Saturday, January 11, 2020

New (Extinct) Maniraptors of 2019

A longstanding tradition on this blog was to poll readers on their favorite newly-named maniraptors of the previous year. Following the removal of Blogger's poll widget, I was forced to discontinue this tradition. Last year, I tried out a different way of honoring new taxa by writing a paragraph about every extinct maniraptor named in 2018.

I received some positive feedback for this new format, but I'm thinking that I'll change it up again this year. Drafting a paragraph on every new species required me to spend roughly the same amount of time on species known from a single, fairly nondescript bone as those known from essentially complete or particularly bizarre specimens. Although nearly all fossil descriptions have some scientific value, I suspect that isolated coracoids are generally not of as much interest to most of my readers.

This year, I will instead divide this post up into several sections based (approximately) on phylogeny, and briefly discuss each new maniraptor of 2019 under the relevant section. Every new species of extinct maniraptor that was named last year will at least get a mention, but I won't make myself write a full paragraph on each one. This will probably also result in a shorter post that is presumably less daunting to read... though writing about more than forty species produces a sizable post no matter how it's sliced.

Alvarezsaurs
Two new theropods were described as alvarezsaurs last year, which is a decent number considering that 2013-2017 went without any new alvarezsaurs being named (with the possible exception of Aorun, which wasn't originally recognized as an alvarezsaur). One of the 2019 alvarezsaurs, Shishugounykus, hails from the Late Jurassic Shishugou Formation of China, making it one of the oldest known alvarezsaurs alongside Haplocheirus and potentially Aorun. Shishugounykus is known from a partial skeleton, including a nearly complete hand, and appears to have been more distantly related to the Late Cretaceous alvarezsaurids than Haplocheirus was. Given the famously bizarre anatomy of alvarezsaurids, any finding that sheds light on their origins is a welcome one.

That's assuming, of course, that Shishugounykus was indeed an alvarezsaur. The phylogenetic analysis in the description of the troodont Hesperornithoides (discussed later in this post) recovered Aorun and Haplocheirus as compsognathids instead of alvarezsaurs, and Shishugounykus reportedly comes out as a compsognathid in that dataset, too. In contrast, a recent unpublished iteration of Andrea Cau's dataset corroborates an alvarezsaur identity for both Haplocheirus and Shishugounykus.

The other new alvarezsaur of 2019 was Nemegtonykus, which was also named after the geologic formation it was found in, the Late Cretaceous Nemegt Formation of Mongolia. Prior to the description of Nemegtonykus, the only alvarezsaur previously known from the Nemegt had been Mononykus. The holotype of Nemegtonykus is a partial skeleton including much of the tail, trunk, and left hindlimb. It exhibits patterns of bone fusion in the hip, shoulder girdle, and feet that are unique among alvarezsaurs.

Skeletal reconstruction of Nemegtonykus showing preserved elements, from Lee et al. (2019).

Therizinosaurs
Therizinosaurs are another group of maniraptors for which new species are described relatively infrequently. Last year gave us Lingyuanosaurus from the Early Cretaceous Jehol Biota of China, known from some vertebrae and partial limbs. The holotype is quite small (coyote-sized), though it probably represents a juvenile. The specimen is incomplete enough that it is unclear whether it really was a therizinosaur; Mickey Mortimer found it as an oviraptorosaur using the Hesperornithoides dataset, but also noted that a therizinosaurian identity was only slightly less parsimonious.

Oviraptorosaurs
In recent times oviraptorosaurs have usually gotten away with at least one or two new entries every year. Two were described in 2019. One was Xingtianosaurus from the Early Cretaceous Yixian Formation of China, a Caudipteryx-like form known from a partial skeleton with incompletely preserved wing feathers. The other was Gobiraptor from the Nemegt Formation, known from partial remains of the skull, hip, limbs, and tail. Bone histology suggests that the holotype of Gobiraptor was an immature individual, but, at over a meter in length, it was already larger than the adults of many other oviraptorosaurs. Oviraptorosaur researcher Greg Funston has mentioned on social media that unpublished evidence indicates that Gobiraptor is actually the same species as a previously-named oviraptorosaur.

Basal Paravians
2019 was a good year for what Justin Tweet calls "coming attractions" in dinosaur paleontology, which are essentially fossil dinosaurs known to the paleontological community through brief descriptions, conference presentations, and word of mouth, but have yet to receive a formal name. Although not all of them were included in Tweet's list (which was not meant to be exhaustive), I would consider the ornithopod Convolosaurus, the sauropod Wamweracaudia, the allosauroid Asfaltovenator, and the tyrannosauroid Suskityrannus to all qualify as long-standing "coming attractions" that were finally named last year.

