FIdiornithidae and fElaphrocnemus

Most representatives of the Cariamae from the Paleogene of Europe were assigned to the Idiornithidae. These birds were first reported from the Quercy fissure fillings, where they constitute the most abundant medium-sized birds and occur in middle Eocene to late Oligocene deposits (Mourer-Chauvire 1983a, 2006). Idiornithids were also identified in the middle Eocene of Messel and the Geisel Valley in Germany (Peters 1995; Mayr 2000d, 2002a). Mourer-Chauvire (1999b, p. 85) further mentioned the presence of still undescribed idiornithid-like birds in the Paleocene of Brazil.

As currently recognized (Mourer-Chauvire 1983a, 2006), the Idiornithidae include the taxa Idiornis, Elaphrocnemus, Oblitavis, Occitaniavis, and Propelargus. Only the first two of these are well represented by numerous postcranial bones, and as detailed below, a clade including these five taxa still needs to be established with derived characters.

Mourer-Chauvire (1983a) distinguished the following six species of Idiornis in the Query material: Idiornis cursor (Milne-Edwards, 1892), I. gaillardi Cracraft,

1973, I. gallicus (Milne-Edwards, 1892), I. gracilis (Milne-Edwards, 1892), I. minor (Milne-Edwards, 1892), and I. itardiensis Mourer-Chauvire, 1983. The species from Messel were described as Idiornis tuberculata Peters, 1995 and Idiornis cf. itardiensis. The former is based on a largely complete but poorly preserved skeleton, and the latter on an isolated foot (Peters 1995; Mayr 2000d). The large ?Idiornis anthracinus Mayr, 2002 from the Geisel Valley is known from a tarsometatarsus.

The Quercy species of Idiornis greatly vary in size and most are smaller than extant Cariamidae, with the tarsometatarsus of the smallest species, I. gracilis, measuring less than one third of that of the extant C. cristata. The largest Quercy species, I. itardiensis, corresponds in size to I. tuberculata from Messel.

Osteologically, the taxon Idiornis is very similar to extant Cariamidae (Fig. 13.2). The small species were long-legged birds with gracile hindlimbs. As in extant Cariamidae the hypotarsus is block-like and does not enclose canals for the flexor tendons of the toes. The coracoid exhibits the characteristic derived morphology of that bone in modern seriemas, in that the acrocoracoid and procoracoid processes are connected, or at least nearly so, by an osseous bridge (Fig. 13.2). Likewise, the other limb bones closely correspond to those of extant Cariamidae.

The holotype specimen of I. tuberculata still constitutes the only articulated skeleton of an idiornithid. This species is also the only one in which a cranium is preserved, and is further most remarkable for the occurrence of numerous small bony tubercles on the cervical vertebrae and a few other bones. Similar vertebral tubercles were also reported from another as yet undescribed species from Messel and from an isolated cervical vertebra from Quercy, the latter possibly belonging to the Idiornithidae (Mayr 2007e). As evidenced by the I. tuberculata skeleton and in contrast to the hallux of extant Cariamidae, the hallux of Idiornis was well developed.

The tarsometatarsi of the middle Eocene Messel and Geisel Valley species (I. tuberculata, I. cf. itardiensis, and ?I. anthracinus) are stouter than the gracile ones of most idiornithid species from the Quercy fissure fillings. Accordingly, these species were probably less cursorial than the Quercy species of Idiornis, and the different proportions of the tarsometatarsi may reflect a different paleoenvironment of the fossil sites, which was forested in the German localities but more arid and open in the Quercy ones.

The species of Elaphrocnemus represent the most abundant medium-sized birds in the nineteenth century Quercy collections. Mourer-Chauvire (1983a) recognized three species, E. phasianus Milne-Edwards, 1892, E. crex Milne-Edwards, 1892, and E. brodkorbi Mourer-Chauvire, 1983, which mainly differ in size. She further noticed that the wing bones assigned to "Filholornis" by Milne-Edwards (1892) belong to the same taxon as the hindlimb elements described as Elaphrocnemus by that author (see also Olson 1985). New excavations have shown that E. phasianus occurs in late Eocene deposits, whereas E. crex is only known from Oligocene sites (Mourer-Chauvire 1983a). The few fossils of E. brodkorbi lack stratigraphic data.

The Elaphrocnemus species were rather small birds, the size of small to medium-sized phasianids. Some skeletal elements are very different from those of Idiornis and extant seriemas. Although the humerus, for example, is of similar

Heterodontosaurids

Fig. 13.2 Comparison of selected skeletal elements of some Idiornithidae from the Quercy fissure fillings in France (b-f) with the extant Red-legged Seriema, Cariama cristata (Cariamidae) (a, g, h). a Right tarsometatarsus; b right tarsometatarsus of Idiornis gallicus (Milne-Edwards, 1892) (Muséum National d'Histoire Naturelle, Paris, France, MNHN QU 15502 [3002]); c left tarsometatarsus of I. minor (Milne-Edwards, 1892) (MNHN QU 15547 [3047]); d left tarsometatarsus of I. gaillardi Cracraft, 1973 (MNHN QU 15534 [3034]); e left coracoid of I. cursor (Milne-Edwards, 1892) (MNHN QU 15775 [3275]); f right carpometacarpus of I. cursor (MNHN QU 15751 [3251]); g left coracoid; h right carpometacarpus. Same scale for b-h. (Photos of the idiornithid bones courtesy of Cécile Mourer-Chauviré)

