Tooth marks preserved on bones can yield a wealth of information regarding the behavior an ecology of the carnivores that produced them. For this reason, scientists studying both moder and fossil vertebrates have inspected and interpreted these features for decades. Although pre vious studies have provided important insights, they have also described tooth marks usin sets of terms that have been incompletely defined, have incorporated behavioral hypothese in definitions, and/or have been inconsistently applied. To address these problems, we intro duce the category-modifier (CM) system, the first system to both sort tooth marks into clearl defined main categories and use descriptive modifiers to characterize their appearance mor precisely. The CM system is designed to apply to a wide range of vertebrates, to enable com parisons across disciplines and studies, and to help researchers keep their investigations int behavioral hypotheses free of circular reasoning.

Preserved records of tooth–bone interactions, known as tooth marks, can yield a wealth of information regarding organismal behavior and ecology. For this reason, workers in a wide range of disciplines, but particularly paleontology, have inspected and interpreted these features for decades. Although previous studies have gleaned invaluable insights, they have also described tooth marks using terminological frameworks that have been incompletely defined, have incorporated behavioral hypotheses in definitions, and/or have been inconsistently applied. To address these problems, we introduce the category-modifier (CM) system, the first system to both sort tooth marks into clearly defined main categories and use descriptive modifiers to characterize their appearance more precisely. The CM system is designed to apply to a wide range of vertebrates, to enable comparisons across disciplines and studies, and to help researchers keep their investigations into behavioral hypotheses free of circular reasoning.

The trace fossil record provides key insights into the evolution of early animals during the Ediacaran/Cambrian transition. By examining the diversity of these fossils, we can understand how early animal behaviors and body plans developed. We introduced a new mathematical method based on vectors to measure differences in trace fossil diversity. Using this method, we analyzed a large dataset of trace fossils and discovered the timings of important evolutionary events. Our findings show that early animals diversified in two stages and more quickly in shallow-marine environments and gradually specialized their ecological roles.

The trace fossil record provides important insights into the evolution of early animals during the Ediacaran/Cambrian transition, with changes in ichnodiversity through time and between environments informing on the diversification of major body plans, behaviors, and niches. To quantify variation in the diversity of trace fossils across this critical interval, we propose a measure of trace fossil dissimilarity (ichnodissimilarity) based on vector calculation. Furthermore, by comparing discrepancies between the angular bisector and mean vector of two sets of vectorized fossil data, we are able to weigh the relative contribution of increases and decreases in the variation of occurrences of taxa. We used this metric to analyze an expansive dataset of Ediacaran/Cambrian trace fossils. The results allowed us to quantify the diversification of traces across this transition, informing on the timing of first appearance of different behaviors (e.g., foraging, grazing, and resting) and functional groups. By interpreting the results in the context of environmental changes and advancements in motility and sensory capabilities, we were able to pinpoint the onset and sequence of the Fortunian diversification event, Cambrian information revolution, and agronomic revolution, shedding light on the evolution of organismal body plans, behaviors, and locomotion during the Ediacaran/Cambrian transition. We identified two phases of origination and expansion during the divergence of early animal traces. Furthermore, by analyzing shallow- and deep-marine trace fossils, we were able to uncover evidence for a more rapid diversification of traces in shallow-marine environments, with progressive niche partitioning through the Ediacaran to Cambrian.

The placement of landmarks or points on three-dimensional (3D) digital fossils allows for the visualization and characterization of shape. Eublastoidea, an ancient (443–251 million years ago) echinoderm (e.g., sea urchins) group, is an ideal group for such analysis, because they are composed of skeletal elements whose connections are inherited and easily identifiable on all species. Herein, we use 3D landmarks on fossil echinoderms to investigate relationships, change through time, and whether the varying proportions of skeletal elements that produce the animals' overall shapes are distinguishable in morphospace. The plating around the animals' mouths (oral plates) shows visible patterns in morphospace, while other ratios examined show no disambiguation in morphospace. Applying modern analytical methods to previously explored questions allows for an updated understanding of this important echinoderm group and provides a framework for others to assess echinoderms in a similar manner.

