Five partially preserved mammaliaform petrosals recovered from Middle Jurassic sediments of the Berezovsk coal mine (Krasnoyarsk Krai, Russia) show similarities to other early mammaliaforms like the morganucodontan Morganucodon and the docodontan Haldanodon in having an inflated promontorium, and a curved and apically inflated cochlear canal. But they are distinct from dryolestoid and derived mammalian petrosals by the weak coiling of the cochlear duct and the presence of a perilymphatic foramen with an open perilymphatic sulcus. The two larger and robust specimens exhibit striking similarities to docodontan petrosals. Inside the bone an intricate circumpromontorial venous plexus was discovered as recently described for the docodontan Borealestes, confirming this structure is consistently present in basal mammaliaforms. The three smaller and slender petrosals likely belong to haramiyidans and are unique in showing a septum-like structure medially along the cochlear nerve entrance. The protruding perforated bony bar that is preserved in two of the three is interpreted here to be a remnant of a bony septum with multiple foramina for cochlear nerve fibers, representing an autapomorphic feature of Haramiyida. This newly described passageway for nerve fibers shows that the formation of the osteological structure surrounding the nervous pathways of the cochlea is more plastic among the most basal mammaliaforms than previously thought.

Petrosals were picked from the >2.0 mm fraction of the screen washed clay and scanned with the 180 kV X-ray tube of the v|tome|x s µCT device (GE Sensing & Inspection Technologies GmbH phoenix|x-ray) of the Institute of Geosciences, Section Paleontology, Rheinische Friedrich-Wilhelms-Universität Bonn, Germany. Image size was 1024 × 1024 pixels. Reconstruction software datos|x rec (GE Sensing & Inspection Technologies GmbH phoenix|x-ray) and VG Studio Max 2.0 (Volume Graphics) was used to produce CT images stacks. Avizo® 6.3 (VSG Visualization Sciences Group, FEI Company) was used for reconstuction of endocasts and surface models. The 3D PDF files were created using DAZ studio v4.15 and Adobe Acrobat X pro.

Data and file overview:

PIN5087_37-CT_Image_stack.zip
ZIP-folder of CT image stack raw data (.jpg) and scan settings (.vgi); unpack ZIP-folder to use, open .vgi with Editor of Microsoft Windows

PIN5087_38-CT_Image_stack.zip
ZIP-folder of CT image stack raw data (.jpg) and scan settings (.vgi); unpack ZIP-folder to use, open .vgi with Editor of Microsoft Windows

PIN5087_69-CT_Image_stack.zip
ZIP-folder of CT image stack raw data (.jpg) and scan settings (.vgi); unpack ZIP-folder to use, open .vgi with Editor of Microsoft Windows

PIN5087_70-CT_Image_stack.zip
ZIP-folder of CT image stack raw data (.jpg) and scan settings (.vgi); unpack ZIP-folder to use, open .vgi with Editor of Microsoft Windows

PIN5087_71-CT_Image_stack.zip
ZIP-folder of CT image stack raw data (.jpg) and scan settings (.vgi); unpack ZIP-folder to use, open .vgi with Editor of Microsoft Windows

3D_PDF_instructions_Schultz_etal_Siberian_Petrosals.pdf
PDF file with instructions to view the 3D-PDF files; open with any PDF viewer

PIN5087-37.pdf
3D-PDF of petrosal PIN 5087/37: polygonal model of petrosal, reconstructed endocast, blood vessels, and innervation pattern; open with any PDF viewer

PIN5087-38.pdf
3D-PDF of petrosal PIN 5087/38: polygonal model of petrosal, reconstructed endocast, blood vessels, and innervation pattern; open with any PDF viewer

PIN5087-69.pdf
3D-PDF of petrosal PIN 5087/69: polygonal model of petrosal, reconstructed endocast, blood vessels, and innervation pattern; open with any PDF viewer

PIN5087-70.pdf
3D-PDF of petrosal PIN 5087/70: polygonal model of petrosal, reconstructed endocast, blood vessels, and innervation pattern; open with any PDF viewer

PIN5087-71.pdf
3D-PDF of petrosal PIN 5087/71: polygonal model of petrosal, reconstructed endocast, blood vessels, and innervation pattern; open with any PDF viewer

PIN5087-37_clean_smoothed_reduced.stl
polygonal model of petrosal PIN 5087/37; open with e.g. 3D viewer of Microsoft Windows

PIN5087-38_clean_reduced.stl
polygonal model of petrosal PIN 5087/38; open with e.g. 3D viewer of Microsoft Windows

PIN5087-69_clean_smoothed_reduced.stl
polygonal model of petrosal PIN 5087/69; open with e.g. 3D viewer of Microsoft Windows

PIN5087-70_Berezovsk_cochlear_canal.stl
polygonal model of petrosal PIN 5087/70; open with e.g. 3D viewer of Microsoft Windows

PIN5087-71_Berezovsk_complete_petrosal_reduced.stl
polygonal model of petrosal PIN 5087/71; open with e.g. 3D viewer of Microsoft Windows

README.txt
information to use the dataset; open with Editor of Microsoft Windows