A new ichthyosaur mimic: Sclerocormus

A new Nature paper
by Jiang et al. 2016 introduces Sclerocormus, a large sister to the much smaller Cartorhynchus. Like a marine Cotylorhynchus, this odd basal sauropterygian had a tiny skull not much larger than that of its much smaller, big-headed sister (Fig. 1).

Figure 1. Large Sclerocormus and its much smaller sister, Cartorhynchus. These nest with basal sauropterygians, not ichthyosauriforms.

Figure 1. Large Sclerocormus and its much smaller sister, Cartorhynchus. These nest with basal sauropterygians, not ichthyosauriforms. Click to enlarge. Note the skull size of the two are within a short range.

These two nested
with Qianxisaurus, a basal sauropterygian/pachypleurosaur, not basal ichthyosauriforms. The authors are still in the dark about ichthyosaur ancestors. You can trace them, or any taxon, back to basal tetrapods here.

Figure 1. Although the pectoral girdle was preserved just behind the skull, in all sister taxa there are about 19 cervicals and 19 dorsals. Plus the pectoral girdle itself is very wide, better suited to the widest ribs. Perhaps Cartorhynchus had a longer neck than commonly assumed.

Figure 2. Although the pectoral girdle was preserved just behind the skull, in all sister taxa there are about 19 cervicals and 19 dorsals. Plus the pectoral girdle itself is very wide, better suited to the widest ribs. Perhaps Cartorhynchus had a longer neck than commonly assumed.

The authors
report that Sclerocormus had no teeth and that the nasals extended to the tip of the rostrum. I have to disagree with both observation given the photographic data and lack of similarity in sister. They also misidentified a few bones. Their big scapula is a posterior coronoid + smaller scapula.

More coming in later posts.

References
Jiang D-Y, Motani R, Huang J-D, Tintori A, Hu Y-C, Rieppel O, Fraser NC, Ji C, Kelley NP, Fu W-L and Zhang R 2016. A large aberrant stem ichthyosauriform indicating early rise and demise of ichthyosauromorphs in the wake of the end-Permian extinction. Nature Scientific Reports online here.

Nesting Triceratops and its juvenile

No surprises here. 

Figure 1. Triceratops mount from an auction house. Pectoral girdle repaired. Skull colorized.

Figure 1. Triceratops mount from an auction house. Pectoral girdle repaired. Skull colorized. Dorsal view comes from another specimen – always a dangerous proposition.

Triceratops (Fig. 1, Marsh 1889) and its juvenile (Fig. 2) nest together with Yinlong downsi (Xu et al. 2006) Late Jurassic ~150 mya, ~1.2 m in length; Fig. 3) a primitive bipedal hornless pro-ceratopsian ornithischian, dinosaur, archosaur, archosauriform, archosauromorph, reptile. The large reptile tree is now up to 678 taxa.

Figure 3. Juvenile Triceratops compared to subadult Triceratops (in shadow).

Figure 2. Juvenile Triceratops compared to subadult Triceratops (in shadow).

Liike all ornithischians, 
ceratopsians fuse the postfrontal to the frontal. However, in Yinlong, cracks (sutures?) appear where the postfrontal would have appeared and where the orbital horns ultimately appeared. So are the postorbital horns actually derived from postfrontal buds? We won’t know until we can determine a suture from a crack in the ontogenetically youngest and phylogenetically most primiitive specimens. It is also possible that, like the nasal horn, the orbital horns arose from novel ossificatiions that ultimately fused to the underlying bone.

Figure 4. Yinlong skull showing possible postfrontal in the position of the future orbit horns.

Figure 3. Yinlong skull showing possible postfrontal in the position of the future orbit horns.

Another juvenile nests with its adult counterpart!
Several workers and readers have pointed to studies (sorry, I don’t have the reference here) in which juveniles did NOT nest with adults in morphological analysis. Notably these samples  (as I recall…) came from taxa that metamorphosed during ontogeny, like caterpillars > butterflies and tadpoles > frogs.

