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Every few years we get rewarded with a new dinosaur described from the Lance/Hell Creek Formations. In this crazy year we finally have one. Finally an Alvarezsauridae has been described from the Hell Creek Formation: Trierarchuncus prairiensis. Sorry its paywalled cannot make comments https://www.sciencedirect.com/science/article/pii/S0195667120302469 Here is some info on this very different dinosaur, one of my favorites, including some of my material so you can see what the paper is describing. Far better than what you see in the paper

Albertonykus borealis was theropod described by Philip Currie and Nicholas Longrich in 2008 from the lower Maastrichtian of the Horseshoe Canyon Formation in Alberta. Its range also extends into Montana, SD and Wyoming in the Hell Creek and Lance Formation. It is noted for having a single hand claw and is a very small theropod, see photo. Very few folks pay attention to small dinosaurs but this one is very cool and material does come out all of the time so I thought it might be interesting to post. If you collect North American dinosaurs the claws are a must have. Teeth have been found on its Asian cousin Mononykus olecranus but no cranial elements to my knowledge have been found in North America. Maybe one of our forum members can find one or has more information to add. Material found in the Hell Creek and Lance formation should be labeled as Trierarchuncus prairiensis I've seen hand and foot claws as well as phalanges sold but few sellers know what they have and label them theropod. I've personally collected some specimens and have purchased others. Published literature and the New York Museum of Natural History Mononykus display help pull the picture together for identification of specimens. Trierarchuncus prairiensis Was described has the Alvarezsaurid from the Hell Creek Formation July 10, 2020 https://www.sciencedirect.com/science/article/pii/S0195667120302469 Hand Claw : They are typically recurved but can be straight. A shallow vascular groove on either side, ventral foramens are present, see second photo (arrow) Carpal : Called the Alular digit and just has one. Photos L to R Medial, Ventral and Dorsal Views Associated Alular Digit : Foot digits in the following post. My collection: