Fig 1.
Geographical and geological context of the Prince Charles’s Point tracksite.
The tracksite is situated on the northwest coast of the Trotternish peninsula. (A) Overall map of the Isle of Skye. MiniScale® [EPS geospatial data], Scale 1:1000000, Tiles: NG; NM, Updated: 20 November 2023, Ordnance Survey (GB), Using: EDINA Digimap Ordnance Survey Service (https://digimap.edina.ac.uk/os), Downloaded: April 2024. Contains public sector information licensed under the Open Government Licence v3.0. Available at: https://www.nationalarchives.gov.uk/doc/open-government-licence/version/3 (B) Overview map with the tracksite highlighted by a yellow polygon. OS VectorMap™ District [TIFF geospatial data], Scale 1:25000, Tiles: ng36_clipped, ng46_clipped, Updated: 23 September 2024, Ordnance Survey (GB), Using: EDINA Digimap Ordnance Survey Service (https://digimap.edina.ac.uk/os), Downloaded: December 2024. Contains public sector information licensed under the Open Government Licence v3.0. Available at: https://www.nationalarchives.gov.uk/doc/open-government-licence/version/3 (C) Stratigraphic log of the Kilmaluag Formation exposed at Prince Charles’s Point. Log is adapted from [40,48 ] to show new observations – including beds with dinosaur tracks.
Fig 2.
Sediment thin sections of track-bearing beds.
Bed 2 (A, B) preserves abundant ostracods while Bed 5 (C, D) lacked ostracods. Sections were examined under plane polarised light (A, C) and cross polarised light (B, D).
Table 1.
Pes tracks are categorised by their length in accordance with [58].
Fig 3.
Theropod track and trackway measurements and track phalangeal pads.
(A) Measurements for theropod tracks included: overall length (L), width (W), digit lengths (LII-LIV), toe extension length (te), and interdigital angles between digits ii-iii (α) and digits iii-iv (β). (B) Theropod track phalangeal pad configuration (2:3:4 formula) between digits ii-iv (right to left). (C) Bipedal trackway measurements derive from [55] and included: pace – the distance between common reference points (intersecting point (IP) of track length and width lines) on a sequential right and left track (RP and LP respectively); stride (λ) – the distance between two successive right or left track IPs; width of the pes angulation pattern (WAP) – overall width of stride from the IP of a respective alternate track; angle of rotation (α) – measured between the pace line and trackway midline (TML); and pace angulation (γ) – the angle of two intersecting pace lines from a preceding and proceeding track in the stride. The TML was drawn from the midpoints of pace lengths.
Fig 4.
Sauropod track and trackway measurements.
Measurements are based on [55,58]. (A-B) Pes and manus trackway measurements included overall pes (P) or manus (M) length (PL or ML) and width (PW or MW). As per bipedal tracks, right and left pes or manus paces (RPP or RMP and LPP or LMP) were measured between alternating track IPs, while strides (Pλ or Mλ) from the IP of two consecutive right or left tracks. Further measurements included the width of the pes angulation pattern (WAP), width of the manus angulation pattern (WAM), and the pes and manus angles of rotation (α) and pace angulation (γ). A track midline (PMD for pes and MMD for manus trackways) was drawn from the midpoint of pace lengths. Progression (PG) was based on the Pythagorean theorem and determined the distance between an IP of one track and WAP intersection point of a consecutive track within a respective stride. (C) The pes trackway ratio (gauge) was based on measurements perpendicular to the TMD including: side width ‘SW’ – measured across an individual track; and overall width ‘OW’ – measured across the outermost side width lines of consecutive pes tracks – as stipulated by [64].
Fig 5.
Track morphotypes recorded at Prince Charles’s Point.
Note outlines for morphotypes 1b and 2 are right pes tracks, the rest are left.
Fig 6.
Overview orthomosaic of Prince Charles’s Point.
UAV orthomosaic of full tracksite with Section One and Section Two divided accordingly by a dashed line. Track clusters in each section are highlighted in each by a yellow polygon.
Fig 7.
UAV orthophoto and outline map of main track cluster in Section One.
(A) In the orthophoto, the rippled sandstones of bed 2 gradually wear down toward the worn surface of bed 1 exposed toward the present-day high-tide mark due to a ~ 4° south-westerly dip. The orthophoto was composited from photographs taken by our UAV during fieldwork in April 2023. (B) The outline map highlights the position and distribution of tracks. Each track is labelled with its tracksite catalogue number. Trackways of ‘TH’ represent theropods, ‘SA’ signify sauropod, and ‘TH-A’ denote theropod track associations. Dark grey outlines highlight the bedding plane edge. Pale grey outlines signify boulders.
