Researchers discovered the oldest fossils of multicellular eukaryotes in northern China, dating back 1.63 billion years; These fossils reveal early complex life forms and suggest an earlier appearance of multicellularity. In a published study Science Developments On January 24, researchers led by Professor Maoyang Zhu from the Nanjing Institute of Geology and Paleontology, Chinese Academy of Sciences, reported their recent discovery of a 1.63 billion-year-old multicellular fossil in northern China.

These beautifully preserved microfossils are now considered to be the oldest record of multicellular eukaryotes. This study is another breakthrough after researchers previously discovered decimeter-sized eukaryotic fossils in the Yanshan region of northern China, pushing back the emergence of multicellularity in eukaryotes by about 70 million years.

Multicellularity: the major evolutionary transition

All complex life on Earth, including various animals, land plants, macroscopic fungi, and marine algae, are multicellular eukaryotes. Multicellularity is key to eukaryotes gaining organismic complexity and large size, and is often viewed as a major transition in the history of life on Earth. However, scientists are not sure when eukaryotes developed this innovation.

The fossil record provides compelling evidence that simple multicellular eukaryotes, such as red and green algae and possibly fungi, appeared as early as 1.05 billion years ago. Older records claimed that these were multicellular eukaryotes, but most are disputed due to their simple morphology and lack of cellular structure.

The solution to ancient complex life

“The recently discovered multicellular fossils come from the late Paleoproterozoic Chuanlinggou Formation, approximately 1.635 million years old. They consist of two or more large cylindrical or barrel-shaped cells with a diameter of 20-194 μm and an incomplete length of up to 860 μm.” “These filaments show a certain degree of complexity depending on their morphological variation,” said researcher Lanyun Miao.

The filaments are continuous or tapered along their entire length or tapered at only one end. Morphometric analysis reveals their morphological continuity and shows that they represent a single biological species rather than separate species. Fossils were named Qingshania magnificence1989 is a form taxon with similar morphology and size and is described as belonging to the Chuanlinggou Formation.

A particularly important feature Qingshania Some cells have a round intracellular structure (15-20 µm in diameter). These structures are comparable to asexual spores known from many eukaryotic algae; Qingshania, probably spread by spores.

Distinguishing eukaryotic features

In modern life, single-stranded filaments are common in both prokaryotes (bacteria and archaea) and eukaryotes. The combination of large cell size, wide range of filament diameters, morphological diversity, and intracellular spores indicates a eukaryotic affinity. Qingshania No known prokaryote is this complex. Filamentous prokaryotes are generally very small, about 1-3 µm in diameter, and are distributed in more than 147 genera across 12 phyla. Some cyanobacteria and sulfur bacteria can reach large sizes, up to 200 microns thick, but these large prokaryotes are very simple in morphology, have disc-shaped cells and do not reproduce by spores.

The best modern analogues are some green algae, but filaments are also found in other groups of eukaryotic algae (e.g., red algae, brown algae, yellow algae, charophytes, etc.), as well as fungi and oomycetes.

“This shows that Qingshania It is likely a photosynthetic alga that belongs to the extinct archeplastid stem group (the main group consisting of red algae, green algae and land plants, as well as glaucophytes), but their exact affinity is still unknown, Miao said.

Chemical composition and evolutionary consequences

Additionally, the researchers performed a Raman scattering spectroscopic study to confirm eukaryotic affinity. Qingshania Three cyanobacterial taxa in terms of chemical composition were used for comparison. Raman spectra revealed two broad peaks characteristic of disordered carbon. Additionally, burial temperatures estimated using Raman parameters ranged from 205-250°C, indicating low-grade metamorphism. Analysis of the main components of the aligned Raman scattering spectrum Qingshania and dividing cyanobacterial taxa into two separate clusters Qingshania differs from cyanobacterial fossils further confirming eukaryotic affinity Qingshania.

Currently, the oldest definitive eukaryotic fossils are single-celled forms from late Paleoproterozoic sediments (~1.65 billion years ago) in northern China and northern Australia. Qingshania This appeared only slightly later than the single-celled forms; This suggests that eukaryotes acquired simple multicellularity very early in their evolutionary history.

Because eukaryotic algae (archaeplastids) arose after the last eukaryotic common ancestor (LECA), this discovery Qingshania, if indeed algal in nature, further supports the early appearance of LECA in the late Paleoproterozoic – consistent with many molecular clock studies – rather. by the late Mesoproterozoic period, about 1 billion years ago.