Fossil Friday: The Abrupt Origins of Treeshrews (Scandentia) and Colugos (Dermoptera)
This Fossil Friday features the small mammal Eudaemonema webbi from the Late Paleocene of Western Canada (Scott 2010) as we look today into the origins of two orders of Southeast Asian placental mammals, the treeshrews (Scandentia) and colugos (Dermoptera). The 23 living species of treeshrews belong to only two families (Ptilocercidae and Tupaiidae) and look like a mixture of a shrew and a squirrel. The two living genera and species of colugos belong to the single family Cynocephalidae (= Galeopithecidae) and look like a mixture of a lemur and a flying squirrel, which is why they have sometimes been called flying lemurs. They are cat-sized arboreal animals that can glide more than 100 meters from tree to tree.
Treeshrews and colugos not only look like chimeras of different beasts, but indeed both proved to be notoriously difficult to place in the system of animals. Treeshrews were at times associated with genuine insectivores (Wagner 1855, Haeckel 1866), “menotyphlan” insectivores (esp. Macroscelidea) (Gregory 1910), and primates (Carlsson 1922, Simpson 1945, Le Gros Clark 1924, 1926, 1971, Luckett 1980, Novacek 1980, Sargis 2004). They were later removed from primates (Van Valen 1965, 1967, McKenna 1966, Szalay 1968, 1969) and recognized as a distinct order of placental mammals (Butler 1972), related to extinct Leptictida (Van Valen 1965, 1967) or of unclear relationship (Luckett 1980). This situation was even worse with colugos (Wible 1993), about which the famous German zoologist Alfred Brehm (1883) remarked in his animal encyclopedia Brehms Thierleben:
Linné stellt sie zu den Halbaffen, Cuvier zu den Fledermäusen, Geoffroy zu den Raubthieren, Oken zu den Beutelthieren und Peters endlich, wohl mit Recht, zu den Kerbthierfressern, deren Reihe sie eröffnen. Entsprechend der Unsicherheit der Forscher heißt die bekannteste Art unter anderen noch geflügelter Affe, Flattermaki, fliegende Katze, wundersame Fledermaus usw.
[Linné placed them with lemurs, Cuvier with bats, Geoffroy with carnivores, Oken with marsupials and Peters last but not least, likely correct, with insectivores right at their base. Corresponding to this uncertainty of the scientists the most common species has also been called winged monkey, flying lemur, flying cat, or wondrous bat, etc.]
Today, both orders are generally believed to be close relatives of primates in a group called Euarchonta (e.g., Sarich & Cronin 1976, Cartmill & MacPhee 1980, Adkins & Honeycutt 1991, Liu & Miyamoto 1999, Waddell et al. 1999, 2001, Liu et al. 2001, Murphy et al. 2001a, 2001b, Springer et al. 2003, 2004, 2007, Kemp 2005, Rose 2006, Kriegs et al. 2007, Halliday et al. 2015; contra Arnason et al. 2002). Together with the Glires (rodents, hares, rabbits, and pikas) the euarchontans belong to one of the four major supergroups (cohorts) of placental mammals, which has rather unimaginatively been named Euarchontoglires (Murphy et al. 2001a, 2001b) or more rarely Supraprimates (Waddell et al. 2001, Kriegs et al 2007).
As all too often in phylogenetics the relationships of treeshrews and colugus within Euarchotoglires are still a matter of considerable scientific controversy (Knyshov et al 2022:
Some scientists think that treeshrews are closer related to colugos in a group called Sundatheria (Adkins & Honeycutt 1991, Liu & Miyamoto 1999, Asher et al 2009, Liu et al. 2001, Murphy et al. 2001b, Sargis 2002d, 2004, Eizirik et al. 2004, Olson et al. 2005, Marivaux et al. 2006, Bloch et al. 2002, 2007, 2016, Sánchez-Villagra et al. 2007, Nie et al. 2008, Asher & Helgen 2010, Silcox et al. 2010, 2017, Chester and Bloch 2013 , O’Leary et al. 2013, Chester et al. 2015, 2017, 2019, Naish 2015, Nowak 2018, Upham et al. 2019) or Paraprimates (Springer et al. 2003, 2004, 2007). Other scientists rather believe treeshrews represent the sister group to a clade of colugos and primates called Primatomorpha (Beard 1991, 2006, Kalandadze & Rautian 1992, Murphy et al. 2001a, Waddell et al. 2001, Janečkaet al. 2007, Sargis 2007, Martin 2008, Perelman et al. 2011, Ni et al. 2013, 2016, Lin et al. 2014, Mason et al. 2016, Esselstyn et al. 2017, Boyer et al. 2018, Phillips & Fruciano 2018, Morse et al. 2019, Scornavacca et al. 2019, Zhang et al. 2019, Seiffert et al. 2020, Zachos et al. 2020, Knyshov et al. 2022, Osozawa and wakabayashi 2023). But see Sargis (2002d, 2004), who cautioned that the support for Primatomorpha is considerably reduced when the primitive treeshrew Ptilocercus is included in the analyses. Why am I citing this boring list of all these publications? Simply to make the point very clear that the two alternative hypotheses arguably are supported by numerous independent studies based on many different data sets, but they cannot both be right. But it gets much worse.
