Abstract
AbstractFossils sometimes show unusual morphological features absent in living organisms, making it difficult to reconstruct both their affinity and their function. We describe here a new lacewing larva, Ankyloleon caudatus gen. et sp.n. (Neuroptera) from the Cretaceous amber of Myanmar, characterized by an abdomen unique among insects, with ‘tail‐like’ terminal segments bearing a ventral pair of vesicles. Phase‐contrast X‐ray microtomography reveals that these structures were dense and equipped with a median duct, suggesting that they were likely pygopods used for locomotion, holding the position through adhesive secretions. Our phylogenetic analyses, combining genomic and morphological data from both living and fossil lacewings, proved critical to placing Ankyloleon gen.n. on the lacewing tree of life as an early representative of the antlion clade, Myrmeleontiformia. These results corroborate the view that derived myrmeleontiform lacewings ‘experimented’ with unusual combinations of features and specializations during their evolutionary history, some of which are now lost.Zoobank registration: urn:lsid:zoobank.org:pub:0C0AC565‐1AC9‐42CC‐831D‐EDA38BA36F64
Highlights
There is general agreement among scientists that winged insects (Pterygota) spawned the most spectacular radiation of metazoans on Earth (Misof et al, 2014; Haug J.T. et al, 2015)
We examined the morphology of this fossil through synchrotron X-ray phase-contrast microtomography (XPCT) to explore in detail fine, internal anatomical features and hypothesize which selective forces likely shaped this extreme shape within the broader context of lacewing evolution
We provided a morphological dataset inclusive of fossils, allowing Evolutionary Placement Algorithm (EPA) to estimate the likelihoods of fossil placement in the genomic tree through the morphological weights (Fig. S5)
Summary
There is general agreement among scientists that winged insects (Pterygota) spawned the most spectacular radiation of metazoans on Earth (Misof et al, 2014; Haug J.T. et al, 2015). The abdomen is reminiscent of the division in meso- and metasoma characterizing scorpions, in this case the function is completely unknown These modifications are unique throughout all known fossil and living insects and among all hexapods, suggesting highly specialized habits. XPCT is a nondestructive 3D imaging technique endowed with higher image contrast and spatial resolution than conventional tomography, which detects minor electronic density variations due to sensitivity to phase shift This technique appears helpful when applied to fossils, yielding detailed information, especially if combined with conventional micro-CT (Tafforeau et al, 2006; Lak et al, 2008; Soriano et al, 2010; Perreau & Tafforeau, 2011; Bidola et al, 2015). Our findings suggest that (i) complex anatomical structures evolved as dead-end innovations during a phase of morphological diversification and (ii) the integration of genomic data with morphological information allows for the determination of the affinities of enigmatic stem-group phenotypes
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