Phylogenetic relationships between Monotremata and Monotremaformes: parallelism with appendages and habits of aquatic moles

Lambert, Olivier, Muizon, Christian De, Bianucci, Giovanni (2015): A new archaic homodont toothed cetacean (Mammalia, Cetacea, Odontoceti) from the early Miocene of Peru. Geodiversitas 37 (1): 79-108, DOI: 10.5252/g2015n1a4, URL: http://dx.doi.org/10.5252/g2015n1a4

This article is a Commentary on Edwards et al. (2022a,b), 233: 1440–1455 and 1456–1465.

The origin of land plants was one of the most important events in the history of life on Earth. It was a major macroevolutionary event in its own right, with profound ecological consequences, but it also had enormous effects on the environment of planet Earth, altering atmospheric composition, weathering and soil formation, etc., and hence climate and biogeochemical cycles. Understanding the timing of the origin of land plants is a long term goal. In this issue of New Phytologist, Rubinstein et al. (pp. 365–369) provide new evidence that this event occurred 8–12 million yr earlier than previously accepted. 'Thus, although reports are currently few, attention is turning to the possibility that the centre of origin of land plants may have been located on Gondwana.' The land plants (Embryophytes) are a monophyletic group that evolved as an adaptive response to the migration from a freshwater aquatic to terrestrial subaerial habitat. Phylogenetic analysis of extant plants suggests that charophycean green algae share a sister group relationship with the Embryophytes, that is, the land plants probably evolved from a freshwater aquatic multicellular green alga similar to extant Chara and Coleochaete (Graham, 1993). Within the Embryophytes liverworts are the most basal group, followed by mosses, and then hornworts and vascular plants sharing a sister group relationship (Qiu et al., 2006). However, it is to the fossil record we must turn if we are to understand what the first land plants were like and when and where they evolved. Traditionally the earliest evidence for land plants was actual megafossils (fossils representing a significant portion of the plant). Until the late 1950s the simple rhyniophytoid plant Cooksonia provided this benchmark (Lang, 1937), and it is still the oldest generally accepted megafossil, being reported from the Late Silurian (late Wenlock) (Edwards et al., 1983). However, evidence from a new technique called palynology became widely available from the late 1950s. This technique involves dissolving rock to release small organic particles trapped within it as it was deposited. Among these particles are the subaerially released spores of land plants. All land plants produce spores, or their homologue pollen, in vast numbers. They are enclosed within a thick resistant wall that protects them from physical abrasion and exposure to UV-B radiation during dispersal. Upon release, spores/pollen are widely dispersed by wind (or other vectors such as insects) before eventually being deposited, often after remobilization by water. Thus, spores/pollen tend to accumulate wherever sediment is being deposited. Sporopollenin is one of the most resistant organic macromolecules known to man and readily fossilizes. Thus palynology yields a remarkably complete fossil record of the dispersed spores/pollen of land plants. However, it is important to note that spores/pollen enclosed in a resistant sporopollenin wall are a synapomorphy of land plants (Wellman, 2003). When plants migrated out of water and into the subaerial environment sexual reproduction became problematic as reproductive structures could no longer simply be released into the aquatic environment to swim to one another. Rather, they must be transported through the harsh subaerial environment. Thus sporopollenin-coated spores/pollen are absolutely essential for subaerial existence as a land plant, but of little or no use to an aquatic plant (in fact, secondarily aquatic 'land plants' generally lose the sporopollenin coat of their spores/pollen). An early palynological discovery was that the fossil record of trilete spores (similar to the isospores of homosporous plants such as many modern lycopsids and ferns) extends back into the earliest Silurian (Hoffmeister, 1959). This predated the earliest land plant megafossils and provided a new benchmark for the origin of land plants (Fig. 1). It also suggested that the land plant megafossil record was patchy (i.e. incomplete and biased) as might be expected: megafossils are produced in smaller numbers and are much less likely to survive the fossilization process than dispersed spores/pollen. Geological time scale for the Ordovician–Silurian illustrating benchmark palaeontological studies relevant to dating the origin of land plants. Figures refer to ages in millions of years. A further palynological shockwave was provided by Gray & Boucot (1971). They described spores that occur in unusual configurations (now termed cryptospores) in even older rocks, subsequently shown to extend down into the Ordovician (Gray, 1985). This work was at first highly controversial. Many claimed that these spores did not represent land plants. After all, where were the plant megafossils? However, supporting evidence has subsequently accumulated to the extent that land plant affinities