Fred Ruhe
Well-known member
Delphine Angst & Eric Buffetaut, 2018
Ontogenetic change in the giant bird Gastornis
Abstracts of the 5th International Paleontological Congress – Paris, 9th-13th July 2018
Free pdf https://ipc5.sciencesconf.org/data/IPC5_Abstract_Book.pdf pg. 167
The genus Gastornis includes large terrestrial herbivorous birds known from Europe, North America and China during the Paleocene and the Eocene. The Thanetian Mont-de-Berru site in north-eastern France has yielded remains referred to two species, G. parisiensis and G. russelli. While many specimens of G. parisiensis are known, including post-cranial as well as cranial material, the species G. russelli Martin, 1992 is based on a single left tarsometatarsus (the holotype), and a referred fragmentary beak, both in the collections of the Paris Natural History Museum. Martin (1992) briefly described this beak and provided a drawing, in which the missing tip is reconstructed as forming a distinct hook, for which there is no factual evidence.
A new preparation and reexamination of this beak leads to a new interpretation. The specimen (R2583) corresponds to the fused premaxillae and maxillae showing a very large naris which is much larger and anteriorly placed than the naris observed on the known Gastornis beaks, in which it is clearly very small and posterodorsally located. This significant difference at first sight challenges the attribution of this beak to Gastornis. However, an examination of the skull bones of both juvenile and adult specimens of Sylviornis neocaledoniae shows that in this bird both the position and size of the naris changed during ontogeny, from a large and anterior naris in juveniles to a small and posterodorsal naris in the adults. Assuming that the same kind of allometric growth occurred in Gastornis, we interpret the beak R2583 as a juvenile, not an adult, specimen.
The attribution of this beak to a juvenile therefore challenges the referral of this specimen to the species Gastornis russelli. The holotype tarsometatarsus of G. russelli belonged to an adult, to judge from the complete fusion of its bony components. The beak is too large to consider it as a juvenile of G. russelli, but is consistent with G. parisiensis, the other Gastornis species known from the same site. Therefore, we suggest that specimen R2583 belongs to a juvenile of G. parisiensis. The type tarsometatarsus of G. russelli differs from that of G. parisiensis only in its smaller size. A revision is required to establish if G. russelli is a valid species or should be included in G. parisiensis, in which case the small size of the tarsometatarsus currently attributed to G. russelli would imply significant size variation or sexual dimorphism in G. parisiensis.
Enjoy,
Fred
Ontogenetic change in the giant bird Gastornis
Abstracts of the 5th International Paleontological Congress – Paris, 9th-13th July 2018
Free pdf https://ipc5.sciencesconf.org/data/IPC5_Abstract_Book.pdf pg. 167
The genus Gastornis includes large terrestrial herbivorous birds known from Europe, North America and China during the Paleocene and the Eocene. The Thanetian Mont-de-Berru site in north-eastern France has yielded remains referred to two species, G. parisiensis and G. russelli. While many specimens of G. parisiensis are known, including post-cranial as well as cranial material, the species G. russelli Martin, 1992 is based on a single left tarsometatarsus (the holotype), and a referred fragmentary beak, both in the collections of the Paris Natural History Museum. Martin (1992) briefly described this beak and provided a drawing, in which the missing tip is reconstructed as forming a distinct hook, for which there is no factual evidence.
A new preparation and reexamination of this beak leads to a new interpretation. The specimen (R2583) corresponds to the fused premaxillae and maxillae showing a very large naris which is much larger and anteriorly placed than the naris observed on the known Gastornis beaks, in which it is clearly very small and posterodorsally located. This significant difference at first sight challenges the attribution of this beak to Gastornis. However, an examination of the skull bones of both juvenile and adult specimens of Sylviornis neocaledoniae shows that in this bird both the position and size of the naris changed during ontogeny, from a large and anterior naris in juveniles to a small and posterodorsal naris in the adults. Assuming that the same kind of allometric growth occurred in Gastornis, we interpret the beak R2583 as a juvenile, not an adult, specimen.
The attribution of this beak to a juvenile therefore challenges the referral of this specimen to the species Gastornis russelli. The holotype tarsometatarsus of G. russelli belonged to an adult, to judge from the complete fusion of its bony components. The beak is too large to consider it as a juvenile of G. russelli, but is consistent with G. parisiensis, the other Gastornis species known from the same site. Therefore, we suggest that specimen R2583 belongs to a juvenile of G. parisiensis. The type tarsometatarsus of G. russelli differs from that of G. parisiensis only in its smaller size. A revision is required to establish if G. russelli is a valid species or should be included in G. parisiensis, in which case the small size of the tarsometatarsus currently attributed to G. russelli would imply significant size variation or sexual dimorphism in G. parisiensis.
Enjoy,
Fred
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