1. Introduction

Europe has a comparatively rich early and middle Eocene fossil record and numerous avian remains were also described from Neogene fossil sites (Mlíkovský 2002; Mayr 2009). Late Eocene and Oligocene avifaunas, however, are less well known, even though at those times large parts of the continent were covered by a shallow inland sea, the Paratethys, which offered favorable conditions for the preservation of fossil remains.

Indeed, most of the few early Oligocene (Rupelian) fossil sites in Central Europe that yielded avian remains originate from sediments of the Paratethys (Mayr 2009; Bochenski et al. 2013a; Mayr & Smith 2013; Maxwell et al. 2016). This is also true for various localities in southeast Poland, from which bird remains have been described in the past years (Bochenski et al. 2013a). The reported avifaunas from the Polish sites are diverse and include remains of the procellariiform Diomedeoididae (Elzanowski et al. 2012), Galliformes (Tomek et al. 2014), stem group Trochilidae (Bochenski & Bochenski 2008; a very small foot of uncertain affinities described by Bochenski et al. 2016 is likely to be also from a stem group representative of the Trochilidae), Ralloidea (Mayr & Bochenski 2016), Upupiformes (Mayr et al. in press b), various Passeriformes (Bochenski et al. 2011, 2013b, 2014a, b, 2018), and fragmentary remains of uncertain affinities (Bochenski et al. 2010).

Here, I describe a new avian fossil from the locality Jamna Dolna in southeast Poland. The specimen consists of a partial skeleton of a small bird, which was found by an amateur collector and was acquired by the Senckenberg Research Institute Frankfurt in 2018. The locality Jamna Dolna comprises two fossil sites — Jamna Dolna 1 and 2 — which are separated by two kilometers and differ in their lithology (Bieńkowska-Wasiluk 2010). The new fossil is from the black shales of the Menilite beds of Jamna Dolna 2, which are exposed on the eastern side of the Jamninka river (Bieńkowska-Wasiluk 2010). It is the second avian specimen described from this site, which has before yielded an unnamed small species of the Ralloidea (Mayr & Bochenski 2016). From Jamna Dolna 1, records of the Passeriformes (Bochenski et al. 2011) and Upupiformes (Mayr et al. in press b) were described.

2. Material and methods

Like other bird skeletons from the Menilite beds in southeast Poland, the new fossil was split in two halves so that only the interior of the bones is exposed. A transfer preparation is not feasible, because the small and delicate bones are embedded in a very hard matrix, which can neither be acid prepared nor dissolved in water.

The fossil is deposited in the Senckenberg Research Institute Frankfurt, Germany (SMF). Measurements refer to the maximum length of a bone along its longitudinal axis.

Fig. 1.

The holotype of Carpathiavis meniliticus gen. et sp. nov. from the Rupelian of Jamna Dolna 2 in southeast Poland. A: specimen SMF Av 649a. B: specimen SMF Av 649b. To enhance the contrast of the photos, the fossil was coated with ammonium chloride. Abbreviations: cor, ?left coracoid; fur, furcula; lcm, left carpometacarpus; lfe, left femur; lhu, left humerus, lra, left radius; ltb, left tibiotarsus; lul, left ulna; pel, pelvis; rcm, right carpometacarpus; rfe, right femur; rhu, right humerus, rra, right radius; rul, right ulna; sca, ?left scapula; sku, skull; ste, sternum. The scale bars equal 10 mm.

3. Systematic paleontology

Fig. 2.

Carpathiavis meniliticus gen. et sp. nov., overview of the two slabs containing the holotype in their actual (uncoated) state and detail of cervical column. A: specimen SMF Av 649a. B, C: specimen SMF Av 649b. The cervical vertebrae are numbered (note that identification of some individual vertebrae is tentative and the total count uncertain). Abbreviations: cer, ceratobranchiale; otr, ossified tracheal rings. The scale bars equal 10 mm. In C, the fossil was coated with ammonium chloride.

Fig. 3.

Carpathiavis meniliticus gen. et sp. nov., details of the pectoral girdle. A: furcula and coracoid of SMF Av 649b; the white arrows delimit the processus lateralis of the coracoid. B, C: furcula and coracoid of SMF Av 649a. D: sternum of SMF Av 649b. E: sternum of SMF Av 649a. F: coracoid of C. meniliticus with surrounding matrix digitally removed. G: furcula of C. meniliticus with surrounding matrix digitally removed; the grey areas indicate reconstructed parts of the bone. H: left coracoid of Pardirallus maculatus (Rallidae). I: left coracoid of Coua cristata (Cuculiformes). J, furcula of Aramides saracura (Rallidae). K: furcula of C. cristata. Abbreviations: acr, acromion of scapula; agm, angulus medialis; apc, apex carinae; apf, apophysis furculae; cpp, crista procoracoidei; exo, extremitas omalis of furcula; fns, foramen nervi supracoracoidei; icl, incisura lateralis; icm, incisura medialis; pac, processus acrocoracoideus; pcl, processus craniolateralis; ppc, processus procoracoideus; rhu, right humerus; spe, spina externa; tim, trabecula intermedia; tla, trabecula lateralis; tmd, trabecula mediana. The scale bars equal 10 mm. In all images, the fossil was coated with ammonium chloride.

