Small bivalve crustaceans are the most abundant fossil arthropods since the Ordovician and play an important role in paleo-environmental reconstruction and evolutionary biology.
The vast majority of fossil ostracodes are represented by calcified shells, and their soft parts, which can provide invaluable information on ancient ostracod autoecology, are extremely rare.
Recently, Dr. Wang He and Prof. Wang Bo of the Nanjing Institute of Geology and Palaeontology of the Chinese Academy of Sciences (NIGPAS) and their collaborators exceptionally well-preserved soft-bodied ostracodes (pendants and reproductive organs) from the middle -Cretaceous Myanmar amber (~ 1
The study was published in Procedures of the Royal Society B on September 15th.
The Ostracod collection in the amber consists of 39 people in one amber piece and includes males, females and young.
X-ray micro-computed tomography was used to obtain high-resolution three-dimensional images of their soft parts. The micro-CT reconstruction provided direct evidence of the male clasper, sperm pumps (Zenker organs), hemipens, eggs, and female seminal vesicles containing giant semen.
This is the first time that giant ostracod semen was found in chalk-ostracod fossils; its length was at least one-third of the body length of the ostracode. This discovery is also the earliest known record seed for animal semen, and approx. 50 million years older than the former oldest fossil records of animal semen.
Analyzes of the fossil and existing ostracods show that during sexual reproduction, the male used his sexually dimorphic fifth limb, which has hook-like endopods, to grab a woman while introducing his hemipenes into the woman’s mated vaginas. The male pair of Zenker organs then transmitted the unusually long but immotile sperm cream via the male hemipenes in the female.
The zenker organ is readily identified in existing cypridoidean ostracods as a large, spiny, sclerotated portion of the exposing spermatic canal. Muscle fibers next to the organ connect the many spines, which are often arranged in a number of curls that are taxonomically characteristic at the family level.
Once in the female, the sperm cells are pushed up the two long sperm ducts, each ending in a sac-like sperm box for sperm storage; there they finally become mobile, arrange themselves in a more organized collection and fertilize eggs during the laying process.
Research reveals that the repertoire of reproductive behavior in ostracods, which is associated with significant morphological adaptations, has remained unchanged for at least 100 million years – a general example of evolutionary stasis.
The appearance of a complex reproductive mechanism involving giant sperm, enhanced mating success and may have been a major contributor to the late Mesozoic explosive radiation of the superfamily Cypridoidea, which today includes the vast majority of non-marine ostracod species.
Old giant sperm discovered at Riversleigh World Heritage Fossil Site
Extraordinary preservation of reproductive organs and giant semen in chalk skin Procedures of the Royal Society B (2020). rspb.royalsocietypublishing.or… .1098 / rspb.2020.1661
Provided by Chinese Academy of Sciences
Citation: Finding in 100 million year old amber reveals intercourse between ostracods (2020, September 15) retrieved September 15, 2020 from https://phys.org/news/2020-09-million-year-old-amber-reveals – sexual intercourse.html
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