Nortedelphys minimus UCMP
|
publication ID |
https://doi.org/ 10.26879/1177 |
|
persistent identifier |
https://treatment.plazi.org/id/1A3B87CC-FFE2-B466-07D0-F8FE3B65FCEE |
|
treatment provided by |
Felipe |
|
scientific name |
Nortedelphys minimus UCMP |
| status |
|
Nortedelphys minimus UCMP 72211 inv
-
-
-
-
0.002
0.027
0.001
0.004
-
0.028
0.019
0.093
0.002
0.015
0.011
0.027
0.073
-
0.020
0.002
0.003
0.021
0.026
0.026
0.001
0.002
0.004
0.006
0.013
0.203
0.156
0.103
0.131
0.005
0.030
0.004
0.002
0.017
0.001
0.004 0.002 - 0.529 0.466*
0.005 0.004 - 0.725 0.266
0.006 0.004 - 0.799 0.191
0.012 0.008 - 0.692 0.288
0.026 0.021 - 0.671 0.280
0.435 0.185 0.029 0.086 0.239
0.010 0.008 - 0.770 0.211
0.060 0.042 - 0.564 0.330
0.001 0.001 - 0.846 0.153
0.375 0.195 0.013 0.137 0.251
0.192 0.115 0.014 0.211 0.450
0.442 0.394* 0.003 0.038 0.029
0.044 0.029 - 0.611 0.314
0.403 0.141 0.020 0.113 0.307*
0.292* 0.121 0.005 0.225 0.346
0.349 0.156 0.055 0.086 0.328*
0.444 0.291 0.033 0.048 0.112
0.003 0.002 - 0.815 0.180
0.171 0.120 0.006 0.282 0.401
0.037 0.031 - 0.724 0.205
0.159 0.049 0.004 0.259 0.526
0.236 0.145 0.006 0.249* 0.343
0.227 * 0.169 0.003 0.298 0.277*
0.312 0.181 0.008 0.196 0.278*
0.011 0.009 - 0.669 0.311
0.022 0.016 - 0.530 0.430*
0.070 0.044 0.001 0.515 0.367
0.068 0.044 0.002 0.370 0.510
0.128 0.061 0.118 0.082 0.597
0.388 0.375* 0.027 0.002 0.005
0.397 0.251 0.193 - 0.003
0.436 0.383* 0.007 0.034 0.037
0.435 0.331* 0.060 0.011 0.032
0.073 0.044 0.003 0.358 0.518
0.312 0.189 0.010 0.180 0.279*
0.073 0.039 0.001 0.423* 0.460
0.021 0.017 - 0.567 0.393
0.170 0.141 0.001 0.446 0.226
0.013 0.013 - 0.706 0.267
nine instances in which specimens of the same extinct species were classified differently from one another ( Tables 9–10). In seven out of nine cases of the extant species, slight differences in wear among the specimens may have led to the different dietary assignments. In the other two cases, we did not detect differences in the amount of wear between the specimens of the same species. In both those cases, one specimen was classified as an invertivore and the other as a soft-invertebrate specialist, highlighting the substantial overlap in morphospace of these two invertebrate-eating diets ( Figure 3 View FIGURE 3 ). Thus, we highlight the need for further standardization and ground truthing of DTA methods. We recommend that whenever possible, studies should attempt to account for intraspecific variation by sampling more than one specimen per species and by controlling for wear across and within taxa.
