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.

Full text

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Scientific RepoRts | 7:46016 | DOI: 10.1038/srep46016
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Central nervous system and
muscular bundles preserved in a
240 million year old giant bristletail
(Archaeognatha: Machilidae)
Matteo Montagna1, Joachim T. Haug2, Laura Strada3, Carolin Haug2, Markus Felber4 &
Andrea Tintori3
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.
e exceptional preservation of so tissues in compression fossils has been reported only in few occurrences
within invertebrates, as in the case of Cambrian arthropods from Chengjiang (e.g., refs 1–5) and Burgess Shale
(e.g., refs 6–8). Such so tissue preservation has been only exceptionally achieved by tissue mineralization, usu-
ally involving pyritisation and phosphatization9,10 or, in the case of non-mineralized fossils, in the form of ker-
ogenized carbon lms11. Phosphatization of organic matter is a process occurring in anoxic conditions and it
is usually mediated by bacteria9; the diusion of phosphate released from the decaying animal’s tissues to the
surrounding media is prevented by a microbial lm acting as insulation10. Approximately one third of the fos-
sil insects collected from the Kalkschieferzone (239.51 ± 0.15 Ma)12 of Monte San Giorgio (UNESCO World
Heritage Site, Switzerland-Italy) are completely or partially phosphatized13. In this Lagerstätte, phosphatiza-
tion has been observed also in crustaceans but, interestingly, never among vertebrates (A.T. pers. obs). Here we
describe two completely phosphatized specimens we assign to an extant bristletail group (Insecta: Archaeognatha:
Machiloidea: Machilidae). ey exhibit giant size, compared to known extinct and extant species (overall organ-
ism length of ~80 mm, body plus lum terminale), and extraordinarily preserved internal so tissues, notably
components of the central nervous system (CNS) and muscular bundles.
e fossil record of Archaeognatha (Machiloidea plus †Monura) is sparse and is oen represented by frag-
mentary material. Specimens attributed to archaeognathan lineages span from Late Devonian (~379 Ma)14 to
Miocene (~13 Ma)15. So far, most of the Paleozoic and Mesozoic samples are representatives of Dasyleptus, the
1Dipartimento di Scienze Agrarie e Ambientali - Università degli Studi di Milano, Via Celoria 2, I-20133 Milano, Italy.
2Functional Morphology, Department of Biology II and GeoBio-Center, LMU Munich, Großhaderner Str. 2, 82152
Planegg-Martinsried, Germany. 3Dipartimento di Scienze della Terra “Ardito Desio” - Università degli Studi di Milano,
Via Mangiagalli 34, I-20133 Milano, Italy. 4Consulenze Geologiche e Ambientali SA, Via Comacini 31, CH-6834 Morbio
Inferiore, Switzerland. Correspondence and requests for materials should be addressed to M.M. (email: matteo.
montagna@unimi.it)
Received: 15 June 2016
Accepted: 28 February 2017
Published: 07 April 2017
OPEN

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only ingroup of †Dasyleptidae and †Monura (hence equivalent to these), while most of Cenozoic species are rep-
resentatives of Machilis (Machilidae). e oldest bristletail fossils are fragments that date back to the Devonian
Period14,16. A specimen described from Gaspé Bay (390–392 Ma) is a head capsule plus a separate thoracic frag-
ment from the same organism16. e presence of large but dorsally not converging eyes on the head capsule, a
synapomorphic trait of all modern bristletails17, suggest the assignment of this specimen to the Paleozoic monu-
ran rather than to modern lineages. Findings from the compressed shales of Gilboa (376–379 Ma) are repre-
sented by partial tergites plus an eye fragment. e tergites bear con-shaped sockets compatible with structures
present in extant bristletails, while the eye fragment was “tentatively identied as belonging to machilid insect” by
the authors14. So far, fossils of certain attribution to Machilidae are known only from the Eocene18–20. Complete
or almost complete Palaeozoic specimens of clear systematic aliation have been described only for the extinct
genus Dasyleptus (†Monura)21–27. ree specimens of Dasyleptus triassicus (†Monura) have been recovered from
the same stratigraphic unit of our ndings28, and many specimens from the German Upper Buntsandstein depos-
its (Obere Röttonsteine, Early Anisian) in Lower Franconia and uringia29. ese ndings extend the presence
of Dasyleptus well aer the end-Permian mass extinction (252.3 Ma) and demonstrate that these organisms were
still quite common in the Middle Triassic. Here we provide an updated reconstruction of character evolution
leading towards the modern forms of bristletails based on the comparison between the ancient-type D. triassicus
and the modern-type represented by the new species described. Furthermore, we provide evidence for the acqui-
sition of a new body organization in a lineage of apterygote insects at the end of the Permian or during the Triassic
Period, aer the end-Permian mass extinction.
