Figure 1.
Representative cross sections and corresponding sketches of femora, tibiae, and humeri.
A–B: Large femur GPIT/RE/3588, cut distally to the base of the fourth trochanter; C–D: Medium-sized femur GPIT/RE/3587, cut close to the base of the fourth trochanter; E–F: Medium-sized tibia GPIT/RE/3724, cut proximal to the lateral bulge; G–H: Large tibia SMNS T 3, cut close to the lateral bulge; I–J: Large humerus GZG.V 6223, cut distal to the mid diaphysis; K–L: Large humerus GPIT/RE/4877/8929, cut proximal to the mid diaphysis. All sections are oriented and scaled consistently. Internal red area represents CCCB (B, D, H, J) or an endosteal layer (L). Lines in green mark cross sectional damage. Growth cycles are shaded (B) or lined (D, F, H, J, L) in gray, annuli/LAGs are lined in red. The blue area in H represents medullary bone.
Figure 2.
Details of cross sections of Dysalotosaurus femora showing resorption and bone tissue types.
A–B: GPIT/RE/3588, A – Interior margin of posterolateral corner demonstrating the resorptive nature of the marrow cavity, under polarized light. Note the angle of the zonation towards the marrow cavity at the top. B – The same as in A under normal light. C–D: SMNS F 2, C – Part of the posterolateral bone wall with numerous primary osteons under polarized light. The orientation of bone fibers and primary osteons varies between the darker and the strongly birefringent zones. The marrow cavity lies in the direction to the top right. D – The same as in C under normal light. E–F: GPIT/RE/3587, E – Part of the anterior corner under polarized light showing parallel-fibered tissue with mainly circumferential primary osteons and a small cluster of secondary osteons at the top right (arrows). F – The same as in E under normal light. G–H: GPIT/RE/3414, G – Part of the anterior wedge of CCCB (Compacted Coarse Cancellous Bone) under polarized light. Note the difference between the continuous transitions between the trabeculae of the CCCB and the interruptions in the lamellar bone originating from secondary osteons of various developmental stages. The marrow cavity is located at the bottom. H – The same as in G under normal light. Scale bars = 1 mm in A, B. Scale bars = 500 µm in C–H.
Figure 3.
Variation of vascular organization in cross sections of Dysalotosaurus femora.
A–D: GPIT/RE/3588, A – Part of the medial corner with numerous poorly organized primary osteons and weakly birefringent bone matrix, under polarized light. B – The same as in A under normal light. C – Part of the lateral wall with well organized laminar and circumferential primary osteons as well as mainly transverse and strongly birefringent bone fibers, under polarized light. D – The same as in C under normal light. E–F: GZG.V 6590 28, E – Medial part of the anterior corner with the CCCB wedge involving about half of the bone wall thickness and apparently compressing the primary bone wall exteriorly, under polarized light. F – The same as in E under normal light. G–H: SMNS F2, G – Internal part of the anterior corner beside the CCCB wedge (starts beyond the left frame of the image) showing the typical knitted pattern with small, laminar and mainly longitudinally oriented primary osteons nested between thick cords of matrix, under polarized light. The marrow cavity is at the bottom to the left. H – The same as in G under normal light. Scale bars = 500 µm in A–D, G–H. Scale bars = 1 mm in E–F.
Figure 4.
Cross sectional units in Dysalotosaurus femora with unusual bone tissue.
A–H: GPIT/RE/3414, A – Overview of the oriented cross section (a = anterior, l = lateral), under normal light. B – Magnification of the lateral corner demonstrating the interruption of the usual vascularisation by the cloud of reticular canals of the Posterolateral Plug, under normal light. C – Magnification of the section framed in B, under polarized light. Arrows indicate scattered secondary osteons. D – The same as in C under normal light. Note the high density of osteocyte lacunae. E – Magnification of the anterior corner under polarized light and slightly rotated clockwise relative to A. F – The same as in E under normal light. G – Magnification of the upper center of E. Note the weak development of many primary osteons. H – The same as in G under normal light. Scale bars = 5 mm in A. Scale bars = 1 mm in B, E–F. Scale bars = 500 µm in C–D, G–H.
Figure 5.
Growth cycles in Dysalotosaurus femora.
