Thursday, 14 October 2021

MIGUASHA BOTHRIOLEPIS CANADENSIS

Bothriolepis canadensis
A stunning replica of Bothriolepis canadensis from Upper Devonian (Frasnian), Escuminac formation, Parc de Miguasha, Baie des Chaleurs, Gaspé, Québec, Canada.

Bothriolepis was found and originally described by geologist Abraham Gesner in 1842 as "a tortoise with fossil foot-marks." He was wrong, of course, but these placoderm fish in the order Antiarchi do bear a superficial resemblance to turtles.

For nearly two centuries, the Late Devonian Miguasha biota from eastern Canada has offered up a near-complete brackish water community — 20 species of lower vertebrates — anaspids, osteostra-cans, placoderms, acanthodians, actinopterygians and sarcopterygians — a limited invertebrate assemblage, and terrestrial plants and arthropods — scorpions and millipedes.

Originally interpreted as a freshwater lacustrine environment, recent paleontological, taphonomic, sedimentological and geochemical evidence corroborates a brackish estuarine setting. 

Over 18,000 fish specimens have been recovered from the rock lain down in these brackish waters. They show various modes of fossilization, including uncompressed material and soft-tissue preservation. 

Most vertebrates are known from numerous, complete, articulated specimens. Exceptionally well-preserved larval and juvenile specimens have been identified for fourteen out of the twenty species of fishes, allowing growth studies. 

Numerous horizons within the Escuminac Formation are now interpreted as either Konservat or Konzentrat–Lagerstätten. 

The fine replica above was purchased at the Musée d'Histoire Naturelle, Miguasha (MHNM) and is in the collection of the deeply awesome — and well-travelled — John Fam, Vice-Chair of the Vancouver Paleontological Society.

Great Canadian Lagerstätten 4. The Devonian Miguasha Biota (Québec): UNESCO World Heritage Site and a Time Capsule in the Early History of Vertebrates, Richard Cloutier, Département de Biologie, Chimie et Géographie, Université du Québec à Rimouski, 300 allée des Ursulines, Rimouski, QC, Canada, G5L 3A1, richard_cloutier@uqar.ca, http://dx.doi.org/10.12789/geocanj.2013.40.008

Image: Restoration of the upper and underside of B. canadensis. By Unknown author - Popular Science Monthly Volume 82, Public Domain, https://commons.wikimedia.org/w/index.php?curid=20672589