About a year and a half ago,
Huang et al. 2016 brought us a complete and articulated skeleton of a new ornithurine bird, Changzuiornis ahgmi (Fig. 1), from the Early Cretaceous very close to Yanornis. The rostrum is more elongate with a large naris and tiny teeth (Fig. 2).
the better detail DGS brings to understanding where the bones are in this crushed fossil. The original line drawing (Fig. 2 below) leaves almost everything up to the imagination.
The maxilla clearly makes up most of the rostrum
in Changzuiornis. And this came as a surprise to Huang et al., who report this is “a characteristic not present in the avian crown clade in which most of the rostrum and nearly the entire facial margin is made up by premaxilla.” (Fig. 3)
It’s actually much worse than they think.
Their interpretation (Fig. 3) of the avian crown clade rostrum is too short, at least for tested taxa like Changzuiornis and Yanornis. Huang et al. do not extend the anterior maxilla far enough anteriorly, ignoring the portion where it overlaps and laminates to the lateral premaxilla (Fig. 2). For comparison, here’s a new interpretation of Struthio, the ostrich with a larger maxilla (Fig. 4) similarly laminated to the lateral premaxilla.
If I’m wrong
I’ll gladly go through a spanking machine (a silly kid’s party game).
If that’s not enough, check out
Yanornis, Cariama, Phoenicopterus, Sagittarius, Llallawavis, Falco and Tyto for a similar anteriorly extended maxillae. All are now repaired from my earlier mistakes as I wrongly followed traditional interpretations.
Changzuiornis is a close sister to Yanornis, with a longer rostrum and some other minor differences apparently a wee bit closer to Gansus, Ichthyornis and Hesperornis. For instance, pedal digits 3 and 4 are similar in length.
Speaking of Hesperornis
It’s difficult to find photographic data on the the rostrum of Hesperornis and Parahesperornis. I failed to do so because authors from Marsh to Gingreich to Martin instead provided line drawings (Fig. 4), which purported to show a tiny maxilla beneath a naris with a premaxilla forming at least half of the ventral margin of the naris. Unfortunately, no sister taxa have such a morphology. Martin 1984 let loose a clue that Parahesperornis had an anteriorly extended maxilla with that line extending anterior to the naris. I provide that option here (Fig. 4 in green) and wish for actual fossil images to work on.
Ichthyornis and Gansus can’t help us.
Their skulls are too poorly known.
Huang J, Wang X, Hu Y-C, Liu J, Peteya JA and Clarke JA 2016. A new ornithurine from the Early Cretaceous of China sheds light on the evolution of early ecological and cranial diversity in birds. PeerJ.com
Martin L 1984. A new Hesperornithid and the relationships of the Mesozoic birds. Transactions of the Kansas Academy of Science 87:141-150.