Eremopezus is a prehistoric bird genus of uncertain affinities. It is known only from the fossil remains of a single species, the huge and presumably flightless Eremopezus eocaenus. This was found in Upper Eocene Jebel Qatrani Formation deposits around the Qasr el Sagha escarpment, north of the Birket Qarun lake near Faiyum in Egypt. The rocks its fossils occur in were deposited in the Priabonian, with the oldest dating back to about 36 million years ago (Ma) and the youngest not less than about 33 Ma.Rasmussen et al. (1987, 2001)
It is not precisely known from which strata the first few remains of this bird were collected. They were formerly considered of Early Oligocene age—some 33-30 Ma—but this is now assumed incorrect, as only the upper and not the entire Jebel Qatrani Formation is of Oligocene age. It is also possible that they are from the slightly older Qasr el Sagha Formation, but as both this and the Oligocene parts of the Jebel Qatrani Formation were laid down in an ecosystem markedly different from that of the Eocene Jebel Qatrani Formation, it is now assumed that all material of E. eocaenus is from the lowest rocks of the Jebel Qatrani Formation.Brodkorb (1963) pp.205-206, Rasmussen et al. (1987, 2001)
Material, taxonomy and systematics It was originally described from a distal left tibiotarsus piece (specimen BMNH A843); a toe phalanx bone found soon thereafter was tentatively assigned to this bird. Eremopezus was initially believed a ratite and loosely allied with the elephant birds of Madagascar. Thus, when a piece of tarsometatarsus shaft was found some time later north of the ruins of Dimeh (Dimê; itself a bit north of the Birket Qarun) this was described as Stromeria fajumensis; though it had a size to match the holotype tibiotarsus it was thought to resemble an elephant bird even more. The shaft (specimen BSPG 1914 I 53) has a prominent plantar (backside) ridge also found in Mullerornis betsilei, and this was used to ally the fossil bone with this rather small and gracile elephant bird. The Eremopezus specimen on the other hand has deep ligamental pits on the lateral and medial sides of the distal condyles, which are not found in the elephant birds proper. These pits together with a crisply defined ridge held a sling of ligament, which in turn—in place of the bony supratendinal bridge found in some other birds—kept the ankle tendons from dislocating. The tarsometatarsus is also more similar to that of an unspecific ratite, such as an emu, ostrich or rhea, rather than to the apomorphic one of the elephant birds.
Almost 100 years after the discovery of the holotype, more Eremopezus fossils were unearthed from the famous quarry L-41 at Tel Akgrab near . These are also all leg and foot bones, namely specimens DPC 20919 (a distal right tibiotarsus and its entire tarsometatarsus), DPC 5555 (the lower half of a left tarsometatarsus) and DPC 18309 (the distal end of a left tarsometatarsus).Rasmussen et al. (2001)
Some fossil eggshells from the Maghreb, described as Psammornis and resembling those of ratite eggs, were assigned to Eremopezus by various authors. They were at first believed to date from the Paleogene also, but today are generally considered far younger (of late Neogene age, probably less than 5 Ma) and indeed to have been laid by ostriches or close relatives thereof.Brodkorb (1963): p.205, Rasmussen et al. (2001)
The scientific name Eremopezus eocaenus is rather ambiguous in meaning; a possible translation is "walking hermit from the Eocene". Eremos (ἐρῆμος) is an Ancient Greek term signifying a lonely or solitary place or person: a hermit, a desert or a wasteland. Yet while Faiyum is located at the edge of the Libyan Desert, it is a well-vegetated location even today; some 35-30 Ma it was a lush region and teemed with life. On the other hand, is it not at all likely that such a large and quite likely predatory bird like E. eocaenus was in any way gregarious or occurred at high population densities. It might therefore be described as a "hermit" with some justification, but certainly not as a "desert-dweller". pezus is Latinized Greek from pezós (πεζός), "someone who walks". eocaenus refers to the bird's age; as noted, the initial 1904 assessment of C. W. Andrews was indeed correct. Stromeria fajumensis was named in honor of the paleontologist Ernst Stromer von Reichenbach, and the bone's place of discovery.Woodhouse (1910), Rasmussen et al. (1987), Gagnon (1997)
Systematics Careful study of the remains suggests that their apparent similarity to ratites is misleading. They actually combine a number of traits not found in any known ratite lineage, and in particularly not in the ostriches and elephant birds (the only ratites biogeographically close to Eremopezus). Ratites are polyphyletic, with multiple origins of the ratite bodyplan among Palaeognathae, so it is possible that Eremopezus represents a separate example of this, but it could equally be a flightless neognath of some kind. This is potentially supported by several peculiar traits not at all found in ratites, but present in certain neognaths: its toes were widely divergent and could flex through a wide range of positions, while strong tendons gave the bird a firm grip. In the associated anatomical details of the tarsometatarsi, E. eocaenus resembled the secretarybird (Sagittarius serpentarius) and the shoebill (Balaeniceps rex), two rather singular African endemics; both use their feet to manipulate objects, prey in the case of secretarybirds and floating vegetation in the case of the shoebill, and this suggests that Eremopezus behaved similarly in the swamps of the Jebel Qatrani Formation. Nonetheless, more recent studies seem to group it among "aepyornithid-like" taxa.Agnolin et al, Unexpected diversity of ratites (Aves, Palaeognathae) in the early Cenozoic of South America: palaeobiogeographical implications Article in Alcheringa An Australasian Journal of Palaeontology · July 2016 DOI: 10.1080/03115518.2016.1184898
The secretarybird is an accipitriform that can fly well, but prefers to walk around on its long legs, especially when foraging. It uses its flexible toes to grab prey—large arthropods and small to mid-sized terrestrial vertebrate. It throws the prey around and kicks it forcefully, smashing it to death or breaking its spine. The shoebill, meanwhile, for lack of a better theory was long considered a large aberrant stork relative in the Ciconiiformes. This eventually proved incorrect, as genetic studies consistently place it within Pelecaniformes as a close relative of pelicans, hamerkop, herons and ibises, diverging from its nearest relatives 31-45 mya. Like the pelicans, it uses its massive bill and throat sac to catch large fish and similar aquatic vertebrates, but unlike them it is a wading, not a swimming bird, and correspondingly has long legs like a stork; it is unclear whether this is convergent or represents a wading ancestry for Pelecanimorphae. It clambers through reed beds in search of good fishing spots, and uses its flexible toes to firmly hold on to such uncertain substrate as heaps of wind-blown vegetation at the edge of the open water or roots and logs of trees.Wing (1995), Rasmussen et al. (2001), Cracraft et al. (2004)
But this does not mean that Eremopezus was a close relative of either secretarybird or shoebill. Even though modern taxonomy generally tries to avoid using monotypic families as much as possible, its placement in a distinct family Eremopezidae may well be warranted, as its closest relatives remain completely obscure.
