Flat-headed Peccary - Platygonus compressus

Taxonomy

Platygonus compressus, often known as the flat-headed peccary, is an extinct tayassuid from North America. Described from Illinois remains in 1848 by John LeConte, it is the type species of the prolific genus Platygonus. As many as seventeen species have been described from this genus over the years, not including other genera and species that have been synonymized with species of Platygonus (1). Most of these have been ascribed to intraspecific variation, and as of 2021, there are six North American species considered to be valid. Out of these, only one species, P. compressus, persisted into the latest Pleistocene, with the others being known from the Miocene into the mid-Pleistocene (2).

P. compressus is quite similar to its congeners apart from cranial differences and size. Earlier, less derived Platygonus species had more exaggerated facial features, with zygomatic processes that would have made them superficially resemble warthogs. P. compressus had a more streamlined face with smaller processes, which were often absent altogether on female specimens. This species was also somewhat smaller than its earlier relatives, despite being quite large by modern peccary standards (2).

The flat-headed peccary, along with the rest of its genus and the modern peccaries, belongs to the tribe Tayassuini (1, 2). The genus bears a close resemblance with the extant Chacoan peccary (Parachoerus/Catagonus wagneri), causing some to suggest they are sister taxa (3). However, molecular and morphological analyses seem to agree that Platygonus and its closest relatives (a few Neotropical genera) are sister to a clade containing all three extant peccaries (2, 4). The tribe would have evolved in the Nearctic during the late Miocene and Pliocene before spreading into South America and giving rise to the extant species.

The closest relative of P. compressus is likely P. vetus, an Irvingtonian – early Rancholabrean species of a large size and flaring facial features (2).         

Distribution and Age

While earlier species of Platygonus can be traced as far back as the Miocene, P. compressus is currently understood to be a late Pleistocene species. Former, more inclusive descriptions of the species included specimens dated as far as the early Pliocene, but this is no longer the case. Regardless, P. compressus went extinct at the end of the Pleistocene along with the vast majority of the continent’s other megafaunal species (1, 2).

The sheer geographic range of this species is unmatched by any other peccary species known apart from perhaps the extant collared peccary (Dicotyles tajacu). P. compressus occupied a wide range of habitats across the breadth of the continent, from the Yukon to northern Mexico, and from the Pacific coast of California to the Atlantic shores of Florida and New York (1, 2, 5). Particularly large populations existed in the Appalachians and Ozarks (3). Such a distribution suggests a degree of habitat plasticity unmatched by extant tayassuids.

An adaptable species with a wide range, capable of persisting in many different habitats and climates and sustaining itself on a wide variety of foods, it seems unlikely that this species perished due to climate change. Ancient DNA analysis revealed no sign of genetic diversity loss prior to their sudden extinction (4). Some have postulated that the low number of sites preserving evidence of peccary hunting by humans is indicative of a lack of interaction between this species and ours (6). However, it has been noted that peccaries are an uncommon component of fossil sites in general; only a few individuals of P. compressus were recovered from Rancho La Brea despite it being well within their geographic range and a fruitful site for the preservation of megafaunal fossils (2). Regardless, Platygonus bones have been found at palaeo-Indian fossil sites, indicating humans hunted them to some degree (7).

Morphology and Ecology

The flat-headed peccary was an exceedingly variable species, with notable differences in body size and proportions between different populations. Significantly more gracile than its forebears such as Platygonus vetus, it was one of the smaller and slimmer members of its genus. The average adult has been estimated at 44 kg, and a degree of sexual size dimorphism can be observed (2, 3). The species is long-legged, with a proportionally-short humerus, suggesting it was more cursorial than extant peccaries (8). Such capabilities would’ve been beneficial when sharing open habitats with species such as American lions and cheetahs.

In life, it would have most closely resembled the extant Chacoan peccary, its closest extant ecological (but not taxonomic) analogue (2, 3). A short but large nasal cavity would’ve helped warm and filter inhaled air, and downturned upper tusks would have been helpful for foraging, defense against predators, and intraspecific combat (2). A covering of coarse, shaggy fur is likely, though it was likely thicker than modern peccaries, at least at certain times of year and certain parts of its range.

As previously mentioned, an exceptionally wide range of habitats can be inferred for this species from the distribution of its remains. P. compressus seems to have preferred closed environments such as forest and shrubland, but also would’ve been comfortable in grassland and savanna habitats. Climatic tolerances ranged from humid to arid, and subpolar to subtropical (2, 9, 10, 11).

P. compressus is also well-known for having occurred in caves, with remains of up to 650 individuals having been found in one cavern, with groups of 70-100 being common (1, 2, 3, 6, 8). In fact, most of the fossils known of this species have been recovered from caves. It is relatively uncommon in many above-ground fossil deposits, but can make up 90% of the fauna from cave sites (2). This behavior allowed groups to take shelter from adverse weather conditions, like heavy snowfall and frigid temperatures (8, 12, 13). While not uncommon amongst other North American megafauna at the time (short-faced bears, ground sloths, etc.), cave sheltering is relatively atypical behavior for peccaries and ungulates in general, making Platygonus rather unique in this regard. Regardless, this behavior was likely responsible for the species’ existence in far northern rangelands. Even with sheltering behaviors, occurrence at such high latitudes is indicative of a cold tolerance unheard of in extant tayassuids.

