taxonID	type	description	language	source
038687E9FFDDFFC73F0BFF46FE75E4BF.taxon	description	Fossil Taxon. Obdurodon dicksoni (Archer et al., 1992). Specimens. QMF 20568 (Queensland Museum), holotype of Obdurodon dicksoni is a near-complete skull with left and right upper pre-molars and is sufficient for phylogenetic placement. A partial, edentulous dentary (QMF 18977) and several cheek teeth (QM F 18978, QMF 30249, QMF 30716 and QMF 30717) are slightly older, providing the calibration minimum bound. The slightly older cheek teeth closely match the holotype skull for size and “ insertion ” and are near-identical to other dental material from the same site as the skull, thus justifying conspecificity (Archer et al., 1993; Musser and Archer, 1998). Phylogenetic Justification. All formal and informal cladistic analyses of monotremes favour grouping Obdurodon with the modern Ornithorhynchus to the exclusion of tachyglossids (e. g., Musser, 1999; Luo et al., 2007; Rowe et al., 2008). Moreover, Phillips et al. (2009) found high statistical support for an Obdurodon - Ornithorhynchus sister-grouping, for which unambiguous synapomorphies include rostral elements (nasal, maxilla, septomaxilla) forming a board ‘ bill’, a robust posterolateral maxillary process and several endocranial characters (see Macrini et al., 2006). The sister relationship between living ornithorhynchids and tachyglossids is uncontroversial in molecular and morphological studies (e. g., van Rheede et al., 2006; Luo et al., 2007; Phillips et al., 2009). Hard Minimum Age. 15.97 Ma. Soft Maximum Age. 113.0 Ma. Age Justification. Obdurodon dicksoni occurs in Faunal Zones B and C of the Riversleigh local faunas (northwestern Queensland). The holotype is known from the early Middle Miocene Faunal Zone C (Ringtail Site). However, slightly older Ob. dicksoni molars and a partial dentary are known from Faunal Zone B sites (Neville’s Garden and Dirk’s Towers). Early Miocene dates have consistently been attributed to Faunal Zone B sites by biocorrelation (e. g., Black, 1997; Travouillon et al., 2006). More recently Black et al. (2012) noted that U / Pb radiometric dating of speleothems now confirms this timing. However, until the new dates are published I consider the top of the Early Miocene to provide a minimum for Riversleigh Faunal Zone B and hence, for the crown Monotremata divergence. Potential crown monotremes are traceable at least back to the Paleocene (~ 61 Ma) Monotrematum sudamericanum from Argentina, which is known from several ornithorhynchid-like molars (Pascual et al., 1992) and distal femora (Forasiepi and Martinelli, 2003). Earlier (Maastrichtian) well-sampled South American faunas lack any monotremes. However, sparse Australasian fossil records provide no solid evidence for mammal faunas lacking crown monotremes until the Albian Lightning Ridge (Flannery et al., 1995) and Dinosaur Cove (Rich and Vickers-Rich, 2003) faunas. I use the base of the Albian as a soft maximum for Monotremata.	en	Phillips, MJ (2015): Four mammal fossil calibrations: balancing competing palaeontological and molecular considerations. Palaeontologia Electronica (Basel, Switzerland) 1 (7): 1-16, DOI: 10.26879/490, URL: http://dx.doi.org/10.26879/490
038687E9FFDDFFC73F0BFF46FE75E4BF.taxon	discussion	Discussion. In light of sparse fossil records and ‘ platypus’ morphology being ancestral among crown monotremes (see Gregory, 1947; Musser, 2003; Phillips et al., 2009), molecular timetrees calibrated independently of Monotremata have been particularly important for estimating monotreme crown divergence. Modern relaxed-clock molecular dating estimates concur on a Tertiary divergence between the platypus and echidnas, with most estimates falling between 21 - 48 Ma (e. g., Janke et al., 2002; Hugall et al., 2007; Warren et al., 2008). One exception (Rowe et al., 2008) provided mean estimates of 79.5 Ma and 88.9 Ma, although their exclusion of non-mammals prevented accurate estimation of evolutionary rates on either side of the root between monotremes and therians. Rectifying this issue again resulted in mid-Tertiary estimates (Phillips et al., 2009). Hence, molecular dates for the crown monotreme