Maiasaura, a model organism for extinct vertebrate population biology: a large sample statistical assessment of growth dynamics and survivorship

Abstract

Abstract.-Fossil bone microanalyses reveal the ontogenetic histories of extinct tetrapods, but incomplete fossil records often result in small sample sets lacking statistical strength. In contrast, a histological sample of 50 tibiae of the hadrosaurid dinosaur Maiasaura peeblesorum allows predictions of annual growth and ecological interpretations based on more histologic data than any previous large sample study. Tibia length correlates well (R 2 > 0.9) with diaphyseal circumference, cortical area, and bone wall thickness, thereby allowing longitudinal predictions of annual body size increases based on growth mark circumference measurements. With an avian level apposition rate of 86.4 μm/day, Maiasaura achieved over half of asymptotic tibia diaphyseal circumference within its first year. Mortality rate for the first year was 89.9% but a seven year period of peak performance followed, when survivorship (mean mortality rate = 12.7%) was highest. During the third year of life, Maiasaura attained 36% (x = 1260 kg) of asymptotic body mass, growth rate was decelerating (18.2 μm/day), cortical vascular orientation changed, and mortality rate briefly increased. These transitions may indicate onset of sexual maturity and corresponding reallocation of resources to reproduction. Skeletal maturity and senescence occurred after 8 years, at which point the mean mortality rate increased to 44.4%. Compared with Alligator, an extant relative, Maiasaura exhibits rapid cortical increase early in ontogeny, while Alligator cortical growth is much lower and protracted throughout ontogeny. Our life history synthesis of Maiasaura utilizes the largest histological sample size for any extinct tetrapod species thus far, demonstrating how large sample microanalyses strengthen paleobiological interpretations.Holly N. Woodward*. Museum of the Rockies,

A new multi-faceted framework for deciphering diplodocid ontogeny

“…MOR 790 7-23-95-122), while a 27 m individual is at least 24 years old (D. carnegii CM 94). These growth rates are not nearly as accelerated as those recorded in some other dinosaurs -such as a 3 m body lengths within the first year in Maiasaura (Woodward et al, 2015) -but they are still consistent with rapid growth rates. In terms of historical perceptions of longevity, sauropods have run the estimation gamut -attaining maximum body size within a decade (Curry, 1999) or taking up to several centuries (and finally sexually mature at 72 years of age; Case, 1978).…”

“…In exceptional ontogenetic studies, large sample sizes including representatives of multiple growth stages allow for more comprehensive histologic and morphological comparisons (e.g., Dodson, 1975;Carr, 1999;Scannella and Horner, 2010;Horner et al, 2011;Frederickson and Tumarkin-Deratzian, 2014;Woodward et al, 2015). While Morrison diplodocids are by far one of the most common of all North American dinosaur groups, taphonomic biases, stratigraphic resolution, and taxonomic uncertainties generally result in largely incomplete and less well understood individuals.…”

Taphonomical and palaeoecological investigation of the Late Cretaceous (Maastrichtian) Tuştea vertebrate assemblage (Romania; Haţeg Basin) - insights into a unique dinosaur nesting locality

“…Study of these remains indicates that they represent ontogenetic developmental stages ranging from near-term embryos to early-to-late hatchlings (Grigorescu and Csiki, 2006;Benton et al, 2010;Grigorescu et al, 2010), and thus document the simultaneous presence of individuals with different body sizes and representing different age classes in the Telmatosaurus hatchling material. Despite the relatively wide size range of the limb bones (suggesting the presence of babies of different sizes in the nesting ground), these size differences do not represent a long time interval, and it is probable that these different sized neonates hatched during the same breeding season, followed by a rather rapid early ontogenetic development, as already suggested for hadrosauroids (e.g., Horner and Weishampel, 1988;Horner et al, 2000;Grigorescu and Csiki, 2006;Woodward et al, 2015).…”

“…It was already suggested that the chance of preservation for hatchling remains is relatively high in their nesting areas. This is because here the baby skeletal elements are very abundant as a consequence of high mortality rates during the hatching period, resulting from intrinsic causes such as disease, abandonment, trampling or siblicide (e.g., Horner, 1994;Rogers and Kidwell, 2007;Brinkman et al, 2007;Woodward et al, 2015). Horner (1994) even suggested that most, if not all, baby dinosaur mortality occurred in the nesting areas, since baby dinosaur remains are extremely rare in the fossil record except in nesting grounds or accumulations reworked directly from these.…”

“…There is also a growing body of evidence indicating that juvenile hadrosauroids remained in the vicinity of the nest after they hatched, and joined the adult community only when they reached about half of the adult body size (Horner and Makela, 73 1979;Horner, 1982Horner, , 1994Horner, , 1997Horner, , 1999Horner and Currie, 1994;Carpenter, 1999;Lauters et al, 2008;Dewaele et al, 2015;Woodward et al, 2015). Horner and Makela (1979) and Horner (1982Horner ( , 1994Horner ( , 1997 also suggested that altricial perinatal hadrosauroids were fed by their parents while remaining in the nesting area, a type of social interaction that also contributes to the common occurrence (and thus potentially relatively high preservation rate)…”