are almost universally accepted. It was also realized that the earliest land plants were probably 'bryophyte-like' (liverworts are the most basal extant land plants). Bryophytes lack abundant recalcitrant (e.g. lignified) tissues and consequently do not fossilize easily and have a negligible fossil record. This probably explains why the earliest land plants left a rich dispersed spore record but only a very limited megafossil record (Wellman et al., 2003). The evidence for land plant affinities of cryptospores may be summarized as follows: Cryptospores are morphologically similar to land plant spores in terms of size and possession of a thick, resistant wall (see (7) below). However, they occur as monads, dyads and tetrads, rather than strictly as monads formed from the dissociation of a meiotic tetrad. Furthermore, they are often enclosed within a thin envelope that is difficult to equate with similar structures in extant plants (e.g. Richardson, 1996) (Fig. 2). Cryptospores occur in terrestrial deposits. They are also recovered from marine deposits where they decline rapidly in abundance offshore (as do modern spores/pollen flushed into the sea). Phylogenetic analyses in the mid-1980s suggested that liverworts are the most basal extant land plants. Certain cryptospores (notably permanent tetrads enclosed within an envelope) resemble the spores of certain extant liverworts (Gray, 1985). Taylor (1995) demonstrated that some cryptospore dyads have spore wall ultrastructure only known among extant liverworts. Remarkably preserved Lower Devonian plants contain in situ cryptospores and these plants have certain bryophytic characters (Edwards et al., 1999). Complete sporangia (including covering) with in situ cryptospores were recovered from the Ordovician (Katian) of Oman (Wellman et al., 2003). Those containing dyads also have spore wall ultrastructure known only among extant liverworts. Recent geochemical analysis has demonstrated that the spore wall in cryptospores is chemically similar to that of known land plant spores (Steemans et al., 2010). Cryptospores from the Late Ordovician (Katian) of Oman. (a) Naked dyad; (b) dyad enclosed in a thin walled envelope, part of which is discernible on the edges of the specimen; (c) naked tetrad; (d) tetrad enclosed in a thin-walled envelope, part of which is discernible on the edges of the specimen. All specimens approx. 30 microns in maximum diameter. Until now the earliest reported cryptospores were from the Darriwilian (Middle Ordovician) from the Czech Republic and Saudi Arabia (Strother et al., 1996). Interestingly both of these reports concern the large Ordovician supercontinent of Gondwana and its margins. Now Rubinstein et al. provide an even earlier report (by some 8–12 million yr) of cryptospores from the early Middle Ordovician (Fig. 1). This provides a new benchmark for the origin of land plants. Their report is from Argentina which was also situated on the supercontinent of Gondwana. Thus, although reports are currently few, attention is turning to the possibility that the centre of origin of land plants may have been located on Gondwana. This mirrors the situation whereby the centre of origin of vascular plants is currently hypothesized to have occurred on this continent (Steemans et al., 2009). Understanding the origin of land plants is a multidisciplinary effort with diverse strands of evidence derived from palaeontological, biological and geological investigation. Palaeontological research continues to throw up new finds, like that reported by Rubinstein et al., that modify an emerging picture of the nature of the earliest land plants, where and when they first appeared, and how they colonized the Earth's surface. However, much work remains to be done as we struggle to unravel the vagaries of the fossil record and many controversies persist. There are claims that thick-walled palynomorphs from the Cambrian represent an even earlier record for land plants. However, many interpret these as the resting cysts, or even body cells, of aquatic algae (Wellman, 2003). The jury is out and more evidence is required. Even more intriguing is the unusual configuration of the earliest land plant spores (cryptospores). What does the envelope represent? Why do they often occur in dyads? It is clear that most extant and fossil land plants produce spores/pollen in tetrads by meiosis and usually the tetrads dissociate into four monads before dispersal. Presumably, dyads are normal meiotic products but developed via separation between two successive meiotic divisions. But why did dyad formation operate among land plants for the first 65 million yr of their existence before entirely disappearing? Possibly two lineages of embryophyte existed and the dyad-producers were simply outcompeted by the tetrad producers owing to some other factor unrelated to reproduction. These, and other problems will be addressed by new evidence from a variety of disciplines. This will include new fossil finds, interpreted, as always, in the light cast by our understanding of extant plants. I suspect that this will be forced onward by the current revolution in evo-devo studies, fuelled by the proliferation of molecular data, including whole-genome sequences from more basal land plants such as Physcomitrella and Selaginella.