divergence (including the estimates in Table 1) fall within the younger end of the 15.97 - 113.0 Ma bounds. Although the Early Miocene minimum bound for crown monotreme origins is based primarily on the platypus, Obdurodon dicksoni, further support comes from the earliest tachyglossid fossil, the already somewhat derived Gulgong echidna, Megalibgwilia robusta (Dun, 1895). The age of the Gulgong deposit is 13 - 14 Ma, based on estimates from overlying basalt (Woodburne et al., 1985), although this has been contentious, because the fossil preservation is similar to much younger nearby Pleistocene sites (Augee et al., 2006). It does not necessarily follow that the platypus affinity of Obdurodon dicksoni secures crown monotreme placement for the dentally similar Late Oligocene (~ 25 Ma) Obdurodon insignis or Paleocene Monotrematum. None of the unambiguous synapomorphic characters linking Obdurodon dicksoni with Or. anatinus from Rowe et al. (2008) are preserved in either of these older ‘ platypuses’. Determining where Monotrematum and Ob. insignis fall relative to the divergence of the platypus from the edentulous echidnas will require further non-dental material. The suggested basal Albian soft maximum bound for Monotremata is challenged by the recent proposals of Rowe et al. (2008) that the Albian Kryoryctes cadburyi (an isolated, incomplete humerus) could be a stem tachyglossid and the Aptian Teinolophos trusleri (several partial dentaries) is a stem ornithorhynchid. The former suggestion is based on gross morphology and ignores features such as a shallow ulna trochlea and an olecranon fossa, which place the specimen well outside platypuses and echidnas, for which distal humeri are substantially more specialized (Pridmore et al., 2005). Furthermore, Rowe et al. ’ s (2008) placement of T. trusleri depends on numerous redundant characters all based on an enlarged mandibular canal. Without this redundancy, cladistic analyses place T. trusleri outside of crown monotremes with high statistical support (Luo et al., 2007; Phillips et al., 2009). The mid-Tertiary molecular dates for the monotreme crown divergence indicate that the 113.0 Ma maximum softbound is conservative, although necessarily so, reflecting the sparse and fragmentary nature of the monotreme fossil record. In the absence of any narrow temporal range within which stem-crown transitional monotremes appear it may be advisable to employ the monotreme bounds as a uniform prior.	en	Phillips, MJ (2015): Four mammal fossil calibrations: balancing competing palaeontological and molecular considerations. Palaeontologia Electronica (Basel, Switzerland) 1 (7): 1-16, DOI: 10.26879/490, URL: http://dx.doi.org/10.26879/490
038687E9FFD3FFCA3DA5FE06FDF9E6E2.taxon	description	Fossil Taxon. Tanzanycteris mannardi (Gunnell et al., 2003). Specimen. TNM MP- 207 (Tanzanian National Museum), holotype and only specimen of Tanzanycteris mannardi is a partial skeleton including skull, mandibles, vertebral column anterior to the sacrum, shoulder girdle, partial humeri, and left radius. Teeth are unknown. Phylogenetic Justification. Gunnell et al. (2003) identified a suite of characters that place T. mannardi within Yinpterochiroptera, specifically with Rhinolophoidea. These include extremely enlarged cochlea, broadened first rib, and a dorsally flared iliac blade (this later character is also shared with some probable stem chiropterans). In my combined parsimony analysis of morphological data from Gunnell and Simmons (2005) and DNA sequences from Meredith et al. (2011), T. mannardi groups with rhinolophoids with 58 % bootstrap support, while its placement within crown Chiroptera receives 83 % bootstrap support. In this analysis the enlarged cochlea and broadened 1 st rib are unambiguous apomorphies for Rhinolophoidea, including T. mannardi. These characters are highly conserved among bats. The enlarged cochlea is otherwise only known from one species of mormoopid (although, without the enlarged cochlea fenestra) and a similar rib morphology is known from one other genus, Nycteris. Hard Minimum Age. 45.0 Ma. Soft Maximum Age. 58.9 Ma. Age Justification. Tanzanycteris mannardi was recovered from the lacustrine