Article
To read the full-text of this research, you can request a copy directly from the authors.

Abstract

Non-avian dinosaurs went extinct 66 million years ago, geologically coincident with the impact of a large bolide (comet or asteroid) during an interval of massive volcanic eruptions and changes in temperature and sea level. There has long been fervent debate about how these events affected dinosaurs. We review a wealth of new data accumulated over the past two decades, provide updated and novel analyses of long-term dinosaur diversity trends during the latest Cretaceous, and discuss an emerging consensus on the extinction’s tempo and causes. Little support exists for a global, long-term decline across non-avian dinosaur diversity prior to their extinction at the end of the Cretaceous. However, restructuring of latest Cretaceous dinosaur faunas in North America led to reduced diversity of large-bodied herbivores, perhaps making communities more susceptible to cascading extinctions. The abruptness of the dinosaur extinction suggests a key role for the bolide impact, although the coarseness of the fossil record makes testing the effects of Deccan volcanism difficult.

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the authors.

... In this study, we apply Fossil BAMM and PyRate to the clade Ornithischia, one of the three major radiations of dinosaurs (Gauthier 1986; Baron et al. 2017;Langer et al. 2017), whose fossil record is ideally suited to testing the performance of the two frameworks. First, the ornithischians represent a wholly extinct, species-rich clade with an evolutionary history spanning at least a ∼134 myrlong period from the Early Jurassic at the latest (Agnolín and Rozadilla 2018;Baron 2019) to the Cretaceous-Paleogene (K-Pg) extinction event (Archibald and Fastovsky 2004;Brusatte et al. 2015). Second, the ornithischians have been subject to extensive phylogenetic research (Boyd 2015;Han et al. 2018;Dieudonné et al. 2020), allowing phylogenetic information to be used in diversification rate estimation. ...
... In terms of size and completeness, ornithischian phylogenetic and occurrence data are thus typical of the data sets widely in use by vertebrate paleontologists, whose broad availability may lead them to be repurposed for diversification rate estimation as methods like Fossil BAMM and PyRate grow in popularity. Finally, there is an ongoing controversy concerning ornithischian diversity trends and diversification rates, especially those prior to the K-Pg extinction (Wang and Dodson 2006;Barrett et al. 2009;Lloyd 2012;Brusatte et al. 2015;Sakamoto et al. 2016;Chiarenza et al. 2019;Bonsor et al. 2020), further motivating the application of state-of-theart diversification rate analysis to their fossil record. ...
... Previous analyses of ornithischian macroevolutionary dynamics have mostly focused on absolute species richness rather than speciation or net diversification rates (Barrett et al. 2009;Lloyd 2012;Brusatte et al. 2015;Chiarenza et al. 2019), hindering comparisons of the present results with earlier literature. Multiple studies have hypothesized that Ornithischia and other Mesozoic dinosaurs entered a period of decline prior to the K-Pg mass extinction Wang and Dodson 2006;Chiarenza et al. 2019). ...
Article
Full-text available
Changes in speciation and extinction rates are key to the dynamics of clade diversification, but attempts to infer them from phylogenies of extant species face challenges. Methods capable of synthesizing information from extant and fossil species have yielded novel insights into diversification rate variation through time, but little is known about their behavior when analyzing entirely extinct clades. Here, we use empirical and simulated data to assess how two popular methods, PyRate and Fossil BAMM, perform in this setting. We inferred the first tip-dated trees for ornithischian dinosaurs, and combined them with fossil occurrence data to test whether the clade underwent an end-Cretaceous decline. We then simulated phylogenies and fossil records under empirical constraints to determine whether macroevolutionary and preservation rates can be teased apart under paleobiologically realistic conditions. We obtained discordant inferences about ornithischian macroevolution including a long-term speciation rate decline (BAMM), mostly flat rates with a steep diversification drop (PyRate) or without one (BAMM), and episodes of implausibly accelerated speciation and extinction (PyRate). Simulations revealed little to no conflation between speciation and preservation, but yielded spuriously correlated speciation and extinction estimates while time-smearing tree-wide shifts (BAMM) or overestimating their number (PyRate). Our results indicate that the small phylogenetic datasets available to vertebrate paleontologists and the assumptions made by current model-based methods combine to yield potentially unreliable inferences about the diversification of extinct clades. We provide guidelines for interpreting the results of the existing approaches in light of their limitations, and suggest how the latter may be mitigated.
... Determining trends in Mesozoic dinosaur species-richness immediately prior to the K-Pg boundary is a contentious issue and has been the focus of numerous previous studies (e.g. [3,[8][9][10]). Many different hypotheses have been proposed, but there are currently three schools of thought. ...
... Many different hypotheses have been proposed, but there are currently three schools of thought. The first, reviewed extensively by Brusatte et al. [3], suggests that there is little evidence for a global downturn in dinosaur speciation rates prior to the K-Pg boundary. The second, reviewed by Sarjeant & Currie [11], Barrett et al. [12] and Archibald [13], suggests a decline on the timescale of hundreds of thousands or several millions of years related to non-bolide factors such as Deccan flood volcanism [10,14,15]. ...
... Finally, and most recently, Sakamoto et al. [16] proposed that dinosaurs were in global decline with falling speciation rates up to 35 Myr before the end-Cretaceous extinction and that non-avian dinosaurs were on a long-term trajectory toward extinction regardless of other external environmental factors. Nevertheless, proponents of all three hypotheses found evidence for continued high speciation rates among ceratopsid and hadrosaurid ornithischians in the latest Cretaceous compared to those in other dinosaur groups [3,16]. ...
Article
Full-text available
Determining the tempo and mode of non-avian dinosaur extinction is one of the most contentious issues in palaeobiology. Extensive disagreements remain over whether their extinction was catastrophic and geologically instantaneous or the culmination of long-term evolutionary trends. These conflicts have arisen due to numerous hierarchical sampling biases in the fossil record and differences in analytical methodology, with some studies identifying long-term declines in dinosaur richness prior to the Cretaceous-Palaeogene (K-Pg) boundary and others proposing continued diversification. Here, we use Bayesian phylogenetic generalized linear mixed models to assess the fit of 12 dinosaur phylogenies to three speciation models (null, slowdown to asymptote, downturn). We do not find strong support for the downturn model in our analyses, which suggests that dinosaur speciation rates were not in terminal decline prior to the K-Pg boundary and that the clade was still capable of generating new taxa. Nevertheless, we advocate caution in interpreting the results of such models, as they may not accurately reflect the complexities of the underlying data. Indeed, current phylogenetic methods may not provide the best test for hypotheses of dinosaur extinction; the collection of more dinosaur occurrence data will be essential to test these ideas further.
... The direct evolutionary descendants of non-avian dinosaurs, birds still make up one of the most proliferate and diverse group of vertebrates. However, non-avian dinosaurs themselves suddenly disappeared about 66 Myr ago [1]. ...
... There are astounding number and variety of hypotheses about causes of the dinosaur extinction [1,2]. However, the current research is concentrated around three major ones: 1) an impact of a giant bolid (asteroid or comet) [3,4,5]; 2) Volcanic activity in modern-day India's Deccan Traps [6]; 3) Marine regression (drop in sea level) and the corresponding global environmental deterioration [7,8]. ...
... Nevertheless, modern research [1,9] found support for a bolide impact as the primary factor of the end-Cretaceous mass extinction. Evidence of the bolid impact, coinciding in time with dinosaur extinction, is ubiquitous, including the huge 150 km wide Chicxulub crater in the Yucatán Peninsula in Mexico, impact related iridium anomaly worldwide, sediments in various areas of the world dominated by impact melt spherules and an unusually large amount of shocked quartz. ...
Article
Full-text available
It is believed that an asteroid/comet impact 65 million years ago ended the dinosaur era. The researchers named the corresponding impact crater Chicxulub, the Mayan word roughly translated as “the dragon's tail.” We estimate the expected magnitudes of the Schumann resonance fields immediately after the Chicxulub impact and show that they exceed their present-day values by about 5×104 times. Long-term distortion of the Schumann resonance parameters is also expected due to the environmental impact of the Chicxulub event. If Schumann resonances play a regulatory biological role, as some studies indicate, it is possible that the excitation and distortion of Schumann resonances after the asteroid/comet impact was a possible stress factor, which, among other stress factors associated with the impact, contributed to the demise of dinosaurs.
... Determining trends in Mesozoic dinosaur species-richness immediately prior to the K-Pg boundary is a contentious issue and has been the focus of numerous previous studies (e.g. [3,[8][9][10]). Many different hypotheses have been proposed, but there are currently three schools of thought. ...
... Many different hypotheses have been proposed, but there are currently three schools of thought. The first, reviewed extensively by Brusatte et al. [3], suggests that there is little evidence for a global downturn in dinosaur speciation rates prior to the K-Pg boundary. The second, reviewed by Sarjeant & Currie [11], Barrett et al. [12] and Archibald [13], suggests a decline on the timescale of hundreds of thousands or several millions of years related to non-bolide factors such as Deccan flood volcanism [10,14,15]. ...
... Finally, and most recently, Sakamoto et al. [16] proposed that dinosaurs were in global decline with falling speciation rates up to 35 Myr before the end-Cretaceous extinction and that non-avian dinosaurs were on a long-term trajectory toward extinction regardless of other external environmental factors. Nevertheless, proponents of all three hypotheses found evidence for continued high speciation rates among ceratopsid and hadrosaurid ornithischians in the latest Cretaceous compared to those in other dinosaur groups [3,16]. ...
Article
Determining the tempo and mode of non-avian dinosaur extinction is one of the most contentious issues in palaeobiology. Extensive disagreements remain over whether their extinction was catastrophic and geologically instantaneous or the culmination of long-term evolutionary trends. These conflicts have arisen due to numerous hierarchical sampling biases in the fossil record and differences in analytical methodology, with some studies identifying long-term declines in dinosaur richness prior to the Cretaceous-Palaeogene (K-Pg) boundary and others proposing continued diversification. Here, we use Bayesian phylogenetic generalized linear mixed models to assess the fit of 12 dinosaur phylogenies to three speciation models (null, slowdown to asymptote, downturn). We do not find strong support for the downturn model in our analyses, which suggests that dinosaur speciation rates were not in terminal decline prior to the K-Pg boundary and that the clade was still capable of generating new taxa. Nevertheless, we advocate caution in interpreting the results of such models, as they may not accurately reflect the complexities of the underlying data. Indeed, current phylogenetic methods may not provide the best test for hypotheses of dinosaur extinction; the collection of more dinosaur occurrence data will be essential to test these ideas further.
... This would have caused a global collapse of photosynthesis 4 , resulting in high levels of extinction across the tree of life. Among vertebrates, iconic Mesozoic groups such as non-avian dinosaurs 6 , pterosaurs 7 , and mosasaurs 8 disappeared at the K-Pg boundary. Other clades persisted but suffered severe reductions in diversity, including birds 9 , mammals 2 , and squamates 10 . ...
... Using our calibration set, we consistently recovered a diversification of crown Afrophidia (used here to refer to all alethinophidians, except Tropidophiidae + Aniliidae) near the K-Pg transition, and near-contemporaneous originations of the Amerophidia, Leptotyphlopidae, and Typhlopoidea crown groups, irrespective of the statistical framework, molecular clock model, priors, or phylogeny used ( Fig. 1 and Supplementary Figs. [4][5][6][7][8][9][10][11][12][13][14][15][16]. Implementing alternative assumptions regarding the quality of the fossil record by manipulating parameterizations of priors on fossil calibrations influenced mean estimated ages, but confidence intervals for nodes of interest-in particular for crown Afrophidia-converged near the K-Pg boundary. ...
... In snakes, vertebral morphology can be indicative of ecological niche and overall body size 40,71 . The extinction of non-avian dinosaurs 6 and other terrestrial predators may have enabled snakes to exploit relatively abundant small vertebrate prey in the early Cenozoic. Similarly, the K-Pgassociated extinction of marine reptiles and large teleosts may have facilitated the exploitation of marine ecosystems by large Paleocene marine snakes (Supplementary Fig. 28). ...
Article
Full-text available
Mass extinctions have repeatedly shaped global biodiversity. The Cretaceous-Paleogene (K-Pg) mass extinction caused the demise of numerous vertebrate groups, and its aftermath saw the rapid diversification of surviving mammals, birds, frogs, and teleost fishes. However, the effects of the K-Pg extinction on the evolution of snakes—a major clade of predators comprising over 3,700 living species—remains poorly understood. Here, we combine an extensive molecular dataset with phylogenetically and stratigraphically constrained fossil calibrations to infer an evolutionary timescale for Serpentes. We reveal a potential diversification among crown snakes associated with the K-Pg mass extinction, led by the successful colonisation of Asia by the major extant clade Afrophidia. Vertebral morphometrics suggest increasing morphological specialisation among marine snakes through the Paleogene. The dispersal patterns of snakes following the K-Pg underscore the importance of this mass extinction event in shaping Earth’s extant vertebrate faunas.
... T he most famous mass extinction was the disappearance of non-avian dinosaurs at the end of the Cretaceous, 66 million years ago (Mya), after ruling the Earth for 170 million years [1][2][3] . The best-supported extinction model is the impact of a large asteroid in the Yucatán Peninsula (Chicxulub, Mexico), which set off a global cataclysm and environmental upheaval 4,5 . ...