Dietary Inferences and Dietary Diversity of NALK Metatherians
Although most Mesozoic mammals have conventionally been portrayed as small-bodied, terrestrial invertivores (e.g., Van Valen and Sloan, 1977; Kielan-Jaworowska et al., 2004), recent fossil discoveries and ecomorphological analyses have provided counterexamples, both among non-therians and therians, implying a much broader range of ecologies (e.g., Luo, 2007; Wilson et al., 2012; Grossnickle and Polly, 2013; Chen et al., 2019; Grossnickle et al., 2019). Our quantitative study of dental ecomorphology in part reinforces the conventional view by reconstructing most NALK metatherians (81%, 34 of 42 species) as either invertivores or soft-invertebrate specialists ( Tables 10, 12; Figure 6 View FIGURE 6 ). These results are consistent with previous inferences from other studies using other methods (Gordon, 2003; Wilson, 2013; Williamson et al., 2014; Grossnickle and Newham, 2016) and with the observation that the most taxonomically rich families of Cretaceous metatherians (e.g., alphadontids and pediomyids) have conservative tribosphenic molar morphologies. Nevertheless, our DFA diet reconstructions predicted that a few NALK metatherians had diets beyond invertivory, indicating that NALK metatherians as a whole achieved greater dietary diversity than is conventionally portrayed. For example, our DFA reconstructed Glasbius as a plant-dominated omnivore, a prediction that is in line with previous interpretations that this taxon was either herbivorous or frugivorous (Clemens, 1966, 1979; Gordon, 2003; Kielan-Jaworowska et al., 2004; Wilson, 2013; Williamson et al., 2014). Overall, we see evidence of the following diets in NALK metatherians: invertivory, carnivory, animal- and plant-dominated omnivory (including durophagy), and likely frugivory.
Dietary predictions for several taxa in our study conflicted with diet inferences from previous studies. In each case, however, the diet classification with the second highest posterior probability in our DFA matched with previous diet inferences. These taxa and their alternative diet classifications include (i) Iugomortiferum thoringtoni as a plant-dominated omnivore, (ii) Apistodon exiguus as an invertivore, and (iii) Alphadon halleyi , Alphadon wilsoni , and Protalphadon foxi as soft-invertebrate specialists. Below we discuss the diet reconstructions of these taxa in more detail.
Seven taxa ( Pariadens kirklandi , Eoalphadon lillegraveni , Apistodon exiguus , Alphadon halleyi , Alphadon wilsoni , Turgidodon lillegraveni , Protalphadon foxi ) were reconstructed in our DFA as plant-dominated omnivores. Most of these taxa lack most of the gross morphological features (e.g., large talonid basin, large protocone, bunodont cusps) characteristic of the crushing and grinding function necessary for most plant-based diets. Instead, most of these taxa have the conservative tribosphenic molar morphology (e.g., sharp shearing crests and unexpanded protocones) that is typically found among invertivores (e.g., Cifelli, 1990; Johanson, 1996; Davis, 2007; Williamson et al., 2014; Cohen, 2018). Such discrepancies between our diet reconstruction and those from previous studies are expected, considering the difficulty that the DFA model had in correctly predicting animal-dominated omnivory, and to a lesser extent, plant-dominated omnivory, frugivory, and carnivory. For Pariadens kirklandi , Eoalphadon lillegraveni , and Turgidodon lillegraveni , the second highest posterior probabilities were for the animal-dominated omnivore category, and posterior probabilities of other dietary categories were much lower ( Table 10); this provides additional evidence for omnivory despite the dearth of supportive qualitative evidence. We consider there to be less overall evidence of omnivory for Apistodon exiguus , Alphadon halleyi , Alphadon wilsoni , and Protalphadon foxi ; instead invertivore or soft-invertebrate specialist may be a more plausible diet reconstructions for these taxa. Evidence for Apistodon exiguus being an invertivore includes its very small body size, previous interpretations of its gross dental morphology ( Williamson et al., 2014), and invertivory having the second highest posterior probability for this taxon in our DFA. The interpretations of Alphadon halleyi and Alphadon wilsoni as soft-invertebrate specialists are in line with analyses of the jaw morphology (Grossnickle and Polly, 2013; Brannick and Wilson, 2020; Morales-García et al., 2021), gross dental morphology (Gordon, 2003; Wilson, 2013; Grossnickle and Newham, 2016), and the DFA results, in which the soft-invertebrate specialist category has the second highest posterior probability for both of these species. Evidence for P. foxi as a soft-invertebrate specialist includes its dietary classification in a similar DTA study on lower molars ( Smith, 2017) and our DFA results, in which the soft-invertebrate specialist category has the second highest posterior probability (within 0.10 of the highest posterior probability) for this taxon. Thus, we consider Apistodon exiguus , Alphadon halleyi , Alphadon wilsoni , and Protalphadon foxi to likely have had insect-dominated diets, but the DTA and DFA results indicate that their diets also had a plant component; this is consistent with the view of the ancestral tribosphenic molar morphology being adapted for consuming both animal and plant materials (Butler, 1972).
