Hesperornithes

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Hesperornitheans
Temporal range:
Ma
Restored skeleton of
Hesperornis regalis
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Saurischia
Clade: Theropoda
Clade: Avialae
Clade: Ornithurae
Clade: †Hesperornithes
Fürbringer, 1888
Subgroups[4]
Synonyms

Hesperornithiformes Sharpe, 1899[3]

Hesperornithes is an extinct and highly specialized group of aquatic

Canadaga arctica, may have reached a maximum adult length of 2.2 metres (7.2 ft).[5]

Hesperornitheans were the only Mesozoic avialans to colonize the oceans. They were wiped out in the Cretaceous–Paleogene extinction event, along with enantiornitheans and all other non-avian dinosaurs.

Anatomy and ecology

Life restoration of Hesperornis regalis

Most of what is known about this group rests on analyses of single species, as few provide sufficiently complete

hesperornithids like Hesperornis and Baptornis had only vestigial wings. As in the case of modern foot-propelled diving birds, the femur and metatarsus of these animals were short, whereas the tibia was long. The legs were also set far back on the body, as in loons, grebes or penguins. Hesperornithids must have been powerful swimmers and divers but extremely ungainly on the land, and probably spent little time ashore except to nest. They were rather long-bodied, and measured about 6 feet (180 cm) long.[6]

Some researchers think that on land they had to slide on their bellies and push with their legs; the hip and knee joints were shaped such that these species could not move them dorsoventrally, and in a resting position the feet projected sideways from the body, which would have prevented them from walking upright.

diving ducks and cormorants rather than with loons or grebes.[8]

The snout was long, and tipped with a slightly hooked beak. Behind the beak, the jaws were filled with a series of simple, sharp teeth which were set into a longitudinal groove. These probably helped to seize

mergansers.[9][10] Unlike modern birds, they retained a joint between the lower jaw bones. It is believed that this allowed them to rotate the back portion of the mandible independently of the front, thus allowing the lower teeth to disengage.[6]

Evolution

Currently, the hesperornitheans are recognized as a very specialized lineage that is not ancestral to modern birds. Still, their relationship is close enough that they probably diverged from the ancestors of modern birds as late as the earliest Cretaceous.

The earliest known hesperornithean is the Early Cretaceous Enaliornis. The majority of hesperornithean species are known from the Late Cretaceous of North America. Small hesperornithean bones are known from the freshwater deposits of the Late Cretaceous of the Judith River Group as well as the Hell Creek and Lance Formations, and in several Eurasian sites. These species were about the size of a cormorant or a loon.

Classification

The clade Hesperornithes was originally named as a subclass of

phylogenetics. Clarke defined Hesperornithes as all species closer to Hesperornis regalis than to modern birds, and regarded Hesperornithiformes as a junior synonym, though she did not define the latter name. Clarke also defined the more inclusive group Hesperornithidae as all hesperornitheans closer to Hesperornis than to Baptornis.[3]

Hesperornitheans were originally combined with

bony palate).[13] 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,[14] are today considered to be due to convergent evolution.[15][16]

Relationships

In 2015, a species-level phylogenetic analysis found the following relationships among hesperornitheans.[17]

Hesperornithes

References

  1. ^
    doi:10.1016/j.palwor.2012.02.005
    .
  2. ^ Tomonori Tanaka; Yoshitsugu Kobayashi; Ken'ichi Kurihara; Anthony R. Fiorillo; Manabu Kano (2017). "The oldest Asian hesperornithiform from the Upper Cretaceous of Japan, and the phylogenetic reassessment of Hesperornithiformes". Journal of Systematic Palaeontology. Online edition. doi:10.1080/14772019.2017.1341960.
  3. ^
    hdl:2246/454
    .
  4. ^ Holtz, Thomas R. Jr. (2012) Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages, Winter 2011 Appendix.
  5. doi:10.1080/14772019.2010.502910
    .
  6. ^
    ISBN 978-0895770653
    .
  7. doi:10.1006/cres.1997.0102
    .
  8. S2CID 133964417
    .
  9. ^ Marsh, Othniel Charles (1880): Odontornithes, a Monograph on the Extinct Toothed Birds of North America. Government Printing Office, Washington DC.
  10. JSTOR 1364594
    .
  11. ^ Fürbringer, M. (1888): Untersuchungen zur Morphologie und Systematik der Vögel (2 vols). Von Holkema, Amsterdam.
  12. JSTOR 2413412
    .
  13. S2CID 27583011
    .
  14. JSTOR 4087243
    .
  15. S2CID 11147804
    .
  16. ^ Bogdanovich, I.O. (2003). "Морфологiчнi аспекти філогеніі Hesperornithidae (Ornithurae, Aves)" [Morphological Aspects of the Phylogeny of the Hesperornithidae (Ornithurae, Aves)] (PDF). Vestnik Zoologii (in Ukrainian, Russian, and English). 37 (6): 65–71. Archived from the original (PDF) on August 31, 2021.
  17. S2CID 83686657
    .
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