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A tyrannosaurid pedal ungual from the Williams Fork Formation (Campanian) of Colorado and its implications for the biogeography of Laramidian dinosaurs

Yun Chan-Gyu

Acta Geologica Polonica

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2023

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Vol. 73, no. 1

63--72

EN

A right theropod pedal ungual phalanx II-3 from the Campanian Williams Fork Formation of northwestern Colorado is described, and a combination of features, including the large size, tapering distal tip, robust and stout overall form, triangular cross-section, and a relatively flat ventral surface allows a confident referral to Tyrannosauridae Osborn, 1906. Although this specimen was found in a relatively southern state, the proximal articular surface of this ungual is similar to that of Gorgosaurus libratus Lambe, 1914, a taxon found in the northern state, Alberta. Although based on limited evidence, this may suggest that the range of tyrannosaurids considered endemic to the north of Laramidia extended farther south than previously thought.

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Genus-level versus species-level extinction rates

Trammer J.

Acta Geologica Polonica

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2016

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Vol. 66, no. 3

261--265

EN

The average extinction rates of index species per m. y. are computed by means of a count-of-biozones metric (Trammer 2014). These rates and the average extinction rates of genera belonging to biostratigraphically important groups, calculated according to three different methods, show congruent rises and falls from the Cambrian to the Neogene. The extinction rates of genera are, thus, a relatively good predictor of species extinction rates.

3

Echinoids as substrates for encrustation : review and quantitative analysis

Borszcz T.

Annales Societatis Geologorum Poloniae

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2012

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Vol. 82, No. 2

139-–149

EN

The existing literature, including records of both fossil and extant echinoid encrustation, is quantitatively analysed and reviewed. This shows that echinoid encrustation (number of encrusted echinoid taphocoenoses) has increased nearly continuously and dramatically to the present day, as confirmed by linear regression values of more than 85 per cent. It also demonstrates that current levels of echinoid fouling stabilised by the Miocene, while there has been a more or less continuous record of echinoid encrustation since the Late Cretaceous. Several increases have been identified since echinoid encrustation first noted occurrence from the Late Carboniferous. This trend is explained as the probable result of corresponding increases in productivity (richness, biomass, energetics, ecospace utilisation) and resources in the marine environment, including epibionts and their hosts. This conclusion matches other indicators, including the number and thickness of shell beds, bioerosion and predation intensity or biodiversity. The trajectory might have been altered to some degree by biases (e.g. selective recording, sampling effort, outcrop area, rock volume) in the same way as palaeobiodiversity estimates. Two recognised long-term gaps in echinoid encrustation (Upper Ordovician–Lower Carboniferous and Permian–Lower Cretaceous) are explained in part as bias and as biological and taphonomic signals. These gaps are caused mostly by the rapid disarticulation of Palaeozoic-type echinoids, the methodology applied here, and a lack of interest in the encrustation of Jurassic echinoids. Conversely, three short-term gaps in the Cenozoic are interpreted exclusively as bias. If correct, the present study demonstrates quantitatively the step-wise increase of productivity through time. It also suggests potential focus on further study, including the collection of new data from the field and pre-existing collections, as best for other encrustation proxies (e.g., percent of coverage by epibionts, ratio of encrusted to nonencrusted shells, taxa richness or numerical abundance of sclerobionts) in cases of large-scale analyses.