Still other authors explicitly or implicitly suggested that treeshrews could be sister to primates only (Gregory 1910, Carlsson 1922, Le Gros Clark 1924, 1926, 1971, Simpson 1945, Simons 1964, McKenna 1966, Wible & Covert 1987, Kay et al. 1992, Novacek 1992, Kupfermann et al. 1999, Wible et al. 2007, Song et al. 2012, Kumar et al. 2013, Lin et al. 2014, Zhou et al 2015), even though some of these studies did not include colugos in their analyses. A few scientists suggested treeshrews as the sister group of Glires+Primatomorpha together (Kumar et al. 2013, Esselstyn et al 2017, Knyshov et al. 2022), or even suggested them to be the sister group of Glires (Meredith et al. 2011, Zhou et al. 2015, Foley et al. 2016; but see Lin et al. 2014), or of Lagomorpha (Bailey et al. 1992), or of Rodentia (Arnason et al. 2002), which would all imply that Euarchonta and Sundatheria would not be valid clades (also see Madsen et al. 2001). Finally, some studies recovered Dermoptera nested within primates as sister group of Anthropoidea (Murphy et al 2001a, Arnason et al. 2002, contra Schmitz et al. 2002 and Schmitz & Zischler 2003).
Originally, scientists believed that the order of bats (Chiroptera) belongs to the same supergroup as colugos and primates (Archonta sensu lato) (e.g., Gregory 1910, McKenna 1975, Wible & Covert 1987, Novacek 1992, Szalay & Lucas 1993, Kupferman et al 1999). Prior to the advent of molecular phylogenetics most scientists believed that bats and colugos belong to a common clade that was named Volitantia (Szalay & Drawhorn 1980, Novacek & Wyss 1986, Wible & Covert 1987, Wible & Novacek 1988, Baker et al. 1991, Novacek 1992, Simmons 1993, 1995, Szalay & Lucas 1993, 1996, Wible 1993, Stafford & Thorington 1998, Bloch & Silcox 2001, Silcox 2001a, Sargis 2002d, 2002e, 2007, Silcox et al. 2005; also see Halliday et al. 2015: fig. 1). This was based on a substantial number of anatomical similarities, mainly related to gliding/flying adaptations, but also including the morphology of the teeth and the ear capsule. Based on features of penis morphology Smith & Madkour (1980) suggested a clade of only Dermoptera + Megachiroptera as sister group of primates, with tree shrews and Microchiroptera as more basal outgroups. The results from modern phylogenomics did not agree at all and consequently bats were ultimately removed from archontans (Asher and Helgen 2010) and are now considered as basal members of completely different supergroup called Laurasiatheria. Prior to this recognition there were some wild theories seriously discussed, such as the diphyly of bats and the “fallen angel” hypothesis (Pettigrew et al. 1989; contra Bailey et al. 1992), which suggested that primates derived from a gliding common ancestor with colugos and megabats. Nothing seems impossible or forbidden in Darwinian fantasy land, except anything that smacks of purposeful development and design.
So, let’s focus on the hard evidence, and what could be harder than petrified fossils? Unfortunately, the fossil record of treeshrews and colugos is quite sparse, but it still provides some useful information about their origins. This evidence strongly contradicts the Darwinian predictions from molecular clock studies, which suggested that colugos should have branched from the Primatomorpha lineage about 79.6 million years ago, and treeshrews even earlier about 86.2 million years ago during the Cretaceous “golden age” of dinosaurs (Janecka et al 2007)
Roberts et al. (2011: fig. 3) accordingly suggested that the two families of crown group treeshrews already diverged in the Paleocene about 60 million years ago. Foley et al. (2016) proposed a similar estimate with the lineages of treeshrews originating 76.94 million years ago and colugos 75.47 million years ago. Of course, the fossils tell a very different story that is better agreeing with recalibrated datings of a “soft explosive model of placental mammal evolution” (Phillips & Fruciano 2018, also see Upham et al. 2019: fig. 4), which has all the orders appearing abruptly during a brief window of time in the early Paleogene. This is exactly what we heretical ID proponents always said.