In another argument, perhaps reflecting a majority view, a peerJ reviewer expressed concern/fear/trepidation that: – “Finally, I don’t know that a phylogenetic analysis including juvenile specimens alongside adult specimens is going to give you a particularly trustworthy result.“ citing no references, but noting that juvenile hadrosaurs have distinct characters in the skull from adults, which we all know.

Such arguments have been raised whenever I suggested workers include tiny Solnhofen pterosaurs in phylogenetic analyses, especially so since we KNOW that hatchling pterosaurs were virtual copies of adults. Not so with dinosaurs in which the rostrum is shorter and the orbits are larger than in adults. Even with that handicap, the differences, at least in this one case, were not enough to separate adult from juvenile Triceratops, given the present taxon list, which, frankly has no other ceratopsians.

References
Marsh OC 1898. New species of Ceratopsia. Am J Sci, series 4 6: 92.
Xu X, Forster CA, Clark J M and Mo J 2006. A basal ceratopsian with transitional features from the Late Jurassic of northwestern China. Proceedings of the Royal Society B: Biological Sciences. First Cite Early Online Publishing. online pdf

wiki/Yinlong 
wiki/Triceratops

 

 

 

What?? No scapula??

In a few marine younginiforms,
Tangasaurus (Haughton 1924, Currie 1982), Hovasaurus (Piveteau 1926, Currie 1981) and Thadeosaurus (Carroll 1981, Currie 1984) the scapula cannot be found (Fig. 1). But in a young thadeosaur (if conspecific), a scapula is present (in gray). These are all currently sisters in their own clade in the large reptile tree, The lack of a scapula is not currently a scored trait in the large reptile tree.

Figure 1. Tangasaurus, Hovasaurus and Thadeosaurus, three marine younginiformes, apparently have no scapula.

Figure 1. Tangasaurus, Hovasaurus and some specimens of Thadeosaurus, three marine younginiformes, apparently have no scapula. Click to enlarge. The young Thadeosaurus, if that is indeed what it is (in gray box) shows what a scapula should look like.

When you first encounter these specimens
you scratch your head and search, looking for the scapulae to no avail. Then, when you realize these three sisters share this trait — it still is difficult to accept. The coracoids and sternae + interclavicle form a chest plate. What holds that pectoral girdle in place? What locks the humerus down?  It is hard to look at those naked anterior ribs. Usually something is there to cover them~ Maybe I just missed it…

It is at this node in the evolution of marine younginiforms
that they were moving from a terrestrial niche into an aquatic one. From such Late Permian taxa we get plesiosaurs, placodonts, mesosaurs, thalattosaurs and ichthyosaurs, along with the widely varied sinosaurosphargids including Atopodentatus. So the change in niche is echoed and sometimes amplified in the morphology of descendant taxa, starting with these three (Fig. 1).

References
Carroll RL 1981. Plesiosaur ancestors from the Upper Permian of Madagascar. Philosophical Transactions of the Royal Society London B 293: 315-383
Currie PJ 1984. Ontogenetic changes in the eosuchian reptile Thadeosaurus. Journal of Vertebrate Paleontology 4(1 ): 68-84.
Currie PJ 1981. Hovasaurus boulei, an aquatic eosuchian from the Upper Permian of Madagascar. Palaeontologica Africana, 24:99-163.
Currie P 1982. The osteology and relationships of Tangasaurus mennelli Haughton. Annals of The South African Museum 86:247-265. http://biostor.org/reference/111508
Haughton SH 1924. On Reptilian Remains from the Karroo Beds of East Africa. Quarterly Journal of the Geological Society 80 (317): 1–11.
Piveteau J 1926. Paleontologie de Madagascar XIII. Amphibiens et reptiles permiens. Annls Paleont. 15: 53-180.
Reisz RR, Modesto SP and Scott DM 2011. A new Early Permian reptile and its significance in early diapsid evolution. Proceedings of the Royal Society B 278 (1725): 3731–3737.

wiki/Hovasaurus
wiki/Tangasaurus

 

The Archosauria according to the U of Maryland website

The University of Maryland website on the Rise of the Dinosauria includes the following cladogram (Fig. 1) which pretty much follows paleo traditions. Note the proximal position of pterosaurs to ‘Dinosauromorpha’ and the distant position of crocodylomorphs, which makes room for many intervening taxa to be considered archosaurs (= birds + crocs).

