Mass survival of birds across the Cretaceous-Tertiary boundary: molecular evidence (original) (raw)
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Rapid recovery of life at ground zero of the end- Cretaceous mass extinction
Nature, 2018
The Cretaceous/Palaeogene mass extinction eradicated 76% of species on Earth 1,2. It was caused by the impact of an asteroid 3,4 on the Yucatán carbonate platform in the southern Gulf of Mexico 66 million years ago 5 , forming the Chicxulub impact crater 6,7. After the mass extinction, the recovery of the global marine ecosystem-measured as primary productivity-was geographically heterogeneous 8 ; export production in the Gulf of Mexico and North Atlantic-western Tethys was slower than in most other regions 8-11 , taking 300 thousand years (kyr) to return to levels similar to those of the Late Cretaceous period. Delayed recovery of marine productivity closer to the crater implies an impact-related environmental control, such as toxic metal poisoning 12 , on recovery times. If no such geographic pattern exists, the best explanation for the observed heterogeneity is a combination of ecological factors-trophic interactions 13 , species incumbency and competitive exclusion by opportunists 14-and 'chance' 8,15,16. The question of whether the post-impact recovery of marine productivity was delayed closer to the crater has a bearing on the predictability of future patterns of recovery in anthropogenically perturbed ecosystems. If there is a relationship between the distance from the impact and the recovery of marine productivity, we would expect recovery rates to be slowest in the crater itself. Here we present a record of foraminifera, calcareous nannoplankton, trace fossils and elemental abundance data from within the Chicxulub crater, dated to approximately the first 200 kyr of the Palaeocene. We show that life reappeared in the basin just years after the impact and a high-productivity ecosystem was established within 30 kyr, which indicates that proximity to the impact did not delay recovery and that there was therefore no impact-related environmental control on recovery. Ecological processes probably controlled the recovery of productivity after the Cretaceous/Palaeogene mass extinction and are therefore likely to be important for the response of the ocean ecosystem to other rapid extinction events. The recent joint expedition of the International Ocean Discovery Program and International Continental Drilling Program (hereafter, Expedition 364) recovered what is, to our knowledge, the first record of the few hundred thousand years immediately after the impact within the Chicxulub crater. Site M0077, which was drilled into the peak ring of the crater 7 (Extended Data Fig. 1), sampled an approximately 130-m-thick, generally upward-fining suevite (that is, melt-bearing impact breccia) overlying impact melt rocks and fractured granite 17. The boundary between the suevite and overlying earliest-Palaeocene pelagic limestone is in core 40-1 (Fig. 1), and comprises a 76-cm-thick upward-fining, brown, fine-grained micritic limestone that we term the 'transitional unit'. The lower portion of the transitional unit is laminated below 54-cm core depth and contains no trace fossils (Fig. 1 and Extended Data Fig. 2). The laminations are thin, graded beds with sub-millimetre-scale cross-bedding that indicates bottom currents, and are likely due to the movement of wave energy-including tsu-nami and/or seiches-in the days after the impact. The fine grain size (primarily clay to silt, with some sand-sized grains concentrated in the graded beds) suggests that much of the material in the transitional unit was deposited from resuspension and settling. The transitional unit is overlain by a white pelagic limestone. The lowermost sample taken in this limestone (34 cm core depth) contains the planktic foraminifer Parvularugoglobigerina eugubina (which marks the base of Zone Pα), other foraminifer of the same genus (P. extensa, P. alabamensis) and Guembelitria cretacea. Because many other species that originate within Zone Pα first appear a few centimetres higher in the section (31-32 cm), we conclude that the base of the limestone lies very near the base of this zone, 30 kyr after the impact 18. Biostratigraphy and basic assumptions about depositional and crater processes indicate that the transitional unit was deposited between several years and 30 kyr after impact (Fig. 2). To better constrain this, we use the abundance of extraterrestrial 3 He to determine sediment accumulation rates (see Methods). This proxy provides a firm upper limit of 8 kyr for deposition, assuming none of the 3 He is reworked. If even a small amount of 3 He is reworked (which is very likely given the prevalence of reworked microfossils and impact debris), then the transitional unit was deposited in a period of time of less than about 2 8 8 | N A t U r e | V O L 5 5 8 | 1 4 J U N e 2 0 1 8
Mass extinction of birds at the Cretaceous-Paleogene (K-Pg) boundary
Proceedings of the National Academy of Sciences, 2011
The effect of the Cretaceous-Paleogene (K-Pg) (formerly Cretaceous–Tertiary, K–T) mass extinction on avian evolution is debated, primarily because of the poor fossil record of Late Cretaceous birds. In particular, it remains unclear whether archaic birds became extinct gradually over the course of the Cretaceous or whether they remained diverse up to the end of the Cretaceous and perished in the K–Pg mass extinction. Here, we describe a diverse avifauna from the latest Maastrichtian of western North America, which provides definitive evidence for the persistence of a range of archaic birds to within 300,000 y of the K–Pg boundary. A total of 17 species are identified, including 7 species of archaic bird, representing Enantiornithes, Ichthyornithes, Hesperornithes, and an Apsaravis-like bird. None of these groups are known to survive into the Paleogene, and their persistence into the latest Maastrichtian therefore provides strong evidence for a mass extinction of archaic birds coinciding with the Chicxulub asteroid impact. Most of the birds described here represent advanced ornithurines, showing that a major radiation of Ornithurae preceded the end of the Cretaceous, but none can be definitively referred to the Neornithes. This avifauna is the most diverse known from the Late Cretaceous, and although size disparity is lower than in modern birds, the assemblage includes both smaller forms and some of the largest volant birds known from the Mesozoic, emphasizing the degree to which avian diversification had proceeded by the end of the age of dinosaurs.