The Fossil Record of Treeshrews
It is worth noting that not only the affinity of treeshrews and the intraordinal relationships among the living species of treeshrews proved to be a contentious issue (Olson et al. 2004, 2005, Roberts et al. 2011), but even the very number of species itself, which for example varied in the genus Tupaia between 11 and 32 species (Olson et al. 2005). The fossil record of treeshrews is relatively poor (Sargis 1999, 2004, Olson et al. 2004, 2005, Rose 2006). The oldest fossil record of the order Scandentia is Eodendrogale parvum that was described by Tong (1988), based on a few isolated teeth from the Middle Eocene (48.6-37.2 mya) of Xichuan in China. A few extinct members of modern treeshrews have been described from Miocene localities in East Asia, such as Prodendrogale and Tupaia storchi from the Late Miocene (11.1-4.9 mya) of Yunnan in China, and Palaeotupaia and Sivatupaia from the Miocene and Pliocene (23.03-5.33 mya) Śiwalik deposits in India and Pakistan (Dutta 1975, Chopra & Vasishat 1979, Chopra et al. 1979, Jacobs 1980, Qiu 1986, Sargis 1999, 2004, Ni & Qiu 2012, Sehgal et al. 2022), as well as Tupaia miocenica from the Miocene (ca. 18 mya) of Thailand (Mein & Ginsburg 1997). The oldest crown group treeshrew is Ptliocercus kylinfrom the Earliest Oligocene (ca. 34 mya) of the Yunnan Province in China (Li & Ni 2016), which has been interpreted as evidence that treeshrews are slowly evolving “living fossils.” The press release about the discovery also mentioned that morphological comparisons and phylogenetic analysis support the long-standing idea that the pen-tailed treeshrews of the living relict species Ptilocercus lowii “are morphologically conservative and have probably retained many characters present in the common stock that gave rise to archontans, which include primates, flying lemurs, plesiadapiforms and treeshrews” (Chinese Academy of Sciences 2016; see also Sargis 2002a, 2002b, 2002c, 2002d, 2007 and Olson et al. 2005). That seems to be a rather bold conclusion considering the above-mentioned fact that scientists cannot even agree on the phylogenetic affinities of treeshrews in the first place.
Some fossil taxa that were previously assigned to the relationship of treeshrews have meanwhile been debunked: Following Lemoine (1885), the extinct Adapisoriculidae were considered as fossil Tupaiidae by Simpson (1928), Van Valen (1965, 1967) and Szalay (1968). Most later studies rather considered them to be lipothylan insectivores (e.g., Rose 2006), but Smith et al. (2010) made a strong case for a position among basal Euarchonta. However, more recent studies even disputed their position within crown group placental mammals (Goswami et al. 2011, Manz et al. 2015). Matthew (1918) provisionally listed the Eocene genus Entomolestes as a possible fossil Tupaiidae, but it was later recognized as a close relative of erinaceoid insectivores (= hedgehogs) by McKenna (1966) and Novacek et al. (1985). McKenna (1966) also considered other suggested candidates as very doubtful, such as the genera Macrocranion (likely a hedgehog as well) and the Paleocene mixodectid Eudaemonema that we featured in this article. The latter genus was considered as a Plagiomenidae within Dermoptera by KcKenna (1960) and McKenna & Bell (1997), which was arguably corroborated by the cladistic analysis of Ni et al. (2013, 2016 SI). The Paleogene family Anagalidae was considered as closely related to Tupaiidae by Simpson (1931), but this was strongly disputed by McKenna (1966). Anagalids are today considered as closer related to Glires within a clade Gliriformes, which we will look into more detail next week’s Fossil Friday.