Fig. 4.

Carpathiavis meniliticus gen. et sp. nov., details of the wing and pelvis. A, B: left humerus of SMF Av 649a (A) and SMF Av 649b (B; note that this specimen represents only a mold of the bone). C: hand section of right wing (SMF Av 649a). D: hand section of left wing (SMF Av 649b). E, F: left carpometacarpus (E: SMF Av 649a, F: SMF Av 649b). G, H: pelvis (G: SMF Av 649a, H: SMF Av 649b). Abbreviations: api, ala praeacetabularis ilii; cdv, condylus ventralis; cmc, carpometacarpus; ito, intratendinous ossification; lfe, left femur; min, phalanx digiti minoris; pda, phalanx digiti alulae; pdm, phalanx distalis digiti majoris; pex, processus extensorius; ppm, phalanx proximalis digiti majoris; pub, pubis; rfe, right femur; syn, synsacrum. The scale bars equal 10 mm. In all images, the fossil was coated with ammonium chloride.

Fig. 5.

Furcula (A, B), left humerus (C, D), and sternum (E, F) of Carpathiavis and Eocuculus. A, C, E: Carpathiavis meniliticus (SMF Av 649a). B, D: ?Eocuculus sp. from the early Oligocene of the Luberon area in France (SMF Av 424). F: Eocuculus cf. cherpinae from the early Oligocene of the Luberon area in France (SMF Av 425). Abbreviations: apc, apex carinae; apf, apophysis furculae; lhu, left humerus; pcl, processus lateralis; rco, right coracoid. The scale bars equal 10 mm. In all images, the fossils were coated with ammonium chloride.

4. Discussion

Carpathiavis meniliticus gen. et sp. nov. is a small bird, about the size of the smallest extant Rallidae (e.g., Porzana flaviventer). The holotype displays very poor bone preservation and critical osteological features, such as the morphology of the beak and feet, are not preserved. However, even though only a limited amount of osteological details can be recognized, a few characteristic features are visible. The most distinctive of these is the long, rodlike apophysis furculae (“hypocleidium”) of the broadly Ushaped furcula. An apophysis furculae of similar length occurs in only a few extant avian taxa, that is, some Galliformes and Cuculiformes, as well as in the otherwise very different Opisthocomiformes (in which the furcula is Vshaped and fused with the coracoids and the sternum) and Sagittariidae (Accipitriformes); in the gruiform Heliornithidae and in the Trogoniformes, the apophysis is also rodshaped but shorter than in C. meniliticus. Another characteristic of the new fossil concerns the length proportions of the wing bones, with the ulna being subequal in length to the humerus. This latter feature distinguishes C. meniliticus from most representatives of the arboreal land bird clade (Telluraves), in which the ulna is usually distinctly longer than the humerus.

Compared with previously described birds from the early Oligocene of Europe, C. meniliticus shows some resemblance to the taxon Eocuculus, which has been reported from the late Eocene of North America and the early Oligocene of France (Chandler 1999; Mayr 2006). Originally described as a representative of the Cuculiformes (Chandler 1999), Eocuculus has later been considered to be possibly related to the early Eocene Pumiliornis tessellatus (Mayr 2008). Subsequent analyses identified Pumiliornis as a stem group representative of the Passeriformes (Mayr 2015; Ksepka et al. 2019), and although some of these analyses suggested close affinities between Eocuculus and the clade including Pumiliornis and Passeriformes, the affinities of Eocuculus remain poorly resolved. Carpathiavis and Eocuculus cherpinae, the only named species of the taxon Eocuculus, share a furcula with a long apophysis (Fig. 5A, B) and similar length proportions of the major wing bones. However, Carpathiavis is distinguished from Eocuculus fossils from the early Oligocene of France (Mayr 2006, 2008) in the narrower humerus (Fig. 5C, D), the rounded apex carinae of the sternum (Fig. 5E, F), the shorter processus lateralis of the coracoid (compare Figs. 3A and 5D), and the narrower pelvis. The morphologies of the apex carinae and processus lateralis are not visible in the North American holotype of E. cherpinae, but the pelvis of this fossil is likewise wider than in the new species, and the E. cherpinae holotype furthermore differs from Carpathiavis in the longer processus internus indicis of the phalanx proximalis digiti majoris of the wing. With regard to possible affinities between Carpathiavis and Eocuculus, it is worth mentioning that Bochenski et al. (2010) reported a partial foot from the Menilite beds, which they considered similar to the foot of Eocuculus and Pumiliornis. However, with a tarsometatarsus length of 21.7 mm, this fossil is too large to belong to Carpathiavis (with a humerus length of 27.0 mm, E. cherpinae is much larger than C. meniliticus but has a tarsometatarsus length of only 17.0 mm; Chandler 1999).