Figure 1. The Archosauria according to the University of Maryland. Here pterosaurs are close to dinosaurs.

Figure 1. The Archosauria according to the University of Maryland. Here pterosaurs are close to dinosaurs. Click to enlarge.

By contrast
in the large reptile tree, pterosaurs nest far from dinosaurs and crocs nest alongside them. So there are no intervening taxa between dinosaurs and crocs (Fig. 2). And there are no odd nesting partners here, like pterosaurs nesting with taxa with small hands and tiny fingers and no toe 5, etc. etc

Figure 2. Same cladogram rearranged to more closely match the large reptile tree. Note how, even at this scale, the gradual evolution of dinosaur traits is not interrupted by the odd morphology of pterosaurs. And how the basal bipedal crocs nest close to the basal bipedal dinos. Click to enlarge. 

Figure 2. Same cladogram rearranged to more closely match the large reptile tree. Note how, even at this scale, the gradual evolution of dinosaur traits is not interrupted by the odd morphology of pterosaurs. And how the basal bipedal crocs nest close to the basal bipedal dinos. This tree is missing SO many taxa, it puts the reader into the position of having to believe the relationships, not observe them. Click to enlarge.

There is a clinging to tradition at the U of Maryland
that needs to be revisited. If students need to regurgitate these antiquated hypotheses in order to get a good grade, then what does that teach them at the university level?

Take a look at those key traits (in red) above (Fig. 1).

  1. Elongate pubes and ischia: also found in basal bipedal crocs and prodinosaurs, like the PVL 4597 specimen. Also in poposaurs, like Poposaurus an Turfanosuchus.
  2. Parasagittal stance and hinge-like ankle joint: also found basal bipedal crocs, like Scleromochlus and Terrestrisuchus. Sure pterosaurs have such a stance and ankle, but so do fenestrasaurs (tritosaur lepidosaurs) like Sharovipteryx.
  3. Ellongate tibiae and metatarsi; loss of bony armor: again, basal bipedal crocs and fenestrasaurs.
  4. The lower traits are synapomorphies.

Students,
put your thinking caps on. Ask the hard questions. Do the experiments yourself. This is Science. Don’t be satisfied with answers that don’t make sense and can’t be validated up and down the entire cladogram.

The large reptile tree does not use suprageneric taxa, as shown above. Only species- and specimen-based taxa are included there. All taxa demonstrate a gradual accumulation of derived traits. All subsets retain the tree topology. The tree has grown from 200+ taxa to 674 taxa with the same 228 characters lumping and splitting them to full resolution.

Plus pterosaurs and plus basal therapsids drive this taxon list into the 900s.

 

 

The origin and evolution of bats, part 4, an inverted thought experiment

There are no fossils
that currently document the origin of bats from non-volant carnivores or omnivores. Birds have a long fossil history. So do pterosaurs. For bats we have to conduct thought experiments in order to get from points we know: 1) a skilled arboreal omnivore like Ptilocercus, to 2) an Eocene fossil bat, like Icaronycteris (Fig. 1). It won’t help to have a Paleocene tooth, or skull. Those don’t change much in bat origins. We need to see, or visualize, the post-cranial body. Earlier forays into bat origins can be seen here, here and here.

Figure 1. GIF animation thought experiment on the origin and evolution of bats from a Ptilocercus-like omnivore.

Figure 1. GIF animation thought experiment on the origin and evolution of bats from an inverted Ptilocercus-like omnivore. Click to enlarge. Perhaps long fingers originally pulled maggots out of fruit and excellent hearing helped probate find where to dig.

