Ankylopollexia

Ankylopollexia is an extinct clade of dinosaurs within the order Ornithischia that lived from the Late Jurassic to the Late Cretaceous. It is considered a more derived clade of iguanodontians and contains the subgroup Styracosterna and Hadrosauriformes.[1] The name stems from the Greek word, “ankylos”, meaning stiff, fused, and the Latin word, “pollex”, meaning thumb. Originally described in 1986 by Sereno, this most likely synapomorphic feature of a conical thumb spine defines the clade.[2] Many ankylopollexians have not yet been placed in the phylogeny because of the lack of data on the specimens or simply just not analyzed yet. One of the most famous and most derived members of the Ankylopollexia clade is the Iguanodon.

First appearing around 156 million years ago, Ankylopollexia died out as a clade around 65.5 million years ago.[3] Mostly found in China, Eastern and Western Europe, and the Western United States, ankyllopolexians not have been found in Africa or South America. Even though they grew to be quite large, comparable to some carnivorous dinosaurs, they were herbivorous iguanodontians. Most ankylopollexians were bipedal.[4] However, most, also when grazing or moving slowly, would stand on all fours because of their shorter forelimbs.

Description

As a member of the order Ornithischia, the ankylopollexia had a pubis bone that points down and towards the tail. The ischium pointed forward to support the abdomen and is now parallel to the pubis as well. Both the ischium and the pubis are parallel to the vertebral column. This pelvic structure is sturdier compared to other orders in Dinosauria. Also, ornithischians, in general, have a smaller anteorbital fenestra. Characteristic of ornithischians, many ankylopollexians probably had cheek-like structures to hold food in their mouths. They could have been muscular or non-muscular tissue.[5]

As mentioned before, most ankylopollexians were bipedal. There are a few exceptions to this rule, including the Mantellisaurus. Because of its short forelimbs and short body, Mantellisaurus was bipedal when moving, but when standing or moving slowly, it used its forelimbs to balance itself.[6]

They also possess elongated skulls with powerful jaws for grazing. Many had teeth batteries to constantly replace the teeth that fell out from the grazing.[7]

Thumb

As the name implies, ankylopollexians possess a conical thumb spike. This feature is possessed by almost all species of ankylopollexians, including the famous Iguanodon. The purpose of these spikes is still debated. As they are herbivores, ankylopollexians could have used them for foraging or defense. The hadrosauroid Batyrosaurus possessed a thumb claw of about 4 cm in length.[8]

Size

Ankylopollexians vary greatly in size. The largest known ankylopollexian, also belonging to the hadrosaurid family, is the Shantungosaurus. It was about 14.7-16.6 meters in length and weighed, for the largest individuals, up to 16 tonnes (18 tons).[9][10] It is also one of the more derived species of the clade. Meanwhile, the previously mentioned Mantellisaurus weighed about 0.75 tons.[11] The type species of Camptosaurus is thought to have been only 6-7.9 meters in length and weighed around 785–874 kg.[12] In fact, Paul contends that the Camptosaurus was no more than 5 meters long and weighed no more than 0.5 tonnes.[13] Primitive ankylopollexians tended to be smaller as compared to the more derived Hadrosauridaes. Of course, there are exceptions to this trend, including one of the more basal genera of Hadrosauroidea, Bolong. They were thought to be around 200 kg.[14] Another exception of this trend is Tethyshadros, a more derived genera of Hadrosauroidea. Thought to be around 350 kg, Tethyshadros have been found only on certain islands in Italy. Their unusual size is explained by insular dwarfism.[15]

