Table 1.
Data basis of the current study.
Figure 1.
Growth mark record in polished sections of sauropodomorph individuals used in this study.
Arrows indicate considered growth marks which are oriented parallel to the growth direction of the bone surface. The outer bone surface is at the top. Most samples extend from the outer cortex into the medullary region, but the center of medullary region is not covered by all samples. The primary bone tissue generally is laminar fibrolamellar bone. All samples except for the indeterminate mamenchisaurid sample are polished sections, which originate from core samples. Except for A) and G), which are photographed in normal incident light, all other images are in bright field illumination, with light reflected off the polished sample surface. A) Femur sample of Plateosaurus engelhardti (IFG 192.1; 740 mm) with 12 lines of arrested growth deposited. The outermost cortex does not show an external fundamental system (EFS), which indicates that this individual had not yet reached asymptotic growth, but growth rate clearly had decreased due to the close spacing of the growth marks in the outer cortex. B) Femur sample of Apatosaurus sp. (SMA 0014; 1,640 mm) with 20 growth marks consisting of lines of arrested growth and polish lines. The outer cortex is incomplete due to post mortem damage. C) Femur sample of Apatosaurus sp. (BYU 601-17328; 1,580 mm) with five growth marks consisting of polish lines. The outer cortex exhibits an EFS which contains another 13 resting lines deposited. D) Femur sample of Camarasaurus sp. (CM 36664; 1,452 mm) with five growth marks consisting of polish lines and lines of arrested growth. The outermost cortex exhibits an EFS, which contains another four resting lines. E) Femur sample of an indeterminate diplodocid (MfN.R.NW4; 1,350 mm) with 16 growth marks in form of lines of arrested growth and polish lines. The outermost cortex lacks an EFS. F) Humerus sample of an indeterminate diplodocid (MfN.R.2625, 610 mm) with nine growth marks in the form of lines of arrested growth and polish lines visible in the cortex. The outermost cortex lacks an EFS. G) Humerus sample of the indeterminate mamenchisaurid (SGP 2006/9; approx. 1,400 mm) showing 16 growth marks consisting of lines of arrested growth in the outer cortex and cyclic variation in vascularity (modulations) in the inner cortex. The outermost cortex shows an EFS which is too thin to see at the magnification of this image.
Table 2.
Results of growth curve fitting for Sauropodomorpha.
Figure 2.
Logistic growth models established for Sauropodomorpha individuals.
Two curve fitting techniques were applied to construct growth curves from the growth mark record laid down in long bones (Table 1). Only the statistically best supported models are shown, except for Apatosaurus sp. (BYU 601-17328) and Camarasaurus sp. For these two individuals, the logistic growth models (dotted line) based on the non-EFS growth marks only are also shown. Triangles refer to different estimates of age at sexual maturity. Age at the inflection point of the growth curve (white triangle) is the lower limit (50% of asymptotic mass = M50%), whereas age at 90% asymptotic mass (black triangle) is the upper limit (M90%) of the onset of reproduction. The grey triangle (ASM) indicates the arithmetic mean of these time spans and corresponds to the arithmetic mean of the earliest and latest age at which first reproduction could have occurred. Parameter values of the best models are summarized in Table 2. Model selection was based on the AIC approach [75].
Figure 3.
Allometries derived for Sauropodomorpha and comparison with the literature data.
A) Age at death vs. body mass, B) asymptotic age vs. body mass, C) age at sexual maturity (ASM) vs. body, mass and D) maximum growth rate vs. body mass. Regression lines (continuous line) and 95% confidence interval (dashed lines) are shown. Filled square in A): age at death of Massospondylus [21]. Filled triangles with error bars in all graphs: estimates of life history traits for Alamosaurus from Lehman and Woodward [34]. Error bars in C): lower limit (age at inflection point of the growth curve), and upper limit (age at which 90% of the asymptotic mass is reached, [49], [52], see Figure 2C) of age at sexual maturity. Error bars in D): average daily increase in body mass during the quasi-linear phase (between 10% and 90% of the asymptotic mass, [77]). Statistics of allometric functions: A) R2 = 0.841, intercept p = 0.010, slope p = 0.003; B) R2 = 0.538, intercept p = 0.271, slope p = 0.061; C) R2 = 0.494, intercept p = 0.230, slope p = 0.079; D) R2 = 0.895, intercept p = 0.230, slope p = 0.001. n.s. p>0.05, * p≤0.05, ** p<0.01, *** p<0.001.
Table 3.
Comparison of growth models with histological data for Sauropodomorpha.
Figure 4.
Comparison of life history traits of Sauropodomorpha, extant ratites and extant mammalian megaherbivores.
All regression lines for extant species are extrapolated to the body masses of Sauropodomorpha. In all panels the dashed blue lines and dashed green lines are regression lines for ratites and megaherbivores, respectively. These regression lines were calculated based on all data points for the respective taxon. None of the dashed regression lines is statistically significant. Open circles in A) to D) are Sauropodomorpha. Data for megaherbivores are from Owen-Smith [50] and those for ratites are from del Hoyo [81]. Symbol explanation for megaherbivores (green): elephant: Loxondonta africana (open diamonds), hippo: Hippopotamus amphibius (open circles), giraffe: Giraffa camelopardalis (open squares), rhinos: Rhinoceros unicornis (crosses), Diceros bicornis (asterisks), Ceratotherium simum (open triangles). Symbol explanation for ratites (blue): ostrich: Struthio camelus (filled diamonds), emu: Dromaius novaehollandiae (crosses), cassowary: Casuarius casuarius (filled triangles), rhea: Rhea americana (asterisks). A) Life expectancy in wild populations. Vertical bars connect minimum and maximum life expectancies for elephant, hippo, rhinos, and emu. Ostrich data are from captive animals; green line: allometry of life expectancy in mammals [4]. B) Asymptotic age in wild populations. Bars: minimum and maximum values for elephant (male, female), hippo and emu. C) Age at sexual maturity in wild populations. Vertical bars connect minimum and maximum values for all species; brown line: virus-to-mammals allometry of maturation time [4]; green line: allometry of age at first conception in mammals [50]. Age at sexual maturity of Sauropodomorpha is based on ASM of the best growth model (Figure 2C, grey triangle). D) Maximum growth rate. Sauropodomorpha (black line, 95% confidence interval dotted), eutherian mammals (green line, [77]), precocial birds (blue line, [77]), reptiles (red line, [77]). Growth rates of Sauropodomorpha are in the realm of precocial birds. The regression line of eutherian mammals is clearly above the 95% confidence interval for Sauropodomorpha, and the line for reptiles is well below the confidence interval. Maximum growth rates of Sauropodomorpha are based on the inflection points of the best growth models (Figure 2D).