Mahenge locality in north-central Tanzania. Zircon at the base of the Mahenge sequence (~ 1.2 m below the fossil) was 206 Pb / 238 U dated by Harrison et al. (2001) to 45.83 ± 0.17 Ma. The authors also considered sedimentation rates, for which minimum estimates and error on the 206 Pb / 238 U dates allow a minimum bound of 45.0 Ma for T. mannardi and the crown chiropteran divergence. This mid-Eocene age is also consistent with the Mahenge fossil fish fauna (e. g., Murray, 2000). Several possible crown bats with putative yangochiropteran affinities occur in Early Eocene localities (Eiting and Gunnell, 2009). Bats are remarkable among mammals in that accepted crown fossil records are closely bracketed by older stem fossils from all continents except Antarctica (Ravel et al., 2011). Although no stem bats are known from prior to the Eocene, some of these records that may be used to bracket the calibration are very close to the Thanetian-Ypresian boundary and so I use the base of the Thanetian (no older than 58.9 Ma) as a soft maximum for the age of crown Chiroptera.	en	Phillips, MJ (2015): Four mammal fossil calibrations: balancing competing palaeontological and molecular considerations. Palaeontologia Electronica (Basel, Switzerland) 1 (7): 1-16, DOI: 10.26879/490, URL: http://dx.doi.org/10.26879/490
038687E9FFD3FFCA3DA5FE06FDF9E6E2.taxon	discussion	Discussion. Modern bats have traditionally been divided morphologically into the mainly frugivorous or nectivorous Megachiroptera (Pteropodidae, flying foxes, etc.) and the primarily insectivorous Microchiroptera (all other families). Many of the oldest fossil bats share features associated with echolocation and general body form with microchiropterans to the exclusion of megachiropterans and other mammals. This in turn has resulted in some of the earliest bats (e. g., Icaronycteris, Australonycteris) being linked phylogenetically to microchiropterans (Simmons and Geisler, 1998) and used to calibrate the chiropteran crown divergence (e. g., dos Reis et al., 2012). Analyses of multiple nuclear genes (Teeling et al., 2000, 2005) and mitochondrial genomes (Lin et al., 2002) now provide overwhelming evidence for microchiropteran paraphyly, with rhinolophoids grouping with pteropodids. The use of molecular phylogenetic scaffolds have resulted in all Early Eocene bats that have been included in matrix-based cladistic analyses falling as stem chiropterans (Teeling et al., 2005; Simmons et al., 2008), with their “ microchiropteran ” traits found to be plesiomorphic for bats. The finding that incorrect placement of pteropodids distorts character covariation on the tree for inferring the placement of fossil bats (Teeling et al., 2005) is also relevant here. Hermsen and Hendricks’ (2008) molecular scaffold analysis of Gunnell and Simmons’ (2005) morphological matrix clearly favoured rhinolophoid affinities for Tanzanycteris. In contrast, their combined data analysis found this rhinolophoid placement to be equally parsimonious with exclusion of Tanzanycteris from crown Microchiroptera, but with this fossil taxon still falling within crown Chiroptera. By replacing the Teeling et al. (2005) molecular matrix with the nearly 3 - fold longer Meredith et al. (2011) DNA matrix, pteropodids fall back into their expected placement and most parsimonious trees again favour rhinolophoid affinities for Tanzanycteris. Hence, Tanzanycteris might yet prove to be appropriate for calibrating the younger Yinpterochiroptera node. However, only 58 % bootstrap support in the present combined analysis is reason for caution. Additionally, it would have to be shown that exclusion of pteropodids from the Tanzanycteris / Rhinolophoidea grouping is not also an artefact of the morphological homoplasy that attracts pteropodids towards the chiropteran root. Given the historical difficulties for inferring relationships among bats from morphological data, some authors may reasonably consider that a soft, rather than hard minimum bound of 45 Ma is warranted, based on the non-dental Tanzanycteris alone. Support for the minimum bound firms however, when considered in the wider fossil record context. A Tunisian rhinolophoid (dental) taxon