Taming the wild world of mammalian taxonomy with Connor Burgin

The Illustrated Checklist of the Mammals of the World treats and illustrates ALL of the mammals of the world and offers their most recent taxonomic classification, updating everything from orders and families to species and subspecies. We asked Editor Connor J. Burgin about the massive work behind the scenes of this two-volume publication, the major challenges that were faced, and how they were overcome, especially during the global pandemic that affects us all in this strange 2020.

How did your interest in the global diversity and radiation of mammals begin?

As is the trope of any naturalist, my childhood was spent exploring the natural world whenever I could; digging for insects and worms in gardens and taking inspiration from nature documentaries by attempting to tell others about the natural world. My passion for mammalian diversity began when I was around the age of twelve. I initially developed an interest in the discovery and description of new mammalian species after doing a class project on a new species of sengi, Rhynchocyon udzungwensis. The fact that new mammals were still being described was enthralling and the obscurity of this strange little insectivorous relative to elephants fueled my curiosity. This led me down a path of naive exploration of the literature surrounding mammalian species discovery, and ultimately taxonomy, evolution, and global biodiversity. With this, I also had a curious motivation to create a taxonomic listing of the world’s mammals, which I developed over my teenage years until I had a functional listing based on the most up-to-date literature I could muster. This list was my ticket into the rich research associated with mammalian biodiversity and is now the framework (with a starting point of the HMW series) for the species listing of the Illustrated Checklist of the Mammals of the World and the Mammal Diversity Database.


Approximately what amount of changes were applied to the HMW series in the process of updating the content for the Checklist in terms of taxonomy, maps and illustrations?

With the inertia of recent mammalian taxonomic research, a menagerie of newly recognized species has rendered the HMW series incomplete, as is the eventual fate of all published compendia. The Checklist provides a fully updated taxonomic arrangement compared to that presented in the HMW series, as well as the associated distribution maps, illustrations, and text. Over 400 species ended up having altered taxonomic arrangements (including generic changes), including the addition of over 100 species that were not included in the HMW series.

Aside from taxonomic changes, the volumes also include fully updated maps for all species, which is most evident in species with greatly expanded distributions based on new records. For example, Balaenoptera omurai (Omura’s Whale) has been shown to occur over much of the Indo-Pacific and into the Atlantic, contrary to its more restricted Indo-Pacific distribution in the HMW series. In total, nearly 400 species have heavily altered or newly generated maps to accommodate for recent range shifts, taxonomic changes, and new records. The volumes also include updated common names in English, German, French, and Spanish and provide the current conservation status based on the “2020.1” listing of the IUCN Red List.

The superb illustrations associated with the HMW series are among the defining characteristics that set these volumes apart from other mammalian catalogues. As such, readers will be happy to hear that the Checklist includes almost all of the illustrations previously published in the HMW series, as well as over 100 new illustrations for recently recognized species and updated illustrations for a number of species. Possibly the most substantial of these new incorporations involves the meticulous illustration of over 700 Primates. With these updates, the Checklist provides a fully updated and illustrated platform to ponder the world’s mammalian diversity.


What do you think the present Checklist offers the general public, especially those readers who don’t have the HMW volumes?

The Checklist offers a uniquely in-depth experience for both professional mammalogists and those who are merely interested in the natural world. As well as providing updated taxonomic and distributional treatments of the world’s mammals, the Checklist also offers all its readers the unique opportunity to visualize the world’s mammalian biodiversity, both in terms of appearance and distribution. For the specialized reader, the volumes provide a succinct and updated taxonomic note on each species, including pertinent references associated with recent research on the species evolution and taxonomy. These accounts can be glazed over by the generalist reader, who will likely be entranced by the impressive illustrations and distribution maps. Unlike other compendia, the Checklist is also ordered phylogenetically rather than alphabetically to enhance the usability of each plate for comparison between related species. Along with living species, the Checklist also includes accounts for both extinct and domesticated species with short descriptions on the cause of extinction and history of domestication, respectively, which were not included in the HMW series. Overall, the Checklist provides a distinctive experience for both specialist and generalist readers alike.


You have been investigating the changes in mammalian taxonomy and global biodiversity for your PhD. Can you explain some of the main changes to the higher order that have been applied recently in comparison with the traditional taxonomy of mammals?

Mammalian taxonomy has evolved just as much in higher level taxa as it has at the species level. The now widespread use of genetics in taxonomic and evolutionary research has upended many of the morphology-based groups included in earlier taxonomic arrangements.

A major distinction between the taxonomy presented in the Checklist and that of traditional arrangements (i.e. before the general use of molecular techniques) is the breakup of the order Insectivora, which previously included a wide variety of unrelated mammalian families now spread over five mammalian orders. This includes the order Eulipotyphla, which was more recently considered two separate orders, Soricomorpha to include shrews, moles, and solenodons and Erinaceomorpha for hedgehogs and gymnures. Another large change includes the inclusion of whales, dolphins, and porpoises under the same order as even-toed ungulates following recent advances in phylogenetic studies and the fossil record (discussed below).

A number of other changes have also occurred at the family and genus level associated with studies sampling a wider selection of mammalian species. These changes, such as the inclusion of Capromyidae and Myocastoridae under Echimydae rather than as separate families, better reflect the evolutionary history of these groups and are thus more informative as taxonomic units. The Checklist includes a higher level taxonomy that reflects the most up-to-date phylogenetic studies at the time of publication.


The covers of the Checklist volumes and their box illustrate the relationships of the different groups, using some iconic species to help the reader understand the present knowledge. Could you try to explain to the readers, for example, the relationship of whales with antelopes and hippos, or leopards and hyaenas with sea otters?

