Fossil Occurrences Research Articles

Persistence of a shallow-marine environment in the western Kunlun area (northwestern Tibet) until the early Maastrichtian: evidence from radiolitid rudist bivalves

The closing of the Tethys Ocean during the Mesozoic and Cenozoic dramatically affected the palaeogeography, palaeoenvironment and biotic evolution of the Tibetan Plateau and surrounding areas. The timing of closure of the Tethys Ocean in different areas is recorded by the youngest marine deposits. In the western Kunlun area of northwestern Tibet, the Tielongtan Group represents the youngest marine deposits, and is rich in rudist bivalves; however, its depositional age, particularly the age of final deposition, is poorly constrained. Systematic and palaeobiogeographic analyses were conducted on rudists from the Tielongtan Group in the eastern Loqzung Mountains. Four genera and two species were identified: Biradiolites boldjuanensis, Gorjanovicia acuticostata, Durania sp. and Radiolites sp. The occurrence of the lower Maastrichtian index fossil, Biradiolites boldjuanensis, indicates that deposition of the Tielongtan Group continued until the early Maastrichtian. Therefore, the results of this and previous studies indicate that deposition of the Tielongtan Group spanned from at least the Turonian to the early Maastrichtian. Palaeobiogeographical analyses show that B. boldjuanensis was endemic in Central Asia, whereas G. acuticostata might have extended beyond the Mediterranean region. During the Late Cretaceous, the shallow ocean in the western Kunlun area contained both cosmopolitan and endemic rudists.

Was Palaeolake Messel a death-trap? Insight from modern bat drownings and decay experiments

AbstractThe Messel Pit is an ancient maar lake that preserves an ecosystem from the last greenhouse phase of Earth’s climate with exceptional fidelity. There are two main competing hypotheses to explain the occurrence of animal fossils at Messel: asphyxiation in layers of heavy, toxic gases like carbon dioxide, and death following ingestion of surface water contaminated by cyanobacterial toxins. Both hypotheses imply mortality much higher than the null hypothesis of accidental death, for instance by drowning. We tested these hypotheses amongst bats by recourse to a unique survey on bats that drowned in modern swimming pools. We further conducted experiments on the fate of fresh bat carcasses that simulate drowning. Finally, we estimated the annual rate of bat fossil production at Messel. Overall, there are few good surveyed predictors of whether bats drown in swimming pools: most physical parameters like pool size or the height and distance of obstructions were not associated with mortality, although pool liner type would be a good candidate parameter for future study. In our experiments, carcasses with water-filled lungs tend to sink more quickly than those with air-filled lungs; all carcasses that initially sink “bloat and float” at shallow depths, but all floaters eventually disarticulate and sink within days to weeks. Our estimates of annual bat mortality at Palaeolake Messel are of the same order of magnitude as mortality in swimming pools. Mass mortality horizons for vertebrates are very rare at Messel. In sum, our quantitative analyses provide no evidence that bat mortality at Messel rises above background levels.

The fossil record of female sexual ornamentation in Empididae (Diptera: Empidoidea), with description of four new species

Females of the subfamily Empidinae (Diptera: Empididae s.s.) often exhibit sexual ornamentation, an adaptation that, within the animal world at large, is most often associated with males, especially in vertebrates. Ornaments of female Empidinae include: 1) legs with rows of relatively large pennate scales, 2) enlarged and/or darkly pigmented wings and 3) inflated abdominal sacs. Ornamentation makes the females appear larger, a characteristic that may make them appear, albeit deceptively, more fecund, and therefore more attractive to potential mates. Given the rarity of female sexual ornamentation, these flies, particularly those of the tribe Empidini, have become a model system for study of this phenomenon. The family’s fossil record consists of 111 known occurrences including several genera from the middle Jurassic. This fossil record however is dominated by two genera, Empis and Rhamphomyia, which account for nearly 60% of all fossil occurrences. Unfortunately, there has been no fossil record of empidine sexual ornamentation other than pennate leg scales. Herein, we review this fossil record and describe the first empidine fossils, all from the Middle Eocene Kishenehn Formation, with enlarged and/or darkly pigmented wings, Rhamphomyia kitadai sp. nov. and R. brunnipennis sp. nov., and two new species of Rhamphomyia which display pennate leg scales, R. decens sp. nov. and R. pennipes sp. nov. Rhamphomyia enena Cockerell, 1921, the oldest known fossil that exhibits pennate leg scales, is redescribed.

