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Книга по требованию: Transactions, Vol. 10

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Of the Eighteenth and Nineteenth Annual Meeting of the Kansas Academy of Science, 1856-86, With the Reports of the Secretary (Classic Reprint)

Вес: 0.28 кг.
Год издания: 2015
Страниц: 172 Переплет: мягкая обложка
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Excerpt from Transactions, Vol. 10: Of the Eighteenth and Nineteenth Annual Meeting of the Kansas Academy of Science, 1856-86, With the Reports of the Secretary

That the track is probably that of a right foot rather than a left, is indicated by the wider separation of the outer toe from the middle toe, resulting from the greater versatility of the outer toe as compared with the inner toe - a character illustrated in many families of existing birds, and carried to an extreme in the cuckoos and the woodpeckers, in which the outer anterior toe is entirely reversed in its direction and becomes a backward-pointing member.

It will be seen from the accompanying cut that our bird-track exhibits the imprint of all four of the toes. The outer anterior toe is represented for fully two-thirds of its length. The middle and inner anterior toes are entirely impressed, even to the claws at their extremities - the claw being very distinctly marked upon the middle toe. The ball of the foot has left a deep impression, and the posterior toe has made an unmistakable imprint upon the sand similar to those made at the present time by birds whose hind toes just reach the ground. That this impression is avian in its character rather than reptilian, is evident from the imprint of the hind toe, for no dinosaur or other reptile, either recent or extinct, is known to have a backwardly directed toe. Some dinosaurs have a fourth small or rudimentary anterior toe, but in no case has a posterior toe been discovered. The absence of the impression of a posterior toe in the so-called bird-tracks of the Connecticut river Triassic sandstone has led the best authorities to consider those tracks reptilian rather than avian. The small size of our Dakota track is a confirmatory indication of its avian character. It measures only two inches from anterior middle claw to claw of posterior toe, being a little larger than the foot of Professor O. C. Marsh's Ichthyornis victor as restored by him in his famous monograph of the Odontornithes. The restoration of the foot of Ichthyornis, however, was based upon a single phalangal bone, the only portion of the foot yet found, the rest of the skeleton of the foot having been restored in exact imitation of a living species of tern, which among recent birds Ichthyornis seems most closely to resemble.

The discovery of this avian footprint in the Dakota rocks considerably lowers the geological horizon of Kansas birds. The Niobrara group of the Cretaceous has hitherto furnished all our knowledge of ancient bird-life in Kansas.

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