Cariama

Fig. 13.2 Comparison of selected skeletal elements of some Idiornithidae from the Quercy fissure fillings in France (b-f) with the extant Red-legged Seriema, Cariama cristata (Cariamidae) (a, g, h). a Right tarsometatarsus; b right tarsometatarsus of Idiornis gallicus (Milne-Edwards, 1892) (Muséum National d'Histoire Naturelle, Paris, France, MNHN QU 15502 [3002]); c left tarsometatarsus of I. minor (Milne-Edwards, 1892) (MNHN QU 15547 [3047]); d left tarsometatarsus of I. gaillardi Cracraft, 1973 (MNHN QU 15534 [3034]); e left coracoid of I. cursor (Milne-Edwards, 1892) (MNHN QU 15775 [3275]); f right carpometacarpus of I. cursor (MNHN QU 15751 [3251]); g left coracoid; h right carpometacarpus. Same scale for b-h. (Photos of the idiornithid bones courtesy of Cécile Mourer-Chauviré)

overall proportions, it exhibits a strongly protruding, triangular deltopectoral crest. The scapula is peculiar in that it bears an extremely elongated acromion that serves to close the triosseal canal, which in Idiornis and extant Cariamidae is achieved by fusion of the procoracoid and acrocoracoid processes of the coracoid (Figs. 13.2, 13.3; Mayr and Mourer-Chauvire 2008). The tarsometatarsus is proportionally shorter than that of Idiornis and extant Cariamidae, and exceeds the femur only slightly in length. Mayr and Mourer-Chauvire (2006b) tentatively assigned a three-dimensionally preserved skull and several crania from an unknown locality and horizon of the Quercy fissure fillings to Elaphrocnemus phasianus. The skull

Elaphrocnemus

Fig. 13.3 Selected skeletal elements of the putative idiornithid Elaphrocnemus phasianus Milne-Edwards, 1892 from unknown horizons of the Quercy fissure fillings. a Skull (Muséum National d'Histoire Naturelle, Paris, France, MNHN QU 15688); b left coracoid (Naturhistorisches Museum Basel, Basel, Switzerland, NMB Q.D.242); c cranial extremity of left scapula (NMB Q.D.293); d left humerus (NMB Q.W.1755); e right femur (NMB Q.D.678); f right tibiotarsus (NMB Q.D.304/330); g left tarsometatarsus (NMB Q.H.158). All images to scale. (Photos by Sven Tränkner)

Fig. 13.3 Selected skeletal elements of the putative idiornithid Elaphrocnemus phasianus Milne-Edwards, 1892 from unknown horizons of the Quercy fissure fillings. a Skull (Muséum National d'Histoire Naturelle, Paris, France, MNHN QU 15688); b left coracoid (Naturhistorisches Museum Basel, Basel, Switzerland, NMB Q.D.242); c cranial extremity of left scapula (NMB Q.D.293); d left humerus (NMB Q.W.1755); e right femur (NMB Q.D.678); f right tibiotarsus (NMB Q.D.304/330); g left tarsometatarsus (NMB Q.H.158). All images to scale. (Photos by Sven Tränkner)

exhibits articulation facets for well-developed supraorbital processes, but in several features differs from that of extant Cariamidae, especially concerning the shape of the more slender beak (Fig. 13.3).

An assignment of Elaphrocnemus to the Cariamae can be established with the presence of well-developed supraorbital processes, and various derived similarities in the postcranial skeleton, in particular the humerus, ulna, and carpometacarpus (Mourer-Chauvire 1983a). The species of this taxon seem to have been less cursorial than those of Idiornis, the Phorusrhacidae, and extant Cariamidae, and probably had better flight capabilities. However, Elaphrocnemus lacks characters that are shared by Idiornis and modern Cariamidae, such as a well-developed procoracoid process and a hooked acrocoracoid process of the coracoid, as well as a block-like hypotarsus, and may be outside a clade including the latter two taxa (Mayr 2002e).

Mourer-Chauvire (1983a, 2006) identified three further taxa of the Idiornithidae among the avian material of the Quercy fissure fillings. These were classified into the species Propelargus cayluxensis Lydekker, 1891 (from an unknown horizon), Occitaniavis elatus (Milne-Edwards, 1892) (late Eocene), and Oblitavis insolitus Mourer-Chauvire, 1983 (unknown horizon). The material of the large P. cayluxensis consists of a distal tarsometatarsus and tibiotarsus, the equally sized O. elatus is based on a distal tibiotarsus, referred carpometacarpi, and a femur, and the smaller O. insolitus is known from humeri and a coracoid, which in contrast to that of other Paleogene Cariamae exhibits a foramen for the supracoracoideus nerve (see Figs. 9, 10 in Mourer-Chauvire 2003 ).

Gypsornis cuvieri Milne-Edwards, 1869 from the late Eocene of the Paris Gypsum was classified into the Rallidae by earlier authors (e.g., Brodkorb 1967; Brunet 1970), but was referred to the Idiornithidae by Cracraft (1973a). The fossil material of this species consists only of an incomplete tarsometatarsus and associated pedal phalanges. G. cuvieri is distinguished from the Idiornithidae in the presence of a hypotarsal canal. Its affinities are best considered uncertain until more material is found, but the species is probably a representative of the Gruoidea and may belong to the roughly coeval and similarly sized Parvigruidae (Sect. 9.3.1).

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