DOI: 10.5061/dryad.vhhmgqp6f
title: Data from: Palaeohistology and life history of the early Palaeocene taeniodont Conoryctes comma (Mammalia: Eutheria)

description: The life histories of Palaeocene mammals are poorly known, but may have
 been central to their success in diversifying across terrestrial
 ecosystems after the end-Cretaceous extinction. Among these mammalian
 groups, the eutherian Taeniodonta are particularly enigmatic, with few
 modern analogues and no living descendants, despite being one of the only
 lineages to apparently traverse the Cretaceous-Palaeogene (K-Pg) boundary.
 Here we investigate the life history of an early Palaeocene taeniodont,
 Conoryctes comma, based on a multi-individual, multi-element sample. We
 produced palaeohistological thin sections of skeletal elements, including
 one tooth and 26 postcranial bones, to produce 36 slides. Nearly all
 elements sampled exhibit similar osteohistological architecture, with a
 small internal zone of compacted coarse cancellous bone surrounded by an
 internal cortex of periosteally-derived fibrolamellar bone of variable
 thickness, and an outer cortex of lamellar bone. The well-vascularized
 fibrolamellar complex in the limb bones, lacking cyclical growth marks, is
 indicative of overall rapid growth to near adult body size. Cyclical
 growth marks are present in the outer cortex after the transition to
 slow-growing lamellar bone, but not in the inner cortex, suggesting sexual
 maturity was reached in one year. In some elements, an internal growth
 mark shares histological similarities with weaning marks in living mammals
 and other contemporary Palaeocene mammals, and occurred at the body size
 predicted for this transition in therian mammals. The unusual presence of
 compacted coarse cancellous bone near the midshafts of multiple limb bones
 may be related to cortical thickening, and is similar to the arrangement
 described in some fossorial mammals, supporting previous assertions of
 this lifestyle in Conoryctes. Altogether, these palaeohistological signals
 suggest a life history in Conoryctes comma similar to living eutherians,
 despite uncertainty about whether it is within crown Placentalia or a
 close outgroup. Thus, our data are consistent with an early origin of
 placental-like reproductive strategies in their eutherian ancestors,
 although this attribute was likely shared more broadly among Mesozoic
 lineages prior to the end-Cretaceous extinction. These data may be useful
 in the future for broader evaluations of early Palaeocene mammal growth
 and life history, or for other physiological proxies.
description: Specimens: We selected a range of postcranial
 skeletons of <em>Conoryctes comma</em>, all collected from the
 Nacimientio Formation in the San Juan Basin of New Mexico (Fig. 1). In
 this paper, we consider <em>Conoryctes</em> to likely be
 synonymous with, or very closely related to, another named taeniodont
 genus, <em>Huerfanodon</em>, following Kynigopoulou (2023).
 Both taxa overlap in time and are nearly identical in size, being
 distinguished only by relatively minor differences in premolar morphology
 (e.g., presence/absence of P4 protocone; presence/absence of p4
 metaconid), which is highly variable even between members of the same
 species (Kynigopoulou, 2023). However, it is outside the scope of this
 study to formally synonymize these names, and this endeavour is in
 progress elsewhere. Where the postcranial material in our sample is
 associated with dental material (e.g., NMMNH P-48198), the teeth are
 referrable to <em>Conoryctes comma</em> (Kynigopoulou et al.,
 2024). Further, because duplicate postcranial elements are identical in
 morphology and palaeohistological growth signals (i.e., they do not
 exhibit different growth trajectories), we consider them all to represent
 a single taxon, <em>Conoryctes comma</em>. The San Juan Basin
 where the specimens were collected is the historic territory of the Ute
 and Navajo (Diné) peoples, and all specimens were collected under permit
 from public lands administered by the United States Bureau of Land
 Management. All specimens are accessioned at the New Mexico Museum of
 Natural History and Science (NMMNH). Specimens range in age from middle
 (To2) to late (To3) Torrejonian, spanning from about 62.7 to 62.2 Ma
 (Flynn et al., 2020; Leslie et al., 2018). Specimen details and parts of
 the specimens sampled are outlined in Table 1.      
