Close up of OUMNH-ZC-7483 Section of blue whale intestine with mysterious acanthocephalan parasites

Worms of Discovery

By Mark Carnall, Life Collections manager

The Museum’s zoology collections contain a dizzying diversity of animal specimens. It is a collection that would take multiple lifetimes to become familiar with, let alone expert in. So we benefit hugely from the expertise of visiting researchers – scientists, artists, geographers, historians – to name just a few of the types of people who can add valuable context and expand our knowledge about the specimens in our care.

Earlier this year, Dr Andrew McCarthy of Canterbury College (East Kent College Group) got in touch to ask about our material of Acanthocephala, an under-studied group of parasitic animals sometimes called the spiny-headed worms.

Although there are around 1,400 species of acanthocephalans, they are typically under-represented in museum collections. Dr McCarthy combed through the fluid-preserved and microscope slide collections here, examining acanthocephalan specimens for undescribed species, rare representatives and unknown parasitic associations.

Close up of OUMNH-ZC-7483 Section of blue whale intestine with mysterious acanthocephalan parasites
Close up of OUMNH-ZC-7483 Section of blue whale intestine with mysterious acanthocephalan parasites

One such specimen, catchily referenced OUMNH.ZC.7483, was of particular interest. It is a section of blue whale intestine packed with acanthocephalan adults, labelled ‘Echinorhynchus sp. “Discovery Investigations”’, and dated 13 March 1927. Drawing on his expert knowledge, Dr McCarthy spotted an unusual association here because the genus Echinorhynchus was not known to infect Blue Whales, meaning the specimen could represent a species to new science.

However, identifying different species of acanthocephalans cannot be done by eye alone, so Dr McCarthy requested to remove one of the mystery worms from the intestine and mount it on a slide to examine its detailed anatomy. When we receive a destructive sampling request like this it triggers an investigation of the specimens in question: we need to weigh up their condition, history, and significance against the proposed outcome of the research before we decide whether the permanent alteration of the specimen justifies the outcome.

Image of Oxford University Museum of Natural History zoology collections accession register entry for this specimen showing the donation of the specimen and collector information.
Image of Oxford University Museum of Natural History zoology collections accession register entry for this specimen showing the donation of the specimen and collector information.

This particular investigation began to yield a much richer story than the Museum’s label suggested. It turned out that the specimen was collected by Sir Alister C. Hardy who was serving as zoologist on RRS Discovery’s scientific voyage to the Antarctic. Fortunately, Discovery’s scientific findings were meticulously documented and published by many libraries of the world, including the fantastic Biodiversity Heritage Library where it was easy to find the report mentioning acanthocephalans collected during the voyage.

Alongside descriptions of acanthocephalans from seals, dolphins and icefish there is no mention of Echinorhynchus sp. from Blue Whales, though there are a few references to another genus, Bolbosoma, collected from Blue Whales on seven occasions: a single individual of Bolbosoma hamiltoni, so obviously not this specimen, and six occurrences of Bolbosoma brevicolle from the intestines of Blue Whales from South Africa and South Georgia.

These specimens and others reported in the Discovery reports. Image from Biodiversity Heritage Library

Piecing together the evidence, the association with Hardy, the dates, and the descriptions of RRS Discovery’s acanthocephalans, it seems likely that our specimen is one of the six samples of Bolbosoma brevicolle and not Echinorhynchus at all. So in this instance we decided not to grant destructive sampling as the likelihood of identifying a new species seemed much lower when all the information was brought together.

Although sampling wasn’t granted, Dr McCarthy was delighted that his initial research request had prompted the discovery of some important historical connections to the humble specimen, and the new identification seemed to fit.

We still weren’t sure when or why this specimen was mislabelled some time between the Discovery reports and its donation to the Museum in 1949, so Dr McCarthy conducted some further investigations. He found out that Echinorhynchus was the original name combination for Bolbosoma brevicolle, and that H. A. Baylis, a parasitologist and author of Discovery reports, had links with the University of Oxford.