The Fossil Record of Colugos
The two species of the extinct genus Dermotherium from the Eocene and Oligocene of Thailand, Myanmar, and Pakistan are the oldest and only definitive fossil dermopterans (Ducrocq et al. 1992, Marivaux et al. 2006). The older of these two species is Dermotherium major from the Late Eocene (37.2-33.9 mya) of the Krabi Basin in Thailand. Stafford & Szalay (2000) cautioned that this purported dermopteran fossil is poorly preserved and of little help, but the affinity to modern Dermoptera was corroborated by Silcox et al. (2005) and Smith et al. (2010). Apparently they were already quite similar to modern colugos and were therefore included in the same family Cynocephalidae together with the two living genera, which are by the way much more distinct than was often believed (Stafford & Szalay 2000). Some alleged fossil dermopterans have been reported from Neogene localities in Africa (see PaleoDB), but these seem to be only brief records in obscure checklists, which have been totally ignored in the technical literature on dermopteran evolution. Several enigmatic Paleogene groups of small insectivorous mammals have also been associated with Dermoptera (Anonymous 2023) and merit a closer look.
Plagiomenidae
This extinct family is known exclusively from the Paleocene and Early Eocene of North America. According to Bloch et al. (2007) they belong to Sundatheria, together with colugos and treeshrews. Several authors had more specifically attributed this family to Dermoptera (Matthew 1918, Simpson 1937, 1945, Romer 1966, Van Valen 1967, Szalay 1969, Rose 1973, 1975, 2006, Krishtalka & Setoguchi 1977, Rose & Simons 1977, Bown & Rose 1979, Novacek 1980, Carroll 1988, Gunnell 1989, McKenna 1990, Ducrocq et al. 1992, McKenna & Bell 1997, Silcox 2001a, 2001b, Agusti & Antón 2002, Kemp 2005). Such a position was also confirmed by the cladistic studies of Ni et al. (2013, 2016 SI), Halliday et al. (2015), and Morse et al. (2019). On the other hand, MacPhee et al. (1989) considered plagiomenids in his seminal study as eutherians of uncertain affinity, which was concurred by Marivaux et al. (2006). Szalay& Lucas (1993) also cautioned that the affinity of Plagiomenidae needs reexamination, and Dawson et al. (1993) remarked:
The phylogenetic position of Plagiomenidae with respect to other mammals is also not yet clear. Earlier interpretations of plagiomenids as members of the order Dermoptera have been questioned on several grounds (MacPhee et al. 1989, Beard 1990, Kay et al. 1990). At present, we follow MacPhee et al. (1989) in classifying these animals as placental mammals of unknown ordinal affinities.
A lot of this uncertainty concerning the affinities of Plagiomenidae, and the other taxa of fossil small mammals mentioned below, comes from the fact that the fragmentary fossil evidence is mostly restricted to dental characters. Yapuncich et al. (2011) reported the first dentally associated skeleton of Plagiomenidae, which surprisingly did not exhibit any arboreal adaptations, so that the authors concluded that “on functional morphological and cladistic grounds we consider Plagiomenidae to be more likely allied with laurasiatheres than dermopterans or other euarchontans.” Oopsy, there goes almost a hundred years of previous research down the drain. In this context, it is interesting that more recent studies of living treeshrews suggested that the arboreal adaptations already belonged to the archontan ground plan and thus do not suggest a uniquely primate relationship of treeshrews (Godinot 2017).
Anyway, What About the Age of Plagiomenids?
Three species in the genus Plagiomene and Planetetherium mirabile are known from Late Paleocene and Early Eocene (56.8-50.3 mya) localities in North America (Matthew 1918, Simpson 1928). The genus Thylacaelurus, which was described from the Middle Eocene Kishenehn Formation in Canada (Russell 1954), has also been reported from the Paleocene (61.7-56.8 mya) Paskapoo Formation in Alberta, Canada (Fox 1990), but only in a list without any description, figure, or justification. McKenna (1990) included three more genera (Tarka, Tarkadectes, and Ekgmowechashala) from the Middle Eocene and Oligocene of northwestern USA, all classified in a separate plagiomenid subfamily Ekgmowechashalinae. This subfamily was recently recognized as a family of adapiform primates by Ni et al. (2016). Another genus and species Ellesmene eureka has been described from Early Eocene (55.8-50.3 mya) of the Arctic region of Ellesmere Island (Dawson et al. 1993), which had a subtropical climate and vegetation during this period of earth history, but still a polar light regime that made it to a very unique environment that was also colonized by other early Primatomorpha like the plesiadapiform genus Ignacius (Miller et al. 2023).
There are two more taxa that may belong to Plagiomenidae:
Worlandia inusitata was described from the Paleocene (Clarkforkian, 56.8-55.8 mya) of Wyoming and considered to be closely related to plagiomenids like Planetetherium in a subfamily Worlandiinae (Bown & Rose 1979). This was accepted by McKenna & Bell (1997)and Rose (2006), and the cladistic study of Paleocene mammals by Halliday et al. (2015)supported its place within Plagiomenidae.
