Published on February 15th, 2021 | by David Marshall
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Episode 121/122: Dietary ecology of Smilodon fatalis
Smilodon is probably one of the most iconic mammalian apex predators with its extended upper canines and robustly-built forearms. In fact, when we compare Smilodon to modern cats (felids), we don’t see these same characteristics. So what were they used for? Was Smilodon specialised for any particular behaviour?
Owing to the unique preservation of the tar seeps at Rancho La Brea, Los Angeles, USA, we can find an overabundance of predators, including Smilodon fatalis, Canis dirus, Panthera atrox and Puma concolor. This allows researchers to reconstruct the predatory landscape of the area in the Pleistocene. Who was eating what? Was there any competition between predators?
All of these questions feed in to the ‘dietary ecology’ of Smilodon and here to discuss that, and more, is Dr Larisa DeSantis of Vanderbilt University.
The DeSantis DREAM Lab (Dietary Reconstructions and Ecological Assessments of Mammals) uses modern, historic, and fossil records to clarify ecological and evolutionary responses to climate change across the globe and throughout the Cenozoic, with a focus on mammalian communities..Larisa DeSantis drilling the teeth of ancient carnivores at the La Brea Tar Pits. Since you are what you eat, the study of Carbon isotopes preserved in layers of enamel of a carnivore can reveal which kinds of plants their prey were eating and thus which environments they were likely to have lived.Study of microwear patterns on the teeth is also another line of evidence. Comparison with modern carnivores can provide a proxy as to the degree of ‘carcass utilisation’ i.e. was it eating just flesh or also bone? Image: Dental microwear textures from a cheetah (C), striped hyaena (D), African lion (E), and Smilodon fatalis. Published in Janis et al. 2019, Peer J.Finite Element Analysis (FEA) is an further line of evidence. This is a tool used in mechanical engineering to simulate stresses in a model. It can reveal whether or not a certain behaviour was mechanically possible. Image: FEA on Smilodon as published in Janis et al. 2019 in Peer J. This study aimed to compare Smilodon fatalis and Thylacosmilus atrox via FEA, morphology and dental microwear textures.The La Brea Tar Pits are a natural asphalt seep located in Los Angeles, USA. The Page Museum is just a stone’s throw from Hollywood. Image: Dr Larisa DeSantis (left) with two former Vanderbilt University undergraduate students, Elizabeth Hall (centre) and Margaret Dorhout (right) during a research trip.The excavations at the La Brea tar pits could easily make for an separate episode of Palaeocast! Image: Dr Larisa DeSantis at Pit 91 at Rancho La Brea.Rancho La Brea collections of the Page Museum. This is just one of the hallways that houses fossils, every drawer is filled with fossils collected over the past 100 years.This episode focuses on the dietary ecology of Smilodon fatalis (foreground) and that of other predators from Rancho La Brea, such as Panthera atrox (background).Lower right jaw of Smilodon fatalis with dental microwear material (blue) setting on the tooth. When dry, the mould is removed with no damage to the teeth. A cast is made at the lab and subsequently analysed under a confocal microscope.Area demonstrating bone growth (circled) after the sabre-tooth lost its right upper canine. Given that the bone shows regrowth, the individual must still have been alive for some time after losing its canine.When looking at the relations between ancient carnivores, Smilodon isn’t placed on the same branch as all other modern felids. Instead it closer-related to other sabre-toothed cats in a sub-family called the machairodonts. Image: Phylogeny of ancient mammals from Janis et al. 2019, published in Peer J.Panthera atrox (front), or the ‘American lion’, was another large felid found in the La Brea tar pits. Studies show that it would have been a solitary hunter and mostly the flesh of its prey.A larger percentage (33%) of Panthera atrox are found with broken teeth, thus demonstrating that they are lost in to solitary take-down of prey.Other predators at the time include the dire wolf (Canis dirus), which represents by far the most common species found at Rancho La Brea. Image: Wall of over 400 dire wolf skulls at the La Brea Tar Pits Museum.Such studies of dietary ecology can help piece together the Pleistocene ecosystem at Rancho La Brea. Understanding how each species lived can help reveal why some went extinct. Such lessons from the past can be applied to modern conservation efforts. Image: Reconstruction of Rancho La Brea by Mauricio Anton.Dr Larisa DeSantis
Unless otherwise stated, all images courtesy of Dr DeSantis.
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