Part 1: main hall, Trilobites, and Permian vertebrates
Field Museum in Chicago with high-rise housing behind it.We entered hesitantly. This was the first potentially-crowded place we have visited in two years.Sign of change: the Field Museum’s Land Acknowledgment.…and rather fantastic bronze entry doors.To our relief, the entry hall wasn’t too crowded. But quite remarkable.The Argentine Titanosaur is a remarkable centerpiece. Look at those vertebral spines!Late Cretaceous giant.Note the way the ilium is fused to multiple vertebrae via extensions that look almost like parallel bridges.A sign of even deeper change: signage in Ojibwe first. The Field Museum has a huge collection of modern birds, and their exhibits are organized to show whole ecosystems.The birds are described in the native language of the region where they are located. In this case, Dine.Each wing of the Field is huge, with multiple types of exhibits. The central court, with its Titanosaur, helped keep us oriented.And the positioning of the mounted fossil skeleton enables us to see the head up close from the second story.One of the many great collections was Trilobites in their extraordinary diversity. Trilobites are early arthropods; they emerged in the early Cambrian (521 mya) and lived through the entire Paleozoic Era until the mass-extinction at the end of the Permian (252 mya). This one is Ordovician (485-444 mya).Also Ordovician, but very different Trilobites.Trilobite, possibly Silurian (444-419 mya) or Devonian (419-359 mya). Look at that much larger tail and longer jointed legs.Trilobite from Devonian. End legs in lieu of a tail fan. And horns!Another Devonian-era Trilobite.Another Devonian-era Trilobite, with horns arching back, and side-whiskers, and whisker-like rear legs.Fourth Devonian Trilobite. An extremely successful class of animals: numerous, diverse in each era, and living for almost 270 million years. This one, unfortunately, looks like a bedbug.Moving on to the tetrapods! This Seymouria is ‘anapsid’ like modern turtles and frogs: the only holes in its skull are actual eye-sockets and nasal passages. Tetrapods are early land vertebrates, relatively recently descended from lobe-finned fish. So the legs are morphologically similar to fins. Forelegs remained ‘floating’ over the ribcage, with a scapula (shoulder blade) attached by ligaments and tendons to the body. Rear fins in fish were also linked by floating over the rear ribcage with a scapula-analog. Eventually this fused to several rear vertebrae to form the hip.Seymouria tetrapods are from the Permian (299-252 mya), the end of the Paleozoic era. This species had already evolved a sort of hip, although the ilium is short and did not provide a strong point of leverage for leg-muscle attachments.One of the larger tetrapods from the Permian was Bradysaurus. Also anapsid, also with splayed legs and probably relatively inefficient locomotion. Chonky!
