#FossilAdventCalendar Day 24
Our journey #north ends with one of the most important #fossils ever found. Like Puijila, Tiktaalik roseae is known from #Nunavut 
, has an #Inuktitut name (meaning "large freshwater #fish"), and records an important #evolutionary transition, this time from #sea to #land. #Tiktaalik shares traits with both fish and #tetrapods, making it a close relative of all of us land-living #vertebrates. This replica and model are from the #CanadianMuseumOfNature.
#FossilAdventCalendar Day 23
#FossilFriday
The #Canadian #Arctic has yielded some especially important #fossils documenting major #evolutionary changes. This 3D-printed replica of a #fossil from #Nunavut and displayed in the #CanadianMuseumOfNature is one of these. It's Puijila darwini, whose name means "young sea #mammal" in #Inuktitut. It looks like an otter, but it's one of the earliest relatives of #seals and #sealions - with still-functional hands and feet, unlike modern #pinnipeds.
#FossilAdventCalendar Day 22 (delayed due to time with the family)
Our first #fossil from north of the #Arctic Circle is from the most iconic of #IceAge #megafauna. This woolly #mammoth, Mammuthus primigenius, was found over a century ago in the far #north of Siberia and gifted to Paris' #MuseumNationalD'HistoireNaturelle by the tsar. Like the squirrel featured yesterday, this mammoth was partially preserved in #permafrost; you can see its #mummified face and leg in the case at the right.
#FossilAdventCalendar Day 21 (delayed by a busy travel day)
As we move towards the far #North we encounter one of the (literally) coolest kinds of #fossilization. When the #frozen ground known as #permafrost forms, it can #freeze dry #animals buried in it. This ground #squirrel, Urocitellus undulatus from #Alaska 
and displayed in the #AmericanMuseumOfNaturalHistory, burrowed into the ground in life and was #mummified by it after death, providing a remarkable window into life in the #IceAge.
#FossilAdventCalendar Day 20
#Terrestrial Tuesday
Today we think of #lions as predators of the African savanna, but during the last #IceAge, they had a much wider distribution. Some lived in what's now the continental US, while another - the so-called cave #lion - lived in cold environments across the #Northern Hemisphere. This skull, displayed in the #AmericanMuseumOfNaturalHistory in front of its distant relative Smilodon, was found in #Alaska - our first specimen from the Last Frontier!
#FossilAdventCalendar Day 19
It's appropriate that this #MarineLifeMonday our journey #north reaches the shores of #Hudson'sBay at #Churchill, #Manitoba . It's here that the largest complete #trilobite #fossil ever found was uncovered from #Ordovician rocks. If you want to see the more than two foot long Isotelus rex in person, head to #Winnipeg's #ManitobaMuseum, where it's displayed in all its splendor.
#FossilAdventCalendar Day 18
The original of this cast #skeleton, displayed in the #ArizonaMuseumOfNaturalHistory, was found along the Northern Dvina River. It's from Inostrancevia alexandri, a #gorgonopsian from the #Permian. Its huge size is the first thing you'll notice about it; this #animal and its relatives were clearly among the most imposing #predators of their time. Look closer and you'll see that it shares many traits with #mammals, of which it was a not-very-distant relative.
#FossilAdventCalendar Day 17
This #whale-sized #marine #reptile in the #RoyalTyrrellMuseum is the #ichthyosaur Shastasaurus sikkaniensis. Unusually, it was not only one of the earliest members of its group, but one of the very largest. Its #species name comes from where it was found, along the Sikanni Chief River which flows out of the #RockyMountains of #BritishColumbia . Its #genus name comes from Mt. #Shasta in the #CascadeRange, where other species of this Triassic titan have been found.
#FossilAdventCalendar Day 16
#FossilFriday
This exploration of #fossils from the #Arctic nations wouldn't be complete without one of the most spectacular #dinosaur fossils ever found that happens to be named for the #North. Borealopelta, meaning "#Northern Shield," is a #nodosaur, a type of #ankylosaur, or #armored dinosaur. This #fossil, uncovered in the tar sands of #Alberta and displayed in the #RoyalTyrrellMuseum, preserves much of that armor in incredible detail.
#FossilAdventCalendar Day 15
Today we return to the #Nordic countries, specifically to the #Nationalmuseet in #Copenhagen 
to meet the #aurochs (Bos primigenius), the #extinct wild ancestor of modern #cattle. This #bull lived and died over 10,000 years ago in #Vig, on the #Danish island of #Sjaelland, but unlike many #IceAge #megafauna, it survived until surprisingly recently. In #Denmark, it persisted in #Jutland until around 2000 years ago; the last aurochs died in #Poland only in 1627.