We start with what we know

  1. All or most bats hang inverted
  2. The basal phylogenetic split is between Megachiroptera (fruit eaters) and Microchiroptera (insect eaters)
  3. Bat embryos probably recapitulate the development of those unknown phylogenetic predecessors, And they have big webbed hands early on.
  4. Bats don’t fly until their wings are nearly full size.
  5. What separates Ptilocercus from Icaronycteris is chiefly the size of the hands.
  6. There is no evidence that bats find their wings or wing size sexually attractive
  7. Caves are derived roosting spots. You have to fly in those to get a spot.
  8. Likewise, catching insects on the wing and echolocation follows the advent of flying, but listening to maggots munching fruit might have been a precursor skill.

The big question has always been
how do you get a flight stroke out of quadruped? Pterosaur and bird ancestors were both bipeds with strong hind limbs and they evolved wings as 1) gaudy secondary sexual traits; and 2) to aid in locomotion, especially up steep inclines (Heers et al. 2016 and references therein). The only way that bats were bipeds was inverted with weak hind limbs, which is a whole different story, or, in this case, a whole different thought experiment.

Figure 2. Pteropus, a fruit bat.

Figure 2. Pteropus, a fruit bat, has relatively shored clavicles and larger scapulae extending over most of the rib cage. The extremely long toes are derived. Parallel interphalangeal joints present on bat wings show the phalanges flex in sets.

Hypothetical stages in bat development

  1. Start with an agile arboreal omnivore like Ptilocercus, derived from long-legged arboreal carnivores in the Cretaceous/Paleocene, like Chriacus.
  2. Hanging fruit and the maggots therein can be attacked by likewise hanging on the supporting branch.
  3. The tiny hands of Ptilocercus could hold the fruit more steadily if the f fingers were longer. Maybe digging out maggots was aided by longer, thinner fingers.
  4. Webbing on even longer fingers would help trap juices, pieces, maggots from dropping out, and (see #6).
  5. At this stage the inverted biped no longer uses those hyper-elongate fingers for climging, so they are capable of being folded, not from the metatarsophalangeal joint, but at the wrist.
  6. In tropical forests bats use their wings as fans to cool themselves off (see video here), often after salivating on themselves for evaporative cooling. This is one of two pre-flight-stroke actions I have found.
  7. To rise from an inverted position on a branch, bats will flap vigorously (Fig. 3), which is the other pre-flight-stroke action.
  8. Mother bats wrap developing infants in their folded wings, but that doesn’t get them into the air.
  9. At a certain point, the pro-bat has wings that are capable of fanning the air, but incapable of flying. This is when the first branch-to-branch and tree-to-tree flapping leaps took place. If the pro-bat falls to the ground, it dies. Only successful arboreal flapping ‘acro-bats’ survive and improvements increase those odds.
Figure 1. Is this the origin of bat flapping. From an inverted position, this bat rises to horizontal by flapping, still clinging to its perch until release and flight. Click to open video.

Figure 3. Is this the origin of bat flapping. From an inverted position, this bat rises to horizontal by flapping, still clinging to its perch until release and flight. Click to open video.

In summary,
hanging pro-bats first developed long fingers to hold hanging fruit and perhaps remove maggots. Fanning for cooling could only develop with large webbed hands. Vigorous flapping from an inverted configuration is one solution to elevating the head and body. Letting go with the feet during this activity is the first awkward and potentially lethal stage to ultimately perfecting the flight stroke over many generations. The origin of flapping in bats is only a thought experiment at present with no other evidence currently available.

References
Heers AM, Baier DB, Jackson BE & Dial  KP 2016. Flapping before Flight: High Resolution, Three-Dimensional Skeletal Kinematics of Wings and Legs during Avian Development. PLoS ONE 11(4): e0153446. doi:10.1371/journal.pone.0153446
http: // journals.plos.org/plosone/article?id=10.1371/journal.pone.0153446

Huaxiagnathus: yet another basal tyrannosauroid!

