A non-archaeopterygid avialan theropod from the Late Jurassic of southern Germany.

Oliver WM Rauhut,Helmut Tischlinger,Christian Foth

doi:10.7554/elife.43789

Abstract

The Late Jurassic 'Solnhofen Limestones' are famous for their exceptionally preserved fossils, including the urvogel Archaeopteryx, which has played a pivotal role in the discussion of bird origins. Here we describe a new, non-archaeopterygid avialan from the Lower Tithonian Mörnsheim Formation of the Solnhofen Archipelago, Alcmonavis poeschli gen. et sp. nov. Represented by a right wing, Alcmonavis shows several derived characters, including a pronounced attachment for the pectoralis muscle, a pronounced tuberculum bicipitale radii, and a robust second manual digit, indicating that it is a more derived avialan than Archaeopteryx. Several modifications, especially in muscle attachments of muscles that in modern birds are related to the downstroke of the wing, indicate an increased adaptation of the forelimb for active flapping flight in the early evolution of birds. This discovery indicates higher avialan diversity in the Late Jurassic than previously recognized.

Highlights

The so-called ‘Solnhofen limestones’ of southern Germany have long been known for their exceptionally preserved fossils
Most fossils reported from these rocks come from the Altmuhltal Formation, as these were subject to intensive quarrying for several commercial purposes, from construction to lithography, probably since Roman times (Neumeyer, 2015)
All paravian specimens from the late Kimmeridgian - early Tithonian laminated limestones of southern Germany have been identified as Archaeopteryx, and this would be an obvious identification for the new specimen as well

Summary

Introduction

The so-called ‘Solnhofen limestones’ of southern Germany have long been known for their exceptionally preserved fossils (see Arratia et al, 2015). The medial rim of the groove is formed by a broad longitudinal ridge that is slightly offset laterally from the medial margin of the distal humerus and fades into the shaft some 15 mm proximal to the distal end This groove and ridge have not been described for Archaeopteryx so far (due to the fact that the anterior side of the distal humerus is not exposed in any of the specimens referred to this genus), but they are present in the humeri of the dromaeosaurids Deinonychus (Ostrom, 1969), and Bambiraptor (Burnham, 2004), in Balaur (Brusatte et al, 2013) and the basal avialans Confuciusornis (Chiappe et al, 1999) and Sapeornis (Provini et al, 2009). As in the other unguals, the sheath extends the ungual for slightly more than one third of the length of the bony element, and its tip is placed c. 5.2 mm below the proximal articular facet

Discussion

Materials and methods

Findings

Funding Funder Volkswagen Foundation