Diversity, environments, and biogeography of Homoloida (Decapoda: Brachyura) from the Late Jurassic to the present

ABSTRACT The section Homoloida with the sole superfamily Homoloidea comprises both extinct and extant brachyuran crab taxa, with records ranging from the Tithonian (Jurassic) to the present. Examination of fossil and modern occurrence records for this clade provides insight into the biogeography, biodiversity, and environmental preference of the homoloid crabs over time. The fossil record of Homoloidea, comprised of the families Tithonohomolidae, Mithracitidae, Homolidae, Latreilliidae, and Poupiniidae, is global in distribution and peaks in diversity during the uppermost Cretaceous with the most recent fossils known from the Miocene. Modern homoloids are absent from only a handful of regions globally, with particularly high diversity and abundance in the tropical Indo-West Pacific. Comparison of interpreted depositional environments for fossil occurrences and depth records for modern occurrences sheds light on the environmental preferences and potential spatial sampling biases of this clade. By assessing both fossil and modern records of Homoloidea, patterns (e.g., absence from cold-water latitudes, Oligo-Miocene disappearance from the northeastern Pacific) emerge that may have important implications for future study of this clade, particularly in relation to dispersal/turnover events and environmental constraints.

Radiolarians from Cambrian Series 2 Niujiaohe Formation in southern Jiangxi, South China

The origin and early evolution of radiolarian fossils have always provoked great interest among paleontologists. Yet, little is known about the earliest morphological and evolutionary characteristics of radiolarians largely due to the lack of documentation of early Cambrian radiolarian fossils. Herein, we conduct a thorough examination of the basinal Niujiaohe Formation in Chongyi County of southern Jiangxi and report two types of radiolarians: a large number of spherical radiolarians and a minor occurrence of ellipsoidal radiolarian fossils with bipolar rodded spines. The lengths of the spines on ellipsoid radiolarian fossils vary, and typically, the main spines are slightly offset from the polar axis, resulting in an asymmetrical appearance in some specimens. Through systematic taxonomic examination, this radiolarian fossil form is tentatively identified as Beothuka sp. of the spherical polycystine group. The genus Beothuka is commonly found in the Early Ordovician and has not yet been reported in the early Cambrian. Combined with previous reports, four species of radiolarians in three genera are identified from the Niujiaohe Formation in South China, including Paraantygopora porosa, Paraantygopora sp., spherical radiolarian, and Beothuka sp. Overall, the radiolarian fossils in the Niujiaohe Formation are characterized by low diversity and small size, in contrast to the relatively more diverse fauna found in the contemporary shallow-water Shuijingtuo Formation. Therefore, we speculate that radiolarians may have initially originated in shallow water areas and gradually expanded to deep water. This study further enriches the fossil record of the Cambrian Series 2 radiolarians. Combined with relevant data from South China, the radiolarian fauna began to exhibit diversity and complex morphology, indicating the presence of various, advanced spherical-skeletons in early radiolarians, and radiolarians from the early Cambrian appeared to display multiple evolutionary trends.

Palaeoenvironment and taphonomy of the Hypsilophodon Bed, Lower Cretaceous Wessex Formation, Isle of Wight