P. compressus is thought to have occurred in sounders of various sizes, numbering up to 100 individuals, similar to modern peccaries but unlike Mylohyus (3). Sounders were mostly made up of younger individuals, and mating events were synchronous and seasonal, both of which match up with what is known of the life histories of extant peccaries (12). The species coexisted with Mylohyus fossilis over most of its range, as well as the collared peccary in Florida and the southwest, indicating a system of niche partitioning was in place (14).

The diet of the flat-headed peccary was likely not dissimilar from modern peccaries; omnivorous and generalist, consuming a mixture of foliage, fruit, tubers, and animal matter (9, 10, 11). Analysis of dental microwear suggests that, while this species was highly adaptable and able to alter its diet in synchrony with shifting vegetation communities, it appears to have consumed a great deal of tough (mostly C3) plant materials; silicaceous grass, rough leaves and forbs, legumes, and cacti, more so than its sympatric relative Mylohyus (9, 11).

The species was an important prey item of the dire wolf (Aenocyon dirus), and likely a large contingent of other Pleistocene carnivores, including red wolves, dhole, American lions, American cheetahs, jaguars, cougars, sabre-toothed cats, bears, and crocodilians (6, 8).

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References

1.       Platygonus. The Palaeobiology Database. Retrieved from https://paleobiodb.org/classic/basicTaxonInfo?taxon_no=42437

2.       Prothero, Donald R. (2021). The systematics of North American peccaries (Mammalia: Artiodactyla: Tayassuidae). New Mexico Museum of Natural History & Science Bulletin 85. Alburquerque, New Mexico.

3.       Flat-headed Peccary, Platygonus compressus. Illinois State Museum. Retrieved from http://iceage.museum.state.il.us/mammals/flat-headed-peccary-0.

4.       Perry, Tahlia & van Loenen, Ayla & Heiniger, Holly & Lee, Carol & Gongora, Jaime & Cooper, Alan & Mitchell, Kieren. (2017). Ancient DNA analysis of the extinct North American flat-headed peccary (Platygonus compressus). Molecular phylogenetics and evolution. 112. 10.1016/j.ympev.2017.03.024.

5.       Beebe, B.. (2011). Pleistocene peccary, Platygonus compressus Le Conte, from Yukon Territory, Canada. Canadian Journal of Earth Sciences. 17. 1204-1209. 10.1139/e80-126.

6.       Wilson, Kurt M., "Late Pleistocene extinction of the flat-headed peccary on the Ozark Plateau: Paleozoological insights from Peccary Cave, Arkansas" (2017). Graduate Theses and Dissertations. 15461

7.       Brian G. Redmond, PhD., Curator of Archaeology (March 2006). "Before the Western Reserve: An Archaeological History of Northeast Ohio" (PDF). The Cleveland Museum of Natural History. p. 2. Retrieved January 28, 2020.

8.       Nye, April Season, "Pleistocene Peccaries from Guy Wilson Cave, Sullivan County, Tennessee." (2007). Electronic Theses and Dissertations. Paper 2115. https://dc.etsu.edu/etd/2115

9.       Bradham, Jennifer & DeSantis, Larisa & Jorge, Maria Luisa & Keuroghlian, Alexine. (2018). Dietary variability of extinct tayassuids and modern white-lipped peccaries ( Tayassu pecari ) as inferred from dental microwear and stable isotope analysis. Palaeogeography, Palaeoclimatology, Palaeoecology. 10.1016/j.palaeo.2018.03.020.

10.   Yann, Lindsey & DeSantis, Larisa. (2014). Effects of Pleistocene climates on local environments and dietary behavior of mammals in Florida. Palaeogeography, Palaeoclimatology, Palaeoecology. 414. 370–381. 10.1016/j.palaeo.2014.09.020.

11.   Schmidt, Christopher. (2008). Dental microwear analysis of extinct flat-headed peccary (Platygonus compressus) from southern Indiana. Proc. Indiana Acad. Sci.. 117. 95-106.

12.   Aaron & Schubert, Blaine. (2019). Seasonal denning behavior and population dynamics of the late Pleistocene peccary Platygonus compressus (Artiodactyla: Tayassuidae) from Bat Cave, Missouri. PeerJ. 7. e7161. 10.7717/peerj.7161.

13.   Finch, W. I., Whitmore, F. C., & Sims, J. D. 1972. Stratigraphy, morphology, and paleoecology of a fossil peccary herd from western Kentucky. US Government Printing Office.

14.   Hulbert, Richard & Morgan, Gary & Kerner, Andreas. (2009). Collared peccary (Mammalia, Artiodactyla, Tayassuidae, Pecari) from the late Pleistocene of Florida.