Late Devonian and Early Carboniferous alpha diversity, ecospace occupation, vertebrate assemblages and bio-events of southeastern Morocco

Abstract

The Late Devonian was a time of dramatic environmental perturbations affecting marine ecosystems. Both the Kellwasser (latest Frasnian) and the Hangenberg crises (latest Famennian) are primarily reported as phases of drastic decreases in marine diversity while the Hangenberg Crisis is also described as a bottleneck in vertebrate evolution. Fossil-bearing localities with Upper Devonian strata are of great interest to assess variations in the effects of environmental perturbations on biodiversity. For this purpose, we examined changes in alpha diversity and ecospace utilization of 21 Famennian (Late Devonian) and early Tournaisian (Early Carboniferous) invertebrate associations containing 9828 specimens from Madène el Mrakib and Aguelmous (southern Maïder Basin, northeastern Anti-Atlas, Morocco), where some layers yield exceptionally preserved gnathostome remains. Both the invertebrate and vertebrate associations contain predominantly opportunistic and pelagic taxa indicating oxygen depletion near the seafloor in this region. Nevertheless, the ecospace extension was fluctuating and correlated with regional and/or global sea-level changes and oxygenation of bottom waters. In the Maïder Basin, the ecospace was depleted after and during several bioevents such as the Kellwasser and Hangenberg crises, the Annulata event (middle Famennian) as well as during the early Tournaisian. Abiotic as well as biotic changes (instability of the invertebrate ecosystem) are considered to have influenced Famennian vertebrate diversity because they were more or less directly dependent on invertebrates as a food source.

Fossil‐Lagerstätten, palaeoecology and preservation of invertebrates and vertebrates from the Devonian in the eastern Anti‐Atlas, Morocco

“…Regional palaeoecology was examined by Frey et al . (, ) for the Early Devonian of the southern Tafilalt Platform and the Famennian to Tournaisian and locally for the Pragian to Eifelian by Klug et al . ().…”

“…Palaeoecological changes throughout the Famennian and Tournaisian of the southern Maïder were studied by Frey et al . ().…”

“…Within the sedimentary succession of early middle Famennian age (probably Palmatolepis rhomboidea or Pa. marginifera conodont Zone), we discovered a reddish claystone layer a few tens of centimetres thick and rich in iron oxides in the southern Maïder Basin (Frey et al . ). This layer is characterized by abundant flat nodules, mostly 50–100 mm in diameter and usually containing the carapaces and sometimes (primarily chitinous) appendages, eyes, gills and possibly other organs (ongoing research) of thylacocephalans (Figs , ).…”

“…Although the oxygen content was probably varying, both benthic and non‐benthic diversity was at a higher level than previously until the end of the Zlíchovian (early Emsian; Massa ; Frey et al . , ).…”

“…This Thylacocephalan Layer (Frey et al . ) also yields articulated gnathostome remains, mostly of chondrichthyans, especially cladoselachian‐like forms, symmoriids and phoebodontids as well as sarcopterygians and various arthrodires (Figs ). Placoderms are commonly preserved in huge nodules, which probably reflect the outline of the entire body (Fig.…”