Our DFA reconstructed different diets for the two specimens of the relatively large-bodied Didelphodon vorax ; one specimen as an invertivore and one as an animal-dominated omnivore. We favor the animal-dominated omnivore classification because it is in line with previous interpretations that D. vorax was a predator-scavenger with durophagous capabilities (Clemens, 1966, 1968, 1979; Fox and Naylor, 1986, 2006; Wilson et al., 2016; Brannick and Wilson, 2020) or an omnivore as indicated by dental microwear ( Wilson et al., 2016). The bulbous premolars of Didelphodon are well suited for crushing hard objects, like bone and shells (Clemens, 1966; Fox and Naylor, 1995, 2006; Wilson et al., 2016; Cohen, 2018). One possible explanation for the invertivore reconstruction of one specimen is that we used relatively unworn molars (earlier ontogenetic wear stage) of Didelphodon in our analysis. That is, Didelphodon and other stagodontids may have experienced an ontogenetic shift in diet that tracks body size (Fox and Naylor, 1995, 2006; Peng et al., 2017) with younger individuals having been more faunivorous (e.g., molars with enhanced postvallum/prevallid shear and dentary shapes more capable of withstanding dorsoventral bending forces) and older individuals having been omnivorous/durophagous (e.g., horizontally worn grinding platforms and dentary shapes more capable of withstanding mediolateral forces; Fox and Naylor, 1995, 2006; Peng et al., 2017; Brannick and Wilson, 2020). Moreover, having analyzed only molar morphology, we did not account for critical dietary data from other tooth positions, such as premolars ( Wilson, 2013; Smith, 2017). We suggest that future studies more deeply explore potential biases by comparing dietary inferences from DTA on a single tooth position to those from larger functional units like cheek tooth rows (Evans et al., 2007; Wilson et al., 2012). In a similar manner, further study of tooth wear as it relates to ontogenetic stage, functional efficiency, and dietary preference could lend important nuance to the dietary characterization of extinct taxa in studies using DTA ( Ungar, 2010). Another productive line of inquiry for other taxa would be to compare dietary inferences from DTA to those from other quantitative methods that are independent of gross morphology of teeth (e.g., microwear, isotopic analyses, mandibular bending strength), as has been done for Didelphodon ( Wilson et al., 2016; Brannick and Wilson, 2020).
Although our DFA classified Iugomortiferum thoringtoni as a carnivore, this taxon has lowcrowned molar morphology with inflated cusps and weakly developed conules (Cifelli, 1990), all of which is inconsistent with interpretation of carnivory (de Muizon and Lange-Badré, 1997). The DNE value of I. thoringtoni is within the range of extant carnivores, plant-dominated omnivores, and frugivores, whereas its RFI value is within the range of extant carnivores, plant-dominated omnivores, and invertivores. Further, its low OPCR value is within the range of extant carnivores and invertivores. The OPCR value of I. thoringtoni may be underestimated because we used an epoxy cast of the specimen (OMNH 20936) and the small size of the specimen might have amplified any infidelities of the cast (although see discussion of cast fidelity and OPCR values in López-Torres et al., 2017). In addition, we analyzed only one specimen of I. thoringtoni , which has some wear and an uncertain identification of its position in the molar series (“M1?” in Cifelli, 1990). Taking these considerations into account, we consider it very likely that I. thoringtoni was a plant-dominated omnivore rather than a carnivore, and further studies are needed to resolve this issue.
