Hsiangolestes, Zheng and Huang, 1984

Ting, Suyin, Wang, Xiaoming & Meng, Jin, 2023, Cranial And Postcranial Morphology Of The Insectivoran-Grade Mammals Hsiangolestes And Naranius (Mammalia, Eutheria) With Analyses Of Their Phylogenetic Relationships, Bulletin of the American Museum of Natural History 2023 (463), pp. 1-129 : 102-105

Hsiangolestes is the most similar to that of Sinosinopa among the Sarcodontidae .

The next node in the majority rule tree, where Prosarcodon and Sarcodon are clustered (fig. 56: node 69), is strongly supported by six dental synapomorphies (chars. 69, 87, 96, 100, 106, 115). Prosarcodon and Sarcodon are sister group in 100% of shortest trees. Prosarcodon , represented by type species P. lonanensis , was originally assigned to Micropternodontidae under Palaeoryctoidea , Soricomorpha , Lipotyphla ( McKenna et al., 1984; McKenna and Bell, 1997). Sarcodon , represented by S. pygmaeus, Matthew and Granger, 1925 , was first referred to order uncertain (? Carnivorous Marsupial). Szalay and McKenna (1971) assigned it to the family Deltatheridiidae, Palaeoryctoidea , Insectivora . It was placed within Micropternodontidae under Palaeoryctoidea , Soricomorpha , Lipotyphla by McKenna and Bell (1997). Postcingulum extending lingual to metaconule (char. 100) shared by Prosarcodon and Sarcodon show more similarities in their dental morphology compared with Hsiangolestes . The distinctive character in Prosarcodon is presence of two molars (char. 70), which indicate that this clade may represent a subfamily of the family Sarcodontidae differing from Hsiangolestes and Sinosinopa as Lopatin (2006) suggested.

In reporting some new Asian early Paleocene to middle Eocene insectivoran-grade mammals, Lopatin and Kondrashov (2004) proposed two lineages of the family Micropternodontidae . They suggested that Prosarcodon lonanensis , Prosarcodon matures ( Lopatin and Kondrashov, 2004) , Sarcodon pygmaeus , Sarcodon minor ( Meng et al., 1998) , Sarcodon zhai ( Huang, 2003) , Hyracolestes ermineus ( Matthew and Granger, 1925) , Metasarcodon udovichenkoi ( Averianov, 1994) , Metasarcodon reshetovi ( Lopatin and Kondrashov, 2004) , and Carnilestes palaeoasiaticus represented a separate Asian micropternodontid lineage and established a new subfamily, Sarcodontinae , under Micropternodontidae . Another proposed lineage, including Asian Hsiangolestes youngi , Sinosinopa sinensis , Bogdia orientalis ( Dashzeveg and Russell, 1985) , and North American Micropternodus and Clinopternodus , was under the subfamily Micropternodontinae . They also mentioned that their Sarcodontinae “clearly differs from Micropternodontinae in lacking the M3/3 and in the absence of the hypoconal shelf on the P4 and M2” ( Lopatin and Kondrashov, 2004: 183). Lopatin (2006) later listed Sarcodontinae and Micropternodontinae under family Micropternodontidae ( Soricomorpha , Lipotyphla ). We propose raising Sarcodontinae to the family level Sarcodontidae . Differing from Sarcodontinae proposed by Lopatin and Kondrashov (2004), the family Sarcodontidae includes Hsiangolestes , Sinosinopa , Prosarcodon , and Sarcodon , whereas Carnilestes is excluded. Although, we did not choose Metasarcodon for phylogenetic analysis, its dental morphology is similar to that of Sarcodon and Prosarcodon . We include it in the family Sarcodontidae . In describing Prosarcodon, McKenna et al. (1984) suggested that Prosarcodon , Sarcodon , and Sinosinopa were soricomorph lipotyphlans, mainly based on the presence of a piriform fenestra in Prosarcodon . Although, a piriform fenestra occurred in some extant soricids, it was considered a primitive character “very like Palaeoryctes ” ( Butler, 1988: 135) and with “moot significance” ( MacPhee and Novacek, 1993: 27), which by itself is insufficient to indicate a Soricomorpha relationship. Therefore, this character was not listed as a valid synapomorphy for the lipotyphlans ( Butler, 1988; MacPhee and Novacek, 1993). The rest of the cranial characters of Prosarcodon described by McKenna et al. (1984) are basically primitive characters for eutherians ( Butler, 1988; MacPhee and Novacek, 1993).

