Ichthyornithiformes, a large group birds including bay-gulls, surfbirds, and harpies, is a clade with a very long lineage.  Ichthies little different  from today's bay-gulls were common as far back as the Cretaceous, represented by such famous genera as Ichthyornis .  Although a few clades have diverged from this root (a few are spectacularly weird), many have changed little since the Mesozoic.  

    Ichthyornithiforms can, however, be distinguished from gulls (true alcids) as soon as they open their beaks --- the rear part of the upper beak and the entire lower beak are lined with conical teeth.  The lower beak also possesses three joints -- one at the tip, the other two at its rear ends some distance in front of the jaw joints -- that allow ichthies' jaws to gape wide, allowing them to eat larger prey than other birds of similar size. 

NEOICHTHYORNITHIDAE (Bay-gulls)

Though its Cretaceous representative genera are long dead, the very similar Neoichthyornithidae is still alive and well in Spec.  Bay-gulls closely resemble their ancestors, and occupy most of the Northern Hemisphere's large sea-bird niches.   

In Spec, no sea-side habitat is complete without its contingent of screaming bay-gulls. These large piscivores are common the world over, and eat a variety of marine detritus, including fish, carrion, crustaceans, and the young of other sea-birds.  These generalists can even be found far inland, as long as the requisite piles of refuse are present to feed them.

LEVIGNATHIDAE (Surf-birds, wavesters, and toothauks)

Levignaths form the largest and most wide-spread clade of ichthyornithiforms.  Similar to classic ichthyornithids, surf-birds have headed toward a range of smaller-size niches.  Their skeletons are quite lightly-built, run through with an extensive air-sack system, and their skulls have undergone even greater reduction.  Levignaths' name-sake jaws are intensely neumatisized (even more so than other ichthies) reduced to a mere scaffolding of bone over cartilage.  

Most surfbirds are tern-like skimmers or fish-eating generalists (genera Aestavis and Larianus ), but a few have explored auk and cormerant-like niches.
 
The waters of the north Atlantic, warmed as they are by the Gulf Stream, are rich and warm, filled with fishes and cephalopods that are food for many larger vertebrates.  Sharks, selkies, and seaguins are, of course, quite common in these waters, but not all piscivores are swimmers.  Every island of any size here off the coast of British Columbia is home to a bustling colony of little, rotund diving birds---toothauks.  

 Though a toothauk (genus Odontalca) looks and behaves a great deal like a Home-Earth puffin, this resemblance is pure convergence; the tooth-filled lower bill of the toothauk belies its ichthyornithiform heritage.  Toothauks are specialized predators of small fishes and cephalopods, which they catch by diving from the air and "swimming" in pursuit of their prey using their wings in a manner similar to the penguins of the Southern Hemisphere.

While toothauks are better fliers than penguins, their wings have been adapted to underwater flight and so they are, at best,  mediocre aerialists.  These fat little birds are often robbed in flight by their more nimble cousins and so travel in vast flocks to confuse predators and aerial pirates.

 

 
HARPIAVIIDAE (Harpies)
    As the Oligocene grasslands began to develop, huge herds of grazing dinosaurs swept across the plains. When dead, such animals form a considerable food resource in the dry steppes. As ichthies have always gladly taken carrion that was lying on the shore, one group of them has shifted inland and become the northern hemisphere's vulture analogues.

 
    From a distance, harpies are almost indistinguishable from their RL counterparts.  With wide black wings and small, naked heads, harpies have taken the body-type of carrion birds everywhere, but a closer look will reveal some clear distinctions between harpies and Home-Earth’s carthids


  Most of the obvious differences between a harpy and a vulture are to be found in the head.  As ichthyorniforms, harpies possess teeth, which are generally serrated and angled sharply backwards, like the teeth of a predatory lizard.  These teeth are most prominent on the outward-jutting lower jaw, where they form a cutting tool that slices flesh and tendons, allowing the birds to quickly hack apart and unwieldy carcass and carry it to safety in pieces.

(fig. 4) Phineus harpy, Harpiavis phineas (central North America---great plains)

Daniel Bensen and David Marjanovic

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                     ,=Neochyornithidae= Neoichthyornis atlanticus (Atlantic bay-gull )
                  ,=|
                 |  |                            ,=O. scopulis (Siren)
                 |   `=Levignathidae=Odontacala=|
                 |                               `=O. pictus ( Painted toothauk)
Icthyorthiformes=|
                 |                           ,=H. aeneas (Aeneus harpy)
                  `=Harpiaviidae= Harpiavis=|
                                             `=H. phineas (Phineus harpy )

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