Trilobite fossils reveal unseen 'footprint' maker
Fossils found in Morocco from the long-extinct group of sea creatures called trilobites, including rarely seen soft-body parts, may be previously unseen animals that left distinctive fossil 'footprints' around the ancient supercontinent Gondwana.
University of Adelaide-led research published in the journal Scientific Reports describes three specimens of the 480 million-year-old trilobite Megistaspis (Ekeraspis) hammondi, up to 30 centimetres long and with preserved soft-parts showing a unique combination of digestive structures and double-branched legs.
"One of the most striking aspects of the discovery is that the first three pairs of legs, those located in the head, bear short, strong spines, while those further back in the thorax and tail are smooth," says Dr Diego Garcia-Bellido, ARC Future Fellow with the University of Adelaide's Environment Institute and South Australian Museum.
|Megistaspis (Ekeraspis) hammondi with preserved cephalic and thoracic appendages |
from the late Tremadocian Fezouata Lagerstätte (Moroccan Anti-Atlas)
[Credit: Juan C. Gutiérrez-Marco et al., Scientific Reports]
"The legs we can see on these new fossils match the traces we've known as Cruziana rugosa."
Dr Garcia-Bellido, Juan Gutierrez-Marco of the Spanish National Research Council and colleagues present for the first time the preserved gut with associated digestive structures plus a complete set of both branches of the trilobite legs.
|An illustration of a trilobite (a different species than the recent find) [Credit: University of Adelaide]|
The digestive structures seen also include a unique combination of features: a 'crop' together with several pairs of digestive glands or caeca in the upper parts of the digestive system. Other trilobite fossils have been seen with either a crop or the paired digestive caeca but, until now, they have never been found together.
Trilobites have three main parts: a head with eyes, antennae, mouth, and three pairs of appendages or legs; a thorax with many joined segments, each bearing a pair of legs; and a tail with a number of fused segments and several pairs of legs. Trilobite appendages are soft, with an outer branch which is a gill, and an inner branch used for walking and feeding. The preservation of their soft-body is extremely rare, restricted to only a couple of dozen cases, because their external 'skin' and internal anatomy was normally lost through scavenging and decay soon after death, or overprinted by the mineralised exoskeleton.
Author: Robyn Mills | Source: University of Adelaide [January 17, 2017]