Another clade in the majority rule tree (fig. 56: node 54), clustering 10 lipotyphlan (or eulipotyphlan) genera ( Eosoricodon , Gobigeolabis , Changlelestes, Centedoton , Micropternodus , Blarina , Erinaceus , Luchenus , Eogalericius , and Eochenus ), is strongly supported by six dental synapomorphies (chars. 58, 85, 110, 118, 121, 127). Eosoricodon terrigetta and Gobigeolabis verigranum have been identified as a nyctitheriidid and a geolabidid soricomorph lipotyphlan respectively ( Lopatin, 2006). Changlelestes dissetiformis was identified as a soricomorph ( Tong and Wang, 1993, 2006), and was later considered as an erinaceidid lipotyphlan ( Lopatin, 2006). Micropternodus is in a clade with extant lipotyphlan genera, Blarina and Erinaceus (fig. 56: node 61). The clade is strongly supported by one cranial (char. 156) and six dental synapomorphies (chars. 21, 32, 40, 47, 78, 130). Asian erinaceidid lipotyphlan taxa, Luchenus ernaceanus (Tong and Wang, 2006) , is in a clade with other two Asian erinaceidid lipotyphlan, Eogalericius butleri (Lopatin, 2004) and Eochenus sinensis ( Wang and Li, 1990) (fig. 56: node 58). This clade is supported by one cranial (char. 143) and eight dental synapomorphies (chars. 40, 49, 58, 66, 84, 85, 91, 113). The family Sarcodontidae and the lipotyphlan clade are paraphyletic (fig. 56).

It is beyond the scope of our work to consider the higher-level relationships of lipotyphlan mammals in detail, but we will make some brief comments on the issue related to the phylogenetic relationship of Hsiangolestes . The order Lipotyphla today include families Erinaceidae , Soricidae , Talpidae , and Solenodontidae ( Asher, 2018b) . Butler (1988) proposed six derived characters supporting the monophyly of the Lipotyphla ( Erinaceidae and Soricomorpha ), including absence of the cecum, reduction of the pubic symphysis, large maxillary contribution to the orbital wall, mobile snout or proboscis, reduction of the jugal, and the hemochorial placenta. MacPhee and Novacek (1993) later reviewed the six characters and suggested that absence of the cecum, reduction of the pubic symphysis, and large maxillary contribution to the orbit (less certainly) can be considered as the basis for defining Lipotyphla as a monophyletic group, while the other three characters are inappropriate. Unfortunately, the pelvic girdle of Hsiangolestes described in this paper did not preserve the relevant part of the pubic symphysis. Almost all extant lipotyphlans show a large maxillary contribution to the orbital wall, and the maxilla interposes between the lacrimal and the frontal dorsally and the palatine ventrally, separating the palatine from the lacrimal and the frontal ( MacPhee and Novacek, 1993). In Hsiangolestes , the frontal extends deeply ventrally and occupies the most anterior part of the orbital wall, so that the maxilla is almost fully excluded from the orbital wall and contributes only a very small portion to the lower aspect of the orbital wall. The maxilla mainly comprises the anterior part of the orbital floor. There is no contact between the maxilla and the frontal in the medial wall of the orbit, because of a large intrusion of the palatine bone in that region. In Hsiangolestes , the maxilla does not separate the palatine from the lacrimal and the frontal as in the lipotyphlans; instead, it is more similar to the leptictids in this aspect. For reference, we also compare Hsiangolestes to the lipotyphlans in some other characters proposed by Butler (1988). Hsiangolestes differs from the lipotyphlans in having a longer infraorbital canal, large jugal, normal postglenoid process, and obliquely positioned tympanic membranes.