Fig 8.
UAV orthophoto and outline map of main track cluster in Section Two.
(A) In the orthophoto, extensive bed wear has revealed a variety of ripple wavelengths and bearings across multiple bed 2 horizons. The orthophoto was composited from photographs taken by our UAV during fieldwork in April 2023. (B) Outline map highlights the position and distribution of trackways. Each track is labelled with its tracksite catalogue number. Trackways of ‘TH’ represent theropods, ‘SA’ signify sauropod, and ‘TH-A’ or ‘SA-A’ denote track associations. Dark grey outlines highlight the edge of a bedding plane. Pale grey outlines signify boulders.
Fig 9.
(A) Orthophoto, (B) DEM, (C) outline with trackways highlighted by dashed lines – PC-TH-1 is pale grey, while PC-TH-2 is dark grey. Both trackways are oriented in the opposite direction to the palaeocurrent inferred from ripples. A horizon which directly underlies the track-bearing surface features ripples oriented in a southeasterly direction, from which we infer variation in the current direction across relatively short timescales. Note PC-TH-2-15 is excluded from imagery as the track was most clearly exposed after the photogrammetric dataset was collected.
Fig 10.
Photographs of selected PC-TH-1 and 2 tracks.
(A) PC-TH-1-07 (right) and PC-TH-2-11 (left). (B) The distal regions of digit iii and ii on PC-TH-1-08 (left) overprint the lower margins of digit ii and heel region of PC-TH-2-12 (right). (C) PC-TH-1-09 (left) penetrated the substrate more deeply but suffers from present-day erosion, while PC-TH-2-13 (right) features a shallower relief with greater sediment infill and ripples.
Table 2.
Morphotype 1a track measurements.
Fig 11.
(A) Orthophoto with software-based shadowing, (B) DEM, (C) outline highlights the trackway. Note the greyed-out tracks of PC-TH-5 (37 and 38) can be seen crossing the path of PC-TH-4 in a northerly direction. The tracks of PC-TH-4 gradually become less well-defined through the sequence as present-day erosion exposed underlying layers.
Fig 12.
Digital representations of selected PC-TH-4 tracks.
Textured orthophotos, outlines, contour maps, and DEMs are respectively represented for: (A-D) PC-TH-4-29, (F-H) PC-TH-4-28, and (I-L) PC-TH-4-26. The tracks likely represent worn surface tracks with morphotype-1a configurations (i.e., longer digit iv than ii) and low ~ 1.2 mesaxony. (M) Selected tracks, indicated by red boxes, in context to the rest of the trackway sequence. Due to present-day erosion, track margin definitions gradually decline across the sequence.
Fig 13.
(A) Textured orthophoto with software-based shadowing, (B) DEM, (C) outline highlights the trackway. Note the greyed-out tracks of PC-TH-4 can be seen intersecting the south-westerly path of PC-TH-4. Although most tracks are eroded, some featured large divarication angles.
Fig 14.
Digital representations of selected PC-TH-5 tracks.
Textured orthophotos, outlines, contour maps, and DEMs are respectively represented from left to right. (A-D) PC-TH-5-40 enables other poorly preserved PC-TH-5 tracks to be referred as morphotype-1a. PC-TH-5 tracks are variably preserved: (E-H) much of PC-TH-5-38 is obscured by sediment, (I-L) PC-TH-5-35 exhibits wide digit ii-iv divarication which may have reflected the trackmaker turning, (M-P) PC-TH-5-34 was similarly widely divaricated. (Q) Selected tracks, indicated by red boxes, in context to the rest of the trackway.
Fig 15.
Photographs, outlines, contour maps, and DEMs are respectively represented from left to right. (A-D) PC-TH-A-4-49 was posteriorly heavily intruded by ripples and partially infilled on digits iii and iv. Unusually, the phalangeal pad creases for Piv3-1 are distinguishable. (E-H) PC-TH-4-50 retains most of its sediment infill and possesses a wider digit divarication angle than PC-TH-4-49.
Fig 16.
Photographic and digital representations of selected isolated tracks.
