The origin of the jawed vertebrate face: new insights from a synchrotron scanned skull of the primituve placoderm Romundina
2013 (English)In: Program and abstracts / [ed] Maxwell, E., Miller-Camp, J., Anemone, R.,, Los Angeles, U.S.A., 2013, 118-118 p.Conference paper, Abstract (Other academic)
Jawless cyclostomes and jawed gnathostomes show very different face patterns.Cyclostomes have a single median nasohypophysial duct, an anterior hypophysis and ashort telencephalon, while gnathostomes have a pair of nasal sacs opening externally, amore posterior separate hypophysis opening in the palate and a longer telencephalon.Embryonic processes differ as well. In cyclostomes, infraorbital premandibular crest cellsmigrate forwards either side of the nasohypophysial placode to form the upper lip; ingnathostomes they migrate between the hypophysial and nasal placodes to form thetrabecular-ethmoid region. Supraoptic neural crest remains posterior to thenasohypophysial duct in cyclostomes; it moves forward to create the nasal capsules ingnathostomes. Some fossil forms illustrate a sequenced transition between these twopatterns. The Silurian galeaspid (jawless stem gnathostome) Shuyu has a nasohypophysialduct, a short telencephalon, and an anteriorly oriented hypophysis, but the paired nasalsacs and hypophysis are separated by a rudimentary trabecula. A synchrotron scannedskull of the primitive Early Devonian placoderm (jawed stem gnathostome) Romundinashows a cranial cavity reminiscent of that of Shuyu (anteriorly directed hypophysis, veryshort telencephalon). The trabecular-ethmoid region is long and wide, extending anteriorto the small nasal capsule which is located just in front of the orbits. We interpret thesefeatures as uniquely primitive among gnathostomes. In size and position the trabecularethmoidregion of Romundina resembles the upper lip of cyclostomes and Shuyu,suggesting a cyclostome-like pattern of proliferation coupled with a gnathostome-likemigration path for the premandibular crest. The position of the nasal capsule suggests thatthe supraoptic crest had not migrated forwards. A new phylogenetic analysis suggeststhat the evolutionary sequence for the creation of the extant gnathostome face from acyclostome ancestral pattern involved 1) separation of the nasal and hypophysialplacodes (galeaspids: Shuyu), 2) loss of the nasohypophysial duct (basal placoderms:antiarchs, Brindabellaspis, Romundina), 3) shortening and narrowing of the trabecularethmoidregion, the nasal capsule becoming anterior (derived placoderms such asarthrodires); 4) lengthening of the telencephalon (crown gnathostomes). Galeaspid facialanatomy appears closer to gnathostomes than that of osteostracans, but it is unclearwhether osteostracans are primitive or autapomorphic in this respect.
Place, publisher, year, edition, pages
Los Angeles, U.S.A., 2013. 118-118 p.
IdentifiersURN: urn:nbn:se:uu:diva-213347OAI: oai:DiVA.org:uu-213347DiVA: diva2:681758
73rd Meeting of the Society of Vertebrate Paleontology
FunderEU, European Research Council, 233111
Supplement to the online Journal of Vertebrate Paleontology October 20132013-12-202013-12-202015-07-28Bibliographically approved