Mold Pigs: Strange Creatures with Features of Mites and Tardigrades Found in Amber

A previously unknown family, genus and species of microinvertebrates has been found in amber from the Dominican Republic. Nicknamed ‘mold pigs,’ these tiny creatures lived some 30 million years ago (Paleogene period) and had features of both mites and tardigrades.

A mold pig (Sialomorpha dominicana). Image credit: George Poinar Jr.

A mold pig (Sialomorpha dominicana). Image credit: George Poinar Jr.

“There is no extant group that the mold pigs fit into, and we have no knowledge of any of their descendants living today,” said Professor George Poinar Jr., an entomologist at the Oregon State University College of Science.

“This discovery shows that unique lineages were surviving in the mid-Tertiary.”

The mold pigs were about 100 μm long and grew by molting their exoskeleton.

Scientifically named Sialomorpha dominicana, these creatures had flexible heads and four pairs of legs.

They fed mainly on fungi, supplementing that food source with small invertebrates.

“No claws are present at the end of their legs as they are with tardigrades and mites,” Professor Poinar said.

“Based on what we know about extant and extinct microinvertebrates, Sialomorpha dominicana appears to represent a new phylum.”

“The structure and developmental patterns of these fossils illustrate a time period when certain traits appeared among these types of animals.”

“But we don’t know when the Sialomorpha lineage originated, how long it lasted, or whether there are descendants living today.”

The mold pigs shared warm, moist surroundings with pseudoscorpions, nematodes, fungi and protozoa.

“Every now and then we’ll find small, fragile, previously unknown fossil invertebrates in specialized habitats,” Professor Poinar said.

“And occasionally, as in the present case, a fragment of the original habitat from millions of years ago is preserved too.”

“The mold pigs can’t be placed in any group of currently existing invertebrates — they share characteristics with both tardigrades and mites, but clearly belong to neither group.”

The discovery is described in a paper in the journal Invertebrate Biology.

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George Poinar Diane R. Nelson. A new microinvertebrate with features of mites and tardigrades in Dominican amber. Invertebrate Biology, published online September 28, 2019; doi: 10.1111/ivb.12265

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