Neohelos
Creators: name: Beck, Robin M. D.
name: Voss, Robert S.
name: Jansa, Sharon A.
Publisher: name: Zenodo
Year: 2022
Subjects: Biodiversity
Taxonomy

description: †Diprotodontoidea Gill 1872   CONTENTS: † Neohelos, † Ngapakaldia, † Nimbadon, and † Silvabestius.   
STEM AGE: 30.5 Mya (95% HPD: 27.3–34.1 Mya).  
CROWN AGE: 24.4 Mya (95% HPD: 20.2–27.9 Mya).  
UNAMBIGUOUS CRANIODENTAL SYNAPOMORPHIES: Extensive pneumatized endocranial sinuses present within parietal (char. 33: 0→1; ci = 0.500); principal labial and lingual cusps of upper molars connected by well-developed lophs (char. 144: 1→2; ci = 0.200); paraconids and paracristids indistinct or absent on m2 and m3 (char. 161: 0→1; ci = 0.667); cristid obliqua absent or indistinct (char. 167: 0→1; ci = 0.500); and m3 hypoconid lingual to salient protoconid (char. 173: 0→1; ci = 0.045).  
 COMMENTS: Beck et al. (2020: table 1) defined †Diprotodontoidea as the most inclusive clade including † Diprotodon opatum, but not Phascolarctos cinereus, Thylacoleo carnifex or Vombatus ursinus. Following Archer and Bartholomai (1978), the superfamily †Diprotodontoidea is currently considered as comprising the families † Diprotodontidae and † Palorchestidae (see also Archer, 1984c; Archer et al., 1999; Long et al., 2002; Archer and Hand, 2006; Black, 2008; Black et al., 2012b). We have not included any palorchestids (the so-called marsupial tapirs; Bartholomai, 1978a; Archer, 1984c; Flannery and Archer, 1985; Murray, 1986, 1990; Archer et al., 1999; Long et al., 2002; Archer and Hand, 2006; Black, 2006, 2008; Mackness, 2008; Black et al., 2012b; Trusler, 2016; Trusler and Sharp, 2016; Richards et al., 2019) as terminals here, so we cannot distinguish between craniodental apomorphies for †Diprotodontoidea and those for † Diprotodontidae; however, future inclusion of palorchestids should reveal which apomorphies apply to †Diprotodontidea and which are specific to † Diprotodontidae.   
Of the four unambiguous craniodental synapomorphies identified here, three are related to molar morphology, specifically: (1) the presence of well-developed lophs connecting the principal labial and lingual cusps of the upper molars (the fully lophodont condition, also seen in most macropodiforms; char. 144), (2) absence of distinct paraconids or paracristids from m2 and m3 (whereas these structures are retained in fully lophodont macropodiforms; char. 161), and (3) absence of a distinct cristid obliqua (whereas this crest is well developed and forms a midlink on the lower molars of fully lophodont macropodiforms; char. 167).  
 The oldest diprotodontoids (including members of the family † Diprotodontidae) date to the late Oligocene (Archer et al., 1999; Long et al., 2002; Archer and Hand, 2006; Black, 2008; Black et al., 2012b), and the first diversification among the diprotodontid taxa included here is estimated as having occurred in the late Oligocene or early Miocene. †Diprodontidae includes the largest known marsupials, reaching an extreme with Pleistocene forms such as † Zygomaturus and † Diprotodon, which have not been included here due to their extremely derived craniodental morphologies (Archer, 1984c; Archer et al., 1999; Long et al., 2002; Wroe et al., 2004; Archer and Hand, 2006; Black, 2008; Price, 2008; Price and Piper, 2009; Black et al., 2012b).
description: Published as part of Beck, Robin M. D., Voss, Robert S. & Jansa, Sharon A., 2022, Craniodental Morphology And Phylogeny Of Marsupials, pp. 1-353 in Bulletin of the American Museum of Natural History 2022 (457) on page 231, DOI: 10.1206/0003-0090.457.1.1, http://zenodo.org/record/6971356