#FossilAdventCalendar Day 14
This #fossil of Albertonia cupidinia, from Wapiti Lake, #BritishColumbia and displayed in the #RoyalOntarioMuseum, comes from an important time in fish #evolution. It was during the #Triassic Period, as dinosaurs and mammals were getting their start on land, that #ray-finned fish (the group that dominates our planet's #waters today) were really starting to take off. Its large fins supported by thin bony rays show that Albertonia was was part of this #radiation.
#FossilAdventCalendar Day 13
#TerrestrialTuesday
#BritishColumbia is full of #lagerstätten (sites of exceptional #fossil #preservation), including the sites of the #Eocene #Okanagan. Here, a series of #ancient #lakes preserve #fossils of #leaves, #insects, and the oldest #salmon. Rarest of all are #arachnids: this fossil of the #spider Palaeoperenethis thaleri in the #RoyalOntarioMuseum is the only one of its kind, but it's #preserved well enough to identify it as a relative of fishing #spiders
#FossilAdventCalendar Day 12
#MarineLifeMonday
#BritishColumbia's #BurgessShale is one of our planet's most important important (and beautiful) #fossil sites. Sitting high in #BC's #RockyMountains, it's a window into the early evolution of #animals. Among its weird wonders is Hallucigenia (seen here in fossil and sculpture form at the #RoyalOntarioMuseum), a distant relative of #arthropods so unlike anything alive today that for years it was reconstructed upside down and backwards.
#FossilAdventCalendar Day 11
The #badlands of eastern and central #Alberta are probably the best place in the world to find #hadrosaurs ("duck-billed" #dinosaurs like this #Hypacrosaurus in the #CanadianMuseumOfNature). While they're immediately recognizable by their broad mouths and (in many species) large crests, their #teeth also set them apart. Their large, grinding teeth allowed them to chew their food, a behavior that's the norm in us mammals but rare in other #animals.
#FossilAdventCalendar Day 10 (belated, thanks to a busy weekend)
It's no secret what #DinosaurProvincialPark, #Alberta is famous for, but it's the #plants from this #WorldHeritageSite that tell the clearest story about this #Cretaceous #ecosystem. #PetrifiedWood like this, along with other aspects of the park's #geology and #paleontology, paint a picture of a low-lying coastal #wetland, perhaps similar to the #bayous of the modern Gulf Coast.
#FossilAdventCalendar Day 9
#FossilFriday
The #extinction that wiped out all non-bird dinosaurs didn't affect every organism the same way. These #gar fossils, found in #Okotoks, #Alberta and displayed in the #RoyalTyrrellMuseum, represent a group of #fish that weathered the #extinction fairly well. #Gars are great survivors, with many species having been found alongside #dinosaurs, many - like these - at post-extinction sites, and many still plying the rivers of #NorthAmerica today.
Because I can't resist a local-#fossil-makes-good story, I feel compelled to post a follow-up to this #FossilAdventCalendar entry. The #PuntledgeRiver #elasmosaur is so well-preserved that casts of its #skeleton are a star of #museum exhibit halls from the #UniversityOfWashington's #BurkeMuseum to #Ottawa's #CanadianMuseumOfNature. Running across it in #museums is always a pleasant surprise, like unexpectedly meeting an old friend.
#FossilAdventCalendar Day 8
The #PacificNorthwest makes its #AdventCalendar debut today in the form of one of our most impressive #fossils: the #PuntledgeRiver #elasmosaur. #Cretaceous #marine #reptiles are common from the Great Plains, but this specimen is from #VancouverIsland, #BritishColumbia . Found in 1988 by a 12 year old taking a walk with her dad, the #fossil, housed in the #Courtenay #museum, shows that these long-necked #plesiosaurs inhabited the #ancient #seas of the #PNW as well.
#FossilAdventCalendar Day 7
This #bird #skeleton is from #Newfoundland, but it's displayed in #Reykjavik's #Safnahúsið, because it was in #Iceland 
that the great #auk (Pinguinus impennis) last lived. Its black and white #feathers, #flightlessness, and ability to swim make it look like a #penguin, but #auks are really #puffin relatives. Driven to #extinction only in 1844, it's become a cautionary tale in #conservation #biology and an illustration of the impact our species has on #biodiversity.
#FossilAdventCalendar Day 6
#TerrestrialTuesday
This #fossil, Erpetonyx aresnaultorum from the #RoyalOntarioMuseum, may look a bit like a #lizard, but it's something else entirely. Uncovered from the #Carboniferous #EgmontBay Formation on #PrinceEdwardIsland , it's one of the oldest #parareptiles, a lineage of #animals related to but distinct from true #reptiles. While they were among the first vertebrates to transition to life on land, parareptiles went #extinct over 200 million years ago.