Results
Systematic palaeontology. Euarthropoda sensu Walossek, 199930; Insecta Linnaeus, 1758; Archaeognatha
Börner, 1904; Machiloidea Handlirsch, 1904; Machilidae Grassi, 1888; Gigamachilis gen. nov. http://zoobank.org/
urn:lsid:zoobank.org:act:58CF94C0-30E8-4102-B4CD-918FDE929C02
Type species. Gigamachilis triassicus new species here designated. http://zoobank.org/urn:lsid:zoobank.
org:act:760D7E33-357C-430E-BB93-F71EF36B32DA
Etymology. Giga- (from Greek gígas) means giant, referring to the very large size; -machilis from Machilidae
to which Gigamachilis is ascribed; triassicus (Latin) refers to the Triassic Period.
Material. e two G. triassicus types were recovered at the UNESCO World Heritage Middle Triassic site
of Monte San Giorgio (Switzerland) in locality D (Val Mara, Meride) on the uppermost part of the Lower
Kalkschieferzone. Detailed information regarding geology, dating of the collecting site and on the fossil assem-
blage is reported in Supplementary Note 1.
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).
Taphonomy and preservation. Holotype and paratype are fully phosphatized. e holotype preserves the
entire body, including so tissues, with the exception of the distal part of the body appendages as the maxillary
palps, the antennae, the walking legs and the lum terminale. is preservation, including the loss of the delicate
appendages, suggests that G. triassicus was rapidly transported from its original habitat to the depositional basin
by a high-energy event, such as oods caused by heavy rains. e rapid transportation of the specimens to the
anoxic condition of the depositional basin represents a requirement to obtain so tissue preservation through the
bacteria-mediated process of phosphatization. Since the body outline of both specimens is preserved, we can infer
that underwater currents and bioturbation were absent in the depositional environment.
Diagnosis. Huge machilids, almost twice the size of the largest species of Machilidae known so far. e pat-
tern of coxal vesicles distribution is not congruent with any previously described form, both extinct and extant.
Description. G. triassicus is ascribed to Archaeognatha based upon the following characters: large maxillary
palps with several elements, abdominal coxopodites with coxopodal vesicles and styli, paired annulated cerci and
lum terminale (basal parts preserved). e presence of styli-like structures on the second thoracic leg and of
scales on appendages prompts its attribution to the extant group Machilidae.
Here we describe the new taxon based on the almost complete holotype (MCSN8463; Figs1, 2 and 3); the
description of the partially preserved paratype (SupplementaryFig.S1) is provided in the Supplementary Note 1.
General habitus: specimen with head and thorax slightly rotated in the sagittal plane, only visible in ventral
view; body length from the apex of the head to the apex of the last abdominal segment, thus excluding lum ter-
minale, of 40 mm; body maximum width of 12.5 mm (second thoracic segment) (Fig.1). On the base of the ratio
between the length of the lum terminale and that of the whole organism in extant taxa, the length of G. triassicus
was estimated in approximately 80 mm.
Head: eyes very large, developed laterally. Antennae partially preserved, only proximal parts visible: antennal
socket, scapus, pedicellus and a portion of the annulated agella (length 2.9 mm). Mouthparts partially preserved.
e terminal element of the right labial palp and the rst three elements of the large leg-like maxillary palps are
visible; labium prementum, maxillary palpifers and glossae are partially visible.
orax: total length 9.8 mm, maximum width at mesothorax 12.5 mm. Impression of lateral rims of pronotum
and mesonotum preserved on the right side (respectively 1.8 and of 3.6 mm long; mesonotum thickness 0.6 mm),
rim of mesonotum partially preserved on the le side. Procoxae (length: right 3.9 mm, le 3.3 mm), proximal
part of protrochanters, mesocoxae (length: right 4.2 mm, le 2.8 mm) and mesotrochanters (length: right 3.5 mm,

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le 4.3 mm) preserved. Le mesocoxa bearing the proximal part of the coxal stylet (length 0.9 mm). Trochanter
distally lobe-shaped. Right metacoxa (length 4.7 mm) and metatrochanter preserved (length 9.2 mm), the rst
bearing coxal stylet (length 4.3 mm), setae (length 0.35 mm) and scales (Figs1 and 2). Le metatrochanter only
partially visible.