Geometric morphometrics facilitates the quantification and visualization of variation in shape and proportion through the comparison of homologous features. Eublastoidea, a Paleozoic echinoderm clade with a conservative body plan, is an ideal group for morphometric analysis, because their plate junctions are homologous and identifiable on all species. Eublastoids have previously been grouped taxonomically by generalized shape types (e.g., globose). These shapes are often used in taxonomic descriptions and as characters in phylogenetic analyses. The underlying homology of these broad shape types has never been explored. Herein we apply the first comprehensive use of three-dimensional geometric morphometrics (3D GMM) on fossil echinoderms to investigate taxonomic assignments, temporal distribution, and whether the varying proportions of skeletal elements that produce the gross thecal morphology are distinguishable. Taxonomic assignments specifically at the ordinal and family levels show varying amounts of overlap in morphospace, suggesting that many assignments may not be reevaluated. Our results suggest that none of the generalized shape types are distinct in morphospace and, therefore, likely do not capture the homologous changes in taxa. The plate circlet ratios showed trends specifically relating to the deltoid plate circlet, which has the most variability. We reanalyzed previous work and subsetted our data to be more comparable and found that there are key differences between methodologies and landmarks that will require future evaluation. Applying modern technological methods to previously explored questions allows for an updated understanding of this important fossil clade and provides a framework for others to assess fossil clades in a similar manner.

The quantification of shape in 3D for marine extinct arthropods remains rarely documente Based on both heads and tails of some trilobites, we compare the overall shape and explore th ontogenetic patterns and the phylogenetic signal for the first time in 3D versus 2D. We dem onstrate that there are rather congruent results between 3D and 2D to discriminate taxa; 2 and 3D landmarks capture different levels of detail, and the third dimension in 3D is ver important for making taxonomic distinctions at the genus level; there is congruity betwee 2D and 3D datasets for ontogenetic patterns; the phylogenetic morphospaces show tre branches that do not intersect, suggesting possible phylogenetic constraints on morphospac occupation for each species; and the morphological descriptors in morphometric analyses i 2D and 3D throughout trilobite evolution are effective.

Phacopid trilobites are well documented during the Paleozoic. Nevertheless, while 2D quan titative analyses have advanced our understanding of the morphological relationships amon trilobites, the quantification of their morphological traits in 3D remains rarely documented Based on two sets of morphological data (head and tail), 2D versus 3D shape quantificatio approaches were used to explore shape allometries as well as to explore how the shape vari ations can be explained by the phylogenetic relationships among phacopid trilobite species fo the first time. We demonstrate that (1) there are similar patterns of morphological variabilit across taxa in 3D and 2D; (2) there are rather congruent results between 3D and 2D to dis criminate taxa; (3) 2D and 3D landmarks capture different levels of detail, and the thir dimension in 3D is very important for making taxonomic distinctions at the genus level (4) there is congruity between 2D and 3D datasets for allometric patterns with results showin similar allometric slopes among species exhibiting a glabellar length decrease during growt leading to wider cephala; (5) the phylomorphospaces show tree branches that do not intersect suggesting possible phylogenetic constraints on morphospace occupation for each species an supporting the idea that the Austerops and Morocops groups are sister clades that experience different modes of morphological evolution; and (6) the morphological descriptors in mor phometric analyses in 2D and 3D throughout phacopid evolution are effective.

Planktonic foraminifera are single-celled marine protists, roughly the size of a grain of sand. They have an extremely detailed fossil record: a teaspoonful of seafloor sediment contains more than 1000 fossil shells. Some species have unusually ornamental shapes, but it is not clear why or how these shapes evolved. Here, we study the developmental changes that led to the speciation of one particularly ornate species: Globigerinoidesella fistulosa. We find that changes in the developmental timing of adult life stages likely account for the complex morphology. This study highlights the complex morphological and developmental changes required to produce unusual shell shapes and highlights the importance of developmental changes in evolutionar origination.

Planktonic foraminifera are extremely well suited to studying evolutionary change in the fossil record due to their abundant deposits and global distribution. Species are typically conservative in their shell morphology, with the same geometric shapes appearing repeatedly through iterative evolution, but the mechanisms behind the architectural limits on foraminiferal shell shape are still not well understood. To determine how these developmental constraints arise, we study morphological change leading up to the origination of the unusually ornate species Globigerinoidesella fistulosa. We measured the size and circularity of more than 900 specimens of G. fistulosa, its ancestor the Trilobatus sacculifer plexus, and intermediate forms from a site in the western equatorial Pacific. Our results show that the origination of G. fistulosa from the T. sacculifer plexus involved a combination of two heterochronic expressions: earlier onset of protuberances (pre-displacement) and a steeper allometric slope (acceleration) as compared with its ancestor. Our work provides a case study of the complex morphological and developmental changes required to produce unusual shell shapes and highlights the importance of developmental deviations in evolutionary origination.