Echinoderms are a major group of invertebrate deuterostomes that have been an important component of marine ecosystems throughout the Phanerozoic. Their fossil record extends back to the Cambrian, when several disparate groups appear in different palaeocontinents at about the same time. Many of these early forms exhibit character combinations that differ radically from extant taxa, and thus their anatomy and phylogeny have long been controversial. Deciphering the earliest evolution of echinoderms therefore requires a detailed understanding of the morphology of Cambrian fossils, as well as the selection of an appropriate root and the identification of homologies for use in phylogenetic analysis. Based on the sister‐group relationships and ontogeny of modern species and new fossil discoveries, we now know that the first echinoderms were bilaterally symmetrical, represented in the fossil record by Ctenoimbricata and some early ctenocystoids. The next branch in echinoderm phylogeny is represented by the asymmetrical cinctans and solutes, with an echinoderm‐type ambulacral system originating in the more crownward of these groups (solutes). The first radial echinoderms are the helicoplacoids, which possess a triradial body plan with three ambulacra radiating from a lateral mouth. Helicocystoids represent the first pentaradial echinoderms and have the mouth facing upwards with five radiating recumbent ambulacra. Pentaradial echinoderms diversified rapidly from the beginning of their history, and the most significant differences between groups are recorded in the construction of the oral area and ambulacra, as well as the nature of their feeding appendages. Taken together, this provides a clear narrative of the early evolution of the echinoderm body plan.

Relatively well-preserved echinoids from Palaeozoic strata are exceptionally rare fossils. New fossil finds can thus have an important impact on our understanding of the morphology, phylogenetic relationships and history of diversification of early sea urchins. The Devonian strata of Germany have long been known to contain echinoids, predominantly through the relatively abundant record of disarticulated plates and spines. In contrast, only select articulated or semi-articulated specimens are recorded. We herein describe new specimens from the Middle and Late Devonian belonging to two Palaeozoic echinoid taxa, Rhenechinus hopstaetteri and Lepidocentrus eifelianus. These specimens are amongst the most-complete known for these two taxa, and provide novel insight into their morphology and stratigraphic range. Additionally, the record of Rhenechinus is the youngest occurrence of an echinocystitid echinoid in the fossil record, indicating that this family ranged from the Silurian (Aeronian or Telychian) to at least the Middle Devonian (Givetian), prior to going extinct. The morphological details provided by the new specimen of L. eifelianus highlights similarities between this species and other Devonian echinoids known from elsewhere in Europe and North America, and suggest that the lepidocentrids were widely dispersed and abundant during the Devonian.

Bogidiellidae is the most diverse and cosmopolitan family of stygobiotic amphipods, and inhabits a variety of subterranean biotopes, especially interstitial habitats. While the family is characterized by considerable sexual dimorphism, this dimorphism has adversely affected our understanding of the systematics of the group. Most species have restricted geographic ranges and occur in difficult to sample habitats, so it is common for individual species descriptions to be based on a single sex. In this work we revisit an analysis of morphological characters in an attempt to clarify their phylogenetic utility in resolving taxonomic relationships among genera by introducing a new species, two additional characters, and phylogenetic statistical support values. Eobogidiellavenkataramanisp. n., from a spring fed brook in the Shirawati River basin along the escarpment of the Western Ghats (Karnataka, India) differs from the only known congener, Eobogidiellapurmamarcensis, from Argentina, in the structure of mouthparts, the shape and ornamentation on gnathopods and characters of the telson. Our phylogenetic analyses indicate that the available morphological characters are not sufficient to resolve phylogenetic relationships within Bogidiellidae, thus these characters alone cannot be used to determine the phylogenetic placement ofEobogidiellavenkataramanisp. n. within the family. Nevertheless, Eobogidiellavenkataramanisp. n. shares diagnostic characters with Eobogidiella, supporting placement of the new species in this genus. Our findings point towards a critical need to resolve relationships within the family using molecular approaches, along with the development of a suite of additional morphological characters for Bogidiellidae. This is the third species of Bogidiellidae from southern India.