The ‘ Hypsilophodon Bed’ occurs at the top of the Wessex Formation (Early Cretaceous, Barremian) on the Isle of Wight, England. Numerous remains of the small ornithopod dinosaur Hypsilophodon foxii have been recovered from the bed since the mid-19th century. Previous theories for these fossil occurrences have focused on catastrophic mass death events including miring and flood-related mortality. However, only limited sedimentological and taphonomic analyses of the horizon and its fossil assemblage have been undertaken, hindering efforts to evaluate different theories for how the assemblage formed. Here, we undertake a sedimentological study of the bed to constrain its depositional environment, examine matrix from Hypsilophodon fossils to identify where they were collected from within the bed, and undertake taphonomic investigation of Hypsilophodon specimens. Results reveal a floodplain which became a marsh and then mudflats at the edge of a lagoon. Hypsilophodon fossils are spatially and stratigraphically distributed throughout the bed. Specimens are largely incomplete and unabraded suggesting most perished on or near to the floodplain and may have lain exposed for some time prior to burial. Overall, evidence suggests the fossil assemblage of the Hypsilophodon Bed formed as an accumulation of remains over time.

How to engineer a habitable planet: the rise of marine ecosystem engineers through the Phanerozoic

AbstractEcosystem engineers are organisms that modify their physical habitats in a way that alters resource availability and the structure of the communities they live in. The evolution of ecosystem engineers over the course of Earth history has thus been suggested to have been a driver of macroevolutionary and macroecological changes that are observed in the fossil record. However, the rise to dominance of ecosystem engineers has not been thoroughly reconstructed. Here, we investigate the history of bioturbation and reef‐building (two of the most important marine ecosystem engineering behaviours today) over the Phanerozoic. Using fossil occurrences from the Paleobiology Database, we reconstruct how common communities influenced by ecosystem engineers were in the oceans, how dominant ecosystem engineers were within their own communities, and the taxonomic and ecological composition of bioturbators and reef‐builders. We find that bioturbation has become an increasingly common ecosystem engineering behaviour over the Phanerozoic, while reef‐building ecosystem engineers have not become more dominant since their Devonian apex. We also identify unique bioturbation and reef‐building regimes that are characterized by different ecosystem engineering taxonomic groups, ecological modes, and dominance, suggesting that the nature of ecosystem engineering has at times rapidly shifted over the course of the Phanerozoic. These reconstructions will serve as important data for understanding how ecosystem engineers have driven changes in biodiversity and ecosystem structure over the course of Earth history.

The rise and fall of notoungulates: How Andean uplift, available land area, competition, and depredation driven its diversification dynamics

Unraveling the biotic and abiotic drivers likely influencing clades’ diversification dynamics (differential speciation and extinction rates) is crucial for understanding life on Earth. Here, we present a comprehensive analysis of the diversification dynamics of notoungulates (Mammalia: Notoungulata), the most diverse and widespread Cenozoic herbivore mammals that evolved in South America (SA) but are now entirely extinct. Employing fossil occurrences restricted to the southern part of the SA and a Bayesian framework, we examined the historical speciation and extinction rates across all notoungulates, suborders, and three body size categories and tested whether these dynamics could be driven by biotic (e.g., diversity dependence, competition) and abiotic (e.g., Andean uplift and temperature changes) factors. Our findings reveal significant variability in diversification rates over time and groups driven by biotic and abiotic factors. We observed an increase in notoungulate speciation rates correlated with lower group self-diversity, likely related to limited environmental productivity and more extensive emerged continental areas that can provide increased environmental and ecological heterogeneity. In contrast, elevated extinction rates were correlated with intensified Andean uplift events, which can trigger landscape modifications and the arrival of placental carnivores after the Great American Biotic Interchange, probably due to notoungulate vulnerability to novel predation pressures. Furthermore, sparassodont diversity appears to increase speciation and extinction rates of notoungulates, although the direct mechanism relating them remains uncertain. The heterogeneity in the observed patterns of speciation and extinction across distinct size categories and taxonomic clades provides valuable perspectives on how ancient global and regional changes impacted the diversification dynamics of mammals and underscores the intricate interplay between environmental changes and biological interactions in shaping the evolution of life on Earth.