Metatherian Ecomorphology through the Late Cretaceous
By the beginning of the Late Cretaceous (ca. 100 Ma) metatherians in North America had diversified into at least four clades (Deltatheriidae, Stagodontidae , Aquiladelphidae , Alphadontidae , and possibly Glasbiidae , Pediomyidae , and Marsupialia were also present, see Wilson et al., 2016). This higher-level taxonomic diversification was associated with moderate dietary diversity—three of the six dietary categories that we recognize here (plant-dominated omnivory, invertivory, and soft-invertebrate specialists; Figure 6 View FIGURE 6 ; Tables 10, 12). Raw species richness peaked in the Judithian (32 recognized species) and stayed relatively high in the Lancian leading up to the K-Pg mass extinction (22 species), although this peak might shift earlier in time or flatten if we account for differential sampling intensity through the Late Cretaceous (e.g., Grossnickle and Newham, 2016; Cohen, 2018; Bennett et al., 2018; Cohen et al., 2020). Nevertheless, according to our results, dental ecomorphological disparity did not significantly change throughout the Late Cretaceous and only in the Lancian did ecomorphological diversity (number of diet categories) increase slightly to include animal-dominated omnivory ( Figures 5–6 View FIGURE 5 View FIGURE 6 ). Indeed, over 80% of the taxa sampled (34 of 42) were interpreted as either invertivores or soft-invertebrate specialists ( Table 12; Figure 6 View FIGURE 6 ). A literal reading of our results would thus suggest that ecomorphological diversity and disparity did not track increases in taxonomic richness of NALK metatherians. This decoupled pattern has also been found in other taxonomic groups, such as anomodont therapsids ( Ruta et al., 2013), graptoloids (Bapst et al., 2012), and angiosperms (e.g., Wing and Boucher, 1998; Lupia et al., 1999). That said, we caution that additional sampling might change this pattern. We were unable to sample several important stagodontids, including the middle Turonian (pre-Aquilan) Hoodootherium , and Fumodelphodon , the Aquilan through possibly “Edmontonian” Eodelphis , and Judithian and “Edmontonian” members of Didelphodon . These taxa, which have previously been interpreted as carnivores and animal-dominated omnivores (e.g., Scott and Fox, 2015; Cohen, 2018; Brannick and Wilson, 2020), would have likely pushed back the appearance of those diet categories and increased disparity values earlier in the Late Cretaceous. The Lancian deltatheriid Nanocuris , which has also been considered carnivorous on the basis of its distinctive, sectorial molars with carnassial notches (Fox et al., 2007; Wilson and Riedel, 2010), would have further added to the range of Lancian ecomorphologies and would have likely increased disparity values. We also did not sample the middle Turonian Scalaridelphys and Aquilan Aquiladelphis , respectively, both of which are pediomyoids that have both been interpreted as plant-dominated omnivores (Cohen et al., 2020). Thus, we underscore that our results should be taken as minimum estimates both for the magnitude of dietary diversity and dental ecomorphological disparity achieved by NALK metatherians and for when they achieved it.
The oldest known dental fossils of metatherians, which date to ca. 110 Ma (Davis et al., 2008; Davis and Cifelli, 2011 and see Williamson et al., 2014; Bi et al., 2018 for discussion regarding Sinodelphys szalayi and the earliest eutherians), strongly suggest that invertivory was plesiomorphic for the clade (e.g., Williamson et al., 2014; Grossnickle and Newham, 2016). Together, our dietary inferences and those for the taxa that we were not able to sample indicate that by the early Late Cretaceous (ca. 100 Ma) metatherians were exploiting other food sources beyond insects (Cohen, 2018; Cohen et al., 2020). Notably, the dietary shifts toward omnivory (plant-dominated and animal-dominated omnivory) and carnivory largely occurred in metatherian subclades other than the most taxonomically prolific clades (the Alphadontidae and Pediomyidae ) ( Figure 6 View FIGURE 6 ). Plant-dominated omnivory first appeared by the late Cenomanian (ca. 96 Ma) in the Stagodontidae ( Pariadens kirklandi ) and possibly Aquiladelphidae ( Dakotadens morrowi , see discussion of phylogenetic relationships in Cohen et al., 2020). Later in the middle Turonian, stagodontids began their more thorough exploration of the carnivore and animal-dominated omnivore regions of the dietary ecomorphospace, culminating in the Lancian with the relatively large-bodied, durophagous predator-scavenger Didelphodon vorax . Glasbiidae is another group that shows up in the fossil record only at the very end of the Cretaceous (last 300– 500 ky; Wilson, 2005); this sister taxon to Pediomyidae has only two known species ( Glasbius twitchelli and Glasbius intricatus ), but they are the most morphologically distinctive examples of plant-dominated omnivory-frugivory among NALK metatherians. Finally, deltatheroidans were likely the most carnivorous among the NALK metatherians, culminating in the highly specialized, Lancian carnivore Nanocuris (Fox et al., 2007; Wilson and Riedel, 2010). (Note that some Aptian–Albian members with a relatively larger talonid and a less reduced metaconid likely had diets other than strict carnivory [Rougier et al., 2015].)
