[ad_1]
The robust, calcite-infused exoskeletons and fragmented shells of trilobites are found almost everywhere in fossil beds from the Cambrian Period to the Permian. But this treasure trove of trilobite fossils has revealed frustratingly little about how Paleozoic animals reproduced over 250 million years of life on ancient Earth.
A recently reexamined fossil Burgess Shale It pulls back the veil of mystery over the sex lives of ancient arthropods and reveals that some trilobites likely had a loving grip. In a study published Friday geologyPaleontologists at Harvard University have identified a pair of modified appendages that, similar to modern horseshoe crabs, help males of a trilobite species grasp females during mating.
The team studied several spiny Olenoides serratus. Trilobites collected from the Cambrian region. Most were shorter than four inches. while The Burgess Shale is known for its detailed preservation. Even from delicate tissue, one of the olenoides The specimens the team examined at the Royal Ontario Museum in Toronto looked more like a badly broken lobster tail than a solid trilobite.
“One example that looks sad – most of his head and half of his body are missing,” said Sarah Losso, PhD. Candidate at Harvard and author of the study.
The fragmented nature of the specimen was a lucky break, as it revealed anatomy that was often hidden beneath a trilobite’s shell. More importantly, nine of the rarely fossilized appendages of arthropods have been preserved in detail. “There are millions of broken trilobites, and in most of them you don’t see a limb,” said Javier Ortega-Hernández, a co-author of the new study and Ms. Losso’s Ph.D. advisor. “Having this specimen broken so you can see these limbs is one in a million cases.”
Two sets of limbs stood out. The standard trilobite limb is divided into three distinct parts – a walking leg, or endopodid, and a gill structure, the exopodite, connected to the body by an organ. prickly food processing division, protopodite. However, the anatomy of the two appendages in the middle portion of the trilobite was visibly distorted. Instead of a spiny, triangular protopodite for handling food, they had a smooth, rounded structure attached to a short, flexible, finger-like endopodite that was only half the size of the creature’s other walking legs. These modified appendages could not reach the seafloor while the trilobite stood on its other legs.
Based on their growth patterns, the researchers were able to conclude that the strange morphology of these shriveled limbs was probably not caused by an injury or regeneration.
Instead, Ms. Losso and Dr. Ortega-Hernández concluded that these altered legs served a sexual purpose. They based their hypotheses on this horseshoe crabs, distant relatives of the trilobites that swim on modern beaches today. Crabs are often used as a trilobite surrogate because of their similar body form. They use gripping appendages called claws to attach themselves to a female’s spine and provide males with an internal pathway to fertilize the female’s eggs as soon as they are released from a chamber in her head. Olenoides trilobites may likewise have used clamping appendages, as female trilobites probably also practiced external fertilization, releasing their eggs into eddies to fertilize males.
The structure and arrangement of these pincer-like appendages on the trilobite are somewhat different from those of living horseshoe crabs. Rather than being close to the head in contemporary species, the modified legs are along the trilobite’s midsection, placing them in the perfect spot to latch onto the female’s spiny hindquarters.
But it is unlikely that all trilobites mate in this way. “I think there’s probably a real variation in the mating of trilobites,” said paleontologist Thomas Hegna of the State University of New York in Fredonia. First cluster of trilobite eggs ever found. “I don’t think everyone hugged each other.”
Ms Losso admits that various species of trilobites probably use a variety of reproductive approaches beyond docking. Many trilobites lack the spines of Olenoides, making them difficult to grasp.
However, he believes identifying one of these sexual methods underscores the early evolution of complex reproductive strategies.
“The behavior of holding a female in place for fertilization evolved in the mid-Cambrian,” said Ms. Losso. “Just a few million years after the first trilobites, they have already evolved this unexpectedly complex behavior.”
[ad_2]
Source link