Other areas of interest to paleornithologists are the early sea-birds "Ichthyornis", "Hesperornis", and others. The first was as a node-based clade uniting "Ichthyornis" with modern birds. All other supposed species of "Ichthyornis" have not been supported as valid. Many were coastal birds, strikingly resembling modern shorebirds, like "Ichthyornis", or ducks, like" Gansus". Older specimens of "Ichthyornis" were, on average, smaller than younger ones. Also less common was the early toothed bird, "Ichthyornis". The holotype specimen of "Ichthyornis dispar", YPM 1450, had a humerus about long. "Apatornis" also lacked the ossified tendons covering the top of the sacral region in "Ichthyornis". "Ichthyornis" shared the sky with large pterosaurs such as "Nyctosaurus" and "Pteranodon". All other "Ichthyornis" species are synonymous with "I. dispar". "Ichthyornis" is perhaps most well known for its teeth. "Ichthyornis" has been historically important in shedding light on bird evolution. "Ichthyornis" was a seabird that resembled the gulls and petrels of today.