Some recent non-dino papers in open access that may be of interest concerning evolution of angiosperms during the Cretaceous.
Michael P. Donovan, Ari Iglesias, Peter Wilf, Conrad C. Labandeira & N. Rubén Cúneo (2016)
Rapid recovery of Patagonian plant–insect associations after the end-Cretaceous extinction.
Nature Ecology & Evolution 1, Article number: 0012 (2016)
The Southern Hemisphere may have provided biodiversity refugia after the Cretaceous/Palaeogene (K/Pg) mass extinction. However, few extinction and recovery studies have been conducted in the terrestrial realm using well-dated macrofossil sites that span the latest Cretaceous (late Maastrichtian) and early Palaeocene (Danian) outside western interior North America (WINA). Here, we analyse insect-feeding damage on 3,646 fossil leaves from the latest Maastrichtian and three time slices of the Danian in Chubut, Patagonia, Argentina (palaeolatitude approximately 50° S). We test the southern refugial hypothesis and the broader hypothesis that the extinction and recovery of insect herbivores, a central component of terrestrial food webs, differed substantially from WINA at locations far south of the Chicxulub impact structure in Mexico. We find greater insect-damage diversity in Patagonia than in WINA during both the Maastrichtian and Danian, indicating a previously unknown insect richness. As in WINA, the total diversity of Patagonian insect damage decreased from the Cretaceous to the Palaeocene, but recovery to pre-extinction levels occurred within approximately 4 Myr compared with approximately 9 Myr in WINA. As for WINA, there is no convincing evidence for survival of any of the diverse Cretaceous leaf miners in Patagonia, indicating a severe K/Pg extinction of host-specialized insects and no refugium. However, a striking difference from WINA is that diverse, novel leaf mines are present at all Danian sites, demonstrating a considerably more rapid recovery of specialized herbivores and terrestrial food webs. Our results support the emerging idea of large-scale geographic heterogeneity in extinction and recovery from the end-Cretaceous catastrophe.
Palaeontological evidence from both continental and marine deposits suggests that the Southern Hemisphere may have harboured biodiversity refugia in the wake of the bolide impact at Chicxulub, Mexico, 66.0 Myr ago (Ma)1,2,3,4. The extinction rate of Southern Hemisphere nannoplankton was lower than that of their Northern Hemisphere counterparts, and their populations recovered nearly immediately2. Nominally Mesozoic plant groups, including corystosperms and bennettitaleans, survived until at least the Palaeogene in Australia1,5. Palynological data from New Zealand revealed a sudden but short-lived disturbance, with low overall extinction rates6,7. In Patagonia, Argentina, palynomorphs from the latest Maastrichtian–early Danian Lefipán Formation exhibited low extinction, followed by the reappearances of Cretaceous pollen types3. Early Danian macrofloras from the Salamanca Formation in Patagonia are more diverse than comparable North American Palaeocene floras8,9,10. A number of surviving lineages from other plant3 and vertebrate11,12 groups have also been identified, especially in Patagonia4, although marine invertebrate faunas in Antarctica underwent severe extinction13. K/Pg boundary sections in New Zealand have provided important insights into the response of terrestrial ecosystems6,7,14,15,16, but until recently there has not been a series of well-dated, heavily sampled continental macrofloral localities anywhere in the Southern Hemisphere that spans both the terminal Cretaceous and earliest Palaeogene.
Plant–insect interactions are fundamental components of terrestrial food webs, and their sensitivity to major environmental perturbations is well known from deep time as well as the modern world17,18,19,20. The diversity of insect-feeding damage on extant leaves in two tropical rainforests is positively correlated with the richness of insects that caused the damage, supporting the widespread use of insect damage on fossil leaves as a proxy for herbivorous insect diversity when suitable insect body fossils are absent21. In North Dakota, USA, insect-damage diversity on fossil leaves, especially specialized feeding such as mining and galling, declined considerably across the K/Pg boundary and remained low throughout WINA before increasing with the latest Palaeocene warming, approximately 9 Myr after the K/Pg boundary17,18,20. The only exception to this pattern is the early Palaeocene (about 65 Ma) Mexican Hat locality in south-eastern Montana, USA, which has typical low-diversity flora but anomalously high insect damage diversity for the time; this pattern is attributed to a short-lived interval of decoupled plant and insect diversity following the K/Pg mass extinction17,20.
