Friday, October 7, 2011

Aquatic Birds

AQUATIC BIRDS (Hesperornithes line) 

  • Pterosaur (Pterodactylidae/Ctenochasmatidae) eg. Pterodactylus --> 
  • Baptornithidae (Hesperornithes) --> 
  • (primarily foot-propelled) WEB FOOT diving bird orders, eg. Cormorants (Phalacrocoracidae), Loons (Gaviidae),   Penguins  (Sphenisciformes)

  • Pterosaur (Pterodactylidae/Ctenochasmatidae) eg. Pterodactylus -->
  • Hesperornithidae (Hesperornithes) --> 
  • (primarily foot-propelled) LOBE FOOT diving bird orders eg. Grebes (Podicipedidae).

Baptornis (Baptornithidae)

Hesperonis (Hesperornithidae)



Example of "web foot"

Example of "lobe foot"

 is an extinct genus of flightless aquatic birds that lived during the Santonian to Campanian sub-epochs of the Late Cretaceous (89–65 mya).
Although some of the smaller species might have been able to fly,Hesperornis and Baptornis had only vestigial wings. Like living foot-propelled diving birds, the femur and metatarsus were short, whereas the tibia was long. The legs were also set far back on the body, as in loonsgrebes or penguins."
"The cladistics vs. phenetics debate of the mid-20th century revived scientific interest in generalizing comparisons. As a consequence, the discredited grebe-loon link was discussed again. This even went as far as proposing monophyly for grebes, loons, and the toothed Hesperornithiformes "
These birds were originally combined with Ichthyornis in the paraphyletic "Odontornithes" by Othniel Charles Marsh, in 1873. In 1875, they were separated as Odontolcae. The group was often considered to be allied to loons and grebes,[4]or to the Paleognathae.[5] These similarities, however, as the more recently determined fact that the osteons of their bones - at least in Hesperornis - were arranged in a pattern similar to that in Neognathae,[6] are today considered to be due to convergent evolution.[7]

"The skull of Hesperornis proves to be neognathous in the majority of diagnostic
characters including the presence of the intrapterygoid joint."
"A cladistic analysis of the skeletons of loons (Gaviidae), grebes (Podicipedidae), and the Cretaceous diving birds, Hesperornisand Baptornis, supports the hypothesis that they form a monophyletic group (here called the Gaviomorphae) within the class Aves. Two lineages within the gaviomorphs can be delineated: (1) loons + grebes, and (2) Hesperornis + Baptornis. The Early Cretaceous Enaliornis and the Late Cretaceous Neogaeornis are related to the second lineage; the Late Cretaceous Lonchodytes, often placed near loons, is apparently not a gaviomorph but perhaps a charadriiform. Skeletal evidence also suggests that penguins (Spheniscidae) are the sister-group of the Gaviomorphae. Arguments that similarities of gaviomorph taxa represent convergence are not well founded. First, morphological differences among taxa do not constitute valid evidence against their monophyly, as many previous workers have argued. Second, in no case has anyone supporting convergence presented a corroborated alternative phylogenetic hypothesis. A close relationship among gaviomorphs, penguins, and apparently also the Procellariiformes and Pelecaniformes implies that a lineage of aquatic birds was established very early in avian history, presumably in the Early Cretaceous or Late Jurassic." (Joel Cracraft 1982)

Looks like Joel Cracraft was on the right track!
(Note the issue here is not whether grebes and loons go together but that hesperornithiformes is linked to modern birds such as grebes and/or loons.)

I was quite surprised/pleased to see this:
"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 [ancestral to] the crown group birds. It is not entirely clear whether the Palaeognathae too are paraphyletic, or represent a primitve grade of birds.[6]"

This seems to be saying exactly what I have been saying. 
Modern bird taxa developed from such taxa as Hesperornithes and Ichthyornithes etc.

Diving birds are birds which plunge into water to catch fish or other food. They may enter the water from flight, as does the brown pelican (Pelecanus occidentalis), or they may dive from the surface of the water. More than likely they evolved from birds already adapted for swimming that were equipped with such adaptations as lobed or webbed feet forpropulsion.

Foot-propelled diving birds

Some diving birds - for example, the extinct Hesperornithes of the Cretaceous Period - propelled themselves with their feet. They were large, streamlined, flightless birds with teeth for grasping slippery prey. Today, Cormorants (familyPhalacrocoracidae), Loons (Gaviidae), and Grebes (Podicipedidae) are the major groups of foot propelled diving birds.

Wing-propelled diving birds

Other diving birds are wing - propelled, most notably the Penguins (Sphenisciformes), Dippers (Cinclus) and Auks(Alcidae).

"Thus the toes of Baptornis were probably webbed as in loons or ducks, rather than lobed as in grebes and Hesperornis: for birds with lobed toes, rotating the toes is necessary to reduce drag when pulling the foot forward for a new stroke."
Loss and/or fusion of caudal vertebrae in pygostyle-like structures was a general trend in Cretaceous avian evolution, and a full pygostyle and associated structures may have evolved more than once to similar shapes. The fact that Gansus had non-pneumatized, dense bones, like those of hesperornithines, although it was not a specialized diver, is interesting to note. Similarly, the bone structure of Hesperornis indicates that as opposed to Enantiornithes and in line with other Ornithurae it showed rapid, uninterrupted growth to adult size.[5]
They [cormorants] are coastal rather than oceanic birds, and some have colonised inland waters - indeed, the original ancestor of cormorants seems to have been a fresh-water bird, judging from the habitat of the most ancient lineage. They range around the world, except for the central Pacific islands.
We report on the bone microstructure of the Cretaceous birds Hesperornis regalis and Ichthyornis victor. Thin sections of representative elements of both these ornithurine birds show a rapid, sustained bone deposition without any pauses or interruptions in bone formation. This growth pattern contrasts sharply with the cyclical pattern of bone deposition previously reported for the Cretaceous non-ornithurine birds Patagopteryx and representatives of the enantiornithines. These findings suggest physiological advancement in Cretaceous ornithurine birds. The bone microstructure of the diving Hesperornis shows similarities to the bone structure of modern penguins, and to that of a loon from the Cretaceous of Antarctica.

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