Editing Magnetoreception (section)

==== Iron-based ====

The second proposed model for magnetoreception relies on clusters composed of [[iron]], a natural mineral with strong magnetism, used by magnetotactic bacteria. Iron clusters have been observed in the upper beak of homing pigeons,<ref name="Fleissner2003">{{cite journal |last1=Fleissner |first1=Gerta |last2=Holtkamp-Rötzler |first2=Elke |last3=Hanzlik |first3=Marianne |last4=Winklhofer |first4=Michael |last5=Fleissner |first5=Günther |last6=Petersen |first6=Nikolai |last7=Wiltschko |first7=Wolfgang |date=26 February 2003 |title=Ultrastructural analysis of a putative magnetoreceptor in the beak of homing pigeons |journal=[[Journal of Comparative Neurology]] |volume=458 |issue=4 |pages=350–360 |doi=10.1002/cne.10579 |pmid=12619070|s2cid=36992055 }}</ref> and other taxa.<ref name="Falkenberg2010">{{Cite journal |last1=Falkenberg |first1=Gerald |last2=Fleissner |first2=Gerta |last3=Schuchardt |first3=Kirsten |last4=Kuehbacher |first4=Markus |last5=Thalau |first5=Peter |last6=Mouritsen |first6=Henrik |last7=Heyers |first7=Dominik |last8=Wellenreuther |first8=Gerd |last9=Fleissner |first9=Guenther |date=2010-02-16 |title=Avian Magnetoreception: Elaborate Iron Mineral Containing Dendrites in the Upper Beak Seem to Be a Common Feature of Birds |journal=[[PLoS One]] |language=en |volume=5 |issue=2 |pages=e9231 |doi=10.1371/journal.pone.0009231 |doi-access=free |issn=1932-6203 |pmc=2821931 |pmid=20169083|bibcode=2010PLoSO...5.9231F }}</ref><ref name="Hore 2016"/><ref name="Solov'yov Greiner 2007">{{cite journal |last1=Solov'yov |first1=Ilia A. |last2=Greiner |first2=Walter |date=September 2007 |title=Theoretical Analysis of an Iron Mineral-Based Magnetoreceptor Model in Birds |journal=[[Biophysical Journal]] |volume=93 |issue=5 |pages=1493–1509 |doi=10.1529/biophysj.107.105098 |pmid=17496012 |bibcode=2007BpJ....93.1493S |pmc=1948037 }}</ref><ref name="Treiber2012">{{cite journal |last1=Treiber |first1=Christoph Daniel |last2=Salzer |first2=Marion Claudia |last3=Riegler |first3=Johannes |last4=Edelman |first4=Nathaniel |last5=Sugar |first5=Cristina |last6=Breuss |first6=Martin |last7=Pichler |first7=Paul |last8=Cadiou |first8=Herve |last9=Saunders |first9=Martin |last10=Lythgoe |first10=Mark |last11=Shaw |first11=Jeremy |last12=Keays |first12=David Anthony |title=Clusters of iron-rich cells in the upper beak of pigeons are macrophages not magnetosensitive neurons |journal=Nature |date=April 2012 |volume=484 |issue=7394 |pages=367–370 |doi=10.1038/nature11046 |pmid=22495303 |bibcode=2012Natur.484..367T }}</ref> Iron-based systems could form a magnetoreceptive basis for many species including turtles.<ref name="Rodgers Hore 2009" /> Both the exact location and ultrastructure of birds' iron-containing magnetoreceptors remain unknown; they are believed to be in the upper beak, and to be connected to the brain by the [[trigeminal nerve]]. This system is in addition to the cryptochrome system in the retina of birds. Iron-based systems of unknown function might also exist in other vertebrates.<ref name="Kishkinev Chernetsov 2015">{{cite journal |last1=Kishkinev |first1=D. A. |last2=Chernetsov |first2=N. S. |title=Magnetoreception systems in birds: A review of current research |journal=Biology Bulletin Reviews |volume=5 |issue=1 |year=2015 |doi=10.1134/s2079086415010041 |pages=46–62|bibcode=2015BioBR...5...46K |s2cid=18229682 }}</ref>