Hot off the press are two new papers about fossil creatures, an insect and a “lobopod” that may be closely related to the ancestor of modern arthropods (insects, spiders, crustaceans, millipedes, etc.)
In the newest issue of Nature, Liu et al. (reference below) describe a fossil lobopod from the Chengjiang formation: a Chinese formation containing an amazing array of fossils from the early Cambrian (ca. 525-520 million years ago). Chengjiang has yielded many bizarre creatures—like the later Burgess Shale, it preserved many delicate animals—but this is one of the most striking. It’s a new lobopod, Diania cactiformis (note the species name: it really does look like a cactus):
The quality of preservation is amazing. What are lobopods? They are an early group of anomalous animals that bear a certain resemblance to the living onycophorans (“velvet worms”), once thought to be a “missing link” between annelid worms and arthropods. Lobopods have often been seen as a stem group of modern arthopods: a stem group is an extinct group that is more closely related to the common ancestor of a diverse modern group than to the ancestor of any other group, but is not itself part of the first group.
Liu et al. confirm through phylogenetic analysis that Diania cactiformis is closely related to the ancestor of modern arthropods, but not descended from that common ancestor. It has arthopod-like “sclerotinized” limbs (sclerotin is a protein found in the hard arthropod cuticle), and arthopod-like jointed limbs. Here’s a reconstruction:
Liu et al.’s analysis also shows that the fossil and other lobopods are “paraphyletic”: that is, some members of the “lobopod” group are more closely related to other non-lobopod taxa than they are to other lobopods. That makes the Lobopodia a false grouping, since it does not include all the descendants of one common ancestor. The authors conclude:
Irrespective of its exact position, Diania, with its stout and spiny limbs attached to a slender, vermiform body, remains a highly unusual creature. It is hard to envisage it as the progenitor of any modern arthropod group, yet it may derive from a grade of lobopodian that acquired a key evolutionary innovation—and the name-giving character for Arthropoda—whereby sclerotized, jointed appendages began to fully develop.
The second beast is a fossil cricket Schizodactylus groeningae, whose description was published by Sam Heads and Léa Leuzingers in a fairly obscure journal, ZooKeys (reference below, access free). The description was based on two specimens from the remarkable Crato Formation of Brazil, dating back about 112 million years. The formation is amazing because it preserved many delicate creatures, especially insects. You can see the veins of their wings, and sometimes even their colors! Here are a couple of non-crickets from Crato.
First, an Ephemeropteran (mayfly). Remember, this insect lived more than a hundred million years ago:
Here’s the fossil cricket described by Heads and Leuzinger. It was formerly named Brauckmannia groeningae:
Notice the coiled wings and the “lateral processes” on the feet. These are similar to those of living “splay-footed crickets” that are placed in the genus Schizodactylus. And that’s the excuse for posting the fossil, for I didn’t know of these crickets, and they’re weird. Crickets in the family Schizodactylidae live largely in the sand dunes of Asia and Africa. Their splayed feet act, in fact, like snowshoes, helping them make their way over unstable sand. Here’s a modern one, Schizodactylus inexpectatus (photo copyright by Jan Sevcik):
The authors conclude that the fossil cricket shares so many features with the modern ones in this genus, including coiled wings and those “sandshoes,” that it should be placed in the genus Schizodactylus as well; and they renamed the fossil beast Schizodactylus groeningae. When a species is renamed (“synonymized”) in this way, that means that the earlier genus name, Brauckmannia, can never be used again.
Heads, S. W. and L. Leuzinger. 2011. On the placement of the Cretaceous orthopteran Brauckmannia groeningae from Brazil, with notes on the relationships of Schizodactylidae (Orthoptera, Ensifera). ZooKeys 77:17-30.
Liu, J., M. Steiner, J. A. Dunlop, H. Keupp, D. Shu, Q. Ou, J. Han, Z. Zhang, and X. Zhang. 2011. An armoured Cambrian lobopodian from China with arthopod-like appendiges. Nature 470:526-530.