... There is a debate about how these events affected non-avian dinosaurs, and yet little evidence exists for a global decline across dinosaur groups prior to their extinction at the end of the Cretaceous 3,7,28-31 . The latest thorough analyses of fossil data found no evidence for a decline of non-avian dinosaurs before their extinction 3,30 , and little evidence of any decline in dinosaur species richness or ecological diversity during the last million years of the Cretaceous. However, a phylogenetic study using dinosaur timetrees 10 challenged the idea of a sudden extinction, but instead supported a diversity decline with extinction rates exceeding speciation rates well before the K/Pg event, which has been disputed recently 32 . ...
... Although the dinosaur fossil record provides invaluable data for our understanding of macroevolutionary patterns and processes through time, it is biased and incomplete 3,11,33 . Previous attempts to estimate dinosaur diversity dynamics were based on simple counts of the numbers of species in specific time intervals 8,9 . ...
Article
Full-text available
The question why non-avian dinosaurs went extinct 66 million years ago (Ma) remains unresolved because of the coarseness of the fossil record. A sudden extinction caused by an asteroid is the most accepted hypothesis but it is debated whether dinosaurs were in decline or not before the impact. We analyse the speciation-extinction dynamics for six key dinosaur families, and find a decline across dinosaurs, where diversification shifted to a declining-diversity pattern ~76 Ma. We investigate the influence of ecological and physical factors, and find that the decline of dinosaurs was likely driven by global climate cooling and herbivorous diversity drop. The latter is likely due to hadrosaurs outcompeting other herbivores. We also estimate that extinction risk is related to species age during the decline, suggesting a lack of evolutionary novelty or adaptation to changing environments. These results support an environmentally driven decline of non-avian dinosaurs well before the asteroid impact.
... The direct evolutionary descendants of non-avian dinosaurs, birds still make up one of the most proliferate and diverse group of vertebrates. However, non-avian dinosaurs themselves suddenly disappeared about 66 Myr ago [1]. ...
... There are astounding number and variety of hypotheses about causes of the dinosaur extinction [1,2]. However, the current research is concentrated around three major ones: 1) an impact of a giant bolid (asteroid or comet) [3,4,5]; 2) Volcanic activity in modern-day India's Deccan Traps [6]; 3) Marine regression (drop in sea level) and the corresponding global environmental deterioration [7,8]. ...
... Nevetheless, modern research [1,9] found support for a bolide impact as the primary factor of the end-Cretaceous mass extinction. Evidence of the bolid impact, coinsiding in time with dinosaur extinction, is ubiquitous, including the huge 150 km wide Chicxulub crater in the Yucatán Peninsula in Mexico, impact related iridium anomaly worldwide, sediments in various areas of the world dominated by impact melt spherules and an unusually large amount of shocked quartz. ...
Preprint
Full-text available
We estimate the expected magnitudes of the Schumann resonance fields immediately after the Chicxulub impact and show that they exceed their present-day values by about $5\times 10^4$ times. Long-term distortion of the Schumann resonance parameters is also expected due to the enviromental impact of the Chicxulub event. If Schumann resonances play a regulatory biological role, as some studies indicate, it is possible that the excitation and distortion of Schumann resonances as a result of the asteroid/comet impact was a possible stress factor, which, among other stress factors associated with the impact, contributed to the demise of dinosaurs.
... The transition from the Mesozoic to the Cenozoic (66 Ma) marks one of the largest terrestrial mass extinction events in Earth's history, shifting vertebrate ecosystems from dinosaur dominated to mammal dominated (Brusatte et al. 2015). As the most recent of the "big five" mass extinctions, the Cretaceous-Paleogene (K/Pg) extinction has been studied intensely, resulting in one of the best-sampled fossil records of these major mass extinctions (Sloan 1976;Russell 1977;Alvarez et al. 1980;Clemens et al. 1981;Krassilov 1981;Benton 1985;Galbreath 1988;Archibald 1992;Clemens 1992;Novacek 1999;Buffetaut 2004;Archibald and MacLeod 2007;Krug et al. 2009;Archibald et al. 2010;Schulte et al. 2010;Larson et al. 2016;Bazzi et al. 2018;Schoene et al. 2019). ...
... Accordingly, it is arguably our best window into the causes and consequences of mass extinctions and provides invaluable insights into our current biodiversity crisis (Novacek and Cleland 2001;Barnosky et al. 2011;Payne et al. 2016). However, substage-level understandings of diversity dynamics, ecological interactions, and abundance patterns of terrestrial vertebrates leading up to the K/Pg transition are limited to a few basins worldwide (Brusatte et al. 2015). Of these, the Hell Creek Formation and equivalent terrestrial beds in the Western Interior Basin of the northwestern United States represent, by far, the best studied and sampled example of a latest Maastrichtian dinosaurdominated ecosystem (Fig. 1, Supplementary Table 1). ...
Article
Full-text available
The end-Cretaceous (K/Pg) mass extinction event is the most recent and well-understood of the “big five” and triggered establishment of modern terrestrial ecosystem structure. Despite the depth of research into this event, our knowledge of upper Maastrichtian terrestrial deposits globally relies primarily on assemblage-level data limited to a few well-sampled formations in North America, the Hell Creek and Lance Formations. These assemblages disproportionally affect our interpretations of this important interval. Multiple investigations have quantified diversity patterns within these assemblages, but the potential effect of formation-level size-dependent taphonomic biases and their implications on extinction dynamics remains unexplored. Here, the relationship between taphonomy and body size of the Hell Creek Formation and Lance Formation dinosaurs and mammals are quantitatively analyzed. Small-bodied dinosaur taxa (<70 kg) are consistently less complete, unlikely to be articulated, and delayed in their description relative to their large-bodied counterparts. Family-level abundance (particularly skeletons) is strongly tied to body mass, and the relative abundance of juveniles of large-bodied taxa similarly is underrepresented. Mammals show similar but nonsignificant trends. The results are remarkably similar to those from the Campanian-aged Dinosaur Park Formation, suggesting a widespread strong taphonomic bias against the preservation of small taxa, which will result in their seemingly depauperate diversity within the assemblage. This taphonomically skewed view of diversity and abundance of small-bodied taxa amid our best late Maastrichtian samples has significant implications for understanding speciation and extinction dynamics (e.g., size-dependent extinction selectivity) across the K/Pg boundary.
... Whatever the cause, the K-Pg extinction eradicated nearly 70% of the living species on Earth [17,18]. Among vertebrates, this event led to the disappearance of several groups, including non-avian dinosaurs, enantiornithine birds, pterosaurs, mosasaurs, plesiosaurs, and several lineages of crocodylomorphs, among others [19][20][21][22][23]. However, the mechanism by which they became extinct and how fast they did so remain difficult questions for researchers, as is the issue of how determinant the Chicxulub impact was on the stability of the ecosystems. ...
... However, the mechanism by which they became extinct and how fast they did so remain difficult questions for researchers, as is the issue of how determinant the Chicxulub impact was on the stability of the ecosystems. Except for the Hell Creek Formation in North America, whose vertebrate faunas are well known [22,24,25] and their chronostratigraphic framework is well constrained [26][27][28][29], the main difficulty in assessing the end-Cretaceous extinction is the lack of well-studied sedimentary formations with vertebrate remains encompassing the K-Pg boundary. In Europe, a great effort has been made in recent decades to characterize the terrestrial uppermost Cretaceous-Paleocene formations, especially in Spain, France, and Romania (e.g., [30][31][32][33]). ...
Article
Full-text available
The South-Pyrenean Basin (northeastern Spain) has yielded a rich and diverse record of Upper Cretaceous (uppermost Campanian−uppermost Maastrichtian) vertebrate fossils, including the remains of some of the last European dinosaurs prior to the Cretaceous-Paleogene (K-Pg) extinction event. In this work, we update and characterize the vertebrate fossil record of the Arén Sandstone and Tremp formations in the Western Tremp Syncline, which is located in the Aragonese area of the Southern Pyrenees. The transitional and continental successions of these sedimentary units are dated to the late Maastrichtian, and exploration of their outcrops has led to the discovery of numerous fossil remains (bones, eggshells, and tracks) of dinosaurs, including hadrosauroids, sauropods, and theropods, along with other tetrapods such as crocodylomorphs, testudines, pterosaurs, squamates, and amphibians. In particular, this fossil record contains some of the youngest lambeosaurine hadrosaurids (Arenysaurus and Blasisaurus) and Mesozoic crocodylomorphs (Arenysuchus and Agaresuchus subjuniperus) in Europe, complementing the lower Maastrichtian fossil sites of the Eastern Tremp Syncline. In addition, faunal comparison with the fossil record of Hațeg island reveals the great change in the dinosaur assemblages resulting from the arrival of lambeosaurine hadrosaurids on the Ibero-Armorican island, whereas those on Haţeg remained stable. In the light of its paleontological richness, its stratigraphic continuity, and its calibration within the last few hundred thousand years of the Cretaceous, the Western Tremp Syncline is one of the best places in Europe to study the latest vertebrate assemblages of the European Archipelago before the end-Cretaceous mass extinction.
... This 'nocturnal bottleneck' hypothesis suggests that mammals were restricted to nocturnal activity by antagonistic interactions with the ecologically dominant diurnal dinosaurs during the Mesozoic 11,13,18 . The Cretaceous-Palaeogene (K-Pg) mass extinction event circa 66 million years ago (Ma) led to the extinction of all non-avian dinosaurs along with the marine and flying reptiles and the majority of other vertebrate, invertebrate and plant taxa 19,20 . This event marks the end of the Mesozoic 'reign of dinosaurs' and the transition to the mammal-dominated Cenozoic fauna. ...
... Even if we accept the appearance of cathemeral mammals as an expansion of the temporal niche before the K-Pg event, it does not necessarily provide strong evidence against the nocturnal bottleneck hypothesis. Declines in dinosaur diversity long before the K-Pg event have been suggested, either globally, starting at least 40 million years before the K-Pg event 35 , or locally-herbivorous dinosaurs in present-day North America were declining for up to 15 million years before the event 20 . In contrast, fossils show that mammals had evolved considerable eco-morphological diversity as early as the mid-Jurassic period (174-164 Ma) and diversified along all axes of the ecological niche 36,37 except the temporal axis. ...
Preprint
Full-text available
Most modern mammals, including strictly diurnal species, exhibit sensory adaptations to nocturnal activity, thought to be the result of a prolonged nocturnal phase or ‘bottleneck’ during early mammalian evolution. Nocturnality may have allowed mammals to avoid antagonistic interactions with diurnal dinosaurs during the Mesozoic. However, understanding the evolution of mammalian activity patterns is hindered by scant and ambiguous fossil evidence. While ancestral reconstructions of behavioural traits from extant species have the potential to elucidate these patterns, existing studies have been limited in taxonomic scope. Here, we use an extensive behavioural dataset for 2415 species from all extant orders to reconstruct ancestral activity patterns across Mammalia. We find strong support for the nocturnal origin of mammals and the Cenozoic appearance of diurnality, although cathemerality (mixed diel periodicity) may have appeared in the late Cretaceous. Simian primates are among the earliest mammals to exhibit strict diurnal activity, some 52-33Mya. Our study is consistent with the hypothesis that temporal partitioning between early mammals and dinosaurs during the Mesozoic led to a mammalian nocturnal bottleneck, but also demonstrates the need for improved phylogenetic estimates for Mammalia.
... 6), these two eras are separated by the most recent of the big five mass extinctions in Earth's history. The Cretaceous-Paleogene (K/Pg) mass extinction was the result of a combination of factors including an extended period of strong volcanism in the Indian subcontinent and an asteroid impact in Central America (Brusatte et al. 2015a;Sprain et al. 2019). Among terrestrial animals, the K/Pg event had its worst effect on large-sized species, many of them vertebrates. ...
... Among terrestrial animals, the K/Pg event had its worst effect on large-sized species, many of them vertebrates. This is probably because large animals could not effectively hide from radiation and forest fires (Field et al. 2018), and because they relied on the primary productivity of plants in terrestrial ecosystems (Sheehan and Hansen 1986;Brusatte et al. 2015a). It is thought that a general darkening of the atmosphere, caused by ejecta * from the volcanism and the bolide impact, affected photosynthesis and, thus, production of plant biomass would have been slowed down or even halted for some period of time (Sheehan and Hansen 1986). ...
Chapter
If we imagine walking through Mesozoic lands, we would be able to observe vertebrates with peculiar combinations of morphological traits, some of which would seem to be intermediary to animals seen today. We would witness a terrestrial vertebrate fauna dominated by dinosaurs of various sizes and diversity, accompanied by many other animal groups that often are overlooked. Current research suggests that many of the main vertebrate clades existing today originated or diversified sometime in the Triassic or Early to Middle Jurassic. Herein, we profile some of the major transformations in both terrestrial and aquatic vertebrate evolution during the Mesozoic. We highlight: the appearance of features that allowed sauropod dinosaurs to become the largest animals to ever walk on Earth’s continents, the appearance of herbivory among the usually carnivorous theropod dinosaurs, and we follow the specific changes that led to the evolution of avian flight. Our Mesozoic tour across the globe will allow us to see how different evolutionary forces led to convergent shifts to quadrupedality in ornithischian dinosaurs and to an aquatic lifestyle in turtles, crocodiles, and plesiosaurs. Last, but not least, we examine changes in the Mesozoic fauna linked to the rise of mammals, and the diversification patterns in several clades of fishes after the End-Permian Mass Extinction.