The secretarybird is an early-diverging member of Accipitriformes (possibly the earliest if Cathartidae is elevated to order status) and now endemic to Africa alone. Its fossil relatives include the genus Pelargopappus, which occurred at about the same time as E. eocaenus in today's France, separated from the site of Faiyum by more than 1,500 kmOver half the distance between Africa and South America in our time of the shrinking Tethys Sea. The Maghreb was closer to Europe however, not more than today's Mediterranean where it is widest, and numerous bird lineages are known to have occurred in Africa as well as in Europe during the Eocene. Pelargopappus seems to be an ancient secretarybird, not an ancestor of the living species but not far removed from the last common ancestor either. Its remains, and how they differ from secretarybirds, give an idea how the Sagittariidae of that time looked like. So even though Pelargopappus has not yet been directly compared to the African fossil in a cladistic analysis, the pronounced differences between Eremopezus and Sagittarius and the biogeography of Pelargopappus suggest that Eremopezus was not especially close to the secretarybird's lineage. Thus, even if Eremopezus belongs within Accipitriformes, it would probably remain in its distinct family.Mourer-Chauviré & Cheneval (1983)
The same is true if it were placed in the Pelecaniformes (as a tentative stem-balaencipitid). Goliathia andrewsi, an ancestral shoebill that was slightly larger and presumably far less apomorphic than the living species, lived at about the same time and in the same region as E. eocaenus. It is only known from a single ulna and referred tarsometatarsus; these suggest it was a comparable size to the living shoebill, smaller than Eremopezus and certainly able to fly well.Rasmussen et al. (1987)
But all things considered, very little can be said about the affiliations of Eremopezus. As ratites are nowadays considered polyphyletic, with many distinct origins from volant paleognaths similar to tinamous after the Cretaceous—see also Palaeotis—the Egyptian fossil may be a distinct lineage of flightless palaeognath after all, comparable or even related to the Paleocene Remiornis from France. And indeed, as noted by the first scientists that studied it, its known bones—in particular the distal tarsometatarsus—are more similar to those of ratites in general shape and in some details than to other birds. The details (such as lack of the supratendinal bridge) may however be simply plesiomorphies, while the overall resemblance might be the result of convergent evolution—for the autapomorphies of its toes are starkly unlike those found in any ratite. Thus, if it was a palaeognath, it probably was the most unusual known to date (while the hardly better-known Remiornis may very well have been a rather conventional proto-ostrich).
No palaeognaths are known to have evolved gripping feet like seen in the fossils, however, nor did they fare very successfully in wetland habitat as represented in the Jebel Qatrani Formation. The latter holds true for Galliformes, which are ancient neognaths of the fowl clade (Galloanserae). Anseriformes, the other living member of this group, include the typical waterfowl such as ducks, and many of them independently evolved flexible toes, giving them the ability to perch despite having only a vestigial hallux (see also Cairinini). The Anseriformes also contain the gigantic flightless mihirungs (Dromornithidae) of Australia (which were, at first, also believed ratites). It is not inconceivable that E. eocaenus was a more aquatic African equivalent of these.Livezey (1986), Cracraft et al. (2004) Similarly, Gastornithidae are also giant flightless birds sometimes thought to be related to anseriforms, and Gastornis has partially-splayed toes, though to a lesser extent than Eremopezus.
Until more fossils are found, all that can be said is that Eremopezus is unlikely to have been a galliform or to have close affinities with tree-dwelling birds such as Psittacopasseres, coraciimorphs or Strisores (not least because many of these have reversed toes). But beyond that, it cannot even be ruled out with reasonable certainty that the initial assessment—however lacking by the standards of today's scientific method—was correct and that E. eocaenus was indeed a highly apomorphic paleognath.
Description