described by Sigé (1991) adds slightly older dental evidence for Rhinolophoidea on the same continent. Chiroptera is also very likely constrained to be at least 47 Ma by Tachypteron, which is generally regarded as an emballonurid (Storch et al., 2002), placed on the opposite side of the chiropteran root to Tanzanycteris. More material is needed for the Tunisian rhinolophoid, and Tachypteron is yet to be tested with formal matrix-based phylogenetic analyses, but both push the balance of evidence substantially in favour of Chiroptera being at least as old as the hard minimum bound suggested here. Complete mitochondrial genome molecular dating for the chiropteran crown divergence (~ 54 Ma, Phillips et al., 2009), independent of chiropteran calibrations further supports the hard minimum suggested here being conservative. Bats have relatively low fossil record completeness at the genus level (Eiting and Gunnell, 2009). This may be due in part to often sparse diagnostic characters available at this taxonomic level from mandible fragments and isolated teeth, as well as the restriction of many genera to regions with low preservation potential or that are poorly sampled. At the ordinal level, however, the global bat fossil record is exceptional among mammals in its potential for providing a tight maximum bound. As flying mammals that filled new ecological space, bats first appear early in the Ypresian almost simultaneously in North America, Asia, Europe, Australia, Africa, and South America. In all cases (except for fragmentary dental material of uncertain affinities) these first appearances have been assigned stem, rather than crown placements (Simmons et al., 2008, Tabuce et al., 2009; Ravel et al., 2011; Smith et al., 2007). Hence, it is likely that crown Chiroptera originated in the Ypresian, although I use the base of the Thanetian as a more conservative soft maximum. More primitive stem bats are likely to have been geographically restricted without strong flight and difficult to distinguish from archaic insectivores (Gunnell and Simmons, 2005), but this is not directly relevant to the question of crown Chiroptera calibration. Substantially earlier absence of crown bats is also unlikely to be explained by sampling artefacts. From their first appearance, bats occur in every subsequent sub-epoch in the fossil records of North America, Eurasia, and in at least one of the Gondwanan continents (Gunnell and Simmons, 2005). Most molecular dates for the origin of crown bats fall inside or very close to the bounds suggested here (e. g., Nikaido et al., 2001; Jones et al., 2005; dos Reis et al., 2012). The best estimate from the present study (Table 1, excluding large-bodied clade calibrations) is 55 Ma, coincident with the initial radiation of bats in the fossil record. Several studies have dated crown Chiroptera more than 5 Ma older than the 58.9 Ma maximum suggested here. These studies typically employ multiple calibrations among large-bodied groups with far slower rates of molecular evolution and use possible stem bats (e. g., Ageina, Honrovits) as crown calibrations (e. g., Bininda-Emonds et al., 2007; Meredith et al., 2011) or place a mean prior on the age of Chiroptera that is far older than any recognised bats (e. g., 65 Ma in Teeling et al., 2005). Even without the questionable bat calibrations, re-including the large-bodied clade calibrations in the present study and removing the maximum bound for Chiroptera increases the crown age of bats to 60.2 Ma, with only 13 % of the posterior distribution younger than the maximum bound. Employing the soft maximum bound buffers the influence of the large-bodied clade calibrations and pulls the mean estimate and 65 % of the posterior distribution within the chiropteran calibration bounds (Table 1). This underlines the potential importance of the chiropteran maximum bound for informing models of substitution rate variation in mammalian molecular dating studies.	en	Phillips, MJ (2015): Four mammal fossil calibrations: balancing competing palaeontological and molecular considerations. Palaeontologia Electronica (Basel, Switzerland) 1 (7): 1-16, DOI: 10.26879/490, URL: http://dx.doi.org/10.26879/490
