480-Million-Year-Old Mystery Creature Finally Identified from Its Preserved Guts

By Laura Geggel, Senior Writer | February 22, 2019 07:46am ET

An illustration of the stylophoran genus Thoralicystis.

Credit: Copyright Rich Mooi/California Academy of Science

Nos últimos 150 anos, os cientistas debateram calorosamente uma misteriosa criatura que viveu centenas de milhões de anos atrás, muito antes de os dinossauros caminharem pela Terra. E agora, com a descoberta de fósseis incrivelmente detalhados no Marrocos, os paleontologistas finalmente identificaram as bizarras formas de vida.

 
As criaturas, conhecidas como stylophorans, pareciam decorações de parede achatadas e blindadas que tinham um longo braço saindo de seus lados. Mas, embora antes não estivesse claro onde eles se encaixam na árvore genealógica dos animais, o novo estudo revelou que eles são equinodermas, os antigos parentes de animais modernos, como ouriços-do-mar, estrelas-do-mar, estrelas-do-mar, estrelas de penas e pepinos-do-mar.

A descoberta foi possível graças a fósseis com "evidência inequívoca de partes moles excepcionalmente preservadas, tanto no apêndice quanto no corpo de estiloforanos", disse o pesquisador-chefe do estudo Bertrand Lefebvre, pesquisador do Centro Nacional de Pesquisa Científica (CNRS) do Laboratório. de Geologia de Lyon na França. [Fotos: Trevo de Fósseis Marinhos Descobertos no Marrocos].

Os fósseis incríveis foram descobertos durante uma escavação em 2014 na Formação Fezouata, localizada ao longo da borda do deserto do Saara no sul do Marrocos. A escavação rendeu uma recompensa de fósseis, incluindo cerca de 450 espécimes de estiloforos, cada um com cerca de 478 milhões de anos atrás.

Mas os pesquisadores não perceberam imediatamente que alguns dos fósseis incluíam tecidos moles preservados. "É somente quando desfazemos a mala e olhamos para eles sob o binóculo [microscópio], no laboratório de Lyon, que pudemos ver as partes moles", disse Lefebvre à Live Science por e-mail. "Sua presença e identificação foram então confirmadas pelo SEM (scanning electron microscope) observations and analyses."

The team of researchers who excavated the fossils from the Fezouata Formation in Morocco.

Credit: Bertrand Lefebvre

O achado de tecido mole foi sem precedentes. Fósseis de Stylophoran foram encontrados em todo o mundo desde a década de 1850, permitindo aos pesquisadores determinar que essas criaturas viviam desde o período cambriano médio até o final do período carbonífero, ou cerca de 510 milhões a 310 milhões de anos atrás, quando as criaturas foram extintas. Mas, como os tecidos moles raramente fossilizam, os estiloforanos eram conhecidos apenas por suas partes esqueléticas duras e não por suas entranhas moles.

"Sua anatomia interna não era apenas inteiramente desconhecida, mas também - e principalmente - altamente controversa", disse Lefebvre.

What did they look like?

Stylophorans had two main parts: a core body and a weird appendage attached to it. Both the core body and the appendage were small, each about 1.2 inches (3 centimeters) long, Lefebvre said.

Previously, other researchers came up with all kinds of ideas about stylophorans.

From the 1850s to 1950s, most researchers thought that stylophorans were "normal" echinoderms. Their weird appendage was interpreted as the equivalent to the stem of sea lilies.

Normal echinoderms have internal skeletons made of mineralized, calcitic plates (although this is extremely reduced in sea cucumbers) and so-called water vascular systems that help them move and breathe, said Peter Van Roy, a paleobiologist at Ghent University in Belgium, who was not involved with the study.

Most echinoderms, including starfish, have a five-rayed symmetry. They're closely related to another invertebrate group, the acorn worms, and to vertebrates (animals with backbones). Together, echinoderms, acorn worms and vertebrates make up an overarching group known as deuterostomia, Van Roy said. [Deep-Sea Creepy-Crawlies: Images of Acorn Worms]

A photo of a Thoralicystis fossil from Morocco.

Credit: Emmanuel Robert

Then, in the early 1960s, Belgian paleontologist Georges Ubaghs noticed that the appendage was different from a stem but similar to a feeding arm, as seen in modern starfish.

In the late 1960s, British paleontologist Richard Jefferies proposed an entirely different idea. He thought that the stylophoran main body was a head (holding a pharynx and brain) and that the appendage housed muscles and a notochord (a type of primitive backbone). Jefferies thought that stylophorans were the "missing link" between echinoderms and chordates (a group that includes vertebrates).

In the 2000s, British paleontologist Andrew Smith suggested yet another interpretation. He said that stylophorans were probably not the "missing link" between echinoderms and vertebrates but were more likely primitive deuterostomes, filling the gap between acorn worms and echinoderms.

The new discovery of the fossilized soft tissue, however, has changed everything. Researchers could test, for the first time, whether the soft tissue matched what you would expect from any of these different scenarios, Lefebvre said.

Hard evidence

The newfound fossils align most closely with Ubaghs' interpretation. The stylophorans' flat bodies contained intestines, and the appendage was not closed off as a stem would be and rather looked like a starfish arm. This arm contained a water vascular system that would have helped the creatures move and eat, just like the arms of starfish do, Van Roy said.

Because stylophorans don't have five-rayed symmetry, they likely lost it, meaning they were more "advanced" evolutionarily than other five-rayed echinoderms, Van Roy added.

"This discovery is of particular importance, because it brings to an end a 150-year-old debate about the position of these bizarre-looking fossils in the tree of life," Lefebvre said.

The study is "very thorough," Van Roy said, "and I have no reservations about any of the methods used or conclusions drawn." Moreover, it highlights the importance of the well-preserved fossils of the Fezouata Formation, a place where Van Roy has previously found spectacular specimens.

The study was published online in the February issue of the journal Geobios.