Updating the Upper Cretaceous (Campanian) Two Medicine Formation of Montana: Lithostratigraphic revisions, new CA-ID-TIMS U-Pb ages, and a calibrated framework for dinosaur occurrences

The Campanian Two Medicine Formation of northwestern Montana, USA, is richly fossiliferous, and discoveries made within the unit over the past century have greatly advanced our appreciation of dinosaur paleobiology and evolution. Previously undifferentiated from a lithostratigraphic perspective, the formation is now subdivided into four new members that include (from base to top) (1) the Rock City Member, (2) the Shields Crossing Member, (3) the Hagans Crossing Member, and (4) the Flag Butte Member. These new formal units and their associated fossil occurrences are also now included in an age model founded on eight high-resolution chemical abrasion−isotope dilution−thermal ionization mass spectrometry (CA-ID-TIMS) U-Pb ages. New age data confirm that the Two Medicine Formation accumulated during much of the Campanian, with deposition spanning ca. 82.4 Ma to 74.4 Ma. New age data further indicate that a major reorganization of depositional systems, marked by a shift from predominantly lacustrine to alluvial facies and accompanied by a dramatic increase in accommodation, transpired near the base of the new Flag Butte Member at ca. 76.3 Ma. This change in depositional regime correlates in age with the Judith River−Belly River discontinuity, which marks the contact between the McClelland Ferry and Coal Ridge Members in the Judith River Formation and coincides with the onset of the Bearpaw transgression in north-central Montana. The new lithostratigraphic and chronostratigraphic framework for the Two Medicine Formation serves to contextualize and calibrate the formation’s rich dinosaur fossil record, which can now be interrogated with increased clarity and precision. These results also provide ground truth for numerical models that explore the structure of the fossil record in relation to alluvial architecture and terrestrial sequence stratigraphy.

A MaxEnt predictive model for palaeontological sites in the Siwalik Hills: A case study from the Pinjor Formation of the Upper Siwalik Hills near Chandigarh, northern India

This study presents application of the MaxEnt predictive model to identify potential palaeontological sites in the Siwalik Hills, focusing on the Pinjor Formation near Chandigarh, northern India. The Siwalik region holds rich vertebrate palaeontological records, yet lacks comprehensive site prediction models. This research employs MaxEnt (3.4.0) software, to predict areas suitable for fossil occurrences. Georeferenced presence data was derived from literature and field surveys, for training the model. Environmental predictors including Pinjor geological deposit boundary, Vegetation Index (NDVI), and Slope and Aspect were from a digital elevation model. Furthermore, model development involved parameter tuning, for developing a potentially useful model. Field validation of the model through pedestrian surveys identified new fossil localities, demonstrating the model's practical applicability. This research emphasizes the importance of MaxEnt in developing site predictive models, offering a valuable tool for optimizing palaeontological field surveys. While highlighting the model's success, the study also recognizes its limitations, especially concerning landscape and vegetation changes over time. Overall, this work establishes a foundation for further research in predictive modelling for palaeontological exploration in the Siwalik region and emphasizes the need for multidisciplinary efforts in salvage palaeontology to mitigate anthropogenic threats.

“Out-of-India” dispersal of the extinct fabaceous genus Podocarpium Braun ex Stizenberger

Podocarpium is a well-known extinct single-seeded legume genus having extensive Cenozoic fossil occurrences from East Asia to central Europe. To date, there have been no fossil records of this genus from South Asia, including India. Here, we report and describe for the first time a well-preserved fossil pod from the early Eocene of Rajasthan, western India, assigned to extinct Podocarpium based on detailed morphology. It is characterized by an asymmetrical, oblique valve with a single oblong seed, a distinctly curved stipe, a wingless margin, a prominent vascular strand along the dorsal suture that anastomoses into the apex, a weakly curved ventral suture, fine reticulate veins, a short acuminate apex, and a narrowly acute base. This discovery is the oldest fossil evidence of Podocarpium recorded to date worldwide. Together with previous fossil records, we suggest an “Out-of-India” dispersal hypothesis to explain the biogeography of this extinct legume genus. It might have originated under warm and humid tropical climate conditions in the early Eocene of India (South Asia), then migrated to China (East Asia), and subsequently spread north and westward to Europe.

