Chauvireria bulgarica sp. n. – an extinct Early Pleistocene small phasianid of Phasianinae Horsfield, 1821 from Bulgaria

A new species of small phasianid is described, based on 54 bone findings of 21 skeletal elements of forelimb and pectoral girdle (9) and hindlimb and pelvic girdle (12) representing at least four individuals. The holotype is the scapula. The new species differs from the type species (Chauvireria balcanica Boev, 1998) of the genus by: (1) the longer acromion scapulae, which is more upright and dorsally instead of cranially directed, (2) the thinner humeral part of the coracoid, and (3) the wider condylus dorsalis of the humerus. The species probably inhabited rocky, open shrubby and dry habitats in the middle Villafranchian (Villanyian; first half of MNQ 18 a; 2.1–1.95 Mya) in western Bulgaria.


Introduction
Small phasianids (Phasianinae Horsfield, 1821) are a highly diversified group of gallinaceous birds, both in recent and fossil faunal assemblages. They inhabit a wide range of habitats, both of open and forested landscapes. Recent world fauna of small phasianids (former Perdicinae) numbers 106 species (McCowan, 1994). The fossil record of the subfamily after Brodkorb (1964) covers at least 24 species. Bochenski (1997) lists ca. 38 species only in Europe, while Mlíkovský (2002) reduces their number to 14 species (of Cenozoic).

Description of the Slivnitsa locality site
The material was collected from a stockpile -a landfill containing a rock mass of a blasted cave (karst cavern) in Jurassic limestone. According to Spassov (1997), the even distribution of finds of the same species of large and small mammals, the uniform fossilisation of the bones and the homogeneity of the faunistic mammalian complex confirm the chronological identity of the palaeozoological material. The existence of a former cave where the remains had been accumulated was also confirmed by the presence of fragments of stalactites.

Systematic part
All the 21 skeletal elements morphologically (and morphometrically) resemble the homologous elements of partridges, quails and francolins, i. e. to small-sized phasianids. No species of small phasianids in the fossil record of Europe and the Middle East of the same or similar size are known except Chauvireria balcanica Boev, 1997, the only species of genus Chauvireria.
Locality: A destroyed cave in a rocky hill in the operating area of the Kozyaka stone quarry (Fig. 1) (Spassov, 1998). Recently, the site was dated between ca. 2.1 and 1.95 Ma (Spassov, 2016).
Horizon: Unconsolidated, unstratified bone elements accumulated in the filling of clay terra-rossa. Most of the fossil bones were broken. All finds were disarticulated. The bone material was collected from the transported and dumped mass of stones and soil in the quarry (Boev, 1998a).
Etymology: The name "bulgarica" is given after the name of the state of Bulgaria, where the finds originated from.
Comparison: The articular surface of the scapula differs from that of Ammoperdix griseogularis Brandt, 1843 by the sharper acromion. It differs from C. balcanica by the longer acromion, which is more upright and dorsally, instead cranially, directed. (Plate 1: a). This feature is very clear. It differs from A. heyi (Temminck, 1825) by the wider f. a. hum. and the longer acromion. Chauvireria bulgarica sp. n. has the longest acromion of all compared small phasianids (see below). It is distinguished from Ptilopachus petrosus Gmelin, 1789 by the bigger f. a. clavicularis and the less sharpened caudal edge of the f. a. hum., as well as by the absence of the fovea between the humeral and clavicular articular surfaces. The new species differs from Synoicus ypsilophorus (Bosc, 1792) by the bigger size (Table 1) and the more square than triangle f. a. hum. It differs from Caloperdix oculeus (Temminck, 1815) by the smaller dimensions, the longer and thinner f. a. clavicularis and the sharper ventromedial angle of f. a. hum.  Table 3): C. bulgarica sp. n. differs from C. balcanica by the more protruding tuberculum bicipitale radii and the narrower cotyla hum. It differs from A. griseogularis by the less protruding tuberculum bicipitale radii and the narrower cotyla hum. From A. heyi the compared species differs by the narrower longitudinal ridge on the medio-cranial surface in the prox. half of diaphysis. From Ptilopachus it differs by the narrower prox. epiphysis, and the more developed tuberculum bicipitale radialis. From S. ypsilophorus it differs by the more rounded, instead of oval, cotyla hum. and the bigger size. It differs from C. oculeus by the smaller dimensions and the less developed tuberculum bicipitale radii.

