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

Abstract

In some Devonian strata in the eastern Anti‐Atlas, fossil invertebrates are abundant, display a high taxonomic diversity and indicate many shifts in palaeoecology. This is reflected in changes in faunal composition of invertebrates and vertebrates. Fossils of jawed vertebrates of late Lochkovian and younger age have been recorded and are relatively common with their abundance and diversity increasing towards the Late Devonian. Environmental changes in the Devonian also left their mark in the preservation of vertebrates and invertebrates from the Anti‐Atlas, which varies strongly through time and regionally. This variation partially reflects environmental changes linked with the evolution of small marine basins during the disintegration of the continental shelf of Gondwana in this region, fluctuations of the regional sea level and other environmental changes. To improve our understanding of these ecological changes, of shifts in preservation through the succession and of the formation of Fossil‐Lagerstätten, we analysed the mineral composition of some invertebrate and vertebrate samples of Devonian and Early Carboniferous age by Raman spectroscopy and X‐ray diffraction. Additionally, we characterized some of these Fossil‐Lagerstätten using palaeontological and sedimentological parameters. We examined eight Devonian Konzentrat‐Lagerstätten and two Konservat‐Lagerstätten with soft‐tissue preservation (the Famennian Thylacocephalan Layer and the Hangenberg Black Shale of the southern Maïder). The last two are the first Konservat‐Lagerstätten described from the Devonian of North Africa. The taphonomic and oceanic settings suggest that these Konservat‐Lagerstätten are formed because of stagnation (related to vertical restriction of water exchange and water depth rather than limited spatial water exchange and a lateral restriction) in the relatively small Maïder Basin with limited water exchange with the neighbouring Tafilalt Basin. The temporally low oxygen levels in the Maïder Basin are a possible reason for the reduced chondrichthyan diversity (missing demersal and shallow water species) compared to the Tafilalt Platform.

First African thylacocephalans from the Famennian of Morocco and their role in Late Devonian food webs

“…The Middle Famennian outcrops contain a layer attributed to the Maeneceras genozone 13,[17][18][19] , erroneously called 'Phyllocarid Layer' in an earlier paper (Ref. 15 , renamed in 20 ). The specimens 1 University of Zürich, Zürich, Switzerland.…”

“…Thirdly, the interior angle of the eye is sharper in C. submarinus than in C. bradleyi, here it is more rounded. 20 . This includes poorly sclerotized structures such as the appendages of thylacocephalans and non-mineralized organs such as muscles and livers of chondrichthyans 20 .…”

“…20 . This includes poorly sclerotized structures such as the appendages of thylacocephalans and non-mineralized organs such as muscles and livers of chondrichthyans 20 . In line with the interpretations of Frey et al 15,20 , we also assume that the exceptional preservation is linked with low oxygen levels of the bottom waters in the Maïder Basin.…”

“…This includes poorly sclerotized structures such as the appendages of thylacocephalans and non-mineralized organs such as muscles and livers of chondrichthyans 20 . In line with the interpretations of Frey et al 15,20 , we also assume that the exceptional preservation is linked with low oxygen levels of the bottom waters in the Maïder Basin. In the case of thylacocephalans, they demonstrated the presence of phosphate in the carapace, eyes and appendages, while the coarse crystals filling the void in the carapaces of most specimens are composed of yellow calcite.…”

Biogenic Iron Preserves Structures during Fossilization: A Hypothesis

“…Although fossil mineralization is common in the geological record, [ 52–57 ] little work has been done to investigate the role of tissue chemistry during the mineralization process. Recently, it was suggested that the recurrent association of particular mineralogical phases such as fluorapatite, or Fe‐sulfides (pyrite, pyrrhotite) with specific tissues in crustacean fossils preserved within carbonate‐rich concretions from the Jurassic exceptionally preserved biota of La Voulte‐sur‐Rhône (Ardèche, France) were linked to differences in the original biochemical signal of the organic matter.…”