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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

Schematic reconstructions and alternative scenarios of Archaeognatha evolution.(A) Reconstruction of Gigamachilis triassicus and Dasyleptus triassicus in ventral view. Coxa or coxopodite (=basipod of Euarthropoda) marked yellow; endopod and derivatives marked green; exopod derivatives in blue. Left: G. triassicus. Right: D. triassicus, based on information provided by Bechly and Stockar28; two pairs of ventral structures (visible in the original figures) have been reconstructed: the median one originally interpreted as the styli is here re-interpreted as eversible vesicles (due to position correlation; in green), the lateral smaller ones represents the styli (in blue). Middle: D. triassicus in the same scale as G. triassicus to show the size ratio. (B) Alternative scenarios proposed for the Archaeognatha (Machiloidea and Dasyleptus) evolution; left: evolution of modern-type archaeognathans in Permian-Triassic Period from a Dasyleptus-like ancestor; right: evolution of modern-type archaeognathans in Silurian Period. Horizontal bars on branches represent the fossil record: in black those of sure attribution to Archaeognatha, in grey the Devonian specimens. KSZ: Kalkschieferzone; *: the most recent common ancestor (MRCA) of insect is dated according to Misof et al.47, whereas the MRCA of †Monura and extant lineages of Archaeognatha is placed before the fossil from Gaspé Peninsula (Early Devonian)16; dashed vertical line of the dendrogram is reported when no information on the date of the cladogenetic event is available.
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f4: Schematic reconstructions and alternative scenarios of Archaeognatha evolution.(A) Reconstruction of Gigamachilis triassicus and Dasyleptus triassicus in ventral view. Coxa or coxopodite (=basipod of Euarthropoda) marked yellow; endopod and derivatives marked green; exopod derivatives in blue. Left: G. triassicus. Right: D. triassicus, based on information provided by Bechly and Stockar28; two pairs of ventral structures (visible in the original figures) have been reconstructed: the median one originally interpreted as the styli is here re-interpreted as eversible vesicles (due to position correlation; in green), the lateral smaller ones represents the styli (in blue). Middle: D. triassicus in the same scale as G. triassicus to show the size ratio. (B) Alternative scenarios proposed for the Archaeognatha (Machiloidea and Dasyleptus) evolution; left: evolution of modern-type archaeognathans in Permian-Triassic Period from a Dasyleptus-like ancestor; right: evolution of modern-type archaeognathans in Silurian Period. Horizontal bars on branches represent the fossil record: in black those of sure attribution to Archaeognatha, in grey the Devonian specimens. KSZ: Kalkschieferzone; *: the most recent common ancestor (MRCA) of insect is dated according to Misof et al.47, whereas the MRCA of †Monura and extant lineages of Archaeognatha is placed before the fossil from Gaspé Peninsula (Early Devonian)16; dashed vertical line of the dendrogram is reported when no information on the date of the cladogenetic event is available.

Mentions: The discovery of G. triassicus, a representative of Machilidae, besides tracing the origin of this lineage back to the Middle Triassic and extending the range of this group by approximately 200 My, sheds light also on the evolution of archaeognathan body organization. Archaeognatha with a different body organization co-occur in the same stratigraphic unit at Monte San Giorgio: (i) G. triassicus representing the new lineage with the presence of well developed cerci and with filum terminale and a large, possibly arched, metathorax supporting jumping capabilities; and (ii) D. triassicus, the more ancestral-type, surviving the end-Permian mass extinction (Fig. 4). The latter, according to the fossil record2829, was near to its extinction while the former was just blooming.


Central nervous system and muscular bundles preserved in a 240 million year old giant bristletail (Archaeognatha: Machilidae)
Schematic reconstructions and alternative scenarios of Archaeognatha evolution.(A) Reconstruction of Gigamachilis triassicus and Dasyleptus triassicus in ventral view. Coxa or coxopodite (=basipod of Euarthropoda) marked yellow; endopod and derivatives marked green; exopod derivatives in blue. Left: G. triassicus. Right: D. triassicus, based on information provided by Bechly and Stockar28; two pairs of ventral structures (visible in the original figures) have been reconstructed: the median one originally interpreted as the styli is here re-interpreted as eversible vesicles (due to position correlation; in green), the lateral smaller ones represents the styli (in blue). Middle: D. triassicus in the same scale as G. triassicus to show the size ratio. (B) Alternative scenarios proposed for the Archaeognatha (Machiloidea and Dasyleptus) evolution; left: evolution of modern-type archaeognathans in Permian-Triassic Period from a Dasyleptus-like ancestor; right: evolution of modern-type archaeognathans in Silurian Period. Horizontal bars on branches represent the fossil record: in black those of sure attribution to Archaeognatha, in grey the Devonian specimens. KSZ: Kalkschieferzone; *: the most recent common ancestor (MRCA) of insect is dated according to Misof et al.47, whereas the MRCA of †Monura and extant lineages of Archaeognatha is placed before the fossil from Gaspé Peninsula (Early Devonian)16; dashed vertical line of the dendrogram is reported when no information on the date of the cladogenetic event is available.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f4: Schematic reconstructions and alternative scenarios of Archaeognatha evolution.(A) Reconstruction of Gigamachilis triassicus and Dasyleptus triassicus in ventral view. Coxa or coxopodite (=basipod of Euarthropoda) marked yellow; endopod and derivatives marked green; exopod derivatives in blue. Left: G. triassicus. Right: D. triassicus, based on information provided by Bechly and Stockar28; two pairs of ventral structures (visible in the original figures) have been reconstructed: the median one originally interpreted as the styli is here re-interpreted as eversible vesicles (due to position correlation; in green), the lateral smaller ones represents the styli (in blue). Middle: D. triassicus in the same scale as G. triassicus to show the size ratio. (B) Alternative scenarios proposed for the Archaeognatha (Machiloidea and Dasyleptus) evolution; left: evolution of modern-type archaeognathans in Permian-Triassic Period from a Dasyleptus-like ancestor; right: evolution of modern-type archaeognathans in Silurian Period. Horizontal bars on branches represent the fossil record: in black those of sure attribution to Archaeognatha, in grey the Devonian specimens. KSZ: Kalkschieferzone; *: the most recent common ancestor (MRCA) of insect is dated according to Misof et al.47, whereas the MRCA of †Monura and extant lineages of Archaeognatha is placed before the fossil from Gaspé Peninsula (Early Devonian)16; dashed vertical line of the dendrogram is reported when no information on the date of the cladogenetic event is available.
Mentions: The discovery of G. triassicus, a representative of Machilidae, besides tracing the origin of this lineage back to the Middle Triassic and extending the range of this group by approximately 200 My, sheds light also on the evolution of archaeognathan body organization. Archaeognatha with a different body organization co-occur in the same stratigraphic unit at Monte San Giorgio: (i) G. triassicus representing the new lineage with the presence of well developed cerci and with filum terminale and a large, possibly arched, metathorax supporting jumping capabilities; and (ii) D. triassicus, the more ancestral-type, surviving the end-Permian mass extinction (Fig. 4). The latter, according to the fossil record2829, was near to its extinction while the former was just blooming.

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