Abdomen: composed of 10 visible segments, the rst only partially visible on the right side, the last segment
bearing the proximal part of the two cerci and of the lum terminale. Total length 26.3 mm, maximum width at
abdominal metamere I 10.1 mm. Inferior rim of the tergite and right coxopodite preserved on abdominal meta-
meres I to VIII, whereas in metamere IX these structures are visible but poorly preserved (Fig.1). Coxopodal ves-
icles present on abdominal segments I to VII (Figs1 and 2E–H). Abdominal styli are clearly visible on abdominal
appendages II (le) and IV (right). Cerci and lum terminale on segment X partially preserved.
Soft tissue preservation. Notably, in the holotype of Gigamachilis triassicus so tissues are preserved,
namely parts of the central nervous system and muscular bundles within legs, abdominal appendages and in the
head. e following structures of the central nervous system, are preserved: (i) optic lobes and, possibly, compo-
nents of the lateral protocerebrum (right side) (Figs1, 2A,B and 3D–G); (ii) partial ventral nerve cord composed
Figure 1. Gigamachilis triassicus holotype. (A) Macrophotography under cross-polarized light.
Autouorescence (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;  = lum 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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of four pairs of abdominal ganglia with their connectives (Figs1 and 3A,B). Symmetrically to the postmentum,
two semispherical structures are preserved (Figs1, 2A,B and 3D–G). Due to their position and to the striated
structures they are interpreted as compound retinae (Fig.3D–G). Posteriorly to the retina the optic lobes are
visible (Figs1, 2A,B, 3D–G). On the right side the outline of the three nested retinotopic neuropils characteristic
of the optic lobes of extant archaeognathans (Fig.3E–G) can be distinguished, namely, from outside to inside: the
lamina, the medulla on which it is possible to recognize the Cuccati’s bundle (indicated by the arrow in Fig.3F)
and the protolobula. In addition, three other areas, possibly belonging to the lateral protocerebrum are preserved
(Fig.3D–G). A bundle-like feature is visible below the optic lobes; considering its position and its brous nature,
it might represent segmental cephalic muscular bundles such as those present below the posterior tentorium or as
the superimposed muscles of the labial palp (distal part of the labial right palp visible in Fig.2A,B).
More clearly than in the head region, in four abdominal segments of G. triassicus ganglia joined by their paired
connectives are visible (Figs1 and 3A,B). e exceptional preservation of these structures allows the identica-
tion of two hemiganglia in three out of the four preserved ones and, possibly, the commissure in ganglion VIIa
and VIIIa. ey are compatible with neuropils within the ganglia (length and width of the ganglia: VIa ~440 μ m,
~320 μ m; VIIa ~580 μ m, ~310 μ m; VIIIa ~370, ~260 μ m).
Muscular bundles, hypothesized as femur-trochanter and adductor muscles are preserved respectively in the
mesotrochanter and within the right hind leg in coxa and trochanter (Figs1B,C and 2C,D). In addition, within
abdominal plates I to IV muscles of stylets and of coxal vesicles are visible.
Discussion
Gigamachilis triassicus, with an estimated total length of ~80 millimeters, is known from two phosphatized spec-
imens preserved in ventral view. e exceptional preservation of so tissues at ultrastructural level observed in
G. triassicus includes abdominal ganglia, compound retina, optic lobes with the possible presence of the three
nested neuropils found in modern archaeognathans, components of the lateral protocerebrum and muscular
bundles. is preservation occurred through the microbially mediated taphonomic process of phosphatization9
and it has never been reported so far among compression fossils of terrestrial arthropods. A remarkable case of
Figure 2. Exomorphological details of Gigamachilis triassicus. Head region, original image (A) and color-
marked version (B). ird thoracic appendage, original image (C) and color-marked version (D). Second
abdominal appendage, original image (E) and color-marked version (F). Fourth abdominal appendage, original
image (G) and color-marked version (H). All composite autouorescence images. Abbreviations as in Fig.1
with the addition of: cv = coxal vesicle; lip = labial palp; sc = scale; sp = spines.

