Actinocerid Cephalopods from the Ordovician of Myanmar, and their Paleobiogeographic Implications for Northern Gondwana

Characterization of two new superorders Nautilosiphonata and Calciosiphonata and a new order Cyrtocerinida of the subclass Nautiloidea; siphuncular structure in the Ordovician nautiloidBathmoceras(Cephalopoda)

“…The inner layer is a direct, structurally modified, continuation of the nacreous layer of the septal neck. This siphuncular-type is present in the fossil nautiloid orders Plectronocerida, Orthocerida, Actinocerida and probably also in Barrandeocerida (Mutvei 1996(Mutvei , 1998(Mutvei , 2002b, 2012; Mutvei et al 2007;Kröger 2004Kröger , 2006Niko & Sone 2014). The orders Orthocerida and Actinocerida are closely related.…”

Middle Ordovician actinocerid nautiloids (Cephalopoda) from Xainza County, Tibet, western China, and their paleogeographic implications

“…Pomphoceras resembles Ordosoceras in external form, inner construction, and systematic phylogeny; the latter is the Middle Ordovician index fossil of North China (Chang, 1959; Chen and Zou, 1984). Ordosoceras is also recorded from Myanmar (Sibumasu Terrane; Niko and Sone, 2014), which indicates that the actinocerids from Sibumasu have close affinities with those of North China. Discoactinoceras is recorded in Inner Mongolia (Zou, 1981) and Liaoning (Kobayashi, 1978), both from North China, so its occurrence in the Xainza Region of Tibet also supports a close relationship of the two terranes.…”

“…All specimens were cut in median section, polished, and photographed with a Nikon D600 digital camera, Leica M125 microscope, and Leica DSC450C camera enhanced by Leica’s LAS software. Our identifications are based mainly on the position and shape of the siphuncle, the types of the septa and septal neck, the details of the connecting rings, the shape of the segment, and the endosiphuncular canal system, following Teichert et al (1964), Chao et al (1965), Flower (1968), Frey (1995), Zhu and Li (1996), and Niko and Sone (2014). The siphuncle segment compression ratio (SCR) is an important term introduced by Frey (1995) and is defined as the ratio of the maximum diameter of the connecting rings to the length of camerae.…”

“…Wutinoceras was originally described from the Majiagou Formation (Wuting Formation; Darriwilian) in Benxi (Pen-his-hu) and Nanpiao, Liaoning, North China (Endo, 1930, 1932; Kobayashi and Matumoto, 1942), and has also been recorded in the Kakit Bukit Formation (partly Darriwilian) in the Langkawi Islands, Malaysia (Stait and Burrett, 1982; Stait et al, 1987), and in the Whiterock (Darrwilian) of North America (Flower, 1968). Armenoceras is very common in the Middle Ordovician of North China (Endo, 1932; Chao et al, 1965; Zhu and Li, 1996) and was discovered in the Thung Song Group and the Tha Manao Formation of Thailand (Kobayashi, 1958, 1959; Stait and Burrett, 1984), the Whiterock part of the Kakit Bukit Formation of Malaysia (Kobayashi, 1958, 1959; Stait and Burrett, 1984; Stait et al, 1987), the Wunbye Formation of Myanmar (Niko and Sone, 2014), the Middle Ordovician in Queensland and Tasmania, Australia (Whitehouse, 1936; Teichert and Glenister, 1952), and in North America, Greenland, and Siberia, Russia (Balashov, 1962). Therefore, the age of the actinocerid nautiloids from the Lhasai Formation of Xainza is Middle Ordovician, and most probably Darriwilian.…”

First record of a nonpaleotropical intejocerid cephalopod from Darriwilian (Middle Ordovician) strata of central Spain

“…The absence of critical internal structures in many of these specimens does not allow for a taxonomic identification at genus or species level, and many taxa are in need of a revision. We hope that the recent reappraisals of early Paleozoic peri-Gondwanan cephalopod faunas from elsewhere (e.g., Kröger and Lefebvre, 2012; Evans et al, 2013, 2015; Bogolepova et al, 2014; Niko and Sone, 2014, 2015; Aubrechtová, 2015; Cichowolski et al, 2015, 2018; Ghavidel-Syooki et al, 2015; Rolet and Plusquellec, 2016; Aubrechtová and Turek, 2018; Manda and Turek, 2018; Ebbestad et al, 2019; Fang et al, 2019) will stimulate future research on the Iberian cephalopods.…”