Kollikodon ritchiei: a Second Specimen of the Rare Australosphenidan Mammal Found, Sister Group to Monotremes

The upper dentition and relationships of the enigmatic Australian Cretaceous mammal Kollikodon ritchiei

Authors:

Pian et al

Abstract:

Mesozoic mammals from Australia are rare, so far only known from the Early Cretaceous, and most are poorly represented in terms of dentitions much less cranial material. No upper molars of any have been described. Kollikodon ritchiei is perhaps the most bizarre of these, originally described on the basis of a dentary fragment with three molars. Here we describe a second specimen of this extremely rare taxon, one that retains extraordinarily specialised upper cheekteeth (last premolar and all four molars). Each molar supports rows of bladeless, rounded cuspules many of which exhibit apical pits that may be the result of masticating hard items such as shells or chitin. Reanalysis of the phylogenetic position of this taxon suggests, based on a limited number of apparent synapomorphies, that it is an australosphenidan mammal and probably the sister group to Monotremata. This reanalysis also supports the view that within Monotremata, tachyglossids and ornithorhynchids diverged in the early to middle Cenozoic.

Determining the Phylogeny of Monotremes

On the phylogenetic position of monotremes (Mammalia, Monotremata)

Authors:

Averianov et al

Abstract:

Henosferida from the Middle-Upper Jurassic of Western Gondwana is the most probable sister group for monotremes. They share the derived pretribosphenic structure of lower molars combined with the presumably absent protocone on the upper molars and the plesiomorphic retention of postdentary bones and pseudangular process of the lower jaw. In addition, the two groups share the dental formula with three molars and the position of the Meckel’s groove, which passes ventral to the mandibular foramen. In the course of subsequent evolution, monotremes acquired the mammalian middle ear with three auditory ossicles independently of therian mammals and multituberculates. Jurassic Laurasian Shuotheriidae are probably a sister group of the Gondwanian clade Henosferida + Monotremata. The Jurassic shuotheriid Pseudotribos shows a great plesiomorphic similarity to monotremes in the structure of the pectoral girdle, with a large interclavicle immovably connected to the clavicle. In the lineages leading to therian mammals and multituberculates, the pectoral girdle changed probably independently and in parallel in connection with the establishment of the parasagittal posture of the forelimbs (reduction of the interclavicle, mobile articulation of the interclavicle with clavicle, reduction of the procoracoid, and development of a supraspinous fossa of the scapula) and formation of the mammalian middle ear with three auditory ossicles.

Paleogene (?) Deposits Found in Australia

IN an astounding discovery, palaeontologists think they might have found an even more fossil-rich site in northwest Queensland than the world-renowned Riversleigh World Heritage Area.

The site could become one of the planet’s most important prehistoric places because scientists hope it holds the missing link between the demise of the dinosaurs and the emergence of mammals.

The dig is near Riversleigh but can be accessed only by helicopter or foot.

Renowned palaeontologist Mike Archer initially visited for just a couple of hours two years ago, the first time the area had likely been trod by Europeans.

He had been tipped off by Xtrata employee Ned Stephenson who had been using satellite images to examine landscapes.

ut what has really excited scientists is that the new fossil deposits, dubbed New Riversleigh, are either on or near marine rocks that are about 500 million years old and which have not been below sea level since.

“Theoretically, it means limestone sediment of any age could have accumulated their way back to the dinosaur age,’’ he said. “I’m not interested in dinosaurs but what happened between the age of the dinosaurs and the earliest mammals.’’

This was a dark age of emerging mammal species, roughly from the end of the dinosaurs 65 million years ago to 24 million years ago.

link.

Obdurodon tharalkooschild: Largest Fossil Platypus Found in Miocene Neogene Australia

No living mammal is more peculiar than the platypus. It has a broad, duck-like bill, thick, otter-like fur, and webbed, beaver-like feet. The platypus lays eggs rather than gives birth to live young, its snout is covered with electroreceptors that detect underwater prey, and male platypuses have a venomous spur on their hind foot. Until recently, the fossil record indicated that the platypus lineage was unique, with only one species inhabiting the Earth at any one time. This picture has changed with the publication of a new study in the latest issue of the Journal of Vertebrate Paleontology that describes a new, giant species of extinct platypus that was a side-branch of the platypus family tree.

The new platypus species, named Obdurodon tharalkooschild, is based on a single tooth from the famous Riversleigh World Heritage Area of northwest Queensland. While many of Riversleigh's fossil deposits are now being radiometrically dated, the precise age of the particular deposit that produced this giant platypus is in doubt but is likely to be between 15 and 5 million years old.