Much less is known about the extinction and recovery of insect herbivores outside WINA. Late Palaeocene floras from Colombia are associated with low richness of plants and specialized insect-damage diversity as in Palaeocene WINA22, contrasting with high plant and insect-damage diversity on middle Palaeocene floras from France23 and Spitsbergen24. However, until now, no studies have investigated changes in insect-damage diversity based on terminal Cretaceous and early Palaeocene leaf floras from any non-WINA study area.
Angiosperms evolved and diversified during the Cretaceous period. Early angiosperms were short-stature weedy plants thought to have increased fire frequency and mortality in gymnosperm forest, aiding their own expansion. However, no explorations have considered whether the range of novel fuel types that diversified throughout the Cretaceous also altered fire behaviour, which should link more strongly to mortality than fire frequency alone.
We measured ignitability and heat of combustion in analogue Cretaceous understorey fuels (conifer litter, ferns, weedy and shrubby angiosperms) and used these data to model palaeofire behaviour.
Variations in ignition, driven by weedy angiosperms alone, were found to have been a less important feedback to changes in Cretaceous fire activity than previously estimated. Our model estimates suggest that fires in shrub and fern understories had significantly greater fireline intensities than those fuelled by conifer litter or weedy angiosperms, and whilst fern understories supported the most rapid fire spread, angiosperm shrubs delivered the largest amount of heat per unit area.
The higher fireline intensities predicted by the models led to estimates of enhanced scorch of the gymnosperm canopy and a greater chance of transitioning to crown fires. Therefore, changes in fire behaviour driven by the addition of new Cretaceous fuel groups may have assisted the angiosperm expansion.
Camiel Doorenweerd, Erik J. van Nieukerken & Robert J. B. Hoare (2016)
Phylogeny, classification and divergence times of pygmy leaf-mining moths (Lepidoptera: Nepticulidae): the earliest lepidopteran radiation on Angiosperms?
Systematic Entomology (advance online publication)
Nepticulidae represent one of the early diverging Lepidoptera lineages, and the family currently comprises over 850 described species. The larvae of the vast majority of the species are leaf miners on Angiosperms and highly monophagous, which has led to persistent ideas on coevolution with their plant hosts. We present here a molecular phylogeny based on eight gene fragments from 355 species, representing 20 out of 22 extant Nepticulidae genera. Using two fossil calibration points, we performed molecular dating to place the origin of the family in the Early Cretaceous, before the main Angiosperm diversification. Based on our results we propose a new classification, abandoning all ranks between family and genus, as well as subgenera to allow for a stable classification. The position of Enteucha Meyrick within Nepticulidae remains somewhat ambiguous, and the species-rich cosmopolitan genus Stigmella Schrank, with nearly half of all described Nepticulidae, requires further study. Ectoedemia Busck, Zimmermannia Hering, Acalyptris Meyrick, Etainia Beirne, Parafomoria Borkowski, Muhabbetana Koçak & Kemal and Fomoria Beirne appear to have diversified in a relatively short evolutionary period, leading to short branches in the molecular phylogeny and unclear suprageneric relations. Otherwise support values throughout the phylogeny are mostly high and the species groups, genera and higher clades are discussed in respect of their supporting morphological and life-history characters. Wing venation characters are confirmed to be mostly reliable and relevant for Nepticulidae classification, but some other previously used characters require reinterpretation. The species groups of most genera are recovered, but only partly so in the large genus Stigmella. The molecular dating results are compared with existing knowledge on the timing of the Angiosperm radiation and reveal that the diversification of Nepticulidae could largely have been contemporaneous with their hosts, although some of the genera restricted to a single plant family appear to have begun to diversify before their hosts.