A Life Table for Psittacosaurus lujiatunensis: Initial Insights Into Ornithischian Dinosaur Population Biology

Abstract

Very little is known about nonavian dinosaur population biology. Multi-individual sampling and longevity estimation using growth line counts can be used to construct life tables-the foundation for population analyses in ecology. Here we have determined the size and age distribution for a sample consisting of 80 individuals of the small ornithischian, Psittacosaurus lujiatunensis from the early Cretaceous Yixian Formation of China. Their ages ranged from less than a year to eleven years and the distribution was strongly right-skewed. This is consistent with taphonomic interpretations that these animals derive from a catastrophic death assemblage. The static life table analysis revealed the same general pattern of survivorship as tyrannosaurs including increased attrition before the attainment of full adult size. This may reflect increased physiological demands and/or predation exposure associated with reproduction. Collectively these findings suggest that most nonavian dinosaurs may have had a similar life history strategy. Anat Rec, 292:1514Rec, 292: -1521Rec, 292: , 2009. V V C 2009 Wiley-Liss, Inc.

Histology and postural change during the growth of the ceratopsian dinosaur Psittacosaurus lujiatunensis

“…By contrast, the largest known P. lujiatunensis femur measures 202 mm (ref. 20), and must have been close to final size because the largest femur sampled in the present study is only about 160 mm long but appears almost fully grown on the basis of histology. This femur represents an individual (IVPP V12617) that we consider to be 10 years old on histological grounds, although it was previously interpreted as a 6 year old based on femur size alone 20 .…”

“…Femur length comparisons informed by histology suggest larger adult body size in P. mongoliensis, but inferred growth curves for the two species 19,20 show a considerably higher mass for P. lujiatunensis than for P. mongoliensis (38 kg in the former versus 25 kg in the latter). There are several possible solutions to this paradox, including the fact that the mass estimates used to construct the growth curves were based on circumference rather than length measurements 19,20 and could represent a difference in robustness between the two species, but distinguishing among the various possibilities will require an analysis directly comparing the two species in terms of both histology and skeletal proportions.…”

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

“…The consequence for high energy demands early in ontogeny is high juvenile mortality followed by rapid senescence after the peak performance window (Jones et al 2008). If proportionally few dinosaurs in a population survived beyond the onset of sexual maturity (only 28% in our Maiasaura sample), and mortality related to senescence rose immediately following the peak performance plateau, this may explain why exceptionally large, skeletally mature dinosaurs with thick EFS are rare in the fossil record (e.g., Erickson 2005;Erickson et al 2006;Erickson et al 2009;Horner et al 2011).…”

“…Survivorship, Maturity, and Longevity.-Dinosaur population survivorship has been previously modeled for Albertosaurus, Gorgosaurus, Daspletosaurus, Tyrannosaurus, and Psittacosaurus (Erickson et al 2006;Erickson et al 2009;Erickson et al 2010). Unfortunately, due to the difficulty presented by fossil scarcity and in obtaining multiple specimens for histological sampling, such modeling has been criticized for its lack of biologically statistically significant sample sizes (Steinsaltz and Orzack 2011).…”

“…For each scenario, apposition rates of cortical thickness between the outermost LAG and the periosteal surface were not calculated as this thickness does not represent a single year of growth (either less than a year in growing animals, or many years if the external fundamental system is present). Survivorship curves were previously modeled for Albertosaurus, Daspletosaurus, Tyrannosaurus, and Psittacosaurus (Erickson et al 2006;Erickson et al 2009;Erickson et al 2010), but our study is the first to model extinct tetrapod survivorship using a sample size with more than 30 specimens for which age has been histologically determined for each. The 95% confidence intervals for the survivorship curve were calculated using the method of Steinsaltz and Orzack (2011): of N individuals in the sample, k individuals survive x years, so the 95% confidence interval for each year is calculated using the formula k=N ± 1:96 ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi kðNÀkÞ=N 3 p .…”