Every living organism is categorized as either a prokaryote (having single chromosomes) or eukaryote (having pairs of chromosomes). Eukaryotes also contain a nucleus surrounded by a membrane, and its DNA is bound together by proteins (histones) into chromosomes. Eukaryotic cells also contain endoplasmic reticulum and numerous specialized organelles not present in prokaryotes––especially mitochondria, Golgi bodies, and lysosomes.
Who said that science can ever be “settled”? This report [below] goes against the long-standing dogma that eukaryotes appeared evolutionarily between 635 and 542 million years ago (MYA). In the attached article, authors report the discovery of macroscopic fossils from the 1,560-MYA Gaoyuzhuang Formation (Yanshan area of North China). These fossils exhibit both large size and regular morphology. Preserved as carbonaceous compressions, the Gaoyuzhuang fossils have statistically regular linear-to-lanceolate
[narrow oval shape, tapering to a point at each end] shapes, and are as much as 30 cm long and ~8 cm wide––suggesting that these fossils represent multicellular eukaryotes of unprecedentedly large size.
Syngenetic fragments, showing closely packed ~10-mm cells arranged in a thick sheet, further reinforce the authors’ interpretation. Comparisons with living thalloid (“twig-like”) organisms suggest that these organisms were photosynthetic––although their phylogenetic placement within the Eukarya remains uncertain. [Maybe someone can provide us with genomic DNA-sequencing before long?] The new fossils provide the strongest evidence yet that multicellular eukaryotes with decimetric dimensions, and a regular developmental program, populated the marine biosphere at least a billion years earlier than the Cambrian Explosion (est. ~542 MYA).
Nature Commun 2o16; 7: 11500