Comparison of other skeletal elements
Coracoid (Plate 1: h; Table 4): C. bulgarica sp. n. differs from A. griseogularis metrically (it is smaller). Its prox. part is much thinner. It is thinner even than that of C. balcanica and the hook of pr. acrocoracoideus is more prominent. F. a. hum. of C. bulgarica sp. n. is more concave. The impressio ligamenti acrocoracoidei is narrower and shallower than that of A. griseogularis. It differs from A. heyi by the narrower acrocoracoidal part and the bigger hook of pr. acrocoracoideus and the deeper impressio ligamenti acrocoracohumeralis. Ammoperdix heyi has a dent on the hook of pr. acrocoracoideus. Ptilopachus differs from C. bulgarica sp. n. by the lacking of a hook of pr. acrocoracoideus and the rounded acrocoracoid, as well as by the lighter medio-lateral inclination in cranial view and the less protruded latero-caudal ridge of f. a. hum. S. ypsilophorus differs from C. bulgarica sp. n. by the smaller sizes, the lacking hook of pr. acrocoracoideus and the less concave f. a. clavicularis. Chauvireria bulgarica sp. n. differs from C. oculeus by its smaller size, the lacking hook of pr. acrocoracoideus, the stronger caudal bend of f. a. hum. and the stronger cranio-lateral inclination of f. a. clavicularis.
Cmc (Plate 1: g; Table 5): The new species from Slivnitsa locality is smaller than A. griseogularis and C. balcanica. It differs by the almost perpendicular cranial ridge of pr. extensorius towards the axis of os met. majus. Its pr. pisiformis protrudes less than in C. balcanica. Its trochlea carpalis is narrower and in cranial profile it is almost even or slightly protruding, but it is not concave as in A. griseogularis. It is also concave in C. balcanica. Os met. majus is straighter and thinner in the distal end than in C. balcanica and A. griseogularis. Chauvireria bulgarica sp. n. has the deepest sulcus interosseus in comparison with the other two species. It differs from A. heyi by the thinner pr. extensorius in cranial view, the better-expressed ridge between the cranio-lateral and the dorsal surface of os met. majus, the shorter synostosis of met. dist., the deeper fovea between f. a. dist. of os met. majus and f. a. dist. of os met. minus, the deeper fovea between the os m. majus and os m. minus on the ventral surface of the distal end. It differs from Ptilopachus in the sharper and more cranially positioned pr. pisiformis, the sharper pr. extensorius, the narrower trochlea carpalis (3.2 mm and 2.6 mm, respectively) and the narrower dist. epiphysis. It differs from S. ypsilophorus by the straighter instead of concave latero-cranial ridge of proc. extensorius and the straighter diaphysis of os met. majus. It differs from C. oculeus by the sharper pr. extensorius, the straighter diaphysis of the os met. majus, a less prominent in caudo-lateral direction facies articlaris distalis metacarpalis minus, and the sharper pr. pisiformis.
Ulna (Plate 1: f; Table 6): C. bulgarica sp. n. differs from C. balcanica by the smaller dimensions, blunter and more round dist. end of impressio brachialis, smaller tuberculum carpale, and the shallower incissura tendinea. It differs from A. griseogularis by the smaller size and the sharper prominent distally condylus ventralis ulnaris. It is distinguished from A. heyi by the sharper edge between c. dorsalis ulnaris and diaphysis and sharp strongly protruding caudally c. vent. ulnaris and the shallower fovea. The described new species of Chauvireria differs from Ptilopachus by the narrower dist. epiphysis, narrower and longer c. vent. ulnaris and by the presence of a dent. It differs from S. ypsilophorus by the higher and sharper c. vent. ulnaris, bigger size, and the more round shape of c. dorsalis ulnaris. It also differs from C. oculeus by the smaller dimensions, the longer c. vent. ulnaris, the shallower depressio radialis, and the more rounded instead of a triangle-shaped cross-section of the diaphysis in its distal end. Furcula (Plate 1: i, j; Table 7): C. bulgarica sp. n. differs from A. griseogularis and resembles C. balcanica by the ribbing of the hypocleidium in lateral view. In contrast to A. griseogularis its symphysis furculae is concave in cranial view instead protruding at the base of the hypocleidium. C. balcanica differs by the steeper caudal orientation of the caudal ridge of hypocleidium and thus resembling to A. griseogu-laris. It differs from A. heyi by the lacking of a cranial concaveness in lateral view and the wider symphysis in frontal view. It differs from C. oculeus by the concave cranial surface of symphysis furculae and the smaller size.