Callistoe vincei, a new Proborhyaenidae (Borhyaenoidea, Metatheria, Mammalia) from the Early Eocene of Argentina

The present study aims to supplement anatomical data about the cranial skeleton and describe some cranial modifications of the common hoopoe, Upupa epops Linnaeus, 1758, by using several techniques. The common hoopoe has small skull and characterized by presence of air space (pneumatization) within their bones. The degree of pneumatization increased especially within the temporal region. The skull of the common hoopoe possesses different types of kinetic hinges; one hinge locates between frontal and nasal region (frontonasal hinge) allows depression/elevation of upper beak relative to brain case. The other one exhibits between the upper beak and jugal bar (maxilla-jugal hinge). The skull of the common hoopoe characterizes by presence of powerful jaw ligamentous system. One of these ligaments exhibits ossification (Lig. Jugomandibularis medialis). In addition, a long mandibular symphysis observes between the two rami of the anterior third of the lower beak. This mandibular symphysis seems longer in the dorsal surface than the ventral one form ventral gap between the two rami of mandible. These modifications of the cranial skeleton of common hoopoe and jaw ligaments consider features of adaptation for probe mechanism, as well as exhibit its phylogenetic relationship with other avian species.

Newly prepared material of Keichousaurus hui demonstrates that the nasals are very reduced and do not contribute to the margins of external nares, the quadrate lacks a posterior condylar process, the premaxilla and anterior dentary teeth are enlarged and procumbent, the maxilla has a pair of ‘canines,’ the vomers are co-ossified, the suborbital fenestrae are very reduced or lost, a distinct coronoid process is present, and both the mandibular symphysis and retroarticular process are elongated. The presence of an ectopterygoid could not be confirmed. The shape of the prefrontal, length of the quadrate ramus of the squamosal, and length of the quadrate and quadratojugal all indicate that the skull profile of Keichousaurus is much lower than previously thought. A new reconstruction attributes a distinctly eusauropterygian gestalt to the skull. A phylogenetic analysis, although equivocal, suggests that Keichousaurus is more appropriately considered a basal nothosauroid rather than a pachypleurosauroid, and that the Eusauropterygia is paraphyletic.

ABSTRACTSabinosuchus coahuilensis, n. gen. et sp., is a marine crocodyliform from the Upper Cretaceous Sauz Creek Member or lower part of the Cuevas Creek Member of the Escondido Formation (Maastrichtian) near Sabinas in Coahuila, Mexico. The type specimen exhibits two synapomorphies of family Dyrosauridae: dentary alveolus 7 is reduced in size compared with the eighth, and the mandibular symphysis is nearly as wide as it is high for most of its length. Sabinosuchus coahuilensis is distinguished from all other known members of Dyrosauridae on the basis of three autapomorphic traits: the posterior section of the mandible is distinctly broad and flat, the mandibular rami are considerably longer than the symphysis, and the posterior mandibular alveoli are uniquely arranged. Sabinosuchus coahuilensis joins Hyposaurus rogersii as the second known North American dyrosaurid. Although the two were contemporaneous, they differed notably in rostrum length and shape; S. coahuilensis has a relatively shorter rostrum with a much wider and flatter posterior mandibular symphysis. Phylogenetic analyses and biostratigraphy suggest that S. coahuilensis occupies a basal position in Dyrosauridae.http://zoobank.org/urn:lsid:zoobank.org:pub:0B48E2C2-B1AA-4539-8F67-0F217AE1A914SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVPCitation for this article: Shiller, T. A., II, H. G. Porras-Muzquiz, and T. M. Lehman. 2016. Sabinosuchus coahuilensis, a new dyrosaurid crocodyliform from the Escondido Formation (Maastrichtian) of Coahuila, Mexico. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2016.1222586.