Several maniraptoran "coming attractions" came to light in 2019 as well. One of these was the so-called "Naze dromaeosaurid", known from a foot from the Late Cretaceous Snow Hill Island Formation in Antarctica. First mentioned publicly in 2005 and then briefly described in 2007, this dinosaur was formally named Imperobator last year. Despite its original nickname, the describers of Imperobator found its precise phylogenetic position within Paraves difficult to place, and Andrea Cau has argued that it may not even be a maniraptor at all. The title of the paper that named Imperobator called it a "gigantic" paravian, yet its visible dimensions are comparable to those of Deinonychus. That's larger than average for a paravian, but "gigantic" may be overstating it.

One of the most highly anticipated "coming attractions" described last year was Hesperornithoides, a troodont from the Late Jurassic Morrison Formation of the United States. First announced in a conference abstract in 2004, Hesperornithoides (then nicknamed "Lori") was a big deal for several reasons, particularly the fact that Jurassic paravians other than Archaeopteryx were essentially unknown at the time. With the discovery of Anchiornis and its ilk since then, this is no longer the case, but Hesperornithoides remains notable for the three-dimensional preservation of its skeletal elements (as opposed to the flattened state anchiornithids tend to be preserved in) and for being the best-represented Jurassic paravian from North America.

Skeletal reconstruction of Hesperornithoides showing preserved elements, from Hartman et al. (2019).

Hesperornithoides also generated some buzz for the phylogenetic analysis that accompanied its description. The dataset used has greater taxon sampling than any other published analysis of Mesozoic theropods (it includes nearly all Mesozoic maniraptoromorphs known at the time of study and even a handful of Cenozoic birds), and originated from reevaluating the Theropod Working Group phylogenetic dataset, which has been the basis for the majority of Mesozoic theropod analyses. This resulted in several novel findings, such as Haplocheirus as a compsognathid (as mentioned previously) and Pelecanimimus as an alvarezsaur. Time will tell whether these results hold up, but this analysis highlights the importance of independently evaluating phylogenetic datasets, as repeatedly building directly on previous datasets can create an illusion of consensus.

Strangely enough, no new (definite) dromaeosaurids were named in 2019. Someone drew the short end of the stick.

Basal Avialans
In recent times, Archaeopteryx has generally been considered the only known paravian from the Late Jurassic of Germany, but this has started to change in the past few years. In 2017, one supposed Archaeopteryx specimen was reevaluated as an anchiornithid and given the new genus Ostromia. Last year added another new paravian to the lineup, Alcmonavis from the Mörnsheim Formation. Although it is known only from a forelimb, Alcmonavis appears to differ from Archaeopteryx in the robusticity of certain bones as well as the prominence of various muscle attachment sites.

Another exciting find in the Mesozoic avialan department was Fukuipteryx from the Early Cretaceous Kitadani Formation of Japan. Not only is it the first Early Cretaceous avialan to be found in Japan, Fukuipteryx is known from a partial, three-dimensionally preserved skeleton including much of the front and hind limbs. Despite having a short tail with a pygostyle, it was found to have been less closely related to modern birds than the long-tailed Jeholornis was, which may indicate that the pygostyle evolved more than once among avialans, as some other recent studies have suggested.

Skeletal reconstruction of Fukuipteryx showing preserved elements, from Imai et al. (2019).

Enantiornitheans
The "opposite birds" had a good showing last year, and probably the most intriguing new taxon was Elektorornis from the Late Cretaceous of Myanmar, known from hindlimbs and wing feathers preserved in amber. Burmese amber has produced some of the most spectacular fossils of Mesozoic dinosaurs in recent years, including partial specimens of juvenile enantiornitheans and the tail of a non-pygostylian theropod, but Elektorornis is the first of these fossils to be named. It had an unusually long third toe, which the authors suggest may have been used as a probing tool for foraging. It is likely also the smallest known mature Mesozoic dinosaur, the holotype being of comparable size to juvenile enantiornitheans from the same locality despite apparently being an adult or subadult.

Holotype of Elektorornis, from Xing et al. (2019).