Shells of foraminifers provide indispensable data for paleoceanography, paleoecology, and paleoclimate reconstruction. This study analyzes the preservation of shell, specifically where and why bioerosion (i.e., drill holes) occur in planktonic foraminifera shells. We examined 2588 specimens from eight species and used statistical analyses and numeric models to map the distribution of these drill marks within each species. Our findings reveal that the density and location of drill holes differ between spinose and non-spinose species, with spinose species tending to have more holes. Species with thinner tests (spinose) are preferentially perforated in the earlier whorls, while those with thicker shells (non-spinose) exhibit more holes in the ultimate chambers. Foraminiferal bioeroders likely select drilling sites based on a balance between minimizing the effort required to penetrate the test and maximizing access to nutrient-rich content. In summary, our study revealed distinct bioerosion patterns across foraminiferal species, suggesting that morphological characteristics contribute to the varying vulnerability of sectors and species to bioerosion.

Despite advances in understanding planktonic foraminifera environmental interactions, their role as prey remains elusive, often inferred from indirect evidence such as drill holes. Bioerosional traces offer valuable insights into fossil assemblages, although knowledge for planktonic foraminifera remains limited compared with benthic species. This study addresses this gap by analyzing bioerosional site selectivity in late Quaternary planktonic foraminifera from the western South Atlantic. We examined 2588 specimens from eight species to map trace patterns using kernel density estimation, sector-based, and hotspot mapping approaches. Drilling traces were located, transposed to graphical representations, and transformed into x,y coordinates. We analyzed specimen frequency per trace quantity and trace frequency, sectoring them per chamber and test regions. Correspondence analysis and exact test of goodness of fit assessed groupings among the species and preferential regions. Frequencies revealed that spinose species had more multiple-drilled specimens than non-spinose ones. Bioerosional traces were prevalent in the final whorl, decreasing toward earlier chambers. However, when normalized by surface area, the penultimate whorl had higher trace frequencies, particularly for spinose species, while the ultimate whorl had higher trace density for some non-spinose ones. Spinose species are preferentially drilled in the early chambers, likely due to their thinner walls. Thus, bioeroders prioritize regions with a higher cost–benefit ratio, which is evident in the prevalence of successful–failed traces in early chambers of spinose species, but not in thicker-walled, non-spinose ones. Our study reveals distinct bioerosion patterns, highlighting strategic site selectivity and suggesting that morphological differences between spinose and non-spinose species contribute to varying vulnerability to bioerosion.

The Cretaceous/Paleogene (K/Pg) mass extinction is well known for the global extinction of non-avian dinosaurs and other dominant vertebrate groups. However, plants also experienced a massive turnover at this time, propelling the expansion of modern lineages into the Cenozoic. Our study of plants across the K/Pg boundary in northeastern Montana highlights the geographic heterogeneity of plant turnover during the K/Pg mass extinction and the differing effects of mass extinctions on various plant taxonomic groups. Overall, we find a high percentage of plant species disappeared across the K/Pg boundary, even though vegetation recovered relatively quickly in the earliest Paleocene in Montana. We compare this record with other studies of plant communities around the globe during the K/Pg interval.

The Cretaceous/Paleogene (K/Pg) mass extinction was a pivotal event in Earth history, the latest among five mass extinctions that devastated marine and terrestrial life. Whereas much research has focused on the global demise of dominant vertebrate groups, less is known about changes among plant communities during the K/Pg mass extinction. This study investigates a suite of 11 floral assemblages leading up to and across the K/Pg boundary in northeastern Montana constrained within a well-resolved chronostratigraphic framework. We evaluate the impact of the mass extinction on local plant communities as well as the timing of post-K/Pg recovery. Our results indicate that taxonomic composition changed significantly from the Late Cretaceous to Paleocene; we estimate that 63% of latest-Cretaceous plant taxa disappeared across the K/Pg boundary, on par with other records from North America. Overall, taxonomic richness dropped by ∼23–33% from the Late Cretaceous to the Paleocene, a moderate decline compared with other plant records from this time. However, richness returned to Late Cretaceous levels within 900 kyr after the K/Pg boundary, significantly faster than observed elsewhere. We find no evidence that these results are due to preservational bias (i.e., differences in depositional environment) and instead interpret a dramatic effect of the K/Pg mass extinction on plant diversity and ecology. Overall, plant communities experienced major restructuring, that is, changes in relative abundance and unseating of dominant groups during the K/Pg mass extinction, even though no major (e.g., family-level) plant groups went extinct and communities in Montana quickly recovered in terms of taxonomic diversity. These results have direct bearing on our understanding of vegetation change during diversity crises, the differing responses of plant groups (e.g., angiosperms vs. gymnosperms), and spatial variation in extinction and recovery timing.