Updated May 23, 2016 with a deeper maxilla posterior to the antorbital fenestra. This was needed, as pointed out by M. Mortimer, to house the tooth roots. I missed the splinter that made the difference and someday may try to trace the palatal elements, which I have avoided at present. 

Huaxiagnathus orientalis
(Hwang et al. 2004, Fig. 1) was originally considered a large compsognathid. The Hwang et al tree (now 12 years old) nested Huaxiagnathus with Compsognathus and Sinosauropteryx in the clade Compsognathidae, derived from a sister to Ornitholestes, and basal to therizinosaurs, alvarezsaurs, oviraptors, birds, and deinonychosaurs.

Figure 1. Huaxiagnathus in situ with reconstructed skull, pes, manus and pelvis. Note the relatively large pedal digit 3, the large hyoid, and the twisty lacrimal. Hwang et al. did not provide a reconstruction.

Figure 1. Huaxiagnathus in situ with reconstructed skull, pes, manus and pelvis. Note the relatively large pedal digit 3, the large hyoid, and the twisty lacrimal. Hwang et al. did not provide a reconstruction.

Here
in the large reptile tree Huaxiagnathus nests at the base of the tyrannosauroids, between Tianyuraptor + Fukuivenator and Zhenyuanlong. Yet, another heresy…

Hwang et al. reported the absence of a sternum. 
That’s odd because all current sisters have a sternum. The fossil was collected by farmers, but no preparator was mentioned. Perhaps there was a village preparator. After many tests  conducted by AMNH personnel, the fossil was determined to be genuine, singular and not a chimaera. Given the presence of both humeri where they are, the sternum should be between them. It is not, so one wonders if the sternum was removed by the preparators to expose the underlying humerus. A DGS tracing appears to show the remains of a posterior sternum (Fig. 2, magenta, contra Hwang et al.).

Figure 2. Pectoral region of Huaxiagnathus with various elements colored for clarity. The magenta bone appears to be posterior rim of a sternum, overlooked or considered an elbow by Hwang et al.

Figure 2. Pectoral region of Huaxiagnathus with various elements colored for clarity. The magenta bone appears to be posterior rim of a sternum, overlooked or considered an elbow by Hwang et al. A second overlay colorizes bits and pieces of the possible sternum extending toward the coracoids.

The Hwang et al. diagnosis reports: 
“Differs from other known compsognathids in having

  1. a very long posterior process of the premaxilla that overlaps the antorbital fossa,
  2. a manus as long as the lengths of the humerus and radius combined,
  3. large manual unguals I and II that are subequal in length and 167% the length of manual ungual III,
  4. a first metacarpal that has a smaller proximal transverse width ( i.e. “narrower”) than the second metacarpal and
  5. a reduced olecranon process on the ulna.”

Comments:

  1. The premaxilla doesn’t overlap the maxillary fossa, but tyrannosaurs have a similar long posterior process
  2. true! and no related taxa share this trait, even those with more bird-like morphologies
  3. okay… but that’s a pretty exact percentage for ungual three! (similar to Zhenyuanlong, though)
  4. if so, then just barely a smaller transverse width
  5. as in several basal tyrannosauroid sisters
  6. Not mentioned above, but those pedal proportions seem unique, with a dominant pedal digit 3. The hyoid is enormous. So few and so large are the maxillary teeth that they seem to be unusual, especially compared to the tiny teeth of Compsognathus. There seem to be many ossified stiffening element scattered throughout the vertebral column. Higher resolution should solve this problem.

Like tyrannosauroids
Huaxinagnathus had a short neck and large skull longer than the cervicals and just about as long as half the presacral length. The convex maxilla orients the premaxilla into an ‘up’ orientation. The quadratojugal, here broken into several parts, has a mushroom dorsal process that meets a squamosal ‘lid’. The lacrimal has the familiar tyrannosaur-ish in and out twist. The the maxillary teeth are BIG and few.

