DOI: 10.5061/dryad.d7wm37q4c
title: Fossil Dorylinae CT data

description: Among social insects, army ants are exceptional in their voracious
 coordinated predation and nomadic life history: the synthesis of these
 remarkable ecological traits is referred to as the army ant syndrome.
 Despite molecular evidence that the army ant syndrome evolved twice during
 the mid-Cenozoic, once in the Neotropics and once in the Afrotropics,
 fossil army ants are markedly scarce, comprising a single known species
 from the Caribbean 16 Ma. Here we report the oldest army ant fossil and
 the first from the Eastern Hemisphere (EH), Dissimulodorylus perseus,
 preserved in Baltic amber dated to the Eocene. Using a combined
 morphological and molecular Ultra Conserved Elements dataset spanning
 doryline lineages, we find that D. perseus is nested among extant EH army
 ants with affinities to Dorylus “driver ants.” Army ants are characterized
 by limited extant diversification throughout most of the Cenozoic; the
 discovery of D. perseus suggests an unexpected diversity of now-extinct
 army ant lineages in the Cenozoic, some of which were present in
 Continental Europe. 
description: <em>Specimen</em> Type material is
 preserved within a ~1cm x 0.8cm piece of transparent Baltic amber with
 crazing (surface cracks). It is possible that a previously applied resin
 meant to affix the specimen to a microscope slide contributed to intense
 crazing (Sadowski et al. 2021). Specimen PALE-8463 is deposited within the
 Museum of Comparative Zoology (MCZ) at Harvard University. The precise
 collection date is unknown, however, the specimen number is recorded in a
 ledger titled ‘Catalogue of Fossil Insects in the Museum of Comparative
 Zoölogy’ on the same page (98) as a specimen received in 1937; the
 following page (99) also contains two entries dated 1937. In addition, the
 method of storage (the specimen was initially mounted to a microscope
 slide, a practice no longer followed) and aging on the specimen label are
 in line with this approximate date. The age of Baltic amber is not precise
 and likely varies depending on outcrop, however, an Eocene age (~34 Ma)
 has been suggested through multiple lines of evidence (Seyfullah 2018;
 Wolfe 2009). <em>Photomicrograph and microCT
 Imaging</em> The specimen was not prepared
 further to avoid damage due to crazing or chemical reactions with
 previously applied polymers. Microphotographs were taken using a Nikon
 SMZ25 stereomicroscope and DS-Ri2 camera with NIS Elements software, which
 generates extended focus composites of several individual focal plane
 images. X-ray micro-computed tomography (microCT) scanning was performed
 at the New Jersey Institute of Technology Otto H. York Center for
 Environmental Engineering and Science using a Bruker SkyScan 1275 microCT
 scanner. The type specimen was scanned at a voltage of 34kV and current of
 160μA for 110ms exposure times averaged of 5 frames per rotation with a
 voxel size of 5.94μm. Z-stacks were generated using NRecon (Micro
 Photonics, Allentown, PA) and segmented using 3D Slicer v5.1 (Federov et
 al. 2012). An .stl file of the segmented 3D model was rendered using
 Blender v3.2.1 (Blender 2008).