             The sample aimed to include not only multiple
 individuals of varying sizes, for evaluating ontogenetic variation in
 tissue types, but also multiple elements from each individual, to assess
 intraskeletal histovariability. This is because bones from individuals of
 different ages record different windows of life, and bones from different
 regions of the skeleton can vary in how their local growth patterns
 reflect overall mass increase in the body. Thus, broad sampling is
 necessary when studying lineages with poor histological characterization,
 particularly because the elements whose growth records most closely
 reflect overall body mass increase are not necessarily consistent between
 clades (Cullen et al., 2014; Horner et al., 2000; Klevezal, 1996; Kolb et
 al., 2015; Montoya‐Sanhueza et al., 2021; Padian et al., 2016, 2013;
 Woodward, 2019; Woodward et al., 2015, 2014). In
 <em>Conoryctes</em>, like in other Palaeocene eutherians
 studied (Funston et al., 2022), we found minimal variation in the overall
 growth signal between bones (see discussion). Where possible, sampling
 targeted the minimum shaft circumference of each bone, because this is
 typically closest to the neutral growth zone and more closely reflects the
 overall growth of the individual (Enlow, 1963; Padian et al., 2013),
 particularly in simply cylindrical elements like the tibia. However, in
 many cases, this area was not preserved, the bones had more complex
 shapes, or the specimens available for sampling were small but
 identifiable fragments of the element. Accordingly, some sections had to
 be taken closer to the metaphyses, which typically have more complex
 growth signals that reflect not only size increase, but also shape change
 and soft tissue attachments. Likewise, for some sections only an
 approximate position of the sample relative to the entire element is
 known. Specimens were photographed using a Nikon D850
 camera with a 60 mm MicroNikkor lens prior to thin-sectioning. Some
 elements were digitized using photogrammetry in Agisoft Metashape Standard
 (version 1.6.1), to produce three-dimensional models for conservation of
 morphology.             Specimens were thin sectioned
 following the protocol of Funston et al. (2022), which is a modified
 version of the method described by Lamm (2013). In brief, sample regions
 were removed from specimens either using natural breaks, or by stabilizing
 with paraloid and cutting on a Buehler Isomet 1000 Precision saw. A major
 difference from other thin-sectioning protocols is that sample regions
 were adhered in predetermined orientations to pre-cured epoxy bases using
 Loctite cyanoacrylate, to facilitate sampling in the correct plane.
 Specimens on bases were then embedded in Buehler Epothin II epoxy resin
 under a vacuum and left to cure for 24 hours. Embedded blocks were
 sectioned at the plane of interest using the Isomet 1000 saw, but unlike
 the protocol of Lamm (2013), specimens were kept as blocks, rather than
 serially cut into wafers, as this minimized the potential for loss of the
 friable bones and teeth. Cut block faces were consolidated using
 cyanoacrylate as necessary, before being frosted using 600 grit silicon
 carbide abrasive slurry. Unlike most thin-sectioning protocols (Cerda et
 al., 2020; Chinsamy and Raath, 1992; Cuccu et al., 2025; Lamm, 2013;
 Montoya-Sanhueza and Chinsamy, 2017), but critical for optimal adhesion of
 fragile dental tissues, frosted acrylic slides were inverted to mount onto
 the blocks using cyanoacrylate without applying any pressure. Typically,
 glass slides and epoxy adhesive are used, and specimens are weighed down
 or clamped for mounting, but this often temporarily warps the slide, which
 results in flexion and breakage of dental tissues when slides are polished
 to low thicknesses. Cyanoacrylate and acrylic make a stronger bond than
 glass and epoxy, because the acrylic ‘melts’ in contact with
 cyanoacrylate, merging into a single material, and thus the bond does not
 rely on the surface area adhesion of two materials (epoxy and glass).
 Acrylic provides a further advantage in that it is more resistant to
 shattering, prolonging the lifespan of the completed section. Mounted
 samples were resectioned using the Isomet 1000 saw to a thickness of 700
 µm, and were then manually ground on a glass plate using 600- and
 1200-grit silicon carbide abrasive slurries. Slides were ground until they
 reached the desired optical clarity, although for many specimens in the
 sample, taphonomic or diagenetic alteration of the material resulted in
 replacement of original bone matrices with extensive regions of opaque
 minerals. Because of the modified mounting protocol, these slides could be
 polished to very low thicknesses, in some cases &lt; 15–30 µm thick,
 to maximize light transmission. Thus, some information was still
 accessible from these specimens using cross-polarized light, which would
 not have been available using standard palaeohistological
 methods.             Slides were imaged using a Leica
 DMLP Transmitted Light Polarizing Microscope with Leica Application Suite
 4. Photomontages were created using the automated ‘photomerge’ feature of
 Adobe Photoshop 2022. Images were taken under plane polarized light,
 cross-polarized light, and cross-polarized light with a 430 nm ‘lambda’
 filter, which aids in distinguishing opaque regions from extinct regions
 under cross-polarized light. 
description: # Data from: Palaeohistology and life history of the early Palaeocene
 taeniodont Conoryctes comma (Mammalia: Eutheria) Dataset DOI:
 [10.5061/dryad.vhhmgqp6f](10.5061/dryad.vhhmgqp6f) ## Description of the
 data and file structure These folders contain overview images of
 palaeohistological thin sections of Conoryctes comma from Funston et al.
 “Palaeohistology and life history of the early Palaeocene taeniodont
 Conoryctes comma (Mammalia: Eutheria)” in Journal of Anatomy. Each folder
 pertains to a single specimen, and for some specimens, multiple elements
 were thin-sectioned. The file naming convention is as follows: Specimen
 number/Element/Section number (if applicable)/Light type (PP = plain
 polarized, XP = cross-polarized, Lambda = cross-polarized with lambda
 filter)/Panorama.jpg Some additional terms may be included in the file
 name. Questions about the dataset can be addressed to the corresponding
 authors as outlined in the manuscript.