Nevertheless, the two most taxonomically rich clades of NALK metatherians, the Alphadontidae and Pediomyidae , show relatively little dietary diversity ( Figure 6 View FIGURE 6 ). Alphadontids originated by at least the Cenomanian (but probably earlier; Wilson et al., 2016) and peaked in taxonomic richness in the Judithian (15 species, including alphadontids not sampled here). The oldest known pediomyids are from the middle Turonian (Cohen et al., 2020), but like alphadontids, probably originated earlier and reached their highest taxonomic richness in the Judithian (five species, including pediomyids not sampled here) and sustained that level through the Lancian. Many of these alphadontid and pediomyid species were sympatric; for example, Protalphadon lulli , Alphadon marshi , Alphadon wilsoni , Turgidodon rhaister , Pediomys elegans , Leptalestes cooki , Leptalestes krejcii , Protolambda florencae , and Protolambda hatcheri are all found in the Lance Formation (see Williamson et al., 2014 for a tabulation of species occurrences per locality). Although previous studies have hypothesized that pediomyids had greater crushing and grinding capacity relative to other metatherian groups and, in turn, likely incorporated more plant material into their diets ( Wilson, 2013; Cohen et al., 2020), our DFA shows that both pediomyids and alphadontids fed on mainly insects. Diet partitioning within the invertivore adaptive zone may help explain how alphadontids and pediomyids were able to maintain their tremendous taxonomic richness (e.g., eight species in the Hell Creek fauna) (Hardin, 1960). As more pediomyid taxa appear in the Judithian, alphadontids appear to experience a dietary shift from invertivory to soft-invertebrate specialization, whereas pediomyids were mostly invertivores ( Table 12; Figure 6 View FIGURE 6 ). It is possible that further dietary differences, such as specialization for particular species of insects, drove the niche partitioning, but that level of diet specificity cannot be detected by the methods utilized here. Other potential explanations of niche or resource partitioning include spatial separation (using different habitats), temporal avoidance, or separation along an ecological axis different from diet, such as locomotor mode or body size (e.g., Schoener, 1975; Keddy, 1989). For example, the two pediomyid species Protolambda florencae and Pediomys elegans are contemporaneous (Lance and Hell Creek faunas) and were both reconstructed by our DFA as invertivores. Resource partitioning may have occurred along the axis of body size (i.e., P. florencae is larger and so probably consumed larger insects than did Pediomys elegans ), which might have enabled these pediomyids to co-exist. However, other potential ecological axes on which partitioning might have occurred are difficult to discern in this fossil record (e.g., locomotion/substrate use, diel activity pattern, etc.).
