The Ameghinornithids are a group
poorly understood and possibly flightless Birds known from the Eocene and
possibly the Oligocene of Europe, and possibly the Palaeocene of China. They
are thought to be related to the modern Cariamidae (Seriemas), as well as the
extinct Bathornithidae and Idiornithidae. Like other Bird groups the bones of
Ameghinornithids were hollow and light, which meant they had rather poor
preservational potential, with the group being known largely from very
fragmentary remains, making it hard to access their palaeobiology (the biology
of the living animals).
In a paper published in the
journal Palaeontologica Electronica in February 2015, Thomas Stidham of the
Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences and Adam Smith of the National Evolutionary Synthesis Center and the North Carolina Museum of Natural Sciences describe a potential
Ameghinornithid Bird from the Early Oligocene Jebel Qatrani Formation of the Fayum
Depression in Egypt.
The Jebel Qatrani Formation has a
calculated age of 33 million years, placing it within the Eocene-Oligocene
Climatic Transition, an interval in which Avian and Mammalian faunas underwent
considerable turnover, with many Early Cainozoic groups disappearing and being
replaced by early members of modern groups. The Jebel Qatrani is interpreted to
be of fluvial (riverine) origin, and has produced a variety of Bird fossils in
the past, including Cuckoos (Cuculiformes), Falcons (Falconiformes), Cranes
(Gruiformes), Shorebirds (Charadriiformes), Flamingos (Phoenicopteriformes),
Cormorants (Pelecaniformes) and Herons (Ardeidae) and Storks (Ciconiiformes).
The specimen described by Stidham
an Smith comprises the distal end of a right tibiotarsus. This lacks an
ossified supratendinal bridge, a feature thought to have been present in the
common ancestor of all modern Birds, but secondarily lost in certain groups,
including the Ratites (Ostriches, Emus etc.), Owls, Hoatzin, and Hornbills,
Oilbirds and some Parrots, as well as some extinct groups, including the
Ameghinornithids. The specimen lacks a concave distal margin, a feature found
in all known Owls, and is considered too large to have come from a Parrot or
Oilbird; and is morphologically quite distinct from the bones of Ratites,
Hoatzin and Hornbills.
The distal tibiotarsus of the Fayum Ameghinornithid-like Bird. (1)
Lateral view. (2) Cranial view. (3) Medial view. (4) Caudal view. (5) Distal
view. Abbreviations: ep, elongate pit; es, extensor sulcus; fs, flattened spot;
g, groove; is, intercondylar sulcus; lc, lateral condyle; mc, medial condyle;
me, medial epicondyle; mf, medial flange of the tibial cartilage articulation;
r, ridge; s, sand/sediment grains. Stidham & Smith (2015).
As well as being potentially the
first Ameghinornithid from Africa, this specimen is also possibly the youngest
known member of the group. This conforms with our general understanding of
palaeobiogeography in Europe at the beginning of the Oligocene, when European
animals were beginning to appear in Africa and African animals were beginning
to appear in Europe; the two continents were at this time still separated by a
rapidly narrowing Tethys Ocean, and the exact details of how some groups were
crossing this while others did not are unclear, but this is a consistent
pattern across many groups. Seen in this light, it is likely that Ameghinornithids
arose in Europe and/or Asia then crossed the Tethys into Africa at the beginning
of the Oliocene. However Birds in general and Ameghinornithids in particular
have a very poor fossil record, and Bird fossils are more-or-less unknown in
the Palaeocene and Eocene of Africa, so it is also possible that this group
arose in Africa (closer to the origin of their purported relatives, the
flightless Seriemas of South America) and subsequently spread to Europe.
Maps showing the geographic range of fossil localities with ameghinornithid specimens (left panel; (1) Quercy, France; (2) Messel, Germany; (3) Geiseltal, Germany; (4) Fayum Depression, Egypt) and the location of the Fayum Depression in northern Egypt (right panel) where the ameghinornithid-like specimen was collected. Stidham & Smith (2015).
See also…
The Phorusrhacid ‘Terror Birds’ were large, carnivorous flightless Birds that appear to have held the role of top terrestrial predators in South America throughout much of the Cenozoic. They are known to have colonized...
The Palaeocene Epoch lasted from 65 to 55.8 million years ago. It is during this time that terrestrial faunas recovered from the mass-extinction at the end of the Cretaceous that wiped out the non-avian dinosaurs...
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