Record of climate-driven morphological changes in 376 Ma Devonian fossils

Abstract

The Lower and Upper Kellwasser horizons represent two anoxic events that mark the mass extinction at the Frasnian-Famennian (F-F) boundary. Among other groups, conodont animals were severely affected, but the genus Palmatolepis survived with a complete turnover at the F-F boundary. Here the fi ne morphological variations of the genus Palmatolepis and the sea-surface temperature evolution are quantifi ed in two F-F boundary sections using morphometrics and oxygen isotopic composition of apatite, respectively. In accordance with other F-F sections, the isotope records show two positive excursions of ~1‰ during the Lower and Upper Kellwasser anoxic events. The conodont shape and the oxygen isotopic composition of the genus Palmatolepis are signifi cantly correlated within the Frasnian and Famennian Stages, suggesting a strong environmental infl uence on the morphology of the feeding apparatus of the conodont animal. We propose that the morphological differences are linked to changes in the trophic position of Palmatolepis: enhanced organic carbon burial, which is supported by global positive carbon isotope excursions in inorganic and organic carbon during both the Lower and Upper Kellwasser events altered the primary biomass production and thus, the subsequent nutrient supply to higher trophic levels. While the carbon and oxygen isotopic shifts are of similar amplitude during Lower and Upper Kellwasser events, the variation of the shape of Palmatolepis during the Upper Kellwasser, i.e., the F-F boundary, is more pronounced than during the Lower Kellwasser.

Pulses of enhanced continental weathering associated with multiple Late Devonian climate perturbations: Evidence from osmium-isotope compositions

“…A significant increase in global-scale continental weathering rates would likely have resulted in a greatly enhanced delivery of nutrients to the marine realm, elevating primary-productivity levels and consequently stimulating widespread marine anoxia and burial of organic carbon (as previously proposed by e.g., Wilder, 1994;Algeo et al, 1995;Algeo and Scheckler, 1998;Averbuch et al, 2005), which may then have been sustained by remobilization of nutrients from aquatic sediments under those low-oxygen conditions (Murphy et al, 2000). Together with this organic-carbon burial, the enhanced silicate weathering could also have resulted in a drawdown of CO 2 and consequential global cooling, which has also been reported for the two Kellwasser crises (e.g., Joachimski and Buggisch, 2002;Balter et al, 2008;Xu et al, 2012;Le Houedec et al, 2013;Huang et al, 2018). Thus, the pattern of enhanced continental weathering rates immediately prior to/during the onsets of the two Kellwasser crises is consistent with evidence of several other environmental perturbations in effect during those times, and follows a relationship between climate change, continental weathering, and/or marine anoxia that is similar to scenarios proposed for a number of other major events throughout the Phanerozoic Aeon (e.g., Kaiser et al, 2006;Bond and Grasby, 2017;Jenkyns, 2018).…”

“…Numerous triggers have been postulated for the Kellwasser crises, including extra-terrestrial impacts (e.g., Wang, 1992;Claeys et al 1996;Du et al, 2008), large-scale volcanic activity potentially linked to the Viluy Traps in Siberia (e.g., Courtillot et al, 2010;Ricci et al, 2013;Racki et al, 2018), orogenic uplift and erosion (Averbuch et al, 2005), and the expansion of vascular-rooted terrestrial flora (Algeo et al, 1995;Algeo and Scheckler, 1998). Many of the environmental perturbations also appear to have coincided with climate cooling (e.g., Streel et al, 2000;Joachimski and Buggisch, 2002;Balter et al, 2008). The Annulata anoxic event was coeval with a major marine transgression (Johnson et al, 1985), and may also have coincided with a major pulse of volcanic activity (Percival et al, 2018).…”

Disparity Changes in 370 Ma Devonian Fossils: The Signature of Ecological Dynamics?

“…Indeed, several Palmatolepis groups displayed oriented trends that mirrored, within each lineage, the trend followed by the genus as a whole. Fine-scale evolutionary analyses also demonstrated the ability of Palmatolepis species to track and adapt rapid temperature changes during the F/F crisis [20], [76]. Further integrative studies attempting to combine paleoenvironmental, paleoecological and evolutionary studies over intermediate time-scales will be necessary to decipher how evolutionary and ecological responses over short-time scale interplay and condition the mid- to long-term variation of the ecosystem, and contribute to an emergent macro-evolutionary signal.…”

Mass Extinction of Species

“…Devonian mass extinction events (McGhee 1996;Hallam and Wignall 1997) include a *387 Ma extinction (*30 % of Genera) and *374 Ma extinction (58 % of Genera) affecting pelagic fauna (Ammonoids, Cricoconaids, Placoderms, Conodonts, Agnathans) and benthic groups (Rugose corals, Trilobites, Ostracods and Brachiopods). The extinction involved collapse of Stromatoporoid reefs (Keller 2005 (Balter et al 2008). The late Devonian mass extinctions are superposed on a protracted cooling trend associated with a decline in CO 2 levels from a range of *3,200-5,200 ppm to below *500 ppm.…”

“…The number of impact events, size and age of craters follows largely the Earth Impact Database (2005 http://www.unb.ca/fredericton/science/research/passc/), with modification by the author (Glikson and Uysal 2013b) (Courtesy G. Keller) 3. End-Devonian *360 Ma impact cluster (Woodleigh, Siljan, Charlevoix, Alamo, possibly Warburton East) and the destruction of reefs (McGhee 1996;Balter et al 2008). 4.…”