Archaeohyracidae

Cast of the holotype of Archaeohyrax patagonicus (MACN A52-617) in right lateral (left), dorsal (center), and anterior (right) views.  The specimen was collected by Carlos Ameghino from the Deseadan beds of Chubut, Argentina and was described by Florentino Ameghino.

Archaeohyracids ("ancient hyraxes") traditionally have been one of the most poorly known groups of  notoungulates. They tend to be rare in most faunas in Argentina and until recently, only a single skull had ever been described (the holotype of Archaeohyrax patagonicus.) The earliest representatives of the group appear in Casamayoran faunas and are notable for being among the first taxa in South America to exhibit hypsodont (high-crowned) cheek teeth; hypsodonty is a characteristic feature of even early archaeohyracids, and geologically younger species tend to have increasingly hypsodont teeth. Like interatheriids, archaeohyracids retain a complete, closed dentition; all have a full complement of teeth with only small spaces (diastemata) separating some of the more anterior teeth. The postcranial skeleton of archaeohyracids is unknown, though specimens are likely present in fossil collections from Bolivia and Chile (see below). Despite the group's name, archaeohyracids are in no way related to hyraxes (nor do they closely resemble them). The reconstruction to the left (from Savage and Long, 1986) probably isn't very accurate, but it is one of the few that is out there; no postcranial bones from archaeohyracids have yet been described.      Archaeohyracid teeth, when newly erupted, display the "face" pattern of fossettes typical of other groups of typotheres. In more hypsodont taxa the central fossa and the labial fossettes are lost with wear; the smaller fossettes generally disappear before the larger, more persistent, central fossa. The lower teeth resemble those of hegetotheriids, but retain varying numbers of isolated fossettids that can be diagnostic of various taxa. Phylogenetic studies suggest that archaeohyracids are not a natural (i.e., monophyletic) group, but rather represent a paraphyletic collection of taxa related to hegetotheriids (see cladogram to right from Croft et al., 2003). Both archaeohyracids and hegetotheriids share several derived character states of the skull including a vertical septum in the auditory bulla and a more anterior placement of the carotid foramen (medial to the auditory bulla). In Deseadan faunas where archaeohyracids and hegetotheriids co-occur - such as Salla, Bolivia - specimens of the "advanced" archaeohyracid Archaeohyrax can be difficult to distinguish from specimens of the basal hegetotheriid Prohegetotherium.

Archaeohyracid specimens from the Tinguiririca Fauna, central Chile, in occlusal view. From left to right:  palate of Archaeotypotherium tinguiriricaense with P1-M2 on both sides; right maxilla of Archaeotypotherium pattersoni with P2-M3; fragmentary right mandible of Pseudhyrax eutrachytheroides with m2 talonid and complete m3; palate of Protarchaeohyrax minor with P2-M3 on both sides. For detailed descriptions of these and other archaeohyracids, see Reguero et al., 2003 and Croft et al., 2003.

Interest in archaeohyracids has increased over the past decade due to the discovery of the Tinguiririca Fauna of central Chile and active collecting in the Salla Beds of Bolivia by research groups from the University of Florida and Duke University. In both of these faunas, archaeohyracids are quite common. Besides Argentina, Bolivia, and Chile, archaeohyracids have only been recorded in Uruguay, primarily due to the scarcity of appropriately-aged faunas in other countries. Archaeohyracids are absent from several appropriately-aged faunas, including Santa Rosa (Peru), Tremembé (Brazil), and Moquegua (Peru), though these are probably just sampling artifacts.      Six species of archaeohyracids have been recorded from the Tinguiririca Fauna, the greatest diversity of archaeohyracids known from a single locality.  At least two skulls of Archaeotypotherium tinguiriricaense have been collected and postcranial remains are likely present but unidentified. Archaeohyracids are also abundant at Tinguiririca, accounting for many of the identified specimens.  (Due to the very hard matrix covering these fossils, however, relatively few have been fully prepared.)  The diversity and abundance of Tinguirirican archaeohyracids - all of which are very hypsodont - provide strong evidence that the mammals of Tinguiririca were living in an open woodland or grassland-like habitat. Species from Tinguiririca also have been recorded at some other central Chilean localities.

Archaeohyracid (Archaeohyrax suniensis) upper teeth from Salla, Bolivia in occlusal view; anterior is to the right and specimen on right has been flipped virtually to match left. Both are from collections at the University of Florida. The specimen on the left illustrates relatively unworn teeth from a young individual; the last tooth (M3) has only partially erupted. The specimen on the right illustrates very worn teeth from an older individual. Note the loss of fossettes and the very differently-shaped teeth in the older individual. For detailed descriptions see Billet et al., 2009.

At Salla, Bolivia Archaeohyrax suniensis (see above) is one of the most abundant animals in the fauna; for this reason, a nearly complete ontogenetic series has been recovered, permitting the changes in occlusal morphology with wear to be studied in detail. This species has extremely hypsodont cheek teeth, only forming roots in old individuals. In later stages of wear, the teeth resemble those of hegetotheres in their lack of any enamel folds or fossettes. It is the latest-occurring member of the group. Stratigraphic Range:  Casamayoran (Vacan; ?middle Eocene) to Deseadan (late Oligocene) Geographic Distribution: southern Argentina, northeast Argentina, northwest Argentina, western Bolivia, central Chile, Uruguay Taxonomy:  Order Notoungulata: Suborder Typotheria: Family Archaeohyracidae (this probably is not a monophyletic group) Representative Taxa: Eohyrax, Pseudhyrax, Punahyrax, Archaeotypotherium, Protarchaeohyrax, Archaeohyrax Selected References: Billet, G., B. Patterson, and C. de Muizon. 2009. Craniodental anatomy of late Oligocene archaeohyracids (Notoungulata, Mammalia) from Bolivia and Argentina and new phylogenetic hypotheses. Zoological Journal of the Linnean Society 155:458-509. Croft, D.A. and D. Weinstein. 2008. The first application of the mesowear method to endemic South American ungulates (Notoungulata). Palaeogeography, Palaeoclimatology, Palaeoecology 269:103-114. [Focuses on three species from Salla, Bolivia, including Archaeohyrax] Croft, D.A., M. Bond, J.J. Flynn, M.A. Reguero, and A.R. Wyss. 2003. Large archaeohyracids (Typotheria, Notoungulata) from central Chile and Patagonia including a revision of Archaeotypotherium. Fieldiana: Geology (New Series) 49:1-38. Reguero, M.A., D.A. Croft, G.M. López, and R.N. Alonso. 2008. Eocene archaeohyracids (Mammalia: Notoungulata: Hegetotheria) from the Puna, northwest Argentina. Journal of South American Earth Sciences 26:225-233. Reguero, M.A., D.A. Croft, J.J. Flynn, and A.R. Wyss. 2003. Small archaeohyracids (Typotheria, Notoungulata) from Chubut, Argentina and central Chile: trans-Andean temporal correlation. Fieldiana: Geology (New Series) 48:1-17. Simpson, G.G. 1967. The beginning of the age of mammals in South America. Part II. Bulletin of the American Museum of Natural History 137:1-260. [Describes Eocene archaeohyracids]