Marine vertebrates from the Hartland Shale (Upper Cretaceous: Upper Cenomanian) in southeastern Colorado, USA

The Hartland Shale Member of the Greenhorn Limestone was deposited in the middle of the Late Cretaceous Western Interior Seaway of North America. Rock samples rich in micro-vertebrate fossils were collected from the lower part of the Hartland Shale (ca. 94.6 Ma: early Late Cenomanian) in southeastern Colorado, USA. Through acid treatment of the rock samples, 25 marine vertebrate taxa are identified including chondrichthyans, osteichthyans, and a reptile. Chondrichthyans are represented by seven species: Ptychodus anonymus, Squalicorax curvatus, Carcharias saskatchewanensis, Archaeolamna kopingensis, Cretoxyrhina mantelli, Cretomanta canadensis, and Rhinobatos incertus. Osteichthyan fishes consist of 17 taxa: Micropycnodon kansasensis, cf. Palaeobalistum sp., Caturidae indet., Protosphyraena sp., Plethodidae indet., Elopopsis sp., Pachyrhizodus minimus, cf. Pachyrhizodus sp., Albulidae indet., Cimolichthys nepaholica, Enchodus cf. E. gladiolus, E. cf. E. shumardi, Apateodus sp., and four unidentified teleosts. The only reptilian recognized is the small aquatic lizard Coniasaurus crassidens (Dolichosauridae). The taxonomic composition of the Hartland Shale fauna is similar overall to the extensively sampled, underlying mid-Cenomanian Lincoln Limestone fauna in Colorado and Kansas, although the occurrence of Apateodus and Cimolichthys from the Hartland Shale is notable as they represent geologically the oldest record for the two genera. The vertebrates identified are mostly carnivores that include piscivorous and durophagous forms, providing new insights into the trophic structure of the palaeocommunity

Effects of an experimental short-term cortisol challenge on the behaviour of wild creek chub (Semotilus atromaculatus) in mesocosm and stream environments

The consequences of stress on the behaviour of wild creek chub Semotilus atromaculatus outside the reproductive period were studied using a single intra-coelomic injection of cortisol, suspended in coconut butter, to experimentally raise plasma cortisol levels. Behaviour between cortisol-treated, sham-treated (injected with coconut butter) and control S. atromaculatus was compared in a mesocosm system, using a passive integrated transponder array, and in a natural stream system (excluding shams), using surgically implanted radio transmitters. While laboratory time-course studies revealed that the cortisol injection provided a physiologically relevant challenge, causing prolonged (c. 3 days) elevations of plasma cortisol similar to that achieved with a standardized chasing protocol, no differences in fine-scale movements were observed between cortisol-treated, sham-treated and control S. atromaculatus nor in the large-scale movements of cortisol-treated and control S. atromaculatus. Moreover, no differences were observed in diel activity patterns among treatments. Differential mortality, however, occurred starting 10 days after treatment where cortisol-treated S. atromaculatus exhibited nearly twice as many mortalities as shams and controls. These results suggest that, although the experimental manipulation of cortisol titres was sufficient to cause mortality in some individuals, there were compensatory mechanisms that maintained behaviours (i.e. including activity and movement) prior to death. This study is one of the first to use experimental cortisol implants outside a laboratory environment and during the non-reproductive period and yields insight into how wild animals respond to additional challenges (in this case elevated cortisol) using ecologically meaningful endpoints