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Mass mortality events of autochthonous faunas in a Lower Cretaceous Gondwanan Lagerstatte.

ABSTRACT: Mass mortality events are unusual in the Crato Formation. Although mayflies' accumulations have been previously reported from that unit, they lacked crucial stratigraphic data. Here we provide the first taphonomic analysis of a mayfly mass mortality event, from a layer 285 cm from the top of the Formation, with 40 larvae, and an overview of the general biological community structure of a three meters deep excavated profile. The only other autochthonous taxon observed in the mayfly mortality layer was the gonorynchiform fish Dastilbe. The larvae and fishes were smaller than usual in the layer 285 cm, suggesting that they lived in a shallow water column. Their excellent preservation and a lack of preferential orientation in the samples suggest an absence of significant transport. All mayflies belong to the Hexagenitidae, whose larvae lived in quiet waters. We also recovered allochthonous taxa in that layer indicative of drier weather conditions. Adjacent layers presented crystals and pseudomorphs of halite, suggesting drought and high salinity. In other layers, Dastilbe juveniles were often found in mass mortality events, associated with a richer biota. Our findings support the hypothesis that the Crato Formation's palaeolake probably experienced seasonal high evaporation, caused by the hot climate tending to aridity, affecting the few autochthonous fauna that managed to live in this setting.

SUBMITTER: Storari AP

PROVIDER: S-EPMC7997927 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:The question of when modern birds (Neornithes) first diversified has generated much debate among avian systematists. Fossil evidence generally supports a Tertiary diversification, whereas estimates based on molecular dating favor an earlier diversification in the Cretaceous period. In this study, we used an alternate approach, the inference of historical biogeographic patterns, to test the hypothesis that the initial radiation of the Order Psittaciformes (the parrots and cockatoos) originated on the Gondwana supercontinent during the Cretaceous. We utilized broad taxonomic sampling (representatives of 69 of the 82 extant genera and 8 outgroup taxa) and multilocus molecular character sampling (3,941 bp from mitochondrial DNA (mtDNA) genes cytochrome oxidase I and NADH dehydrogenase 2 and nuclear introns of rhodopsin intron 1, tropomyosin alpha-subunit intron 5, and transforming growth factor ss-2) to generate phylogenetic hypotheses for the Psittaciformes. Analyses of the combined character partitions using maximum parsimony, maximum likelihood, and Bayesian criteria produced well-resolved and topologically similar trees in which the New Zealand taxa Strigops and Nestor (Psittacidae) were sister to all other psittaciforms and the cockatoo clade (Cacatuidae) was sister to a clade containing all remaining parrots (Psittacidae). Within this large clade of Psittacidae, some traditionally recognized tribes and subfamilies were monophyletic (e.g., Arini, Psittacini, and Loriinae), whereas several others were polyphyletic (e.g., Cyclopsittacini, Platycercini, Psittaculini, and Psittacinae). Ancestral area reconstructions using our Bayesian phylogenetic hypothesis and current distributions of genera supported the hypothesis of an Australasian origin for the Psittaciformes. Separate analyses of the timing of parrot diversification constructed with both Bayesian relaxed-clock and penalized likelihood approaches showed better agreement between geologic and diversification events in the chronograms based on a Cretaceous dating of the basal split within parrots than the chronograms based on a Tertiary dating of this split, although these data are more equivocal. Taken together, our results support a Cretaceous origin of Psittaciformes in Gondwana after the separation of Africa and the India/Madagascar block with subsequent diversification through both vicariance and dispersal. These well-resolved molecular phylogenies will be of value for comparative studies of behavior, ecology, and life history in parrots.

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Mass mortality events of autochthonous faunas in a Lower Cretaceous Gondwanan Lagerstatte.

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