The trace fossils presented here belong to the category of animal behavior that Seilacher had defined and called “mortichnia.” However, Vallon and colleagues did not recommend the usage of this ethological category, because its recognition not only depends on trace fossil morphology, but also on tracemaker physiology and environmental interpretation. The two latter assumptions in particular cannot always be deduced correctly, rendering the whole interpretation false (especially when modern analogues of such environments or closely related organismal groups do not exist). Nevertheless, the category exists, and with the recently recovered specimens, a redefinition is attempted.

The specimens from Lebanon are all traces left by dying fish. At the beginning, the traces show the greatest physical strengths of the tracemakers, as their body movements were still relatively powerful. Over the course of the mortichnion, the traces reflect increasing exhaustion. The undulating movements of the tail fin decrease, and the resulting trail becomes more and more asymmetrical. Its depth becomes shallower. During last moments of the tracemakers' lives, their movement was reduced to barely discernible movements. Finally, the trail ends with the death and the preserved corpse of the tracemaker.

In our redefinition of mortichnia, we argue that trace fossils included in this ethological group must contain the fossilized corpse of the tracemaker. The corpse must ideally show signs of illness or predation (the tracemaker body fossil, however, is neither part of the trace fossil nor is it to be regarded as the actual trace fossil). Other trails or trackways, especially from non-fish tracemakers like Solemya at the Solnhofen Lagerstätte (Kimmeridgian–Tithonian; Germany), may show signs of loss of orientation, or the tracemakers might try to avoid certain areas that impose hostile living conditions (e.g., ripples, crests) if the environment is drying out and the tracemakers breath via gills.

Proper identification of behavioral patterns is an important prerequisite for the identification of any trace fossil and even more so for its interpretation. For the last 70 yr, the continually advancing state of ichnological knowledge has led to a gradual recognition of recurrent patterns of organismal behavior documented in the fossil record, which in turn gave rise to the ethological categories. “Mortichnia” was proposed for traces created during a death struggle of the tracemaker but has been reported only in a few cases. Fish mortichnia so far have only been reported in one specimen recovered from the Upper Jurassic Plattenkalk of Nusplingen (SW Germany). The category mortichnia is refined herein, but remains ambiguous. Eight newly discovered unique specimens of mortichnia from Upper Cretaceous marine sediments in central Lebanon (Haqil, En Nammoura) are preserved together with their tracemakers and described herein. In addition, 14 further incomplete specimens were collected where no tracemakers are present. However, morphology and close provenance allow them to be assigned to the same ichnotaxon.

The Lebanese mortichnia originate from fish that were subjected to significant environmental or individual stress leading to their deaths. During death convulsions, their bodies created sedimentary structures with a specific recurring morphology. The ichnogenus Pinnichnus n. igen. with ichnospecies P. haqilensis and P. emmae n. ispp. is proposed for these specimens.

Around 66 million years ago, a massive extinction event wiped out many species, including the dinosaurs. However, some animals, like turtles, managed to survive. Scientists have been debating whether this extinction event affected the variety of turtle species. This study creates a detailed curve showing the number of turtle species over time. It was found that the variety of turtles was already decreasing before the extinction event and continued to drop afterward. This suggests that the extinction event had a significant impact on turtle diversity, which had already been in decline.

The last mass extinction event some 66 million years ago at the Late Cretaceous/Paleogene boundary caused the extinction of many clades, including the non-avian dinosaurs. Turtles, as well as several other vertebrate clades, survived. However, the debate about whether the diversity of turtles was affected during this event is still ongoing. Here, I calculate a global turtle diversity curve at the species level that shows that the diversity of turtle species was already in decline since the Campanian, before the extinction event, and was further reduced during the Danian. The sample coverage of turtle occurrences at the stage level is also calculated and discussed.

Sharks today live in a variety of habitats, but the range of environments occupied by extinct sharks is not well known. The water temperature and chemistry of marine environments is incorporated in the composition of fish teeth, as well as the way organisms regulate their body temperature. To better understand the ecology of ancient sharks, we analyzed the chemical composition (stable oxygen isotope values) of six Late Cretaceous–age (86–79 million years ago) shark species from the Gulf Coastal Plain of Alabama, USA. We also analyzed teeth from the fish Enchodus petrosus, which should record ambient water temperature and chemistry, and compared the shark data with that of E. petrosus. Two of the shark taxa (Ptychodus mortoni and Cretoxyrhina mantelli) have much lower values compared with other fossil sharks and the fish E. petrosus. The low P. mortoni values are best explained by P. mortoni having a higher body temperature than the surrounding water, either through active or passive body heating. Similarly, the low C. mantelli values are best explained by both migration and higher body temperatures. It was proposed from other evidence that C. mantelli had higher body temperatures, but this study marks the first quantitative evidence of higher body temperatures in P. mortoni. If P. mortoni had an elevated body temperature, then it is likely that body temperature regulation evolved many times in sharks in the geologic past, as this species is not closely related to other species in which this phenomenon is documented.