A Phanerozoic gridded dataset for palaeogeographic reconstructions

Global Plate Models are widely used in the Earth Sciences to reconstruct the past geographic position of geological and palaeontological samples. However, the application of Global Plate Models to retrieve ‘palaeocoordinates’ is not trivial. Different Global Plate Models exist which vary in their complexity, spatiotemporal coverage, reference frame, and intended use. Consequently, careful consideration of which models are appropriate for any given research question is required. Here, we document and provide access to reconstruction datasets for five Global Plate Models in the palaeomagnetic reference frame. These datasets provide ‘true’ palaeolatitudes for three discrete global grids reconstructed at one-million-year intervals throughout the Phanerozoic (540–0 Ma), offering three key benefits for the Earth Science community: (1) allow users to look up palaeocoordinates for their samples (e.g. fossil occurrences) through simple indexing without having to learn additional software packages; (2) provide palaeocoordinates which have been generated consistently with thorough documentation; (3) provide static files which preserve model output and which can be used to evaluate palaeogeographic differences between Global Plate Models.

Rapid volcanic ash entombment reveals the 3D anatomy of Cambrian trilobites.

Knowledge of Cambrian animal anatomy is limited by preservational processes that result in compaction, size bias, and incompleteness. We documented pristine three-dimensional (3D) anatomy of trilobites fossilized through rapid ash burial from a pyroclastic flow entering a shallow marine environment. Cambrian ellipsocephaloid trilobites from Morocco are articulated and undistorted, revealing exquisite details of the appendages and digestive system. Previously unknown anatomy includes a soft-tissue labrum attached to the hypostome, a slit-like mouth, and distinctive cephalic feeding appendages. Our findings resolve controversy over whether the trilobite hypostome is the labrum or incorporates it and establish crown-group euarthropod homologies in trilobites. This occurrence of moldic fossils with 3D soft parts highlights volcanic ash deposits in marine settings as an underexplored source for exceptionally preserved organisms.

THE FIRST RECORD OF THE ORECTOLOBIFORM SHARK GENUS <em>CEDERSTROEMIA</em> (ELASMOBRANCHII, ORECTOLOBIDAE) IN ASIA (KASHIMA FORMATION, UPPER CRETACEOUS; OYUBARI AREA, HOKKAIDO, JAPAN)

We described fossil teeth assigned to the orectolobiform shark genus, Cederstroemia collected from the tuffaceous sandstone of the Kashima Formation (Santonian) in the Oyubari area, Hokkaido, Japan. This is the first report of fossil remains of Cederstroemia from Asia. Due to the small number of specimens and their poor preservation, we left the studied material in open nomenclature as Cederstroemia sp. At the same time, the studied material may belong to a new previously undescribed morphology of Cederstroemia. The occurrence of Cederstroemia fossils in Japan indicates that this genus dispersed to the northwestern part of the Pacific Ocean in the Late Cretaceous, which considerably extends the range and previously known habitat of this genus.

New Late Cretaceous (Cenomanian) fossil mayfly nymphs (Oligoneuriidae, Heptageniidae, Hexagenitidae) from the Redmond Formation, Labrador, Canada

Three new fossil mayfly (Ephemeroptera) larvae from the Redmond Formation (Cenomanian) of Newfoundland and Labrador, Canada, are described: Alatuscapillus icarus gen. et sp. nov. (family Oligoneuriidae), Cruscolli sheppardae gen. et sp. nov. (family Heptageniidae), and Protoligoneuria borealis sp. nov. (family Hexagenitidae). This discovery marks the first juvenile insect nymphs to be described from this formation and helps fill gaps in our understanding of the global and temporal distribution of mayflies during the Cretaceous period. Of these, C. sheppardae marks the oldest occurrence of the family Heptageniidae in the fossil record, while A. icarus and P. borealis mark the first fossil occurrences of the families Oligoneuriidae and Hexagenitidae in North America. The anatomy, preservation, and behaviour of these new mayfly species inferred from modern taxa consolidate the hypothesis that the Redmond Formation’s palaeoenvironment was lacustrine in nature.