The taxa included in the Sarcodontidae have been referred to the family Micropternodontidae ( McKenna et al., 1984; Ting and Li, 1987; Ting, 1998; Lopatin and Kondrashov, 2004; Lopatin, 2006). The family Micropternodontidae Stirton and Rensberger, 1964 (= Micropternodidae Stirton and Rensberger, 1964) was originally established only for the North American taxon, Micropternodus , including M. (Kentrogomphios) borealis and M. morgani . The phylogenetic position of Micropternodus has been controversial since it was first reported ( Matthew, 1903). Matthew (1903: 205) considered that the genus “must be placed among the Zalambdodonta, with no very near relatives among living species, although it is not so strikingly different from modern types.” It has been also placed within Solenodontidae ( Schlaikjer, 1933; Scott and Jepson, 1936), Nyctitheriidae ( White, 1954; McDowell, 1958), Apternodontidae ( Hough, 1956) , “insectivorans” in a broad sense ( Russell, 1960), and Erinaceoidea ( Stirton and Rensberger, 1964). In his overall review of insectivorans, Van Valen (1966) first included the Asian taxon, Sarcodon pygmaeus , in micropternodontid and later established a new order Deltatheridia , in which he listed Sarcodon with Micropternodus , as other Palaeoryctidae under his new order, and a year later, he grouped Sarcodon and Micropternodus in the family Micropternodontidae in the order Deltatheridia ( Van Valen, 1967) . Van Valen (1966: 61) mentioned considerable similarities between Sarcodon and Micropternodus , but the prominent characters are the “development of the metacrista and the general configuration of the hypocone region.” Szalay and McKenna (1971: 287, 288) realized that the lower dentition of Sarcodon differs from that of Micropternodus , and suggested that “the similarity of the upper molars of Sarcodon , but not the lower molars, to those of Micropternodus is the result of convergence” and that “ Micropternodus is probably a nyctitheriid insectivore, but we hold that Sarcodon is similar to Micropternodus partly because nyctitheres originated from Cretaceous palaeoryctoid stock via Batodon .” McKenna et al. (1984), however, reconsidered that Micropternodus is similar to Asian Sinosinopa , Sarcodon , and Prosarcodon , among palaeoryctoids and palaeoryctoid-like derivatives, because it has Sarcodon -like hypocones on P4–M2. Although McKenna et al. (1984: 13) realized that the highly specialized snout of Micropternodus separates it from Asian genera by a considerable morphological distance, the authors mentioned “they do not alter cladistics relationships based upon postulated sharedderived cheek-tooth patterns” and included Prosarcodon , Sarcodon , and Sinosinopa in Micropternodontidae under superfamily Palaeoryctoidea of order Soricomorpha ( McKenna et al., 1984) . The major character to connect Sarcodon to Micropternodus provided by both Van Valen (1966) and McKenna et al. (1984) is an enlarged jutting hypocone and expanded hypoconal shelf. Actually, the dental morphology of Sarcodon is very different from that of Micropternodus . The hypocone in Sarcodon is smaller and situated much further lingually than the protocone, and the hypocone shelf is smaller and expanded linguoposteriorly. The upper molar of Sarcodon is basically triangular. On the other hand, the hypocone in Micropternodus is larger and aligned with the protocone, and the hypocone shelf is largely expanded posteriorly, so that the upper molar of Micropternodus is square. Butler (1988: 135) suggested that Micropternodus “is much too specialized to be considered as a primitive soricomorph; more probably it is a palaeoryctoid that has paralleled the Soricomorpha in some respects.” Our study supports the monophyletic clade Sarcodontidae for Asian taxa Hsiangolestes , Prosarcodon , Sarcodon , and Sinosinopa . Micropternodus is excluded from this clade, indicating that Micropternodus is not related to Asian forms previously assigned to “micropternodontids” (now sarcodontids). We agree with Asher (2002: 109) that the “affinity of Micropternodus must await an analysis that has a better sample of erinaceomorphs, soricomorphs, palaeoryctids, and Asian micropternodontids.” We suggest that the family Micropternodontidae may best be restricted to Micropternodus borealis and its North American allies, as Stirton and Rensberger (1964) had proposed.