The three newly-identified species show combinations of features not previously seen before in other living or fossil monotremes, according to Professor Kris Helgen from the Australian Museum Research Institute and colleagues.
Six monotremes living in the same place at the same time, 100 million years ago at Lightning Ridge, New South Wales, Australia; clockwise from lower left: Opalios splendens; Stirtodon elizabethae, the largest monotreme of the time; Kollikodon ritchiei, with hot-cross-bun shaped molars; Steropodon galmani, now known from additional opalized fossils; Parvopalus clytiei, the smallest monotreme of the time; and Dharragarra aurora, the earliest known species of platypus. Image credit: Peter Schouten.
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The discovery of these several new species in one small area suggests that the family tree of the egg laying monotremes is far more complicated than the living platypus and echidna alone suggest.”
original paper where it gets interesting...
The Finch Clay facies fossils are preserved in SiO2•nH2O (hydrated silica dioxide), either as ‘potch’ or common opal, or as precious opal displaying plays of colour. These formed as pseudomorphs (amorphous potch replacements), or as opal replacements in which silica mineralization was coupled to decomposition. If the opal is translucent, fine internal anatomical details are sometimes visible. Opalized fossils are also usually three-dimensional and undistorted by compaction or diagenesis, but may show a variable degree of pre-burial weathering. The majority of recovered specimens have passed through mechanical agitators—large rotating barrels that wash out and remove softer sediments to leave tailings of harder claystone and opal, including fossils. This process breaks delicate fossils, rounds edges and often removes the crowns of teeth and other projections. All of the fossil monotreme jaws described herein exhibit fresh breaks due to mechanical excavation and processing. However, alveoli containing remnant claystone indicate that the teeth were lost prior to burial. Notably, the opal-mining process also biases against the recovery of smaller vertebrates, with the smallest mammal remains recovered to date (see below) having posterior molars estimated at almost twice as long as the largest molars of Australian Cretaceous tribosphenidans (Flannery et al. Citation2022b). The Finch Clay facies also produces perinatal (possibly embryonic) ornithopod dinosaurs with an estimated body mass of 113 g (Kitchener et al. Citation2019), and tiny elements from fish, turtles, crocodylomorphs and birds (Bell et al. Citation2019b). We suspect that tribosphenidans were present in the Lightning Ridge faunal assemblage, and that careful excavation may yet yield evidence of them.
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