Eopachypteryx

Mayr, Gerald, 2015, Towards completion of the early Eocene aviary: A new bird group from the Messel oil shale (Aves, Eopachypterygidae, fam. nov.), Zootaxa 4013 (2), pp. 252-264 : 258-261

publication ID	https://doi.org/ 10.11646/zootaxa.4013.2.6
publication LSID	lsid:zoobank.org:pub:3C01B34C-0C84-4BF1-97C1-375798C05A3E
DOI	https://doi.org/10.5281/zenodo.5669207
persistent identifier	https://treatment.plazi.org/id/690F87EA-A93E-FFFF-FF3F-33D6FEBC5243
treatment provided by	Plazi
scientific name	Eopachypteryx
status	gen. nov.

Treatment

? Eopachypteryx sp.

Referred specimen. SMF-ME 11417A+B (cranial portion of skeleton on two slabs, preserved in association with a fragmentary fish jaw; Fig. 5 View FIGURE 5 ).

Locality and horizon. Messel near Darmstadt; early Eocene ( Lenz et al. 2015).

Measurements. See Table 1 View TABLE 1 .

Remarks. This fossil is somewhat smaller than the specimens referred to Eopachypteryx praeterita ( Tab. 1 View TABLE 1 ), but closely resembles the former species in most features, which can be directly compared. Shared characteristics include a similar shape of the caudal end of the mandible, a robust humerus with a wide proximal end, a welldeveloped tuberculum dorsale and narrow condylus dorsalis, as well as a craniocaudally narrow carpometacarpus. The only notable morphological difference concerns the absence of a dorsal (second) fossa pneumotricipitalis, but as noted above, the presence of this fossa in one specimen of E. praeterita may well be a preservational artefact.

Description and comparisons. SMF-ME 11417 allows the recognition of various osteological details that are not visible in the specimens assigned to Eopachypteryx praeterita , and the following description focuses on these features. The beak is ventrally folded, so that its original proportions are difficult to assess. Its relative length, however, appears to have been similar to that of E. praeterita . The nostrils do not reach into the distal third of the upper beak. The pterygoid is long and rod-like, a facies articularis basipterygoidea is not visible. Of the left quadrate, parts of the processus mandibularis and the capitulum squamosum are visible, with the latter still articulating with the cotyla quadratica squamosa; the processus mandibularis of the right quadrate is seen in ventral view ( Fig. 6 View FIGURE 6 B–E). The condylus medialis is only moderately prominent and not as strongly ventrally projected as in rollers ( Coraciiformes ). It forms a small lateral lip and lacks a concave lateral articulation surface, which occurs in various only distantly related taxa ( Mayr & Clarke 2003: character 37). The condylus pterygoideus is well-defined.

As in E. praeterita , the mandible bears lateral fossae in the midsection of the rami. The caudal end exhibits an overall resemblance to the caudal mandible of the Cathartidae (New World vultures) ( Fig. 6 View FIGURE 6 F, G). The processus medialis is well-developed, the cotyla medialis wide and shallow. The narrow cotyla lateralis does not form a notch for a ventrally prominent processus lateralis of the quadrate as in, e.g., rollers ( Coracias sp.). A processus retroarticularis is absent, but the caudal extension of the cotyla lateralis tapers to a projection, which is medially bordered by a small notch ( Fig. 6 View FIGURE 6 F).

The axis bears a long processus ventralis ( Fig. 7 View FIGURE 7 B); the processus spinosus and the paired processus transversi form three projections, which project beyond the caudal border of the corpus vertebrae. As in many other birds, the body of the third cervical vertebra exhibits a pair of lateral foramina, which are delimited by osseous struts connecting the processus transversi and the zygapophyses caudales ( Fig. 7 View FIGURE 7 A). These foramina are absent in the fourth cervical vertebra. The tips of the zygapophyses caudales of the third cervical vertebra are dorsally projecting as in, e.g., Cathartidae .

As in E. praeterita , the furcula features robust scapi clavicularum and a wide extremitas sternalis; an apophysis furculae is absent ( Fig. 4 View FIGURE 4 D). The processus lateralis of the coracoid seems to be well developed.

The carina sterni is of moderate depth. The pointed apex carinae is strongly cranially protruding, the cranial margin of the carina is therefore deeply concave ( Fig. 7 View FIGURE 7 C). The caudal margin of the sternum bears a pair of deep incisions, of which the medial ones are slightly deeper than the lateral ones; the trabeculae laterales et mediales do not show a distal widening. Overall, the sternum resembles that of a fossil referred to the late Eocene/early Oligocene Eocuculus ( Fig. 8 View FIGURE 8. A and discussion).

The humerus corresponds with that of E. praeterita in its proportions and in most morphological features of the proximal and distal ends ( Fig. 7 View FIGURE 7 F–H). A second fossa pneumotricipitalis (i.e., a fossa pneumotricipitalis dorsalis), however, appears to be absent. As in E. praeterita , the tuberculum dorsale on the proximal end is well-developed. The condylus dorsalis, on the distal end of the bone, is narrow, and the condylus ventralis bears a depression. The ulna has a short olecranon. On the distal end of the bone, the condylus ventralis forms a marked ventral projection. The condylus dorsalis is well developed, whereas the tuberculum carpale is rather small ( Fig. 7 View FIGURE 7 I). The carpometacarpus has similar proportions to that of E. praeterita , and like in this species the strap-like os metacarpale minus broadens proximally. Although poorly preserved, feather remains indicate a rather long and narrow wing.