Saratovia glickmani, gen. et sp. nov., is described based on a dentary symphysis fragment from the Upper Cretaceous (upper Cenomanian) Melovatka Formation at Saratov, Russia. This specimen was found by L.S. Glickman in late 1940s and was referred previously to Ornithocheirus, Anhanguera, or Coloborhynchus. S. glickmani is attributed to Targaryendraconia because of strongly scalloped and subparallel lateral margins of dentary symphysis, which is transversely narrow, with the interalveolar width subequal to the alveolar width. It differs from all known targaryendraconians by having a dentary crest. The new taxon differs from all toothed pterodactyloids by lack of median groove on dentary symphysis. Instead, it has a raised flat platform pierced by numerous relatively large nutrient foramina, which are connected by short canals with a median canal within this platform. S. glickmani is one of the latest toothed pterosaurs known in the fossil record.

Mass media and popular science journals commonly report that new fossil discoveries have 'rewritten evolutionary history'. Is this merely journalistic hyperbole or is our sampling of systematic diversity so limited that attempts to derive evolutionary history from these datasets are premature? We use two exemplars-catarrhine primates (Old World monkeys and apes) and non-avian dinosaurs-to investigate how the maturity of datasets can be assessed. Both groups have been intensively studied over the past 200 years and so should represent pinnacles in our knowledge of vertebrate systematic diversity. We test the maturity of these datasets by assessing the completeness of their fossil records, their susceptibility to changes in macroevolutionary hypotheses and the balance of their phylogenies through study time. Catarrhines have shown prolonged stability, with discoveries of new species being evenly distributed across the phylogeny, and thus have had little impact on our understanding of their fossil record, diversification and evolution. The reverse is true for dinosaurs, where the addition of new species has been non-random and, consequentially, their fossil record, tree shape and our understanding of their diversification is rapidly changing. The conclusions derived from these analyses are relevant more generally: the maturity of systematic datasets can and should be assessed before they are exploited to derive grand macroevolutionary hypotheses.

Dramatic headlines touting new fossil discoveries often proclaim that our view of human evolution has been revolutionized. While this is occasionally the case, it is more often true that new fossils enrich our understanding of our own ancestry or answer scientific questions that could not be resolved with previous data. Even spectacular new discoveries, such as the now famous “hobbit” skeleton (Homo floresiensis), can usually be included in the human family tree without any significant change in the inferences about the phylogenetic relationships or taxonomic status of the rest of its members. It is a testament to the power of evolutionary theory and the careful comparative study of human and other fossils that what we know about human evolution changes so little, even when spectacular new discoveries are announced.

A new oviraptorosaur Nankangia jiangxiensis gen. et sp. nov. is described on the basis of a partial postcranial skeleton with a partial lower jaw collected from the Upper Cretaceous Nanxiong Formation of Ganzhou, in Jiangxi Province of southern China. The new taxon is diagnosed by: (1) a mandibular symphysis that is not turned down; (2) neural spines of the cranial caudal vertebrae that are wider transversely than anteroposteriorly, forming a large posterior fossa with rugose central areas; (3) a femoral neck extending at an angle of about 90 to the shaft; and (4) a ratio of femur to tibia length of 0.95. Phylogenetic analysis recovers Nankangia as basal to the oviraptorid Yulong, but more derived than Caenagnathus, which also has a mandibular symphysis that is not turned down. The coexistence of Nankangia jiangxiensis, Ganzhousaurus nankangensis, Jiangxisaurus ganzhouensis, an unnamed oviraptorid from Nanxiong Basin and Banji long suggests that they occupied distinct ecological niches. Nankangia may have been more herbivorous than carnivorous.

The Known Fossil Record represents museum collections and the published literature, and it is subject to multiple large-scale megabiases grouped into four major categories: (1) taphonomy; (2) rock preservation; (3) fossil discovery; and (4) fossil study. Taphonomic megabiases are largescale patterns in the quality of the fossil record that affect paleobiologic analysis at provincial to global levels and at timescales usually exceeding ten million years. Taphonomic megabiases are intrinsic (form and behavior) and extrinsic (biotic and abiotic controls on preservation). Other megabiases are the preservation and exposure of rock strata, kyreonomy (discovery) and concipionomy (study). Kyreonomy megabiases include location of fossil sites, mineral evaluation, mineral extraction and colonialism. Concipionomy megabiases include the Taxophile Effect, language and development and distribution of technology.