Gallinuloides wyomingensis Eastman, 1900

Weidig, Ilka, 2010, New Birds from the Lower Eocene Green River Formation, North America, Records of the Australian Museum 62 (1), pp. 29-44 : 30-31

Gallinuloides wyomingensis Eastman, 1900

Holotype. MCZ 342221 , complete articulated skeleton on a slab.

Referred specimen. WDC-CGR-012, complete articulated skeleton, from the 18-inch-layer (F1-locality of Grande, 1980), Upper Fossil Butte Member of Fossil Lake, Kemmerer, Wyoming ( Fig. 1 ) (also shown in Mayr & Weidig, 2004).

The locality of the holotype ( MCZ 342221) is described as “fish-bearing shales near Fossil, Wyoming ” by Eastman (1900: 54), which, according to Grande (1980), belongs to the same locality as the WDC specimen.

Remarks. An emended diagnosis of the Gallinuloididae , a differential diagnosis to separate Gallinuloides from Paraortygoides , characters pertinent to the systematic position of Gallinuloididae as well as the dimensions of the WDC specimen are already given in Mayr & Weidig (2004). In the following, additional characters of Gallinuloides wyomingensis visible on the WDC specimen are described.

Description. The skull of Gallinuloides is small in relation to overall body size as in other galliform birds. The beak of this fossil bird is relatively short and its oval nasal openings are large. Gallinuloides differs from extant galliforms in having a small processus postorbitalis, lacking an ossified aponeurosis zygomatica, having a well-developed os ectethmoidale (Mayr & Weidig, 2004) and a rather small prefrontal. In accordance with modern galliforms, the foramen magnum is shifted caudad. On the quadratum, the small knob between the processus oticus and the processus mandibularis which occurs in all Cracidae is absent in Gallinuloides .

The mandible of Gallinuloides has a short symphysis mandibularis and fenestrae mandibulares seem to be absent. Lucas (1900) stated that a processus retroarticularis is not present; in this respect, Gallinuloides would differ from all modern galliforms. However, the mandible of the holotype is only very poorly preserved and the presence, or absence, of a processus retroarticularis cannot be determined. Unfortunately, the WDC-CGR-012 specimen cannot clarify this point. Due to a slight slant of the mandible, the caudal end is not clearly visible and it is not possible to discern whether a processus retroarticularis is present.

The coracoid is rather stout; the processus acrocoracoideus is somewhat larger than that of Paraortygoides and is slightly hooked. In agreement with Paraortygoides and Paraortyx ( Mayr, 2000a; Mourer-Chauviré, 1992), a very small processus procoracoideus is present. The processus lateralis of the coracoid is only moderately extended, but, in contrast to extant genera, is divided into two tips. The facies articularis sterni is very high as in modern galliforms.

The humerus most closely resembles that of the extant Leipoa ocellata (Megapodiidae) and has a rounded and short crista deltopectoralis. Eastman (1900) remarked that Gallinuloides has a “broad deltopectoral crest”; however, it is not very broad for a galliform bird, having approximately the same relative size as that of Leipoa and is thus somewhat larger than that of Paraortygoides . As in extant galliforms, the ventral surface of the crista deltopectoralis is perpendicular to the cranial surface of the humerus shaft. The crista bicipitalis is rather small and the humeral shaft is slightly sigmoidally curved. The fossa m. brachialis is large but only moderately deep as in modern Leipoa , Alectura (Megapodiidae) and Ortalis (Cracidae) . The tuberculum supracondylare ventrale is rather pronounced.

The ulna is considerably curved and shows no papillae remigiales, its overall morphology resembles that of Paraortygoides . However, in contrast to Paraortygoides , the ulna of Gallinuloides is slightly longer than the humerus. The olecranon of Gallinuloides is moderately long, it is slightly longer than that of Paraortygoides . An impressio brachialis is present. The dorsal side of proximal end bears a distinct impression, distally of the processus cotylaris dorsalis. This impression is also exhibited by Paraortygoides ( Mayr, 2000a) and the cracids.

The carpometacarpus resembles that of Paraortygoides , the ossa metacarpalia are straight and parallel, the spatium intermetacarpale is narrow (Mayr & Weidig, 2004). The processus extensorius is large, and its tip is pointed proximo-cranially. The distal end of the carpometacarpus resembles that of Paraortygoides very closely: the synostosis metacarpalis distalis is long and fairly wide, the os metacarpale majus protrudes cranially, and the proximal phalanx of the digitus major has a long, deep sulcus and a deep, but small, oval fenestration. The distal phalanx of the digitus majoris distalis is longer than the proximal phalanx and the digitus alulae bears a claw.

In accordance with the condition seen in extant galliforms and Paraortygoides , the tibiotarsus of Gallinuloides is the longest limb element. The proximal end bears medium-sized cristae cnemiales. At the distal end, the condylus medialis is narrower mediolaterally than the condylus lateralis but protrudes considerably farther cranially. The same proportions are found in modern galliforms. However, in contrast thereto, both condyli have about the same size in Paraortygoides ( Mayr, 2000a) . The incisura intercondylaris is narrower than in Paraortygoides . A comparatively broad pons supratendineus is present.

The tarsometatarsus measures about two thirds of the length of the tibiotarsus. Not many details are discernible on the proximal end of the tarsometatarsus. At least one foramen vasculare proximale is present. The hypotarsus is not visible in either the holotype or the new specimen, therefore Lucas’ (1900) comments on it are only speculation. The tarsometatarsus of Gallinuloides has a large foramen vasculare distale, that of Paraortygoides is smaller. In distal view, the trochleae metatarsorum are situated along a curved line. The trochlea metatarsi III is the longest trochlea, followed by the trochlea metatarsi IV. The trochlea metatarsi II is considerably shorter than the trochlea metatarsi IV. In Gallinuloides , the trochlea metatarsi II extends plantad, to approximately the same degree as in Paraortygoides .

Discussion. Since the original description of Gallinuloides wyomingensis , various taxa have been included in the Gallinuloididae , and different systematic positions have been proposed (see e.g., Crowe et al., 2006; Crowe & Short, 1992; Dyke, 2003; Lucas, 1900; Mayr, 2008a; Mayr & Weidig, 2004). Based on the WDC specimen, Mayr & Weidig (2004) published an amended diagnosis of the Gallinuloididae , including only Gallinuloides and Paraortygoides in the taxon. According to Mayr & Weidig (2004), the Gallinuloididae belong to the stem-group of the Galliformes and represent a sister-taxon to all modern crown-group galliforms, since they exhibit several plesiomorphic characters such as the presence of a well-developed os ecthemoidale, poorly developed processus postorbitales, a cup-like cotyla scapularis of the coracoid, a long, slender scapula with a pointed caudal end, robust scapi claviculae of the furcula, a sternum with an apex carinae that is not displaced caudally, a narrow, elongated carpometacarpus with a straight os metacarpale minus, splayed trochleae metatarsorum, and the absence of ossified tendons. This result was recently supported by a phylogenetic revision using both morphological and molecular data of Gallinuloides wyomingensis and modern galliforms undertaken by Ksepka (2009), which also placed Gallinuloides clearly outside crown-group galliforms.

Figures

Figure 1. Gallinuloides wyomingensis, referred specimen WDC-CGR-012, scale bar 20 mm.