Edit 1: u/Kelpie-Cat has linked their excellent and far more in-depth answer to the question of North American Indigenous land ownership, as well as concepts of private property below. Please go and check that out. I'm going to drop the link here for visibility: https://www.reddit.com/r/AskHistorians/comments/kf01cw/is_it_true_that_the_native_americans_had_no/

I'll leave the first two questions for folks more with more experience in Mississippian prehistory, but I may be able to shed a bit of light on your third question.

Depending on where you are in the states, a lot of what's taught as "Native American history" comes from two specific contexts: the colonial period along the East Coast and the westward expansion through the mid to late 1800s. The particular subject of land ownership is likely coming from the US experiences treaty-making with the various Plains and Plateau tribes across the western US.

As the US expanded west across North America, the federal government attempted to make treaties legalizing the sale of tribal lands to the US government, but ran into an issue of fundamentally different epistemologies regarding the use and ownership of land (Deloria Jr. 1974, Dunbar-Ortiz 2014, Washburn 1971). In short, the Western concepts of land as property to be allotted and owned simply did not translate into many of the Indigenous concepts of communal land use and common ethics, nor vice versa. Adding to the confusion, most of these treaty negotiations were held via interpreters and the treaties were ultimately written in English (all of which are available on the national archives). This is one of the key reasons for the first two canons that the SCOTUS uses in interpreting Treaty Law, that the treaties must be interpreted as the tribes would have understood them and that the treaties must be interpreted liberally in favor of the Tribes (Washburn 1995, Jones v Meehan 1899, Tulee v Washington 1942, United States v Washington 1974).

One example of this fundamental disconnect between Native and Western epistemologies that comes to mind is in the treaty negotiations between territorial governor Stevens and representatives from the Walla Walla, Cayuse, and Umatilla tribes on the columbia plateau. During these negotiations, several prominent men from the various tribes tried to communicate the fundamental inability of the tribes to sell land under their social, political, and religious law, which they referred to as tamánwit. Many of the chiefs tried to explain that it was as impossible to sell the land as it was to sell part of themselves, as they were created from the land and for the land, to care for one another (Karson 2006). This, of course, did not sway Stevens any more than similar arguments had swayed US officials across the rest of the west, and ultimately the Treaty of Walla Walla was drafted and signed in 1855, ceding much of the lands in modern-day southeastern Washington, northeastern oregon, and southwestern Idaho to the United States.

Edit 2, for clarity. Apologies, I wrote my first post quickly and without much proofreading. Cuts in strikethrough, additions in italics.

All of that is to say - it's complicated. While the idea taught by the US school system that Native Americans did not understand the US system of land ownership is technically correct, to a degree and in very specific contexts, it is certainly an over-generalization that glosses over some important details. While the idea commonly taught within the US school system is accurate for specific Tribes in specific times, it is certainly not all-encompassing. Critical to remember when discussing Native American history is that Tribes and First Nations are not and never were a monolith, and what may be true of one group at one time may not be true even of that same group 200 years earlier. The US school system, partly out of necessity when tackling such as massive topic and partly due to systemic racism and social trends better discussed in a standalone post, glosses over the vast majority of that diversity, losing many details that shed light on the interpersonal and intergovernmental conflicts that formed the modern Federal-Tribal relationships. Most important, and certainly most impactful for treaty law cases to the present day (Boldt I and II come to mind), being that the US negotiators and legal system at the time had no way of understanding or interpreting the Indigenous concepts of land use and common resources.

References:

Deloria Jr, Vine. 1974. Behind the Trail of Broken Treaties: An Indian Manifesto.

Dunbar Ortiz, Roxanne. 2014. An Indigenous People's History of the United States.

Karson, Jennifer (ed.) 2006. Wiyáxayxt: as days go by.

US Supreme Court. 1899. Jones v Meehan. 175 U.S. 1

US Supreme Court. 1942. Tulee v Washington. 315 U.S. 681

US Supreme Court. 1974. United States v Washington. 443 U.S. 658

Washburn, Wilcomb. 1971. Red Man's Land White Man's Law.

You might be interested in my answer to a previous question about Native American concepts of land ownership; long-distance trade; and the Doctrine of Discovery.

So, as /u/OGPuffin points out with regards to Plateau groups (something I can elaborate upon a little), I'll cover this a little more from the Southern Northwest Coast, with peoples who are deeply interconnected with Plateau tribes like the Yakama, Klickitat, et al. Though I mainly discuss Coast Salishan attitudes, it should be important to keep in mind that neighboring groups such as Wakashan, Quileute, and Chinookan speaking peoples mostly have similar if not identical views towards the subject.