The Elasmobranch Fossil Record of the Indo-Australian Archipelago since the Miocene: A Literature Review and New Discoveries from Northern Borneo

The Indo-Australian Archipelago (IAA) today exhibits the highest marine biodiversity, which has been evolving since the early Miocene. The existence of this high palaeobiodiversity is attested to by the presence of many fossil invertebrates; however, the region’s fossil fish record is sparse and understudied, which is also the case for cartilaginous fishes. Elasmobranch fossils are dominantly represented by shark and ray teeth in the geological record and can give a quick overview of the composition of the fauna. The first IAA elasmo fossils, shark teeth were described from Java (Indonesia) at the end of the 19th century, and until today, most of the publications are known from this island. In the early and middle of the 20th century, remarkable fossils were also reported from the islands of Madura (NE Java) and Sulawesi, some with detailed taxonomical descriptions. In addition, only sporadic reports on fossil occurrences exist elsewhere from the IAA, but these lack any detailed taxonomic accounts. In 2019 our research group reported a late Miocene elasmobranch fauna from Brunei (Borneo), which is now the most diverse known shallow water fossil assemblage from the entire IAA. This fauna was described from a single fossiliferous outcrop, called Ambug Hill. However, several new localities have been discovered and studied over the years, as a result the number of fossils increased, and their age range extended. Here we provide an overview of these new sites and their elasmobranch fossils, and describe remains from ten taxa among, of which eight are new to the IAA fossil record (Chiloscyllium sp., cf. Hemitriakis sp., Paragaleus sp., Carcharhinus borneensis, C. limbatus, Lamiopsis sp., Scoliodon sp., Rhinobatos sp.). The overall north Bornean elasmo assemblage is then compared with other IAA occurrences. An extended fauna list is given based on literature review and preliminary investigation of the Naturalis Biodiversity Centre collection in Leiden (The Netherlands) where most of the fossil fishes of the early explorations are stored. These assemblages are also briefly summarized, and attention is drawn to some of the unique and thus far unreported taxa (e.g., Dalatias licha).

Selection by differential survival among marine animals in the Phanerozoic

The Gaia hypothesis posits that the Earth and its biosphere function as a single self-stabilizing system, but a key challenge is explaining how this could have arisen through Darwinian evolution. One theory is that of “selection by differential survival,” in which a clade’s extinction probability decreases with age as it accumulates adaptations resisting environmental disturbances. While this is hard to assess during early Earth history, we can assess whether this process operated among marine animal genera throughout the Phanerozoic. To that end, we analyzed time ranges of 36,117 extinct animal genera using fossil occurrence data from the Paleobiology Database in order to calculate marine metazoan extinction age selectivity, extinction rates, and speciation rates over the Phanerozoic. We identify four signatures of selection by differential survival: lower extinction rates among older lineages, heritability and taxonomically nested propagation of extinction resistance, reduced age selectivity during rare environmental perturbations, and differential extinction rather than speciation as the primary driver of the phenomenon. Evidence for this process at lower taxonomic levels also implies its possibility for life as a whole – indeed, the possibility of Gaia.

Deep-water first occurrences of Ediacara biota prior to the Shuram carbon isotope excursion in the Wernecke Mountains, Yukon, Canada.