Phalanx proximalis digitis majoris (Plate 1: l; Table 9): C. bulgarica sp. n. differs from A. griseogularis and C. balcanica by the longer fovea in the dist. end on the lateral (dorsal) side, the thinner ventral ribbing ridge on the medial (ventral) side. It differs from A. heyi by the relatively wider phalanx in the middle (4.2 and 3.75 and 3.7) and by the deeper fovea on the f. vent. (medialis). It differs from Ptilopachus by the longer phalanx, the shallower cut of the ventr. part. The compared species differs from S. ypsilophorus by the arc-like ventro-caudal edge, the larger size and more protruding caudally tip backwards. It differs from C. oculeus by the more elongated phalanx in lateral view, smaller size, more concave caudal half of the latero-caudal surface.
Hindlimb and pelvic girdle • Femur (Plate 2: a, b; Table 10): C. bulgarica sp. n. differs from C. balcanica and A. griseogularis by the deeper fossa poplitea, bigger cranio-caudal dimension, and the thinner c. medialis in cranial view. It differs from A. heyi by the more round c. medialis, the straighter transition of the condyle to the diaphysis, the shallower impressio ligamenti cruciati cranialis. From Ptilopachus the species differs by the narrower sulcus intercondylaris and the less developed crista tibiofibularis. It differs from S. ypsilophorus by the deeper fossa poplitea and the more round c. medialis in medial view. It differs from C. oculeus by the shallower fossa poplitea and the relatively narrower and deeper sulcus intercondylaris.
Tbt (Plate 2: c-e; Table 11): C. bulgarica sp. n. metrically fits in the range of the type species C. balcanica. C. bulgarica sp. n. differs from C. balcanica by the longer pons supratendineus, wider dist. opening of incissura supratendinea, the sharper verge and the deeper incissura intercondylaris. It differs from C. balcanica and A. griseogularis by the smaller epicondylus medialis and the shallower and wider intercon-dylar space. The compared species differs from A. heyi by the smaller epicondylus medialis, the round instead straight ridge of pons supratendineus, the shallower incissura intercondylaris, and the longer and narrower incissura tendinea lat. over distal epiphysis. Differences from Ptilopachus: narrower dist. epiphysis, narrower dist. opening of pons supratendineus, narrower sulcus extensorius, pons supratendineus, incissura intercondylaris, prox. epiphysis, area intercondylaris and the shorter crista cnemialis cranialis, as well as the smaller diameters of c. lat. and c. medialis. It differs from S. ypsilophorus by the oval instead round profile of c. lat., less concaved pons supratendineus, larger epicondylus lat., more elongated cranio-caudally f. a. proximalis. It differs from C. oculeus by the relatively deeper incissura intercondylaris, more prominent instead concave pons supratendineus, more clearly shaped epicondylus lat., narrower prox. epiphysis, less developed longitudinal ribbing of f. caudalis in the middle part of diaphysis.