Photographs, outlines, contour maps, and DEMs are respectively represented from left to right. (A-D) PC-TH-I-46, (E-H) PC-TH-I-16, (I-L) PC-TH-I-01, and PC-TH-I-41 (M-N). PC-TH-I-46 and PC-TH-I-16 occur in close proximity to sauropod trackways and were likely impressed in the same horizon. Unlike these tracks, PC-TH-I-01 was used to define morphotype-1a due to its clear digit margins, ‘2:3:4’ phalangeal pad formula, and sharp, elongated ungual marks. The track heel region is intruded by ripples. Due to a large boulder covering the anterior portion of the track, a photogrammetric model could not be produced for PC-TH-I-41.
Table 3.
PC-TH-1 track measurements.
Table 4.
PC-TH-2 track measurements.
Table 5.
Trackway measurements for PC-TH-1.
Table 6.
Trackway measurements for PC-TH-2.
Table 7.
Stride and overall trackway velocities and gait ratios for PC-TH-1.
Table 8.
Stride and overall trackway velocities and gait ratios for PC-TH-2.
Table 9.
Track measurements for PC-TH-4.
Table 10.
Trackway measurements for PC-TH-4.
Table 11.
Stride and overall trackway velocities and gait ratios for PC-TH-4.
Table 12.
Track measurements for PC-TH-5.
Table 13.
Trackway measurements for PC-TH-5.
Table 14.
Stride and overall trackway velocities and gait ratios for PC-TH-5.
Table 15.
Track measurements for PC-TH-A-4.
Table 16.
Track measurements for selected isolated tracks.
Fig 17.
Digital representations of PC-TH-I-55.
(A) Textured orthophoto, (B) outline, (C) contour, (D) DEM. Unlike morphotype-1a tracks, PC-TH-I-55 possesses an anteromedially oriented digit i ungual impression. The digits are slenderer than morphotype-1a with well-defined phalangeal pad margins.
Fig 18.
Photographic and digital representations of PC-TH-3 tracks.
(A-D) From left to right, textured orthophoto, outline, contour map, and DEM of PC-TH-3-20 - a complete convex epirelief track with a ‘U’ shaped heel and poorly defined digit margins. (E-F) Photograph and outline of PC-TH-3-22, a partial convex epirelief track composed of lateral digits. (G-H) Photograph and outline of PC-TH-3-19, a second partial concave epirelief track with poorly defined digit ii and iii margins. The latter two tracks could not be attributed to morphotype-1b due to their incompleteness, isolated digits and absent digit i impression. Despite this, the tracks are described due to their occurrence in a trackway sequence with PC-TH-3-20.
Table 17.
Track measurements for morphotype-1b.
Fig 19.
Photographic and digital representations of morphotype-1c tracks.
From left to right, textured orthophoto, outline, contour map, and DEM. (A-D) PC-TH-I-56 was the only recorded concave epirelief morphotype-1c track. The track is situated in a slightly younger bed 2 horizon behind an igneous intrusion. (E-H) PC-TH-I-59 is distinguished as morphotype-1c due to its smaller track length, more slender digits, and wider > 60° digit ii-iv divarication angle. (I) Photograph and (J) outline of PC-TH-I-65. The track is referred to morphotype-1c and is partially metamorphosed. The track occurs in the same horizon as PC-TH-I-59.
Table 18.
Track measurements for morphotype-1c tracks.
Fig 20.
(A) Photograph cropped to model area, (B) DEM, (C) outline of PC-TH-A-3. Although characterised by a smaller < 30 cm overall length, the tracks of PC-TH-A-3 are classified under morphotype-1 due to a similar average l/w ratio (1.46), < 60° digit ii-iv divarication angle, and ‘2:3:4’ phalangeal pad configuration to morphotype-1a. From left to right, photographs, outline, contour map, and DEM of (D-G) PC-TH-A-3-47 and (H-K) PC-TH-A-4-48. Although worn, PC-TH-A-4-48 features clear phalangeal pad creases on digit ii. The creases of Piv1 and Piii3 are also visible.
Table 19.
Measurements for tracks used to define morphotype-1d.
Fig 21.
(A) Textured orthophoto with software-based shadowing, (B) DEM, (C) outline. Unlike PC-SA-1-82, most pes tracks lack digits and pads. Each are surrounded by wide, rippled displacement rims. Manus tracks are crescentic and possess a posterolaterally oriented pollex. The tracks gradually become increasingly scoured toward the present-day shoreline due to bed dip, exposing under tracks impressed down into bed 1.
Fig 22.
(A) Photograph, (B) DEM, (C) contour map, (D) outline of PC-SA-1-82 – the only pes track in sequence with digits preserved. Digits, except digit i, possess anterolaterally oriented, triangular shaped ungual marks. The heel pad and heel-demarcating crease are also preserved. The widest displacement rim widths are lateral to the pes track.