In addition to the proportionally shorter ulna, C. meniliticus differs from crown group Passeriformes, which are comparatively abundant in early Oligocene localities of southeast Poland (Bochenski et al. 2011, 2013b, 2014a, b, 2018), in the smaller and much more robust furcula and in the absence of a processus intermetacarpalis (carpometacarpus). Like most other Telluraves, crown group passerines have 19 praesacral vertebrae, but 21 praesacral vertebrae were reported for putative stem group representatives (i.e., the early Eocene Psittacopedidae; Mayr 2015).

Compared to extant birds, C. meniliticus resembles some Cuculiformes in the morphology of the pectoral girdle, especially the long apophysis furculae (Fig. 3K), the slender coracoid, and the short sternum. However, these similarities are not very specific and there are numerous differences between C. meniliticus and extant Cuculiformes, including a higher number of praesacral vertebrae (Cuculiformes only have 18 praesacral vertebrae), a rounded apex carinae of the sternum (pointed in the Cuculiformes), the absence of marked papillae remigales (ulna), the proportionally longer and more elongate carpometacarpus, and the narrower pelvis. Except for the similar morphology of some of the pectoral girdle bones, no osteological features convincingly suggest closer affinities between Carpathiavis and cuculiform birds.

In addition to the largely obscured surface details of most major bones, a major impediment in determining the phylogenetic affinities of Carpathiavis is the lack of the feet of the fossil. These preservational limitations make it difficult to narrow down the higher level affinities of C. meniliticus, and in overall morphology, especially regarding the shape of the long and slender carpometacarpus and the narrow pelvis, the new species also has a somewhat “raillike” appearance. As noted in the introduction, the type locality (Jamna Dolna 2) yielded an unambiguous record of the Ralloidea, the clade including the extant Sarothruridae, Rallidae, and Heliornithidae (Mayr & Bochenski 2016). However, this fossil exhibits the characteristics of extant Rallidae and Sarothruridae and although it represents a rather small species by comparison with extant Rallidae, it distinctly exceeds the new species in size (humerus length 28.2 mm versus 18.5/20.0 mm in C. meniliticus). The new species is furthermore clearly distinguished from all extant Ralloidea in a number of osteological characteristics, including the stouter humerus, the proportionally longer ulna (which is distinctly shorter than the humerus in extant Ralloidea), the long apophysis furculae (compare Figs. 3G and 3J), as well as the more slender shaft of the coracoid, which does not form a crista procoracoidei (compare Figs. 3F and 3H).

With regard to the proportions of the wing bones, Carpathiavis corresponds to the extinct Paleogene Songzia, which is the type genus of the putatively ralloidean taxon Songziidae (Wang et al. 2012). The shape of the apophysis furculae of Songzia is unknown, but in Carpathiavis the scapi clavicularum are proportionally wider and the new taxon also differs from Songzia in the deeper incisions in the caudal margin of the sternum (compare Fig. 5E with Wang et al. 2012: fig. 7). Songzia was initially reported from the early Eocene of China, but Songzialike birds have also been described from the late Paleocene of France (Mayr et al. 2019) and from the early Eocene of Canada (Mayr et al. in press a). However, no postEocene records of Songzialike birds were identified and C. meniliticus is more than 15 million years younger than previous fossils of the taxon.

A superficially raillike morphology of the limb bones is also found in some Paleogene Galliformes, such as the Eocene Gallinuloididae and Quercymegapodiidae (Mourer-Chauviré 1992; Mayr & Weidig 2004), but C. meniliticus is distinguished from all galliform birds in the welldeveloped processus procoracoideus of the coracoid and in the shape of the processus acrocoracoideus, which is more sharply bent and less protruding in omal direction in Galliformes, as well as in the shorter sternum and the absence of a notarium. In most galliform birds, the apophysis furculae is furthermore bladelike rather than rodshaped.

Even though it is not possible to determine the exact affinities of C. meniliticus, the new species clearly represents a distinctive taxon that has not previously been reported from the early Oligocene of Europe. As such, it contributes to a better understanding of local Rupelian avifaunas in southeast Poland and documents our poor knowledge of the avifaunas of this geological stage. Whereas early Eocene avifaunas are characterized by extinct taxa without close extant counterparts, early Oligocene avifaunas often include birds that more closely resemble modern avian groups (Mayr 2009). C. meniliticus clearly differs from all extant avian clades in its skeletal morphology and adds to a number of equally enigmatic early Oligocene taxa, such as the abovementioned Eocuculus or the tiny, putatively piciform Sylphornithidae (Mayr & Smith 2002). Given the pace of new discoveries from the Rupelian localities in southeast Poland, it is to be hoped that a more complete and better preserved specimen of C. meniliticus will be found in the near future, in order to shed more light on the phylogenetic affinities of this enigmatic species.