Osteohistological description of ostrich and emu long bones, with comments on markers of growth.

Ostriches and emus are among the largest extant birds and are frequently used as modern analogs for the growth dynamics of non-avian theropod dinosaurs. These ratites quickly reach adult size in under 1 year, and as such do not typically exhibit annually deposited growth marks. Growth marks, commonly classified as annuli or lines of arrested growth (LAGs), represent reduced or halted osteogenesis, respectively, and their presence demonstrates varying degrees of developmental plasticity. Growth marks have not yet been reported from ostriches and emus, prompting authors to suggest that they have lost the plasticity required to deposit them. Here we observe the hind limb bone histology of three captive juvenile emus and one captive adult ostrich. Two of the three juvenile emus exhibit typical bone histology but the third emu, a 4.5-month-old juvenile, exhibits a regional arc of avascular tissue, which we interpret as a growth mark. As this mark is not present in the other two emus from the same cohort and it co-occurs with a contralateral broken fibula, we suggest variable biomechanical load as a potential cause. The ostrich exhibits a complete ring of avascular, hypermineralized bone with sparse, flattened osteocyte lacunae. We identify this as an annulus and interpret it as slowing of growth. In the absence of other growth marks and lacking the animal's life history, the timing and cause of this ostrich's reduced growth are unclear. Even so, these findings demonstrate that both taxa retain the ancestral developmental plasticity required to temporarily slow growth. We also discuss the potential challenges of identifying growth marks using incomplete population data sets and partial cortical sampling.

Growing up Tyrannosaurus rex: Osteohistology refutes the pygmy "Nanotyrannus" and supports ontogenetic niche partitioning in juvenile Tyrannosaurus.

Despite its iconic status as the king of dinosaurs, Tyrannosaurus rex biology is incompletely understood. Here, we examine femur and tibia bone microstructure from two half-grown T. rex specimens, permitting the assessments of age, growth rate, and maturity necessary for investigating the early life history of this giant theropod. Osteohistology reveals these were immature individuals 13 to 15 years of age, exhibiting growth rates similar to extant birds and mammals, and that annual growth was dependent on resource abundance. Together, our results support the synonomization of "Nanotyrannus" into Tyrannosaurus and fail to support the hypothesized presence of a sympatric tyrannosaurid species of markedly smaller adult body size. Our independent data contribute to mounting evidence for a rapid shift in body size associated with ontogenetic niche partitioning late in T. rex ontogeny and suggest that this species singularly exploited mid- to large-sized theropod niches at the end of the Cretaceous.

A new fossil assemblage shows that large angiosperm trees grew in North America by the Turonian (Late Cretaceous).

The diversification of flowering plants and marked turnover in vertebrate faunas during the mid-Cretaceous transformed terrestrial communities, but the transition is obscured by reduced terrestrial deposition attributable to high sea levels. We report a new fossil assemblage from multiple localities in the Upper Cretaceous Ferron Sandstone Member of the Mancos Shale Formation in Utah. The fossils date to the Turonian, a severely underrepresented interval in the terrestrial fossil record of North America. A large silicified log (maximum preserved diameter, 1.8 m; estimated height, ca. 50 m) is assigned to the genus Paraphyllanthoxylon; it is the largest known pre-Campanian angiosperm and the earliest documented occurrence of an angiosperm tree more than 1.0 m in diameter. Foliage and palynomorphs of ferns, conifers, and angiosperms confirm the presence of mixed forest or woodland vegetation. Previously known terrestrial vertebrate remains from the Ferron Sandstone Member include fish teeth, two short dinosaur trackways, and a pterosaur; we report the first turtle and crocodilian remains and an ornithopod sacrum. Previous studies indicate that angiosperm trees were present by the Cenomanian, but this discovery demonstrates that angiosperm trees approaching 2 m in diameter were part of the forest canopies across southern North America by the Turonian (~92 million years ago), nearly 15 million years earlier than previously thought.