Detritus feeding as a buffer to extinction at the end of the Cretaceous
Geology, 1986
At the end of the Cretaceous the principal animals that became extinct, such as dinosaurs, marine animals that lived in the water column, and benthic filter feeders, were in food chains tied directly to living plant matter. Animal groups less affected by extinction, including marine benthic scavengers and deposit feeders, small insectivorous mammal!;, and members of stream communities, were in food chains dependent on dead plant materuil. The proposal that an asteroid or comet impact at the end of the Cretaceous produced a duiit cloud that cut off photosynthesis for several months is consistent with this pattern of extincti on. Food chains dependent on living plant matter crashed, while food chains based on detritus were buffered from extinction because there was a food supply adequate for the interval when photosynthesis was halted.
The fossil record and recent molecular phylogenies support an extraordinary early-Cenozoic radiation of crown birds (Neornithes) after the Cretaceous- Paleogene (K-Pg) mass extinction. However, questions remain regarding the mechanisms under- lying the survival of the deepest lineages within crown birds across the K-Pg boundary, particularly since this global catastrophe eliminated even the closest stem-group relatives of Neornithes. Here, ancestral state reconstructions of neornithine ecology reveal a strong bias toward taxa exhibiting predominantly non-arboreal lifestyles across the K-Pg, with multiple convergent transitions toward predominantly arboreal ecologies later in the Paleocene and Eocene. By contrast, ecomorphological inferences indicate predominantly arboreal lifestyles among enantiornithines, the most diverse and widespread Mesozoic avialans. Global paleobotanical and palynological data show that the K-Pg Chicxulub impact triggered widespread destruction of forests. We suggest that ecological filtering due to the temporary loss of significant plant cover across the K-Pg boundary selected against any flying dinosaurs (Avialae) committed to arboreal ecologies, resulting in a predominantly non-arboreal post-extinction neornithine avifauna composed of total-clade Palaeognathae, Galloanserae, and terrestrial total-clade Neoaves that rapidly diversified into the broad range of avian ecologies familiar today. The explanation proposed here provides a unifying hypothesis for the K-Pg-associated mass extinction of arboreal stem birds, as well as for the post-K-Pg radiation of arboreal crown birds. It also provides a baseline hypothesis to be further refined pending the discovery of additional neornithine fossils from the Latest Cretaceous and earliest Paleogene.
Dinosaurs and the Cretaceous Terrestrial Revolution
The observed diversity of dinosaurs reached its highest peak during the mid- and Late Cretaceous, the 50Myr that preceded their extinction, and yet this explosion of dinosaur diversity may be explained largely by sampling bias. It has long been debated whether dinosaurs were part of the Cretaceous Terrestrial Revolution (KTR), from 125–80Myr ago, when flowering plants, herbivorous and social insects, squamates, birds and mammals all underwent a rapid expansion. Although an apparent explosion of dinosaur diversity occurred in the mid-Cretaceous, coinciding with the emergence of new groups (e.g. neoceratopsians, ankylosaurid ankylosaurs, hadrosaurids and pachycephalosaurs), results from the first quantitative study of diversification applied to a new supertree of dinosaurs show that this apparent burst in dinosaurian diversity in the last 18 Myr of the Cretaceous is a sampling artefact. Indeed, major diversification shifts occurred largely in the first one-third of the group's history. Despite the appearance of new clades of medium to large herbivores and carnivores later in dinosaur history, these new originations do not correspond to significant diversification shifts. Instead, the overall geometry of the Cretaceous part of the dinosaur tree does not depart from the null hypothesis of an equal rates model of lineage branching. Furthermore, we conclude that dinosaurs did not experience a progressive decline at the end of the Cretaceous, nor was their evolution driven directly by the KTR.