ORIGINAL ARTICLE Gross intestinal morphometry and allometry in Carnivora Amanda McGrosky 1,2 & Ana Navarrete 3 & Karin Isler 1 & Peter Langer 4 & Marcus Clauss 5 Received: 12 February 2016 /Revised: 2 April 2016 /Accepted: 4 April 2016 # Springer-Verlag Berlin Heidelberg 2016 Abstract Although typical anatomical features of the diges- tive tract of carnivores are well known, such as the presence or absence of a caecum in various carnivore taxa, and although a large number of length measurements have been published, the body mass measurement of the corresponding specimens has mostly not been reported. Here, we add original mass and intestine length measurements for 36 carnivore species to lit- erature data. Using Phylogenetic Generalized Least Squares, we demonstrate that marine Carnivora (pinnipeds and the sea otter Enhydra lutris) have significantly longer total and small intestines relative to body mass than terrestrial Carnivora, and both pinnipeds and mustelids in general have particularly long total intestines amongst terrestrial Carnivora. The natural diet explains little about variation in relative intestinal length mea- sures. However, amongst species that do have a caecum, a higher proportion of plant material in the diet might be asso- ciated with a longer caecum. In particular, a diet with higher proportions of plant material provided by humans could have led to a particularly long caecum in the domestic dog. Keywords Canid . Felid . Ursid . Viverrid . Jejunum . Colon Introduction Because the natural diet of carnivores is typically of a very high digestibility, the digestive anatomy of carnivores is com- paratively simple when compared to other feeding types (Stevens and Hume 1995), and there appears to be little dif- ferentiation between carnivore groups in terms of major nutri- ent digestibility (Clauss et al. 2010). In several carnivore groups, such as the ursids, mustelids, procyonids, and in spe- cies like the binturong (Arctitis binturong) or sea elephants (Mirounga spp.), the simplification of the intestinal tract in- cludes the loss of the caecum (Mitchell 1903–6; Mitchell 1916; Kostanecki 1926). The perception of carnivore intes- tines as unspectacular may be one of the reasons why few images and length measurements have been reported for these species. Thus, while it is generally thought that the intestines of herbivorous mammals are longer than those of carnivores (Orr 1976), this difference has not been statistically confirmed to date (Lavin et al. 2008), presumably due to a lack of data. On the other hand, the difference in the length of the intestinal tract between terrestrial and marine carnivores has always attracted attention (Mitchell 1903 – 6; Mitchell 1916 ; Williams et al. 2001): marine carnivores have noticeably lon- ger intestinal tracts than terrestrial carnivores. One possible * Marcus Clauss mclauss@vetclinics.uzh.ch Amanda McGrosky amcgrosk@asu.edu Ana Navarrete afn2@st-andrews-ac.uk Karin Isler karin.isler@biol.uzh.ch Peter Langer Peter.Langer@anatomie.med.uni-giessen.de 1 Anthropological Institute and Museum, University of Zurich, Winterthurerstr. 190, 8057 Zurich, Switzerland 2 Present address: School of Human Evolution and Social Change, Arizona State University, Tempe, AZ, USA 3 School of Biology, University of St. Andrews, Fife, Scotland, UK 4 Institute of Anatomy and Cell Biology, Justus-Liebig-University, Aulweg 123, 35385 Giessen, Germany 5 Clinic for Zoo Animals, Exotic Pets and Wildlife, Vetsuisse Faculty, University of Zurich, Winterthurerstr. 260, 8057 Zurich, Switzerland Eur J Wildl Res DOI 10.1007/s10344-016-1011-3