Fossils of Blackberry Hill, Wisconsin, USA: the first animals on land, 500 million years ago

Abstract

Recent discoveries of trackways and trails on ancient tidal flats at Blackberry Hill, Wisconsin, USA, have transformed our understanding of the initial invasion of land, 500 Ma. Huge slug‐like molluscs grazed on microbial mats. Euthycarcinoid (stem myriapod) death traces (mortichnia) suggest that they did not come onto land to feed or breed, but simply to survive; Moon was closer to Earth then, and massive tides stranded animals in tidal pools that gradually dried up.

Not the first leech: An unusual worm from the early Silurian of Wisconsin

“…Arthropods dominate—mainly abundant and diverse trilobites (an undescribed dalmanitid and at least 12 other species; Wendruff et al, 2020a; Gass et al, 1992; Gass and Braddy, in press), crustaceans (including three species of the phyllocarid Ceriatocaris Jones, Feldmann, and Schweitzer, 2015, leperditicopid ostracodes, and the thylacocephalan Thylacares brandonensis Haug et al, 2014), a chelicerate (synziphosurine; Moore et al, 2005), and various enigmatic arthropods. These include Parioscorpio venator Wendruff et al, 2020b, originally considered the oldest scorpion, but probably a cheloniellid-like arthropod with a pair of large raptorial appendages (Braddy and Dunlop, 2021; Braddy et al, 2022, but see Anderson et al, 2021, and Van Roy et al, 2022).…”

Was There a Cambrian Explosion on Land? The Case of Arthropod Terrestrialization

“…Another site famous for its Cambrian traces of life on land is the middle to late Cambrian Blackberry Hill in central Wisconsin, which preserves diversity of arthropod trackways in a tidal flat and nearshore environment, along with the remains of the oldest euthycarcinoid, Mosineia [ 104 ]. Massive trackways from the intertidal zone left by euthycarcinoids with walking legs during the Cambrian and Ordovician indicate longer stays on land where these amphibious animals may have come in pursuit of shallow lagoons and freshwater pools [ 105 ], albeit their excursions on land may have been short-lived [ 106 ]. Other early arthropods to make temporary excursions to near-shore habitats were the trilobites, whose trace fossils in tidal-flat deposits are known since the Cambrian, albeit their traces were likely made subaqueally [ 107 , 108 ].…”

“…Although a decade-old bounty of 1000 dollars has been put on an undisputable insect fossil from the pre-Devonian [ 124 ], this sum remains to be claimed. Instead, the hunt for early hexapods yielded a number of dubious records, like fossils only seen once and never again [ 125 ], suspected modern contaminants [ 106 ], and miss-identifications, such as purported Devonian insect wings that turned out to be malacostracan tail fans [ 126 , 127 ]. A recent review is provided by [ 128 ].…”

A eurypterid trackway from the Middle Ordovician of New York State

“…However, a Protichnites was then discovered with a drag mark that morphed into the shingled imprints as the animal made a sharp turn, which correspond in morphology to the postabdomen of the euthycarcinoid Mosineia macnaughtoni Collette and Hagadorn, 2010, from the same locality (Collette and Hagadorn, 2010; Collette et al, 2012). Mosineia probably carried its tail to the side because it was disoriented and near death, spiraling to its demise, unable to keep its tail off the sand (Braddy et al, 2022). Similar death traces (mortichnia) of myriapods have recently been described from Brazil (Netto et al, 2021).…”

“…The earliest trackways on dry land are from Middle-Late Cambrian (500 Ma) eolian deposits (Potsdam Group) of northern New York State, southeastern Ontario (MacNaughton et al, 2002; Hagadorn et al, 2011), and tidal flat deposits in Quebec and at Blackberry Hill, Wisconsin (Gass, 2015; Braddy et al, 2022). Those trackways, 6–13 cm wide, with series of 7–11 tracks, and a medial impression, are assigned to Protichnites Owen, 1852.…”