When it comes to songs, dances, artwork, buildings, tools, pets, and even other human beings, they can be understood within the contexts of Coast Salishan society as personal property. A woman owns her baskets and the cedar bark she wove them from, a man owns his canoe and the paddles used to propel it, people own their dogs, families own songs and dances.

But they would not claim to personally own a particular patch of land, nor the streams, or all the trees in a certain section of the forest. They might own things on top of it or alongside it, such as their house, the things in said house, the harvested materials outside that home in their workspaces (i.e. lumber and whalebone)...yet they wouldn't claim that X owns these here 10 acres and berry picking or not, you're trespassing on private property since X physically lives miles away and doesn't even know where the berry patch is exactly. X might as well be trying to declare he also owns the stars in the sky and every grain of sand in the bay, they exist outside the very concept of human ownership by the right that X will die one day, yet the stars shine on and the sand drifts all the same, as will happen anyone claiming to inherit X's "property".

Recently there was a question by /u/anthropology_nerd regarding whaling among peoples of the Northwest Coast, and my answer to that touches upon an aspect I will further elaborate here. I mention that peoples upon the begining of food gathering seasons will try to maximize the bounty of the season by performing rituals meant to solicit the cooperation of immortal spirits who are responsible for salmon runs, the growth of berries, the proliferation of edible roots, and the presence of game. Without their cooperation, the fishing runs could be bare, the berries sour, the roots stunted, and the game scarce.

So, within the contexts of the historical Coast Salishan worldview, if there is one group that can be definitively said to "own" the land underneath one's feet, it would be these immortal spirits that dwell within the area, who have outlived any human and can bring ruin to their communities if they are displeased. I should also note that these rituals weren't interpreted as a "one size fits all" sort of deal, where one learns a song from a Nisqually and then can use it in Puyallup, or Lummi and use it in Nooksack. They are endemic to a specific watershed alongside the immortal spirits therein, where one needs to know the right rituals for the right area.

"Lushootseed Culture and the Shamanic Odyssey" by Jay Miller is a great work that covers a lot of concepts that comprise the Southern Coast Salishan worldview and how they feature into both historical and contemporary Southern Coast Salishan society.

Follow-up on the Plateau groups below.

It is easier to respond to your questions starting with the third one, because it helps explains many of the misconceptions about N-A land tenure. Until the 19th century, much of the historical archive historians have used to understand Indigenous Peoples came from Europeans with all of the Eurocentric biases and assumptions about land tenure and Native Peoples. The freehold (individual ownership of land) was a European form of tenure, and while many Europeans did not actually own land, they desired to own land, and saw this form of tenure as the most perfect and durable form of tenure. They largely understood land as a commodity and something to own. Colonization represented an opportunity for settlers to get ownership of land and so they were single-minded in emphasizing individual ownership. It should be said that Europeans also practiced forms of use-rights (usufructs), commons, and sharing, and not just individual ownership.

Europeans did not understand Indigenous tenures. Question one -- Native America was an incredibly diverse place, with very diverse forms of tenure. Ownership is just one form, but there were many kinds of land and natural resource claims. Claims and use-rights (usufructs) are forms of tenure that are not absolute ownership. The group I know the best, the Haudenosaunee, claimed land through clan affiliation and a repetitive oral history. They had very clear boundaries between clans and the six nations of their confederacy. They used commons, individual usufruct allotments, and also formalized agreements with Europeans to share the resources of a particular place. They used wampum belts as forms of agreement (like a contract) to formalize these agreements, the most well-known of which was known as Gaswenta.

Question two -- because of the remarkable diversity of Native North American Peoples, it is hard to generalize both about their tenures as well as how these tenures changed after contact with Europeans. However, in my experience, they did not forget their tenures. They were forced to change them by conquest. Several governmental initiatives from the mis-16th century (spanning multiple imperial regimes) tried to force or incentive Native Peoples to adopt European property regimes. Indigenous Peoples' insistence on communal forms of tenure like use-rights seemed "primitive" to Europeans, who thought individual ownership was the most advanced and progressive form of tenure. The most egregious example of this was the 1882 Dawes Allotment Act, in which Native Peoples lost 90 million acres of homelands. Native Peoples resisted these initiatives, and as with the Haudenosaunee, they adapted their tenures to the reservation (a delimited homeland space) and used Euro-American laws to reinforce their preferred tenures.

I hope this contributes to the discussion, and thanks for this opportunity1

I explore these ideas in my forthcoming book from University of Virginia Press in 2023 -- title TBA. Dr. Taylor Spence, Albuquerque, NM