May 7th, 2021

Thanks to Dr. Oksana Vernygora,Β our #FossilFriday is the type specimen of a Late Cretaceous freshwater fish called π»π‘œπ‘Ÿπ‘ π‘’π‘ β„Žπ‘œπ‘’π‘–π‘β„Žπ‘‘β„Žπ‘¦π‘  π‘Žπ‘Ÿπ‘šπ‘Žπ‘ π‘’π‘Ÿπ‘Ÿπ‘Žπ‘‘π‘’π‘  specimen found in the Horseshoe Canyon Formation from the 68.4-million-year-old Albertosaurus bonebed of southern Alberta.

Β 

TMP 2001.045.0093 (holotype) is a rare articulated fossil clupeomorph (herring and relatives) from freshwater Late Cretaceous (Santonian β€” Maastrichtian) deposits of Alberta. This type of preservation is not common for fossil clupeomorphs that are commonly known from isolated elements found in the Cretaceous deposits of Alberta. Articulated specimens like this provide valuable information for evolutionary analysis and allow assignment of isolated elements to species. π»π‘œπ‘Ÿπ‘ π‘’π‘ β„Žπ‘œπ‘’π‘–π‘β„Žπ‘‘β„Žπ‘¦π‘  π‘Žπ‘Ÿπ‘šπ‘Žπ‘ π‘’π‘Ÿπ‘Ÿπ‘Žπ‘‘π‘’π‘  is a member of the double-armoured herring group known for the presence of modified shield-like scales along their back and is the first freshwater described from the Upper Cretaceous of North America. Its name is derived from the location it was found (in the Horseshoe Canyon Formation), and from the serrated texture of its scales (Latin β€˜arma’ for β€˜shielded’ and β€˜serrata’ for β€˜serrated’)

Photo credit: Dr. Oksana Vernygora.

TMP 2001.045.0093 holotype specimen for π»π‘œπ‘Ÿπ‘ π‘’π‘ β„Žπ‘œπ‘’π‘–π‘β„Žπ‘‘β„Žπ‘¦π‘  π‘Žπ‘Ÿπ‘šπ‘Žπ‘ π‘’π‘Ÿπ‘Ÿπ‘Žπ‘‘π‘’π‘ , from southern Alberta’s Horseshoe Canyon Formation.

Photo credit: Dr. Oksana Vernygora.
Fig. 2. Photograph and interpretive tracing of the skull of the holotype of Horseshoeichthys armaserratus, gen. et sp. nov. (TMP 2001.045.0093). (a) The fossil is coated with ammonium chloride; (b) tracing of the fossil. Scale bars = 1 cm. a, angular; asph, autosphe- notic; cl, cleithrum; co, coracoid; den, dentary; epo, epiotic; fr, frontal; hyo, hyomandibula; io1 to io6, infraorbitals 1 to 6; l., left; le, lateral ethmoid; mes, mesethmoid; mx, maxilla; na, nasal; op, opercle; orb, orbitosphenoid; osc, otic sensory canal; pa, parietal; pcl1 and pcl2, postcleithra 1 and 2; pmx, premaxilla; pop, preopercle; psph, parasphenoid; pto, pterotic; ptt, posttemporal; r., right; scl, supracleithrum; scr, sclerotic ring; smx1 and smx 2, supramaxillae 1 and 2; soc, supraoccipital; sop?, probable subopercle; sosc, supraorbital sensory canal; uh, urohyal.
Fig. 1. Left lateral view of the holotype of Horseshoeichthys armaserratus, gen. et sp. nov. (TMP 2001.045.0093). (a) The fossil is coated with ammonium chloride and is embedded in acrylic, which was digitally removed from the image. (b) Tracing of the fossil with the heavy continuous and broken lines indicating possible dorsal scutes and a body line. Scale bars = 1 cm.
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