A broken but fairly complete sternum probably of this genus, specimen LHNB (CC-CP)-1, is known from the Serravallian-Tortonian boundary (Middle to Late Miocene) near Costa da Caparica in Portugal.

[6] It is not clear whether the South American fossils – of similar size and age and not including directly comparable bones – are from one or two species.

Indeed, some of the older Bahía Inglesa Formation remains[7] tentatively referred to Pelagornis were at first assigned to the mysterious Pseudodontornis longirostris in error, and a proximal (initially misidentified as distal) humerus piece (CMNZ AV 24,960), from the Waiauan (Middle-Late Miocene) cliffs near the mouth of the Waipara River (North Canterbury, New Zealand) seems to differ little from either O. orri or P. miocaenus.

[8] Pelagornis sandersi was described in July 2014, whose fossil remains date from 25 million years ago, during the Chattian age of the Oligocene.

[9][10] The only known fossil of P. sandersi was first uncovered in 1983 at Charleston International Airport, South Carolina, discovered by James Malcom, while working construction building a new terminal there.

[11][12] After excavation, the fossil of P. sandersi was catalogued and put in storage at the Charleston Museum, where it remained until it was rediscovered by paleontologist Dan Ksepka in 2010.

The large Gigantornis eaglesomei from the Middle Eocene Atlantic was established based on a broken but not too incomplete sternum and might actually belong in Dasornis.

In Gigantornis the articular facet for the furcula consists of a flat section at the very tip of the sternal keel and a similar one set immediately above it at an outward angle, and the spina externa is shaped like an Old French shield in cross-section.

The slightly smaller LHNB (CC-CP)-1 has a less sharply protruding sternal keel, the articular facet for the furcula consists of a large knob at the forward margin, and the spina externa is narrow in cross-section.

Rather, it is likely that the huge pseudotooth birds form a clade, and in this case, Pseudodontornithidae like Cyphornithidae and Dasornithidae is correctly placed in the synonymy of Pelagornithidae even if several families were accepted in the Odontopterygiformes.

Like all members of the Pelagornithidae, P. sandersi had tooth-like or knob-like extensions of the bill's margin, called "pseudo-teeth," which would have enabled the living animal to better grip and grasp slippery prey.

Further differences between Odontopteryx and Pelagornis are found in the tarsometatarsus: in the latter, it has a deep fossa of the hallux' first metatarsal bone, whereas its middle-toe trochlea is not conspicuously expanded forward.

From the humerus pieces of specimen LACM 127875, found in the Eo-Oligocene Pittsburg Bluff Formation near Mist, Oregon (United States), P. miocaenus differs in an external tuberosity that is not as much extended towards shoulder and that is separated from the elbow end by a wider depression.

However, this calculation is based on the assumption that the bird in question stays aloft by repeatedly flapping its wings, whereas P. sandersi more likely glided on ocean air currents close to the water, which is less power-intensive than reaching high altitudes.

[24] Dan Ksepka of the National Evolutionary Synthesis Center in Durham, North Carolina, who identified that the discovered fossils belonged to a new species, thinks it was able to fly in part because of its relatively small body and long wings,[25] and it spent much of its time over the ocean, like the albatross.