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such exceptional preservation was previously observed in a specimen of Mesolimulus walchi from the Upper
Jurassic, where spiral and coccoid bacteria forming a biolm were preserved in addition to the horseshoe crab
musculature31. In the Kalkschieferzone of Monte San Giorgio approximately one third of the insects recovered
are completely or partially phosphatized13. Noteworthy, the phosphatized specimens belong to insect groups
such as bristletails and stoneies (larvae), in which the cross-link between proteins of the exocuticle and qui-
none occurs only in limited parts of the exoskeleton. In the Kalkschieferzone, phosphatization occurred also in
other arthropods (i.e., crustaceans) but not in vertebrates (A.T. pers. obs.). e depositional environment of the
Kalkschieferzone, a shallow lagoon adjacent to a carbonate platform32,33, has likely facilitated a rapid process of
fossilization, which prevented the consumption of organic matter and allowed the preservation of so tissues
together with their ne structural features. e presence of clay-chips beds, rich in algal lm fragments32,33, may
be considered as a clue that in the depositional environment of the Kalkschieferzone the conditions for the micro-
bially mediated phosphatization of organic matter were established.
Here, for the rst time in compression fossils of terrestrial arthropods, components of the CNS are preserved.
e ventral nerve cord exhibits a homonomous metameric pattern, as to be expected. Notably, the ganglia of
ventral nerve cord observable in G. triassicus highly resemble those of extant Machilidae (Fig.3C). In the optic
lobes, the number and the relative position of the three nested retinotopic neuropils correspond to those of extant
bristletails, indicating a phenotypic stability of these structure lasting at least ~240 My (extant archaeognathan
optic lobes reported in Sinakevitch et al.34 Figure 9D); for an exemplary review on the organization of the optic
lobes across crustaceans and insects see Strausfeld35.
e 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 dierent 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 lum 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).
e latter, according to the fossil record28,29, was near to its extinction while the former was just blooming.
It has been observed that representatives of Dasyleptus markedly resemble juveniles of extant species of
Machiloidea25,36. erefore, two hypotheses could be formulated as possible explanations concerning of the
Figure 3. Details of Gigamachilis triassicus CNS. (A) Close-up on medio-ventral region of abdominal segments
6–8 and color-marked version (B); in blue, structures of ventral nerve cord, including ganglia with hemiganglia
and paired connectives. (C) Abdominal ganglia, VI to VIII, of Machilis sp. ventral nerve cord, for structural
comparison. (D) Head region highlighting the compound retina (marked purple), the optic lobes and the lateral
protocerebrum (CNS structures, marked blue) and the bundle-like features interpreted as possible muscles
(marked yellow). Close-up on the right compound retina, optic lobes and components of the lateral protocerebrum
(E) and color-marked version (F) with arrow pointing to possible Cuccati’s bundle. Colors as in (D). (G) e same
region as (E) and (F) with schematic representation of the three nested neuropils within the optic lobe (marked
blue) and components of lateral protocerebrum (marked light grey). All but (C) composite autouorescence;
(C) macro-photography under transmitted light. Abbreviations: cn = connective; hg = hemiganglion = la =
lamina; lox = lobula complex; me = medulla [insect brain nomenclature as in Ito et al.46].

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co-occurrence of these two forms: (i) representatives of Dasyleptus, including D. triassicus, recovered from
Upper Carboniferous to Middle Triassic, represent immature stages of Machiloidea; or, (ii) fossils described as
Dasyleptus are representatives of separate species. Even if the rst hypothesis is still debated25,36–38, Rinehart and
Figure 4. 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. Le: G. triassicus. Right: D. triassicus, based on information provided by Bechly and Stockar28; two pairs of
ventral structures (visible in the original gures) 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;
le: 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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colleagues39, identied six instars in Dasyleptus brongniarti from Kuznetsk Formation (Middle Permian) and esti-
mated an adult length of 15–20 mm (including the lum terminale). e authors establish that most specimens
of Dasyleptus should represent adults and their morphology would therefore be an ancestral adult condition for
archaeognathans. e morphology of modern archaeognathans, including G. triassicus, would then be a derived
condition (Fig.4) representing an example in which ontogeny recapitulates phylogeny (seen in juvenile machilids,
hence a case of peramorphosis).
