Figure 1. Parargornis messelensis, holotype (HLMD Be 163), skeleton in ventral view. Coated with ammonium chloride to enhance contrast; scale bar equals 10 mm.
Mayr and Peters (1999) described a fragmentary cra- nial half of an articulated skeleton of a swift-like bird from Messel which does not belong to Scaniacypselus szarskii. In size, this bird (HLMD Me 15405, Mayr & Peters 1999: Fig. 3) corresponds to Parargornis messelensis, gen. nov., sp. nov. Although its beak appears to be longer than in the type of P. messelensis, this could be an artefact of preservation. Unfor- tunately, specimen HLMD Me 15405 is too poorly preserved to make a reliable assignment to either Parargornis or another apodiform taxon. Other speci- mens of Parargornis messelensis, gen. nov., sp. nov. are currently unknown.
DESCRIPTION AND COMPARISON
The poorly preserved skull has similar proportions to that of recent swifts.The beak is short and wide, with a pointed tip, and measures about one-third of the entire length of the skull. The narial openings are
A new Eocene swift-like bird
Figure 2. Parargornis messelensis, X-ray photograph of specimen HLMD Be 163.
very long. The ossa maxillaria are similar in shape to those of recent swifts, and are also widely separated. The part of the frontale between the orbitae is slightly wider than in recent Hemiprocne comata (in the extant Common Swift Apus apus it is much narrower).
The lacunae interzygapophysiales of the cervical vertebrae are deep, but otherwise the vertebrae do not allow a meaningful description. Six free tail vertebrae can be counted, which bear long processus transversi.
The coracoid resembles the corresponding bone of Jungornis and Argornis. The extremitas omalis is relatively smaller than in recent Apodidae and Hemi- procnidae. The processus procoracoideus (visible on the left side of HLMD Be 193) is well-developed and of similar shape to Argornis (Karhu 1999: Fig. 3). As in all other apodiform birds, but contrary to the majority of other ‘higher’ landbirds, a foramen nervi supracoracoidei is present (Fig. 5). The angulus medialis protrudes far medially. As in Jungornis and Argornis, the processus lateralis reaches beyond the level of the angulus lateralis (HLMD Be 193, right side; Fig. 5).
© 2003 British Ornithologists’ Union, Ibis, 145, 382–391