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''Rhynchaeites'' (Greek for "beak fossil") is an
The type species, ''R. messelensis'', is known from many well-preserved specimens from the famous
Despite its close resemblance to modern ibises, ''Rhynchaeites'' differs in several aspects of morphology from them, primarily in its much shorter legs and the apparent lack of any sensory nerves in its bill. The latter suggests that ''Rhynchaeites'' primarily relied on sight to find food, as opposed to the tactile probing of modern ibises. The short legs of ''Rhynchaeites'' appear to be a plesiomorphic trait, and suggest that long legs evolved multiple times within the Pelecaniformes.
extinct
Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...
genus
Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...
of wading bird
Birds are a group of warm-blooded vertebrates constituting the class (biology), class Aves (), characterised by feathers, toothless beaked jaws, the Oviparity, laying of Eggshell, hard-shelled eggs, a high Metabolism, metabolic rate, a fou ...
, a stem-group threshkiornithid, from the Eocene. It is one of the oldest members of the ibis family known from fossil remains.
Taxonomy
The type species, ''R. messelensis'', is known from many well-preserved specimens from the famous Lutetian
The Lutetian is, in the geologic timescale, a stage (stratigraphy), stage or age (geology), age in the Eocene. It spans the time between . The Lutetian is preceded by the Ypresian and is followed by the Bartonian. Together with the Bartonian it ...
-aged Messel pit
The Messel Formation is a Formation (geology), geologic formation in Hesse, central Germany, dating back to the Eocene Epoch (geology), epoch (about 47 Ma). Its geographic range is restricted to the Messel pit. There it unconformably overlie ...
of Germany
Germany, officially the Federal Republic of Germany, is a country in Central Europe. It lies between the Baltic Sea and the North Sea to the north and the Alps to the south. Its sixteen States of Germany, constituent states have a total popu ...
. It was initially thought to represent an early relative of painted-snipes (family Rostratulidae), and was still considered an early charadriiform for nearly a century, but was identified as an early ibis in 1983.
In 2023, a second species, ''R. litoralis'' was described from the earlier Ypresian
In the geologic timescale the Ypresian is the oldest age (geology), age or lowest stage (stratigraphy), stratigraphic stage of the Eocene. It spans the time between , is preceded by the Thanetian Age (part of the Paleocene) and is followed by th ...
-aged London Clay
The London Clay Formation is a Sediment#Shores and shallow seas, marine formation (geology), geological formation of Ypresian (early Eocene Epoch, c. 54-50 million years ago) age which outcrop, crops out in the southeast of England. The London C ...
of England. ''R. litoralis'' is mostly known from isolated bones but also multiple partial skeletons. In addition to their differing morphologies, both species appear to have inhabited different habitats, with ''R. messelensis'' inhabiting freshwater habitats and ''R. litoralis'' coastal habitats.
An undescribed, largely complete ''Rhynchaeites'' specimen has been reported from the Green River Formation
The Green River Formation is an Eocene geologic formation that records the sedimentation in a group of intermountain lakes in three basins along the present-day Green River (Colorado River), Green River in Colorado, Wyoming, and Utah. The sedimen ...
of the United States. The potential leg bone fossils of ''Rhynchaeites'' have also been found in the earliest Ypresian Fur Formation in Denmark
Denmark is a Nordic countries, Nordic country in Northern Europe. It is the metropole and most populous constituent of the Kingdom of Denmark,, . also known as the Danish Realm, a constitutionally unitary state that includes the Autonomous a ...
. It has been hypothesized that the supposed parrot
Parrots (Psittaciformes), also known as psittacines (), are birds with a strong curved beak, upright stance, and clawed feet. They are classified in four families that contain roughly 410 species in 101 genus (biology), genera, found mostly in ...
relative '' Mopsitta tanta'', known from a single humerus
The humerus (; : humeri) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius (bone), radius and ulna, and consists of three sections. The humeral upper extrem ...
bone, is the same bird as the leg fossils and thus actually belongs in ''Rhynchaeites'' too.
Morphology
Despite its close resemblance to modern ibises, ''Rhynchaeites'' differs in several aspects of morphology from them, primarily in its much shorter legs and the apparent lack of any sensory nerves in its bill. The latter suggests that ''Rhynchaeites'' primarily relied on sight to find food, as opposed to the tactile probing of modern ibises. The short legs of ''Rhynchaeites'' appear to be a plesiomorphic trait, and suggest that long legs evolved multiple times within the Pelecaniformes.
References
*"The Origin and Evolution of Birds" by Alan Feduccia