Overlooked and infamous ancestors to Hesperornis in the LRT

Archaeovolans repatriatus
(IVPP V12444, Czerkas and Xu 2002) This Early Cretaceous bird had a controversial beginning as Archaeoraptor liaoningensis). Originally the the long stiff tail and hind limbs came from a different specimen, but phylogenetic bracketing indicates this genus did have a long stiff tail (Fig. 1) Zhou and Zhang (2002) considered the specimen another Yanornis, a taxon with a short pygostyle. Here Archaeovolans nests between enantiornithes and the London specimen of Archaeopteryx leading to Hesperornis (Fig. 1) and on the other branch, Eogranivora + higher birds.

Archaeopteryx lithographica
The London specimen – BMNH 37001, is the holoytype for the genus and species. Here it nests between Archaeovolans (above) and the STM9-52 specimen previously assigned to Yanornis (Fig. 1).

“Needs a new name” taxon
(Zhang & Zhou, 2001, STM9-52, Aptian, Early Cretaceous) was originally considered an ornithurine bird, close to Yanornis. Here this toothed bird with oversized hands, a long neck, and small head nests basal to a toothed bird with no hands: Hesperornis (Fig. 1). The sternum was greatly enlarged laterally and posteriorly, without a keel, as an anchor for powerful flight or swimming muscles, as in penguins. Tiny gastralia here are about to disappear. The sacrum is wide and the elements are not fused. The pubis extends the body posteriorly. Tiny triangular patellas are present, precursors to large patellas on Hesperornis.

Hesperornis regalis
(Marsh 1872a, b c) Late Cretaceous ~90 mya, 1.8m in length, was a toothed, flightless, marine loon-mimic with asymmetrical feet. It swam with powerful hind limb tipped by elongate lateral toes (digit #4), seen to a lesser extend in precursor clade members. This is one more example of flightlessness in the largest of its kind together with reduced wings. The premaxilla was elongated. The pectoral girdle was reduced and the humerus was a vestige. Note the large patella (in blue) extending above the femur. Huge muscles were anchored to the long pelvis. The teeth had bulbous roots and were set in a groove, convergent with mosasaurs like Tylosaurus.

Hesperornis, with no hands,
is a sister to the STM9-52 specimen. with the largest hands among tested taxa. At first glance, that might seem weird, but think of it this way. While Hesperornis swam like a loon, the STM9-52 specimen might have swam like a penguin, with those large hands. Apparently
(Fig. 1) ths split had origins prior to the Late Jurassic (based on the London specimen of Archaeopteryx).

As reported earlier,
key to understanding the previously murky origins of hesperornithids is the inclusion of precursor taxa that traditionally did not enter prior analyses. Taxon exclusion continues to be the number one problem in paleontology today. This is just one more example.

This appears to be a novel hypothesis of interrelationships.
If not, please send a citation to I can promote it here.

References
Czerkas SA and Xu 2002. Feathered Dinosaurs and the Origin of Flight, Czerkas SJ ed., The  Dinosaur Museum Journal 1: vi + 136 pp.
Marsh OC 1872a. Discovery of a remarkable fossil bird. American Journal of Science, Series 3, 3(13): 56-57.
Marsh OC 1872b. Preliminary description of Hesperornis regalis, with notices of four other new species of Cretaceous birds. American Journal of Science 3(17):360-365.
Marsh OC 1872c. Notice of a new and remarkable fossil bird. American Journal of Science, Series 3, 4(22): 344.
Marsh, OC 1880. Odontornithes, a Monograph on the Extinct Toothed Birds of North America. Government Printing Office, Washington DC.
Martin L 1984. A new Hesperornithid and the relationships of the Mesozoic birds. Transactions of the Kansas Academy of Science 87:141-150.
von Meyer H 1861. Archaeopteryx litographica (Vogel-Feder) und Pterodactylus von Solenhofen. Neues Jahrbuch für Mineralogie, Geognosie, Geologie und Petrefakten-Kunde. 1861: 678–679.
Owen R 1863. On the Archaeopteryx von Meyer, with a description of the fossil remains of a long-tailed species from the lithographic stone of Solnhofen. Philosophical Transactions of the Royal Society, London 153: 33-47.
Zhang F and Zhou Z 2001. A Primitive Enantiornithine Bird and the Origin of Feathers. Science 290 (5498): 1955-1959.

wiki/Archaeovolans
wiki/Archaeopteryx
wiki/Hesperornis
wiki/Enantiornithes
wiki/Archaeoraptor scandal