A–B: GPIT/RE/3587, A – The outer edge of the posterior bone wall with mainly circumferential primary osteons and a LAG (arrow), under polarized light. B – The same as in A under normal light. C–D: GPIT/RE/3414, C – Interior part of the posterolateral bone wall under polarized light. The growth cycles (fast growing zones darker, slow growing zones brighter) stop at the Posterolateral Plug. Arrows indicate the outer edge of a slow growing zone. D – The same as in C under normal light. The growth cycles are now very difficult to identify. The best verifiable slow growing zones are the second and third where the outer edge is less vascularized and the circumferential orientation of canals is significant. E–H: GPIT/RE/3588, E – Posterolateral corner under normal light with the typical alternation of fast (darker) and slow (brighter) growing zones. The external edge of the slow growing zones is marked by arrows. Note the transition of the internal cyclicity to an almost uniform slow growing zone externally (border at the lower edge of the frame). F – Magnification of the section framed in E showing the strong organizational difference between primary osteons of the fast growing zone (center) and the slow growing zones (top and bottom). G – Close up of a fast growing zone both under polarized and normal light. The image is slightly rotated in comparison to E and F. H – Close up of a slow growing zone both under polarized and normal light. The image is slightly rotated in comparison to E and F. Scale bars = 1 mm in C–E. Scale bars = 500 µm in A–B, F. Scale bars = 200 µm in G–H.
Figure 6.
The Mark of Initial Sexual Maturity (MISM) as well as interior details of the anterior corner in large sampled femora of Dysalotosaurus.
A–D: SMNS F1, A – Part of the posterior bone wall, under polarized light, with the most external fast growing zone (double-headed arrow) and the transition to the thick, non-cyclical slow growing area externally (centre and right of the image). This transition is the MISM. B – The same as in A under normal light. C – Magnification of the top left of A under polarized light. The MISM is again at the right end of the double-headed arrow. Note that the MISM is not a sharp line but just another transition from fast to slower growth without any further fast growing zones towards the periphery. D – The same as in C under normal light. E: GPIT/RE/3414 (in front) and GPIT/RE/3588 (in the back), the sketches demonstrate the perfect overlap of the zonation as well as the MISM in both large femora. The slow growing zones are shaded in the back and their external rim is marked in the front. The dashed lines within the thick external slow growing zone (shaded in both representing growth after reaching sexual maturity) mark unsecured growth cycles. F: GZG.V 6590 28, Close up of the border between the CCCB wedge internally (bottom right) and the primary bone tissue externally within the anterior corner. Secondary osteons are marked by arrows. Note the knitted pattern of the primary bone tissue. G–H: GZG.V 6211 22, G – Internal part of the anterior corner close to the CCCB wedge (starts at the lower right) with knitted pattern of the bone tissue internally and some scattered secondary osteons (arrows) still under development, under polarized light. H – The same as in G under normal light. Scale bars = 1 mm in A–B. Scale bars = 500 µm in C–D, G–H. Scale bars = 200 µm in F.
Figure 7.
Upside down images of longitudinal sections of the distal ends of two femora.
A–C: large specimen GPIT/RE/3518, A – Overview under normal light. The foam-like patches at the distal (here upper) edge consist of calcified cartilage partially divided by trabecular bone. B – Magnification of the upper centre of A under normal light. C – Magnification of the upper centre of B under normal light. The bubbles of calcified cartilage cells are well distinguishable from the osteocyte lacunae within the trabecular bone. D–F: Small specimen GZG.V 6379, D – Overview under normal light. The pads of calcified cartilage reach deeper into the specimen than in A. Trabecular bone is well ossified in the lower centre but there are already centres of ossification close to the distal (here upper) surface. E – Magnification of the lower centre of D. Isolated clusters of calcified cartilage are still present (arrows). F – Magnification of the upper centre of D showing trabecular bone under development and isolated remains of calcified cartilage within bone (arrow). Scale bars = 1 mm in A, D. Scale bars = 500 µm in B, E–F. Scale bars = 200 µm in C.
Figure 8.
Bone histology and growth cycles in juvenile femora of Dysalotosaurus.
A–D: GZG.V 6379, A – Orientated overview (a = anterior, l = lateral) under normal light. Note the wide marrow cavity compared to the bone wall thickness in this early juvenile specimen. B – Magnification of the posterolateral corner under polarized light with only a weak indication of the Posterolateral Plug. The knitted pattern of the bone tissue with mainly longitudinal primary osteons is dominant. C – Magnification of the interior of the anterior corner medially, under both polarized and normal light, with a CCCB wedge under development and the typical knitted pattern of the primary bone tissue. D - Magnification of the interior of the anterior corner laterally, under both polarized and normal light, with the typical knitted pattern of the primary bone tissue. The vascular pattern changes already to more circumferential primary osteons towards the periphery. E–H: GZG.V 6590, E – Three slow growing zones are well visible under polarized light. The Posterolateral Plug starts at the left edge of the image. F – The same as E under normal light. G – Magnification of the utmost slow growing zone with an annulus at its interior border. H – The same as in G under normal light. Scale bars = 1 mm in A–B, E–F. Scale bars = 500 µm in C–D. Scale bars = 200 µm in G–H.