"Monotremes (platypuses and echidnas) are the last remnant of an ancient radiation of mammals unique to the southern continents. A new platypus species, even one that is highly incomplete, is a very important aid in developing understanding about these fascinating mammals," said PhD candidate Rebecca Pian, lead author of the study.

Based on the size of tooth, it is estimated that this extinct species would have been nearly a meter (more than three feet) long, twice the size of the modern platypus. The bumps and ridges on the teeth also provide clues about what this species likely ate.

"Like other platypuses, it was probably a mostly aquatic mammal, and would have lived in and around the freshwater pools in the forests that covered the Riversleigh area millions of years ago," said Dr. Suzanne Hand of the University of New South Wales, a co-author of the study. "Obdurodon tharalkooschild was a very large platypus with well-developed teeth, and we think it probably fed not only on crayfish and other freshwater crustaceans, but also on small vertebrates including the lungfish, frogs, and small turtles that are preserved with it in the Two Tree Site fossil deposit."

The oldest platypus fossils come from 61 million-year-old rocks in southern South America. Younger platypus fossils are known from Australia in what is now the Simpson Desert. Before the discovery of Obdurodon tharalkooschild, these fossils suggested that platypuses became smaller and reduced the size of their teeth through time. The modern platypus completely lacks teeth as an adult and instead bears horny pads in its mouth. The name Obdurodon comes from the Greek for "lasting (obdurate) tooth" and was coined to distinguish extinct toothed platypuses from the essentially toothless modern species.

[...]

The specific epithet of the new species, tharalkooschild, honors an Indigenous Australian creation story about the origin of the platypus. In the Dreamtime, Tharalkoo was a head-strong girl duck inclined to disobey her parents. Her parents warned her not to swim downriver because Bigoon the Water-rat would have his wicked way with her. Scoffing, she disobeyed her parents and was ravished by Bigoon. By the time Tharalkoo escaped and returned to her family, the other girl ducks were laying eggs, so she did the same. But instead of a fluffy little duckling emerging from her egg, her child was an amazing chimera that had the bill, webbed hind feet, and egg-laying habit of a duck, along with the fur and front feet of a rodent—the first Platypus.

link.

Ticklish Platypus

hat tip James.

The Trouble With Monotremes

There's a small war over the evolution of the Monotremes. It was suggested that the echidna recently branched off from the platypus family. Recently means, btw, around the Paleogene-Neogene boundary. The original paper that suggested it is here. This caused a response. There has now been a response to that response.

More on the Mesozoic Platypus

The oldest platypus and its bearing on divergence timing of the platypus and echidna clades

Timothy Rowe*,{dagger}, Thomas H. Rich{ddagger},§, Patricia Vickers-Rich§, Mark Springer¶, and Michael O. Woodburne||

*Jackson School of Geosciences, University of Texas, C1100, Austin, TX 78712; {ddagger}Museum Victoria, PO Box 666, Melbourne, Victoria 3001, Australia; §School of Geosciences, PO Box 28E, Monash University, Victoria 3800, Australia; ¶Department of Biology, University of California, Riverside, CA 92521; and ||Department of Geology, Museum of Northern Arizona, Flagstaff, AZ 86001

Edited by David B. Wake, University of California, Berkeley, CA, and approved October 31, 2007 (received for review July 7, 2007)

Abstract

Monotremes have left a poor fossil record, and paleontology has been virtually mute during two decades of discussion about molecular clock estimates of the timing of divergence between the platypus and echidna clades. We describe evidence from high-resolution x-ray computed tomography indicating that Teinolophos, an Early Cretaceous fossil from Australia's Flat Rocks locality (121–112.5 Ma), lies within the crown clade Monotremata, as a basal platypus. Strict molecular clock estimates of the divergence between platypus and echidnas range from 17 to 80 Ma, but Teinolophos suggests that the two monotreme clades were already distinct in the Early Cretaceous, and that their divergence may predate even the oldest strict molecular estimates by at least 50%. We generated relaxed molecular clock models using three different data sets, but only one yielded a date overlapping with the age of Teinolophos. Morphology suggests that Teinolophos is a platypus in both phylogenetic and ecological aspects, and tends to contradict the popular view of rapid Cenozoic monotreme diversification. Whereas the monotreme fossil record is still sparse and open to interpretation, the new data are consistent with much slower ecological, morphological, and taxonomic diversification rates for monotremes than in their sister taxon, the therian mammals. This alternative view of a deep geological history for monotremes suggests that rate heterogeneities may have affected mammalian evolution in such a way as to defeat strict molecular clock models and to challenge even relaxed molecular clock models when applied to mammalian history at a deep temporal scale.

There are your answers, Zach: paper link above. This is a true platypus...from the Cretaceous of all goodness places. The monotremes seem to be a very old group that didn't follow the same rules as the therians. Fascinating.