Hapalotis boweri Ramsay, 1887b

Parnaby, Harry E., Ingleby, Sandy & Divljan, Anja, 2017, Type Specimens of Non-fossil Mammals in the Australian Museum, Sydney, Records of the Australian Museum 69 (5), pp. 277-420 : 350-354

Hapalotis boweri Ramsay, 1887b

Proc. Linn. Soc. N.S.W. (ser. 2) 1(4): 1153, plate 18. (22 February 1887).

Common name. Golden-backed Tree-rat.

Current name. Mesembriomys macrurus ( Peters, 1876a) , following Jackson & Groves (2015), no subspecies recognized.

Syntype. M.1350 by subsequent determination. Male, skin mount ( Fig. 30 ), skull not in skin. The M Register entry for M.1350 has “ holotype ” written next to it in what appears to be Troughton’s handwriting. M.1350 was registered from the Old Collection in September 1898 with the following entry: “ Conilurus boweri Rams. male NW Aust. OC [= Old Collection], skin, skull in skin?. Type. Figured. (found in stores)” but without a collection date or collector.

? Syntype.?M.1350. A cranium and dentaries ( Fig. 31 ) have been matched with the skin subsequent to the Register entry for skin mount M.1350, but when and by whom is not recorded and there is doubt that the cranium and dentaries belong with the skin. An unsigned, undated note in the skull box, probably written by J. Mahoney, suggests that the cranium and dentaries are mismatched with the skin, “see my notes in checklist of Muridae ”—presumably a reference to the conclusion of Mahoney & Richardson (1988) that the holotype skull remains unlocated. The registration number of M.2350 cited for the type by Mahoney & Richardson (1988) is an error.

Condition. M.1350. Skin mount: five fractures in the tail, ear tips torn, snout torn.?M.1350. Cranium is in good condition but has jugal missing from both zygomatic arches, hole in the left orbitosphenoid bone; both dentaries complete.

Cranial measurements (mm). M.1350?. GL, 56.04; ConL, 56.04; BasL, 52.15; NasL, 20.49; NasB, 6.25; DIL, 15.10; APV, 10.45; PPV, 1.54; PAL, 33.50; UMR (alv.), 9.40; ZB, 27.05; POC, 8.58; BUL, 8.30; MB, 19.45; DL (condyl.), 31.67; LMR (alv.), 8.81. See Table 5 for additional measurements.

Type locality. Derby district , northern Western Australia .

Comments. We are unable to unequivocally determine whether the skull marked M.1350? is Ramsay’s original specimen. Our initial conclusion based on comparisons of the skull with Ramsay’s illustrations was that it could not be the skull upon which the illustrations were based. However, for reasons set out below, a more detailed assessment suggests that the possibility remains open that the skull possibly is the one used by Ramsay.

Ramsay indicated that his original description was based on two specimens. The external description was based on an adult male skin without a skull, while the illustrations of skull and dentition, and possibly also manus and pes, were based on a skin and skull for which Ramsay did not state the sex. As the original description was based on both specimens, we regard them to be syntypes, contra Mahoney & Richardson (1988), who refer to the “ holotype ” which they state was not found in the AM. Ramsay’s original specimens were: (1) an adult male skin, now unlocated, probably without skull, collected by T. H. Bowyer-Bower from the Derby area, northern Australia, and probably collected in 1886, given that Bowyer-Bower died on a field trip in December 1886 (see Mahoney, 1965). Ramsay (1887b) stated that the type specimen was sent in one of Bowyer-Bower’s last batches of specimens; (2) a skin with cranium and dentaries of unspecified sex, from the Derby district, northern Australia, collected by E. J. Cairn. The collecting date is not recorded but likely to have been during 1886, given that Cairn collected in the Derby region with Bowyer-Bower, who arrived there in the first half of 1886.

Ramsay describes the initial specimen as the “ type ” and specifically states that it was forwarded to him by BowyerBower but its whereabouts remains undetermined. It is not clear if Ramsay lodged the skin in the AM Collection, retained it in his private collection, or perhaps sent it in exchange to another institution. It appears that the skin mount M.1350 is the one collected by Cairn. However, we do not know if Ramsay’s first specimen was a skin mount or flat skin subsequently turned into a mount, nor is it known if Ramsay received the first specimen as a dry or wet skin. The tail of the skin mount is set in an unusual position ( Fig. 30 ), being drawn between the legs, but in a manner that would aid transportation—perhaps the specimen was prepared in Northern Australia. Lacerations on the head of the skin mount are consistent either with skull extraction, or to assess whether a skull was in situ .

The text description is based on a male skin, the skull of which Ramsay states is missing. Mahoney (1965) points out that Ramsay might never have received the skull from the collector, and that the skull could have been lost during field preparation of the skin. A footnote in Ramsay’s original account ( Ramsay, 1887b: 1154) indicates that after writing the description, he received another specimen from “Mr. Cairn’s collection” (presumably E. J. Cairn) from the same district, upon which the skull illustrations would be based, “together with the hand and foot”. The ambiguity in Ramsay’s footnote means that it is not clear which specimen was used to illustrate manus and pes, perhaps his second specimen. We see no grounds for rejecting skin mount M.1350 as being one of Ramsay’s original specimens, as indicated in the M Register. However, establishing whether skin mount M.1350 is the first or second of Ramsay’s skins is problematic. The head-body and tail length given by Ramsay for his first skin approximate those of M.1350, but the imprecision of those measurements combined with possible shrinkage limits further interpretation. Although the digits of the right pes of skin mount M.1350 are widely splayed, unlike those illustrated, comparisons would be void if the illustrations were prepared on the skin before it was fixed in its current configuration as a mount. This also applies to differences between the unsplayed digits of the left pes of the mount, had that been used in the illustration after appropriate image reversal. The right manus of M.1350 does resemble the illustration.