... This implies a very rapid recovery of marine productivity (45,46), which argues against the suggested delay in ecosystem reset caused by continued Deccan volcanism after the K/Pg boundary (9,45,46). In contrast to the end-Permian mass extinction, the K/Pg event was geologically instantaneous (2-4, 10, 23, 35), and there is no clear evidence for a prolonged decline (3,4,35,47) that would be required for Deccan volcanism to trigger a mass extinction-level event due to the short residence time of stratospheric aerosols. In addition, studies on marine macrofossils from Antarctica are consistent with a sudden, catastrophic driver for the extinction, such as the bolide impact, rather than a significant contribution from Deccan Traps volcanism during the latest Cretaceous (48). ...
... In addition, studies on marine macrofossils from Antarctica are consistent with a sudden, catastrophic driver for the extinction, such as the bolide impact, rather than a significant contribution from Deccan Traps volcanism during the latest Cretaceous (48). Although some authors have argued for a latest Cretaceous decline in dinosaur diversity, other analytical studies are consistent with relatively high preextinction standing diversity, which is compatible with a sudden extinction scenario for non-avian dinosaurs (47). The extinction of only shallowwater marine organisms (12,45,(48)(49)(50) highlights a lack of prolonged deep-water acidification, while conjoined isotopic and Earth System Modeling results show rapid oceanic acidification (49) and subsequent quick recovery (49), compatible with asteroid-induced effects in the ocean. ...
Article
Full-text available
The Cretaceous/Paleogene mass extinction, 66 Ma, included the demise of non-avian dinosaurs. Intense debate has focused on the relative roles of Deccan volcanism and the Chicxulub asteroid impact as kill mechanisms for this event. Here, we combine fossil-occurrence data with paleoclimate and habitat suitability models to evaluate dinosaur habitability in the wake of various asteroid impact and Deccan volcanism scenarios. Asteroid impact models generate a prolonged cold winter that suppresses potential global dinosaur habitats. Conversely, long-term forcing from Deccan volcanism (carbon dioxide [CO 2 ]-induced warming) leads to increased habitat suitability. Short-term (aerosol cooling) volcanism still allows equatorial habitability. These results support the asteroid impact as the main driver of the non-avian dinosaur extinction. By contrast, induced warming from volcanism mitigated the most extreme effects of asteroid impact, potentially reducing the extinction severity.
... The classic example of this, is the demise of non-avian dinosaurs at the end-Cretaceous (K-Pg) mass extinction event. These taxa had dominated terrestrial environments for over 150 Myrs prior to their extinction and demonstrated little sign of ecological or evolutionary decline prior to the K-Pg bolide impact [50] (but see [66] for an alternative viewpoint). And yet, following the K-Pg mass extinction, only small avian dinosaur clades remained to repopulate terrestrial ecosystems, and thus today, the once majestic dinosaur clade is represented by chickens, doves, and emus. ...
... And yet, following the K-Pg mass extinction, only small avian dinosaur clades remained to repopulate terrestrial ecosystems, and thus today, the once majestic dinosaur clade is represented by chickens, doves, and emus. Beyond this evolutionary change, ecological turnover associated with the K-Pg event led to the famous replacement of dinosaurs by mammals as the dominant large-bodied terrestrial clade on Earth today [9,50,86,87,134,160]. ...
Article
Extinction of species, and even clades, is a normal part of the macroevolutionary process. However, several times in Earth history the rate of species and clade extinctions increased dramatically compared to the observed “background” extinction rate. Such episodes are global, short-lived, and associated with substantial environmental changes, especially to the carbon cycle. Consequently, these events are dubbed “mass extinctions” (MEs). Investigations surrounding the circumstances causing and/or contributing to mass extinctions are on-going, but consensus has not yet been reached, particularly as to common ME triggers or periodicities. In part this reflects the incomplete nature of the fossil and geologic record, which – although providing significant information about the taxa and paleoenvironmental context of MEs – is spatiotemporally discontinuous and preserved at relatively low resolution. Mathematical models provide an important opportunity to potentially compensate for missing linkages in data availability and resolution. Mathematical models may provide a means to connect ecosystem scale processes (i.e., the extinction of individual organisms) to global scale processes (i.e., extinction of whole species and clades). Such a view would substantially improve our understanding not only of how MEs precipitate, but also how biological and paleobiological sciences may inform each other. Here we provide suggestions for how to integrate mathematical models into ME research, starting with a change of focus from ME triggers to organismal kill mechanisms since these are much more standard across time and spatial scales. We conclude that the advantage of integrating mathematical models with standard geological, geochemical, and ecological methods is great and researchers should work towards better utilization of these methods in ME investigations.
... Morphological studies on the skeleton and the plumage have forged a solid link between non-avialan coelurosaurians and birds building a well-accepted framework to understand the dinosaur-bird transition. [2][3][4] Recent works started to look beneath the surface and into the ultrastructure and chemistry in fossil feathers and bones and bring our understanding of this major transition to another new level. 1,[5][6][7][8][9][10][11][12] Chemistry of exquisitely preserved fossil animals including several iconic flying/gliding capable theropods www.at-spectrosc.com/as/article/pdf/202101001 ...
... At. Spectrosc. 2021, 42(1), [1][2][3][4][5][6][7][8][9][10][11] have been investigated to reveal information of their paleobiology and the fossilization process. 1,6,9,10,[12][13][14] Various chemical imaging techniques, e.g., Fourier-transform infrared (FTIR) spectroscopy, Raman spectroscopy, X-ray spectroscopy, and secondary-ion mass spectroscopy (SIMS), have been employed to track the molecular, elemental and isotopic information. ...
... But the knowledge gap on feather morphology of the most recent common ancestor of crown birds has significantly impeded our understanding on the rachidial complexity in extant birds. Although a variety of rachidial configurations have been documented in Mesozoic theropods, the global catastrophe that occurred at the end of the Cretaceous (∼66 million years ago) wiped out all nonavian and most avian theropods (Brusatte et al. 2015a). Some feather morphotypes present in the Cretaceous archaic birds and nonavian theropods hence have also gone extinct. ...
Article
Full-text available
The rachises of extant feathers, composed of dense cortex and spongy internal medulla, are flexible and light, yet stiff enough to withstand the load required for flight, among other functions. Incomplete knowledge of early feathers prevents a full understanding of how cylindrical rachises have evolved. Bizarre feathers with unusually wide and flattened rachises, known as “rachis‐dominated feathers” (RDFs) have been observed in fossil non‐avian and avian theropods. Newly discovered RDFs embedded in early Late Cretaceous Burmese ambers (∼99 Ma) suggest the unusually wide and flattened rachises mainly consist of a dorsal cortex, lacking a medulla and a ventral cortex. Coupled with findings on extant feather morphogenesis, known fossil RDFs were categorized into three morphotypes based on their rachidial configurations. For each morphotype, potential developmental scenarios were depicted by referring to the rachidial development in chickens, and relative stiffness of each morphotype was estimated through functional simulations. The results suggest rachises of RDFs are developmentally equivalent to a variety of immature stages of cylindrical rachises. Similar rachidial morphotypes documented in extant penguins suggest that the RDFs are not unique to Mesozoic theropods, though they are likely to have evolved independently in extant penguins. This article is protected by copyright. All rights reserved
... Indian paleontological records reveal that many terrestrial organisms survived the eruptions 50 . Consequently, the meteorite impact at the end of the Late Cretaceous, which created the Chicxulub Crater off the Caribbean coast of Mexico, is favored as the primary cause for mass extinctions across the globe, and many studies argue that the effects of Deccan volcanism were only accessory to the environmental changes caused by the meteorite impact 45,53 . Some paleontological and geological data suggest the effects of Deccan volcanism were not insignificant, however, leading several researchers to argue that the Deccan eruptions were the primary cause of the global KT mass extinction 49,51,54,55 . ...
Article
Full-text available
The ‘Out of India’ hypothesis is often invoked to explain patterns of distribution among Southeast Asian taxa. According to this hypothesis, Southeast Asian taxa originated in Gondwana, diverged from their Gondwanan relatives when the Indian subcontinent rifted from Gondwana in the Late Jurassic, and colonized Southeast Asia when it collided with Eurasia in the early Cenozoic. A growing body of evidence suggests these events were far more complex than previously understood, however. The first quantitative reconstruction of the biogeography of Asian forest scorpions (Scorpionidae Latreille, 1802: Heterometrinae Simon, 1879) is presented here. Divergence time estimation, ancestral range estimation, and diversification analyses are used to determine the origins, dispersal and diversification patterns of these scorpions, providing a timeline for their biogeographical history that can be summarized into four major events. (1) Heterometrinae diverged from other Scorpionidae on the African continent after the Indian subcontinent became separated in the Cretaceous. (2) Environmental stresses during the Cretaceous–Tertiary (KT) mass extinction caused range contraction, restricting one clade of Heterometrinae to refugia in southern India (the Western Ghats) and Sri Lanka (the Central Highlands). (3) Heterometrinae dispersed to Southeast Asia three times during India’s collision with Eurasia, the first dispersal event occurring as the Indian subcontinent brushed up against the western side of Sumatra, and the other two events occurring as India moved closer to Eurasia. (4) Indian Heterometrinae, confined to southern India and Sri Lanka during the KT mass extinction, recolonized the Deccan Plateau and northern India, diversifying into new, more arid habitats after environmental conditions stabilized. These hypotheses, which are congruent with the geological literature and biogeographical analyses of other taxa from South and Southeast Asia, contribute to an improved understanding of the dispersal and diversification patterns of taxa in this biodiverse and geologically complex region.
... Dinosaurs -understood as non-avian dinosaurs (i.e. all dinosaurs excluding birds, the only group which survived the end-Cretaceous mass extinction event) (Brusatte et al., 2015a) are also an important part of palaeontological tourism. ...
Article
Full-text available
Fossils of dinosaurs and other tetrapods have long aroused interest of scientists and the public opinion alike. Every finding of a new (especially large) species receives coverage in national and international media, and thus, local fossil discoveries might constitute a good basis for local tourism development. The paper aims to examine whether fos-siliferous sites on their own may be enough for the development of palaeontological tourism to occur, or do they require the support of additional amusement infrastructure. For this purpose, the interest in chosen localities was analysed using Google and Wikipedia searches, and was further discussed against a survey on dinoparks and their elements. The above-mentioned data reveal that local tourism can be indeed predicated on local paleontological findings, however, it is deemed considerably more efficient if such attractions are backed with an extensive infrastructure of amusement theme parks.
... Morphological studies on the skeleton and the plumage have forged a solid link between non-avialan coelurosaurians and birds, building a well-accepted framework for understanding the dinosaur-bird transition. [2][3][4] Recent works started to look beneath the surface and into the ultrastructure and chemistry of fossil feathers and bones, and bring our understanding of this major transition to a new level. 1,[5][6][7][8][9][10][11][12] The chemistry of exquisitely preserved fossil animals, including several iconic flying/gliding theropods, have been investigated to reveal information on their paleobiology and the fossilization process. ...
Article
Full-text available
Jianianhualong tengi is a key taxon for understanding the evolution of pennaceous feathers as well as of troodontid theropods. It is known by only the holotype, which was recovered from the Lower Cretaceous Yixian Formation of western Liaoning, China. In this study, we carried out a large-area micro-X-Ray fluorescence (micro-XRF) analysis of the holotype of Jianianhualong tengi via a Brucker M6 Jetstream mobile XRF scanner. The elemental distribution measurements of the specimen show an enrichment of typical bone-associated elements, such as S, P and Ca, which allows to visualize the fossil structure. Additionally, the bones are enriched with several heavier elements, such as Sr, Th, Y and Ce relative to the surrounding rocks. The enrichment is most likely associated to secondary mineralization and the phosphates from the bones. Interestingly, the plumage shape correlates with an enrichment in elements, such as Cu, Ni and Ti, consistent with the findings of a previous study 1 on Archaeopteryx using synchrotron imaging. Elemental variations among the skeleton, the unguis and the sheath blade further indicate their possible compositional or ultrastructural differences, providing new biological and taphonomic information on the fossilized keratinous structures. An in-situ and nondestructive micro-XRF analysis is currently the most ideal way to map the chemistry of meter-sized fossils and has so far been mainly restricted to small samples. Micro-spatial chemical analysis of larger samples usually required a synchrotron facility. Our study demonstrated that a laboratory-based large-area micro-XRF scanner can provide a practical tool for the study of large specimens, thus allowing to collect full chemical data in order to obtain a better understanding of evolutionary and taphonomic processes.
... Dinosaur lineages show significant variability of their evolutionary rates; for example, the theropod lineage leading to birds shows particularly elevated rates [23,24]. However, studies examining rates of dinosaur extinction focus predominantly at higher taxonomic levels, in particular why all non-avian dinosaurs were lost at the Cretaceous/Paleogene mass extinction [25][26][27]. At the species level, analyses focus predominantly on the diversification of lineages, leaving open the question whether there is a robust relationship between individual species' extinction rates and their morphological evolution. ...