Ediacara-type macrofossils appear as early as ~575 Ma in deep-water facies of the Drook Formation of the Avalon Peninsula, Newfoundland, and the Nadaleen Formation of Yukon and Northwest Territories, Canada. Our ability to assess whether a deep-water origination of the Ediacara biota is a genuine reflection of evolutionary succession, an artifact of an incomplete stratigraphic record, or a bathymetrically controlled biotope is limited by a lack of geochronological constraints and detailed shelf-to-slope transects of Ediacaran continental margins. The Ediacaran Rackla Group of the Wernecke Mountains, NW Canada, represents an ideal shelf-to-slope depositional system to understand the spatiotemporal and environmental context of Ediacara-type organisms' stratigraphic occurrence. New sedimentological and paleontological data presented herein from the Wernecke Mountains establish a stratigraphic framework relating shelfal strata in the Goz/Corn Creek area to lower slope deposits in the Nadaleen River area. We report new discoveries of numerous Aspidella hold-fast discs, indicative of frondose Ediacara organisms, from deep-water slope deposits of the Nadaleen Formation stratigraphically below the Shuram carbon isotope excursion (CIE) in the Nadaleen River area. Such fossils are notably absent in coeval shallow-water strata in the Goz/Corn Creek region despite appropriate facies for potential preservation. The presence of pre-Shuram CIE Ediacara-type fossils occurring only in deep-water facies within a basin that has equivalent well-preserved shallow-water facies provides the first stratigraphic paleobiological support for a deep-water origination of the Ediacara biota. In contrast, new occurrences of Ediacara-type fossils (including juvenile fronds, Beltanelliformis, Aspidella, annulated tubes, and multiple ichnotaxa) are found above the Shuram CIE in both deep- and shallow-water deposits of the Blueflower Formation. Given existing age constraints on the Shuram CIE, it appears that Ediacaran organisms may have originated in the deeper ocean and lived there for up to ~15 million years before migrating into shelfal environments in the terminal Ediacaran. This indicates unique ecophysiological constraints likely shaped the initial habitat preference and later environmental expansion of the Ediacara biota.

Diversity-dependent speciation and extinction in hominins

The search for drivers of hominin speciation and extinction has tended to focus on the impact of climate change. Far less attention has been paid to the role of interspecific competition. However, research across vertebrates more broadly has shown that both processes are often correlated with species diversity, suggesting an important role for interspecific competition. Here we ask whether hominin speciation and extinction conform to the expected patterns of negative and positive diversity dependence, respectively. We estimate speciation and extinction rates from fossil occurrence data with preservation variability priors in a validated Bayesian framework and test whether these rates are correlated with species diversity. We supplement these analyses with calculations of speciation rate across a phylogeny, again testing whether these are correlated with diversity. Our results are consistent with clade-wide diversity limits that governed speciation in hominins overall but that were not quite reached by the Australopithecus and Paranthropus subclade before its extinction. Extinction was not correlated with species diversity within the Australopithecus and Paranthropus subclade or within hominins overall; this is concordant with climate playing a greater part in hominin extinction than speciation. By contrast, Homo is characterized by positively diversity-dependent speciation and negatively diversity-dependent extinction—both exceedingly rare patterns across all forms of life. The genus Homo expands the set of reported associations between diversity and macroevolution in vertebrates, underscoring that the relationship between diversity and macroevolution is complex. These results indicate an important, previously underappreciated and comparatively unusual role of biotic interactions in Homo macroevolution, and speciation in particular. The unusual and unexpected patterns of diversity dependence in Homo speciation and extinction may be a consequence of repeated Homo range expansions driven by interspecific competition and made possible by recurrent innovations in ecological strategies. Exploring how hominin macroevolution fits into the general vertebrate macroevolutionary landscape has the potential to offer new perspectives on longstanding questions in vertebrate evolution and shed new light on evolutionary processes within our own lineage.

First fossil pod of Mezoneuron (Caesalpinioideae, Fabaceae) in Asia

The genus Mezoneuron Desf. (Caesalpinioideae, Fabaceae) comprises 23 extant species distributed throughout the Old World tropics and subtropics, yet its fossil record is scarce with finds restricted to Europe and North America. Here, we report a new Mezoneuron pod fossil from the lower Miocene Sanhaogou Formation of Jinggu Basin in Southwest China, representing the first fossil occurrence of this genus in Asia and the only one within its current distribution range. The fossil presents a vascularized wing along the placental suture and with poorly developed, irregular reticulate venation, which are typical pod characters in Mezoneuron. With detailed morphological observation and comparison, it is assigned as a new species, namely M. zhekunii Y.S. Zhao, L.B. Jia et T. Su sp. nov. Together with the historic and modern distribution of Mezoneuron and its relatives, we propose that Mezoneuron originated in the Northern Hemisphere no later than the middle Eocene. Mezoneuron attained relatively low latitudes in Asia no later than the early Miocene, with our fossil representing the lowest latitudinal record. The oblique and fine wrinkles of pod probably suggest a papery texture and low weight observed in mature pods of some extant Mezoneuron species, which favors wind dispersal.