Allqokirus australis (Sparassodonta, Metatheria) from the early Palaeocene of Tiupampa (Bolivia) and the rise of the metatherian carnivorous radiation in South America

Abstract

The present paper describes a disarticulated skull of Allqokirus australis Marshall & Muizon, 1988, a basal sparassodont (Metatheria, Mammalia) from the early Palaeocene (c. 65 Ma.) of Tiupampa (Bolivia). The specimen includes the rostrum and palate with right premaxilla, both maxillae, left lacrimal, palatines and most upper teeth. The second largest element includes the frontals, the left squamosal, the parietals, the supraoccipital, the basisphenoid, the presphenoid, the alisphenoid, and part of the pterygoids. The nasals, basioccipital and exoccipitals are missing. Other elements are the left petrosal, the right jugal and squamosal, and both dentaries. The elements of the specimen allow for a good reconstruction of the skull, which is thoroughly described and compared to that of other sparassodonts and to the Tiupampa pucadelphyids, Pucadelphys and Andinodelphys. The dental morphology of Allqokirus australis is extremely similar to that of Patene simpsoni from the early Eocene of Itaboraí (Brazil) and presents distinct (although incipient) carnivorous adaptations. Furthermore, some characters of the ear region (e.g. medial process of the squamosal, deep groove for the internal carotid artery at the ventral apex of the petrosal) are also present in most other sparassodonts and in the pucadelphyids from the same locality. A parsimony analysis performed on the basis of a data matrix of 364 characters and 38 taxa placed Allqokirus in a sparassodont clade (the Mayulestidae) that also included Mayulestes and Patene. This family constitutes the sister group of all other sparassodonts. Our analysis also retrieved a large clade composed of the sparassodonts and the pucadelphyids, formally named Pucadelphyda n. superord. This superorder represents the large metatherian carnivorous radiation of the Tertiary of South America, which is first known at Tiupampa, and which started to diversify probably slightly earlier, during the late Cretacous in South America. So far, no representative of Pucadelphyda has been discovered in North America. At Tiupampa, Allqokirus and Mayulestes are the largest metatherians of the fauna and they fill the predaceous mammalian ecological niche. They are the earliest representatives of Sparassodonta, a successful metatherian carnivorous radiation which persisted in South America until the late Pliocene, i.e., during more than 63 Ma.

New remains of kollpaniine “condylarths” (Panameriungulata) from the early Palaeocene of Bolivia shed light on hypocone origins and molar proportions among ungulate-like placentals

“…A recent revision of Palaeogene SALMAs agreed with this view and considered a 64 Ma age for the Tiupampan (Woodburne et al 2014a). The age of the Tiupampan has been reconsidered more recently and is regarded as closer to 65 Ma (early Danian), (Muizon et al 2015(Muizon et al , 2018. The Tiupampa mammals have been recovered from beds regarded as belonging to the chron 28r (Marshall et al 1997;Gelfo et al 2009), which, according to Wilson (2013Wilson ( , 2014 and Sprain et al (2015), is bracketed between c. 65 Ma and 64.866 Ma.…”

Chlorocyon phantasma, a Late Eocene Borhyaenoid (Mammalia: Metatheria: Sparassodonta) from the Los Helados Locality, Andean Main Range, Central Chile

“…The pre-late Oligocene record of Sparassodonta is remarkably poor, with most occur¬ rences representing basal sparassodonts (e.g., Patene) or proborhyaenids, a grouping of exclusively Paleogene sparassodonts only distantly related to most Miocene forms (except possibly thylacosmilids; see Babot, 2005;Forasiepi et al, 2015;Engelman et al, 2017). If proborhyaenids are deeply nested within Borhyaenoidea, as is consistently recovered by many studies (Muizon, 1999;Babot et al, 2002;Forasiepi, 2009;Engelman and Croft, 2014;Forasiepi et al, 2015;Suarez et al, 2016;Muizon et al, 2018), then the major lineages of late Cenozoic sparassodonts (e.g., hathliacynids, borhyaenids) must have originated by the mid¬ dle Eocene (Vacan subage of the Casamayoran SALMA), based on the earliest widely accepted occurrence of a proborhyaenid (Babot et al, 2002;Powell et al, 2011), or potentially even the early Eocene, based on possible proborhyaenid remains from the Las Violetas Fauna (Gelfo et al, 2010;Krause et al, 2017). An early or middle Eocene divergence of major sparassodont clades is supported by a recent report of a possible borhyaenid from the middle Eocene locality of La Barda, Argentina (Lorente et al, 2016).…”

“…Acyon myctoderos* UATF-V-000926 Forasiepi et al (2006) Allqokirus australis - Muizon et al (2018) Anachlysictis gracilis - Goin (1997) Arctodictis munizi* - Marshall (1978); Forasiepi et al (2004) Arctodictis Goin et al (2010) Pharsophorus lacerans MACN-A 52-391 Marshall (1978); Patterson and Marshall (1978) Pharsophorus tenax AC 3004 Marshall (1978); Patterson and Marshall (1978) ^Pharsophorus sp.…”

“…Sparassodonts, an extinct group of metatherians, were the predominant mammalian car¬ nivores in South America from the Paleocene (Tiupampan or Peligran South American Land Mammal "Age," or SALMA; Forasiepi and Rougier, 2009;Muizon et al, 2018) to the late early Pliocene (Chapadmalalan SALMA; Goin and Pascual, 1987;Prevosti et al, 2013). Sparassodont finds span the continent, from the La Guajira Peninsula of Colombia (Suarez et al, 2016) to the famous fossil beds of Santa Cruz Province, Argentina (Sinclair, 1906;Prevosti et al, 2012).…”

“…The record of sparassodonts is heavily geographically biased, however, with most fossils coming from Argentina (Forasiepi, 2009) and a few localities in Bolivia (Villarroel and Marshall, 1982;Petter and Hoffstetter, 1983;Muizon, 1998;Forasiepi et al, 2006;Engelman and Croft, 2014;Engelman et al, 2015;Muizon et al, 2018) and Colombia (Marshall, 1977;Goin, 1997).…”