Article
Determining the factors that shape temporal variation in species diversity is an ongoing challenge. One theory is that species exhibiting lower rates of phenotypic evolution should be more likely to go extinct as they are more susceptible to changing environmental conditions. However, little work has been done to assess whether this process shapes comparatively few lineages, or is a common mechanism shaping changes in species diversity. Here, I analyse the correlation between rates of morphological evolution and extinction at the species level using six published morphological matrices of non-avian dinosaurs. I find no correlation between the two rates at different taxonomic scales, suggesting that extinction in these groups is better described by other factors. As there is a strong prior expectation of correlated rates, I suggest that traditional morphological matrices are inappropriate for addressing this question and that the characters governing lineage persistence are independent of those with high phylogenetic signal. This may be comprehensively determined with continued development of phenomic matrices.
... The characteristic European 'island fauna' consisted of titanosaurian sauropods, rhabdodontid iguanodontians, nodosaurid ankylosaurians, basal hadrosauroids, lambeosaurine hadrosauroids, and some abelisauroid and maniraptoran theropods 8,9 . As more fossils of these animals are discovered, they are becoming increasingly important for understanding how dinosaurs and other vertebrates changed before the end-Cretaceous asteroid impact, and for testing hypotheses of rapid 10 vs. gradual extinction 8,11 . ...
Article
Full-text available
A characteristic fauna of dinosaurs and other vertebrates inhabited the end-Cretaceous European archipelago, some of which were dwarves or had other unusual features likely related to their insular habitats. Little is known, however, about the contemporary theropod dinosaurs, as they are represented mostly by teeth or other fragmentary fossils. A new isolated theropod metatarsal II, from the latest Maastrichtian of Spain (within 200,000 years of the mass extinction) may represent a jinfengopterygine troodontid, the first reported from Europe. Comparisons with other theropods and phylogenetic analyses reveal an autapomorphic foramen that distinguishes it from all other troodontids, supporting its identification as a new genus and species, Tamarro insperatus. Bone histology shows that it was an actively growing subadult when it died but may have had a growth pattern in which it grew rapidly in early ontogeny and attained a subadult size quickly. We hypothesize that it could have migrated from Asia to reach the Ibero-Armorican island no later than Cenomanian or during the Maastrichtian dispersal events.
... The reason for this extinction event has been a subject of debate for a very long time (Brusatte et al. 2015). The most widely accepted theory is the catastrophic impact from an asteroid (10 km diameter), which created the Chicxulub crater in Yucatan, Mexico. ...
Chapter
Full-text available
The most recent era of the earth’s history, which began 65.5 million years ago (mya), is known as the “Cenozoic Era.” This is that time frame in which the geological changes gave rise to the world map’s current face, and the biological changes enriched it with today’s flora and fauna. Despite representing only 1.4% of the earth’s history, comprehensive knowledge is available pertaining to this era.
... The second major event of the Cretaceous period is the Cretaceous-Paleogene (K/Pg) extinction, which corresponds to a series of drastic events leading to the most famous mass extinction with the final demise of non-avian dinosaurs (e.g., Brusatte et al. 2015). The origin of this mass extinction event is far from being consensual, but a combination of biotic and abiotic factors likely led to these dramatic events (e.g., Mitchell et al. 2012, Chiarenza et al. 2020, Condamine et al. 2021. ...
Article
Deciphering the timing of lineage diversification and extinction has greatly benefited in the last decade from methodological developments in fossil-based analyses. If these advances are increasingly used to study the past dynamics of vertebrates, other taxa such as insects remain relatively neglected. Our understanding of how insect clades waxed and waned or of the impact of major paleoenvironmental changes during their periods of diversification and extinction (mass extinction) are rarely investigated. Here, we compile and analyze the fossil record of Plecoptera (1,742 vetted occurrences) to investigate their genus-level diversification and diversity dynamics using a Bayesian process-based model that incorporates temporal preservation biases. We found that the Permian-Triassic mass extinction has drastically impacted Plecoptera, while the Cretaceous Terrestrial Revolution corresponds with a turnover of plecopteran fauna. We also unveiled three major gaps in the plecopteran fossil record: the Carboniferous-Permian transition, the late Early Cretaceous, and the late Cenomanian to Bartonian, which will need to be further investigated. Based on the life history of extant Plecoptera, we investigate the correlations between their past dynamic and a series of biotic (Red Queen hypothesis) and abiotic (Court Jester hypothesis) factors. These analyses highlight the major role of continental fragmentation in the evolutionary history of stoneflies, which is in line with phylogeny-based biogeographic analyses showing how vicariance drove their diversification. Our study advocates analyzing the fossil record with caution, while attempting to unveil the diversification and extinction periods plus the likely triggers of these past dynamics of diversification.
... The end Cretaceous (i.e., K-Pg) mass extinction event was a turning point for both terrestrial and marine ecosystems [10][11][12][13]. In marine ecosystems, top predators, such as ammonites, large predatory sh, and mosasaurs, went extinct, as did top predators in terrestrial ecosystems as well. ...
Preprint
Full-text available
Vertebrates evolved tooth replacement over 400 million years ago. Over 200 million years later, the combination of vertical tooth replacement with thecodont implantation (teeth in bone sockets) has been considered a key morphological innovation in mammal evolution. We discovered that an extinct fish taxon, Serrasalmimus secans, that shows this same innovation in a lineage (Serrasalmimidae) that survived the end Cretaceous mass extinction. Carnassial teeth are known in both mammals and pycnodont fish, but these teeth do not share the same tissues nor developmental processes. Therefore, a serrasalmimid pycnodont fish independently acquired mammal-like tooth replacement and implantation, thus showing that fishes and mammals evolved convergent carnassial dental morphologies at about the same time, around 60 Ma, in separate ecosystems.
... The early insectivorous diet was substituted, by scavenging as well as by predator and carnivorous lifestyles [82,[138][139][140][141][142][143][144]. Possibly, however, these early diversification events were dead-end evolutionary experiments, far from the mainstream of diversification that took place in the Cenozoic [145] because of the K-Pg extinction event [146][147][148][149][150][151][152][153]. Such extinction left free the diurnal niche and allowed Cenozoic mammals to develop a wide variation in chronotypes, alimentary modes and body sizes. ...
Article
Full-text available
Mammals evolved from small-sized reptiles that developed endothermic metabolism. This allowed filling the nocturnal niche. They traded-off visual acuity for sensitivity but became defenseless against the dangerous daylight. To avoid such danger, they rested with closed eyes in lightproof burrows during light-time. This was the birth of the mammalian sleep, the main finding of this report. Improved audition and olfaction counterweighed the visual impairments and facilitated the cortical development. This process is called “The Nocturnal Evolutionary Bottleneck”. Premammals were nocturnal until the Cretacic-Paleogene extinction of dinosaurs. Some early mammals returned to diurnal activity, and this allowed the high variability in sleeping patterns observed today. The traits of Waking Idleness are almost identical to those of behavioral sleep, including homeostatic regulation. This is another important finding of this report. In summary, behavioral sleep seems to be an upgrade ofWaking Idleness Indeed, the trait that never fails to show is quiescence. We conclude that the main function of sleep consists in guaranteeing it during a part of the daily cycle.
... Similarly, a substantial extinction of squamate reptiles in North America (Longrich et al., 2012) occurred, although it is possible that similar phylogenetic diversity studies of other squamate clades might reduce the apparent level of extinction. Regardless, the coincidence of these two events-bolide impact and mass extinction-together with plausible kill mechanisms has convinced many that the former caused the latter (Brusatte et al., 2015). Other causes or contributors to the extinction are still being evaluated (Archibald et al., 2010). ...
... This lack of data has confounded identification of unique crown traits demanded by hypotheses explaining K-Pg survivorship. Furthermore, body size and other traits proposed to have influenced dinosaur survivorship are known to scale allometrically (e.g., brain size, flight, growth rate, habitat preference, and metabolism) (4,(9)(10)(11)(12)(13)(14)(15). However, investigations of body mass evolution in Aves have rarely included data from the stem, allowing distantly related non-avialan theropods and basally diverging ratites, both large-bodied, to disproportionately influence ancestral avian body mass estimates. ...
Article
Full-text available
Birds today are the most diverse clade of terrestrial vertebrates, and understanding why extant birds (Aves) alone among dinosaurs survived the Cretaceous-Paleogene mass extinction is crucial to reconstructing the history of life. Hypotheses proposed to explain this pattern demand identification of traits unique to Aves. However, this identification is complicated by a lack of data from non-avian birds. Here, we interrogate survivorship hypotheses using data from a new, nearly complete skull of Late Cretaceous (~70 million years) bird Ichthyornis and reassess shifts in bird body size across the Cretaceous-Paleogene boundary. Ichthyornis exhibited a wulst and segmented palate, previously proposed to have arisen within extant birds. The origin of Aves is marked by larger, reshaped brains indicating selection for relatively large telencephala and eyes but not by uniquely small body size. Sensory system differences, potentially linked to these shifts, may help explain avian survivorship relative to other dinosaurs.
... [5][6][7][8][9][10] Recent evidence indicates that dinosaurs evolved distinctive patterns of growth, reproduction, food assimilation, and lung ventilation, 6,[11][12][13][14][15][16] in some cases without clear modern analogs. These traits are directly related to the underlying biology of dinosaurs, [17][18][19][20] including their thermophysiology, 9,11,12,21 and might therefore be key to understanding their body-size evolution; the selective extinction of non-avian dinosaurs at the Cretaceous/ Paleogene boundary, 66 mya; 22,23 as well as enigmatic aspects of Mesozoic dinosaur communities (e.g., trophic structure and migratory habits). [24][25][26] Given these important biological distinctions, it is likely that climate, among all the biotic and abiotic factors 9 impacting geologically long-term aspects of dinosaur macroecology and evolution, was a major constraint on the group's geographic distribution and diversification. ...
Article
Full-text available
Dinosaurs dominated Mesozoic terrestrial ecosystems globally. However, whereas a pole-to-pole geographic distribution characterized ornithischians and theropods, sauropods were restricted to lower latitudes. Here, we evaluate the role of climate in shaping these biogeographic patterns through the Jurassic–Cretaceous (201–66 mya), combining dinosaur fossil occurrences, past climate data from Earth System models, and habitat suitability modeling. Results show that, uniquely among dinosaurs, sauropods occupied climatic niches characterized by high temperatures and strongly bounded by minimum cold temperatures. This constrained the distribution and dispersal pathways of sauropods to tropical areas, excluding them from latitudinal extremes, especially in the Northern Hemisphere. The greater availability of suitable habitat in the southern continents, particularly in the Late Cretaceous, might be key to explaining the high diversity of sauropods there, relative to northern landmasses. Given that ornithischians and theropods show a flattened or bimodal latitudinal biodiversity gradient, with peaks at higher latitudes, the closer correspondence of sauropods to a subtropical concentration could hint at fundamental thermophysiological differences to the other two clades.
... Bonsor et al. draw from the literature to demonstrate that species richness, morphological diversity (commonly referred to as disparity) [18] as well as diversity in ecological niches [19] all indicate that dinosaurs maintained high diversity to the end of the Cretaceous period. While we do not dispute such observations, we simply highlight that, even if standing diversity appears to be maintained at a constant level, that does not mean that the net-speciation rate is zero. ...
Article
Full-text available
Through phylogenetic modelling, we previously presented strong support for diversification decline in the three major subclades of dinosaurs (Sakamoto et al . 2016 Proc. Natl Acad. Sci. USA 113 , 5036–5040. ( doi:10.1073/pnas.1521478113 )). Recently, our support for this model has been criticized (Bonsor et al . 2020 R. Soc. Open Sci. 7 , 201195. ( doi:10.1098/rsos.201195 )). Here, we highlight that these criticisms seem to largely stem from a misunderstanding of our study: contrary to Bonsor et al .'s claims, our model accounts for heterogeneity in diversification dynamics, was selected based on deviance information criterion (DIC) scores (not parameter significance), and intercepts were estimated to account for uncertainties in the root age of the phylogenetic tree. We also demonstrate that their new analyses are not comparable to our models: they fit simple, Dinosauria-wide models as a direct comparison to our group-wise models, and their additional trees are subclades that are limited in taxonomic coverage and temporal span, i.e. severely affected by incomplete sampling. We further present results of new analyses on larger, better-sampled trees ( N = 961) of dinosaurs, showing support for the time-quadratic model. Disagreements in how we interpret modelled diversification dynamics are to be expected, but criticisms should be based on sound logic and understanding of the model under discussion.
... Part of the confusion has arisen perhaps because analysts switch between global-scale and regional-scale studies. In fact, the sampled fossil record of dinosaurs in North America through the Campanian and Maastrichtian provides a large part of the global signal, with some matching data from European sites, considerable data from Argentina and Mongolia, but with very uncertain dating, and virtually nothing from Africa, Australia and the rest of Asia [18, 20,21]. Counts of dinosaur-bearing geological formations worldwide showed that numbers reached a peak in the Maastrichtian, implying excellent opportunities to sample [16,22]. ...