The cover of the Checklist depicts our current understanding of the evolutionary relationships between the 27 extant mammalian orders based on the most recent molecular phylogenies available. However, our knowledge of these relationships has only dawned upon the scientific community in the last 20 years as a result of the increasing use of genetic material. As genetic data unravel the evolutionary history of mammalian groups that we have traditionally defined with morphology, it has become apparent that groups with similar anatomy aren’t always related. The prime example of this is the relationship of aquatic and semiaquatic mammals.

Whales, dolphins, and porpoises were long regarded under the order Cetacea based on their highly specialized, fully aquatic lifestyle, which is only shared by one other order of mammals (Sirenia). However, numerous molecular studies coupled with a good fossil record have shown that the closest living relatives to cetaceans are the hippopotamuses within the order Artiodactyla, suggesting that they originated from hooved mammals. As a result, this renders the defined order Artiodactyla “paraphyletic” in association to Cetacea, which means that not all the ancestors of Artiodactyla were included within the defined group. In response, taxonomists have combined the two orders into a single order called Cetartiodactyla (although some authors maintain the name Artiodactyla for this order). This same process of taxonomic revision occurs at all taxonomic ranks, from order to subspecies.


An important part of the work on this project was done during the COVID19 upsurge, first as something “distant” (when it appeared in China), but soon after as a real problem for working in Spain, and later in the US. Did the situation present any specific challenges for your work?

Although much of the work being done for the volumes was online, there are still difficulties that made the progress of the Checklist strenuous at times. At a personal level, I have been fortunate thus far that neither I nor my immediate family have come in contact with the sickness, but that is not to say that there has not been hardship relating to the lockdowns and social climate. Staying positive and productive during times like this, where we must be socially isolated, can take its toll on our mental health. However, remaining preoccupied on the Checklist helped me to cope with the pandemic a little better as it began. Unfortunately, this pandemic is still raging within the United States, unlike a number of other countries. Hopefully the Checklist can provide a good read to some during these hard times, especially to those who are in countries with unceasingly high transmission rates.


Creating a book of such characteristics, with so many details to be controlled (references, illustrations, maps, etc.) and people and processes to be coordinated, all in a very limited period of time, is an enormous task. Can you think of an anecdote that you would like to share from this intense collective effort to produce such a large publication?

The production of such an inclusive work within as short of a time frame as we had certainly had its caveats. I’m sure I was personally a pain to the production team as I tried to squeeze in newly recognized species within already finished portions of the book.

Keeping up with production times was probably the most challenging aspect of the publication process. Having worked on three volumes of the HMW series, I have become familiarized with the strict deadlines associated with these publications. However, as the world entered a pandemic and shut down in many aspects, my priorities often shifted during the production process, making it ever more difficult to keep up.

As the Editor in charge of updating the text, I was also responsible for keeping up with the most recent taxonomic changes and dealing with complex and occasionally controversial taxonomic decisions. The hardest of these to make was what to do about the taxonomy of ungulate species, for which the HMW series included a controversial taxonomic arrangement under Bovidae based on Groves and Grubb, 2011 (Ungulate Taxonomy). After strong discussion with the production team and other editors, we determined it would be best to include the taxonomic arrangement in full (discussed fully in the volume).


Do you feel that the Checklist could be used as a tool for Conservation? If so, how?

Although many don’t see the direct connection, the taxonomy of populations directly affects the conservation of those populations, since many conservation organizations focus heavily on the species level. So deciding what populations are and aren’t separate species can have great effects on conservation efforts associated with them. This dilemma became a major discussion point while constructing the taxonomic arrangement within the volume. Once a species is subsumed within another species as a synonym or subspecies, it is often ignored by conservation organizations and country-level agencies. Thus, unless a species is absolutely proven to be synonymous, it is generally retained as distinct within the Checklist following this ideology. This is the case with many species of Primate in particular, where conservation efforts are critical for many restricted and endangered populations. These concepts also hinge on the polarizing views of “lumpers” (the propensity to lump species together) and “splitters” (the propensity to split species apart) within the taxonomic realm, for which this volume would likely be considered splitter-friendly. This is a controversial viewpoint for many mammalogists and is sure to be a point of discussion for specialists reading through the volumes.

I think one of the primary goals of the work is conservation-oriented, both in terms of educating the public on the wide diversity of mammalian fauna and providing updated definitions of the world’s mammal species. As the public has become aware of the beauty and majesty of nature, they have become more willing to fight for its protection. The Checklist and other volumes like it play a crucial role in inspiring people to care about these animals they wouldn’t otherwise know existed. In terms of policy and conservation agencies, defining a species is the first step to conserving it. With how quickly the world’s natural places are deteriorating, volumes like the Checklist provide a taxonomic guidance on what biodiversity exists, and where it exists, thus giving a baseline for where to prioritize conservation areas in terms of biodiversity.


What would be one global message you would like readers of the Checklist to take away from the work?

On the same topic discussed above, aside from being an updated listing of the world’s mammals, the core value of the Checklist comes down to the conservation of the organisms depicted within it. Over a quarter of mammals are currently at threat according to assessments on the IUCN. However, this does not take into account all of the Data Deficient species, for which very few specimens exist. Nor does it account for species we have not discovered yet that may be on the verge of extinction, or those that have gone extinct in recent times without ever being documented. With this in mind, the global message I would want the readers to take away from this work would be that we still have much to learn about mammalian biodiversity, but we need to make sure they stay around for us to document them.

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