by a thick pad of cornified skin derived from the caudodorsal side of the primitive horn sheath comparable to the horny boss of extant muskoxen (Ovibos). We examine extant taxa with skin morphologies similar to Pachyrhinosaurus for consistent adaptive relationships between structure and behavior. We determine that high-energy headbutting is consistently associated with the acquisition of thick cornified pads, seen in muskoxen as well as helmeted hornbills [Buceros (=Rhinoplax) vigil] and African buffalo (Syncerus). The association of the bony ornaments of Pachyrhinosaurus with risky agonistic behaviors casts doubt on the role of species recognition as a primary selection pressure driving the diversity of all ceratopsian horns. We conclude that social selection (a broad form of intraspecific competition) is a more appropriate explanation for the diversity of centrosaurine ceratopsian ornaments in the Late Cretaceous.