Preprint
Full-text available
Signatures of catastrophic mass extinctions have long been reported to be obscured by the edge effect where taxonomic diversity appears to decline gradually. Similarly, models of diversification based on splitting of branches on a phylogenetic tree might also be affected by undersampling of divergences towards the edge. The implication is that long-term declines in diversification recovered from such models – e.g., in dinosaurs – may be artefacts of unsampled divergences. However, this effect has never been explicitly tested in a phylogenetic model framework – i.e., whether phylogenetic nodes (speciation events) close to the edge are under-sampled and if diversification declines are artefacts of such under-sampling. Here, we test whether dinosaur species in temporal proximity to the Cretaceous-Paleogene mass extinction event are associated with fewer nodes than expected, and whether this under-sampling can account for the diversification decline. We find on the contrary that edge taxa have higher numbers of nodes than expected and that accounting for this offset does not affect the diversification decline. We demonstrate that the observed diversification declines in the three major dinosaurian clades in the Late Cretaceous are not artefacts of the edge effect.
Chapter
We discuss some prominent major natural risks to life including the epidemics and pandemics caused by micro-organisms such as bacteria or viruses, with detail on the ongoing covid-19 pandemic. We also consider localised severe climatic or geological events and extra-terrestrial risks from hits by asteroids. We discuss current knowledge of the likely causes of historic mass extinctions, such as the Cretaceous-Paleogene extinction which abolished the majority of the dinosaurs.
Article
Full-text available
Vertebrates developed tooth replacement over 400 million years ago. Then, 200 million years later, the combination of vertical tooth replacement with the thecodont implantation (teeth in bone sockets) appeared a key morphological innovation in mammalian evolution. However, we discovered that an extinct fish taxon, Serrasalmimus secans, showed the same innovation in the line-age Serrasalmimidae, which survived the end Cretaceous mass extinction event. The carnassial teeth are known in both mammals and pycnodont fish, but these teeth do not share the same tissues or developmental processes. Therefore, this serrasalmimid pycnodont fish might have independently acquired mammal-like tooth replacement and implantation, indicating that the fish and mammals convergently evolved the carnassial dental morphologies at about the same time, approximately 60 My ago, in separate ecosystems.
Chapter
We continue our trip back in time through the Mesozoic, visiting several different ecosystems across the planet. Each of these was strongly influenced by the continental breakup from a single landmass into several tectonic plates and associated landmasses during this period. We will visit localities on several continents, observe how their vertebrate faunasVertebrate faunas changed over time, and what external factors might have contributed to these differences. During the Cretaceous, we visit the Iberian Peninsula, where hadrosauroids replaced titanosaurs as the most abundant dinosaur taxon. On the other side of the planet, a succession of geologic formations in Australia shows a gradual change from aquatic to terrestrial faunas resulting from sea-level changes of a now non-existent inland ocean. A visit to two polar ecosystems indicates possible mutual exclusion between amphibians (temnospondyls) and reptiles (crocodylomorphs), because they occupied similar ecological niches. Observing the record of Cretaceous landscapes in what is now Mongolia shows how changes in environment and climate correlate with changes in faunal composition. Heading back, we check if there are distinct differences in vertebrate diversity in space and time in the Late Jurassic of North America. Then we move south, to Argentina, and back to the Middle and Early Jurassic. Here, we will try to understand where these Late Jurassic faunas originated and what influence the fragmentation of the supercontinent Pangea had on their evolution and diversity. Finally, we will stop our trip in the Late Triassic of Central Europe, examining a typical vertebrate fauna from the time when dinosaurs began their domination of the planet.
Chapter
Since 2015, “artificial intelligence” has become a popular topic in science, technology, and industry. New products such as intelligent refrigerators, intelligent air conditioning, smart watches, smart robots, and of course, artificially intelligent mind emulators produced by companies such as Google and Baidu continue to emerge. However, the view that artificial intelligence is a threat remains persistent. An operation is that if we compare the developmental levels of artificial intelligence products and systems with measured human intelligence quotients (IQs), can we develop a quantitative analysis method to assess the problem of artificial intelligence threat?
Article
Full-text available
Late Cretaceous trends in Asian dinosaur diversity are poorly understood, but recent discoveries have documented a radiation of oviraptorosaur theropods in China and Mongolia. However, little work has addressed the factors that facilitated this diversification. A new oviraptorid from the Late Cretaceous of Mongolia sheds light on the evolution of the forelimb, which appears to have played a role in the radiation of oviraptorosaurs. Surprisingly, the reduced arm has only two functional digits, highlighting a previously unrecognized occurrence of digit loss in theropods. Phylogenetic analysis shows that the onset of this reduction coincides with the radiation of heyuannine oviraptorids, following dispersal from southern China into the Gobi region. This suggests expansion into a new niche in the Gobi region, which relied less on the elongate, grasping forelimbs inherited by oviraptorosaurs. Variation in forelimb length and manus morphology provides another example of niche partitioning in oviraptorosaurs, which may have made possible their incredible diversity in the latest Cretaceous of Asia.
Preprint
Jianianhualong tengi is a key taxon for understanding the evolution of pennaceous feathers as well as troodontid theropods, and it is known by only the holotype, which was recovered from the Lower Cretaceous Yixian Formation of western Liaoning, China. Here, we carried out a large-area micro-X-Ray fluorescence (micro-XRF) analysis on the holotypic specimen of Jianianhualong tengi via a Brucker M6 Jetstream mobile XRF scanner. The elemental distribution measurements of the specimen show an enrichment of typical bones couponing elements such as S, P and Ca allowing to visualize the fossil structure. Additionally, to this, the bones are enriched in several heavier elements such as Sr, Th, Y and Ce over the surrounding rocks. The enrichment is most likely associated to secondary mineralization and the phosphates from the bones. Interestingly the plumage shape correlates with an enrichment in elements such as Cu, Ni and Ti, consistent with a previous study [1] on Archaeopteryx using synchrotron imaging. The analysis presented here provide new biological and taphonomic information of this fossil. An in-situ and nondestructive micro-XRF analysis is currently the most ideal way to map the chemistry of fossils, so far this is manly restricted to small samples. Larger samples usually required a synchrotron facility for analysis. Our study demonstrated that laboratory-based large-area micro-XRF scanner can provides a practical tool for the study of large large-sized specimens allowing collect full chemical data for a better understanding of evolutionary and taphonomic processes.
Article
Full-text available
Ornithischians form a large clade of globally distributed Mesozoic dinosaurs, and represent one of their three major radiations. Throughout their evolutionary history, exceeding 134 million years, ornithischians evolved considerable morphological disparity, expressed especially through the cranial and osteodermal features of their most distinguishable representatives. The nearly two-century-long research history on ornithischians has resulted in the recognition of numerous diverse lineages, many of which have been named. Following the formative publications establishing the theoretical foundation of phylogenetic nomenclature throughout the 1980s and 1990s, many of the proposed names of ornithischian clades were provided with phylogenetic definitions. Some of these definitions have proven useful and have not been changed, beyond the way they were formulated, since their introduction. Some names, however, have multiple definitions, making their application ambiguous. Recent implementation of the International Code of Phylogenetic Nomenclature (ICPN, or PhyloCode) offers the opportunity to explore the utility of previously proposed definitions of established taxon names. Since the Articles of the ICPN are not to be applied retroactively, all phylogenetic definitions published prior to its implementation remain informal (and ineffective) in the light of the Code. Here, we revise the nomenclature of ornithischian dinosaur clades; we revisit 76 preexisting ornithischian clade names, review their recent and historical use, and formally establish their phylogenetic definitions. Additionally, we introduce five new clade names: two for robustly supported clades of later-diverging hadrosaurids and ceratopsians, one uniting heterodontosaurids and genasaurs, and two for clades of nodosaurids. Our study marks a key step towards a formal phylogenetic nomenclature of ornithischian dinosaurs.
Article
With advances in data acquisition and processing methods, spectral inversion of time domain induced polarization (IP) data is becoming more common. Geological interpretation of inverted spectral parameters, for instance Cole-Cole parameters, often relies on results from systematic laboratory measurements. These are most often carried out with frequency domain systems on sandstone samples. However, the two different methods of measuring the spectral IP response differ in both measurement technique and scale. One of the main objectives of the current study is, thus, to perform a direct comparison of inverted spectral parameters from time domain IP field data with frequency domain IP spectra from laboratory measurements. To achieve this, field measurements were carried out before a ∼50 m long rock core was drilled down along one of the measurement lines. Solid parts of the core were vacuum-sealed in plastic bags to preserve the natural groundwater in the samples, after which the core samples were measured with frequency domain spectral IP in laboratory. The results showed that the inverted Cole-Cole parameters closest to the borehole were comparable to the IP spectra measured at the core samples, despite differences in measurement techniques and scale. The field site chosen for the investigation was a limestone succession spanning over a well-known lithological boundary (the Cretaceous—Paleogene boundary). Little is known in previous research about varying spectral IP responses in limestones, and an additional objective of this study was, therefore, to investigate possible sources of these variations in the laboratory. The IP spectra were interpreted in light of measured lithological and physicochemical properties. The carbonate texture differed strongly across the Cretaceous—Paleogene boundary from fine-grained calcareous mudstone (Cretaceous) to more well-lithified and coarse-grained wackestone and packstone (Paleogene). Both laboratory and field spectral IP results showed that these differences cause a large shift in measured bulk conductivity across the boundary. Furthermore, carbonate mound structures with limestone grains consisting mainly of ∼cylindrical bryozoan fragments could be identified in the inverted Cole-Cole parameters as anomalies with high relaxation times. A general conclusion of this work is that limestones can give rise to a wide range of spectral responses. The carbonate texture and the dominant shape of the fossil grains seem to have important control over the electrical properties of the material. A main conclusion is that the inverted Cole-Cole parameters from the field scale time domain IP tomography were comparable to the magnitude and shape of frequency domain IP spectra at low frequencies. This opens up large interpretational possibilities, as the comprehensive knowledge about relationships between lithological properties and IP spectra from laboratory research can be used for field data interpretation.
Conference Paper
The availability of large-scale occurrence databases has revolutionized palaeobiology, allowing for investigation of diversity and macroecological trends through deep-time. However, the problem of data absence (i.e. does the lack of a fossil occurrence indicate genuine absence or imperfect detection?) has hindered studies, and potentially biased our understanding of the fossil record. Occupancy modelling, a commonly applied ecological technique that distinguishes between true (taxon genuinely absent) and false (taxon present, but not detected) absences, provides an avenue to explore spatiotemporal biases in the fossil record by producing independent and simultaneous estimates of both occupancy and detection probability. We use occupancy modelling to assess trends in occupancy and detection within three dinosaur groups (Tyrannosauridae, Ceratopsidae and Hadrosauridae) during the Late Cretaceous of North America, to establish whether their apparent decline towards the K-Pg boundary is a product of sampling bias or a genuine ecological signal. Preliminary results suggest that whilst occupancy remained stable, detection of dinosaur occurrences declines from the Campanian to the Maastrichtian, highlighting an increasing spatiotemporal bias towards the K-Pg. The addition of sitespecific lithological covariates provides information on how geological context influences detection capacity. We also highlight the importance of recording absence information in future palaeontological studies.
Chapter
The fossil record of dinosaurs from India provides a highly significant contribution to understanding the origin and evolution of dinosaurs and their paleobiogeographic significance. As India rifted from Gondwana and drifted northwards during the age of dinosaurs, the mobile episode in Indian geology provides a unique opportunity to study the diversity of dinosaurs in time and space. The dinosaurs from the Gondwana and post-Gondwana sediments of India have been collected and studied since their discovery in the 1920s, but the full range of their significance and evolutionary history remained fragmentary. After the independence of India, a renaissance arose in the study of dinosaurs at the Indian Statistical Institute (ISI) under the leadership of Pamela Robinson, as more and more dinosaur skeletons were discovered from different localities. This exploration by ISI paleontologists represented a pivotal moment in the history of vertebrate paleontology in India and became a starting point for a remarkable increase in our knowledge of Triassic, Jurassic, and Cretaceous dinosaur faunas. It inspired a new generation of students working under Ashok Sahni’s direction at Panjab University to engage in the Cretaceous research. This paper offers an updated and comprehensive review of the anatomy, systematics, and evolution of Indian dinosaurs within historical, paleobiogeographic, and paleoecologic contexts. The occurrence of Indian dinosaurs is currently restricted to central and southern India, and the record extends across all three Mesozoic periods. It is generally regarded that dinosaurs originated in the Late Triassic Period in Argentina, about 230 million years ago. However, Alwalkeria, a theropod discovered in the Lower Maleri Formation of India, was contemporaneous with the oldest Argentinean dinosaurs. Similarly, Barapasaurus from the Early Jurassic Kota Formation is considered as one of the oldest, gigantic sauropod dinosaurs with a quadrupedal pose. The Late Triassic and Early Jurassic dinosaurs of India are diverse and document their early radiation. With the breakup of Gondwana, India began to disintegrate and drifted northwards, carrying its dinosaur fauna like a passenger ship, until it collided with the Oman-Kohistan-Ladakh Arc in the Late Cretaceous, forming a biotic corridor to Africa and Europe. The Late Cretaceous dinosaurs from the Lameta Formation, consisting of several species of titanosaurs and abelisaurs, provide intimate documentation of the last ‘geologic minutes’ before their extinction. Along with dinosaur bones, the largest titanosaurid hatchery is known from the Lameta Formation, extending for more than 1,000 km. Most egg clutches contain about 10 to 12 spherical eggs ranging in diameter from 15 to 20 cm. Surprisingly, these eggs were empty, showing no signs of embryos, perhaps indicating hatching failure during some environmental crisis. At the Cretaceous-Paleogene boundary, India was ground zero for two catastrophic events—the Shiva impact and Deccan volcanism—both linked to dinosaur extinction. The combination of twin asteroid impacts (Chicxulub and Shiva), with prolonged Deccan volcanism created an unprecedented and ultimately catastrophic environmental crisis across the globe, triggering the end-Cretaceous mass extinction.