We analyzed the oxygen isotope composition of biogenic apatite phosphate (δ¹⁸O_p) in fossil tooth enameloid to investigate the paleoecology of Late Cretaceous sharks in the Gulf Coastal Plain of Alabama, USA. We analyzed six different shark taxa from both the Mooreville Chalk and the Blufftown Formation. We compared shark δ¹⁸O_p with the δ¹⁸O_p of a co-occurring poikilothermic bony fish Enchodus petrosus as a reference for ambient conditions. Enchodus petrosus tooth enamel δ¹⁸O_p values are similar between formations (21.3‰ and 21.4‰ Vienna Standard Mean Ocean Water [VSMOW], respectively), suggesting minimal differences in water δ¹⁸O between formations. Most shark taxa in this study are characterized by δ¹⁸O_p values that overlap with E. petrosus values, indicating they likely lived in similar habitats and were also poikilothermic. Ptychodus mortoni and Cretoxyrhina mantelli exhibit significantly lower δ¹⁸O_p values than co-occurring E. petrosus (P. mortoni δ¹⁸O_p is 19.1‰ VSMOW in the Mooreville Chalk; C mantelli δ¹⁸O_p is 20.2‰ VSMOW in the Mooreville Chalk and 18.1‰ VSMOW in the Blufftown Formation). Excursions into brackish or freshwater habitats and thermal water-depth gradients are unlikely explanations for the lower P. mortoni and C. mantelli δ¹⁸O_p values. The low P. mortoni δ¹⁸O_p value is best explained by higher body temperature relative to surrounding temperatures due to active heating (e.g., mesothermy) or passive heating due to its large body size (e.g., gigantothermy). The low C. mantelli δ¹⁸O_p values are best explained by a combination of mesothermy (e.g., active heating) and migration (e.g., from the Western Interior Seaway, low-latitude warmer waters, or the paleo–Gulf Stream), supporting the hypothesis that mesothermy evolved in lamniform shark taxa during the Late Cretaceous. If the anomalous P. mortoni δ¹⁸O_p values are also driven by active thermoregulation, this suggests that mesothermy evolved independently in multiple families of Late Cretaceous sharks.

The number of species identified in the fossil record within any given geological time period must partly be explained by both the total number of fossil specimens sampled from that interval and the geographic spread of those samples. The influence of numerical sampling intensity has been well studied, but the effects of geographic variance in sampling are comparatively unknown. To investigate this question, we repeatedly resample a dataset of modern global marine organisms (from the Ocean Biodiversity Information System) using spatial sampling parameters determined by the real geographic spread of fossil organisms as found in the Paleobiology Database. Our findings show that a significant proportion of the variance in fossil diversity through time can be attributed only to changes in the numbers and locations of fossils sampled. This is consistent with the claim that the spatial structure of the fossil record and how it is sampled largely determine the diversity history drawn from it and with the ossibilit that lobal diversit has been relativel constant over time

Variation in observed global generic richness over the Phanerozoic must be partly explained by changes in the numbers of fossils and their geographic spread over time. The influence of sampling intensity (i.e., the number of samples) has been well addressed, but the extent to which the geographic distribution of samples might influence recovered biodiversity is comparatively unknown. To investigate this question, we create models of genus richness through time by resampling the same occurrence dataset of modern global biodiversity using spatially explicit sampling intensities defined by the paleo-coordinates of fossil occurrences from successive time intervals. Our steady-state null model explains about half of observed change in uncorrected fossil diversity and a quarter of variation in sampling-standardized diversity estimates. The inclusion in linear models of two additional explanatory variables associated with the spatial array of fossil data (absolute latitudinal range of occurrences, percentage of occurrences from shallow environments) and a Cenozoic step increases the accuracy of steady-state models, accounting for 67% of variation in sampling-standardized estimates and more than one-third of the variation in first differences. Our results make clear that the spatial distribution of samples is at least as important as numerical sampling intensity in determining the trajectory of recovered fossil biodiversity through time and caution against the overinterpretation of both the variation and the trend that emerge from analyses of global Phanerozoic diversity.