The genus Elpidophorus was described by Simpson (1927, 1937) with two species from the Paleocene (61.7-56.8 mya) of Montana, Wyoming, and Alberta (Fox 1990). It was originally described by Simpson (1927) as a carnivoran, but was attributed to Mixodectidae by most early workers (Simpson 1936, 1937, 1945, Van Valen 1967, Szalay 1969). McKenna (1960) begged to differ and considered Elpidopherus as a plesiadapiform stem primate. This genus was later transferred from Mixodectidae to Plagiomenidae and considered as earliest putative dermopteran by Rose (1975). This was concurred by several subsequent studies (Gunnell 1989, Fox 1990, McKenna & Bell 1997, and Halliday et al. 2015), while Scott et al. (2013) again treated this genus as Mixodectidae. Ni et al. (2013 SI) placed it again with Plagiomenidae in the stem group of Dermoptera, far removed from Mixodectes. So, it looks like Elpidophorus could be the oldest plagiomenid (Rose 2006) or not, related to dermopterans or not.
Mixodectidae
The Mixodectidae represent another extinct family from the Paleocene of North America and are almost exclusively known from their dentition (Simpson 1937, Szalay 1969, Gunnell 1989, Rose 2006, 2008). They have been linked previously with rodents, insectivores (Gunnel 1989), and primates (see McKenna 1966, Szalay 1969, Silcox 2001a: fig. 6.4, and Scott 2010), as well as attributed to (eu)archontans with an affinity to Plagiomenidae and Dermoptera (Simpson 1937, Van Valen 1967, Carroll 1988, Beard 1989, McKenna 1990, Szalay & Lucas 1993, 1996, Silcox et al. 2005, Gunnell & Silcox 2008, Rose 2006, 2008, Scott 2010). Szalay (1968, 1969) already reviewed the checkered history of the taxonomic allocation of mixodectids. He rejected a close relationship with plagiomenids and dermopterans and instead considered mixodectids and adapisoriculids as close relatives of treeshrews. MacPhee et al. (1989) affirmed a sister group relationship of Mixodectidae with Plagiomenidae (also see Rose & Simons 1977, McKenna 1990, Rose 2008), but considered them as Eutheria incertae sedis. Agusti & Antón (2002) considered mixodectids as “archaic placental mammals”. Some more recent studies indeed rather considered mixodectids to belong to the plesiadapiform stem group of Primatomorpha (Ni et al. 2013, 2016 SI) than that of Dermoptera, but Ni et al. (2013, 2016) placed the putative mixodectid Eudaemonema not together with Mixodectes but in the stem group of Dermoptera. Some dental similarities of Mixodectidae with recent colugos have been interpreted as convergences (Scott 2010). Well, that does not help much.
Micromomyidae
Micromomyidae was an extinct family of diminutive euarchontan mammals that lived from the Late Paleocene to the Early Eocene of western North America (with a questionable record from the Eocene of China; Tong & Wang 2006). Because postcranial material was interpreted in terms of an adaptation to gliding behaviour, this family has also been linked with Dermoptera (e.g., Beard 1989, 1993a, 1993b). However, this interpretation as mitten-gliders was arguably refuted by Bloch et al. (2007) and Boyer & Bloch (2008). More recently micromomyids were rather assigned to the plesiadapiform grade in the stem group of primates (Silcox 2001a, Silcox et al. 2005, 2010, 2017, Rose 2006, Bloch et al. 2007, Chester & Bloch 2013, Chester et al. 2015, 2017, 2019, Bloch et al. 2016) or of Primatomorpha (Ni et al. 2013 SI). The cranial inflation shared with dermopterans could more likely be a convergence (Bloch et al. 2016).
Microsyopidae
This extinct family also existed in the Paleocene and Eocene of North America. It has been suggested as member of the stem group of Sundatheria (treeshrews and colugos) by the cladistic study of Bloch & Silcox (2006), but recovered as stem dermopterans by Ni et al. (2013, 2016 SI). Beard (1989) also placed them with plesiadapiforms and Dermoptera. Szalay & Lucas (1993) affirmed an inclusion in Archonta but remained undecided about the specific affinities. However, more recent cladistic studies recovered this family as plesiadapiform-grade stem primates (Silcox et al. 2005, 2010, 2017, Chester & Bloch 2013, Chester et al. 2015, 2017, 2019, Bloch et al. 2016). Indeed, the majority of experts had long considered microsyopids as close relatives of primates or even included them as basal primates (McKenna 1960, 1966, Van Valen 1967, Szalay 1969, MacPhee & Cartmill 1986, Gunnell 1989, Silcox 2001a, and Rose 2006).