This story is just one example of how visiting researchers enrich knowledge and information about our collections, and it illustrates nicely why our work with broader research communities is so important.

Bound by blood

It may sound like we’ve stumbled into a script-writing session for Jurassic Park, but one of our research fellows, Dr Ricardo Pérez-de la Fuente, along with an international team, has discovered a parasite trapped in amber, clutching the feather of a dinosaur. This small fossilised tick, along with a few other specimens, is the first direct evidence that ticks sucked the blood of feathered dinosaurs 100 million years ago. Ricardo tells us all about it…

The paper that my colleagues and I have just published provides evidence that ticks fed from feathered dinosaurs about 100 million years ago, during the mid-Cretaceous period. It is based on evidence from amber fossils, including that of a hard tick grasping a dinosaur feather preserved in 99 million-year-old Burmese amber.

Fluorescence detail of the studied hard tick grasping a dinosaur feather. Extracted from the publication.

The probability of the tick and feather becoming so tightly associated and co-preserved in resin by chance is virtually zero, which means the discovery is the first direct evidence of a parasite-host relationship between ticks and feathered dinosaurs.

Fossils of parasitic, blood-feeding creatures directly associated with remains of their host are exceedingly scarce, and this new specimen is the oldest known to date. The tick is an immature specimen of Cornupalpatum burmanicum; look closely under the microscope and you can see tiny teeth in the mouthparts that are used to create a hole and fix to the host’s skin to suck its blood.

The structure of the feather inside the amber is similar to modern-day bird feathers, but it could not belong to a modern bird because, according to current evidence at least, they did not appear until 26 million years later than the age of the amber.

Feathers with the same characteristics were already present in multiple forms of theropod dinosaurs –  the lineage of dinosaurs leading to modern birds – from ground-runners without flying ability, to bird-like forms capable of powered flight. Unfortunately, this means it is not possible to determine exactly which kind of feathered dinosaur the amber feather belonged to.

But there is more evidence of the dinosaur-tick relationship in the scientific paper. We also describe a new group of extinct ticks, created from a species we have named Deinocroton draculi, or “Dracula’s terrible tick”. These novel ticks, in the family Deinocrotonidae, are distinguished from other ticks by the structure of their body surface, palps and legs, and the position of their head, among other characteristics.

Blood-engorged Deinocroton draculi tick (female). Extracted from the publication.

This new species was also found sealed inside Burmese amber, with one specimen remarkably engorged with blood, increasing its volume approximately eight times over non-engorged forms. Despite this, it has not been possible to directly determine its host animal:

Assessing the composition of the blood meal inside the bloated tick is not feasible because, unfortunately, the tick did not become fully immersed in resin and so its contents were altered by mineral deposition.
Dr Xavier Delclòs, an author of the study from the University of Barcelona and IRBio.

But there was indirect evidence of the likely host for these novel ticks in the form of hair-like structures called setae from the larvae of skin beetles, or dermestids, found attached to two Deinocroton ticks preserved together. Today, skin beetles feed in nests, consuming feathers, skin and hair from the nest’s occupants. But as no mammal hairs have yet been found in Cretaceous amber, the presence of skin beetle setae on the two Deinocroton draculi ticks suggests that their host was in fact a feathered dinosaur.

The hair-like structures, or setae, from skin beetles (dermestids) found attached to two Deinocroton ticks fossilised inside amber, in comparison with extant ones. Modified from the publication.

Together, these findings tell us a fascinating story about ancient tick behaviour. They reveal some of the ecological interactions taking place among early ticks and birds, showing that their parasite-host relationship has lasted for at least 99 million years: an enduring connection, bound by blood.

The paper “Ticks parasitised feathered dinosaurs as revealed by Cretaceous amber assemblages” is published as open access in Nature Communications. Direct link: http://dx.doi.org/10.1038/s41467-017-01550-z