Figure 3. Huaxiagnathus skull with elements colorized and reconstructed in figure 4. Orignal tracing is in black outline. Many of the bones are broken.

Figure 3. Huaxiagnathus skull with elements colorized and reconstructed in figure 4. Orignal tracing is in black outline. Many of the bones are broken.

A reconstruction puts the elements
back into their in vivo positions (Fig. 4). Many of the bones are broken and had to be repaired. The scleral elements are scattered.

Figure 4. Huaxiagnathus skull and hyoid reconstructed. See figure 4b for other clade member skulls.

Figure 4. Huaxiagnathus skull and hyoid reconstructed. See figure 4b for other clade member skulls.

Basal theropod subset of the large reptile tree
shows the nesting of Huaxiagnathus in the basal tyrannosauroids (Fig. 5). Both Compsognathus specimens have a most recent common ancestor, with no intervening taxa. Huaxiagnathus, originally considered a compsognathid is one if the whole clade is considered the Compsognathidae. Otherwise, Only Struthiomimus and the Compsognathus holotype form a clade and are sisters. The CNJ79 specimen of Compsognathus is not the adult form of the holotype (contra Peyer 2006), but deserves a new generic name.

Figure 1. Basal theropod subset of the large reptile tree showing troodontids basal to birds and separate from dromaeosaurs.

Figure 5. Basal theropod subset of the large reptile tree showing the two Compsognathus specimens. Hauxiagnathus is a basal tyrannosauroid derived from a sister to Compsognathus.

So…
with every new taxon repairs do get made to the large reptile tree, but the tree topology does not change very often. The theropod subset just keeps growing without shifting around. You would think that if there were enough scoring mistakes the tree topology would change. The key thought here is that some repairs actually cement relationships. The repairs typically, but not always, remove misinterpreted ‘autapomorpies.’ For instance, the ilium of Zhenyuanlong was earlier misinterpreted as having a longer anterior process, which would be an autapomorphy for the clade. A reexamination revealed the relatively longer posterior process (Fig. 6). So, it’s true what they say about me, I don’t get it right the first time all the time.

Figure 6. Zhenyuanlong has a new ilium with a shorter anterior process.

Figure 6. Zhenyuanlong has a new ilium with a shorter anterior process that was earlier misinterpreted.

Huaxiagnathus further cements
the relationships of Zhenyuanlong, Tianyuraptor and Fukuivenator to the tyrannosaurs (contra Hone 2016) and Brusatte (2015). For its size, it looks like one (Fig. 7) with robust lower limbs, large teeth on a curved maxilla, a large head relative to the neck and torso. And don’t forget to picture this skeleton with lots of feathers as in Zhenyuanlong (Fig. 6).

Figure 7. Huaxiagnathus reconstructed in lateral view.

Figure 7. Huaxiagnathus reconstructed in lateral view, sans feathers.

References
Brusatte S 2015. Rise of the Tyrannosaurs. Scientific American 312:34-41. doi:10.1038/scientificamerican0515-34
Hwang SN. Norell MA, ji Q and Gao K-Q 2004. A large compsognathid from the Early Cretaceous Yixian Formation of China. Journal of Systematic Palaeontology 2(1):13-30.

wiki/Huaxiagnathus

The large French Compsognathus specimen

Updated May 23, 2016 with a new mandible. M. Mortimer pointed out correctly that I had traced two coincident mandibles as one. 

The less well-known
French specimen of Compsognathus corallestris (Bidar et al. 1972b; Peyer 2006; CNJ79) is a bit larger with a different morphology (Fig. 1) than the coeval smaller Bavarian Solnhofen specimen, Compsognathus longipes (Fig. 1 right). Dr. Peyer considers these two Late Jurassic theropods conspecific and representative of ontogenic rather than phylogenetic variation.

Figure 1. The large (from Peyer 2006) and small Compsognathus specimens to scale. Several different traits nest these next to one another, but at the bases of two sister clades. Note the differences in the forelimb and skull reconstructions here. There may be an external mandibular fenestra. Hard to tell with the medial view and shifting bones.

