[D] Ichthyornis antecessor [~/~]
Describer
Wetmore, 1962
Time
Cretaceous Late, Campanian
Classification
Saurischia Theropoda Tetanurae Coelurosauria Maniraptora Avialae Ornithothoraces Ornithurae Cartinatae Ichtyornithiformes
Fossilsite
Moorville Chalk; Alabama, US
Fall Under
Ichthyornis dispar
Info
Ichthyornis dispar (Marsh, 1872) [= Colonosaurus mudgei (Marsh, 1872) including Ichthyornis agilis (Marsh, 1873); Graculavus agilis (Marsh, 1873); Ichthyornis anceps (Marsh, 1872); Graculavus anceps (Marsh, 1872); Ichthyornis victor (Marsh, 1876); Ichthyornis validus (Marsh, 1880); Ichthyornis antecessor (Wetmore, 1962); Plegadornis antecessor (Wetmore, 1962); Angelinornis antecessor (Wetmore, 1962)
Plegadornis antecessor was named by Wetmore (1962) based on a distal humerus. Kashin (1972) noted that Plegadornis was preoccupied, and changed the name to Angelinornis antecessor. Olson (1975) used characters shared by Ichthyornis and Angelinornis antecessor to synonymize the latter genus and refer the specimen to Ichthyornis, but still recognized it as a valid species, Ichthyornis antecessor.
Holotype
USNM 22820 is a left distal humerus and was illustrated in Olson (1975). Referred matarial: TMM 42522–1 is a distal humerus referred to Ichthyornis antecessor (Parris and Echols, 1992). It seems to have been referred to Ichthyornis antecessor because it was approximately the same age as the holotype (Campanian), but it was also judged to match closely the morphology of the holotype.
However, on the points of morphological comparison noted, the specimen is equally like the holotype of Ichthyornis dispar and specimens referred to that species. TMM 42522–1 is smaller than the holotype of Ichthyornis antecessor; the measure of the width of the distal end is 10.1 mm as opposed to 10.5 mm in the holotype. The same measure of the holotype of Ichthyornis dispar is 9.5 mm, making TMM 42522–1 intermediate in size between the holotype of Ichthyornis dispar and that of Ichthyornis antecessor. ET 4396 (L85–6) is a proximal left carpometacarpus described by Parris and Echols (1992).
As these authors mentioned, it cannot be compared to the holotype of Ichthyornis antecessor. It was referred to Ichthyornis antecessor because the humerus from the same formation was referred to that species and is from younger deposits than all named Ichthyornis species other than Ichthyornis antecessor (Parris and Echols, 1992). The fragment was also supposed to differ from other Ichthyornis material in several features of metacarpal I. However, nearly half of metacarpal I is missing and the mentioned attributes could not be confirmed. The carpometacarpus was also supposed to be more gracile than the Niobrara lchthyornis material to which it was compared (although this material in not identified). The other noted differences between the figured specimen and YPM specimens, here referred to Ichthyornis dispar, were not confirmed. The absence of a groove on the carpal trochlea and other figured morphologies correspond with those in YPM specimens referred to Ichthyornis by apomorphy, but it does not preserve any characters used in the diagnosis of Ichthyornis dispar.
Locality and horizon
USNM 22820 is from the top of the Mooreville Formation just below the base of the Arcola Limestone Member (Selma Group; Wetmore, 1962) at Hewletts Farm, Greene County, Alabama (Parris and Echols, 1992). The Mooreville Formation has been inferred to be approximately the same age as or slightly younger than the uppermost deposits represented in the Niobrara Chalk Formation (Martin and Stewart, 1982) and early Campanian in age (Parris and Echols, 1992). (Clarke, 2004)
Wetmore, 1962
Time
Cretaceous Late, Campanian
Classification
Saurischia Theropoda Tetanurae Coelurosauria Maniraptora Avialae Ornithothoraces Ornithurae Cartinatae Ichtyornithiformes
Fossilsite
Moorville Chalk; Alabama, US
Fall Under
Ichthyornis dispar
Info
Ichthyornis dispar (Marsh, 1872) [= Colonosaurus mudgei (Marsh, 1872) including Ichthyornis agilis (Marsh, 1873); Graculavus agilis (Marsh, 1873); Ichthyornis anceps (Marsh, 1872); Graculavus anceps (Marsh, 1872); Ichthyornis victor (Marsh, 1876); Ichthyornis validus (Marsh, 1880); Ichthyornis antecessor (Wetmore, 1962); Plegadornis antecessor (Wetmore, 1962); Angelinornis antecessor (Wetmore, 1962)
Plegadornis antecessor was named by Wetmore (1962) based on a distal humerus. Kashin (1972) noted that Plegadornis was preoccupied, and changed the name to Angelinornis antecessor. Olson (1975) used characters shared by Ichthyornis and Angelinornis antecessor to synonymize the latter genus and refer the specimen to Ichthyornis, but still recognized it as a valid species, Ichthyornis antecessor.
Holotype
USNM 22820 is a left distal humerus and was illustrated in Olson (1975). Referred matarial: TMM 42522–1 is a distal humerus referred to Ichthyornis antecessor (Parris and Echols, 1992). It seems to have been referred to Ichthyornis antecessor because it was approximately the same age as the holotype (Campanian), but it was also judged to match closely the morphology of the holotype.
However, on the points of morphological comparison noted, the specimen is equally like the holotype of Ichthyornis dispar and specimens referred to that species. TMM 42522–1 is smaller than the holotype of Ichthyornis antecessor; the measure of the width of the distal end is 10.1 mm as opposed to 10.5 mm in the holotype. The same measure of the holotype of Ichthyornis dispar is 9.5 mm, making TMM 42522–1 intermediate in size between the holotype of Ichthyornis dispar and that of Ichthyornis antecessor. ET 4396 (L85–6) is a proximal left carpometacarpus described by Parris and Echols (1992).
As these authors mentioned, it cannot be compared to the holotype of Ichthyornis antecessor. It was referred to Ichthyornis antecessor because the humerus from the same formation was referred to that species and is from younger deposits than all named Ichthyornis species other than Ichthyornis antecessor (Parris and Echols, 1992). The fragment was also supposed to differ from other Ichthyornis material in several features of metacarpal I. However, nearly half of metacarpal I is missing and the mentioned attributes could not be confirmed. The carpometacarpus was also supposed to be more gracile than the Niobrara lchthyornis material to which it was compared (although this material in not identified). The other noted differences between the figured specimen and YPM specimens, here referred to Ichthyornis dispar, were not confirmed. The absence of a groove on the carpal trochlea and other figured morphologies correspond with those in YPM specimens referred to Ichthyornis by apomorphy, but it does not preserve any characters used in the diagnosis of Ichthyornis dispar.
Locality and horizon
USNM 22820 is from the top of the Mooreville Formation just below the base of the Arcola Limestone Member (Selma Group; Wetmore, 1962) at Hewletts Farm, Greene County, Alabama (Parris and Echols, 1992). The Mooreville Formation has been inferred to be approximately the same age as or slightly younger than the uppermost deposits represented in the Niobrara Chalk Formation (Martin and Stewart, 1982) and early Campanian in age (Parris and Echols, 1992). (Clarke, 2004)