Marsh explicitly named his second species of "Hesperornis" in 1876 for an incomplete metatarsus recovered from the same layers of the Niobrara chalk as "H. regalis". He named this smaller species "H. gracilis", and it was subsequently involved in the rather confused taxonomy of a specimen which would eventually form the basis of the new genus and species "Parahesperornis alexi". The type specimen of "P. alexi" was assumed to belong to the same specimen as that of "H. gracilis", so when Lucas (1903) decided that the former specimen represented a distinct genus, he mistakenly used the later specimen to anchor it, creating the name "Hargeria gracilis". This mistake was rectified by later authors, who sank "Hargeria" back into "Hesperornis" and renamed the more distinctive specimen "Parahesperornis".