Cranial morphology and systematics of an extraordinary sample of the Late Neogene dwarf tapir,Tapirus polkensis(Olsen)

Abstract

The previously poorly known “Tapiravus” polkensis Olsen, 1960 (Mammalia, Perissodactyla, Tapiridae) is now known from abundant, well preserved specimens from both the type area in central Florida and from the Gray Fossil Site (GFS) in eastern Tennessee. The latter has produced over 75 individuals, the greatest number of tapirids from a single fossil site, including many articulated skeletons. Almost all linear measurements taken on skulls, mandibles, and cheek teeth from GFS have coefficients of variation less than 10 (most between 3 and 7), indicating the presence of a single species. However, the sample reveals considerable intraspecific variation for a few key morphologic features, including development of the sagittal crest, outline shape of the nasals, and number and relative strength of lingual cusps on the P1. The Florida sample of T. polkensis is more limited, but has the same state as the GFS sample for all preserved characters of systematic significance, and while the Florida teeth are on average smaller (especially narrower lower cheek teeth), they fall either within or just below the observed range of the Gray Fossil Site population. The new material supports a reassignment of “Tapiravus” polkensis to the genus Tapirus, and demonstrates that the geologic age of the species is significantly younger than previously thought, Hemphillian rather than Barstovian. Tapirus polkensis is the smallest known North American Tapirus, and smaller than any of the extant species in the genus, with an estimated average mass of 125 kg.

Phylogeography of the Mountain Tapir (Tapirus pinchaque) and the Central American Tapir (Tapirus bairdii) and the Origins of the Three Latin-American Tapirs by Means of mtCyt-B Sequences

“…In contrast, the morphometrics of the current T. bairdii seems to be more related with the North-American fossil tapirs (Ferrero and Noriega 2007) [T. johnsoni, T. simpsoni, T. polkenis and T. webbi for the Miocene; T. merriami, T. haysii from the Pliocene and these last two species plus T. veroensis for the Pleistocene; Hulbert 1995Hulbert , 1999Hulbert and Wallace 2005;Spassov and Ginsburg 1999;Tong 2005;Hulbert et al 2009]. This agrees quite well with the molecular data showed here, which showed T. bairdii as belonging to a different lineage.…”

“…However, the discovery of 75 individuals of T. polkensis in the Gray Fossil Site in eastern Tennessee showed that a unique species was present but it had considerable intraspecific variation including development of the sagittal crest, outline shape of the nasals and the number and relative strength of lingual cusps on the P1 (Hulbert et al 2009). This means that some of the quoted fossils found in South-America should belong to T. terrestris.…”

Interspecific variation in the tetradactyl manus of modern tapirs (Perissodactyla:Tapirus) exposed using geometric morphometrics

“…However, these studies often treat Tapirus either as a single morphological unit (e.g., Holbrook, ), or compare only one or two species of Tapirus with extinct tetradactyl perissodactyls (e.g., Radinsky, ; Simpson, ). Recent studies on the extinct tapirs of North America are beginning to increase species counts when performing comparative analyses, albeit with predominantly qualitative techniques (Holanda, Ribeiro, & Ferigolo, ; Hulbert, ; Hulbert et al, ). Using Tapirus as a solitary morphological unit is greatly beneficial for phylogenetic comparisons with more basal tapiromorph perissodactyls, for example, Lophiodon (Holbrook, ) and Colodon (Colbert, ), as it does not require exhaustive character comparisons across all species of tapir through time.…”

Extraordinary claims require extraordinary evidence: a comment on Cozzuol et al. (2013): Fig. 1

“…In fact, the 1st upper molar (M1) of tapirs erupts while the deciduous premolar dentition (dP2-dP4) is still in place. Specimens that retain dP2-dP4 are considered juveniles by most tapir taxonomists (e.g., Simpson 1945;Hulbert et al 2009;Hulbert 2010), who consider only specimens with erupted P4/p4 to be fully grown. Cozzuol et al (2013), however, mention neither premolar eruption nor any other ontogenetic criterion for sample membership in the context of their multivariate morphometric analysis.…”