Article
Full-text available
Heterochrony, defined as a change in the timing of developmental events altering the course of evolution, was first recognized by Ernst Haeckel in 1866. Haeckel's original definition was meant to explain the observed parallels between ontogeny and phylogeny, but the interpretation of his work became a source of controversy over time. Heterochrony took its modern meaning following the now classical work in the 1970–80s by Steven J. Gould, Pere Alberch, and co-workers. Predicted and described heterochronic scenarios emphasize the many ways in which developmental changes can influence evolution. However, while important examples of heterochrony detected with comparative morphological methods have multiplied, the more mechanistic understanding of this phenomenon lagged conspicuously behind. Considering the rapid progress in imaging and molecular tools available now for developmental biologists, this review aims to stress the need to take heterochrony research to the next level. It is time to synchronize the different levels of heterochrony research into a single analysis flow: from studies on organismal-level morphology to cells to molecules and genes, using complementary techniques. To illustrate how to achieve a more comprehensive understanding of phyletic morphological diversification associated with heterochrony, we discuss several recent case studies at various phylogenetic scales that combine morphological, cellular, and molecular analyses. Such a synergistic approach offers to more fully integrate phylogenetic and ontogenetic dimensions of the fascinating evolutionary phenomenon of heterochrony. Highlights • Heterochrony research focuses on comparative morphology but lags on mechanistic understanding. • We propose integrating the different levels of study into a single analysis flow: from morphology to cells to molecules and genes, using modern techniques.
Article
Full-text available
The ancestors of cyanobacteria generated Earth’s first biogenic molecular oxygen, but how they dealt with oxidative stress remains unconstrained. Here we investigate when superoxide dismutase enzymes (SODs) capable of removing superoxide free radicals evolved and estimate when Cyanobacteria originated. Our Bayesian molecular clocks, calibrated with microfossils, predict that stem Cyanobacteria arose 3300–3600 million years ago. Shortly afterwards, we find phylogenetic evidence that ancestral cyanobacteria used SODs with copper and zinc cofactors (CuZnSOD) during the Archaean. By the Paleoproterozoic, they became genetically capable of using iron, nickel, and manganese as cofactors (FeSOD, NiSOD, and MnSOD respectively). The evolution of NiSOD is particularly intriguing because it corresponds with cyanobacteria’s invasion of the open ocean. Our analyses of metalloenzymes dealing with reactive oxygen species (ROS) now demonstrate that marine geochemical records alone may not predict patterns of metal usage by phototrophs from freshwater and terrestrial habitats.
Article
An asteroid impacted the Yucatan carbonate platform in the Southern Gulf of Mexico about 66 million years ago. The ejecta and impact-vapor plume introduced massive amounts of gases and dust into the atmosphere causing major global environmental effects that led to the Cretaceous-Paleogene mass extinction. The physical parameters of the Chicxulub impact-vapor plume are not completely known and are important to constrain its evolution and the aftermath of the event. Here we reconstruct the impact-vapor plume by laser ablation of target sediments recovered from the Yaxcopoil-1 borehole in the Chicxulub impact crater. The ablation experiment was performed under a reconstructed late Cretaceous atmosphere composed of 0.16% CO2, 30% O2, and 69.84% N2 at 1000 mbar. The initial propagation velocities of the shockwave and impact-vapor plume were ∼4.5 km s⁻¹ and ∼2.3 km s⁻¹, respectively. The temperature and electron density of a simulated Chicxulub impact-vapor plume were determined using calcium emission lines. The initial temperature and electron density were estimated to be ∼1.8(±0.1)✕10⁴ K and ∼5.9(±0.7)✕10¹⁷ cm⁻³, respectively. The plume expanded adiabatically with a specific heat ratio of 1.31 ± 0.03. Its initial pressure was computed to be ∼103 bar. These parameters are required in gas dynamic codes to develop chemical models to study the evolution of the simulated impact-vapor plume and predict the fluxes and nature of gases, vapors and mineral phases injected in the atmosphere. Such chemical models will allow scaling from laboratory to planetary conditions to better constrain the chemical effects to the environment and the biosphere by the asteroid impact.
Article
Documenting the patterns and potential associated processes of ancient biotas has always been a central challenge in palaeontology. Over recent decades, intense debate has focused on the organization of dinosaur-dominated communities, yet no general consensus has been reached on how these communities were organized in a spatial context. Here, we used analytical routines typically applied in metacommunity ecology to provide novel insights into dinosaurian distributions across the latest Cretaceous of North America. To do this, we combined fossil occurrences with functional, phylogenetic and palaeoenvironmental modelling, and adopted the perspective that more reasonable conclusions on palaeoecological reconstructions can be gained from studies that consider the organization of biotas along ecological gradients at multiple spatial scales. Our results showed that dinosaurs were restricted in range to different parts of the Hell Creek Formation , prompting the recognition of discrete and compartmentalized faunal areas during the Maastrichtian at fine-grained scales, whereas taxa with the broadest ranges included those with narrower distributions when combining data from various geological formations across the Western Interior of North America. Although groups of dinosaurs had coincident range boundaries, their communities responded to multiple ecologically-important gradients when compensating for differences in sampling effort. Metacommunity structures of both ornithischians and theropods were correlated with climatic barriers and potential trophic relationships between herbivores and carnivores, thereby suggesting that dinosaurian faunas were shaped by physiological constraints, limited food resources abundance, and a combination of bottom-up and top-down forces across multiple spatial grains and extents.
Chapter
This chapter provides an overview of life and draws near some important questions: When did life on earth begin? What is life? How is it organized? The origins of eukaryotic cells, the endosymbiosis theory, the origins of organelles, the notion of reductive evolution, and the importance of horizontal gene transfer. Knowledge of the complexity and size of current single‐celled eukaryotic organisms calls into question many more complex fossils. Images based on electron microscopy can best show the classic structure and the inner “frozen” dynamics of eukaryotic cells. Double‐stranded DNA molecules of eukaryotic organisms are folded and distributed into chromosomes, which take the form of chromatin. Eukaryotes and prokaryotes prefer different strategies for synthesizing multiple proteins from a single DNA region. In prokaryotes, gene expression is primarily regulated at the level of transcription. The chapter discusses the physical sizes of different unicellular and multicellular eukaryotic organisms.
Article
The Cretaceous–Palaeogene (K–Pg) mass extinction was responsible for the destruction of global ecosystems and loss of approximately three-quarters of species diversity 66 million years ago. Large-bodied land vertebrates suffered high extinction rates, whereas small-bodied vertebrates living in freshwater ecosystems were buffered from the worst effects. Here, we report a new species of large-bodied (1.4–1.5 m) gar based on a complete skeleton from the Williston Basin of North America. The new species was recovered 18 cm above the K–Pg boundary, making it one of the oldest articulated vertebrate fossils from the Cenozoic. The presence of this freshwater macropredator approximately 1.5–2.5 thousand years after the asteroid impact suggests the rapid recovery and reassembly of North American freshwater food webs and ecosystems after the mass extinction.
Article
Full-text available
Both the Chicxulub and Boltysh impact events are associated with the K-Pg boundary. While Chicxulub is firmly linked to the end-Cretaceous mass extinction, the temporal relationship of the ~24-km-diameter Boltysh impact to these events is uncertain, although it is thought to have occurred 2 to 5 ka before the mass extinction. Here, we conduct the first direct geochronological comparison of Boltysh to the K-Pg boundary. Our ⁴⁰ Ar/ ³⁹ Ar age of 65.39 ± 0.14/0.16 Ma shows that the impact occurred ~0.65 Ma after the mass extinction. At that time, the climate was recovering from the effects of the Chicxulub impact and Deccan trap flood volcanism. This age shows that Boltysh has a close temporal association with the Lower C29n hyperthermal recorded by global sediment archives and in the Boltysh crater lake sediments. The temporal coincidence raises the possibility that even a small impact event could disrupt recovery of the Earth system from catastrophic events.
Article
Full-text available
The advent of palaeontological occurrence databases has allowed for detailed reconstruction and analyses of species richness through deep time. While a substantial literature has evolved ensuring that taxa are fairly counted within and between different time periods, how time itself is divided has received less attention. Stage‐level or equal‐interval age bins have frequently been used for regional and global studies in vertebrate palaeontology. However, when assessing diversity at a regional scale, these resolutions can prove inappropriate with the available data. Herein, we propose a new method of binning geological time for regional studies that intrinsically incorporates the chronostratigraphic heterogeneity of different rock formations to generate unique stratigraphic bins. We use this method to investigate the diversity dynamics of dinosaurs from the Late Cretaceous of the Western Interior of North America prior to the Cretaceous–Palaeogene mass extinction. Increased resolution through formation binning pinpoints the Maastrichtian diversity decline to between 68 and 66 Ma, coinciding with the retreat of the Western Interior Seaway. Diversity curves are shown to exhibit volatile patterns using different binning methods, supporting claims that heterogeneous biases in this time‐frame affect the pre‐extinction palaeobiological record. We also show that the apparent high endemicity of dinosaurs in the Campanian is a result of non‐contemporaneous geological units within large time bins. This study helps to illustrate the utility of high‐resolution, regional studies to supplement our understanding of factors governing global diversity in deep time and ultimately how geology is inherently tied to our understanding of past changes in species richness.
Article
Full-text available
Mass extinctions are recognized through the study of fossil groups across event horizons, and from analyses of long-term trends in taxonomic richness and diversity. Both approaches have inherent flaws, and data that once seemed reliable can be readily superseded by the discovery of new fossils and/or the application of new analytical techniques. Herein the current state of the Cretaceous–Tertiary (K–T) biostratigraphical record is reviewed for most major fossil clades, including: calcareous nannoplankton, dinoflagellates, diatoms, radiolaria, foraminifera, ostracodes, scleractinian corals, bryozoans, brachio-pods, molluscs, echinoderms, fish, amphibians, reptiles and terrestrial plants (macrofossils and palynomorphs). These reviews take account of possible biasing factors in the fossil record in order to extract the most comprehensive picture of the K–T biotic crisis available. Results suggest that many faunal and floral groups (ostracodes, bryozoa, ammonite cephalopods, bivalves, archosaurs) were in decline throughout the latest Maastrichtian while others (diatoms, radiolaria, benthic foraminifera, brachiopods, gastropods, fish, amphibians, lepidosaurs, terrestrial plants) passed through the K–T event horizon with only minor taxonomic richness and/or diversity changes. A few microfossil groups (calcareous nannoplankton, dinoflagellates, planktonic foraminifera) did experience a turnover of varying magnitudes in the latest Maastrichtian–earliest Danian. However, many of these turnovers, along with changes in ecological dominance patterns among benthic foraminifera, began in the latest Maastrichtian. Improved taxonomic estimates of the overall pattern and magnitude of the K–T extinction event must await the development of more reliable systematic and phylogenetic data for all Upper Cretaceous clades.
Article
Full-text available
Dinosaur fossils are present in the Paleocene Ojo Alamo Sandstone and Animas Formation in the San Juan Basin, New Mexico, and Colorado. Evidence for the Paleo-cene age of the Ojo Alamo Sandstone includes palynologic and paleomagnetic data. Palynologic data indicate that the entire Ojo Alamo Sandstone, including the lower dinosaur-bearing part, is Paleocene in age. All of the palynomorph-productive rock samples collected from the Ojo Alamo Sandstone at multiple localities lacked Creta-ceous index palynomorphs (except for rare, reworked specimens) and produced Paleocene index palynomorphs. Paleocene palynomorphs have been identified strati-graphically below dinosaur fossils at two separate localities in the Ojo Alamo Sand-stone in the central and southern parts of the basin. The Animas Formation in the Colorado part of the basin also contains dinosaur fossils, and its Paleocene age has been established based on fossil leaves and palynology. Magnetostratigraphy provides independent evidence for the Paleocene age of the Ojo Alamo Sandstone and its dinosaur-bearing beds. Normal-polarity magnetochron C29n (early Paleocene) has been identified in the Ojo Alamo Sandstone at six localities in the southern part of the San Juan Basin. An assemblage of 34 skeletal elements from a single hadrosaur, found in the Ojo Alamo Sandstone in the southern San Juan Basin, provided conclusive evidence that this assemblage could not have been reworked from underlying Cretaceous strata. In addition, geochemical studies of 15 vertebrate bones from the Paleocene Ojo Alamo Sandstone and 15 bone samples from the underlying Kirtland Formation of Late Creta-ceous (Campanian) age show that each sample suite contained distinctly different abundances of uranium and rare-earth elements, indicating that the bones were miner-alized in place soon after burial, and that none of the Paleocene dinosaur bones ana-lyzed had been reworked.