Also particularly interesting was Avimaia from the Early Cretaceous Xiagou Formation of China. The holotype is a partial skeleton preserved with an unlaid egg, a first for Mesozoic avialans. Furthermore, histological examination of the egg revealed a double-layered eggshell, indicating that the unfortunate individual had likely died from egg binding (a usually fatal condition in which an unlaid egg is retained for an abnormally long time). A second specimen of Avimaia had been previously described in 2006, but had not been named.

Holotype of Avimaia, from Bailleul et al. (2019). Note the unlaid egg preserved in its body cavity.

As usual, the Jehol Biota did not skimp on enantiornitheans, giving us the relatively large (pigeon-sized) Gretcheniao and the smaller Mirusavis and Shangyang. Mirusavis is noteworthy for preserving medullary bone (produced by female birds before and during egg laying) throughout much of the skeleton, a more extensive distribution of this type of bone than seen in many modern birds.

Although not newly discovered, another Jehol enantiornithean that was given a new name in 2019 was Camptodontornis. It had been originally named "Camptodontus" in 2010, but this genus turned out to be preoccupied by a beetle. It is likely that Camptodontornis is the same as Longipteryx though, as had already been suggested by other studies.

Mesozoic Euornitheans
An unusual euornithean described last year was Mengciusornis from the Early Cretaceous Jiufotang Formation of China. Its teeth were large and curved, but restricted to the tip of the upper jaw. This deviates from the typical pattern in toothed euornitheans, in which the upper jaw tip was usually toothless.

Holotype of Mengciusornis, from Wang et al. (2019).

More closely related to modern birds was Antarcticavis from the Snow Hill Island Formation, known from a partial skeleton, and Kookne from the Late Cretaceous Chorrillo Formation of Argentina, known from a coracoid. The describers of Kookne suggest that it may even be a neognath, as it shares some similarities with waterfowl, but this is naturally difficult to verify with such a fragmentary specimen.

Paleognaths
One extinct paleognath was named last year, the emu Dromaius arleyekweke from the Miocene Waite Formation of Australia. Known mainly from hindlimb bones, D. arleyekweke was smaller than modern emus and cassowaries (even the dwarf cassowary). Its feet were proportionately very long, however, indicating that it was probably a fast runner.

Galloanserans
Among the galloanserans described last year was what I consider to be one of the most scientifically important new dinosaurs of 2019, the stem-waterfowl Conflicto from the Paleocene López de Bertodano Formation of Antarctica. It is the oldest unequivocal total-group anseriform known from well-represented remains, and may provide evidence that a long-legged, flat-billed body plan was ancestral to all modern waterfowl (including the unusual screamers). I wrote about Conflicto in more detail here. Another Paleocene waterfowl was described last year, the large (swan-sized) Naranbulagornis from Mongolia. It is far less completely known, represented only by a partial carpometacarpus and femur.

Skull of Conflicto, from Tambussi et al. (2019).

On the galliform side of things, 2019 gave us Xorazmortyx from the Eocene of Uzbekistan, which is only known from a partial coracoid. Its describers suggest that it belonged to a group of stem-galliforms called paraortygids, in which case it would be the first paraortygid known from Asia. Better remains are known for a trio of quail from the Macaronesian Islands, Coturnix alabrevis, C. centensis, and C. lignorum. These quail likely went extinct in historic times (within the last 1000 years) due to human activity. Their short wings suggest that they may have been flightless, which would have made them vulnerable to invasive predators.

Columbimorphs
The early fossil record of pigeons and their kin remains stubbornly sparse, but last year did welcome a new species of recently extinct pigeon, Ducula shutleri from Tonga. Known from sites dated to nearly 3000 years old, D. shutleri was the largest known member of the genus Ducula (the imperial pigeons), probably weighing over 1 kg. Despite its large size, there is no evidence that it had reduced flight capabilities.

Gruiforms
Last year we got a new member of the enigmatic Eogruidae, Sinoergilornis from the Miocene Liushu Formation of China. The life appearance of eogruids is mysterious, as they are known mostly from hindlimb bones, and unfortunately Sinoergilornis does not break that curse. Like some other eogruids, Sinoergilornis had only two toes per foot. Although I provisionally treat eogruids as gruiforms here, another study from last year noted that their assignment to Gruiformes is weakly based.

Two species of recently extinct, flightless rails were also described last year, Dryolimnas chekei from Mauritius and the large (chicken-sized) Hypotaenidia vavauensis from Tonga.

