New data on the skeleton of Ichthyornis, a Cretaceous sea bird
Benito et al 2022
added to our knowledge of the previously incomplete taxon, Ichthyornis (Fig 1). Now this toothed sea bird of the Niobrara is missing only a few toe bones (Fig 2).
Interestingly…
Ichthyornis documents gastralia AND a deep sternum, both apparently by convergence with more basal and more derived taxa respectively. The word ‘gastralia’ is not found in the Benito et al text.
Be careful…
with those pedal phalanges. Benito et al reported, “The pedal phalanges of Ichthyornis are described in detail for the first time (Fig. 29); although it is impossible to infer their position with certainty, precluding a complete reconstruction of foot anatomy for Ichthyornis, the proportions of these phalanges in comparison with the rest of hindlimb elements suggest a greatly enlarged pes, presumably adapted for foot-propelled swimming.”
Or a somewhat reduced metatarsus. The difference depends on your starting point. Here (Fig 2) the missing phalanges are estimated based on the closest known relative in the large reptile tree (LRT, 2186 taxa), Early Cretaceous Changzuiornis (Fig 3), which has a relatively longer metatarsus and more of a sand plover morphology overall.
The new data was entered into the LRT. The postion of Ichthyornis did not change.
Changzuiornis
(Fig 3) is not mentioned in Benito et al, Chanzuiornis also has gastralia. The sternum remains unknown, likely buried in the matrix. We need a µCT scan here to see below the rock surface.
Ichthyornis dispar
(Marsh 1872) Late Cretaceous ~90 mya, 24 cm in length, wingspan 43 cm was a deep-breasted, tern-like flying bird derived from Apsaravis, Juehuaornis and Changzuiornis. Like outgroup taxa, the skull of Ichthyornis had a long rostrum with teeth largely missing from the anterior half of the upper rostrum. The premaxilla was extended to form a sharper tip. The naris was larger than the antorbital fenestra. The dorsal ribs were elongated and tied together with short uncinate processes.
Unfortunately, taxon exclusion mars the Benito et al cladogram,
which nests Ichthyornis between Gansus and Hesperornis + Baptornis.
By contrast, in the LRT Ichthyornis (Fig 1) nests with Changzuiornis (Fig 3). These nest with Juehuaornis. These nest with Apsaravis, These nest with Yanornis at the base of the Ichthyornis clade. Hesperornis is not closely related, but is derived from Archaeopteryx lithographica (the London specimen), one of the nine Solnhofen birds tested in the LRT. Benito et al tested only one Solnhofen bird.
References
Benito et al (5 co-authors) 2022. Forty new specimens of Ichthyornis provide unprecedented insight into the postcranial morphology of crownward stem group birds. PeerJ 10:e13919 DOI 10.7717/peerj.13919
Marsh OC 1872. Notice of a new and remarkable fossil bird. American Journal of Science
4(61):344–380 DOI 10.1080/00222937308696770.
Source: https://pterosaurheresies.wordpress.com/2022/12/22/new-data-on-the-skeleton-of-ichthyornis-a-cretaceous-sea-bird/
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