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Central nervous system and muscular bundles preserved in a 240 million year old giant bristletail (Archaeognatha: Machilidae)

View Article: PubMed Central - PubMed

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.

No MeSH data available.


Related in: MedlinePlus

Gigamachilis triassicus holotype.(A) Macrophotography under cross-polarized light. Autofluorescence (473 nm, GFP) composite image, (B) color-marked version and (C) original image. Abbreviations: a = abdominal segment; ant = antenna; ap = abdominal appendage; ce = cerci; cx = coxa/coxopodite; ft = filum terminale; ga = ganglion; gl = glossa; l = labium; l pro = lateral protocerebrum; m = muscle; m? = possible muscle; mxp = maxillary palp; ol = optic lobes; p = prementum; pm = postmentum; re = compound retina; ste = sternite; sty = stylus; t = thoracic segment; tp = thoracic appendage; tr = trochanter; vnc = ventral nerve cord. Arrows pointing to spines.
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f1: Gigamachilis triassicus holotype.(A) Macrophotography under cross-polarized light. Autofluorescence (473 nm, GFP) composite image, (B) color-marked version and (C) original image. Abbreviations: a = abdominal segment; ant = antenna; ap = abdominal appendage; ce = cerci; cx = coxa/coxopodite; ft = filum terminale; ga = ganglion; gl = glossa; l = labium; l pro = lateral protocerebrum; m = muscle; m? = possible muscle; mxp = maxillary palp; ol = optic lobes; p = prementum; pm = postmentum; re = compound retina; ste = sternite; sty = stylus; t = thoracic segment; tp = thoracic appendage; tr = trochanter; vnc = ventral nerve cord. Arrows pointing to spines.

Mentions: Specimen will be deposited at Museo Cantonale di Storia Naturale di Lugano (MCSN) – Switzerland. MCSN8463 (holotype) is an almost complete specimen (Figs 1, 2 and 3) while MCSN8466 (paratype) preserves only the abdomen and the metathorax (Supplementary Fig. S1).


Central nervous system and muscular bundles preserved in a 240 million year old giant bristletail (Archaeognatha: Machilidae)
Gigamachilis triassicus holotype.(A) Macrophotography under cross-polarized light. Autofluorescence (473 nm, GFP) composite image, (B) color-marked version and (C) original image. Abbreviations: a = abdominal segment; ant = antenna; ap = abdominal appendage; ce = cerci; cx = coxa/coxopodite; ft = filum terminale; ga = ganglion; gl = glossa; l = labium; l pro = lateral protocerebrum; m = muscle; m? = possible muscle; mxp = maxillary palp; ol = optic lobes; p = prementum; pm = postmentum; re = compound retina; ste = sternite; sty = stylus; t = thoracic segment; tp = thoracic appendage; tr = trochanter; vnc = ventral nerve cord. Arrows pointing to spines.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5384076&req=5

f1: Gigamachilis triassicus holotype.(A) Macrophotography under cross-polarized light. Autofluorescence (473 nm, GFP) composite image, (B) color-marked version and (C) original image. Abbreviations: a = abdominal segment; ant = antenna; ap = abdominal appendage; ce = cerci; cx = coxa/coxopodite; ft = filum terminale; ga = ganglion; gl = glossa; l = labium; l pro = lateral protocerebrum; m = muscle; m? = possible muscle; mxp = maxillary palp; ol = optic lobes; p = prementum; pm = postmentum; re = compound retina; ste = sternite; sty = stylus; t = thoracic segment; tp = thoracic appendage; tr = trochanter; vnc = ventral nerve cord. Arrows pointing to spines.
Mentions: Specimen will be deposited at Museo Cantonale di Storia Naturale di Lugano (MCSN) – Switzerland. MCSN8463 (holotype) is an almost complete specimen (Figs 1, 2 and 3) while MCSN8466 (paratype) preserves only the abdomen and the metathorax (Supplementary Fig. S1).

View Article: PubMed Central - PubMed

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.

No MeSH data available.


Related in: MedlinePlus