Where nature draws the map – here are 5 ways to look at the US, without state boundaries

State boundaries can be iconic. Many were drawn by human hands, but some of the most recognizable contours were shaped by nature: the boot of southeastern Louisiana, carved by the Mississippi River, or the ocean waves sculpting the hook of Cape Cod in Massachusetts.

For a moment, imagine that there are no state lines. View the United States through its natural contours. As curators at the Smithsonian's National Museum of Natural History, we often look at our nation this way, drawing different kinds of maps that trace mountains, watersheds, animal migrations, biomes, ancient seas and so much more.

These kinds of maps show us how connected we all are by nature, since it transcends state boundaries. That idea is central to our new exhibition, "From These Lands: Sharing Our Natural and Cultural Heritage," now open at our museum to mark the 250th anniversary of the United States. We are co-curators of the show, part of a team of exhibit designers and developers who created the exhibition.

"From These Lands" uses items from the museum's collections to explore these patterns and ideas, offering a way to see the country's natural and cultural heritage beyond state lines.

One country, many pine cones

Pine cones can be easy to overlook.

When you're out for a walk in the woods, you see the forest, maybe even the trees, but not always the cones at your feet. For many people, a pine cone is just a pine cone. But when you look closely, subtle differences in the styles of cones carry clues about the trees that produced them and the places where those trees live.

There are 43 pine species native to the United States, making up nearly a third of the world's pine tree diversity. Together, they stretch across surprisingly different combinations of climate, terrain, plants and animals, the regions scientists call biomes. Something as simple as the pine cone can let you hold that concept in your hand: soils, fire, rain, birds and rodents all helped shape the tree that made it.

For example, cones from the sand pine can shield seeds for years, only to release them as the heat from low-intensity fires melts their resin and opens their scales. These scrubby and fire-shaped landscapes are one part of the larger temperate evergreen forests that spread through the southeastern U.S.

On the other side of the country, the Coulter pine produces cones that can be more than a foot-and-half long (50 centimeters) and weigh up to 8 pounds (3.5 kilograms). This large cone size helps its seeds to survive fires, allowing small birds and mammals to then disperse them into new areas in the Mediterranean Scrub of Southern California.

A pine cone comes from one tree in one place, but its form reflects a wide set of environmental conditions. Pine cones provide an interesting way to view the different biomes found in the United States and its territories.

An ancient ocean in the middle of the country

The land under your feet can be millions of years old, and it has not always been dry ground.

During the late Mesozoic Era – the time interval made famous by the dinosaurs – a warm, shallow inland sea covered states from North Dakota to Texas. This Western Interior Seaway laid down many of the rocks and sediments that you can see today throughout the Great Plains and Badlands. The sea was also full of life, and the rocks it left behind are full of fossils.

There were familiar characters living on this ancient seafloor: clams, snails and sea stars. But swimming in the waters above were the now-extinct animals called ammonites.

These coiled, shelled relatives of squid and octopuses were abundant predators, hunting in the same waters as fish, turtles, sharks and extinct marine reptiles called plesiosaurs. Ammonites used the chambers in their shells to control buoyancy, much like the modern nautilus.

Ammonite fossils demonstrate that much of the central U.S. was an ancient ocean. They also remind us that the landscapes we know today are just the latest version of those reshaped over and over by the slow work of geologic time.

Unlikely pairing: Shorebirds and horseshoe crabs

Animals move. Some travel only short distances with the seasons, but others travel thousands of miles, crossing not only state lines, but countries, oceans and hemispheres. Animal migration routes might look chaotic on a map, but birds, whales, turtles and more forge these paths for specific reasons.

Timing is a key component of migration. Thanks to a critical refueling stop in Delaware Bay, the ruddy turnstone shorebird manages to migrate thousands of miles each year to its breeding grounds in the high Arctic. These East Coast migrants time their layover with the migration of horseshoe crabs, which come ashore to lay millions of nutrient-packed eggs on beaches. The turnstones gorge themselves on those eggs before continuing their journey north.

It is a strange and wonderful handoff between an ancient marine animal hauling itself out of the ocean and a weary shorebird bound for the Arctic. A single bay brings them together, illustrating how the many migration routes through these lands can hinge on key moments and places.

Salamander country

Topography is more than scenic landscapes. Everything from the flat coastal plains to the ridges, valleys and stream-cut mountainsides helps shape where animals can live and how biodiversity accumulates.

The rugged terrain of the Appalachian Mountains creates cool, wet forests, shaded hollows, caves, ponds and streams. These habitats can differ from each other in elevation, temperature, moisture and water flow – and salamanders take note. More salamander species live in the Appalachian Mountains than anywhere else in the world. It can feel as though every other rock you turn over hides yet another species.

The trio of Plethodon salamanders, the southern gray-cheeked, red-cheeked and red-legged salamanders, were once thought to be regional variations of the same species. But these salamanders live at varying elevations in different mountain ranges, and genetic sequencing confirmed that each was, in fact, its own species. Topography and shifting climates had broken up these populations into different habitats, allowing each to evolve into distinct species.

Following the American shad

Chesapeake Bay is the largest estuary in the U.S., fed by a watershed connecting rivers and drainage basins that reach into six states and the District of Columbia. It's home to more than 3,600 species, including oysters and blue crabs. But one fish in particular has become strongly intertwined with the lives and cultures of many people around the bay.

The American shad spends much of its adult life in the Atlantic Ocean but returns to the freshwater rivers in the upper reaches of the Chesapeake Bay to spawn. For more than 12,000 years, this herring's spring migration has been part of Pamunkey Indian Tribe diet and culture.

From 1918 to 2019, to mitigate declining populations of herring, the tribe ran a hatchery to "give back to the river." The Pamunkey Tribe's fishing rights date back to their 1677 treaty with the British Crown. Today, only the Pamunkey and citizens of other tribes in Virginia can legally fish for shad in this region.

A single type of fish moving between salt and freshwater, tracing the paths of the watershed, has helped to shape centuries of diet, law, culture and stewardship, highlighting the many connections between nature and culture.

Different ways to map the country

Pine cones, ammonites, shorebirds, salamanders and shad tell more than individual stories about particular places. Together, they point to older and larger patterns: varied forests, vanished seas, seasonal migrations, mountain habitats and rivers that harbor a fantastic diversity of life.

State lines are one way to picture the U.S., but natural history provides another – one that shows the ancient and living connections running across the landscape.

This article is republished from The Conversation, a nonprofit, independent news organization bringing you facts and trustworthy analysis to help you make sense of our complex world. It was written by: Stewart Edie, Smithsonian Institution and Torben Rick, Smithsonian Institution

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The authors do not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.