In many ways he resembled his descendants living today: the original bird Confuciusornis. Image: Stephanie Abramowicz
Read aloud girl or boy? For many animal fossils, this seemingly simple question is not very easy to answer, for some even not at all. Because most sexual characteristics do not survive the millions of years. However, an international research team has now found a way to determine the sex of a 125-million-year-old bird - and at the same time provided an explanation why some of its conspecifics dragged excessively long tail feathers with them.

The most important information first: DNHM-D1874 was definitely female. This unappealing designation bears a specimen of the primitive bird Confuciusornis sanctus, which is usually found in the Natural History Museum of Dalian in northeastern China. It is one of the eleven selected specimens whose bones the scientists around Anusuya Chinsamy of the University of Cape Town now took a close look at. The study was part of a large-scale international project that aims to learn as much as possible about the life circumstances of C. sanctus.

Hundreds of specimens on the bottom of a primal lake

Because this bird species has a decisive advantage over other primitive birds: to this day almost 1, 000 fossilized specimens of it have been found, with a huge variety of sizes and shapes. Many, including DNHM-D1874, come from the sedimentary rocks of a former lake, also in what is now northeastern China, which was probably originally surrounded by forests and a series of volcanoes. Scientists suspect that several swarms of C. sanctus have been surprised and killed by a volcanic eruption or its consequences, and have survived the millennia in the mud of the lake.

One thing is very noticeable in the fossils: Although definitely belonging to the same species, some of the animals have two extremely long tail feathers, some of which are longer than their entire body, while others have no such ornament. Therefore, paleo-ornithologists suspected relatively early that the decorated specimens might have been males, and that the tail feathers should impress the females - much like the tail feathers of the male peacock do today. Whether the animals with the feather headdresses were actually males, was so far completely unclear. display

Mineral storage in the humerus

Now Anusuya Chinsamy and her colleagues have uncovered an unmastered specimen - DNHM-D1874 - as clear evidence that it must have been a female animal: the inside of a bird's humerus contained remnants of a sponge-like structure of interlinked bone strands. This was evidently so-called medullary bone tissue, explains the team. This tissue is still present in birds, and only in female, which are in their fertile phase of life: It serves as a kind of mineral storage, which includes in particular a calcium reserve for the elaborate formation of the egg shells.

DNHM-D1874 was therefore a female who presumably laid eggs even shortly before his death, concludes the team. Medullary bone is formed immediately after oviposition, and DNHM-D1874 has already begun to recover. Conversely, this meant that the specimens with the long tail feathers were actually the males and that the jewelry was probably really for attracting potential partners.

Early bird is planting

And the scientists even go further in their conclusions: Since there are quite a few rather small fossils where the tail feathers were already well developed, C. sanctus probably already began to reproduce before it was fully grown. In this respect, the primitive bird, which otherwise already showed many features of modern birds, apparently resembled his dinosaur ancestor: they also multiplied before they reached their final height. On the other hand, today's birds rely on growth first and then on reproduction.

Incidentally, C. sanctus is not the first animal to succeed in sexing thanks to a medullary bone: In 2005, the American Mary Schweitzer discovered this particular type of tissue in a Tyrannosaurus rex, and two years later similar reports of the Allosaurus and Tenontosaurus followed. Not only was it clear that the specimens examined were dino-maidens, but there was further evidence that the dinosaurs are actually very closely related to the birds.

Original work of the researchers:

  • Anusuya Chinsamy (University of Cape Town) et al .: Nature Communications, doi: 10.1038 / ncomms2377
Ilka Lehnen-Beyel
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