The skull currently matched with skin M.1350 has “M.1350?” in black ink written on the skull. The right dentary also has “M.1350?”, which partly obscures a faded ink circle with a central dot, possibly remnants of ♀ (Ramsay often included a dot in female, but not male, symbols). Significantly, the right dentary of M.1350? has “ H. boweri ” clearly written in faded ink, in contrast to Conilurus boweri , the name entered when registered in 1898 during Waite’s curatorship. Ogilby (1892) was the first to apply the name Conilurus to this entity, and assuming that the person who wrote “ H. boweri ” on the dentary was conversant with the latest generic nomenclature, it appears that it was written prior to 1892, during Ramsay’s curatorship.

If the drawings accompanying Ramsay’s description are an accurate representation, skull M.1350? cannot be the skull illustrated by Ramsay. There are a number of discrepancies between the two ( Fig. 31 ), the most obvious of which include: (a) the pronounced posterior taper of the nasals contrast with those of the matched skull; (b) the infraorbital foramina are relatively much larger than those of the matched skull (marked “a” in Fig. 31 ), as seen from both dorsal and lateral drawings, yet not the ventral skull illustration; (c) the less anteriorly rounded braincase and broader interparietals of the matched skull; and (d) the greatly expanded angular processes of the dentaries contrast with those of the matched skull. Further, a cavity that appears to be the result of damage to the anterodorsal margin of the right orbit is evident in dorsal and lateral skull illustrations but not in the matched skull, while the anterior accessory cusps on M 1 of the matched skull are not present in the illustrations. The dorsal drawing of both dentaries closely resemble those of the matched skull (other than the angular processes) but the lateral depiction of the left dentary bears no resemblance. Both dentaries are attached in the matched skull and do not appear to have been glued together and this might have forced the artist to draw freehand, with a less than accurate outcome.

Despite significant discrepancies between skull M.1350? and the illustrations of Ramsay’s account, several considerations support the skull as a possible match. First, at our request rodent specialist Dr Ken Aplin examined the skull and compared it with Ramsay’s plate. He drew our attention to several unusual circular bands of bone discolouration across the frontals of M.1350? which he regarded as a possibly unique feature of that skull and which match the three circular marks of Ramsay’s dorsal skull drawing (“b” in Fig. 31 ). He concluded that, in spite of the obvious differences between the skull and illustrations, M.1350? was possibly the skull illustrated by Ramsay (pers. comm. 2016). Further support stems from skull dimensions. Ramsay did not provide cranial or dental measurements but stated that his illustrations are reproduced at life size. A comparison of measurements of the matched skull with those taken from a hardcopy of Ramsay’s plate 18 from the journal ( Table 5 ) show a remarkable agreement for the majority of the 16 measurements, bearing in mind measurement error. Notable exceptions include posterior width across nasals, breadth of the infraorbital foramen and dentary length. The close match between measurements of skull and illustrations are significant considering that few specimens of this taxon were ever likely to have been in the AM Collection. Only three specimens additional to M.1350 have been registered in the AM, two in 1932. It appears that there were no registered specimens of this species in the Collection when M.1350 was registered. Only one specimen (A.4783) had been registered previously but had been exchanged. We do not know how many unregistered specimens existed at the time, but presumably there were few if any .

We do not know how the artist prepared the images accompanying the original description, nor the technique used to produce the plate for publication but they appear to have been prepared from photographic images. The simplest explanation for discrepancies between the matched skull and Ramsay’s illustrations is that the illustrator, possibly not familiar with details of rodent cranial morphology and molar loph patterns, produced an inaccurate rendition. Under this scenario, the artist might have achieved correct size and proportions for most of the skull, yet failed to accurately draw all of the skull proportions. The lateral drawing of the dentary, and the relatively large upper incisor in the lateral skull drawing are likely examples of poor draftsmanship, as is the incongruent depiction of upper molar lophs between left and right molar rows Although we cannot discount this scenario, the pit in the right orbit seen in lateral and dorsal skull views, the sharp posterior nasal taper and possibly the enlarged infraorbital foramen seem incongruent to us. If the matched skull is accepted as being Ramsay’s original, it would be necessary to attribute the later discrepancies to artistic license or poor draftsmanship. This would appear to be a distinct possibility, given the poor renditions accompanying other descriptions of rodent taxa by Ramsay (e.g., Mus burtoni ). Another possibility, however remote, is that the skull was originally selected as a match for the skin on the basis of fortuitous similarities in skull and dental dimensions with the illustrations. This would seem improbable given the small number of specimens of M. macrurus likely to be in the AM Collection.

Figures

Figure 30. AM M.1350, syntype skin of Hapalotis boweri Ramsay, 1887b. (Photography by Sally Cowan).

Figure 31. Comparisons between, left, AM M.1350?, the alleged syntype skull of Hapalotis boweri Ramsay, 1887b and right, skull illustrations from Ramsay’s original account. (a) infraorbital foramen; (b) circular band of bone discolouration. (Photography by Sally Cowan and Jennifer Hull).