A subadult individual of Styracosaurus albertensis (Ornithischia: Ceratopsidae) with comments on ontogeny and intraspecific variation in Styracosaurus and Centrosaurus.

Styracosaurus albertensis is an iconic centrosaurine horned dinosaur from the Campanian of Alberta, Canada, known for its large spike-like parietal processes. Although described over 100 years ago, subsequent discoveries were rare the last few decades, during which time several new skulls, skeletons, and bonebeds were found. Here we described an immature individual, the smallest known for the species, represented by a complete skull and fragmentary skeleton. Although ~80% maximum size, it possesses a suite of characters associated with immaturity, and is regarded as a subadult. The ornamentation is characterized by a small, recurved, but fused nasal horncore; low, rounded postorbital horncores; and short, triangular, and flat parietal processes. Using this specimen, and additional skulls and bonebed material, the cranial ontogeny of Styracosaurus is described, and compared to Centrosaurus. Styracosaurus shows a similar early ontogeny of the nasal horncore, starting thin, recurved, and unfused, but retains the recurved morphology into large adult size, and never develops the procurved morphology common in Centrosaurus. The postorbital horncores of Styracosaurus are lower and more rounded than those of Centrosaurus throughout ontogeny, and show greater resorption later in ontogeney. The length and thickness of the parietal processes increase drastically through ontogeny, but their position and orientation are static across the size series. Several diagnostic Styracosaurus albertensis specimens now preserve medially orientated P3 spikes, causing issues for the diagnosis of S. ovatus. Variability in parietal ornamentation, either expression of P1 and P2 parietal processes, or other cranial ornamentations, does not appear to correlate with stratigraphy.

Painful Medial Ankle in a Young Dancer: A Case Report of a Symptomatic Secondary Ossification Center of the Medial Malleolus

An osseous fragment at the distal tip of the medial malleolus in a skeletally immature individual may represent a secondary ossification center and should not always be interpreted as a fracture. In this case study of a young dance student presenting with bilateral medial ankle pain, we postulated that hindfoot valgus, in combination with extreme loads placed on the foot during ballet training, increased stresses at the medial malleolus and accessory physis. Our patient was treated conservatively for symptomatic secondary ossification of medial malleolus and she returned to dance class at 6 months.

First record of the alien aquatic oligochaete species Monopylephorus limosus (Hatai, 1898) (Annelida) in Central Europe

The paper reports on the first record of the Asian aquatic oligochaete species Monopylephorus limosus (Hatai, 1898) in Central Europe. The species was found in the lower course of the Bolina River (S Poland), which is contaminated with saline mine waters. One immature individual was collected in the late summer of 2017. M. limosus co-occurred with Paranais litoralis, Nais elinguis and juvenile Enchytraeidae. To date, M. limosus is one of the 29 non-native annelids that are known to occur in Poland.

A juvenile specimen of Saurornithoides mongoliensis from the Upper Cretaceous of northern China

A hind limb of Saurornithoides mongoliensis from the Djadokhta Formation equivalent beds (Upper Cretaceous) of Bayan Mandahu (People's Republic of China) provides more information on the anatomy of the leg of this species than any other known specimen. Although it shares apomorphies of all troodontid theropods, the metatarsus is relatively longer and more derived than that of Troodon itself. The specimen is of an immature individual, less than half the size of the holotype. The degree of ossification suggests that troodontids were well developed at birth and that parental care was probably unnecessary.