Soft Tissue in Biggest Ever Cambrian Fossil Bonanza

Chinese scientists are uncovering shale with the best-preserved Cambrian animals ever found.

Welcome the Qingjiang Biota, a collection of Cambrian animal fossils that beats the famous Burgess Shale in Canada. China had already boasted a rich Cambrian bed, the Chengjiang biota. Now, Science Magazine has reported the first pictures and details from four years of research at the new treasure trove of Cambrian animals nearby. Take a look at the delicate antennae in this arthropod that resembles a shrimp:

From Fig. 3, “Leanchoilia sp., showing fine anatomical details, including those of the great appendages.” Dark spots indicate soft tissue preservation.

This is in shale rock, but could hardly be better preserved by amber. It looks as though the creatures was buried instantly. If not, this amount of detail would not have survived a day. Nature summarizes the context of this fossil bed, and notes the delicacy of soft-bodied creatures preserved in this fashion. What does it take to preserve details of a jellyfish, or a comb jelly?

At about 518 million years of age, the fossil bed discovered in South China is slightly older than the celebrated Burgess Shale, a fossil site in the Canadian Rocky Mountains where the forms of hundreds of Cambrian animals have been immaculately preserved. Calling their assemblage the Qingjiang biota, Xingliang Zhang, at Northwest University in Xi’an, China, and his colleagues identify several algal forms and 101 types of animal — over half of which were never before described.

The collection’s abundance of early pristine fossils of squishy animals, such as jellyfish, sea anemones and comb jellies, could be useful for biologists exploring early animal origins. The beds also hold unusually large species of mud dragon, or kinorhynchs; modern-day versions of these moulting invertebrates are visible only under a microscope.

Mud dragons have apparently devolved from their spectacular ancestors. Previous reports showed Cambrian comb jellies with armor, unlike the squishy ones today (Evolution News, 28 July 2016). That seems to be another case of devolution.

Original Soft Tissues?

Of special interest are the possible soft tissues preserved. In the announcement paper in Science, “The Qingjiang biota—A Burgess Shale–type fossil Lagerstätte from the early Cambrian of South China,” the phrase “soft tissue” appears repeatedly. Care must be taken not to misinterpret the phrase; it could refer to organs that were turned to stone during fossilization. Some statements in the paper seem to indicate that primordial biological material may exist. [Note: the term Lagerstätte refers to exceptionally-preserved fossils.]

• Here, we report the discovery of an early Cambrian Burgess Shale–type (BST) fossil Lagerstätte from the Changyang area of South China (Fig. 1), which is characterized by high taxonomic diversity, an unexpectedly large proportion of new taxa, and precise preservation of fine aspects of labile tissue anatomy (Figs. 2 to 4).
• New megacherian preserved with internal soft tissues.
• No authigenic mineral films or mineral replacement of selected soft tissues (e.g., pyrite, phosphate) have yet been observed. The fidelity of preservation is very high, on par with that of Chengjiang and Burgess Shale fossils (1, 7, 28). Apart from lightly sclerotized tissues, such as arthropod and worm cuticle, entirely soft-bodied animals (Fig. 2) (e.g., ctenophores and jellyfishes), labile anatomical features (eyes, gills, and guts), and juveniles are fairly common (Fig. 3 and fig. S2) and offer new phylogenetic information.
• During early diagenesis, both calcite and pyrite precipitated within the sediments but did not result in mineral replacement of soft-tissue morphology.

The team summarizes the work’s contribution to analysis of the Cambrian explosion:

The particularly large proportion of new taxa in the Qingjiang biota (fig. S5), which lies in close temporal proximity to the extensively sampled Chengjiang biota, suggests that the present understanding of the diversity and disparity of metazoan ecosystems in the immediate aftermath of the Cambrian explosion is far from complete and will be greatly informed by future discoveries.

For more information on the Qingjiang site, see the following articles:

• A treasure trove of Cambrian fossils (Allison C. Daley, Science). “At this 508 million–year-old fossil locality, soft-bodied fossils are exquisitely preserved, showing skin, eyes, and internal organs such as guts and brains.”
• Fossil bed reveals a wealth of primeval species in exquisite detail (Nature).
• Treasure trove of marine fossils from ‘Cambrian explosion’ found in China (Phys.org).
• Bonanza of Bizarre Cambrian Fossils Reveals Some of the Earliest Animals on Earth (Mindy Waisberger, Live Science). “Many of the fossils — bell-shaped jellyfish, spiky worms, armored arthropods and more — retain an astonishing level of detail in their preserved soft tissues, such as gills, digestive systems and even eyes.”

Other Cambrian Fossils

Cambrian Sessile, Suspension Feeding Stem-Group Ctenophores and Evolution of the Comb Jelly Body Plan (Current Biology). In the nearby Chengjiang fossil bed, Zhao et al. claim that a sessile (stationary) organism might be the ancestor of comb jellies.

Half-a-billion-year-old fossil reveals the origins of comb jellies (Science Daily). This overstated headline from the University of Bristol asserts as a matter of fact that the new fossil was the ancestor of comb jellies. Paleontologists have long debated where to put comb jellies (ctenophores) in the imaginary phylogeny of Cambrian animals, which appeared nearly simultaneously in the base of the Cambrian fossil beds.

520-Million-Year-Old Sea Monster Had 18 Mouth Tentacles (Live Science). This article mentions controversy about the origin of comb jellies. Casey Dunn of Yale is quoted as being “highly skeptical” of the assertion that the new fossil represents a ‘distant ancestor’ of ctenophores. He puts his own evolutionary spin on the story:

“These are exciting animals no matter how they’re related to each other,” Dunn said. “Even though I’m skeptical that tentacles and comb rows are homologous [evolutionarily related], I think that as we describe more diversity from these deposits, certainly we’re going to learn a lot more about animal evolution.”

Other Lagerstätte 

The Mazon Creek Lagerstätte: a diverse late Paleozoic ecosystem entombed within siderite concretions (Journal of the Geological Society). The state of Illinois has remarkable preservation of Carboniferous fossils, including some with soft tissues.

One of the best records of late Paleozoic ecosystems, the Mazon Creek Lagerstätte is world famous for its striking flora and fauna preserved within siderite concretions. Distinct from other late Carboniferous concretionary Lagerstätten because of the remarkable fidelity of soft tissues and pigments that are frequently preserved, the Mazon Creek has seen a revival in investigations during the last 10 years using modern palaeontological techniques. However, many of these modern investigations build upon a literature that incorrectly interprets the palaeoenvironment of the Mazon Creek and the separate biotas: there is a lack of evidence to support a distinct freshwater fauna. Here, we present a detailed overview of the Mazon Creek Lagerstätte, including the palaeoenvironmental conditions, organisms present and the complex taphonomic processes involved in fossil formation.

Two creationists keep track of soft tissue fossil announcements in the secular science literature. Bob Enyart of Real Science Radio maintains a page listing all the scientific papers announcing soft tissue. Brian Thomas of ICR also reports frequently on the subject. His most recent article debunks the “toast” model for soft tissue preservation in dinosaurs (see 10 Nov 2018).