Friday, October 7, 2011


SEABIRDS (Ichthyornithes line)

  • Pterosaur (eg. Ornithocheiroidea) eg. Pteranodon --> 
  • An Ichthyornithes subgroup --> 
  • Gulls, Skimmers (Charadriiformes/Lari)

  • Pterosaur (eg. Ornithocheiroidea) eg. Pteranodon --> 
  • An Ichthyornithes subgroup --> 
  • Petrels, Albatross (Procellariiformes)




"There exists no single definition of which groups, families, and species are seabirds, and most definitions are in some way arbitrary. In the words of two seabird scientists, "The one common characteristic that all seabirds share is that they feed insaltwater; but, as seems to be true with any statement in biology, some do not."[2] However, by convention all of theSphenisciformes and Procellariiformes, all of thePelecaniformes except the darters, and some of the Charadriiformes (the skuasgullsternsauks andskimmers) are classified as seabirds. The phalaropes are usually included as well, since although they are waders("shorebirds" in North America), two of the three species are oceanic for nine months of the year, crossing the equator to feed pelagically.
Loons and grebes, which nest on lakes but winter at sea, are usually categorized as water birds, not seabirds.Although there are a number of sea ducks in the family Anatidae which are truly marine in the winter, by convention they are usually excluded from the seabird grouping. Many waders (or shorebirds) and herons are also highly marine, living on the sea's edge (coast), but are also not treated as seabirds."
"The wing shape of Pteranodon suggests that it would have flown rather like a modern-day albatross. This is based on the fact that Pteranodon had a high aspect ratio (wingspan to chord length) similar to that of the albatross — 9:1 for Pteranodon, compared to 8:1 for an albatross. Albatrosses spend long stretches of time at sea fishing, and use a flight pattern called "dynamic soaring" which exploits the vertical gradient of wind speed near the ocean surface to travel long distances without flapping, and without the aid of thermals (which do not occur over the open ocean the same way they do over land).[11] While most of a Pteranodon flight would have depended on soaring, like long-winged seabirds, it probably required an occasional active, rapid burst of flapping, and studies of Pteranodon wing loading (the strength of the wings vs. the weight of the body) indicate that they were capable of substantial flapping flight, contrary to some earlier suggestions that they were so big they could only glide.[3]"
"Interestingly, a Lesser Black-Backed Gull and an unrelated charadriiform seabird
with similar flight modes also showed histological similarity to the Procellariiiformes [eg. albatross] studied." 
"According to the famous DNA hybridization study into avian phylogenetic relationships by Sibley and Ahlquist, the split of the Procellariiformes into the four families occurred around 30 million years ago; a fossil bone often attributed to the order, described as the genus Tytthostonyx, has been found in rocks dating around the Cretaceous-Tertiary boundary (70-60 mya), but the remains are too incomplete for placement within the Procellariiformes to be certain.[2] The molecular evidence suggests that the [swimming] storm-petrels were the first to diverge [develop] from the ancestral stock [I propose ichthyornithes], and the albatrosses next, with the procellariids and diving petrels splitting [developing] most recently. Many taxonomists used to retain the diving petrels in this family also, but today their distinctiveness is considered well supported."
"It is thought that Ichthyornis was the Cretaceous ecological equivalent of modern seabirds such as gullspetrels, and skimmers. It was the size of a pigeon, 24 centimetres (9.4 in) long, with a skeletal wingspan (not taking feathers into account) of around 43 centimetres (17 in).[3]"
The jaw tips had no teeth and were covered in a beak. The beak of Ichthyornis, like the hesperornithids and other primitive birds, was compound and made up of several distinct plates, similar to the beak of an albatross, rather than a single sheet of keratin as in most modern birds.[4]
Although the wings and breastbone were very modern in appearance (suggesting strong flight ability and placing it with modern birds in the advanced group Carinatae), the jaws had numerous small, sharp teeth.
Interestingly, studies of ichthyornithines and hesperornithine bone structure shows that they likely had "compound rhamphotheca", and this may have been the ancestral condition for modern birds (Heironymous & Witmer, 2010). While the quintessential bird beak is made up of a single keratin sheet covering the jaw, in species with compound beaks, the keratin is arranged in discrete plates on the jaws. This can best be seen in some modern seabirds like the Albatross.
"The first large, diverse lineage of short-tailed birds to evolve were the Enantiornithes, or "opposite birds", so named because the construction of their shoulder bones was in reverse to that of modern birds. Enantiornithes occupied a wide array of ecological niches, from sand-probing shorebirds and fish-eaters to tree-dwelling forms and seed-eaters.[22] More advanced lineages also specialised in eating fish, like the superficially gull-like subclass of Ichthyornithes (fish birds)."[23]
Five unambiguous autapomorphies of Ichthyornis dispar are identified in the phylogenetic
analysis (i.e., 52, 66, 103, 132, 152;
each is discussed in the Taxonomic Revision
of Part I): (52:0) amphicoelous cervical vertebrae,
(66:1) proximal free caudal vertebrae
with well-developed prezygapophyses clasping
the dorsal surface of preceding vertebra,
(103:1) unprojected acromion on scapula,
(132:1) subequal posterior and distal dimensions
of the distal articular surface of ulna,
and (152:1) internal index process present.
Of these characters, two (i.e., 66, 152) are
also seen in Charadriiformes and some other
neoavians but not in the included Aves. This
distribution, and the absence of these morphologies
in other basal avialans, is consistent
with the hypothesis (e.g., Marsh, 1880)
that several derived aspects of the anatomy
of Ichthyornis dispar may be convergent [actually homologous] on
charadriiform morphologies. It does not,however, support these structures, or ‘‘shorebird’’morphologies generally, as ancestral toAves, as has often been argued (Feduccia,1995, 1999).
[The last sentence is an unsupported assertion.]
Unlike Hesperornis, the species of Ichthyornis were obviously flying
birds. They were the size of gulls or terns and may have had somewhat
similar habits, as Marsh (1880) suggested long ago. It was probably this
allusion that prompted many authors (see those cited by Lambrecht, 1933,
p. 581) to place Ichthyornis near the Charadriiformes. This is certainlyunjustified, as it is likely that Ichthyornis is a relict of an earlier radiation ona line quite apart from modern birds, The enormous deltoid crest in
Ichthyornis is unique among birds in size, shape, and orientation, as noted
by the original describer and later redundantly by Harrison (1973). Thepalate is unknown in Ichthyornis and there is no reason to suppose that thesebirds were even neognathous."
Note: If the palate is unknown then there is no reason NOT to suppose these birds were neognathous.

"In traditional classification, the Neornithes also included a third superorder, the Odontognathae, containing advanced toothed birds from the Cretaceous, like Hesperornis and Ichthyornis.[5] This superorder is likely paraphyletic [ANCESTRAL], and fall outside [is ancestral to]  the crown group birds. It is not entirely clear whether the Palaeognathae too are paraphyletic [ancestral], or represent a primitve grade of birds.[6]"
This seems to be saying exactly what I have been saying.
Some of the modern birds developed from such primitive bird taxa as Hesperornithes and Ichthyornithes.

"The contemporaneous and much larger Sapeornis had longer and narrower wings, superficially resembling those of albatrosses (Zhou and Zhang 2002)."

No comments:

Post a Comment