Associated Champsosaur skeleton in Southwest Saskatchewan discovered by Jack Miligan

Following the K-Pg mass extinction event which wiped out the non-avian dinosaurs, the swamps and floodplains of southwest Saskatchewan were populated by an assortment of small to medium sized vertebrates including turtles, crocodiles, early mammals, and a now-extinct group of semi-aquatic reptiles known as champsosaurs. During a joint research expedition near the town of Climax, Saskatchewan by the Royal Saskatchewan Museum and Carleton University in Ottawa in August 2020, an associated skeleton of a champsosaur was recovered by Jack Miligan. The champsosaur was collected in a terrestrial shale horizon around 3 m above the K-Pg boundary, from the Paleocene aged Grey Facies of the Ravenscrag Formation. The Grey Facies records a low energy, vegetated swamp environment. 

Champsosaur hind foot (middle right in image). Photo by Jack Miligan.

This skeleton is between 35-40% complete and is comprised of several dorsal and caudal vertebrae with intact neural arches and transverse processes, incomplete bones from all four limbs including a humerus and femurs, dozens of ribs, and several elements making up the pectoral and pelvic girdles. Numerous gastralia as well as a near complete hind foot were found in-situ upon examination of the shale horizon from which the bones had eroded out of. More fieldwork is needed to try and recover cranial material to affirm an accurate taxonomic identification of this specimen.

Research into the osteology of the specimen, as well as a review of the paleoecology of the vertebrate fauna of the Ravenscrag Formation is underway and could yield new insight into biostratigraphy, and macroevolutionary trends of champsosaur species across the K-Pg boundary in Saskatchewan.

You can read more about the discovery in this Usask news article.

Written by Jack Miligan

Note: Jack recently joined the ichnofamily at Usask as an M.Sc. student! You can read more about him on his ichnoplanet profile, or follow him on ResearchGate or Twitter. –Brittany

Were all trilobites fully marine?

Trilobites, the poster-fossil of the Paleozoic, have long been considered to be invariably fully marine. Collaborative work between Dr. Mángano, Dr. Buatois, and Argentinian colleagues questions this assumption. Through the integration of multiple datasets they report uncontroversial evidence of the exploration of tide-dominated estuaries by some trilobite groups (olenids & asaphids) throughout the Furongian to Middle Ordovician. Thick siliciclastic successions in northwest Argentina expose vertically-repeating nearly-identical environments and allowed for the comparison of body-fossil and trace-fossil data in tide-dominated estuaries through time. Their research indicates two forays into brackish water, first the colonization of the outer portion of estuaries by olenids, followed by the colonization of inner to middle estuarine zones by asaphids.

The full article is available in the Proceedings of the Royal Society B (including some fantastic photos of trilobite trace fossils in the Supplementary Info!).

Figure. Time-environment matrix showing protracted trilobite expansion into marginal-marine estuarine settings. (From Mángano et al., 2021)

Written by Brittany Laing

Recent field work on the Buda Limestone

During three field campaigns from 2017 to 2019, Fernando Valencia together with Gustavo Valencia and colleagues from the Texas A&M University (Dr. Juan Laya and Dr. Mike Pope) have been describing several stratigraphic sections where the highly-bioturbated Buda Limestone crops out. Most outcrops are distributed along the central and west Texas regions (Fig. 1). The main focus of Fernando’s project is to define the sedimentological model of the Buda Limestone in west-central Texas and the implications of the pervasive bioturbation in the process of porosity creation. Preliminary observations recognized a strong influence of the trace fossils in the diagenetic processes of the carbonate succession (Fig. 2).

Follow Fernando’s Research Gate project detailing this research here!

Picture1

Figure 1. Sharp contact between the Buda Limestone and the overlying Eagle Ford Gp. along the U.S. Highway 90 in the Comstock – Texas area.

Picture2 

Figure 2. Detail of intra-burrow secondary porosity developed in a Thalassinoides isp. Upper-Cretaceous Buda Limestone (west Texas).

By Fernando Valencia

Evidence of motile organisms discovered in 2.1 billion-year-old strata

Recent research by Dr. Mángano and Dr. Buatois, performed in collaboration with researchers from around the world, suggests that organisms were capable of movement much earlier than previously thought.

 

Around 80 specimens of 1 to 6 millimetre-sized, pyritized, string-shaped structures were collected from the Francevillian Basin in Gabon and subjected to a slew of analyses in order to determine their origin. The structures were found to have been formed within the sediment, lithified prior to compaction with open pore spaces, and filled with pyrite formed from sulfide generated by sulfate-reducing microorganisms.

After a careful comparison with several abiotic structures such as syneresis cracks and microbial mat roll-ups, as well as various biotic strucutres, it was determined that these structures were likely produced by a motile organism. It is unlikely that they were produced by a metazoan, since the structures change in width along their length, and sometimes merge. More likely, the research suggests, is that these trace fossils were formed by something akin to a slime mold.

The organism was opportunistic, evolving and living thanks to a temporary rise in oxygen levels at the time. When oxygen levels dropped again, and stayed low until roughly 650 million of years ago, the organism probably went extinct. As a result, it’s impact on the evolution of life on earth was probably short-lived.

Read the CBC article here

Get the full scientific article here

By Brittany Laing