Distribution

Found in Wyoming, the type species of Ankylopollexia, Camptosaurus disapr, dates from possibly around the Callovian-Oxfordian, about 156-157 million years ago.[16] While the clade clearly starts in North America, the rest of the members of Ankylopollexia spreads quickly to Europe and Asia. Until about the Valangnian era of the Lower Cretaceous, it appears that only North America had ankypollexians. But in the early 2000s, an styracostern iguanodont called Lanzhousaurus was found in the north-central Gansu Province of China. Thought to have lived around 130 million years ago, the genus Lanzhousaurus has the characteristic larger lower jaw of ankylopollexians.[17] But even before the Barremian era, there is an even more derived member of the clade Ankylopollexia found in England. The genus Barilium is thought to have existed around 140 million years.[18] The ever so popular and famous Iguanodon, at least the well-substantiated species I. bernissartenesis, lived from the late Barremian to the earliest Aptian ages in Belgium.[19] As one of the more derived ankylopollexians, Iguandons lived in primarily Europe. While their clade eventually died out around 125 million years ago, Hadrosauroidae are believed to have originated in Asia around 122 million years ago.[20] They eventually spread throughout Europe, Asia, and North America where they lived until 65.5 million years ago with the mass extinction of dinosaurs.[21]

Phylogeny

About 157 million years ago, Ankylopollexia and Dryosauridae are believed to have split into two clades. Stemming from Dryomorpha, the dryosauridae are primitive iguanodonts and do not have much more derived species compared to ankylopollexians.[22] Yet, they lived longer than all ankylopollexians except for the family Hadrosauroidae.[23] Originally named and described in 1986 by Paul Sereno, Ankylopollexia received a more formal definition in a later paper by Sereno in 2005.[24] In the 1986 paper, genera Camptosauridae and Styracosterna were used to define the clade, but in the 2005 paper, the type species of Camptosaurus dispar and Parasaurolophus walkeri are used by Sereno to specifically and more formally characterize the clade. The clade encompasses two other major clades of the suborder Ornithopoda: Styracosterna and Hadrosauriformes. One of the most derived species of the clade is the well-known Iguanodon. Many ankylopollexians have not yet been placed in the phylogeny because of the lack of data on the specimens or simply just not analyzed yet.

The cladogram below follows the most up-to-date analysis by Andrew McDonald, 2012.[25]

Iguanodontia

Rhabdodontidae

Tenontosaurus


Dryomorpha

Dryosauridae


Ankylopollexia

Camptosaurus


Styracosterna

Uteodon


Hippodraco

Theiophytalia

Iguanacolossus

Lanzhousaurus

Kukufeldia

Barilium


Hadrosauriformes

Iguanodon

Hadrosauroidea (including Mantellisaurus, and Xuwulong)