Article
Full-text available
[Fassett et al. (2011][1], herein) analyzed fossil bone fragments from the San Juan Basin of New Mexico and claim to have achieved the “first successful direct dating of fossil vertebrate bone” (p. 159). This claim is asserted to establish the survival of dinosaurs into the Paleogene, thus
Article
Full-text available
Vertebrate fossils have been important for relative dating of terrestrial rocks for decades, but direct dating of these fossils has heretofore been unsuccessful. In this study we employ recent advances in laser ablation in situ U-Pb dating techniques to directly date two dinosaur fossils from the San Juan Basin of northwestern New Mexico and southwestern Colorado, United States. A Cretaceous dinosaur bone collected from just below the Cretaceous-Paleogene interface yielded a U-Pb date of 73.6 +/- 0.9 Ma, in excellent agreement with a previously determined Ar-40/Ar-39 date of 73.04 +/- 0.25 Ma for an ash bed near this site. The second dinosaur bone sample from Paleocene strata just above the Cretaceous-Paleogene interface yielded a Paleocene U-Pb date of 64.8 +/- 0.9 Ma, consistent with palynologic, paleomagnetic, and fossil-mammal biochronologic data. This first successful direct dating of fossil vertebrate bone provides a new methodology with the potential to directly obtain accurate dates for any vertebrate fossil.
Article
Full-text available
A comprehensive, but simple-to-use software package for executing a range of standard numerical analysis and operations used in quantitative paleontology has been developed. The program, called PAST (PAleontological STatistics), runs on standard Windows computers and is available free of charge. PAST integrates spreadsheettype data entry with univariate and multivariate statistics, curve fitting, time-series analysis, data plotting, and simple phylogenetic analysis. Many of the functions are specific to paleontology and ecology, and these functions are not found in standard, more extensive, statistical packages. PAST also includes fourteen case studies (data files and exercises) illustrating use of the program for paleontological problems, making it a complete educational package for courses in quantitative methods.
Article
Full-text available
BioOne (www.bioone.org) is a nonprofit, online aggregation of core research in the biological, ecological, and environmental sciences. BioOne provides a sustainable online platform for over 170 journals and books published by nonprofit societies, associations, museums, institutions, and presses. Abstract.—The Cretaceous/Tertiary (K/Pg) mass extinction has long been viewed as a pivotal event in mammalian evolutionary history, in which the extinction of non-avian dinosaurs allowed mammals to rapidly expand from small-bodied, generalized insectivores to a wide array of body sizes and ecological specializations. Many studies have used global-or continental-scale taxonomic databases to analyze this event on coarse temporal scales, but few studies have documented morphological diversity of mammalian paleocommunities on fine spatiotemporal scales in order to examine ecomorphological selectivity and ecospace filling across this critical transition. Focusing on well-sampled and temporally well-constrained mammalian faunas across the K/Pg boundary in northeastern Montana, I quantified dental-shape disparity and morphospace occupancy via landmark-and semilandmark-based geometric morphometrics and mean body size, body-size disparity, and body-size structure via body-mass estimates. My results reveal several key findings: (1) latest Cretaceous mammals, particularly metatherians and multituberculates, had a greater ecomorphological diversity than is generally appreciated, occupying regions of the morphospace that are interpreted as strict carnivory, plant-dominated omnivory, and herbivory; (2) the decline in dental-shape disparity and body-size disparity across the K/Pg boundary shows a pattern of constructive extinction selectivity against larger-bodied dietary specialists, particularly strict carnivores and taxa with plant-based diets, that suggests the kill mechanism was related to depressed primary productivity rather than a globally instantaneous event; (3) the ecomorphological recovery in the earliest Paleocene was fueled by immigrants, namely three multituberculate families (taeniolabidids, microcosmodontids, eucosmodontids) and to a lesser extent archaic ungulates; and (4) despite immediate increases in the taxonomic richness of eutherians, their much-celebrated post-K/Pg ecomorphological expansion had a slower start than is generally perceived and most likely only began 400,000 to 1 million years after the extinction event.
Article
Full-text available
We suggest that a buried 180-km-diameter circular structure on the Yucatan Peninsula, Mexico, is an impact crater. Its size and shape are revealed by magnetic and gravity-field anomalies, as well as by oil wells drilled inside and near the structure. The stratigraphy of the crater includes a sequence of andesitic igneous rocks and glass interbedded with, and overlain by, breccias that contain evidence of shock metamorphism. The andesitic rocks have chemical and isotopic compositions similar to those of tektites found in Cretaceous/Tertiary (K/T) ejecta. A 90-m-thick K/T boundary breccia, also containing evidence of shock metamorphism, is present 50 km outside the crater's edge. This breccia probably represents the crater's ejecta blanket. The age of the crater is not precisely known, but a K/T boundary age is indicated. Because the crater is in a thick carbonate sequence, shock-produced CO 2 from the impact may have caused a severe greenhouse warming.
Article
Full-text available
A comprehensive review and study of the rich dinosaur track record of the Tremp Formation in the southern Pyrenees of Spain (Southwestern Europe) shows a unique succession of footprint localities prior to the end-Cretaceous mass extinction event. A description of some 30 new tracksites and data on sedimentary environments, track occurrence and preservation, ichnology and chronostratigraphy are provided. These new track localities represent various facies types within a diverse set of fluvial environments. The footprint discoveries mostly represent hadrosaurian and, less abundantly, to sauropod dinosaurs. The hadrosaur tracks are significantly smaller in size than, but morphologically similar to, those of North America and Asia and are attributable to the ichnogenus Hadrosauropodus. The track succession, with more than 40 distinct track levels, indicates that hadrosaur footprints in the Ibero-Armorican region occur predominantly in the late Maaastrichtian (at least above the early Maastrichtian-late Maastrichtian boundary). The highest abundance is found noticeably found in the late Maastrichtian, with tracks occurring in the C29r magnetochron, within about the latest 300,000 years of the Cretaceous.
Article
Full-text available
An ˜3 m stratigraphic interval that entirely lacks dinosaur fossils or has very few fossils has been reported at the top of the Hell Creek Formation in the upper Great Plains of North America. The presence of the ``3 m gap'' in fossil distribution has been cited as evidence that dinosaurs had either become extinct or were on the verge of extinction prior to the bolide impact at the end of the Cretaceous Period. A survey in two areas of North Dakota and Montana reveals that dinosaur fossils in the upper 3 m of the Hell Creek Formation occur in numbers that are comparable to their abundance in other levels of the formation. Evidence for a gradual extinction is absent, and data are consistent with an abrupt extinction associated with an impact.
Article
Full-text available
Estimates of past precipitation are of broad interest for many areas of inquiry, including reconstructions of past environments and topography, climate modeling, and ocean circulation studies. The shapes and sizes of living leaves are highly sensitive to moisture conditions, and assemblages of fossil leaves of flowering plants have great potential as paleoprecipitation indicators. Most quantitative estimates of paleoprecipitation have been based on a multivariate data set of morphological leaf characters measured from samples of living vegetation tied to climate stations. However, when tested on extant forests, this method has consistently overestimated precipitation. We present a simpler approach that uses only the mean leaf area of a vegetation sample as a predictor variable but incorporates a broad range of annual precipitation and geographic coverage into the predictor set. The significant relationship that results, in addition to having value for paleoclimatic reconstruction, refines understanding of the long-observed positive relationship between leaf area and precipitation. Seven precipitation estimates for the Eocene of the Western United States are revised as lower than previously published but remain far wetter than the same areas today. Abundant moisture may have been an important factor in maintaining warm, frost-free conditions in the Eocene because of the major role of water vapor in retaining and transporting atmospheric heat.
Article
Full-text available
Rightly or wrongly, dinosaurs are poster children for the Cretaceous-Tertiary (K-T) extinction. The rate and cause of their extinction, however, has been contentious, at least in part because of their rarity. Nonetheless, significant data have accumulated to indicate that the dinosaur extinction, in North America at least, was geologically instantaneous. The evidence comes from field studies in geologically disparate settings involving the reconstruction of dinosaur stratigraphic ranges as well as community structure in the Late Cretaceous, and from quantitative studies of the post-Cretaceous evolution of mammals. The hypothesis of extinction by asteroid impact i s concordant with what is known of the rate of the dinosaur extinction, as well as the patterns of selective vertebrate survivorship across the K-T boundary. The precise nature of the kill mechanism(s), however, remains under discussion.
Article
Full-text available
Climatic and oceanographic variations during the last 2 m.y. of the Maastrichtian inferred from high-resolution (10 k.y.) stable isotope analysis of the mid-latitude South Atlantic Deep Sea Drilling Project Site 525 reveal a major warm pulse followed by rapid cooling prior to the Cretaceous-Tertiary boundary. Between 66.85 and 65.52 Ma, cool but fluctuating temperatures average 9.9 and 15.4 °C in intermediate and surface waters, respectively. This interval is followed by an abrupt short-term warming between 65.45 and 65.11 Ma, which increased temperatures by 2 3 °C in intermediate waters, and decreased the vertical thermal gradient to an average of 2.7 °C. This warm pulse may be linked to increased atmospheric pCO2, increased poleward heat transport, and the switch of an intermediate water source from high to low-middle latitudes. During the last 100 k.y. of the Maastrichtian, intermediate and surface temperatures decreased by an average of 2.1 and 1.4 °C, respectively, compared to the maximum temperature between 65.32 and 65.24 Ma.
Article
Full-text available
Ancient soils (paleosols) of the latest Cretaceous Hell Creek Formation are mildly calcareous, have clayey subsurface (Bt) horizons, and exhibit abundant large root traces, as is typical of forested soils in subhumid climates. The fact that some of the paleosols are capped by thin, impure coals is evidence for seasonally dry swamps. The paleosol evidence thus supports published reconstructions, based on fossil leaves, pollen, and vertebrates, that this area was subtropical, seasonally dry, subhumid, and forested mainly by angiosperms. Paleosols within the earliest Tertiary (Paleocene) Tullock Formation have thicker, coaly, surface (O and A) horizons and are more drab colored and less calcareous than paleosols of the Hell Creek Formation. These features are indications of waterlogging and of a humid climate. Large root traces and clayey subsurface (Bt) horizons are evidence of swamp woodland and forest. Inferred base level and paleoclimate are compatible with evidence from fossil leaves and pollen that indicates more abundant deciduous, early successional angiosperms and swamp conifers compared to those of Late Cretaceous time. Most of the paleosols have drab Munsell hues and can be expected to preserve a reliable fossil record of pollen and other plant remains. The carbonate content of the paleosols declines toward the top of the Hell Creek Formation, and the uppermost 3 m of the formation is noncalcareous. Because of this, the decline in diversity and abundance of bone over this interval is interpreted as a taphonomic artifact. Evidence from paleosols supports paleobotani-cal evidence for catastrophic change in ecosystems at the Cretaceous/Tertiary boundary.
Book
When the The Dinosauria was first published more than a decade ago, it was hailed as "the best scholarly reference work available on dinosaurs" and "an historically unparalleled compendium of information." This second, fully revised edition continues in the same vein as the first but encompasses the recent spectacular discoveries that have continued to revolutionize the field. A state-of-the-science view of current world research, the volume includes comprehensive coverage of dinosaur systematics, reproduction, and life history strategies, biogeography, taphonomy, paleoecology, thermoregulation, and extinction. Its internationally renowned authors-forty-four specialists on the various members of the Dinosauria-contribute definitive descriptions and illustrations of these magnificent Mesozoic beasts. The first section of The Dinosauria begins with the origin of the great clade of these fascinating reptiles, followed by separate coverage of each major dinosaur taxon, including the Mesozoic radiation of birds. The second part of the volume navigates through broad areas of interest. Here we find comprehensive documentation of dinosaur distribution through time and space, discussion of the interface between geology and biology, and the paleoecological inferences that can be made through this link. This new edition will be the benchmark reference for everyone who needs authoritative information on dinosaurs.
Article
Since Alvarez et al. (1980) proposed their argument for dinosaur (and other) extinctions, lengthy debate has provided no consensus and the issue remains strongly polarized. The only test that has been proposed, that of additional fieldwork that sought to fill in the "gap' at the top of the Hell Creek Formation, recently has been conducted by Sheehan et al. (1991). Although the analysis found no indication of a gradual decline through the bulk of the formation, it did not produce the distribution Alvarez sought, a random distribution of remains clear through to the iridium. A second test based on the differing taphonomic predictions of catastrophic and noncatastrophic extinctions, and a comparison with the distribution of remains in the uppermost part of the formation, gives some credence to the latter and places considerable doubt on the former. -Author
Article
The recurring debate over the causes of the massive extinctions of such groups as the dinosaurs, ammonites, and calcareous nannoplankton, and the crash of the distinctive Aquilapollenites pollen province, used by biostratigraphers to mark the close of the Cretaceous, has been considerably enlivened with the resurgence of hypotheses suggesting catastrophic events. The impact of an asteroid, explosion of a supernova, sudden changes in oceanic circulation and composition, or atmospheric perturbations, to mention a few, have been put forward as malefactors. But, just how sound is the evidence of a biotic catastrophe?