Table 1.
Basic dataset of all cross sections of femora used for correlations and the calculation of growth curves.
Figure 9.
Vascular patterns and tissue types in a Dysalotosaurus tibia.
A–H: Large tibia SMNS T3, A – Internal part of the lateral bone wall with laminar to sub-plexiform bone tissue under polarized light. Transversely oriented bone fibers dominate. The knitted pattern is visible at the right close to the marrow cavity. A thick endosteal layer is marked by white arrows. B – The same as in A under normal light. The external border of the prominent slow growing zone of A is also well visible here (green arrow). C – Strongly unordered primary osteons in a weakly birefringent woven matrix within the medioposterior corner under both polarized and normal light. D – Well organized primary osteons in a strongly birefringent almost parallel-fibered matrix at the outer edge of the lateral wall under both polarized and normal light. E – Overview of the anterolateral corner (here anterior to the bottom and lateral to the left) under polarized light. Note the whirl-like Anterolateral Plug within this corner, which interrupts the usual bone tissue, and the wedge of CCCB to the right at the marrow cavity. F – Partial close up of the CCCB wedge with the usual continuous lamellar bone and some interrupting secondary osteons (arrows), under both polarized and normal light. G – Close up of the border between CCCB (upper right) and primary bone tissue (lower left), under both polarized and normal light. The latter strongly resembles the juvenile knitted pattern. H – Magnification of the framed part in E showing an area within the Anterolateral Plug, under both polarized and normal light. Secondary osteons are marked with arrows. Scale bars = 1 mm in A–B, E. Scale bars = 500 µm in C–D, F, H. Scale bars = 200 µm in G.
Table 2.
Basic dataset of all cross sections of tibiae used for correlations.
Figure 10.
Growth cycles in Dysalotosaurus tibiae.
A–B: Large tibia SMNS T3, A – Close up of the anterior bone wall with a slow growing zone flushing externally with an annulus (arrow) and a LAG (at the internal edge of the former), under polarized light. B – The same as in A under normal light. The arrow marks again the annulus. The LAG is visible as up to two thin lines at its internal edge. C–F: Smaller tibia GPIT/RE/3724, C – Anteromedial corner under polarized light with up to five slow growing zones. The three middle growth cycles, consisting of a fast and a following slow growing zone, are completely visible (marked by three double-headed arrows). Whether the utmost slow growing zone is complete or not cannot be verified. D – The same as in C under normal light. Fast and slow growing zones are again difficult to distinguish. Apart from using polarized light, only minor differences in the organization of primary osteons are visible. E – Magnification of C with the two external arrows included. F – Magnification of D with the two external arrows included. Scale bars = 1 mm in C–D. Scale bars = 500 µm in A–B, E–F.
Figure 11.
Details of medullary bone found in a single tibia of Dysalotosaurus.
A–H: Large tibia SMNS T3 with images of the preserved medullary bone tissue at the anterior edge of the marrow cavity. See also Fig. 1G–H for an overview, A – The strongly cancellous medullary bone tissue (mainly in brown colors, under polarized light) is also developed within two large cavities at the edge of the marrow cavity. The difference to the primary bone tissue at the bottom and the CCCB at the lower right is striking. B – Approximately the same as in A under normal light, only slightly rotated image. The strong difference of the medullary bone tissue to the tissue types within the bone wall is still well visible. C – Close up of one part visible in A and B under polarized light. The separation between medullary bone and the actual bone wall tissues is marked by an endosteal layer (arrows). D – The same as in C under normal light. E – Overview of the medial part of the preserved medullary bone tissue under polarized light. The endosteal layer is marked by arrows. F – The same as in E under normal light. G – Magnification of E between its two central arrows under polarized light. The endosteal layer is again marked by an arrow. Note the resorptive nature of this part of the marrow cavity before the development of the endosteal layer. H – Same as in G under normal light. Scale bars = 1 mm in A–B, E–F. Scale bars = 500 µm in C–D. Scale bars = 200 µm in G–H.
Figure 12.
Bone histology of the smallest preserved tibia of Dysalotosaurus.
A–F: Early juvenile tibia GPIT/RE/3795, A – Overview of the anterolateral corner under polarized light. CCCB and the Anterolateral Plug are absent. The interior part of that corner is altered by preservation (see also Fig. S1). B – The same as in A under normal light. C – The posterior wall is well vascularized and the primary osteons are plexiform to reticular in arrangement. The degree of organization as well as of the birefringence seems to increase towards the external surface, under polarized light. D – The same as in C under normal light. E – Magnification of A under polarized light. F – Magnification of B under normal light showing many simple vascular canals oriented radially. Scale bars = 1 mm in A–B. Scale bars = 500 µm in C–F.