Tmt (Plate 2: f-l; Table 12): C. bulgarica sp. n. differs from C. balcanica by the more angular instead of the round cotyla medialis in dorsal view. This makes it look more similar to A. griseogularis, although it differs from that species metrically and by the narrower hypotarsus. In comparison to both species of genus Ammoperdix, C. bulgarica sp. n. has lower eminentia intercondylaris and wider foramen vasculare distale. It differs from A. heyi by the less concave cotyla medialis, the narrower trochlea metatarsi III, and narrower incissura intertrochlearis medialis. It differs from Ptilopachus by the smaller foramen vasculare distale, narrower epiphysis and diaphysis (the whole bone is more gracile), lower crista medialis hypotarsi, a lower cotyla medialis (its medial ridge), a less developed crista plantares medialis and crista lateralis, and a less prominent trochlea metatarsi III over tr. metatarsi II and IV. It differs from S. ypsilophorus by the larger size and the more proximally positioned f. vas. distale, the relatively narrower hypotarsus and the more rounded cotyla medialis in dorsal view. From C. oculeus it differs by the smaller size, and the lacking of a longitudinal ridge on the crista medialis hypotarsi on the caudal side of the diaphysis, the more proximally positioned foramen vasculare distale, as well as the straighter, instead of a rounded, lateral edge of cotyla lateralis.
Phalanx I dig. 1 pedis (Plate 2: m -left): C. bulgarica sp. n. differs from C. balcanica by the relatively wider distal end of diaphysis just before the trochlea.
It differs from A. griseogularis by the higher vault of the phalanx, as well as metrically. It differs from Coturnix coturnix (Linnaeus, 1758) by the triangular instead of a heart-shaped profile of f. art. prox., as well as dimensionally. It differs from A. heyi in the longer phalanx and the more symmetrical trochlea.
Phalanx I dig. 2 pedis (Plate 2: m -middle): It differs from C. coturnix by the deeper fovea. From A. griseogularis it differs by the smaller size, the shallower intercondylar sulcus of the trochlea and the ventrally lowered trochlea in the dist. end.which is slightly prominent in A. griseogularis. The Bulgarian Chauvireria differs from A. heyi by the narrower trochlea and the relatively thinner phalangeal body.
Phalanx I dig. 4 pedis: C. bulgarica sp. n. differs from C. balcanica by the more rounded heart-like profile contour of f. a. prox. and the deeper fovea on the ventral surface of the distal end.
Phalanx II dig. 4 pedis: C. bulgarica sp. n. differs from C. balcanica by the thinner prox. part, the smaller f. a. prox. and the smaller trochlea. It differs from A. griseogularis by the smaller size and the lack of ventral longitudinal ridges.
Phalanx III dig. 4 pedis: C. bulgarica sp. n. differs from A. griseogularis by the relatively longer widening of f. a. prox. of its dorsal end and the more conically, instead of constricted, shape of the middle of the phalangeal body. It differs from C. balcanica by the heart-like profile of f. art. prox. and the thicker corpus phalangis.

Conclusions
Chauvireria bulgarica sp. n. is the second known species in the genus. The type species, C. balcanica Boev 1997 was described also from the early Pleistocene of W Bulgaria and the deposits of its fossil remains are also dated to the middle Villafranchian (MN 17;2.5-2.3 Mya;Spassov, 2016). Chauvireria bulgarica sp. n. lived at least ca. 0.4 Mya later than C. balcanica. In general, C. bulgarica sp. n. is slightly smaller than the older C. balcanica (Tables 1-4, 6-12).
Chauvireria bulgarica, in comparison to other species (C. balcanica), inhabited less forested landscape, although it was recorded also in dry xerophytic open habitats. We know that also rocky massifs and lakes existed in the region of the site. The dominance of (both in species and in finds) Bovidae (Caprinae) over Cervidae suggests more open environments. "The more intense drying in Slivnitsa in comparison with Varshets ought to be connected mainly with the climatic landscape changes in the time." (Spassov, 1997: 675). Numerous chauvirerias (C. balcanica in Varshets locality and C. bulgarica sp. n. in Slivnitsa locality) possibly disappeared because of the changes of grass vegetation or forests expansion before the first cooling of the Pleistocene. Obviously, they both have played an important role in the palaeornithocoenoses as an abundant and accessible prey for the large nocturnal raptors. Large owls (eagle owls of the genus Bubo Duméril, 1805) were the most probable agent for the accumulation of their fossil bones in the former caves of both localities.