References

  1. ↑ McDonald AT (2012) Phylogeny of Basal Iguanodonts (Dinosauria: Ornithischia): An Update. PLoS ONE 7(5): e36745. doi:10.1371/journal.pone.0036745
  2. ↑ Sereno, P.C. (1986). "Phylogeny of the bird-hipped dinosaurs (order Ornithischia)". National Geographic Research 2 (2): 234–56
  3. ↑ McDonald AT (2012) Phylogeny of Basal Iguanodonts (Dinosauria: Ornithischia): An Update. PLoS ONE 7(5): e36745. doi:10.1371/journal.pone.0036745
  4. ↑ Foster, J. (2007). Camptosaurus dispar. Jurassic West: The Dinosaurs of the Morrison Formation and Their World. Indiana University Press. p. 219-221
  5. ↑ Galton, Peter M. (1973). "The cheeks of ornithischian dinosaurs". Lethaia 6 (1): 67–89.
  6. ↑ Paul, Gregory S. (2008). "A revised taxonomy of the iguanodont dinosaur genera and species". Cretaceous Research 29 (2): 192–216.doi:10.1016/j.cretres.2007.04.009.
  7. ↑ Palmer, D., ed. (1999). The Marshall Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals. London: Marshall Editions. p. 145. ISBN 1-84028-152-9.
  8. ↑ Pascal Godefroit, François Escuillié, Yuri L. Bolotsky and Pascaline Lauters (2012). "A New Basal Hadrosauroid Dinosaur from the Upper Cretaceous of Kazakhstan". In Godefroit, P. (eds). Bernissart Dinosaurs and Early Cretaceous Terrestrial Ecosystems. Indiana University Press. pp. 335–358.
  9. ↑ Glut, Donald F. (1997). "Shantungosaurus". Dinosaurs: The Encyclopedia. Jefferson, North Carolina: McFarland & Co. pp. 816–817. ISBN 0-89950-917-7.
  10. ↑ Zhao, X.; Li, D.; Han, G.; Hao, H.; Liu, F.; Li, L.; Fang, X. (2007). "Zhuchengosaurus maximus from Shandong Province". Acta Geoscientia Sinica 28 (2): 111–122. doi:10.1007/s10114-005-0808-x.
  11. ↑ Paul, Gregory S. (2008). "A revised taxonomy of the iguanodont dinosaur genera and species". Cretaceous Research 29 (2): 192–216.doi:10.1016/j.cretres.2007.04.009.
  12. ↑ Erickson, Bruce R. (2003). Dinosaurs of the Science Museum of Minnesota. St. Paul, Minnesota: The Science Museum of Minnesota. p. 33. ISBN 978-0-911338-54-6
  13. ↑ Paul, G.S., 2010, The Princeton Field Guide to Dinosaurs, Princeton University Press p. 284
  14. ↑ Wu Wen-hao, Pascal Godefroit, Hu Dong-yu (2010). "Bolong yixianensis gen. et sp. nov.: A new Iguanodontoid dinosaur from the Yixian Formation of Western Liaoning, China". Geology and Resources 19 (2): 127–133.
  15. ↑ Dalla Vecchia, F. M. (2009). "Tethyshadros insularis, a new hadrosauroid dinosaur (Ornithischia) from the Upper Cretaceous of Italy". Journal of Vertebrate Paleontology 29 (4): 1100–1116.
  16. ↑ Carpenter, K. and Wilson, Y. (2008). "A new species of Camptosaurus (Ornithopoda: Dinosauria) from the Morrison Formation (Upper Jurassic) of Dinosaur National Moument, Utah, and a biomechanical analysis of its forelimb". Annals of the Carnegie Museum 76: 227–263. doi:10.2992/0097-4463(2008)76[227:ansoco]2.0.co;2.
  17. ↑ You, H.-L. (2006) Lanzhousaurus magnidens from the Lower Cretraceous of Gansu province, China: The largest-toothed herbivorous dinosaur in the world. JVP 26(3) Abstracts pp. 142
  18. ↑ Paul, Gregory S. (2008). "A revised taxonomy of the iguanodont dinosaur genera and species". Cretaceous Research 29 (2): 192–216.
  19. ↑ Carpenter, K.; Ishida, Y. (2010). "Early and "Middle" Cretaceous Iguanodonts in Time and Space" (PDF). Journal of Iberian Geology 36 (2): 145–164.
  20. ↑ Norman, David B.; Weishampel, David B. (1990). "Iguanodontidae and related ornithopods". In Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.). The Dinosauria. Berkeley: University of California Press. pp. 510–533. ISBN 0-520-06727-4.
  21. ↑ Sereno, P. C. (1999). The Evolution of Dinosaurs. (cover story). Science, 284(5423), 2137
  22. ↑ Norman, David B.; Weishampel, David B. (1990). "Iguanodontidae and related ornithopods". In Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.). The Dinosauria. Berkeley: University of California Press. pp. 510–533. ISBN 0-520-06727-4.
  23. ↑ Sereno, P.C. (1999). “The Evolution of Dinosaurs:. Science 234 (2): 2137-2147
  24. ↑ Sereno, P.C. (1986). "Phylogeny of the bird-hipped dinosaurs (order Ornithischia)". National Geographic Research 2 (2): 234–56
  25. ↑ McDonald, A. T. (2012). Farke, Andrew A, ed. "Phylogeny of Basal Iguanodonts (Dinosauria: Ornithischia): An Update". PLoS ONE. 7 (5): e36745. doi:10.1371/journal.pone.0036745. PMC 3358318Freely accessible. PMID 22629328.
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