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I frequently come across golfball-sized concretions in the marine sandstones of the Late Campanian Bearpaw formation exposed at Lake Diefenbaker, Saskatchewan. Nearly all have small coalified fossils inside, ranging from fish bones to decapod fragments, wood chips, and all other manner of organic detritus. These remains are often difficult to identify (certainly beyond my ability, anyway), typically because they are either too crushed to be recognizable, or have been split on a bad plane. The following photos shows one of these nodules collected last weekend, that caught my eye with its regularity. As you can see, there is a small row of mostly uniform nodules inside, with thin sandstone rinds discontinuous to the matrix, and filled with a black, coal-like mineral, the same which tends to replace other organic remains found in similar nodules. Any ideas? For reference, here are some other fossils found in similar nodules from a similar layer of the formation, including fish vertebrae and a decapod claw:

I thought the mosasaur fans here might enjoy a fairly recent bit of mosa-research… This paper describes the very well preserved skull and associated postcrania (a few vertebrae, some pectoral and pelvic girdle elements, a partial forelimb and a hindlimb) of a new tylosaurine mosasaur species, Tylosaurus saskatchewanensis. The holotype material of this tylosaur is from the Upper Campanian (Late Cretaceous) Bearpaw Formation of Saskatchewan, Canada. The paper: Jiménez-Huidobro et al. 2018 new Tylosaurus species.pdf A sneak peak at some of the material described (articulated dorsal vertebrae) - scale bar is 10cm: Hope you guys like it