Article
We summarize faunal changes through the thickest and one of the most complete records of terrestrial vertebrates spanning Lancian (~latest Cretaceous) and Puercan (~earliest Paleocene) ages, the type Ferris Formation in the Hanna Basin, southern Wyoming. Observed faunal changes predate tectonic definition of local Laramide basins. Nonmammalian vertebrates exhibit no major changes in taxonomic composition below the Lancian-Puercan boundary; diversity of non-avian dinosaurs remains high within uppermost levels of the Lancian section. Nevertheless, dinosaurian extinction was not necessarily 'catastrophic' within a biologically relevant interval. Primitive condylarths appear locally above the highest known dinosaurs, probably as immigrants. At least in this part of the North American western interior, the first evolutionary radiation of condylarths was subsequent to the last appearance of dinosaurs, not synchronous with or prior to it. Niche-partitioning among condylarths is first recorded near the boundary between Puercan Interval-zones Pu1 and Pu2 (early and middle Puercan time, respectively), by which time the first great mammalian diversification of the Cenozoic had begun. Major experimentations in dental morphology and increasing ranges of body sizes had developed within 400,000 years of the Lancian-Puercan boundary. We recognize no evidence suggesting that placental mammals were 'recovering' from events that led to demise of the dinosaurs. The true diversity of marsupials and condylarths precisely at the Cretaceous-Tertiary boundary, throughout the western interior, remains unknown. We cannot, therefore, evaluate extensiveness of competition, if any, at that time among members of the two groups.
Article
Paleobiologists are reaching a consensus that biases in diversity curves, origination rates, and extinction rates need to be removed using statistical estimation methods. Diversity estimates are biased both by methods of counting and by variation in the amount of fossil data. Traditional counts are essentially tallies of age ranges. Because these counts are distorted by interrelated factors such as the Pull of the Recent and the Signor-Lipps effect, counts of taxa actually sampled within intervals should be used instead. Sampling intensity biases can be addressed with randomized subsampling of data records such as individual taxonomic occurrences or entire fossil collections. Fair subsampling would yield taxon counts that track changes in the species pool size, i.e., the diversity of all taxa that could ever be sampled. Most of the literature has overlooked this point, having instead focused on making sample sizes uniform through methods such as rarefaction. These methods flatten the data, undersampling when true diversity is high. A good solution to this problem involves the concept of frequency distribution coverage: a taxon's underlying frequency is said to be “covered” when it is represented by at least one fossil in a data set. A fair subsample, but not a uniform one, can be created by drawing collections until estimated coverage reaches a fixed target (i.e., until a “shareholder quorum” is attained). Origination and extinction rates present other challenges. For many years they were thought of in terms of simple counts or ratios, but they are now treated as exponential decay coefficients of the kind featuring in simple birth-death models. Unfortunately, these instantaneous rates also suffer from counting method biases (e.g., the Pull of the Recent). Such biases can be removed by only examining taxa sampled twice consecutively, three times consecutively, or in the first and third of three intervals but not the second (i.e., two timers, three timers, and part timers). Two similar equations involving these counts can be used. Alternative methods of estimating diversity and turnover through extrapolation share some of the advantages of quorum subsampling and two-timer family equations, but it remains to be shown whether they produce precise and accurate estimates when applied to fossil data.
Article
This chapter documents survivorship across the Cretaceous/Tertiary (K/T) (and Lancian/Puercan) boundary for all 111 species of nonmarine vertebrates from Garfield and McCone counties, Montana. Species-level survivorship appears to be between about 53 and 64 percent after the artifacts caused by paleobiogeography, rarity of some species, and differing evolutionary rates are taken into account. Without correcting for these artifacts, survival is an artificially low 32 percent. If specimens from the Bug Creek interval are early Paleocene (Puercan) in age, survivorship is an almost certainly incorrectly high value of 82 percent. This is because an undetermined number of latest Cretaceous (Lancian) species in the Bug Creek interval probably were reworked from Cretaceous sediments and were extinct by Bug Creek time. Comparison of the Lancian/ Puercan transition with the older Judithian/Lancian and younger Puercan/Torrejonian transitions suggests percentage survival is similar among the three (55, 48, and 58 percent, respectively) after the Lazarus effect is considered. These results are not easily explained by a catastrophic mass-extinction scenario for the K/T transition, at least for nonmarine vertebrates. Rather, a geologically rapid but noncatastrophic change, such as the loss of range and habitat diversity during the Late Cretaceous marine regression, is commensurate with the analysis.
Chapter
A series of 33 Late Cretaceous (earliest Campanian through Maastrichtian) paleoshoreline maps was developed to document the migrational evolution of the western edge of the North American Western Interior Seaway. The maps represent a geologic span of roughly 18 million years, and portray the estimated positions of the strandline for each standard Western Interior ammonite zone, beginning with the Clioscaphites choteauensis zone and continuing to the end of the Mesozoic. We attempted correlation of all significant mammal-bearing localities known from the Western Interior with the ammonite-based marine zonation. First approximations of correspondence between ammonite zones and North American Land-Mammal "Ages" (NALMAs) include: Lancian (Sphenodiscus through "Triceratops" zones); "Edmontonian" (a name not yet faunally defined; Didymoceras cheyennense through Baculites clinolobatus zones); Judithian (the smooth, late form of Baculites sp. through Exiteloceras jenneyi zones); and Aquilan (Scaphites hippocrepis through Baculites asperiformis zones). Correlations emphasize use of provincial biostratigraphic terminology designed specifically for use in the Western Interior. On the basis of temporal constraints suggested herein, known mammalian fossils from the upper Fruitland and/or lower Kirtland Formations of New Mexico probably are of "Edmontonian," not Judithian age. Although considerable latitudinally based taxonomic diversification of Judithian mammals is now recognizable across the Western Interior, comparative data are inadequate to defend a similar statement for the remaining Late Cretaceous NALMAs. Quantitative evaluation of geographic patterns of shoreline change suggests occurrence of a general, regional regression of the sea during the entire geologic interval represented in the study. We favor explanation by a slow sea-level depression resulting from topographic evolution of the world's mid-oceanic system of ridges and volcanic plateaus. Local and subregional asynchronous episodes of shoreline transgressions, stillstands, and regressions are superimposed upon the general regressive trend, and probably represent influences of local tectonism, not eustatic changes in sea level. Strandline evolution of the epeiric sea during the last 20 million years of the Cretaceous in the North American Western Interior is inconsistent with: (1) existence of geologically brief (1 to 10 m.y.) global fluctuations in sea level; and (2) the concept that the late Campanian was represented by an unusually high global sea level.
Chapter
The disappearance of nonavian dinosaurs is only a small part of a greater class of extinctions known as “mass extinctions.” Mass extinctions are global events characterized by unusually high rates of extinction. The five episodes of mass extinctions in Earth history are the Permo-Triassic extinction, the Late Ordovician extinction, the Late Devonian extinction, the Triassic-Jurassic extinction, and the Cretaceous-Tertiary (K/T) extinction. This chapter focuses on patterns of geologic and biotic changes that occurred during the Cretaceous-Tertiary (K/T) extinction. It also highlights the similarities and differences in interpretations of geologic and fossil records. It concludes with two scenarios explaining the differing views about dinosaur extinction.
Chapter
The amount of CO2 and O2 in the atmosphere over long timescales (>105years) is largely controlled by several key processes. Reconstruction of atmospheric CO2 and O2 in the geologic past can be accomplished either with proxies or by modeling the long-term carbon and sulfur cycles. Application of these two independent approaches yields similar results. CO2 was high during the early Paleozoic (>2000ppm) and parts of the Mesozoic (~1000ppm) but low during the Carboniferous, Permian, and late Cenozoic (<500ppm). These CO2 patterns are strongly coupled to independent evidence for global temperature. O2 records show oscillating values (15-25%) with a distinct peak (>30%) during the Permian. There is a compelling link between this Phanerozoic peak in atmospheric O2 and a concomitant interval of insect gigantism.
Chapter
After three decades of nearly unchallenged wisdom that a large impact (Chicxulub) on Yucatan caused the end-Cretaceous mass extinction, this theory is facing its most serious challenge from the Chicxulub impact itself, as based on evidence in Texas and Mexico and from Deccan volcanism in India. Data generated from over 150 Cretaceous–Tertiary (KT) boundary sequences to date make it clear that the long-held belief in the Chicxulub impact as the sole or even major contributor to the KT mass extinction is not supported by evidence. The stratigraphic position of the Chicxulub impact ejecta spherules in NE Mexico and Texas and the impact breccia within the crater on Yucatan demonstrate that this impact predates the KTB by about 300,000 years. Planktic foraminiferal and stable isotope analyses across the primary impact ejecta layer reveal that not a single species went extinct as a result of this impact and no significant environmental changes could be determined. The catastrophic effects of this impact have been vastly overestimated. In contrast, recent advances in Deccan volcanic studies indicate three volcanic phases with the smallest at 67.5 Ma, the main phase at the end of the Maastrichtian (C29r), and the third phase in the early Danian C29r/C29n transition (Chenet et al. 2007). The main phase of eruptions occurred rapidly, was marked by the longest lava flows spanning 1500 km across India, and ended coincident with the KT boundary. The KT mass extinction may have been caused by these rapid and massive Deccan lava and gas eruptions that account for ∼80% of the entire 3500 m thick Deccan lava pile.
Book
This revised edition of this book continues in the same vein as the first but encompasses recent spectacular discoveries that have continued to revolutionize this field. A thorough scientific view of current world research, the volume includes comprehensive coverage of dinosaur systematics, reproduction, and life history strategies, biogeography, taphonomy, paleoecology, thermoregulation, and extinction. It contains definitive descriptions and illustrations of these magnificent Mesozoic beasts. The first section of the book begins with the origin of the great clade of these fascinating reptile ... More This revised edition of this book continues in the same vein as the first but encompasses recent spectacular discoveries that have continued to revolutionize this field. A thorough scientific view of current world research, the volume includes comprehensive coverage of dinosaur systematics, reproduction, and life history strategies, biogeography, taphonomy, paleoecology, thermoregulation, and extinction. It contains definitive descriptions and illustrations of these magnificent Mesozoic beasts. The first section of the book begins with the origin of the great clade of these fascinating reptiles, followed by separate coverage of each major dinosaur taxon, including the Mesozoic radiation of birds. The second part of the volume navigates through broad areas of interest. Here we find comprehensive documentation of dinosaur distribution through time and space, discussion of the interface between geology and biology, and the paleoecological inferences that can be made through this link. This revised edition of this book continues in the same vein as the first but encompasses recent spectacular discoveries that have continued to revolutionize this field. A thorough scientific view of current world research, the volume includes comprehensive coverage of dinosaur systematics, reproduction, and life history strategies, biogeography, taphonomy, paleoecology, thermoregulation, and extinction. It contains definitive descriptions and illustrations of these magnificent Mesozoic beasts. The first section of the book begins with the origin of the great clade of these fascinating reptile ... More
Article
Ongoing research into the biostratigraphy of the upper Campanian Dinosaur Park Formation (DPF) of Alberta has demonstrated that megaherbivorous dinosaur taxa (ankylosaurs, ceratopsids, hadrosaurids) are not homogeneously distributed throughout the unit. This has compelled proposals of different, informal assemblage zone schemes, and the hypothesis that faunal turnover was driven by environmental change associated with marine transgression. The current study tests previous zonation schemes in addition to the hypothesis of turnover pulses in the DPF. Clustering and ordination methods are used to demonstrate the existence of two broad assemblage zones within the DPF, each of which lasted ~ 600 Ka: a lower zone characterized by the presence of the ceratopsid Centrosaurus apertus and the hadrosaurids Corythosaurus, and an upper zone characterized by the presence of the ceratopsid Styracosaurus albertensis and the hadrosaurid Prosaurolophus maximus. These zones can be further sub-divided, based on the distributions of rarer or shorter-lived ankylosaur, ceratopsid, and hadrosaurid species, into ~ 300 Ka sub-zones. Canonical correspondence analysis is used to explore the association between the turnover of the megaherbivorous dinosaurs and various palaeoevironmental proxies. Megaherbivorous dinosaur turnover most closely corresponds to that of fossil palynomorphs. However, none of the palaeoenvironmental proxies explains dinosaur distribution better than a simple time gradient, suggesting that dinosaur turnover was not inextricably linked to environmental change as predicted by the turnover pulse hypothesis.
Article
Phylogenetic comparative methods provide a powerful way of addressing classic questions about tempo and mode of phenotypic evolution in the fossil record, such as whether mammals increased in body size diversity after the Cretaceous‐Palaeogene (K‐Pg) extinction.Most often, these kinds of questions are addressed in the context of variation in evolutionary rates. Shifts in the mode of phenotypic evolution provide an alternative and, in some cases, more realistic explanation for patterns of trait diversity in the fossil record, but these kinds of processes are rarely tested for.In this study, I use a time‐calibrated phylogeny of living and fossil Mammaliaformes as a framework to test novel models of body size evolution derived from palaeontological theory. Specifically, I ask whether the K‐Pg extinction result