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Norki posted a topic in Fossil IDI have heard that it's not uncommon to find examples of the ammonite placenticeras meeki with evidence of supposed mosasaur predation marks. A certain example of mine has since stood out as a possible contender. This example comes from deposits of the late Campanian Bearpaw Formation, a unit that is already well known for its good preservation of late Cretaceous molluscs, including placenticeras meeki with the supposed predation marks. I know that there are competing theories about the origin of these marks, including abrasion by limpets or other gastropods, so I'm curious about whether any of you are in agreement that this conspicuous pattern is evidence that this particular placenticeras was chomped by a mosasaur. A note about the specimen - I somewhat foolishly decided that a fine grain sandpaper was the solution for getting rid of the stubborn bits of sandstone matrix and pyrite that clung to the nacre, so most of the surface, including the rims of the matrix filling the puncture holes, is slightly polished. Also unfortunate is the fact that this ammonite, on account of most of the internal chambers being completely hollow, smashed into hundreds of little pieces once the concretion containing it was split. Fitting these fragments back together is essentially impossible, and I'm regretful that the specimen was ruined slightly by not being extracted carefully enough, but thankfully there's still a significant amount of it that's still intact. If anything, it seems to be telling that the only part of the fossil that isn't hollow (and therefore more durable) is where the puncture holes are, given that these holes would have allowed water and sediment to enter the chambers they had breached. The chambers which did not fill with matrix, on the other hand, could not handle the stress of the concretion being split, and shattered. Anyway, the first photo here shows the first two holes. These are on the left side of the ammonite. Note that the nacre around the punctures is cracked, where otherwise it is smooth and unblemished. The right side, showing the third puncture hole. It is difficult to tell in the photo, but this hole is depressed slightly into the ammonite. The bit near the end of the tape measure could also be a hole, but it's difficult to tell with so much pyrite encrusting it. Finally, a front-facing view. I've added arrows to approximate the location of the holes on either side. Note the preservation of the nacre of the septum, and how much of it is still covered by pyrite. Note that the other end of the fossil has no obvious septa, leading me to believe that this fragment is from near the body chamber. So, thoughts? I know that the origin of this type of trace fossil is still somewhat contested in paleontology, and I'm really curious about what the forum's consensus will be.
Norki posted a topic in Partners in Paleontology - Member Contributions to ScienceLast summer, on the last day of a long weekend of backcountry fossil hunting around Lake Diefenbaker, Saskatchewan, my friend and I decided to stop our canoe at a beach where on a previous morning I had found a large baculites cuneatus specimen. This beach was an outcropping of a unit of the Bearpaw formation known as the Demaine sand, and dated roughly to the late Campanian. The locality was chock full of golfball to softball-sized nodules, each with a delicate, coalified fossil inside, ranging from crustacean parts, chips of driftwood, to loose vertebrae. It wasn't long before I was looking down at a split nodule containing the symmetrical lines I knew were a skull. So of course, I assembled it together as best as I could, wrapped it in a sock, and we loaded back into the boat to head home. Some typical terrain in the area. The formerly glacial South Saskatchewan River carves deep into the marine clays and sands of the Bearpaw formation: The nodule, rather unceremoniously wrapped in a wool sock: And unwrapped. Note the cervical vertebra just above the posterior end of the skull, and how part of the end of the snout is missing (sorry about the lack of scale bar, there's a photo further down the post with proper scale): I sent a photo to a paleontologist friend, and was quickly referred to the Royal Saskatchewan Museum, who of course were eager to accept the fossil (not to mention that I was technically legally obliged to hand it over, per the Saskatchewan Heritage Property Act... But it's what I wanted to do anyway!). About a month later, my friend and I met with two other paleontologists down at Lake Diefenbaker to deliver the fossil (this time more carefully wrapped in a shoebox...) and to show them the site where we had found it. One long and wet trip in the zodiac raft later, we were there. We assisted in the collection of more samples, this time coming up with an even broader variety of flora and fauna, including a small crinoid, some wood chips with amber, and some more decapods. One of the two paleontologists was excited to suggest that the locality probably represented a near-shore lagoon environment, and that the museum would likely be back to do some more work there at a later date. Unfortunately, we were unable to do so that summer because of the seasonally rising water levels of the lake, which flooded the site, but I've been told that my friend and I will be invited to assist with the operation again this following season. As for the fossil, it has since been delivered to McGill University to be CT scanned. Apparently, distinguishing the bone from the matrix has been long and tedious work, and not much news has reached us since the specimen was delivered some time last September. Here is an individual slice from the CT scan, from near the back of the braincase - notice how porous the bone material is, which is apparently another indicator that this skull belonged to a juvenile: I have been in close correspondence with the paleontologist from the Royal Sask. Museum who will be writing the paper to describe the find, but everything is more or less at a standstill until the work on the CT scan is finished. It's been a rather long wait, but I'm looking forward to its publication - I have been told that the museum intends to hold a press conference after the specimen has been described, and that my friend and I will be credited and involved in the reveal. So far, the museum has kept everything about the discovery deliberately vague, aside from a brief mention in a press conference, which informed an article that circulated around the Canadian media late last summer: https://nationalpost.com/news/canada/scientists-in-saskatchewan-discover-new-multimillion-year-old-fossils It's been an exciting and fulfilling experience overall, and I can't wait to get back into the field, this time with a more meticulous and careful attitude, knowing that there's scientific potential to be had from my future contributions. Anyway, here are some more photos from the lab at the RSM, with scale bar: Decapod claw: Crinoid crown: Thanks for your attention.
Gastropods seem to be quite rare in the tracts of the Bearpaw formation I'm familiar with, so I'm incredibly curious about this lone specimen, the only one I've found. I found it in a hard layer of small conglomerated bivalves, pteria linguiformis, I believe, in sandstone dating roughly to the Campanian-Maastrichtian border. The specimen was collected from the western half of Diefenbaker Lake in southern Saskatchewan. Anyway, here are the photos. If more angles are needed please let me know: Pteria linguiformis (?), which constituted the conglomerate: Thanks for your time.