Figure 13.
Bone histology in Dysalotosaurus humeri.
A–B: GPIT/RE/4402, A – Orientated overview (a = anterior, l = lateral) under normal light. Note the differences in bone wall thickness and between the shapes of the marrow cavity and the whole cross section of this proximally cut section. B – Magnification of the framed area in A (rotated anti-clockwise by app. 120°) under normal light. The thick wedge of lamellar bone of the endosteal layer is marked by an arrow. Note the large amount of small longitudinal primary osteons. C: GZG.V 6664, Close up of the anterolateral corner with circumferential primary osteons separated by very thick cords of matrix. These relations in thickness together with areas of very high concentrations of osteocyte lacunae (left centre of image) are restricted to this cross sectional unit, under both polarized and normal light. D – Magnification of lower centre of B under normal light. The marrow cavity is close by in the direction to the right. Small primary osteons with only a single ring of lamellar infilling are marked by green arrows. Secondary osteons are marked by blue arrows. E–F: GZG.V 6569, E – sketch with the external edges of slow growing zones marked in gray and a LAG marked in red. The dashed line represents an unsecured slow growing zone. F – Image of the framed area in E under normal light. The four secured cycles of E are marked here by arrows. Note the increasing organization of primary osteons towards the periphery and the slight differences between the fast growing zones and the often rather thin slow growing zones. The LAG is marked by the wide-headed arrow. G: GPIT/RE/4402, the internal area of the posterior bone wall is rotated 90° clockwise relative to A and shows many inclined radial canals. These canals are perpendicular to the surface medially. H: GPIT/RE/4877/8929, Arrows indicate two closely located LAGs, under both polarized and normal light. Scale bars = 1 mm in A–B, F. Scale bars = 500 µm in C, G–H. Scale bars = 200 µm in D.
Table 3.
Basic dataset of all cross sections of humeri used for correlations.
Figure 14.
Variation in the bone histology of a single large fibula of Dysalotosaurus.
A–H: Large fibula GPIT/RE/5109, A – Internal area of the posteromedial bone wall, under polarized light, with a thick endosteal layer separating the possible medullary bone tissue from the bone wall. B – Same as in A under normal light and slightly rotated. C – Magnification of the left centre of A under polarized light. The CCCB immediately external to the endosteal layer is much stronger birefringent than the medullary bone tissue. D – Same as in C under normal light. E – External part of the medial wall with only small simple vascular canals and some weakly developed primary osteons. The secondary osteons are rather large and different stages of development are present. F – The same as in E under normal light. G – Close up of the posterior corner with numerous secondary osteons obscuring most of the remaining CCCB, under polarized light. H – The same as in G under normal light. Scale bars = 1 mm in A–B. Scale bars = 500 µm in C–H.
Figure 15.
Orientated images of cross sections of prepubic processes (d = dorsal, l = lateral) of Dysalotosaurus.
A: SMNS P17, proximal section under polarized light with decreasing size of the pseudocavities towards the lateral side. B: SMNS P19, distal section under polarized light. Note the double-layered order of the erosion cavities dorsally and similar single layers of cavities medially and ventrally, respectively. C–D: SMNS P17, C – Magnification of the dorsal centre of A under polarized light showing primary bone tissue with mainly longitudinal, small primary osteons even between the erosion cavities. The latter already possess layers of lamellar bone. D – The same as in C under normal light. E: SMNS P19, Close up of the dorsal primary bone wall with mainly longitudinal but well developed primary osteons. F: SMNS P17, Magnification of the lower centre of A with simple vascular canals and very small, weakly developed primary osteons, under both polarized and normal light. Resorption and secondary infilling of cavities is visible at the top of the image. Scale bars = 1 mm in A–B. Scale bars = 500 µm in C–E. Scale bars = 200 µm in F.
Figure 16.
Fractional growth cycle values of femur group two are correlated to age.
MISM = Mark of Initial Sexual Maturity. ‘F’ is the abbreviation for ‘femur’. Each of the following numbers corresponds to the respective specimens in Tab. 1. Some specimens were sampled at least twice so that additional letters (a, b) advert to the respective section used for this correlation.
Figure 17.
Fractional growth cycle values of tibia group one are correlated to age.
‘T’ is the abbreviation for ‘tibia’. Each of the following numbers corresponds to the respective specimens in Tab. 2. Some specimens were sampled at least twice so that additional letters (b) advert to the respective section used for this correlation.