Plesiadapiformes: To Be or Not to Be a Glider
As we already discussed in my Fossil Friday article on the origin of primates (Bechly 2022), some scientists considered the Paleogene mammal order of Plesiadapiformes as possible close relatives of colugos (Dermoptera) (Kemp 2005, Silcox 2014, Godinot 2017). This was mainly based on the shared reduction of the internal carotid artery (Kay et al. 1990, 1992) and some skeletal characters that were thought to be indicative of an adaptation to gliding in paromomyid genera like Phenacolemur and Ignacius (Beard 1989, 1990, 1993a, 1993b, Martin 1990, McKenna & Bell 1997). Szalay & Lucas (1993) found homologies in the postcranial skeleton. As plesiadapiforms include some of the oldest known placental mammals at all (see Bechly 2022), this could be a very remarkable finding concerning the early origin of the colugo lineage. However, this proposed relationship was seriously questioned by many other experts (Krause 1991, Ducrocq et al. 1992, Szalay & Lucas 1993, 1996, Wible 1993, Van Valen 1994, Stafford & Szalay 2000, Boyer et al. 2001, Bloch & Silcox 2001, 2006, Sargis 2002d, Bloch & Boyer 2002a, 2002b, 2003, Silcox 2001a, 2001b, 2003, Rose 2006, Bloch et al. 2007, and Boyer & Bloch 2008). Simons (1964) had already cautioned that the similarities between Plesiadapis and colugos “could have been acquired independently rather than from a common ancestor.” Also, the cladistic studies by Bloch et al. (2007, 2016), Janečka et al. (2007), and Chester et al. (2015, 2017, 2019), found no evidence supporting a dermopteran relationship of plesiadapiforms and instead recovered them as basal grade in the stem group of primates. But phylogenetics would not be phylogenetics if there would not be an even more recent and more comprehensive cladistic analysis that again confirmed the close relationship of some plesiadapiforms (incl. the putative primate Altiatlasius, also see Ni et al. 2016 SI) and colugos (Morse et al. 2019), and even Boyer et al. (2018: fig. 9) again clustered some plesiadapiforms (incl. the type genus Plesiadapis) with Dermoptera. Sigh, what a frustrating mess indeed!
Last but not least, there is an extinct family Placentidentidae with the single genus and species Placentidens lotus from the Early Eocene (Ypresian, 55.8-48.6 mya) of France, which was attributed to Dermoptera by some scientists (Russell et al. 1973, Carroll 1988, Ducrocq et al. 1992). Rose & Simons (1977) considered Placentidens as a possible Plagiomenidae and thus dermopteran too. However, this genus was more recently shown to belong to the extinct family Nyctitheriidae in the insectivore suborder Soricomorpha (Beard & Dawson 2009), thus related to the true shrews and moles in the totally different supergroup Laurasiatheria. Well, unless you follow Smith et al. (2010), who said that “the purported euarchontan Paleogene family Nyctitheriidae (Hooker 2001) is closer to Scandentia than to adapisoriculids.” But wait, Manz et al. (2015) again found that Nyctitheriidae is related neither to Euarchonta nor to Adapisoriculidae, but to Eulipotyphla, thus true insectivores. Is there anything the experts can agree upon beyond trivial facts like those beasts being extinct small mammals? They all look at the same fossil evidence and constantly come to totally different conclusions. Even as a paleontologist I have to admit that calling this a real scientific discipline seems like an insult to hard sciences like physics or chemistry or molecular biology. To an outsider it must rather resemble a kind of Rorschach test with fossils instead of ink blotches, and all that matters seems to be guesswork, speculation, and opinion.
Long story short: Irrespective of any of the numerous uncertainties, treeshrews and colugos definitely appeared abruptly in the Paleogene. The fossil record shows nothing even remotely resembling a gradual origin of these orders in the Cretaceous that was predicted by Darwinian molecular clock studies. This is just another instance of the countless empirical failures of the theory, more or less ignored by mainstream evolutionary biology.
Next Fossil Friday we will look into the origins of the orders of rodents and Lagomorpha, which form the second major clade (Glires) within the supergroup of Euarchontoglires. I hope that will not be as confusing and wearying as today’s topic.