Fig 23.
Overview of PC-SA-1-79 and 80.
(A) Photograph and (B) DEM showing left manus and pes pair in context. The eroded pes track lacks clear digits and pads. (C) Photograph, (D) outline, (E) contour map, (F) DEM of manus track PC-SA-1-79. The pollex is posterolaterally oriented on the right side of this left manus.
Fig 24.
(A) Textured orthophoto, (B) DEM, (C) outline. The right pes tracks in the sequence partially overprint their correspondent manus tracks. PC-TH-2-15 (partially uncovered) partly over-impresses the displacement rim of PC-SA-2-85. PC-TH-1-10 and PC-TH-2-14 can be seen opposite PC-SA-2-87 and 85 respectively. Worn heel pads are visible on PC-SA-2-88 and 90. (D) photograph and (E) DEM of PC-SA-2-85 (foreground) shows a sharply defined mounded displacement rim with ripples. Such a structure is almost absent from PC-SA-2-87 (background).
Fig 25.
(A) Textured orthophoto, (B) DEM, (C) outline. Most pes tracks lack digits and pad impressions and overprint correspondent manus tracks. Each pes was surrounded by a variably eroded, rippled displacement rim - likely originally mounded as seen on PC-SA-3-111. PC-SA-3-109 is obstructed by a large boulder and was unmeasured. PC-SA-A-1 (PC-SA-A-1-112 to 114) meanwhile intersects PC-SA-3 between PC-SA-3-108 and 110.
Fig 26.
(A) Photograph, (B) outline, (C) contour map, (D) DEM. PC-SA-3-111 is the only pes in the trackway with well-defined digits and a mounded displacement rim with ripples across the surface. Note the widest displacements occur laterally to the track.
Fig 27.
(A) Textured orthophoto, (B) DEM, (C) outline. This pes only trackway is similar to PC-SA-3 in track spacing. However, due to the poor track definition of PC-SA-5-129 and other possible preceding tracks before PC-SA-3-127, trackway measurements could not be recorded. PC-SA-5-127 features four well-defined anterolaterally oriented subtriangular digits – amongst the most clearly defined at the locality.
Fig 28.
(A) Photograph, (B) outline, (C), contour map, (D) DEM. Digit i is the largest digit and anterolaterally oriented to the left. Digits ii-iv gradually decline in length and subtriangular pronouncement and are anterolaterally oriented to the right.
Table 20.
Track measurements used to characterise morphotype-2.
Table 21.
Track measurements for PC-SA-1.
Table 22.
PC-SA-1 gauges.
Table 23.
PC-SA-1 trackway measurements.
Table 24.
Overall trackway velocity and gait ratio for PC-SA-1.
Table 25.
Trackway measurements for PC-SA-2.
Table 26.
Trackway measurements for PC-SA-3.
Table 27.
Trackway and gauge measurements for PC-SA-3.
Table 28.
The overall trackway velocity and gait ratio for PC-SA-3.
Table 29.
Measurements of PC-SA-5 tracks.
Fig 29.
Track and flow-direction (ripple) bearings from magnetic north.
(A) Trackmaker and (B) ripple orientations. Classifications include: theropod trackways (TH), theropod track associations (TH-A) isolated theropod tracks (TH-I), sauropod trackways (SA), and sauropod track associations (SA-A). Ripple orientations were measured opposite respective tracks when present. Both theropod and sauropod trackmakers generally show no favoured direction.
Table 30.
Track and flow-direction (ripple) bearings.
Fig 30.
The hypothesised distribution of forces during track impression.
Blue arrows represent the downward forces exerted by the sauropod’s limb. Red arrows show the direction of displacement. Due to the desiccated (hardened) bed 1-2 boundary horizon and thinness of compliant bed 2 substrate, the horizontal component of sediment displacement was emphasised (black arrows).
Fig 31.
Cross-section demonstrates the hypothesised formation of shallow sauropod tracks.
(A) Tracks were impressed into a thin layer of fine-grained sand with variable moisture content. (B) The lagoonal water table increased and enabled further sediment to be quickly deposited on top of the track-bearing layer. (C) The fine-grained sand was overlaid by finer sediment deposited when water levels continued to increase. This would go on to become the bed 3 shale layer. (D) Present-day exposure of the sauropod tracks, some with eroded displacement rims and uneven sediment infill.