Charadriiforms
Surprisingly, given their diversity and frequent association with aquatic habitats, shorebirds have a relatively poor fossil record, but we did get a new fossil taxon in 2019, Cherevychnavis from the Miocene of Ukraine. Although it is very fragmentary (known only from a coracoid and partial humerus), it is notable for likely being a member of Charadrii (a group that also includes plovers, oystercatchers, etc.), which have a scant fossil record even by shorebird standards.

Ardeans
If any crown-bird group can claim to have a good fossil record, it's the penguins, and last year we gained three new species of extinct penguin, all from New Zealand. Two of these, the giant ?Crossvallia waiparensis from the Waipara Greensand and the smaller Kupoupou from the Takatika Grit, were from the Paleocene, making them some of the oldest known penguins. The third new penguin was Eudyptes warhami, a species of crested penguin that probably went extinct within the last 500 years.

The closest living relatives of penguins, the procellariiforms (petrels, albatrosses, etc.), have a decidedly worse fossil record. As such, the small albatross Aldiomedes from the Pliocene Tangahoe Formation of New Zealand was a pleasant surprise, especially seeing as it is known from a well-preserved skull. Its narrow beak suggests that it may have been more specialized for fish-eating than extant albatrosses (which feed more on squid).

Holotype of Aldiomedes, from Mayr and Tennyson (2019).

Two other waterbirds described last year were the ibis Geronticus thackerayi from the Pliocene-Pleistocene of South Africa, known from numerous (but often fragmentary) bones, and the heron Taphophoyx from the Miocene of the United States, only known from a coracoid and scapula.

Telluravians
The afroavian side of Telluraves only presented one new fossil species last year, but it was a good one: ?Laurillardia smoleni, a small stem-member of Upupides (hoopoes and woodhoopoes) from the Oligocene Tylawa Limestones of Poland. Not only is it known from a nearly complete specimen, the genus Laurillardia had been in severe need of a modern reevaluation.

Holotype of ?Laurillardia smoleni, from Mayr et al. (2019).

Things were more active on the australavian side, with the parrot Heracles from the Miocene Bannockburn Formation of New Zealand receiving substantial press attention. Heracles is known only from partial hindlimb bones, but these are enough to suggest a body mass of around 7 kg, making it the largest known parrot to have ever existed.

2019 was a good year for stem-passerines. The finch-like beaks of the Eocene Eofringillirostrum boudreauxi and E. parvulum showed that stem-passerines had evolved into seed-eating specialists long before true passerines did. E. boudreauxi was found in the Green River Formation of the United States, whereas E. parvulum was found in the Messel Formation of Germany. I wrote about these two species in more detail here. Another new stem-passerine was Zygodactylus ochlurus from the Oligocene Renova Formation of the United States, the youngest known stem-passerine from North America.

Holotype of Eofringillirostrum boudreauxi, from Ksepka et al. (2019).

Among crown-passerines, there was Dasyornis walterbolesi from the Miocene of Australia, the oldest known member of the bristlebirds, a poorly-studied group of Australian songbirds.

Miscellanea
The scansoriopterygids from the Late Jurassic of China continue to prove difficult to place phylogenetically. Already considered unusual since their discovery in 2002, scansoriopterygids rocked the paleontological world again in 2015 with the description of Yi, which appeared to preserve membranous wings partly supported by an elongated wrist bone (known as the styliform). Although this seemed to be the most plausible interpretation of the evidence, some researchers were naturally skeptical. 2019 gave us another new scansoriopterygid, Ambopteryx, which also preserves wing membranes and a styliform, providing support for the original interpretation of Yi.

Holotype of Ambopteryx, from Wang et al. (2019).

Another phylogenetically recalcitrant clade of maniraptors is the pelagornithids, a group of seagoing Cenozoic birds with tooth-like projections in their beaks. Protodontopteryx from the Waipara Greensand is the oldest known pelagornithid and is known from much of the skeleton, potentially making it very valuable for understanding the origins of these mystery birds. It would get my vote for the most scientifically important new dinosaur of 2019 (though Conflicto would be a close second). Protodontopteryx was much smaller than later pelagornithids (which include the largest known wingspans of any bird at up to 7 m wide), about the size of a typical gull.

Skull of Protodontopteryx, from Mayr et al. (2019).

Last but not least, Carpathiavis from the Oligocene of Poland is a small (sparrow-sized) bird of unclear affinities. It is known from a nearly complete (but poorly preserved) skeleton with some similarities to rail-like birds.

No comments:

Post a Comment