Antiarchi

Antiarchi ("Opposite anus") is an order of heavily armored placoderms. The antiarchs form the second-most successful group of placoderms after the arthrodires in terms of numbers of species and range of environments. The order's name was coined by Edward Drinker Cope, who, when examining some fossils that he thought were armored tunicates related to Chelysoma, mistakenly thought that the orbital fenestra (i.e., the hole in the headshield for the eyes, nose and pineal foramen) was the opening for the mouth, or oral siphon, and that the opening for the anal siphon was on the other side of the body, as opposed to having both oral and anal siphons together at one end.

Not to be confused with acritarch.

Antiarchi Temporal range: Late Llandovery[1][2]- Famennian
Bothriolepis canadensis
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	†Placodermi
Order:	†Antiarchi Cope, 1885

The front portions of their bodies were heavily armored, to the point of literally resembling a box with eyes, with the sometimes scaled, sometimes naked rear portions often becoming sinuous, particularly with later forms. The pair of pectoral fins were modified into a pair of caliper-like, or arthropod-like limbs. In primitive forms, such as Yunnanolepis, the limbs were thick and short, while in advanced forms, such as Bothriolepis, the limbs were long and had elbow-like joints. The function of the limbs are still not perfectly understood, but, most hypothesize that they helped their owners pull themselves across the substrate, as well as allow their owners to bury themselves into the substrate.

Phylogeny

Below is a cladogram from Jia et al. (2010):[3]

Antiarchi

Parayunnanolepis       Dayaoshania     Grenfellaspis     Euantiarcha Bothriolepidoidei   Luquanolepis       Nawagiaspis     Jiangxilepididae   Jiangxilepis     Ningxialepis         Dianolepis     Bothriolepididae     Bothriolepis     Grossilepis         Monarolepis     Briagalepis       Microbrachiidae   Wudinolepis       Hohsienolepis     Microbrachius                 Asterolepidoidei   Byssacanthus         Hunanolepis         Kirgisolepis     Pterichthyodes         Gerdalepis     Sherbonaspis             Stegolepis       Asterolepis       Remigolepis     Pambulaspis

Timeline of genera

Chuchinolepis, Vanchienolepis and Yunnanolepis

External links

• Review of Antiarcha at Paleos

References

1. Burrow, Carol; Turner, Susan (September 1998). "A review of placoderm scales, and their significance in placoderm phylogeny". Journal of Vertebrate Paleontology. 19 (2): 204–219. doi:10.1080/02724634.1999.10011135.
2. Wang Junqing (1991). "The Antiarchi From Early Silurian Hunan" (PDF). Vertebrata PalAsiatica. 21 (3): 240–244. Archived from the original (PDF) on 2013-12-12. Retrieved 2013-05-27.
3. Jia, L. T.; Zhu, M.; Zhao, W. J. (2010). "A new antiarch fish from the Upper Devonian Zhongning Formation of Ningxia, China". Palaeoworld. 19 (1–2): 136. doi:10.1016/j.palwor.2010.02.002.

• Long, John A. The Rise of Fishes: 500 Million Years of Evolution Baltimore: The Johns Hopkins University Press, 1996. ISBN 0-8018-5438-5
• Sepkoski, Jack (2002). "A compendium of fossil marine animal genera (Placodermi entry)". Bulletins of American Paleontology. 364: 560. Archived from the original on 2004-10-14. Retrieved 2011-05-20.