Figure 18.
Fractional growth cycle values of the single group of humeri are correlated to age.
‘H’ is the abbreviation for ‘humerus’. Each of the following numbers corresponds to the respective specimens in Tab. 3.
Figure 19.
The nine correlated growth cycle values of femur group one and two were combined with the values of the MISM and were used for the calculation of four growth curves.
All encircled values represent unsecured growth cycles external to the MISM and were plot into the diagram afterwards. The shift of these points onto their respective growth curves resulted in a graphical change of only one additional year in age in average. Thus, 13 years are finally represented by all visible growth cycle values. Abbr.: EFit1 – Growth curve of femur group one, calculated with body masses derived from Erickson & Tumanova [27]; EFit2 – Growth curve of femur group two, calculated with body masses derived from Erickson & Tumanova [27]; AFit1 – Growth curve of femur group one, calculated with body masses derived from Anderson et al. [64]; AFit2 – Growth curve of femur group two, calculated with body masses derived from Anderson et al. [64]; Egroup1 – Correlated fractional growth cycle values of femur group one, the respective body masses are derived from Erickson & Tumanova [27]; Egroup2 – Correlated fractional growth cycle values of femur group two, the respective body masses are derived from Erickson & Tumanova [27]; Agroup1 – Correlated fractional growth cycle values of femur group one, the respective body masses are derived from Anderson et al. [64]; Agroup2 – Correlated fractional growth cycle values of femur group two, the respective body masses are derived from Anderson et al. [64].
Figure 20.
The four complete growth curves derived from the values shown in Fig. 19.
Abbreviations for the curves are as in Fig. 19. The arrows separate the ontogenetic stages observed in the femoral cross sections: II – Early juvenile stage; III – Late juvenile stage; IV – sexually immature stage; V – sexually mature stage. The black point at app. 16.5 years of age represents the largest sampled femur. The black point at app. 19.5 years of age represents the third largest preserved femur.
Figure 21.
In contrast to the diagrams with body mass versus age, the MISM is almost exactly positioned at the inflection point in a curve with body size versus age.
Measured and calculated values of the distal mediolateral width of femora are combined. The age values are an average of the respective values calculated by the methods of Anderson et al. [64] and Erickson & Tumanova [27].
Figure 22.
By comparing the maximum growth rate of Dysalotosaurus with other dinosaurs and recent animals, it is located close to the regression line for dinosaurs and is very similar to large marsupial mammals (modified from [77]).
Abbr.: Sd – Shuvuuia deserti; Pm – Psittacosaurus mongoliensis; Sr – Syntarsus rhodesiensis; Mc – Massospondylus carinatus; Mp – Maiasaura peeblesorum; Ae – Apatosaurus excelsus.
Figure 23.
Size-frequency distribution of all measured right femora.
The MISM is located at a femoral distal mediolateral width (DMW) of app. 55 mm (compare the DMW values with age in Tab. 1).
Figure 24.
Comparison of growth curves of Tenontosaurus tilletti (derived from table 2 in [62]) and Dysalotosaurus lettowvorbecki.
*Note that the maximum body mass of Tenontosaurus is app. ten times higher than in Dysalotosaurus. Thus, for a better comparison, the body mass values of Tenontosaurus were divided by 10 and then used for the growth curve calculation.
Figure 25.
Intervals of cutting levels in the sampled elements.
Abbr.: F – Femur (lateral view); Fb – Fibula (lateral view); H – Humerus (anteromedial view); P – Pubis (lateral view); T – Tibia (posterior view). Elements are not scaled.
Figure 26.
Sketches showing important steps to gain a standardized midpoint in cross sections for the measurement of distances between this midpoint and the external border of each growth cycle.
A–C: Late juvenile femur GZG.V 6590 28: A – First triangle with its vertices on the utmost extremities of each corner; B – Second triangle with vertices extrapolated from the respective opposing straight walls. The blue point in the centre is the midpoint from both triangles; C – The final midpoint of the cross section is derived from the blue midpoint of the triangles and the orange midpoint of the sketched circle. The green line lies parallel to the course of the growth cycles and the distances (e.g. blue double arrow) are then measured perpendicular to the cycles in the posterolateral part of the posterior wall. D – Late juvenile tibia GPIT/RE/3724: The midpoints of an inner and an outer circle (blue and orange, respectively) are used to get the final midpoint (red) for measuring the growth cycle distances. All sketches are not scaled, but consistently oriented with the anterior direction at the top and the medial direction at the left. The red area in A–C represents the anterior CCCB-wedge. Lines in green mark damage of the cross sections.