DOI: 10.5061/dryad.7vg5fd0
title: Data from: Taphonomy of Isisfordia duncani specimens from the Lower Cretaceous (upper Albian) portion of the Winton Formation, Isisford, central-west Queensland

description: Taphonomic analysis of fossil material can benefit from including the
 results of actualistic decay experiments. This is crucial in determining
 the autochthony or allochthony of fossils of juvenile and adult Isisfordia
 duncani, a basal eusuchian from the Lower Cretaceous (upper Albian)
 distal-fluvial-deltaic lower Winton Formation near Isisford. The
 taphonomic characteristics of the I. duncani fossils were documented using
 a combination of traditional taphonomic analysis alongside already
 published actualistic decay data from juvenile Crocodylus porosus
 carcasses. We found that the I. duncani holotype, paratypes, and referred
 specimens show little signs of weathering and no signs of abrasion.
 Disarticulated skeletal elements are often found in close proximity to the
 rest of the otherwise articulated skeleton. The isolated and
 disarticulated skeletal elements identified, commonly cranial, maxillary,
 and mandibular elements, are typical of lag deposits. The holotype QM
 F36211 and paratype QMF34642 were classified as autochthonous, and the
 remaining I. duncani paratypes and referred specimens are
 parautochthonous. We propose that I. duncani inhabited upper and lower
 delta plains near the Eromanga Sea in life. Their carcasses were buried in
 sediment-laden floodwaters in delta plain overbank and distributary
 channel deposits. Future studies should refer to I. duncani as a brackish
 water tolerant species.
description: TABLE 4. Completeness
 (Cp.) and articulation (Art.) scores for I. duncani specimens from
 Isisford (following Beardmore et al. (2012); Syme and Salisbury
 (2014)).Completeness (Cp.) and
 articulation (Art.) scores for I. duncani specimens from Isisford. As per
 Beardmore et al. [40], Xp denotes skeletal units that are not visible due
 to truncation with the edge of the block or blocks missing, and Xh denotes
 skeletal obscured by matrix or overlying skeletal elements. Beardmore et
 al. [40] propose that specimens with 3 instances of either Xp or Xh in the
 dataset should be omitted from further analysis: in this instance, all
 specimens except the holotype QM F36211 were excluded from further
 analyses (denoted by ‘--’). The average completeness and articulation for
 QM F36211 was calculated both with and without the dermal skeletal units:
 with the dermal skeletal units, compared to a maximum total score of 36 (4
 for each of the 9 of 11 units omitting Xp/Xh data); without the dermal
 skeletal units, compared to a maximum total score of 28 (4 for each of the
 7 of 9 units omitting Xp/Xh data). The data was then compared with the
 trend lines proposed by Beardmore et al. [40] where
 possible.TABLE
 4.docxTABLE 3. NISP, MNE, and
 MNI of Isisfordia duncani specimens from Isisford.Summary of the
 Isisfordia duncani fossil elements recovered from the Isisford locality,
 including the number of identified specimens—where ‘specimens’ refers to
 the number of bone fragments—recovered per taxon (NISP), minimum number of
 elements (MNE) which may comprise multiple fragments each, and minimum
 number of individuals (MNI). We have included totals both without dermal
 skeletal units (as NISP and MNE), and with dermal skeletal units such as
 osteoderms included (as NISP inc. ost. and MNE inc. ost.). The relatively
 high NISP and MNE compared to MNI for I. duncani indicates that the
 majority of individuals comprise a multitude of articulated and/or closely
 associated skeletal elements. Approximate size range taken from and
 estimated using Salisbury et al. [66].TABLE
 3.docxTABLE 5. Table
 incorporating all other taphonomic classification systems used in this
 study of the I. duncani specimens from Isisford
 [13,16,20,26–28,32,101–104,106–114] that were used in conjunction with
 Table IV in Dodson [19] and trends classified by Beardmore et al.
 [40].Table incorporating all
 other taphonomic classification systems used in this study of the I.
 duncani specimens from Isisford [13,16,20,26–28,32,101–104,106–114] that
 were used in conjunction with Table IV in Dodson [19] and trends
 classified by Beardmore et al. [40]. We also chose to include counts of
 number of individual specimens (NISP) and minimum number of elements (MNE)
 with and without osteoderms, for ease of comparison in future with other
 tetrapods lacking dermal skeletons. The maximum number of skeletal
 elements in I. duncani, both excluding and including osteoderms, are
 listed next to MNE. Specimens QM F58793 and QM F58794 were found in close
 proximity, therefore NISP, MNE, and MNI are listed both grouped together
 (MNI = 2), and separately, to demonstrate the variation in NISP and MNE
 per individual. Where possible, life stage was determined by identifying
 closure neurocentral sutures in vertebrae (closure proceeds caudally to
 cranially throughout ontogeny, with ‘adult’ defined as possessing closed
 neurocentral sutures in all vertebrae) and size comparison to the holotype
 that has been identified as an adult (see Salisbury et al. [66]). By
 comparing across specimen numbers, we determined whether disarticulated
 elements showed greater degrees of bone surface modifications. Degrees of
 articulation and completeness are the sum total of scores for each
 skeletal unit. The Dodson [19] classification scheme assumes absences are
 true absences; we selected the most likely class per specimen based on
 other taphonomic indicators (such as truncation with block, articulation
 versus completeness, and so on).TABLE
 5.doc