A derived dryolestid mammal indicates possible insular endemism in the Late Jurassic of Germany

Abstract

The Langenberg Quarry near Bad Harzburg has yielded the first Jurassic stem therian mammal of Germany, recovered from Kimmeridgian (Late Jurassic) near shore deposits of a palaeo-island within the Lower Saxony Basin of the European archipelago. The new stem therian is represented by one lower and three upper molars. Hercynodon germanicus gen. et sp. nov. is attributed to the Dryolestidae, a group of pretribosphenic crown mammals that was common in western Laurasia from the Middle Jurassic to the Early Cretaceous. The new taxon is characterised by small size, a reduced cusp pattern in the upper molars lacking a metacone, and enhancement of the shearing crests paracrista and metacrista. Phylogenetic analysis identified Hercynodon gen. nov. as sister taxon of Crusafontia from the Lower Cretaceous (Barremian) of Spain. Both taxa belong to an endemic European clade of dryolestids, including also Achyrodon and Phascolestes from the earliest Cretaceous (Berriasian) of England. Despite its greater geological age, Hercynodon gen. nov. is the most derived representative of that clade, indicated by the complete reduction of the metacone. The discrepancy between derived morphology and geological age may be explained by an increased rate of character evolution in insular isolation. Other insular phenomena have earlier been observed in vertebrates from the Langenberg Quarry, such as dwarfism in the small sauropod Europasaurus, and possible gigantism in the morganucodontan mammaliaform Storchodon and the pinheirodontid multituberculate mammal Teutonodon which grew unusually large.

Paleontology-themed comics and graphic novels, their potential for scientific outreach, and the bilingual graphic novel EUROPASAURUS – Life on Jurassic Islands

“…Food sources of Europasaurus were probably limited on the island, which may have led to island dwarfism over time-a recurring pattern throughout evolution (Sander et al, 2006). The discovery of the first Jurassic mammals in Germany (Martin et al, 2016(Martin et al, , 2019(Martin et al, , 2021a(Martin et al, , 2021b) and a number of other new taxa added to the success story of this research project. Due to the large number of unusual and well-preserved fossil finds, which due to their often fragmentary nature reveal little to non-specialists, a visual reconstruction of the living world of that time was tantalizing.…”

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“…The fossils of Europasaurus are found only in the bone-rich limestone layer 83, with remarkably few accompanying remains of other animals. With more than 20 individuals discovered so far, it is unlikely that the animals were swimming or that all carcasses were washed from the land into the sea 47, 48 . Instead, it appears likely that the animals lived together in a herd and were located in a tidal plain when they died.…”