During the Late Cretaceous in North America, metatherians shared the ecospace with other mammalian groups, including eutriconodontans, multituberculates, spalacotherioids, and their sister taxon eutherians. Among those groups, metatherians were arguably the most dietarily diverse, having occupied up to five categories: invertivory, carnivory, animal- and plant-dominated omnivory, and likely frugivory. It has been suggested that the non-tribosphenic dentitions of most non-therian mammals were more morphologically constrained than tribosphenic dentitions were, and, consequently, non-therians attained less dietary diversity than therians did (Chen et al., 2019; but see Harper et al., 2019 on South American dryolestoids). For instance, spalacotherioids and eutriconodonts were likely restricted to invertivory and faunivory, respectively (Hu et al., 2005; Grossnickle and Polly, 2013; Chen et al., 2019; Morales-García et al., 2021). Multituberculates were the most dietarily diverse non-therian mammal group. Their diets ranged from invertivory to animal- and plant-dominated omnivory, and by the late Late Cretaceous (ca. 84 Ma) even herbivory ( Wilson et al., 2012; Grossnickle and Polly, 2013; Weaver et al., 2019; Weaver and Wilson, 2021). Still, metatherians probably had a broader dietary range than multituberculates and attained that diversity earlier in the Cretaceous. However, unlike multituberculates, metatherians did not continue to diversify in North America after the K-Pg mass extinction ( Wilson, 2014; Williamson et al., 2014). The early eutherians, which include many lineages that retain the plesiomorphic tribosphenic molar morphology, were mostly insectivorous during the Late Cretaceous, although some of the larger-bodied taxa, such as Altacreodus magnus (formerly Cimolestes magnus ), were likely faunivorous (e.g., Wilson, 2013; Grossnickle and Newham, 2016; Chen et al., 2019). Additionally, zhelestid (Harper, 2012; Gheerbrant and Astibia, 2012; Harper et al., 2019) and gypsonictopid eutherians (Crompton and Kielan-Jaworowska, 1978), which both first appear in North America in the Campanian, and the Lancian taeniodont Schowalteria (Fox and Naylor, 2003) are inferred to have included plant material in their diets based on their tooth morphology. Archaic ungulates, which first appear in the very latest Cretaceous but very rarely, and plesiadapiform primates, which have lineages that are believed to extend back into the very latest Cretaceous, have both been interpreted as animal- and plant-dominated omnivores (e.g., Archibald et al., 2011; Fox and Scott, 2011; Wilson Mantilla et al., 2021). Whereas Late Cretaceous eutherians ranged from invertivory, faunivory, and animal- and plant-dominated omnivory, they were less dietarily diverse compared to contemporaneous metatherians and did not expand beyond invertivory until the Campanian (at least in North America; Harper, 2012; Harper et al., 2019), well after metatherians had.
Thus, our study does not exclusively support either the Suppression Hypothesis or the Early Rise Hypothesis. The Suppression Hypothesis predicts that the ecomorphological diversity (number of diets) and disparity (magnitude of morphological difference) in metatherians was low and stable throughout the Late Cretaceous. Whereas our quantitative results of dental disparity and ecomorphological diversity are consistent with this hypothesis— that is, dental disparity does not significantly change through the Late Cretaceous and most metatherians were invertivores and soft-invertebrate specialists ( Figure 6 View FIGURE 6 ); we posit that inclusion of, for example, the middle Turonian stagodontids ( Fumodelphodon and Hoodootherium ) and aquiladelphids ( Scalaridelphys ) and the Lancian Nanocuris would likely increase dental disparity and diversity of dietary categories recorded for at least those intervals. Moreover, the ecomorphological diversity and disparity values are likely greater than those of other contemporary mammalian clades, which exhibit a smaller range of diets and dental morphologies.
The Early Rise Hypothesis predicts that rapid increases in ecomorphological diversity and disparity of metatherians began in the late Late Cretaceous. Although our DFA shows that metatherians were mostly invertivores and soft-invertebrate specialists, it also shows that by the pre-Aquilan—prior to the ecological radiation of angiosperms—they had begun to exploit other diets as well, including plant-dominated omnivory ( Figures 6–7 View FIGURE 6 View FIGURE 7 ). Whereas dietary diversity and disparity were both stable throughout the Late Cretaceous, they were elevated relative to contemporary mammalian groups; we hypothesize that the diversification that produced this relatively high dietary diversity and dental disparity arose during the late Early Cretaceous. As such, we would suggest that the ecomorphological expansion of NA metatherians was not temporally correlated with the ecological rise of angiosperms but perhaps with their earlier taxonomic diversification (Cohen et al., 2020), which occurred during the Cretaceous Terrestrial Revolution (ca. 125–80 Ma). As new species of angiosperms appeared during their taxonomic diversification, they may have provided new food resources for metatherians to exploit, thus catalyzing the ecomorphological expansion of metatherians. Or perhaps other possible co-occurring factors during the Cretaceous Terrestrial Revolution, such as the extinction of eutriconodontans and spalacotherioids (Grossnickle and Polly, 2013; Cohen et al., 2020), allowed metatherians to expand into newly vacated niches. Future studies should test this hypothesis by applying DTA to samples of Early Cretaceous metatherians; however, to achieve this, additional field work should be undertaken to bolster the sparse fossil record from this interval.
No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.