The evolutionary scenario we propose differs from that so far accepted (Fig.4) since it postpones the
divergence between Machiloidea and Dasyleptus. e time and the drivers for the evolution of the new body
organization in this lineage of apterous insects are currently unknown. Possible causes could include peculiar
paleoenvironmental conditions at the end of the Permian and in the Early Triassic. e high temperatures at the
P/T boundary and during the Smithian40 may have favored the small size of Dasyleptus. Conversely, the switch to
a cooler climate during the Spathian40 in association with the adaptive advantage provided by body size diversi-
cation during the biotic recovery following the end-Permian mass extinction41 could be considered the propul-
sive forces that led to the evolution of giant bristletails with new body organization and jumping capability. An
alternative hypothesis relies on a possible, not yet identied abiotic event or on a series of events having occurred
during the Middle Triassic that signicantly contributed to the renewal of insect lineages. e last hypothesis is
supported also by the high rates of insect lineage turnover, origination and extinction in the Middle Triassic42,43,
where some Paleozoic insect lineages become extinct and others have their rst occurrence in the same periods.
Our ndings, associated with the presence of D. triassicus on the same stratigraphic unit, support this interpreta-
tion of insect evolution. However, the evolution of G. triassicus during the Permian, or in earlier period, cannot be
ruled out on the basis of currently available data. Studies integrating further fossil evidences and molecular data
are required to shed light in the evolution of extant representatives of Machilidae.
Materials and Methods
Specimens collection. e two specimens used in this study were collected during the eldwork activities
carried out between 1997 and 2003 in the Lower Kalkschieferzone (KSZ), the uppermost part of the Meride
Limestone, at the Val Mara site D near Meride, on the Swiss side of UNESCO World Heritage site of Monte San
Giorgio (Italy-Switzerland). Specimens belonging to Machilis sp. were collected in Baggero (CO – Italy) in order
to isolate the ventral nerve chord and perform the comparison with that of the fossil G. triassicus.
Image acquisition. Direct observations and measurements were performed using a stereomicroscope Leica
MS5 with an ocular micrometer. e specimens were photographed under two dierent settings. First, mac-
rophotography was performed under cross-polarized light with a Canon Rebel T3i with a MP-E 65 mm lens
and a Canon Macro Twin Flash MT 24EX, taking several image stacks of adjacent areas to achieve an entirely
sharp high-resolution image. e stacks were subsequently fused and stitched with Combine ZM/ZP or Image
Analyzer and Adobe Photoshop CS3. Additionally, microphotography using autouorescence was taken out with
a Keyence BZ-9000, again recording image stacks processed in the same way. e autouorescence of the speci-
mens enhances the contrast against the matrix44,45.
To isolate the ventral nerve chord, dissections of Machilis sp were performed under the stereomicroscope
Zeiss Axio Zoom V16 and images of ganglia were acquired with the digital camera Zeiss Axiocam 506.
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Acknowledgements
We thank C. Lombardo for the hard work during long years of eldwork and for her contribution to the knowledge
of fossils from the Kalkschieferzone; C. Bandi and D. Fontaneto for their suggestions on the manuscript; Steen
Harzsch for discussing the preserved CNS features. We sincerely thank the anonymous reviewers for their
suggestions and comments, in particular those related to the optic lobes interpretation. Holotype MCSN8463 and
paratype MCSN8466 will be deposited at Museo Cantonale di Storia Naturale di Lugano (MCSN) – Switzerland.
e eld work was supported by grants from the Land Department of the Canton Ticino and the Federal Oce
for Environment, Forests and Landscape in Berna to the Museo Cantonale di Storia Naturale in Lugano. A.T.
is partially founded by the Italian Ministry of Education, University and Research MIUR-PRIN 2010-11 (E.
Erba). M.M. received the Systematics Research Fund 2016, funded by the Linnean Society of London and the
Systematics Association, to study the phosphatized fossil insects of Monte San Giorgio. J.T.H. was kindly funded
by the German Research Foundation (DFG Ha 6300/3-1). C.H. was supported with an Equal Opportunities
Sponsorship (BGF) of the LMU.
Author Contributions
M.M., A.T. and L.S. conceived the study. A.T. and M.F. participated in fossil excavations and preparations. M.M.,
L.S., A.T., J.H. and C.H. analysed the specimens. M.M. wrote the manuscript. All authors discussed the results,
commented and revised the manuscript.
Additional Information
Supplementary information accompanies this paper at http://www.nature.com/srep
Competing Interests: e authors declare no competing nancial interests.

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Scientific RepoRts | 7:46016 | DOI: 10.1038/srep46016
How to cite this article: Montagna, M. et al. Central nervous system and muscular bundles preserved in a 240
million year old giant bristletail (Archaeognatha, Machilidae). Sci. Rep. 7, 46016; doi: 10.1038/srep46016 (2017).
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