title: Central nervous system and muscular bundles preserved in a 240 million year old giant bristletail (Archaeognatha: Machilidae).
abstract: Among the incomparably diverse group of insects no cases of central nervous system (CNS) preservation have been so far described in compression fossils. A third of the fossil insects collected from a 240-239 million year old (Ma) level at Monte San Giorgio UNESCO World Heritage (Switzerland-Italy) underwent phosphatization, resulting in the extraordinary preservation of soft tissues. Here we describe Gigamachilis triassicus gen. et sp. nov. (Archaeognatha: Machiloidea: Machilidae) that, with an estimated total length of ~80 millimeters, represents the largest apterygote insect ever recorded. The holotype preserves: (i) components of the CNS represented by four abdominal ganglia, optic lobes with neuropils and compound retina; (ii) muscular bundles. Moreover, G. triassicus, possessing morphological features that prompt its assignment to the extant archaeognathan ingroup Machilidae, places the origin of modern lineages to Middle Triassic. Interestingly, at Monte San Giorgio, in the same stratigraphic unit the modern morphology of G. triassicus co-occurs with the ancient one represented by Dasyleptus triassicus (Archaeognatha: †Monura). Comparing these two types of body organization we provide a new reconstruction of the possible character evolution leading towards modern archaeognathan forms, suggesting the acquisition of novel features in a lineage of apterygote insects during the Permian or the Lower Triassic.
authors.affiliation: Dipartimento di Scienze Agrarie e Ambientali - Università degli Studi di Milano, Via Celoria 2, I-20133 Milano, Italy.
authors.forename: Matteo
authors.initials: M
authors.lastname: Montagna
authors.affiliation: Functional Morphology, Department of Biology II and GeoBio-Center, LMU Munich, Großhaderner Str. 2, 82152 Planegg-Martinsried, Germany.
authors.forename: Joachim T
authors.initials: JT
authors.lastname: Haug
authors.affiliation: Dipartimento di Scienze della Terra "Ardito Desio" - Università degli Studi di Milano, Via Mangiagalli 34, I-20133 Milano, Italy.
authors.forename: Laura
authors.initials: L
authors.lastname: Strada
authors.affiliation: Functional Morphology, Department of Biology II and GeoBio-Center, LMU Munich, Großhaderner Str. 2, 82152 Planegg-Martinsried, Germany.
authors.forename: Carolin
authors.initials: C
authors.lastname: Haug
authors.affiliation: Consulenze Geologiche e Ambientali SA, Via Comacini 31, CH-6834 Morbio Inferiore, Switzerland.
authors.forename: Markus
authors.initials: M
authors.lastname: Felber
authors.affiliation: Dipartimento di Scienze della Terra "Ardito Desio" - Università degli Studi di Milano, Via Mangiagalli 34, I-20133 Milano, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Tintori
mesh_terms: D000818:Animals; D005075:Biological Evolution; D002490:Central Nervous System / Q000033:anatomy & histology*; D005580:Fossils; D007091:Image Processing, Computer-Assisted; D007313:Insecta / Q000033:anatomy & histology*; D009132:Muscles / Q000033:anatomy & histology*; D011309:Preservation, Biological