Figure 1. The large (from Peyer 2006) and small Compsognathus specimens to scale. Several different traits nest these next to one another, but at the bases of two sister clades. Note the differences in the forelimb and skull reconstructions here. There may be an external mandibular fenestra. Hard to tell with the medial view and shifting bones.

From the Peyer abstract:
“The absence of an external mandibular fenestra, dorsally fan-shaped dorsal neural spines with hook-shaped ligament attachments, and a  very short McI and a PhI-1, which is stouter than the radius distinguish compsognathids from other coelurosaurs. Anatomical and morphological characters of the Bavarian specimen of Compsognathus are nearly identical to those of the French specimen. The differences are related to ontogenetic or within-species variation or are caused by preservational factors. Therefore this study proposes that C. corallestris is a subjective junior synonym of Compsognathus longipes from Bavaria.”

You’ll note that “compsognathids” sensu Peyer are scattered throughout this large reptile tree subset of the Theropoda (Fig. 2). Sinocalliopteryx and Juravenator are widely considered compsognathids, yet both nest far from one another here.

I tested the ontogenetic hypothesis of Peyer
in the large reptile tree. Indeed, the two Compsognathus specimens do nest next to one another, but at the bases of two different clades.

The smaller Compsognathus specimen
nested with Struthiomimus, Ornitholestes, Microraptor and T-rex, among others.

The large Compsognathus specimen
nested with the oviraptorid, Khaan, Limusaurus, therizinosaurs, Sinosauropteryx and others. More derived clades include Eotyrannosaurus and other paravians such as dromareosaurids, troodontids and birds.

Figure 2. Compsognathus corrallensis nests close to the holotype smaller specimen, but at the base of the next clade, which includes oviraptors, therizinosaurs, Juravenator and Sinosauropteryx.

Figure 2. Compsognathus corrallensis nests close to the holotype smaller specimen, but at the base of the next clade, which includes oviraptors, therizinosaurs, Juravenator and Sinosauropteryx. That means it is not the adult version of the smaller specimen.

The new reconstruction
of the large Compsognathus skull is relatively shorter. Both the premaxilla and the dentary tip are oriented slightly down. The bones of the mandible slid apart during taphonomy. Put them back together to match the skull length and you might get a mandibular fenestra, as also seen in the smaller Compsognathus. The new skull reconstruction (Fig. 1) was created using DGS, not freehand as in the Peyer reconstruction.

Figure 3. DGS tracing of large French Compsognathus skull. These parts were used to make the reconstruction in figure 1. Only the left side and top elements were colorized.

Figure 3. DGS tracing of large French Compsognathus skull. These parts were used to make the reconstruction in figure 1. Only the left side and top elements were colorized.

Current traditional compsognathids include the following taxa

  1. Compsognathus
  2. Sinocalliopteryx
  3. Juravenator (some say yes, others say no)
  4. Sinornithosaurus
  5. Huaxiagnathus

In the large reptile tree the clade that includes Compsognathus now include the following taxa

  1. Compsognathus
  2. all ornithomimids, including Struthiomimus

References
Bidar AL, Demay L and Thomel G 1972b. Compsognathus corallestris,
une nouvelle espèce de dinosaurien théropode du Portlandien de Canjuers (Sud-Est de la France). Annales du Muséum d’Histoire Naturelle de Nice 1:9-40.
Ostrom JH 1978. T
he osteology of Compsognathus longipes. Zitteliana 4: 73–118.
Peyer K 2006.
A reconsideration of Compsognathus from the upper Tithonian of Canjuers, southeastern France, Journal of Vertebrate Paleontology, 26:4, 879-896,
Wagner JA 1859. Über einige im lithographischen Schiefer neu aufgefundene Schildkröten und Saurier. Gelehrte Anzeigen der Bayerischen Akademie der Wissenschaften 49: 553.

wiki/Compsognathus